Vacuum Forming Guide

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Contents

Section 1..............................................................................3

Introduction .........................................................................3

Section 2..............................................................................4

Applications.........................................................................4

Section 3..............................................................................6

The Vacuum Forming Process ...........................................6

Clamping .............................................................................7

Heating.................................................................................7

Sheet Level...........................................................................8

Pre-stretch ( Bubble) ...........................................................8

Vacuum ...............................................................................8

Plug Assist .............................................................................8

Cooling and Release..........................................................8

Section 4............................................................................10

Plastic Materials and Their Characteristics.....................10

Acrylonitrile Butadiene Styrene– (ABS) ...........................13

Acrylic - PMMA – (Perspex, Oroglas, Plexiglas).............14

Co-Polyester – (PETG / VIVAK) .........................................15

Polystyrene– Polyphenylethene (H.I.P.S / BEXTRENE) ...16

Polycarbonate – (P.C. / LEXAN/ MAKROLON)...............17

Polypropylene – (PP).........................................................18

Polyethelene – (PE, HDPE, LDPE, PE FOAM) ...................19

Polyvinylchloride – (PVC) .................................................20

Section 5............................................................................21

Mould and Mould Design ................................................21

Mould Materials.................................................................22

Male and Female Moulds ................................................28

Baseboards and Mounting ..............................................29

Draught Angles / Tapers...................................................30

Venting...............................................................................30

Shrinkage and Mould Release ........................................31

Undercuts, Split and Multi Impression Moulds ................32

Mould Cooling...................................................................33

Plug Assist Design ..............................................................33

Webbing/ Chill Marks/ Thinning.......................................35

Webbing ............................................................................35

Chill Marks ..........................................................................36

Thinning ..............................................................................36

Section 6............................................................................37

Finishing and Trimming......................................................37

Considerations...................................................................38

Heated knife/ Scalpel.......................................................39

Vertical Bandsaw ..............................................................40

Horizontal Bandsaw (Fig 6.4)............................................40

Rollerpress/ Steel Rule Dies ( g 6.5).................................41

Guillotine ............................................................................42

Clicker / Punch Press.........................................................42

Hand Held Air Powered Router .......................................42

CNC Routers - 3, 4 and 5 axis...........................................43

Circular spindle saw..........................................................43

Circular Cutter mounted from under table. ..................44

Section 7............................................................................45

Trouble Shooting Guide....................................................45

Section 8............................................................................50

Supplier Guide...................................................................50

Section 9............................................................................53

Further Information............................................................53

Introduction

Thermoforming is one of the oldest and most

common methods of processing plastic materials.

Thermoformed plastic products are all around us

and play a major part in our daily lives. It is a very

versatile process used to manufacture a wide

range of products from simple packaging trays to

high impact aircraft cockpit covers. It is also used

extensively to make design prototypes of prod-

ucts to be produced by other processes.

The process, however, is basically the same in

each case. In its simplest form thermoforming

is the heating of a plastic sheet which is then

draped over a mould whilst a vacuum is applied.

The moulding is then allowed to cool before it is

ejected from the mould using a reverse pressure

facility.

Thermoforming covers all processes which involve

heat to shape polymers. However, in this manual

we will concentrate speci cally on the ‘vacuum

forming process’ which applies to the range of

machines Formech supply. Vacuum forming has

generally been promoted as a ‘dark art’ and best

left to companies with sophisticated processing

equipment who are able to supply the facility

and service. However with their range of com-

pact, easy to use machines Formech have, over

the years, endeavoured to introduce vacuum

forming to the ‘masses’ and it is some testament

that there are now over six thousand machines

worldwide, many supplied to those looking to

start vacuum forming for the  rst time. In this man-

ual we hope to provide an insight into this adapt-

able process. However, it is only a guide and can-

not impart the practical experience and skill that

any user will eventually attain. We hope it assists

in taking the ‘guess work’ out of the process and

proves useful as a means of technical and engi-

neering support.

In the following sections we have provided a list

of the various examples of applications for ther-

moformed parts along with an insight into the

forming process and techniques. A plastics sec-

tion follows in which we examine materials and

their characteristics. Information on tooling, trim-

ming and  nishing, a trouble shooting guide and

recommended suppliers list concludes the manu-

al with a glossary of key words to aid navigation

through the manual.

If you are new to the process and have just pur-

chased a Formech machine we trust you  nd this

manual a bene cial aid in getting started and

wish you success in your future business.

Section 1

Applications

Below we have allocated sub-headings to a wide

range of industries using vacuum forming for a mul-

titude of applications. The list is fairly comprehen-

sive and although there are many other potential

applications we have attempted to highlight the

most popular. You can  nd photographic exam-

ples of a selection of vacuum formed products in

the galleries contained in the ‘support’ section of

our web page.

Aeronautical Manufacturers

Interior Trim Panels, Covers and Cowlings

Internal sections for NASA Space Shuttle

Agricultural Suppliers

Seed Trays, Flower Tubs, Animal Containers, Clear

Growing Domes

Calf Milking Receptacles, Machines Parts,

Lawnmower Enclosures and Covers

Architectural Model Makers

Production of Miniature Parts for Architectural

Models

Prototypes.

Automotive and Vehicular Industry

Wheel Hub Covers, Ski-Boxes and Storage Racks

Wind Tunnel Models, Parts for All Terrain Vehicles

Truck Cab Door Interiors, Wind and Rain De ec-

tors

Scooter Shrouds, Mudguards, Bumpers and Pro-

tective Panels

Battery and Electronic Housings, Prototype and

Development work

Utility Shelves, Liners, Seat Backs, Door Innerliners

and Dash Surrounds

Windshields, Motorcycle Windshields, Golf Cart

Shrouds, Seats and Trays

Tractor Shrouds & Door Fascia, Camper Hardtops

and Interior Components

Building and Construction Industry

Drainpipe Anti Drip ttings

Roof Lights, Internal Door Liners, PVC Door Panels

Producing Moulds for Concrete Paving Stones

and Special Bricks

Moulded Features for Ceilings, Fireplaces, Porch-

es and other items.

Boat Building industry

Boat Hulls, Covers and Hatches

Electrical Enclosures, Dashboards

Chocolate industry

Manufacture of Chocolate Moulds for Special-

ised Chocolates and

Easter Eggs etc. and Packaging

Computer Industry

Manufacture of Screen Surrounds

Soft Transparent Keyboard Covers

Enclosures and Ancillary Equipment

Design Industry

Production of prototypes and Pre - Production

Runs

Prototype Cocepts for other Plastic Processes

Section 2

Education

Training Aids for Students Studying Polymers and

Plastic Processing.

Electronics Industry

Manufacturing Enclosures for Specialist Electronic

Equipment

Anti Static Component Trays.

Film and Media Industry

Manufacture of Costumes and Sets

Animation Models and Mock Ups for Computer

Simulation

Furniture Manufacturing Industry

Chair and Seat Backs

Cutlery tray inserts

Kitchen Unit Panels and Storage Modules

Hospitals and Medical Applications

Radiotherapy Masks for Treatment of Cancer Pa-

tients

Pressure Masks for Burn Victims

Prosthesis Parts

Dental Castings

Parts for Wheelchairs and Medical Devices for the

Disabled

Machinery Manufacturers

Fabricating machine guards and electrical en-

closures.

Model Car and Aircraft Industry

Production of bodies fuselages and other parts for

models.

Museums

Variety of applications within Science and Natu-

ral History Museums

Packaging and related Industries

Point of Purchase

Trays and Plates

Cosmetic Cases and Packages

Electronics and Cassette Holders

Blister Pack Products, Skin Pack Products

Food Trays, Cups and Fast Food Containers

Plastic Sheet Extrusion

Testing and Sampling of Extruded Sheet

Sanitary Industry

Bathroom Fittings

Bathtubs, Jacuzzis and WhirlpoolsBath

Shower Surrounds, Shower Trays and Retro t

Shower Components

Signmaking Industry

Vacuum Formed Exterior Signs

Point of Sale Displays

Souvenir Industry

Making parts for and moulds to cast craft souve-

nir’s.

Theatre

Manufacture of Props, Sets and Costumes

Section 2/Applications

The Vacuum

Forming

Process

In its simplest form the process consists essentially

of inserting a thermoplastic sheet in a cold state

into the forming clamp area, heating it to the de-

sired temperature either with just a surface heater

or with twin heaters and then raising a mould from

below. The trapped air is evacuated with the as-

sistance of a vacuum system and once cooled a

reverse air supply is activated to release the plas-

tic part from the mould. The process is shown in

diagram form on  g. 3.1 page 13. In its advanced

stage pneumatic and hydraulic systems com-

plimented with sophisticated heat and process

controllers allow high speed and accurate vac-

uum forming for those heavy duty and high end

volume applications.

The thermoforming industry has developed de-

spite two fundamental shortcomings. Many other

thermoforming processes use a resin base in pow-

der or pellet form. Vacuum forming begins fur-

ther down the line with an extruded plastic sheet

which incurs an additional process and therefore

an extra cost to reach this stage. In addition,

there is generally an area of material which is cut

away from the formed part which unless reground

and recycled has to be considered as waste and

accounted for in any costings made. However

these problems have been invariably resolved by

strict control of sheet quality and by clever mould

design to minimise the amount of waste material.

Throughout this manual you will  nd useful hints

and techniques to assist in maximising the poten-

tial from this process.

Despite the above disadvantages vacuum form-

ing offers several processing advantages over

such others as blow, rotational and injection

moulding. Fairly low forming pressures are needed

therefore enabling comparatively low cost tool-

ing to be utilised and relatively large size mould-

ings to be economically fabricated which would

be otherwise cost prohibitive with other process-

es. Since the moulds witness relatively low forces,

moulds can be made of relatively inexpensive

materials and mould fabrication time reasonably

short. This results in comparatively short lead times.

It provides the perfect solution for prototype and

low quantity requirements of large parts as well as

medium size runs utilising multiple moulds. (Moulds

are discussed in greater detail in section 5).

The typical process steps can be identi ed as fol-

lows: clamping, heating with sheet level activat-

ed , pre-stretch, forming with plug assist, cooling

with air and spray mist, release and trimming They

are examined more closely under the following

sub headings.

Section 3

Clamping

The clamp frame needs to be suf ciently power-

ful enough to handle the thickest material likely to

be formed on the machine – up to 6mm with our

single heater models and up to 10mm with the

twin heater machines. If an automated process

is used the operation of the moving parts must

be guarded and interlocked to avoid acciden-

tal damage. In addition a safety guard ( in the

form of a fabricated guard or light curtain) must

be provided to protect the machine operator at

all times.

Heating

Heaters are generally infra-red elements mount-

ed within an aluminium re ector plate. In order to

obtain the best vacuum forming results, using any

material, it is essential that the sheet is heated uni-

formly over its entire surface area and throughout

its thickness. In order to achieve this it is necessary

to have a series of zones which are controlled by

energy regulators. Ceramics do have some dis-

advantage in that their high thermal mass makes

them slow to warm up (approx 15 minutes) and

slow in their response time when adjustments are

made.

More sophisticated quartz heaters are available

which have less thermal mass enabling more rap-

id response time. Pyrometers enable accurate

heat temperature control by sensing the melting

temperature of the sheet and interacting with

the operating process control. A cooling jacket is

required for the pyrometer. Precise temperature

readout is also available with a computer control-

led system working in unison with the pyrometer(s).

The megapoint system was devised by Formech

for the accurate heating of large areas, using a

standard PC and a minimum of exterior electron-

ics. The heating control system is an extension of

the process controller, allowing rapid visual inter-

pretation of the heater zoning. Temperatures are

controlled precisely using thyristor modules. Full

feedback is available to allow zones to be banked

up or down by percentage amounts. Twin heat-

ers are also recommended when forming thicker

materials as they assist in providing more uniform

heat penetration and faster cycle times.

Twin quartz heaters as used in the Formech FDH

model are advisable when forming high temper-

ature materials with critical forming temperatures.

By close control of areas of heat intensity, heat

losses around the edges caused by convection

air currents and absorption from clamp areas can

be fully compensated for and consistent results

achieved on a continuous basis. Cost savings can

also be considerable if quartz heaters are speci-

 ed as there is an adjustable percentage power

drop when the heaters are in the rear position

during the forming process.

Section 3/The Vacuum Forming

Process

Sheet Level

A photo-electric beam is incorporated in the ma-

chine to scan between the bottom heater and

the sheet of plastic. If the sheet of plastic sags

down and breaks the beam then a small amount

of air is injected into the bottom chamber, thus

lifting the sheet to stop it from sagging.

Pre-stretch ( Bubble)

Once the plastic has reached it’s forming tem-

perature or ‘plastic’ state it can be pre- stretched

to ensure even wall thickness when the vacuum is

applied. Pre-stretch is an invaluable feature when

forming deep draw parts with minimum draft an-

gles and high mould surface detail. The method

of controlling the bubble height should be such

that consistent results are obtainable. Vacuum,

air pressure and optional aids such as a plug assist

are then used to assist in moulding the heated,

stretched plastic.

Vacuum

Once the material is suitably pre-stretched a vac-

uum can be applied to assist in forming the sheet.

A dry vane vacuum pump is used to draw the air

trapped between the sheet and the mould. The

vacuum pump should be capable of maintain-

ing a differential pressure of approx 27” mercury.

With larger machines a vacuum reservoir is used

in conjunction with a high volume capacity vacu-

um pump. This enables a two stage vacuum to be

applied ensuring rapid moulding of the heated

sheet ( before the sheet temperature drops be-

low its ideal forming temperature).

Plug Assist

Plug-assist forming is the term used to describe the

use of a male plug tool, mounted on a pneumat-

ic or hydraulic cylinder situated over the forming

area of the machine, to force the material into a

female cavity within the moulding area. It ena-

bles complicated and deep-draw moulds to be

produced without webbing and with even thick-

ness distribution. The idea behind the process is to

feed as much material into the cavity prior to the

vacuum being applied in order to avoid thinning

in that area. Plug moulds are generally made from

wood or metal and a smooth surface allows the

sheet to slide whilst stretching into the mould. A

felt or leather lining ensures that the risk of prema-

ture chilling on contact is greatly reduced. Resin

plugs provide a good alternative as being good

insulators they do not affect the temperature of

the sheet.

Plug assist is also an essential feature when form-

ing multiple impression male moulds as they can

be placed very close together without the fear of

the material webbing between the formed parts.

Cooling and Release

Once formed the plastic must be allowed to

cool before being released. If released too soon

then deformation of the moulding will result in a

reject part. To speed up the cooling cycle high

speed fans are  tted and activated once the

part is formed. A spray mist option is also avail-

able whereby nozzles are attached to the fans

and a  ne mist of chilled water is directed onto

the sheet. This, in conjunction with the fans can

speed up the cooling cycle by up to 30%.

Mould temperature control units are also avail-

able which regulate the temperature within the

mould ensuring accurate and consistent cooling

times when cooling crystalline and crystallising

polymers such as PP, HDPE and PET.

Section 3/The Vacuum Forming

Process

Once cooled suf ciently the sheet can be released by a reverse pressure activated through the

vacuum system. The part is then stripped from the mould and transferred to the trimming station. See

the relevant section for further details on trimming and  nishing.

The following diagrams display the basic principles of vacuum forming.

Fig. 3.1

Section 3/The Vacuum Forming

Process

Plastics comprise a of a wide range of materials

but fundamentally fall into two groups – thermo-

set and thermoplastic, the latter being a mate-

rial which, due to the molecular structure, has the

property of softening repeatedly when heated

and hardening once cooled. Thermoplastics also

have what is known as a ‘memory’ enabling a

formed part to revert to its original state when re-

heated.

It is the thermoplastic type that is used speci cally

for thermoforming and therefore we will concen-

trate on this category in this section. Further infor-

mation on the complete range of polymers can

be obtained from the contacts listed at the end

of this manual.

Polymers are made up of molecules which in turn

are made up of atoms. These atoms have many

different combinations which all have different

properties and contain a wide range of addi-

tives to give each material its own characteristics.

There is constant research being carried out to

develop new materials suited to an ever increas-

ing range of applications. Later in this section we

have provided a breakdown of the more com-

mon materials used for thermoforming, their char-

acteristics and the applications to which they are

most suited.

Thermoplastics are split into two different groups

– amorphous and crystaline. Crystalline thermo-

plastics contain an ordered manner of molecules

and amorphous contain a random arrangement.

Generally speaking amorphous materials, e.g.

Polystyrene and ABS are easier to vacuum form as

they do not have such a critical forming tempera-

ture. When heat is applied amorphous materials

becomes soft and pliable – when it reaches this

state it is known as its Glass Transition Temperature

(Tg). If heated to a higher temperature it reaches

a Viscous state (Tv). The changes occur over a

range of temperatures and enable the operator

to have a fairly wide forming range.

Semi-crystaline and crystaline materials, e.g. Poly-

ethylene and Polypropylene have a far more criti-

cal forming temperature as they go rapidly from

the Tg state to Tv a change known as the Melt

Transition Temperature (Tm). When using crystal-

line materials is imperative that accurate tem-

perature control is used to monitor the heating

process.

In summary, the forming temperature bands for

amorphous materials is much wider and as a re-

sult are easier to process in comparison to their

semi-crystalline counterparts. In other words they

have a much better melt strength and will not

sag as much as the melt transition temperature is

reached.

The accompanying table 4.1 lists some more

commonly used amorphous and semi crystalline

materials and provides a guideline as to their tem-

perature characteristics.

Section 4

Plastic materials

and their

characteristics

Different thermoplastics have different charac-

teristics and are better suited to speci c appli-

cations. Ideally the material should be easy to

form with a low forming temperature, good  ow

characteristics and thermal strength, high impact

strength and low shrinkage on cooling.

To improve thermal stability in certain materials

like, for example, PVC, stabilisers are added to

help prevent degradation when heated.

Certain materials are known as Hygroscopic –

namely that they absorb moisture which if not pre-

dried prior to forming will result in moisture blisters

which will pit the surface of the sheet resulting in

a reject part. It is a common misconception that

the blisters are as a result of too much heat. This

in turn can lead to incorrect heating cycles being

entered which in turn cause problems with de ni-

tion on the  nished part. ( To avoid the pitting the

operator is forced into forming the part before the

plastic has reached its forming temperature).

To overcome this problem it is therefore necessary

for hygroscopic materials to be pre – dried in an

oven before forming. The drying temperature and

length of drying time depends on the material

and the thickness. It is advisable to contact the

suppliers who will advise exactly what drying tem-

perature and time is required for their materials.

E.g.: Polycarbonate with a thickness of 3mm

would require 4 hours at a drying temperature of

80-120°.

In the following pages we will look at the more

commonly used plastics and list their properties,

features and some of the more popular applica-

tions for which they are used. ( a full schedule of

applications for thermoformed products is listed

in section 2) For more detailed information and

speci cation we recommend you contact the

various suppliers who would be happy to assist

with any enquiries.

In table 4.2 you will  nd a selection of more com-

monly used materials and the heating times re-

quired using a single heater Formech machine

equipped with Infra-red ceramics ( if twin heaters

are used then the heat cycle can be reduced by

up to 30%). These are given as a guideline only

as many different grades of materials exist and

other factors which affect timescales. We would

recommend you contact the plastic manufactur-

er to obtain more accurate  gures prior to com-

mencing production.

Section 4/Plastic materials and their

characteristics

Table 4.1

Section 4/Plastic materials and their

characteristics

Table 4.2

Acrylonitrile Butadiene Styrene– (ABS)

Properties

Hard, rigid amorphous thermoplastic with good impact strength and weather resistance. It contains

a rubber content which gives it an improved impact resistance. Available with different textures and

 nishes in a range of thickness. Needs drying. Available in Fire Retardant and UV stabilised grades.

Formability

Good – forms to a high de nition.

Hygroscopic

Yes – pre drying required at approx 80° (1 hour

per mm)

Strength

Good – High Impact

Shrinkage Rates

0.3 – 0.8%

Availability

From stock

Solvent/ Filler

Methyl Ethyl Ketene (MEK), Toluene and Dichlo-

romethane Solvent will make  ller paste.

Finishing/ Machining

Machines well with Circular Saws, Routers and

Band saws– takes all sprays.

Can be Guillotined and Roller cut.

Clear

Not Available

Colours

Black / White / Grey and limited colours.

Applications

Luggage, Caravan Parts, Vehicular Parts, Sanitary

Parts, Electrical Enclosures.

Price

Medium

Stockist

Stephen Webster, Amari Plastics, Larger quantities

– Doe ex

Section 4/Plastic materials and their

characteristics

Acrylic - PMMA – (Perspex, Oroglas, Plexiglas)

Properties

A high quality hard amorphous plastic with good clarity that can be worked after forming. NOTE:

Only extruded sheet is suitable for vacuum forming effectively. Cast Acrylic will not respond well as

it displays a very small usable plastic zone. As a result it will only produce general contours with large

drape radii. Needs drying. Often replaced by PETG – see separate heading.

Formability

Tends to be brittle and is temperature sensitive.

Hygroscopic

Yes – Consult supplier for drying times.

Strength

Medium to High strength

Shrinkage Rate

0.3 – 0.8%

Availability

Ex stock – 2 weeks

Solvent/ Filler

Tensol, Solvent and gap  ller.

Finishing/ Machining

Prone to Shatter. Takes cellulose and enamel

spray. Good for hand working.

Clear

Yes.

Colours

Solid colours

Applications

Signs, Roof Lights and Domes, Baths and Sanitary

Ware, Light Diffusers

Price

Expensive

Stockist

Amari, Visijar Tuckers, Multiplastics

Section 4/Plastic materials and their

characteristics

Co-Polyester – (PETG / VIVAK)

Properties

An easy forming amorphous thermoplastic. FDA approved for food applications. Optically very good

with excellent fabricating performance. Thermoforms with ease utilising low temperatures and fast

cycle times. Can be sterilised and is resilient to a wide range of acid oils and alcohols. Not recom-

mended for use with highly alkaline solutions.

Formability

Very Good – forms to a high de nition. Forming

range 80 - 120°C

Hygroscopic

Not normally required. If sheet is exposed to high

humidity conditions for an extended time then

pre-drying is required – 8 hours at 60° C.

Strength

Good – High Impact

Availability

From stock

Solvent/ Filler

Cementing can be done using solvents or com-

mercial glues. Can be Ultrasonically Welded.

Section 4/Plastic materials and their

characteristics

Finishing/ Machining

Can be Guillotined, Saw Cut or Routered. Die

Cutting and Punching also possible up to 3mm.

Paints and Inks for Polyester can be used for print-

ing on PETG.

Clear

Yes

Colours

Limited – Contact Supplier

Applications

Point of Sale and Displays, Medical Applications

Price

Expensive – ( competitive with other clear materi-

als e.g. PC/ PMMA

Stockist

ABG, Axxis ViVak

Finishing/ Machining

Needs special etch primer before spraying. Good

machining with all methods.

Clear

Yes – Styrolux ( Clarity not to quality of PETG/ PC/

PMMA

Colours

All colours and also available in a Flocked  nish

ideal for presentation trays and inserts.

Applications

Low cost and disposable items, toys and models,

packaging and presentation, displays.

Price

Low - Medium

Stockist

Stephen Webster, Larger quantities – Doe ex.

Polystyrene– Polyphenylethene (H.I.P.S / BEXTRENE)

Properties

One of the most widely used materials An easy forming amorphous thermoplastic. Thermoforms with

ease utilising low temperatures and fast cycle times. Available with different textures and patterns. No

pre drying required. Poor UV resistance –not suitable for outdoor applications.

Formability

Very Good – forms to a high de nition. Forming

range circa 150°C

Hygroscopic

Strength

Medium to Good impact strength

Shrinkage Rate

0.3 – 0.5%

Availability

From stock

Solvent/ Filler

Dichoromethane, Toluene. Filler can be made

from dissolved plastic in solvent.

Section 4/Plastic materials and their

characteristics

Finishing/ Machining

Good for screen printing. Good machine quali-

ties. Can be ultrasonically welded, drilled and

tapped. Takes spray.

Clear

Yes

Colours

Translucent and solid colours. Opal and diffuser

patterns. Available in a variety of embossed tex-

tures.

Applications

Light diffusers, Signs, Machine Guards, Aircraft

trim, Skylights, Riot Shields, Guards and Visors

Price

Expensive

Stockist

Amari , Comco

Polycarbonate – (P.C. / LEXAN/ MAKROLON)

Properties

Hard, rigid clear amorphous material with high impact resistance and good  re rating. Self extinguish-

ing. Requires high forming temperatures. Needs drying. Excellent clarity. Similar properties to Acrylic.

Formability

Good

Hygroscopic

Yes – Drying temperature 90° C. 1mm – 1 hr. 3mm

– 4hrs. 4mm – 10hrs.

Strength

Very good impact strength

Shrinkage Rate

0.6 – 0.8%

Availability

From stock

Solvent/ Filler

Between PC components Dichloromethane or

MEK solvent. Care must be taken with solvents

as PC is a stress sensitive material and can be

adversely affected by the solvents at its weak

points. Most proprietary adhesives can be used

to join PC with metal, glass and wood.

Section 4/Plastic materials and their

characteristics

SEE PETG AS AN EXCELLENT ALTERNATIVE TO PC

Finishing/ Machining

Does not take spray

Clear

Translucent –

Colours

Black / white and colours available

Applications

Luggage, Food Containers, Toys, Enclosures,

Medical Applications, Chemical Tanks.

Price

Inexpensive

Stockist

Doe ex

Polypropylene – (PP)

Properties

PP is a semi-crystalline thermoplastic which has dif cult form characteristics with sheet sag inevitable.

Chemically inert and very  exible with minimum moisture absorption make it suitable for a wide range

of applications. High forming temperature but no drying required. Many grades of PP are available

containing  llers and additives. Co polymer as opposed to homo-polymer PP is recommended for

vacuum forming, as the copolymerisation process helps reduce stiffness and broaden the melt and

glass transition temperatures increasing thermoforming ability.

Formability

Dif cult – Translucent material goes clear when in

its plastic state – occurs within temperature band

of approx 10°C and provides excellent indicator

to forming temperature. Good temperature con-

trol required in conjunction with a sheet level fa-

cility.

Hygroscopic

Strength

Very good impact strength

Shrinkage Rate

1.5 – 2.2%

Availability

From stock

Solvent/ Filler

No solvent

Section 4/Plastic materials and their

characteristics

Clear

Translucent – Goes clear when in its plastic state

– occurs within temperature band of approx 10°C

and provides excellent indicator to forming tem-

perature.

Colours

Black / white and colours available

Applications

Caravan Parts, Vehicular Parts, Enclosures and

Housings.

Price

Inexpensive

Stockist

PE - Amari, Simona

PE FOAM – Polyformes

CONDUCTIVE PE – Dentec

Polyethelene – (PE, HDPE, LDPE, PE FOAM)

Properties

PE is a semi-crystalline thermoplastic with similar forming properties to PP. Good heat control with

sheet level required for successful forming. High shrinkage rates but good chemical resistance and

strength. Available also as a cross linked closed cell foam (PLASTAZOTE) - ideal for packaging and

liners.

Formability

PE – Dif cult

PE FOAM – Good but form at lower temperatures

to prevent surface scorching.

Hygroscopic

Strength

Very good impact strength

Shrinkage Rate

LDPE - 1.6 – 3.0%

HDPE - 3.0 – 3.5%

Availability

From stock

Solvent/ Filler

No solvents

Finishing/ Machining

Does not take spray. Takes some specialist inks.

Section 4/Plastic materials and their

characteristics

Finishing/ Machining

Does not take spray. Takes some specialist inks.

Clear

Yes – Different web widths available with thick-

ness from 150 microns – 750microns.

Colours

Black / white and colours available

Applications

Packaging, Machine Guards and Car Trim.

Price

Inexpensive

Stockist

Smaller quantities – Stephen Webster

Polyvinylchloride – (PVC)

Properties

Strong, tough thermoplastic with good transparency in thinner gauges. Good chemical and  re re-

tardant properties. Highly resistant to solvents. Thicker materials are rigid with good impact strength

ideally suited to outdoor industrial applications.

Formability

Forms well but with a tendency to web.

Hygroscopic

Strength

Good

Shrinkage Rate

N / A - Contact Supplier

Availability

From stock – Sheet or Reel

Solvent/ Filler

Toluene may be used – no others solvents suit-

able. Hot air weld or glue.

Section 4/Plastic materials and their

characteristics

Mould and

Mould Design

The thermoforming mould can be as simple as a

wooden block or as sophisticated as an injection

mould with all the ancillary elements to enable

in mould trimming. They are one of the most im-

portant parts of the thermoforming cycle. One of

the main advantages of vacuum forming is that

the pressures used are signi cantly less compared

to, for example, the injection moulding process.

The result is that vacuum formed tools can be

produced economically and in a wide range of

materials to suit different prototype and produc-

tion requirements. In this manual we concentrate

on moulds ideally suited to the vacuum forming

process. The prime function of a mould is to en-

able the machine operator to produce the nec-

essary quantity of duplicate parts before degra-

dation.

A wide range of materials can be used but it is

important to determine the correct mould mate-

rial and type most suitable for a particular appli-

cation. In this section we look  rstly at the different

types of mould material available. We then look

more closely at different types of moulds, mould

design and techniques and provide some useful

tips and hints to assist the ‘in house’ production of

moulds.

Mould Materials

Selection of the best suited mould material de-

pends largely on the severity and length of serv-

ice required. If only a few parts are required us-

ing fairly low temperature plastics then wood or

plaster could be used. However, if the quantity

requirements run into the thousands and mate-

rial temperatures are higher then ideally an alu-

minium based resin or aluminium mould would be

recommended.

Once a prototype mould has been fabricated

then it is a simple process to cast a resin mould

into a forming taken from the original tool.

See the heading Resin moulds for further details.

Section 5

1) Modelling Clay, Plaster

Modelling clay is widely used for educational

and model making purposes. It enables the user

to quickly shape a low cost prototype which can

then be cured in an oven overnight. Suitable only

for a few formings as the heat and pressures ap-

plied cause it to deteriorate rapidly.

Plaster is a good material for making inexpensive

prototype moulds. However it is essential that the

plaster is allowed to dry in a warm environment

for up to three days. The reasons are twofold;

1) Moisture can be drawn into the vacuum

system causing internal damage to the machine

and pump.

2) The time is required for the plaster to de-

velop  nal properties and stabilise the water con-

tent.

When using plaster moulds it is also essential to

have a  lter  tted to ensure no powder or parti-

cles are drawn into the vacuum system.

The surface of a plaster mould is sensitive to heat

build up and therefore tend to crack and break

up after about 50 cycles. It is not normally neces-

sary to vent plaster moulds as the surface is po-

rous.

2) Wood

Wooden moulds are cheap and easy to fabricate,

and have a longer life than plaster moulds – in

many cases being used on a production basis for

in excess of 500 formings. Hardwoods are recom-

mended, notably ‘jelutong’ and ‘obeche’ which

both have a close and even grain which makes

them easier to work and less prone to cracking

and splitting during the forming process.

Conventional woodworking techniques are used

to fabricate the moulds. It is important to ensure

the wood is kiln dried before working to ensure

there is no warping or cracking during fabrication.

As with any wood due to expansion and contrac-

tion during the forming process deterioration is

inevitable but can be reduced by sealing with

an enamel or varnish. This will enable countless

mouldings to be produced with minimum re nish-

ing required.

Because of the cost implications there are many

cases where for particularly large applications

such as signs, displays and whirlpools which re-

quire thicker materials wooden moulds are used

on a production basis.

Grease, paraf n and vaseline and silicone release

sprays can all used as a release agent.

Section 5/Mould and Mould Design

3) Cast Epoxy Resins

There are numerous resins available which are

relatively cheap and easy to work. Moulds made

from this material are durable and produce a

forming with good surface  nish. Some synthetic

resins are sensitive to surface heat build up but

this can be alleviated by incorporating aluminium

powders to increase the heat stability and also

the longevity. They are normally supplied as a two

part mix; the resin itself and a hardener.

Once an original pattern has been produced ei-

ther in wood or other material it is possible to use

a forming taken off this as a mould in which to

cast the resin.

You can see from the accompanying pictures

the process in its different stages. The pictures are

supplied courtesy of Ciba Geigy who produce

a compatible resin XD4500 for vacuum forming

applications. Alchemie also supply a range of

resin tooling systems suitable for vacuum forming

moulds.

(see the suppliers section for company details.)

The plastic moulding should be at least 2mm in

thickness, mounted into a wooden frame  lled

with sand for support to avoid distortion. It is then

necessary to mix the resin and hardener accord-

ing to instructions and then allow time for curing.

With larger moulds and to save on resin costs and

reduce mould weight it is normally advisable to  ll

the mould with wooden blocks or foam around

which the resin is poured.

Section 5/Mould and Mould Design

Select the pack size which is

appropriate to the casting

being made. The pack vol-

umes are given below as a

guide :

5kg pack - 3lt

2kg pack - 1.2lt

Pour all of the hardener into the resin container and add accelera-

tor according to the thickness of the cross section to be cast. Mixing

instructions are enclosed with each pack and these de ne accel-

erator additions. Stir thoroughly taking care to mix in resin from the

sides and bottom of the container.

After stirring allow the mix to stand for 3-5 minutes to enable air bub-

bles to rise and break. Alternatively, if the equipment is available

de-aerate in a vacuum chamber.

The mix should be cast well within its pot-life which is 40 min at 21 °C.

As with all resin systems the mix is exothermic in bulk and this effect

is increased by higher temperatures and by the use of XD 4500 ac-

celerator.

Section 5/Mould and Mould Design

Models may be made from a va-

riety of patternmaking materials,

e.g. wood, plastics, and metal etc.

Porous materials should be sealed

before use, for instance with a poly-

urethane varnish. Care taken at the

model making stage will be re ect-

ed in the quality of the  nished tool.

The next stage depends on whether

a male or female production tool is

required.

To produce a female tool, apply a

wax release agent or a suitable al-

ternative to the model in prepara-

tion for the casting operation.

A male tool can be made by taking

a vacuum forming from the model.

The forming should be backed with

a material such as plaster of paris

for rigidity and then be released as

above for casting.

Fig. 5.1

MODEL

MIX

CURING. Allow the resin

casting to harden at room

temperature and then post-

cure as follows:

16 hours at room tempera-

ture - to demould

4 hours at 40 °C

3 hours at 60 °C

2 hours at 80 °C

The above times are minimums.

In the case of tools with a cross section thickness of less than 1 in

(25mm) the room temperature stage must employ a temperature

of at least 15 °C to provide an adequate initial cure for demoulding

and further processing, e.g. machining etc.

When time is at a premium tools may be post-cured by putting them

into service. Care is essential to avoid overheating during the early

stages of tool life.

DRILLING AND MACHINING. Evacuation holes may be drilled by any

one of the engineering techniques available.

Araldite Vacuum Forming Tooling System XD 4500 is formulated to be

easy and clean to machine. It contains no hard  llers and produces

swarf rather than dust.

Section 5/Mould and Mould Design

Pour the mixed resin system slowly

and in a steady stream into the low-

est point of the mould until the re-

quired tool thickness is reached.

For mould surfaces with  ne detail,

 rst carefully brush a thin coat of mix

over the surface and then proceed

as above.

Castings of greater thickness than

the normal maximum of 3 in (75mm)

can be made by pouring subse-

quent layers of mix onto the back

of the preceding one, once it has

gelled but not fully hardened.

Wood or polystyrene blocks can be

suspended in the mould cavity to

reduce cross sectional thickness. This

serves to reduce the risk of excessive

exotherm and to economise on resin

usage.

Fig. 5.2

CAST

FINISHING

Section 5/Mould and Mould Design

Araldite Vacuum Forming Tooling System XD 4500 is designed

to meet a particular need of the toolmaker for small to medium

size cast resin tooling.

The Araldite Tooling resin range also includes resin systems suit-

able for the production of larger vacuum forming tools. These

are produced by employing gel coats, laminating systems in

combination with fabrics, and sometimes aluminium pellets, to

provide a variety of materials and techniques for many appli-

cations

Fig. 5.3

XD 4500 in use on a

small scale vacuum

former

4) Aluminium

Aluminium is frequently the material chosen for

production tooling due to its good surface hard-

ness, heat conductive properties and low wear.

It is lightweight and has an excellent strength to

weight ratio. It can be machined from blocks or

cast from patterns and due to its thermal proper-

ties heat from the formed plastic sheet is quickly

and ef ciently dissipated.

A wide range of surface  nishes are possible but

generally speaking a sand blasted surface is ideal

in that it prevents air being trapped between the

mould and heated sheet.

Aluminium moulds have a virtually unlimited

lifespan.

5) Metaphor – Porous Aluminium

Metaphor – F100 Al is a micro porous air permea-

ble aluminium. It is an exciting new breakthrough

in material science, where a material has been

custom designed speci cally to enhance the per-

formance of tools for vacuum forming. Although

expensive it has the following advantages over

aluminium;

• It permits more accurately  nished thermofor-

mings because the micro vents are micro close

together, allowing the material to be  rmly held in

place over the entire tool during tooling.

• It machines faster than aluminium and does not

require venting as it is naturally porous.

• More intricate moulds with steeper draughts are

possible.

It is available in slab form and can be obtained

through the UK supplier, Alchemie. See the suppli-

ers section for company details.

Fig. 5.4 A metaphor mould demonstrated on

one of the Formech range of vacuum forming

machines

Section 5/Mould and Mould Design

Male and Female Moulds

There are basically two kinds of moulds: male (positive) and female (negative).

See  g 5.5 below.

Male Mould

Female Mould

Several factors will affect the decision as to which is more suited and below we provide a few useful

pointers.

The top surface of a moulding (the part not in contact with the mould) is invariably the better  n-

ished surface, since it cannot pick up any marks such as dust particles from the tool itself. This factor

alone may dictate whether a male or female mould is required. Often a male tool is much easier

to make and more suitable for a single deep-draw object. On the other hand, a compartment tray

with divisions, would typically be of female construction.

Fig 5.6 shows a male and female forming and the effects of thinning to the plastic sheet.

A greater degree of de nition is achieved on the side of the plastic in contact with the

mould. The choice of a male or female should be considered so that the side requiring the

highest de nition is the one in contact with the mould especially thicker plastics.

Section 5/Mould and Mould Design

Fig. 5.5

Fig. 5.6

In general, a mould cavity which is deeper than its

diameter will give unacceptable thinning at the

bottom corners. Negative moulds will produce a

forming progressively thinner towards the bottom,

because, directly vacuum is applied, the material

will cling to the sides of the mould and will tend to

stretch like a piece of elastic. To produce a more

uniform thickness a plug should be used to stretch

the material mechanically before vacuum is ap-

plied. On a positive mould and especially if the

Pre-Stretch (bubble) option is used this mechani-

cal stretching is done automatically. It may be

worth discussing your mould requirements with

the material manufacturer if in any doubt.

Baseboards and Mounting

Generally speaking moulds should be mounted

onto baseboards prior to forming to assist release.

However, from time to time and often when a

quick prototype is required moulds are placed

directly onto the mould table and formed over.

The main setback with this method is that when

it comes to releasing the cooled part from the

mould it often, due to shrinkage, sticks to the

mould. It is then necessary to remove the part

with the mould inside and physically split the two

or trim the part whilst attached to the mould.

e.g. In the case of radiotherapy mask moulds

which have many undercuts and are placed di-

rectly on the table, the part and mould are re-

moved together and trimmed out with an air

powered hand operated slitting saw.

In most cases it is recommended to use a base-

board. The baseboard can be made from hard-

board or steel plate. It’s primary purpose is to lo-

cate and hold down the mould when using the

reverse blow facility. We recommend that a thick-

ness of between 3 – 5mm is used to ensure it sits

 ush with the top of the forming area seal on the

machine.

Depending on which machine you have will de-

termine which size the baseboard should be. We

advise that if, for example, you are utilising the full

forming area (620mm x 620mm) with the mod-

el 660 machine then the baseboard should be

made to  t tightly into this aperture.

To improve further the release the baseboard can

be mounted directly to the table. In order to do

this the table needs  rst to be drilled and tapped

in the four corners which act as the location points

for the baseboard.

When mounting moulds to the baseboard it is

necessary to ensure there is some clearance for

air ow between the mould base and the board.

This can be done by either using a thin gauze or

by incorporating channels.

Section 5/Mould and Mould Design

Draught Angles / Tapers

Most moulds are made with a base to sit  at on the forming table and must be provided with a draught

or taper to facilitate removal, ( g 5.7.) The degree of taper will depend on various factors, such as the

surface quality of the tool, the depth of near vertical faces, type of material used and if the option of

pre-stretch is being utilised. In some instances, an internal recess may be made with zero draft angle,

since the shrinkage will actually pull the sheet away from the mould. However the minimum typical

taper we would recommend to ensure good quality forming and moulding release would be circa 5°.

It therefore goes without saying that the greater the taper, the more even the thickness of sheet and

the easier it will be to release. In summary, if using female moulds we recommend a minimum taper

of 3° and 5° for male moulds.

Venting

An important feature of mould design is the requirement for suitably positioned vent holes to facili-

tate the evacuation of air trapped between the plastic sheet and the mould. Ideally located in parts

where the sheet last makes contact - notably edges, cavities and internal corners. All these areas

need to be vented to ensure good de nition and rapid air evacuation. (  g 5.8 and 5.9)

Section 5/Mould and Mould Design

Fig. 5.7

Fig. 5.8

Depending on plastic used and mould design de-

termines the number of vent holes required. Ide-

ally they should be as few as possible and small

enough to prevent them witnesses on the  nished

parts outer surface. However if too few vent holes

are provided or if the vent area is too small, the

rate of draw-down will be controlled by the rate

of air  owing from the bubble. If this is too slow

then the plastic may cool before the required

de nition has been achieved.

The diameter of vents at the surface should be

less than half the material thickness at the mould

surface or between ½ and 1mm. They can be far

larger below the surface and one solution is to

drill the smaller hole from the surface using a high

speed hand powered drill or pillar drill. The mould

can then be inverted and a larger hole drilled

from the underneath.

As an alternative to a drill it is possible to use spring

steel otherwise known as piano wire. This material

when  attened and sharpened is ideal for vent-

ing dif cult angles and for creating evacuation

holes in deeper moulds when drill lengths restrict

the venting depth.

Shrinkage and Mould Release

On cooling and hardening, a molding will tend to

shrink on to a male mould. Different thermoplastics

have differing shrinkage rates depending on the

grade and thickness. Crystalline and semi crystal-

line materials tend to shrink more than amorphous

normally due to the higher forming temperatures

required. The shrinkage rates of some of the more

widely used plastics are listed in the plastics sec-

tion under the speci ed materials, however, we

do recommend you contact the supplier for more

accurate  gures as different grades of material

may have different shrinkage rates.

The shrinkage rate of the materials will also affect

the mould design in that these differences need

to be taken into consideration during the design

phase especially if tolerances are critical.

Dif culties in stripping the molding from the tool

will depend to a large extent on mould design.

If generous tapers, no undercuts, good surface

 nish exist then removal should be fairly straight

forward.

In order to assist removal there are a number of

oil and silicone based release sprays which when

applied to the mould prior to forming facilitate

easy release.

Section 5/Mould and Mould Design

Fig. 5.9

Typical Vent Whole Position

It is also possible to use a compressed air line to

blow air between the molding and the tool.

The most effective way to ensure that the mold-

ings are released on a repeated basis is to ensure

that the moulds are mounted on baseboards

which in turn can be attached to the mould rise

and fall table on the machine. This ensures that

only the plastic part is ejected when release is ac-

tivated.

(please cross reference with the sub heading

Baseboards and Mounting)

Undercuts, Split and Multi Impression Moulds

A number of other features can be incorporated

into mould design. Although technically not pos-

sible as once formed it is impossible to release, un-

dercuts can be incorporated into a mould design

with the use of split tooling. With the use of a re-

movable side entrant tool it is possible to achieve

undercuts in forming. Tooling costs are higher in

most cases.

If the mould has an undercut at one end but an

equal angle at the other end then the  nished

part can also be released. ( g 5.10)

Section 5/Mould and Mould Design

Fig. 5.10

Not possible

Possible -

As direction of remov-

al has a greater angle

than the undercut

Fig. 5.11

Multi impression moulds are used when production requirements justify the added expense. It is nor-

mally the case that with higher levels of production the maximum forming area of the machine is

utilized by making multi impression moulds.

Mould Cooling

For large production runs we recommend a water

cooled mould. The temperature can be control-

led by a chiller unit which is connected directly

to the mould. Channels are incorporated in the

moulds during manufacture to accommodate

this facility. This helps maintain a constant mould

temperature ensure consistent results combined

with optimum cycle times. It is also possible to

mount the mould onto a cooling bolster which

contains channels for circulating cooling  uid.

Costs for these moulds are considerably higher

than conventional moulds, however it is normally

a justi able expense due to the production levels

required.

Plug Assist Design

The purpose of a plug feature is two fold. It is

used to prevent webbing in the forming of mul-

tiple male moulds which are close together and

to help achieve good wall thickness when form-

ing into deep cavities. Under normal conditions

plastic will start to thin radically once it exceeds

in depth more than 75% of the cross section ( g

5.12).

Fig. 5.12

The plug is used to push the heated material into

a female mould prior or in conjunction with the

vacuum being applied. It is used whenever large

draw ratios are required.

Draw Ratio = depth of the aperture divided by the

length of the shortest cross section. For example a

refrigerator liner has a large draw ratio in that it is

a deep molding with small cross section.

In most cases the plug assist facility is a feature

suspended above the forming area and activat-

ed by pneumatic or hydraulic systems. ( g 5.13)

However on smaller machines with manual op-

eration the plug is often operator handled on a

manual basis. The majority of plug moulds are sim-

ple in design and made from hardwood. A felt or

 ocked surface is often added to ensure the plug

glides into the aperture without tearing or mark-

ing the plastic too much.

Section 5/Mould and Mould Design

Fig. 5.12

* Depth of cavity can be 75% of the width of the

opening on the surface. Excess thinning will occur

beyond this depth.

Section 5/Mould and Mould Design

Fig. 5.13

Webbing/ Chill Marks/ Thinning

Webbing

Another factor which affects mould design is

webbing. This occurs when the material shrinks

back on itself. The cause of this can be any of the

following;

• When the mould is too high in relation to its base

area.

• By sharp vertical corners with minimum draught

angles

• By deep multiple male moulds in close proximity

to each other.(Fig 5.14)

• Excess of sheet material when using small

moulds.

A female mould Fig 5.15 can often overcome the

webbing caused by multiple male moulds.

Webbing can be voided by restricting the amount

of sheet around the mould. This can be in the form

of reducing windows ( g 5.16) or with the use of a

plug. It can be minimized by a slower application

of vacuum or by using thicker sheet. It may be

necessary to modify the mould design if all else

fails to solve the problem.

Section 5/Mould and Mould Design

Fig. 5.14

Fig. 5.15

Fig. 5.16

Chill Marks

When raising a deep draw mould into a heated

sheet, the point which  rst makes contact cools,

reducing its  ow characteristics and producing

a uneven  ow of material at the top which thins

down the sidewalls as the vacuum is applied.

( g 5.17) This can be eliminated by increasing the

draught angles and ensuring the mould is not too

cool. The pre-stretch facility (bubble) is also a

useful feature in overcoming this problem.

Thinning

This is one of the most common problems with

mould design and is the result of deep draw ra-

tios and minimum draught angles. See  g 5.18

shows thinning caused as a result of deep draw

male mould with minimum draft angles. There are

numerous solutions which include pre-stretch

( bubble), plug assist , strengthening ribs incorpo-

rated into the mould design and increased inter-

nal draught angles.

The above three problems are examined further in the trouble shooting section of this manual.

Formech offer a pattern making facility with moulds from wood, resin and aluminium.

For all your mould requirements please contact us at : sales@formech.com

Section 5/Mould and Mould Design

Fig. 5.17

Fig. 5.18

Finishing and

Trimming

Finishing and Trimming

With vacuum forming there are secondary proc-

esses and operations required before a  nished

part will be ready for the customer. Once the

formed part has cooled and been removed from

the machine the excess material is removed,

holes, slots and cut-outs are drilled into the part.

Other post forming processes include decoration,

printing, strengthening, reinforcing and assembly.

A variety of different trimming methods are used

to trim the product from the sheet. The type of

equipment best suited depends largely on the

type of cut, size of the part, draw ratio, thickness

of material and the production quantity required.

They are also factors to consider when determin-

ing the investment cost of such equipment. Be-

low are listed some of the more popular methods

adopted. Thin gauge parts are normally trimmed

on a mechanical trim press – otherwise known as a

Rollerpress. Heavy gauge parts can be removed,

placed into trim “jigs” or  xtures and trimmed with

most of the methods listed below.

Section 6

Section 6/Finishing and Trimming

Considerations

Over time you will usually be able to build up a

gut feel for which particular plastic processing

method is best suited to your particular product.

In order to do a comparison to the other process-

es that are available, you will need to take note

of the following factors:

Quantity: The amount of parts you wish to pro-

duce are critical in determining not only if vacuum

forming is the right process for this particular job,

but also the number of tools you need to make

and the total forming area. If time is limited, then

you may decide to invest in a greater numbers of

tools in order to complete the job in less time.

Price: Very few customers adopt the approach

of “money’s no object”. There is always a good

reason why a product has been produced in a

particular manner and this is usually cost related.

As a general rule once the quality and delivery

issues have been established then price usually

becomes the deciding factor in which process

will be used, although occasionally there are ex-

ceptions.

Finish: What sort of  nish do you require? What

market is the part going in to? Is the part going

to be seen? Is it for indoor or outdoor applica-

tion? How many post forming operations will be

required in order to turn the vacuum forming into

the  nished part?

Accuracy: The more accurate the part the more

expensive it becomes to produce. Vacuum form-

ing will not have the consistency of injection

moulding, because you are only forming over one

face, whereas injection moulding is a totally en-

closed die, with toleranced surfaces on all sides.

Strength: What’s the application? Will the vacu-

um forming require additional fabrication in order

to give it the rigidity it requires? Will the extra parts

be glued , welded or fastened in place?

Time: Most processes require CAD these days, ei-

ther at the design stage or to create the  nished

tool for production. This all takes time and needs

to be added to the total delivery time (including

the actual production of the parts) to work out

when the parts will be on your doorstep.

Example

Let’s assume that you intend to produce a vacu-

um formed machine cover based on the follow-

ing:

Speci cation:

Material: 2mm red high impact polystyrene.

Size: 330mm x 180mm x 50mm high.

Quantity: 500 off per annum. To be produced in

batches of ten at a time.

Machine cover showing the top side and the un-

derside.

This part would  t comfortably on our 300XQ ma-

chine and because of the small quantities and

the size of the part we would form the part one

up. In this particular case you could only  t one

tool on the table of the 300XQ. If you wanted

Section 6/Finishing and Trimming

to produce 500 parts in one go then usually this

kind of part would be produced two up on one

of our larger machines. The bene ts of increasing

the number of tools used to form the parts is that

the job is completed in a shorter time and so you

have reduced labour and machine costs and in

addition when multiples of tools are used, it usu-

ally means that less material is wasted.

Post forming operations

With most vacuum forming projects using the

slightly heavier gauge materials there is always

a certain amount of post forming operations to

be carried out and in most cases people usually

multitask during the machine operation. If you are

using an automatic machine you will have all the

time between clamping one sheet and the next

sheet. A typical automatic cycle will be as follows:

1. Place sheet in machine and clamp the mate-

rial.

2. Heat the material.

3. Pre-stretch the material.

4. Raise the tool up into the material.

5. Apply the vacuum.

6. Start the cooling cycle.

7. Release the formed part from the tool and low-

er the tool.

8. Open the clamping frame and remove the

formed sheet.

Repeat action 1 to start the next cycle.

If you are forming 2mm material with cooling fans,

then you will typically have a 3 minute cycle in

which to carry out additional tasks. It would be

very wasteful just to let the vacuum formings stack

up beside the machine and then do all the trim-

ming at a later date. Try if possible to complete

or carry out as many other operations relating to

the job as possible during the cycle. The longer

parts stand around untrimmed the more dust they

collect and the possibility of damage increases.

There is another factor that is often overlooked –

boredom. Just spending your life waiting for ma-

chines to complete their cycles is tedious. When

the operator is active and focussed on the job

when multitasking there is a tremendous sense of

achievement and the time just  ies by.

Exactly what is required to complete this machine

depends on the equipment you have available.

Let’s assume that you do not have access to a

 ve axis CNC router and that you are going to

trim the part with more conventional equipment.

(Incidentally a  ve axis CNC router would easily

trim the part in under three minutes.

Heated knife/ Scalpel

Educational user / Model maker/ R & D work – thin

plastics only.

Horizontal Bandsaw (Fig 6.4)

This method can be used for both thick and thin thermoplastics formings. The technique has a very

wide application, the essential features being a sliding table whose height relative to the saw blade

can be adjusted ( or vice versa).

Section 6/Finishing and Trimming

Fig. 6.3

Vertical Bandsaw

Fig. 6.4

Rollerpress/ Steel Rule Dies ( g 6.5)

The machine consists of a pair of adjustable, electrically driven rollers, placed one above the other.

The rollers rotate in opposite directions to draw the cutting tool and the material to be cut between

them.

High quality shape and hole cutting can be achieved with low cost cutting dies. Simple and easy

to operate they will form cut virtually all types of  exible and semi rigid materials up to a thickness of

about 4mm. Cutting widths from 700mm upwards can be accommodated.

Please refer to the products section for more information on the range available.

Section 6/Finishing and Trimming

Fig. 6.5

Guillotine

The industrial guillotine is similar to those used to

cut paper. Used to cut non brittle and thinner ma-

terials. Available in manual and powered versions

probably the most well known supplier in the U.K

is the company Edwards who have a good range

of industrial guillotines.

Clicker / Punch Press

A moving head which is moved over the trim jig

containing the formed part and then activated

to press down and cut the part.

Hand Held Air Powered Router

This is a versatile and accurate manual method

of trimming awkward shapes. The moulded part

is located in a ‘trim jig’ with guidelines along

which the operator can run the router. A bearing

is attached to the router cutter to ensure smooth

movement when trimming parts. See  g. 6.6-6.9

for examples of products trimmed using this meth-

od.

Section 6/Finishing and Trimming

Fig. 6.6

Fig. 6.7

De Soutter provide very reliable air tools and

have branches nationwide. Bearings and cutters

are added to suit.

Circular spindle saw

As the name suggests this is a circular cutter mounted on a spindle and  xed in a pillar

drill. The cutting disc is reversed to ensure safety when trimming parts. Cuts vertically from

above.

Section 6/Finishing and Trimming

Fig. 6.8

Fig. 6.9

Circular Cutter mounted from under table.

Larger industrial version of the Formech Gerbil

and powered by a router motor mounted under

a table. Ideal for cutting on a vertical edge.

Below we have provided a guideline to the pre-

ferred trimming methods for a

range of the more commonly used thermoplas-

tics.

Formech are able to assist with any questions you

may have and also provide further details of suit-

able trimming machines and suppliers. Please also

refer to the products section of the web page.

Section 5/Mould and Mould Design

Table 6.1

Trouble

Shooting

Guide

The purpose of the following section is to help the

user in overcoming some problems frequently

encountered in thermoforming. Most of the ma-

jor problems identi ed in thermoforming can be

traced back inadequate process control. Im-

proper sheet temperature at the time of forming is

a primary source of problems. Poor vacuum con-

trol and insuf cient cooling are also typical caus-

es. The table below lists the majority of recurring

problems in thermoforming along with the sug-

gested courses of action to correct or eliminate

the processing problem.

Section 7

Table. 7.1

Problem Cause Remedy

Blisters or Bubbles Overheating/Sheet heated too

rapidly

- Lower the heater temperatures or

reduce the top heater if using twin

heating.

Excessive moisture - Pre-dry sheet

- Pre-heat sheet

- Heat from both sides

- Keep material wrapped until

ready to use

Uneven Heating - Check consumption.

- Increase zone control.

Poor Mould Release Mould or part too hot - Increase cooling cycle.

- Decrease mould temperature.

Mould undercuts - Increase release time and pressure

Insufficient draft angles - Increase draft.

- Convert mould to female.

Poor mould surface - Use mould release. Improve

mould surface.

Sheet Scorching Top/Bottom surface too hot - Decrease heating cycle time.

- Decrease heater temperature.

- Check for faulty heat zones if

problem in isolated area. Pre-heat

material.

Section 7/Trouble Shooting Guide

Problem Cause Remedy

Lack of Definition Material too cold - Increase heating time.

- Increase heater temperature.

- Increase heater density and/or

wattage.

- If localized problem check heater

zone and elements.

Mould too cold - Ensure mould is at optimum temp.

for forming

Insufficient vacuum - Adjust vacuum timings.

- Check vent holes on mould.

- Increase number and or diameter of

vacuum holes.

- Check mould is not restricting

vacuum flow - are vacuum tracks in

mould adequate?

- Check for leakage in vacuum system

- Increase vacuum capacity

Webbing Material too hot - Shorten cycle time.

- Lower heater temperature.

Insufficient vacuum - Check system for leaks

- Increase size of vacuum holes

- Check for blocked holes

Incorrect Pre-Stretch height - Adjust pre-stretch flow and time

Excess material - Reduce material size and use reduc-

ing windows

Poor mould design - Increase radii improve draw ratios

- Use plug/ring assist.

- Use assist blocks to pull out web-

bing.

- Increase spacing between moulds.

- Switch to female mould.

Vacuum speed too fast - Regulate to suit.

- Use smaller vacuum holes.

Section 7/Trouble Shooting Guide

Problem Cause Remedy

Whitening Part removed too early - Part must be below set temp. before

removing

- Increase cooling cycle.

- Add extra cooling fans

- Utilise a spray mist facility

- Use water cooled moulds.

Uneven part cooling - Increase mould temp. and/or temp.

uniformity.

Poor mould design - Redesign. Incorporate ribs/tapers

Poor sheet distribution - Check for uneven heating

- Use plug assist or pre-stretch for

deep draw.

Excessive mould release pres-

sure or timing

- Adjust to suit.

Chill Marks Stretching stops when sheet

makes contact with cold

mould/plug

- Increase mould temp.

- Increase plug temp.

Mould design - Use plug to assist mould flow.

Insufficient pre-stretch - Increase pressure, flow or time

Plug tool too cold - Wrap tool with felt or similar.

Thinning at corners on deep

draw parts

Uncontrolled sheet heat - Improve zone control.

Sheet formed too slow - Use more vacuum

- Increase number and size of vent

holes

Too much pre-stretch - Decrease flow or timing.

Cold spots - Check elements

- Check for draughts.

Too thin gauge - Increase

Uncontrolled material distri-

bution

- Use plug assist and/or pre-stretch

Section 7/Trouble Shooting Guide

Problem Cause Remedy

Tearing of sheet whilst forming Sheet too hot - Decrease heating cycle time.

- Decrease temp. settings.

- Pre-heat sheet.

Sheet too cold - Increase heating cycle time

- Increase temp. settings.

Pre-stretch too large - Reduce time and flow.

Mould design - Increase corner radii and draw

ratio.

Improper material selection - Consult supplier

Parts stick in mould Part temp. too high - Increase cooling cycle.

- Lower mould temp.

- Reduce heating cycle time.

Mould not fixed on base-

board

- Mount mould to baseboard ensure

it is then fixed to table.

Insufficient draft - Increase taper.

Mould undercuts - Increase air eject.

- Remove part earlier and use cooling

jigs.

- Use retractable undercut segments

in mould.

Poor mould quality - Polish mould.

- Use release agent.

- Remove rough edges from wooden

moulds.

Nipples on formed parts Sheet too hot - Reduce heating cycle

- Reduce heat temp.

Vacuum holes too large Plug holes/re-drill.

Excessive sag Sheet too hot - Decrease heat cycle time.

- Decrease heater temp.

Sheet area too large - Improve zone control

- Ensure auto level feature activated.

Section 7/Trouble Shooting Guide

Problem Cause Remedy

Marks on finished moulding Dirty mould - Clean mould with air gun after each

cycle.

Water droplets - Decrease spray mist.

- Check all hoses, gaskets for leaks.

Poor mould surface - Smooth/Polish surface.

Scratched sheet - Inspect handling procedure

- Ensure protective film removed im-

mediatly prior to forming.

Plastic pulls from clamp frame Insufficient clamp pressure - Check clamp pressure.

- Adjust alignment.

- Heat frame prior to inserting sheet.

Material too cold - Increase heat cycle.

Wrong material selection - Consult supplier.

Supplier guide The following list of suppliers has been divided into

four sub sections;

1. Formech Int Ltd – Machines & Spares, An-

cillary Equipment.

2. Plastic Stockists,

3. Plastic Extruders (minimum order 500 - 1000

kilos)

4. Resin/ mould material suppliers.

Section 8

Formech International Ltd

Sales and Administration

Unit 4, Thrales End Business Park

Thrales End Lane

Harpenden

Hertfordshire

AL5 3NS

England

Tel: + 44 (0)1582 469 797

Fax: + 44 (0)1582 469 646

Email: sales@formech.com

www.formech.com

Spare Parts and Service

Unit 4, Thrales End Business Park

Thrales End Lane

Harpenden

Hertfordshire

AL5 3NS

England

Tel: + 44 (0)1582 469 797

Fax: + 44 (0)1582 469 646

Email: service@formech.com

www.formech.com

Suppliers of:

• Vacuum Forming Machines.

• Reducing Windows, Spare Parts and Spare Parts Kit.

• Rollerpresses, Horizontal Bandsaws and Gerbils

• Drying Ovens, Line Bending Equipment.

• Tooling – Prototype and Production

• Tradeforming facility

Section 8/Supplier guide

Plastic Sheet Stockists

ABG Ltd

Galowhill Road

Brackmills

Northampton

NN4 7EE

England

Tel: + 44 (0)1604 70 08 80

Fax: + 44 (0)1604 76 61 13

Email: cs@abgrp.co.uk

www.abgrp.co.uk

Suppliers of:

PETG. Axxis Vivak. Clear polyester

sheet.

Amari Plastic Ltd

Branches nationwide.

Head Of ce:

Holmes House

24 – 30 Baker Street

Weybridge

Surrey

KT13 8AU

England

Tel: + 44 (0)1932 83 50 00

Fax: + 44 (0)1932 83 50 01

Email: ho@amariplastics.com

www.amariplastics.com

Suppliers of:

ABS, PC, PP, PMMA

Multiplastics Ltd

Paycocke Road

Basildon

Essex

SS14 3EU

England

Tel: + 44 (0)1268 28 91 81

Fax: + 44 (0)1268 53 04 76

Email: cturner@multiplastics.co.uk

Suppliers of:

Acrylic, PC.

Simona Ltd

Telford Drive

Brookmead Ind. Park

Stafford

ST16 3ST

England

Tel: + 44 (0)1785 22 24 44

Fax: + 44 (0)1785 22 20 80

Suppliers of:

PE, PP, PETG

Stephen Webster Plastics Ltd

Brick Knoll Park

Ashley Road

St Albans

Herts

AL1 5PL

England

Tel: + 44 (0)1727 86 31 38

Fax: + 44 (0)1727 84 42 91

Email: sales@stephen-webster.

co.uk

www.stephen-webster.co.uk

Suppliers of:

• Holds in stock a large range of

Sheet Polystyrene in black, white,

colours and textures.

• Also supplies ABS, PETG, PVC,

Acrylic Capped ABS.

• Excellent delivery times and no

minimum.

• Discounts for quantity. Free deliv-

ery over £ 50.00

UKAP

Sterling House

21-25 Station Lane

Hornchurch

Essex

RM12 6JL

England

Tel: + 44 (0)1708 44 77 88

Fax: + 44 (0)1708 44 11 11

Email: sales@ukap.co.uk

www.ukap.co.uk

Suppliers of:

Flocked P.S and PVC (reel form

only)

Polyformes Ltd

Cherry court Way

Stanbridge Road

Leighton Buzzard

Beds

LU7 8HU

England

Tel: + 44 (0)1525 85 24 44

Fax: + 44 (0)1525 85 04 84

Email: sales@polyformes.co.uk

www.polyformes.co.uk

Suppliers of:

Closed cell PE foams.

Section 8/Supplier guide

Plastic Extruders

Athlone Extrusions Ltd

Grace Road

Athlone

Co. Westmeath

Ireland

Tel: + 353 (0)902 92 67 9

Fax: + 353 (0)902 94 08 6

Email: info@athloneextrusions.ie

Extruders of:

P.S. ABS (Fire retardant) Acrylic

Capped ABS

Doe ex PLC

Holmethorpe Avenue

Redhill

Surrey

RH1 2NR

England

Tel: + 44 (0)1737 77 12 21

Fax: + 44 (0)1737 77 24 61

Email: sales.doe ex@dial-pipex.

com

Suppliers of:

Polystyrene / Conductive PE and

Wardle Storeys

Brantham Works

Brantham

Manningtree

Essex

CO11 1NJ

England

Tel: + 44 (0)1206 39 24 01

Fax: + 44 (0)1206 39 52 88

Email: sales@wardlestoreys.com

Extuders of:

HDPE, PP.(Minimum order- 500

Kilos)

Resin Suppliers

Alchemie Limited

Warwick Road

Kineton

Warwick

CV35 0HU

England

Tel: + 44 (0)1926 64 16 00

Fax: + 44 (0)1926 64 16 98

Email: sales@alchemie.com

www.alchemie.com

Suppliers of:

• Epoxy Resin Tooling Systems for

vacuum forming.

• Metaphor – Porous Aluminium

Further

Information

We hope this manual has provided a useful insight

into vacuum forming. Whilst we have tried to cov-

er all aspects of the process the following industry

bodies and associations are able to provide fur-

ther assistance and information on the thermofor-

ming process in general. Please see our contacts

section for links to the following companies or you

can link directly below.

Section 9

British Plastic Federation (BPF)

5-6 Bath Place

Rivington Street

London

EC2A 3JE

England

Tel: + 44 (0)20 74 57 50 00

Fax: + 44 (0)20 74 57 50 45

www.bpf.co.uk

British Polymer Training

Association(BPTA)

Hales eld 7

Telford

Shropshire

TF7 4NA

England

Tel: + 44 (0)1952 58 70 20

Fax: + 44 (0)1952 58 20 65

Email: samr@bptaserv.co.uk

www.bpta.co.uk

Institute of Materials

1 Carlton House Terrace

London

SW1Y 5DB

England

Tel: + 44 (0)20 74 51 73 00

Fax: + 44 (0)20 83 91 70 2

www.materials.org.uk

Rubber & Plastics Research Association

of G.B. ( RAPRA)

Shawbury

Shrewsbury

Shropshire

England

Tel: + 44 (0)1939 25 03 83

Fax: + 44 (0)1939 25 11 18

Email: info@rapra.net

www.rapra.net

Vacuum Forming Guide

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