Background of the invention

The present application refers to a method for producing shell-moulded casting structures, particularly interior decorative details for the car industry, such as dashboard panels, door sides and ceiling panels.

For such details it is required that the structure shall have a low weight at the same time as it has sufficient strength for resisting stresses to which it may be subjected before and after the mounting thereof in its position of use, it shall have shock absorbing properties at the same time as it is rigid enough not to be deformed by temporary forces. It is at the same time a desire that the outside of the detail has. an attractive structure.

For producing such shell-structures an earlier often used method is the following:

A plastic sheeting, which shall form the outer casing of the detail is vacuum-formed to the surface shape of the detail.

The vacuum-formed sheeting is located with its outer surface downwards in a lower mould part having the same shape as the sheeting.

Any insert details, commonly made from sheet metal or rigid plastic, are mounted in the mould.

A polyurethane-foam is poured into the mould and the mould is closed by a mould lid. The polyurethane-foam fills all parts of the mould cavity, inter-connects the sheeting and the insert details and acts as a shock absorbing material.

The detail is demoulded after thermo-setting, whereupon it is subjected to a punching operation, at which excess sheeting along the edges is removed, at the same time as desired recesses are punched out, e.g. for instruments, glove pocket, etcetera, when it concerns a dashboard panel.

The detail finally is subjected to a manual cleaning.

The sheeting used is most often an ABS/PVC plastic in which the grain or pattern is pressed directly into the sheeting. In connection to the elongation at the vacuum forming the pattern however will change irregularly due to the fact that the length change, to which the sheeting is subjected in different parts, is dependent on the curvature of the surface.

This vacuum forming of the sheeting intended for the surface layer due to the above mentioned problem provides a drawback at the production, whereby the freedom at the design of the detail will be heavily limited.

The method also involves a comparatively big material wastage, due to the need for punching out excess material from the detail, which is moulded in one piece without recesees.

Instead of using vacuum-formed sheeting for the surface layer it has also been proposed to spray a layer of poly-urtehane elastomer directly upon the bottom surface of the mould, which poly-urtehane elastomer is. allowed to form the surface layer of the detail. The other production steps have been the same as those described hereabove, and the same problem has been observed also here. In the same manner as when using the sheeting the spraying method will give a surface layer of varying or constant thickness, and at the spraying arises additional working environmental problems.

The purpose and most essential features of the invention

The purpose of the present invention is to provide a method of the type mentioned above by which the drawbacks and problems described have been eliminated and this has been achieved in a method for producing shell-moulded casting structures, particularly interior decorative details for the car industry, which incorporates the substeps, a) arranging in a mould bottom part a surface layer for the detail, b) mounting any insert details in the mould, c) pouring an expandable, thermo- setting plastic compound before or after fitting of a mould lid, d) causing said plastic compound to fill out the mould cavity formed by the surface layer and said mould lid, e)

demoulding the moulded detail after the end of the setting time, and f) thereupon cleaning the detail, and which method is characterized therein that said surface layer is produced in that a surfa.ce layer mould lid is fitted in said bottom mould portion, thus that a closed mould cavity is obtained, that a thermosetting compound intended to form surface layer in the detail is injected into said mould cavity, that the mould is opened after terminated setting and said surface layer mould lid is removed, whereupon the substeps b) to f) are performed.

Description of embodiment

The invention hereinafter will be further described as a non-limiting embodiment.

For production e.g. of a dashboard panel for a vehicle there is first produced a mould bottom part, which has a contour exactly corresponding to a reverse image of the outside of the desired dashboard panel. The surface of the mould bottom part can also be equipped with negative engravings or other negative patterns, which shall give the surface structure or grain of the detail.

In the mould bottom part thus produced there is then arranged a surface layer mould lid, which together with the mould bottom part forms a mould cavity, into which is then introduced e.g. an elastomer or a somewhat expandable poly-urethane composition, which is allowed to set in the mould cavity.

It is also possible to apply varnish to the outside of the detail by a so called varnish-in-mould-method, by spraying a varnish into the mould bottom part before injection of the plastic compound, which gives a bigger freedom at the choice of colour as compared to conventional methods.

By this method at production of the surface layer of the detail it is obtained a superior freedom of choice for the

design as compared to the above described older methods, whereby it is possible already at this stage to apply mould cores for desired recesses. It is furthermore possible to vary within rather wide'ranges the layer thickness of the surface layer, in different parts of the surface layer, whereby it is possible to produce reinforcements, which in turn means that it in certain cases may be possible to eliminate or limit the number of insert details, such as sheet metal or plastic members.

The surface layer mould lid is removed after curing, whereby the moulded surface layer is kept in the mould bottom part.

Further plastic compound layers, having different properties can possibly be built on the above mentioned surface layer with use of the same method and with use of different mould lids.

Any insert details are thereupon mounted in the mould, which corresponds to the procedure at the earlier used methods.

A final mould lid is mounted and a poly-urethane foam or another suitable material is poured into the mould. This material is brought to fill out the mould cavity formed between the surface layer and the mould lid, whereupon at the following setting it is obtained a bond between the mould compound, the surface layer and any insert details. The mould compound alternatively may be poured before the mould lid is mounted. Also these steps correspond to the conventional method.

The mould lid may be designed as an insert detail with attachement flanges etcetera, in which case it of course is bond to the detail produced. Otherwise the mould lid is removed after the setting is ended.

The detail is demoulded in common manner, and the detail is also in common manner fine cleaned, whereupon it is ready for use in its intended application.

By the method used for production of the detail surface layer a series, of advantages are gained as compared to earlier methods.

The vacuum-foarming of a sheeting is thus entirely eliminated together with the the problems associated therewith. A bigger freedom is obtained at choice of design. The insert details can be eliminated or at least reduced to number and/or extension due to the possibility to form integrated reinforcements in the surface layer.

As compared to the method of spraying a surface layer of poly- urethane elastomer into the mould it is possible with the method according to the invention in quite another way exactly to control the thickness of layers, and furthermore the work environmental problems occuring at the spraying are eliminated.

The invention is not limited to production of instrument panels or other car decorative details but can be used for a number of other applications, and it is neither limited to the above shown example, but can be modified within the scope of the following claims.