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Examples ofmulti-component mould designs

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Know-how EditionProcessing Technology


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Processing Technology

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Examples of multi-component mould designs

1. Definition of multi-component injection moulding

Process technology Numerous processes have already been developed and successfullyimplemented for producing multi-coloured plastic parts. Such proc-

esses include printing, hot stamping, vacuum deposition, or coating,

laser inscription, the in-mould laminating of printed films as part of

the IMD process, assembly of individually moulded parts of various

colours, and last but not least multi-component injection moulding.

All these processes are tried and tested. When deciding on the ideal

production method it is important to carry out a comparison of the

various options and the different procedures. This is particularly true

when it comes to multi-component injection moulding.

Multi-component injection moulding may offer a huge range of possi-bilities, but these can only be used to the full if there is due regard for

the manufacturing process when the moulded part is being designed.

What really matters in this respect, in addition to the machine equip-

ment, is the mould, the moulds construction and the manner in

which it functions, since not all parts can be produced according

to the same mould concept. The following documentation therefore

provides an overview of the various mould concepts implemented in

the area of multi-component injection moulding.

Multi-component injection moulding

Multi-component injection moulding is a blanket term covering all

those processes that involve treating and processing more than oneplastic component. This makes it possible to introduce the melt into

the cavity via one or more sprue systems inside the mould.


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Illustration: Examples of multi-colour injection moulding

Multi-material injection moulding Multi-component injection moulding does not just allow different

colours of plastic to be combined, but also different types of plastic.

That is why reference is also made to multi-material injection mould-

ing or two component injection moulding.

Hard-soft combinations A large proportion of these two component applications are madeup of what are known as hard-soft combinations. In the majority of

cases, hard-soft combinations consist of a thermoplastic and a ther-

moplastic elastomer. Consequently, components can be produced,

which, in addition to having a hard and abrasion-resistant basic

body, also feature soft areas that are able to act as seals and shock

absorbers, or can make the part more comfortable to hold (better

handling).

Adhesion When combining different materials, attention should be paid to the

adhesion properties of the raw materials, as well as to the differ-

ences in their shrinkage and thermal expansion properties and their

processing temperatures. The adhesive strength which is attainedin the interfacial areas may be produced by chemical bonding or

mechanical anchoring (e.g. undercut shapes).

Two of the processes that can be performed with a sprue system are

the techniques of interval injection moulding and sandwich injection

moulding, both of which entail the use of a special nozzle to combine

the melt streams and deposit them in the conventional mould.

The following document deals exclusively with processes that involveseveral sprue systems and with the special mould technology associ-

ated with these. A clear distinction is made in the document between

multi-colour and multi-material injection moulding. Multi-colour injec-

tion moulding refers to cases where the same material is processed in

a variety of colours and multi-material injection moulding to situations

where different types of material are used.

Multi-colour injection moulding Multi-colour injection moulding involves the production of parts that

are made from different coloured plastics. The individual compo-

nents are not merged, but are kept strictly separate. This means that

visual effects can be created by combining areas of different colours

or even transparent and optically conductive areas. As a result, themoulded parts are resistant to external influences such as chemical,

thermal and mechanical loads.


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Illustration: Examples of hard-soft combinations

Elastomer/LSR and thermoplastic combinations

In addition to combining thermoplastics with TPEs, it is also possible

to create hard-soft combinations from thermoplastics and elastomers

such as NBR or liquid silicone rubber (LSR). However, heat separation

inside the mould becomes a problem here, since higher temperatures

are required for vulcanisation of the elastomers. Even the cold runner

systems that are often used for processing LSR, and which prevent

premature cross-linking of the material inside the sprue, must be ther-

mally insulated from any hot runner systems that might be used for

the thermoplastic components. Of course, with this procedure only

those thermoplastics that can withstand the short-term high vulcanis-

ing temperatures of the elastomers can be used as the other material

in the composite.

Illustration: Hard - soft compounds made from thermoplastics and liquid

silicone rubber (LSR)

Assembly injection moulding In addition to bonding materials in such a way as to make them prac-

tically inseparable, it is also possible to join together twoincompat-

ible materials to make one moulded part. Due to the geometry of the

moulded part and the difference in the shrinkage properties and com-

patibility of the materials, two halves are created which are attached

to one another in such a way that they can move. This means that

when the moulded part leaves the mould it is already equipped withan integrated joint, which enables it to move. This dispenses with

the need for a distinct assembly process at a later stage. Examples

of applications include moveable air exit flaps for vehicle interiors and

action figures.


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2. Mould concepts for multi-component injection moulding

Along with the machine equipment, the mould, its construction and

the manner in which it functions are of the utmost importance. In

order to take full advantage of what multi-component technology hasto offer, there must be due regard for production when the moulded

parts are being designed. It is therefore necessary for part designers

to work closely together with mould engineers, since not all parts can

be produced using the same mould concept.

Mould concepts In principle there are two different types of mould concept. The first

involves transferring the pre-moulded part to another cavity by means

of a rotary movement, by hand or by using a robotics system, so that

it may then be encapsulated by the second component. This entails

switching from one mould cavity to another.

The second concept involves the use of internal movements inside

the mould to free up space for the next set of components, i.e. only

one cavity is used.

Rotary moulds The first process step to be performed when using rotary moulds

is the initial production of a pre-moulded part in one of the cavities.

Subsequently, during the next step, the part is manoeuvred into the

required position by transferring it into a second cavity by means of

a rotary movement of 180, so that it can be encapsulated by the

second component.

The advantage of using rotary moulds is that pre-moulded parts can

be produced at the same time that parts are encapsulated by thesecond component.

Depending on the geometry of the part, the following different design

systems are available for performing the rotary movement, whereby

either the entire mould half or individual parts of the mould are

rotated:

Rotation of a stripper plate

Rotation of a platen by means of an ejector movement

Rotation of an insert

Rotation of the moveable mould half

Rotation of a central platen

Far more is expected of rotary moulds in terms of precision than of

moulds used to produce plastic parts of just one colour, because they

must be spot on.


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Altering the mould using an internal movement inside the mould

By shifting the cores or sliders inside the mould as part of the com-

posite injection moulding process, hollow spaces can first of all be

closed off and subsequently reopened (see illustration).

The mould can be configured in the following ways:

Lifting and lowering movements

Sliding movements

The advantage offered by this process is that parts can be produced

without the need for intermediate opening of the mould and without

further transport of the pre-moulded part. However, production is

performed in a strict sequence, whereas with rotary moulds simulta-

neous operations are possible.

Transfer by hand or robotic system As an alternative to the rotary movement, the pre-moulded part can

also be transferred from the first cavity to a second one ready for the

final injection stage, either by using conventional means (i.e. by hand)

or a robotic system.

Transfer is extremely advantageous when working with cross-linking

materials such as liquid silicones (LSR), because the mould can be

divided into two distinct halves, each of which is completely thermally

insulated from the other.

Simultaneous direct injection Another variation is the direct simultaneous injection of two compo-

nents into a single cavity, without having to alter the mould. However,

the inevitable consequence of using this process is an uneven divid-

ing line between the two materials with the result that it is only used

for parts whose ultimate visual appearance is not of prime concern.


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3. Examples of multi-component mould designs

3.1. Rotary moulds With multi-component injection moulding the pre-moulded parts are

generally transferred by means of a rotary movement as described

previously. All of the processes - multiple injections, transport of thepre-moulded part, ejection of the finished parts and demoulding

of the sprues - are performed automatically as part of the machine

cycle. Consequently, the mould has an extremely important part to

play here, because it comprises the entire process.

3.1.1 The ARBURG indexing unit As described previously, where multi-colour technology is used, the

pre-moulded part is generally transported by means of a rotary move-

ment. This may be performed on an alternating or on a continuous

basis and may include rotation of the entire mould half or the rotation

of one index platen only. Since the installation of an appropriate rotary

drive mechanism in the mould is both time and cost intensive, index-

ing units have been developed which are mounted in a fixed position

on the moveable machine mounting platen and which may be utiliseduniversally for different moulds.

Illustration: ARBURG indexing unit designed to be mounted on the moveable

mould platen

Indexing units that are geared towards specific machines are a

worthwhile accessory for multi-colour injection moulding and enable

the costs associated with the mould to be reduced considerably.

Since the cost of a machine-related indexing unit is only margin-

ally higher than that for a drive directly integrated into the mould,the investment usually starts paying off from as soon as the second

mould. There are generally no technical restrictions on the functional-

ity of the moulds.


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Illustration: Indexing unit with servo-electric drive

Construction and functioning of the indexing unit

The following illustrations show an indexing unit for rotating the

entire moveable mould half by 180 or 120. It consists of a rotating

inner platen and a fixed backing platen which is screwed onto to the

mounting platen of the machine. Roller bearings are used to hold therotating inner platen to its outside diameter, so that it cannot tip for-

wards. It is driven by an externally located hydraulic motor and the

final positions are marked by mechanical positive stops.

The cooling water supply for up to four separate temperature control

circuits is connected to the side of the fixed platen and is supplied

internally to the mould via the centre spindle. Accordingly, the bores

for the cooling system must be central to ensure that the mould can

be connected. What is more, once the final positions have been

reached, the moulds ejection system can be connected to or dis-

connected from the machines hydraulic ejector system so that the

moulds full functionality is ensured. In addition to performing the

ejector movement, it is also possible to perform a lifting or lowering

movement inside the mould by means of a stop dog.

Hydraulic drive The drive for the indexing unit consists of a hydraulic motor, which is

connected and programmed via the core pull control. Pneumatic and

temperature connections for the mould are guided through the centre

shaft.

Electric indexing unit Indexing units with a servo-electric drive permit much quicker move-ments compared to hydraulic indexing units. These movements

can also be carried out independently of the hydraulic axes of the

machine. An additional advantage of the electric drive is that the final

position can be reached with the utmost accuracy without the need

for any final mechanical stop dogs. All the movement sequences and

angles of rotation can be programmed directly via the control system

and saved together with the mould record.


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Construction and functioning of indexing units

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2

3

4

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1 Radial bearings of the rotating platen

2 Radial bearings of the cooling shaft

3 Axial bearings of the rotating platen (

roller bearings)

4 Axial bearings of the rotating platen(plain bearings)

5 Stop ring and stop dog

6 Rotating platen drive

7 Cooling connections (up to 4 coolingcircuits)

8 Switch and control cam for final

position and 2nd speed

9 Bore for ejector pin

10 Bores for lifting and lowering move

ments

11 Mould centring system

12 Stop ring

13 Sliding stop dog connected to

hydraulic cylinder

Indexing unit for alternate rotation of the moveable mould half by 180

Indexing unit for rotating in one direction by 120 or 180

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13

11


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Rotation of a single insert For moulds on which only one insert or platen is to be rotated, the

indexing unit can be modified using a special kit so that only one of

the moulds spindles is operated.

In addition, the indexing units cooling shaft is replaced by the drive

bushing (2). An additional platen (3) is mounted onto the flange (4),so that the rotating platen (1) is free to revolve on the inside and will

only operate the drive bushing (2). A thermostat block (5), which is

connected to the shaft of the mould enables the temperature of the

rotating platen or the rotating insert to be moderated.

So that the rotating insert or rotating platen can be moved backwards

and forwards before rotation, the thermostat block (5) is connected

to the machines hydraulic ejector. This enables the start time and the

stroke movement for the rotating insert to be programmed precisely

via the ejector control system.

If an ejector system is still required for the mould, then this must be

achieved by means of another core pull.

Illustration: Adaptation of an indexing unit


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3.1.2 Rotation of a stripper plate With this mould concept, a pre-moulded part is produced in the

first injection direction at the same time that a second component is

moulded onto the pre-moulded part from the previous cycle in the

second injection direction.

The process Once the holding pressure time and the cooling time have elapsed,the mould is opened. The pre-moulded part and the finished part

remain attached to the mould core and are removed from the side

that is fixed. The tunnel gate connecting with the pre-moulded part

and finished part is detached. The mould moves upwards and the

central spindle that is connected to the rotating platen is pushed

forwards by the machines hydraulic ejector system. By means of

this process the mould cores are removed from the pre-moulded and

the finished parts. An external attachment on the pre-moulded part

ensures that it can come free from the core, but still remains inside

the rotating platen. The finished parts and the sprue for the pre-

moulded and finished parts are now free to drop out of the mould.

The central spindle rotates the rotating platen by 180. The rota-

tion can be performed using a rack-and-pinion device actuated by a

hydraulic cylinder or using an indexing unit with a hydraulic motor. If

the sprues or the finished part have not yet dropped out of the mould

of their own accord, then this will happen as a result of the cen-

trifugal force generated during rotation. Once the rotation has been

performed, only the pre-moulded part will be left inside the mould.

The rotating platen is withdrawn again by the hydraulic ejector. The

second stations core enters the pre-moulded part and lifts it up. Fol-

lowing the close mould operation, it is possible to resume work with

both injection units.

Some typical applications involving the rotation of a stripper plateare the production of multi-coloured keyboard elements or switches,

whereby abrasion-resistant lettering is incorporated into the compo-

nent.

Illustration: Examples of applications involving rotation of a stripper plate


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Example 3.1.2: Rotation of a stripper plate


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3.1.3 Rotation of a platen by means of an ejector movement

It is not always possible to work with a rotating platen that also

acts as a stripper plate. So that the advantages of a rotating platen

may be enjoyed (simpler mould construction), this mould concept

also allows the part to be removed from the mould using an ejec-tor system. In this case the injection moulding machine must be

equipped with an additional core pull.

The process Up until the point where the mould is opened, the procedure is identi-

cal to that of the system described above. Once the mould opening

operation has been performed, the finished part is first of all ejected

by means of an ejector system. The ejector system is operated inside

the mould using additional hydraulic cylinders. The rotating platen

is connected to the machines hydraulic ejector and this prevents

it from lifting up as the part is being ejected. The remainder of the

process is the same as for example 3.1.2, i.e. advancing the hydraulic

ejector, rotating the rotating platen, retracting the hydraulic ejectorand closing the mould.

Illustration: Examples of applications involving rotation of a platen by meansof an ejector movement


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Example 3.1.3: Rotation of a platen by means of an ejector

movement


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3.1.4 Rotation of an insert Both the mould concept and the process involved here are identical

to those for examples 3.1.2 and 3.1.3. However, in this instance it is

not a platen that is rotated, but a single insert inside the mould. As

the illustrations show, both the insert and the ejector system can be

designed in many different ways.

Illustration: Examples of applications involving rotation of an insert

Illustration: Rotation of an insert

These first three mould concepts are all used when the mould con-

tours on the moveableandon the fixed mould halves have to be

swapped over for the second injection stage.

Nevertheless, by using lifting and lowering movements, in certaincases it is even possible to change the mould contour for moulds

whose moveable mould half is rotated.

In such an event, the stamp or inserts must be raised and lowered.

These movements inside the moveable mould half can either be

driven hydraulically or pneumatically, or mechanically via the indexing

unit.


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Example 3.1.4: Rotation of an insert

Figure A

Design variant: Stripper plate moved by means of a core pull

Figure B


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3.1.5 Rotation of the moveable mould half

In this design the ejector side consists of two identical mould halves.

As a result, two ejector systems are also required. As a rule, the pre-

moulded part remains on the core of the moveable mould half and

is then rotated by 180 into the second station on the nozzle side,where it is encapsulated by the second component.

Illustration: Examples of applications involving rotation of the moveable mould

half

Once the mould has been opened, the finished part is ejected by theejector system associated with the second injection shot. The ejec-

tor system is actuated by an ejector cross, which is connected to the

machines hydraulic ejector.

If the moulds ejector plates are retracted into the final position or

are actuated a number of times, it is possible to connect the moulds

ejector system to the ejector of the ejector cross (see figure B).

When the rotational operation is performed, the moulds ejector pins

enter a groove in the indexing units rear platen. The moulds ejec-

tor pin is connected to the ejection tie bar of the ejector cross in the

ejector station.

Illustration: Ejector coupling


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Example 3.1.5: Rotation of the moveable mould half

Figure A

Figure B


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3.1.6 Rotation of the moveable mould half where two sprue systems are used

If sprue systems are used (during the first and second injection shot)

in connection with the rotation of the moveable mould half, then the

sprues for the first and second shot must be ejected along with the

finished parts. This can be performed using two ejector plates, whichare stacked on top of one another.

The ejector pins of the sprue distributor are grouped together on the

front plate that goes all the way through. The ejector pins of the part

are grouped together on the divided rear ejector plates. Both ejec-

tor plates can be actuated separately via three ejector pins using the

ejector cross on the machine (figure B).

Illustration: Examples of applications involving rotation of the moveable

mould half


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Example 3.1.6: Rotation of the moveable mould half

Figure A

Figure B


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Illustration: Making undercut shapes available through movement of thestamp

Moulded parts bearing symbols or characters which are of a different colour

There is a specific type of problem associated with the production

of parts that bear characters or symbols of a different colour. Many

characters and symbols such as A, B and O, for example, contain

one or more islands. These enclosed areas cannot all be injection

moulded individually, but must somehow be combined with the area

outside them.

3.1.7 Rotation of the moveable mould half along with movement of stamps or inserts

In the case of certain applications recesses must be created through

the movement of stamps or inserts. The easiest way to perform these

movements is again through the use of an indexing unit.

Undercut shapes Undercut shapes for mechanical anchoring of the second component

can be made available by moving stamps or inserts. This becomes

necessary if the two materials to be used in the composite are not

conducive to the forming of a chemical bond.

Illustration: Switch elements bearing symbols of different colours


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Illustration: Fashioning of the moulded part in cases where there are enclosed

areas

In the case of symbols that are to be illuminated from behind, as is

necessary for switches for the automotive industry for example, the

connection between the islands and the external contour must be

severed when the parts are ejected (see illustration).

The figure displayed below shows the most commonly used method

for filling in the enclosed areas. First, a basic body (pre-moulded

part) is moulded in the colour to be used for the characters (1). The

lettering on this must be embossed. There also have to be recesses

underneath the characters so that the islands can be filled in with the

plastic of the other colour during the final injection stage (2). Accessto these recesses is achieved by encapsulation with the second com-

ponent by moving a stamp.

Illustration: Fashioning of the moulded part in the case of backlit switches


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The easiest way to move stamps or inserts is to use an indexing unit.

Two platens containing the stamps or inserts are lowered into the first

station. Depending on the part this can also be performed in reverse.

In order that these lifting and lowering movements may be performed

two bores for each of the mould halves are drilled into the indexing

unit. At the station where the inserts or stamps are raised, two pinson the rear platen of the indexing unit are inserted into the bores so

that they are level with the platens surface.

There are no such pins in the other station. The platen can be low-

ered by means of return pins. The pins in the mould can be sunk into

the empty blind holes. During subsequent ejection of the finished

parts (figure B) the platen must be raised along with them. It is only

then that the moveable mould half can be rotated.

The advantage of using rotating platen systems (examples 3.1.2-

3.1.4) is that no additional mechanism is required inside the mould.

The stamps or inserts are simply switched over.

Illustration: Example application involving a hard-soft combination handle

plate


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Example 3.1.7: Movement of stamps or inserts

Figure A

Figure B


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3.1.8 Rotation of a central platen (staged mould)

In the case of certain applications the mould can be constructed as

a staged mould. Pre-injection is performed at one stage, with the

second part being added at the second stage to produce the finished

moulded part. Transfer from the pre-injection station to the finalinjection station is achieved by rotating the intermediate platen.

The advantage of this concept is that it allows the entire surface of

the mould to be exploited. By contrast, in the case of rotary moulds

only half of the moulds surface is available, because it has to be

divided into areas for the pre-injection and final injection stages.

This type of rotary system also offers advantages with regard to parts

that feature widely differing areas of buoyancy, e.g. casing compo-

nents with an injection moulded seal all the way round. In a case such

as this, the part can be moulded centrally so that no asymmetrical

buoyancy forces come into play inside the machine. An additionaladvantage of this system is the reduction it brings in the injection

moulding machines clamping force.

However, the flip plate system can only be used to a limited extent.

This procedure is not suited to situations where mould contours on

both sides must be switched.

A large number of two-component parts remain on the core on the

ejector side during rotation and are ejected from this side. Where

components of this kind are concerned, the flip plate must be

equipped with two ejector systems, which makes the moulds highly

complex and therefore too expensive.

Illustration: Example of an application involving a staged mould


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Example 3.1.8: Rotation of a central platen (staged mould)

Figure A

Figure B


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3.1.9 Rotary moulds for three-component injection moulding

As a rule, three-component parts are produced using two or three-

station moulds.

Two-station mould Where a two-station mould is used, at station 1 the pre-mouldedpart is produced using two injection units, which both inject simul-

taneously. The pre-moulded part is transferred to station 2 by rotat-

ing the moveable mould platen by 180. The finished moulded part

is then produced by encapsulating the pre-moulded part with the

third component. Following opening of the mould, the finished part is

ejected along with the sprues.

Three-station mould Where a three-station mould is used, at station 1 a pre-moulded

part is produced using the first injection unit. By rotating the move-

able mould platen by 120 the second component can be added at

station 2. An additional rotation of 120 transfers the two-component

part to station 3, where the final stage is performed by encapsulating

it with the third component.

Following opening of the mould, the finished part is again ejected

along with the sprues.


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3.1.10 Rotary moulds for four-component injection moulding

Two-station mould A two-station mould can be constructed in a similar manner to that

described for a three-component mould. In the first process step,

the pre-moulded parts are produced by the simultaneous injection of

three components. The entire mould half then rotates by 180 to thesecond position. Here, the fourth component is injected around the

pre-moulded parts to form the finished parts.

Four-station mould A four-station mould can be used to produce multi-layer plastic

parts, for example. The application of regranulated material and

resistive layers which hinder the diffusion of oxygen is possible in a

simple manner. The illustration depicts the step-by-step build-up of

a four-layer moulded part. The innermost layer is produced at thefirst station. The mould then cycles by 90 one station further. There,

the second component is injected around the first. The mould half

then rotates on to the third station, and finally to the fourth station

for the final production step. Once here, the outer protective layer, or

the visible layer of the moulded part, is injected onto the part. After

expiration of the cooling period, the finished multi layer part may be

demoulded from the cavity. In the actual cycle, each time the mould

is opened a completed moulded part is produced.


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3.1.11 Assembly injection moulding using rotary moulds

In the case of certain applications, components that have to be

joined together after injection moulding can be injection moulded

separately using a two-component machine and subsequently

assembled inside the mould.

These kinds of assembly tasks can be performed by means of two-

station rotary moulds, for example. One possible mould concept for

assembly injection moulding is illustrated below. This is based on the

example of a cable bushing to which an internal seal is to be added.

Illustration: Example application involving a cable bushing with seal to be

internally mounted

The process First of all, each of the two individual components are simultane-

ously injection moulded at the relevant station. Then, once the mould

has been opened, the first component is transferred to the second

station by rotating the insert and is then positioned over the core of

the second component. Assembly of the seal and cable bushing is

achieved through the movement of a stamp via a core pull.

The advantage of assembly injection moulding is that it obviates the

need for any additional joining techniques and secondary produc-

tion operations. Under normal conditions very expensive automation

solutions would be required in order to assemble the parts efficientlyfollowing the injection moulding process.


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Example 3.1.11: Assembly injection moulding

1. Process step

Components 1 and 2 injection

moulded

3. Process step

Insert advanced

(using hydraulic ejector)

2. Process step

Mould opened


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Assembly process in detail: A sleeve operated by the core pull is used to join the seal-

ing ring and cable bushing together

4. Process step

Insert rotated

(indexing unit)

5. Process step

Insert retracted(using hydraulic ejector)

Assembly process via core pull


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6. Process step

Insert advanced

(using hydraulic ejector)

Part is stripped

7. Process step

Insert rotated

Ejector retracted

Mould closed


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3.2 Altering the mould using internal movements inside the mould

During a process referred to as composite injection moulding, hollow

areas in the mould are first closed and later reopened by using sliding

cores or inserts. For the production of a part consisting of two com-

ponents, the first element of the piece is injected in an initial injec-tion step, after which a second hollow area is opened by pulling a

seal slide. Finally, the second component is injected against the first,

whereby the completed piece is produced and can be removed from

the mould in its final form. Another option is to change the mould

contour through internal sliding movements inside the mould, follow-

ing the first injection shot (see figure B).

A particular advantage of composite injection moulding is that pro-

duction can be carried out in one mould without intermediate open-

ing of the machine and without further transport of the pre-moulded

part. However, production is performed in a strict sequence, whereas

with rotary moulds simultaneous operations are possible.

With regard to the machine, where moulds with internal sliding

movements are used, it is necessary to have a sufficient number of

freely programmable core pulls. In relation to this, particular atten-

tion should be paid to achieving continuous safety monitoring of the

movements to avoid disruptions to production.

Composite injection moulding may be employed for two or more

components, whereby the complexity of the mould rises significantly

with the number of the components. As in all multi-component proc-

esses, the chemical and thermal compatibility of the melts as well

as other similar process factors must be observed in the selection of

materials.

Illustration: Examples of applications involving composite injection moulding


35/40

Know-how Edition


- 35 -

Example 3.2: Lifting and lowering movements (composite

injection moulding)

Figure A

Figure B


36/40

Know-how Edition


- 36 -

3.3 Transfer by hand or robotic system

In addition to the rotation and composite injection moulding options

described, multi-component parts can also be produced by means

of mould transfer. This process involves the production of the pre-

moulded part at a preliminary station, which, following opening of the

mould, is then transferred to another cavity or another mould using

a robotic system or the conventional method (by hand). This means

that the moulds can be kept simple, since no rotary movements or

internal movements have to be performed.

On the one hand it is possible to operate two different machines and

therefore two separate moulds at the same time. On the other hand,

using a two-component machine, it is also possible to transfer the

pre-moulded part inside the mould from one mould half to the other.

The pre-requisite for using a two-component machine is that the

cycle times for producing the components concerned must be com-

parable so as to ensure economical use of the two cavities.

Example application Rollers with a running surface made from TPE which totally envelops

the outer ring can be transported inside a rotary mould, but only at

greater cost. In this case, the most economically viable method of

production is to transfer the first injection shot to a second mould

contour by hand or using a robotic system (figure A). The main

advantages of staged moulds (such as doubling the number of cavi-

ties or bringing about a reduction in the machine clamping forces)

provide the other alternative of transferring from one stage to another

(see figure B).

Illustration: Example application involving roller

Of course, transfer can also be used for other parts that can be

relocated to the second mould contour. However, in the case of parts

with exacting tolerances or ones that are especially sensitive, it often

makes better sense to leave the pre-moulded part on the core and to

rotate the moveable mould halves.


37/40

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- 37 -

Example 3.3: Transfer from the 1st station to the 2nd by hand

or using a robotic system

Figure A

Figure B


38/40

Know-how Edition


- 38 -

4. Summary Nowadays, thanks to the ongoing further development of machineand in particular of mould technology, a multitude of product specific

solutions involving multi-component technology are possible. These

often involve the use of fully automatic rotary moulds of various

designs. However, by way of alternative, other techniques such as

transfer or insert technologies are also being developed, so that

as many application areas as possible are catered for. This often

obviates the need for additional joining techniques or secondary

operations. The already highly advanced technology makes it

possible to achieve robust and efficient large-scale production, whilst

maintaining consistently high quality.

A special feature of multi-component technology is that it often

makes it possible to realise products with tailor-made properties and

to provide customer-specific solutions to problems in an efficient

manner. It is often possible to create components with highly resist-

ant bonds and multi-functional properties. The multi-component

processes are also opening the way for new design possibilities asfar as components are concerned and for new methods of reducing

production costs.

In future, we can therefore expect multi-component technology to

play an even greater role. In particular, there is still a long way to go

before the potential of hard-soft combinations is fully realised, which

continues to promise a multitude of interesting possibilities in terms

of component design. Similarly, there is no doubt that a considerable

number of functional components can be produced more efficiently

using assembly injection moulding as opposed to joining techniques.

Within this field, the latest trends are aimed in particular at exploiting

the shrinkage behaviour of a material, in order to achieve targetedseparation of the components. Another field to watch in the future is

the production of integrated circuits by combining plastics that can

be metallised with those that cannot.

Although there is no doubt that multi-component technology can now

be considered as one of the well-established specialist processes of

injection moulding, the complexity of the individual processes should

not be underestimated. It is often the problems associated with the

finer details that dictate which specific process is to be used. For this

reason, close collaboration should always be sought between the

production facility, the mould manufacturer and the machine manu-

facturer throughout all the stages of a project. This close collabora-

tion should start as early as the planning phase so as to eliminatefundamental errors that cannot be easily removed at a later date and

to ensure a maximum degree of harmony between all the compo-

nents.


39/40


40/40

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