GB2364951A

GB2364951A - Injection moulding tool

Info

Publication number: GB2364951A
Application number: GB0017483A
Authority: GB
Inventors: Stephen David Cooke
Original assignee: Visteon UK Ltd
Current assignee: Visteon UK Ltd
Priority date: 2000-07-18
Filing date: 2000-07-18
Publication date: 2002-02-13
Anticipated expiration: 2020-07-18
Also published as: GB2364951B; GB0017483D0

Abstract

An injection moulding tool 24 and 26 for producing moulded products with a preformed foil 12 forming the front surface of the product 10, wherein the mould 24 and 26 has a cold runner system 30 entering the mould 24 and 26 and wherein a pin/insert 32 presses the foil 12 against the cavity face 38 of the tool as the tool is closed. The cold runner system 30 may enter the mould 24 and 26 on the tool split line in order to coat the foil 12 with molten plastics.

Description

<Desc/Clms Page number 1> Injection Moulding This invention relates generally to injection moulding, and in particular to injection moulding where a pre-formed foil (sometimes called an appliqu6) or moulding face layer is placed in the mould cavity prior to injection of the plastics. This process is often referred to as 'in-mould film' or 'insert moulding' technology. In this type of moulding, the foil is to form the front face of the moulded component, and to give the component the desired appearance, It is therefore essential that the injected molten plastic material does not penetrate between the foil and the front face of the mould cavity, otherwise the appearance of the component will be marred. Cold runner moulding techniques are typically used in the production of components such as vehicle instrument panels. It is known to construct the mould feed channels (the cold runners) so that the molten plastic is introduced into the mould from a position away from the mould tool split line and behind the foil. This achieves the desired objective of ensuring that the melt does not penetrate around the front of the foil, as the incoming melt forces the foil against the front face of the mould cavity. However the use of a cold runner in this position has two main disadvantages. Firstly the construction of the mould tools is more costly than is the case when the cold runner is located on the

tool split line. Secondly, the necessary longer length of the runner, and the position in which it enters the cavity can lead to undesirable sink marks in the finished moulding. The melt contracts as it freezes in the mould. If the melt in the runner remains molten, the injection pressure will keep acting on the melt where the runner enters the cavity and will ensure that melt continues to flow into the cavity as contraction takes place, thus preventing the appearance of sink marks. The length of the runner and its position both affect the presence or absence of sink marks.

According to the invention, there is provided an injection moulding tool set for producing moulded products with a preformed foil forming the front surface of the product, wherein the mould has cold runner system entering the mould on the tool split line, and wherein the back part of the mould has at least one pin, adjacent the cold runner, which, when the mould is closed, bears against a foil in the mould and presses the foil against the front face of the mould.

The use of a pin internally in the mould allows the mould to be designed with a cold runner on the tool split line. As a result, tool manufacture is cheaper and the positioning of the cold runner avoids the appearance of sink marks on the front face of the finished product. There are preferably two pins, one either side of the or each cold runner. However other pin configurations can be used, provided they achieve the objective of holding the foil against the front face of the mould

The pins will leave witness marks in the back face of the product, but the pins can easily be designed so that the witness marks will not interfere with the final appearance or with the function of the component. The pins preferably have flat end faces which, in use, will lie against the back face of the foil and parallel with the plane of the foil. The length of the pins should be such that they exert a small force (which may lead to minor compression of the material of the foil) when the mould tool is closed. The invention also provides an insert moulding process, wherein a mould tool is prepared, a foil is placed in the cavity side of the tool, an insert is placed in the tool to press the edge of the foil against the cavity face of the tool when the tool is closed, the tool is closed and molten plastics is injected into the tool through a cold runner system adjacent the insert. There can be two pins arranged on opposite sides of the cold runner. The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a moulded product produced by the method of the invention; Figures 2 to 7 show a section through an edge of a mould tool, in sequential stages of a moulding cycle; and

Figure 8 shows a scrap section of the back face of a finished product.

Figure 1 shows a product 10 which, in this case, is part of a motor vehicle instrument panel. The product has an outer face formed by a foil 12 which has been partly cut away in the figure. The foil 12 is supported by an injection moulded body 14. The foil will, for example, have a wood-effect or other decorative finish.

The product has an edge flange 16 which will be used to mount the product in an assembly such as an instrument panel, and openings such as 18 (which can receive a radio/cassette unit), 20 (which can receive the ends of ventilation ducts) and 22 (which can receive a switch) are provided through the product. The process described here is not limited to any particular component, and can find application anywhere a preformed foil or appliqu6 is to be incorporated, as a front face, in an injection moulded product. To manufacture this product, the foil 12 is first formed independently, typically in a vacuum forming process which is not part of this invention. An injection moulding tool with a cold runner system is made and the foil is placed in the tool cavity, with its 'appearance' face against the cavity side of the tool. The tool is then closed with the foil inside, and molten plastics is then injected through the cold runner into the tool, behind the foil. Once moulding has been completed, the tool is opened and the product withdrawn and the injected plastics material will

have bonded fully to the back face of the foil to form the product 10 in which the structural form of the product will be produced by the moulded plastics 14 and the outward appearance of the product will be formed by the foil 12. Details of the tool, at the position where the cold runner is located, are shown in Figures 2 to 6. In Figure 2, the tool is shown closed, with the cavity side of the tool at 24 and the core side of the tool at 26 defining a mould cavity 28 between them. Normally the cavity side will be held stationary and the core side will move towards and away from the cavity side as the tool closes and opens. A groove 30 in the core side forms a cold runner channel. The tool is shut when the face 24a of the cavity side makes contact with the face 26a of the core side. In this condition, the cold runner channel 30 communicates with the cavity 28. A pin 32 protrudes upwards from the core side 26 towards the internal surface of the cavity tool. This pin will be permanently fixed in the core side of the tool, and its function will become apparent from the following description. In Figure 3, the tool is shown open, with the cavity side 24 lifted away from the core side 26. This figure shows that the pin 32 is a separate component embedded in the material of the core side 26, but the pin can be formed by other methods also, including being machined to form part of the cavity face of the core side 26. Figure 3a shows a

view in the direction of arrow A showing two pins 32, arranged either side of the cold runner 30, and formed as limbs of a single embedded component.

Figure 4 shows the same view as Figure 3, but this time the foil 12 is shown, located in the cavity side 24 of the tool. The foil has been previously formed to have a contour corresponding with that of the cavity face of the cavity side. However because the foil is thin and flexible, the periphery 36 of the foil will not lie reliably against the cavity face of the cavity side 24. Indeed, in Figure 4, the periphery 36 is shown slightly diverging from the face 38.

Typically the foil 12 will be vacuum formed and will have a thickness of 0.5mm. (The total depth of the cavity can b e for example 3.Omm, ie the part of the cavity not occupied by the foil 12 can be about 2.5mm deep) . If the tool is closed with the foil diverging in this way and plastics is injected, incoming molten plastic will penetrate between the foil and the cavity face 38 to damage or obscure the appearance of the outer face of the foil. Such components would be substandard and would have to be discarded. The pins 32 are present to stop this happening. In Figure 5, the tool is shown closed. When the tool is closed, the periphery 36 of the foil is pressed by the pins 32 against the cavity face of the cavity side 24, and this effectively prevents penetration of plastics between the foil and the cavity side.

The height of the pins above the core side face 26a will be substantially equal to, or slightly greater than the thickness of the moulding at that point, less the thickness of the foil. If the pins are slightly higher, the foil will be slightly compressed when the tool is closed which will ensure that the foil is pressed firmly against the cavity face.

Figure 5a shows a section on the line B-B, showing how the pins 32 hold the foil in position against the cavity face 38, either side of the cold runner 30.

In Figure 6, injection of plastics 14 is taking place with flow entering the tool cavity through the cold runner system, at 30. Because the foil is held firmly against the cavity face of the mould, none of the molten plastics 40 will penetrate between the foil and the cavity face.

When the plastic has fully filled the mould cavity and has solidified, the tool can be opened as shown in Figure 7. In this Figure, the tool is shown open, with the moulded product 10 separated from the two sides of the tool. At this point, the cold runner 42 is still attached to the edge flange 16, but this will be cut off before the product is finished.

The presence of the pins 32 ensures that there is no plastics penetration across the front face of the foil during injection moulding. Thus, a cold runner injection process can be used to produce parts of satisfactory quality

Although the drawings show two pins 32, arranged either side of the cold runner channel 30, other numbers of pins (including a single pin) and other pin configurations could be used as desired in accordance with the design of the particular product being manufactured. The pins are shown as being generally rectangular in form, but they could have other shapes, for example tapered shapes.

The finished product will be left with two small witness marks 44 (see Figures 7 and 8) but these will be on the reverse side of the part, on the fixing flange and will not penetrate right through the product, so they will not adversely affect the product.

Claims

Claims 1 . An injection moulding tool set for producing moulded products with a preformed foil forming the front surface of the product, wherein the mould has a cold runner system entering the mould on the tool split line, and wherein the core side of the tool has at least one pin, adjacent the cold runner, which, when the tool is closed, bears against a foil in the tool and presses the foil against the front face of the tool cavity. 2. A tool set as claimed in Claim 1, wherein two pins are provided, one either side of the or each cold runner. 3. A tool set as claimed in Claim 1 or Claim 2, wherein the pins have flat end faces which, in use, will lie against the back face of the foil and parallel with the plane of the foil. 4. A tool set as claimed in any preceding claim, wherein the length of the pins is such that they exert a small force (which may lead to minor compression of the material of the foil) when the mould tool is closed. S. An insert moulding process, wherein a mould tool is prepared, a foil is placed in the cavity side of the tool, an insert is placed in the tool to press the edge of the foil against the cavity face of the tool when the tool is closed, the tool is closed and molten plastics is injected into the tool through a cold runner system adjacent the insert.

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6. An insert moulding process as claimed in Claim 5, wherein there are two pins arranged on opposite sides of the cold runner.