MOULDING TOOLING

Abstract: A method of making tooling includes: 1) preparing a master model (A) having a first surface, 2) casting a thin-skinned mould (B) from the first surface of the master model, 3) fabricating a bolster (C) in contact with the thin-skinned mould, 4) removing the bolster (C) and the thin-skinned (B) mould from the master model, 5) supporting the thin-skinned mould (B) by means of the bolster (C), 6) applying a layer of a calibration material (D) to the thin-skinned mould (B), and 7) casting a matching mould (E) set contra half against the calibration material (D) while the calibration material (D) and the thin-skinned mould are supported by the bolster (C). 8) removing the calibration material (D), 9) casting a rigid skin member (F) after the thin-skinned mould (B) and the matching mould (E). By using the rigid skin member (F), a moulded replica of the first surface of the master model (A) is obtained.

Description: MOULDING TOOLING Field of the Invention This invention relates to the manufacture of moulding tooling. It is known to manufacture moulding tools in the form of composite moulds based on low-mass heated or unheated high- temperature composite skins with integral cores. The skins and cores are supported by a profiled shim which is, in turn, supported by suitably shaped frame bolsters. A composite mould can make use of a metal-faced mould. The metal can be deposited as a skin by, for example, metal spraying sheet forming, casting or machining. Whatever means are used to provide a skin, the metal thickness is kept to a minimum and the skin is cradled in a composite material including an embedded heater. It is supported as a skin adapted for high- temperature operation my means of steel support frames which serve to provide for readily matchable mould sets. As originally conceived, solid bonding of the skin to the supporting frame reduced, if it did not actually prevent, allowance for movement between the skin and the frame. Such movement is desirable in order to allow for a degree of relative movement between the skin and the frame arising from differential expansion because of the difference coefficients of thermal expansion of the skin and the frame. In British Patent Specification No. 2 319 205, there is described a process for the manufacture of moulding tooling comprising the use of a thin skin mould supported in a bolster by means of an elastomeric shim extending over the entire under- surface of the skin. The shim is, in turn, supported on an in-fill in the bolster. The specific process described in Specification No. 2 319 205 includes the following steps:- 1 ) forming a skin layer of plastics material on a surface of a master pattern member, the skin layer having an inner face contacting the master pattern member and an exposed outer face, 2) depositing a calibration layer on the exposed face of the skin layer, the calibration layer having an inner face contacting the skin layer and an exposed outer face, 3) depositing a bolster layer incorporating a heat insulating material on the exposed face of the calibration layer, 4) shrouding the exposed face of the bolster layer by means of a bolster frame so as to provide an in-fill volume between the exposed face of the bolster layer and an inner face of the bolster frame, 5) filling the in-fill volume with an aggregate material providing for thermal insulation between the bolster layer and the bolster frame, 6) separating the master pattern member with the skin layer retained thereon from the bolster frame, the bolster layer and the calibration layer, 7) removing the calibration layer to expose the inner face of the bolster layer, 8) providing a release means on the exposed inner face of the bolster layer, 9) relocating the master pattern member with the skin layer retained thereon into the bolster frame and the bolster layer so as to define a volume left on removal of the calibration layer between the exposed outer face of the skin layer and the exposed inner face of the bolster layer, 10) injecting a plastics material into the volume between the two exposed faces to provide a bedding shim reproducing the exposed face of the skin layer, 11) separating the master pattern member from the remainder of the assembly when formation of the bedding shim is complete, and 12) locating the skin layer on the bedding shim in the bolster to provide the tool, which comprises the skin layer releasably mounted on the bolster layer by means of the bedding shim and the bolster layer retained in the bolster frame. It is an object of the present invention to provide a method of tooling manufacture which has a number of advantages as compared to the method described in Specification No. 2 319205. Summary of the Invention According to the present invention there is provided a method of making tooling comprising the following steps:- a) preparing a master model having a first surface, b) forming a thin-skinned mould from the first surface of the master model, the thin-skinned mould having an inner surface corresponding to the first surface of the master model and an outer surface spaced from the inner surface thereof, c) fabricating a bolster in contact with, and releasable from, the outer surface of the thin-skinned mould, which bolster is intended to serve as a support structure for either the thin-skinned mould or a replica thereof, d) removing the bolster and the thin-skinned mould from the master model and thereafter supporting the thin-skinned mould by means of the bolster, the bolster being in contact with the outer surface of the thin-skinned mould, e) locating a layer of a thickness calibration material on the inner surface of the thin-skinned mould, the layer corresponding in thickness to an article to be produced by means of the tooling, f) forming a matching mould set contra half against the layer of calibration material while the calibration material and the thin- skinned mould are supported by the bolster, g) removing the matching mould set contra half from the combination of the calibration material, the thin-skinned mould and the bolster and thereafter removing the calibration material from the inner surface of the thin-skinned mould, h) aligning the combination of the bolster and the thin-skinned mould with the matching mould set contra half to define a cavity corresponding to the space previously occupied by the calibration material, i) coating the surfaces defining the cavity with a release agent and thereafter casting a rigid skin member in the cavity, j) removing the matching mould set contra half from registration with the combination of the bolster and the thin-skinned mould, and k) removing the rigid skin member from the thin-skinned mould. The rigid skin member is preferably then placed on the mould set contra half, in register therewith, to provide a moulded replica of the first surface of the master model. A replica of the first thin-skinned mould is preferably produced by- registering the combination of the bolster and the rigid skin member with the mould set contra half to define a cavity which acts as a mould for a replica of the first thin-skinned mould, and casting the replica in the thus-defined cavity. It is to be appreciated that any desired number of replica thin- skinned moulds may be produced in this way. Forming of the thin-skinned mould may be effected by casting. If desired, a surface of the thin-skinned mould may be produced by a fabrication, pressing, metal spraying or electro- forming process. The step of fabricating the bolster preferably involves a computer numerically controlled machining operation to provide for the subsequent mounting of a thin-skinned mould or replica thereon. The thin-skinned mould or replica is preferably retained on the bolster by the application of a sub-atmospheric pressure. Brief Description of the Drawings Figures 1A, 1B and 1C show the initial stages in the manufacture of mould tooling, and Figures 2A and 2B show the final stages in the manufacture of the mould tooling. Description of the Preferred Embodiment Figure 1A shows a male master model A having a first surface 10 and a female thin-skinned mould B cast from the first surface 10 of the male master model A. The female thin-skinned mould B has an inner surface S1 which corresponds to the first surface 10 of the male master model A. Figure 1A also shows a bolster C which is cast from surface S2 of the female thin-skinned mould B while the female thin-skinned mould B is accurately supported and located by the male master model A. The bolster C acts as a support structure for the female thin-skinned mould B during subsequent production steps. The bolster C may include means for surface heating. It is to be appreciated that, although the specific master model A shown in the drawings is a male master model, the master model may alternatively be a female master model or a flat master model. The initial manufacturing steps comprise the accurate formation of the male master model A by, for example, a CNC machining operation, followed by casting of the female thin-skinned mould B, and then by fabrication of the bolster C. The male master model A is then separated from the assembly comprising the bolster C and the female thin-skinned mould B. Figure 1B shows the bolster C in an inverted condition, the female thin-skinned mould B supported by the bolster C and a layer D of a thickness calibration material, such as a sheet of wax or sheet cork, placed against the inner surface S1 of the female thin- skinned mould B. The female thin-skinned mould B is accurately supported in the bolster C during formation of the calibration layer D. Figure 1B also shows a matching mould set contra half E formed of, for example, a plastics material cast against the upper surface of the calibration layer D, whilst the calibration layer D and the female thin-skinned mould B are both accurately supported by the bolster C. Thus, after the initial manufacturing steps depicted in Figure 1 A, a calibration layer D is carefully and accurately formed on top of the female thin-skinned mould B and then the mould set contra half E is produced. After setting of the plastics material forming the mould set contra half E, the mould set contra half E is displaced upwardly and the calibration layer D is then removed by, for example, melting the wax from which said layer D was produced. The mould set contra half E is then repositioned relative to the bolster C and the female thin-skinned mould B so as to be in precisely the same position as that in which it was produced. Figure 1C shows the mould set contra half E, the bolster C and the female thin-skinned mould B accurately positioned relative to one another so as to define a cavity in which a rigid skin F is cast. The rigid skin F has a configuration which corresponds exactly with the configuration of the calibration layer D. Rigid skin F is a moulded production part, i.e. it has a configuration corresponding to the required moulded end product. The "good" face of the rigid skin F, i.e. the face of the rigid skin F remote from the mould set contra half, can then be polished after opening of the mould set and removal of the female thin-skinned mould B. The polished face of the rigid skin F thus provides an enhanced mouldable surface which is a replica of the presented surface of the original master model A. Replicas of the female thin-skinned mould B are then produced by positioning rigid skin F, when supported by the mould set contra half E, in accurate registration with the bolster C to form a cavity G, as shown in Figure 2A. Filling of the cavity G with resin, followed by opening of the mould once the resin has set enables the manufacturer to produce, at low cost, as many replicas of the female thin-skinned mould B as he may require. The production of multiple replicas of the female thin-skinned mould B greatly improves the efficiency of moulding processes which involve the production of large numbers of identical moulded production parts. Figure 2B then shows a mould set comprising the bolster C, the mould set contra half E and the female thin-skinned mould part B (or a replica of the female thin-skinned mould part B) used to cast further moulded production parts. The present invention thus relates to casting replica multiple mould faces for a closed mould system and is applicable to composite moulds, whether or not they are equipped with an internal temperature control system. The procedures outlined above can readily be applied to metal, ceramic, elastomeric or other suitable mould face materials and are not limited to the use of composite materials, such as reinforced and un-reinforced thermosetting resins. It is to be appreciated that the method described with reference to the drawings has been referred to in general terms and could, in its simplest form, involve pouring a setting liquid matrix or it could involve injecting the matrix under a pressure difference, whether sub- or super-atmospheric pressure, or a combination of both. The method of "thin skin" mould manufacture may include the use of a metal spray coat or cold-formed metal sheet of less thickness dimension that the final "thin skin" dimension, with the S2 surface of the thin-skinned mould B (or the replica of the thin- skinned mould B) subsequently being filled with a castable matrix to ensure replication and thus accurate fit to the supporting production bolster C. The working surface of the thin-skinned mould may also be produced by a fabrication or electro-forming process. The method of the present invention provides for the manufacture of a production bolster C having a contour fit with a thin-skinned mould B produced from a CNC-machined master model A. The method of the invention involves manufacture of the production bolster C which is thereafter used to support either the female thin-skinned mould or a replica thereof. A surface to be contacted by material for casting is typically coated with a metal, alloy, ceramic material, elastomeric material or a reinforced or un-reinforced thermosetting resin. If a metal coating is used, this can be applied by a spraying process. Alternatively, the surface is formed by a metal sheet of reduced thickness by comparison with the desired final thin skin, and the required thickness is achieved by a layer of a castable matrix attached to the rear side of the formed metal sheet.

Claims: Claims:- 1. A method of making tooling comprising the following steps :- a) preparing a master model having a first surface, b) forming a thin-skinned mould from the first surface of the master model, the thin-skinned mould having an inner surface corresponding to the first surface of the master model and an outer surface spaced from the inner surface thereof, c) fabricating a bolster in contact with, and releasable from, the outer surface of the thin-skinned mould, which bolster is intended to serve as a support structure for either the thin-skinned mould or a replica thereof, d) removing the bolster and the thin-skinned mould from the master model and thereafter supporting the thin-skinned mould by means of the bolster, the bolster being in contact with the outer surface of the thin-skinned mould, e) locating a layer of a thickness calibration material on the inner surface of the thin-skinned mould, the layer corresponding in thickness to an article to be produced by means of the tooling, f) forming a matching mould set contra half against the layer of calibration material while the calibration material and the thin- skinned mould are supported by the bolster, g) removing the matching mould set contra half from the combination of the calibration material, the thin-skinned mould and the bolster and thereafter removing the calibration material from the inner surface of the thin-skinned mould, h) aligning the combination of the bolster and the thin-skinned mould with the matching mould set contra half to define a cavity corresponding to the space previously occupied by the calibration material, i) coating the surfaces defining the cavity with a release agent and thereafter casting a rigid skin member in the cavity, j) removing the matching mould set contra half from registration with the combination of the bolster and the thin-skinned mould, and k) removing the rigid skin member from the thin-skinned mould. 2. A method as claimed in Claim 1, in which the rigid skin member is then placed on the mould set contra half, in register therewith, to provide a moulded replica of the first surface of the master model. 3. A method as claimed in either of the preceding claims, in which a replica of the first thin-skinned mould is produced by:- registering the combination of the bolster and the rigid skin member with the mould set contra half to define a cavity which acts as a mould for a replica of the first thin-skinned mould, and casting the replica in the thus-defined cavity. 4. A method as claimed in any one of the preceding claims, in which the step of fabricating the bolster involves a computer numerically controlled machining operation to provide for the subsequent mounting of the thin-skinned mould or replica thereon. 5. A method as claimed in any one of the preceding claims, in which the thin-skinned mould or replica is retained on the bolster by the application of a sub-atmospheric pressure. 6. A method as claimed in Claim 1 , in which the thin-skinned mould is formed by casting. 7. A method as claimed in Claim 1 or Claim 6, in which the matching mould set contra half is formed by casting. 8. A method as claimed in Claim 1 or Claim 6, in which a surface of the thin-skinned mould is produced by a fabrication, pressing, metal spraying or electro-forming process. 9. Tooling made by the method claimed in any one of the preceding claims. 10. Moulded production parts made using the tooling of Claim 9.

Inventors: HARPER ALAN ROGER, HARPER, ALAN, ROGER
Applicants: HARPER ALAN ROGER, PLASTECH THERMOSET TECTONICS L, HARPER, ALAN, ROGER, PLASTECH THERMOSET TECTONICS LIMITED
Application year: 2001
Main classification: B29C33
IPC codes: B29C33, B29C39, B29C43