Disposable Casting Pattern Manufacture The present invention relates to the manufacture of disposable casting patterns particular. but not exclusively, for use in the manufacture of cast press tooling such as punches and dies used for use pressing motor vehicle body panels. ~ A known method of manufacture of metal castings comprises the steps of manufacturing a disposable casting pattern, forming a casting mould around the pattern, and pouring molten metal into the mould to form a casting to the shape of the pattern. Such a method is variously referred to as the"evaporable foam","lost foam"or"full mould"process. Typically the pattern is made from expanded polystyrene which may be"as moulded"to a shape required for use in constructing the pattern or carved or machined from a block of expanded polystyrene. The mould is normally of sand poured and tamped in around the pattern.

For large or complex castings, the pattern is manufactured by bonding together smaller blocks of expanded polystyrene with suitable adhesives, masking tape being normally used to cover the bonded joints. When joining two blocks disposed at an angle to one another the masking tape is also used to form a rounded fillet between the blocks. As will readily be appreciated, the application of the masking tape is a time consuming task, requiring some skill and care in its application if it is to remain in place up to and during casting. It also has a disadvantage of not being fully evaporable and thus leaving a residue which has to be flushed away during casting if it is not to remain as an inclusion and so weaken the casting.

The disposable pattern is placed on a bed of foundry sand and the sand is packed down around the pattern. Hot molten metal is then poured into the mould which causes the expanded polystyrene to gassify and the adhesive and the

masking tape to burn away. The molten metal fills the space previously occupied by the polystyrene pattern and subsequently solidifies to form the casting.

It is an object of the present invention to provide for an improved manufacture of casting patterns.

According to a first aspect of the invention a method of manufacturing a casting pattern includes the steps of assembling at least two casting pattern members to form a casting pattern, at least one of the pattern members defining a cavity which is closed in the assembled pattern. This has the advantage that a reduced volume of polystyrene is used than previously, thereby reducing the volume of gas produced during casting.

Conveniently, the cavity is open in the unassembled pattern member and is closed when the pattern members are assembled together. This facilitates manufacture.

One of the pattern members may be provided with a first connecting means and the other pattern member is provided with a second connecting means complementary to the first connecting means, for example the first connecting means may comprise a tongue and the second connecting means comprise a recess, the tongue being received into the recess. The complementary connecting means substantially reduces the need for adhesives to be used to join together the pattern members.

Preferably, at least one of the pattern members is manufactured by moulding to the required shape, for example by expanding foam in a mould.

The pattern members are preferably formed from expanded polystyrene.

The invention also provides, according to a second aspect, a method of manufacturing a series of casting patterns including the steps of manufacturing a range of standard casting patterns members of different shapes and sizes, assembling a first pattern of the series by including a first selection from the range of standard patterns and assembling a second pattern of the series by including a second selection from the range of standard patterns.

In this way, a pattern c. a desired shape can be built up from a library of pattern members. This is particularly advantageous in the case of press tooling, since many details of a press tooling part are standard and do not vary between different press tooling parts. Such details include bolt slots by which the press tooling part is secured to a bed or a ram of a press tool or lifting lugs by which the press tooling parts are moved into and out of the press tool or for transport.

Preferably at least one standard pattern member is manufactured by moulding to the required shape, for example by expanding foam such as polystyrene in a mould.

Conveniently at least one of the pattern members in each selection defines a cavity which is closed in the assembled pattern in accordance with the first aspect of the invention.

The invention also provides, in accordance with a third aspect, a range of standard casting patterns members for use in a method according to said second aspect. Furthermore, the invention also provides, in accordance with a fourth aspect, a casting pattern manufactured by a method according to said second aspect.

Additionally, according to a fifth aspect, the invention provides a method of manufacturing a casting comprising the steps of providing a casting pattern manufactured by a method according to the first or second aspects of the invention, packing sand about the casting pattern to create a mould, introducing molten metal into the mould to gassify the casting pattern, allowing the molten metal to solidify to form a casting, and removing the casting Lrom the mould.

The invention also provides, according to a seventh aspect, a casting manufactured by a method according to said sixth aspect of the invention.

The invention will now be described by way of example only, with reference to the accompanying drawings, in which: Fig. 1 shows diagrammatically a perspective view of a casting pattern for use in a method according to the present invention; Fig. 2 shows diagrammatically a view from beneath of the casting pattern shown in Fig. 1; Fig. 3 shows diagrammatically a perspective view of a first casting pattern member for use in the present invention; Fig. 4 shows diagrammatically a perspective view of a second casting pattern member for use in the present invention; Fig. 5 shows diagrammatically a perspective view of a third casting pattern member for use in the present invention; Fig. 6 shows diagrammatically a perspective view of a fourth casting pattern member for use in the present invention; Fig. 7 shows diagrammatically a perspective view of a fifth casting pattern member for use in the present invention ; Fig. 8 shows diagrammatically a perspective view of a sixth casting pattern member for use in the present invention;

Fig. 9 shows diagrammatically a perspective view of a seventh casting pattern member for use in the present invention; Fig. 10 shows diagrammatically a perspective view of an eighth casting pattern member for use in the present invention; Fig. 11 shows diagrammatically a perspective view of an ninth casting pattern member for use in the present invention; and Fig. 12 shows in section details of adjacent casting pattern members showing complementary connecting means in exaggerated detail.

Referring first to Fig. 1 and Fig. 2, there is shown a perspective view of a casting pattern 10 manufactured in accordance with the present invention. The pattern is adapted for use with a lost foam casting method in which sand is packed about an expanded polystyrene pattern, the pattern being removed by gassification on the introduction of hot molten metal. The pattern 10 is built up from a plurality of casting pattern members, the edges of some of which are shown in dashed lines in Fig. 1.

The pattern 10 is generally in the shape of an open inverted box comprising an upper surface 12 extending between a front wall 14, a back wall 16 and two side walls 17. 18. The upper surface 12 is provided with a relief 13 corresponding to the desired panel shape to be formed. Box heels 20 are provided at each of four corners of the upper surface 12, each box heel comprising two upstanding walls 22,24 extending from corner edge portions of the walls of the casting pattern. A groove 26 is provided on the inner joint of the two upstanding walls 22,24 for machining relief, the groove extending from the top of the upstanding walls to the upper surface 12. Additional grooves 27,28 are provided along each of the upstanding walls along a joint of each upstanding wall with the upper surface to allow machining of the interior faces 27 as bearing surfaces or for mounting removable bearing plates or cheeks.

The front wall and the back wall are each provided with a pair of lifting lugs 30 shown typically located beneath a box heel. Each lifting lug 30 comprises a pair of protruding members 32,34 extending from the wall, the protruding members being provided with axially aligned passages 36. An outwardly directed flange 40 at the base of each of the front wall and the back wall forms a foot on each side of the pattern. The flange 40 is shown typically with a bolting slot 42 and a reinforcing rib 44. The inside of the pattern 10 is formed with a series of ribs 48 arranged transversely and longitudinally as shown in Fig. 2.

As described so far, the pattern 10 is conventional and would normally be built up from solid sections of expanded polystyrene foam assembled together by adhesive. It has been found that when producing a series of patterns of a certain type, particularly press tooling as shown in Figs. 1 and 2, some parts of the patterns are the same or similar from one pattern in the series to another. In press tooling this is often because the set-up heights and strokes of the presses conform to certain standards and the bolting slots are spaced in a standard array.

However, in accordance with one of the aspects of the present invention, the pattern is, to a substantial extent. built up from casting pattern members selected from a range or library of standard or pre-existing pattern members to form a pattern of the desired shape. In the case of the press tooling shown in Figs. 1 and 2, it can be seen that certain parts, such as the lifting lugs, box heels and bolting slots will differ little, if at all, between different tooling die assemblies and their associated patterns. Further, if a change is required to any one of these parts, a new pattern member may be produced and added to the range, without the need to produce an entire replacement pattern.

Examples of suitable pattern members for use in the method will now be described with reference to Figures 3 to 11.

A first pattern member 50 is shown in Fig. 3, being generally"T"shaped in plan view and comprising a transverse portion 52 and a longitudinal portion 54.

The pattern member 50 comprises three upstanding walls, a first generally flat wall 56 and second and third generally"L"shaped walls 58,60. The walls 56,58, 60 are joined to one another by a first, lower, web 62 connecting a lower edge of each of the walls to one another and a second, upper, web 63 spaced from an upper edge of each of the walls and connecting each of the walls to one another. In this way, the pattern member 50 is generally hollow having a cavity in the form of a passageway 64 extending therethrough, the passageway being defined by the inner surfaces of the walls 56,58,60 and the webs 62.63. The pattern member 50 also has a recess or groove 66 extending along an upper edge.

One end of the transverse portion 52 or the longitudinal portion 54 may be formed with an extending tongue or tenon 70 having an external height and width the same as the internal height and width of the passageway 64. In this way, when two similar pattern members are placed together, an extending portion of one pattern member will fit into a recess or tenon formed by the passageway 64 of an adjacent pattern member. The tongue 70 is optionally provided with one or more through holes which connect with the passageway 64.

The second pattern member 80 shown in Fig. 4. comprises two oppositely disposed upstanding walls 82.84 which are joined to one another by a first, lower, web 92 connecting a lower edge of each of the walls to one another and second, upper, web 93 spaced from an upper edge of each of the walls and connecting each of the walls to one another. In this way, the casting pattern member 80 is generally hollow having a cavity in the form of a passageway 94 extending therethrough, and a recess or groove 96 extending along an upper edge.

One end of the pattern member 80 may be formed with a tongue 100 similar to the tongue 70 shown in Fig. 3, the tongue extending beyond the end face of the member from within the passageway 94. The tongue 100 is optionally provided with one or more through holes which connect with the passageway 94. _ A third, more complex, pattern member 110 is shown in Fig. 5, this being generally"L"shaped in section and comprising two spaced"L"shaped walls 112, 114. The walls 112,114 are joined to one another by a first, upright, web 122 connecting a first edge of each of the walls to one another and second, horizontal, web 123 located spaced from a second edge of each of the walls and connecting each of the walls to one another. In this way, the pattern member 110 is generally hollow having a cavity in the form of a passageway 124 extending therethrough, and a recess or groove 126 extending along an upper edge.

The horizontal portions of the 'L"shaped walls 112,114 form a generally horizontally extending part of the pattern member 110. This is provided with a slot 140 in a boss 150, the slot being formed by providing suitable cut away portions 142,144 in each of the two spaced"L"shaped walls 112,114 with the first web 122 extending along and between the cut away portions. The boss is formed by forming a suitable raised portion 152 in the upper of the two spaced"L"shaped walls 112,114. The pattern member 110 may conveniently be used to form a bolting slot in the completed pattern, similar to the bolting slot 42 in Fig. l.

One end of the pattern member 110 may be formed with an extending tongue 130 which is generally similar to the tongues 70,100 but is"L"shaped to conform to the passageway 124. The tongue 130 is optionally provided with one or more through holes which connect with the passageway 124.

Where required, the pattern members, may be cut or trimmed to size, for example along the dashed lines 15,25 of Fig. 3 and Fig. 4. Where a pattern member is cut to reduce its height, for example by cutting along the dotted line of Fig. 4, a fill-in member such as member 160 shown in Fig. 6 may be used to complete the passageway. This comprises a base member 162 having a raised centre portion 164 which locates between the walls 82,84. The fill-in member 160 can be retained by adhesive, thereby effectively replacing the lower web 92 previously cut away.

The pattern member 170 shown in Fig. 7 may be used to form a smooth corner portion of a completed pattern. The pattern member 170 comprises a first, substantially vertical, side wall portion 172, a second, substantially horizontal, top wall portion 174 and a third, substantially vertical, side wall portion 176 disposed substantially orthogonal to one another. Each wall portion 172,174,176 comprises first and second wails disposed substantially parallel to one another.

A first substantially"L"shaped edge 178 of the pattern member 170 extends along the first and second wall portions 172, 174 and is provided with a groove 180 formed by the first and second walls of the respective wall members and a further wall 182 joining and set back from the edges of the first and second walls of the respective wall portions. A second, substantially"L"shaped, edge 184 extends along the second and third wall portions 174,176 and has extending tongues 186 disposed on a wall 188 which joins the edges of the first and second walls of the second and third wall portions 174. 176. The groove 180 and the tongues 186 are adapted to engage in matching or complementary features in adjacent casting pattern members. Preferably, the pattern member 170 has a substantial cavity.

For example, if there is no base web, a cavity will extend vertically from the lower edge of the vertical wall portions 172,176 and this can act as a recess for a connecting tongue of an adjacent pattern member. The tongues 186 are optionally

provided with one or more through holes 187 which connect with the cavity.

Similarly, the wall 182 is optionally provided with similar through holes 183 which connect with the cavity and can provide a through connection to a matching tongue of an adjacent pattern member.

The sixth pattern member 190 shown in Fig. 8 may be used to form a smooth horizontal edge portion of a completed pattern and comprises a first, substantially vertical, wall portion 192 and a second, substantially horizontal, wall portion 194.

Each wall portion 192,194 comprises first and second walls disposed substantially parallel to one another.

A first, substantially"L"shaped, edge 196 of the pattern member 190 extends along a first side of the wall portions 192,194. The first edge 196 is provided with a groove 198 formed by the first and second walls of the respective wall portions 192,194 and a further wall 200 joining and set back from the edges of the first and second walls. A second, substantially"L"shaped, edge 202 extends along a second side of the first and second wall portions and is provided with extending tongues 204 disposed on a vertical wall joining the edges of the first and second walls.

Another extending tongue 206 is provided on a lower, horizontal, wall 208 joining the first and second walls. The groove 198 and the tongues 204,206 are adapted to engage in matching or complementary features in adjacent casting pattern members. Preferably, there is no rear web, the pattern member 190 being formed with a substantial cavity which extends horizontally from the outer edge of the horizontal wall portion 194 and which can act as a recess for a connecting tongue of an adjacent pattern member. The tongues 204,206 are optionally provided with one or more through holes which connect with the cavity. Similarly, the wall 200 is optionally provided with similar through holes which connect with the cavity and can provide a through connection to a matching tongue of an adjacent pattern member.

It will be understood that the orientation of the pattern member 190, together with the location of and arrangement of the tongue members and the grooves, may be altered to provide for a vertical edge portion of a completed casting pattern. Indeed, the references to upper, lower, vertical, horizontal etc. are for convenient reference to the drawings and all the pattern members described herein may be used in any orientation.

The seventh casting pattern member 210 shown in Fig. 9 may be used to form a"box heel"at an upper corner of a completed casting pattern. The casting pattern member 210 comprises a first, substantially vertical, wall portion 212, a second, substantially vertical, wall portion 214 and a third, substantially horizontal, wall portion 216 disposed therebetween. Each wall portion 212,214, 216 comprises first and second wails disposed substantially parallel to one another.

A top wall 218 joins the first and second walls of the first and second wall portions 212,214 across their upper edges. A first side wall 220 joins the first and second walls of the first wall portion 212 above the level of the third wall portion 216 along a free edge thereof. A first recessed wall 222 joins the first and second walls of the first wall portion 212 below the level of the third wall portion 216 along a free edge thereof. The recessed wall 222 continues along and between the first and second walls of a side of the third wall portion 216 adjacent thereto. In this way the recessed wall 222 forms a substantially"L"shaped groove 224 along the first and third wall portions 212,216.

A second side wall 226 joins the first and second walls of the second wall portion 214 along a free edge thereof and also extends along and between the first and second walls of a side of the third wall portion 216 adjacent thereto. A first tongue 228 is formed on the second side wall on the side of the third wall member.

A second tongue 230 is formed on the second side wall below the level of the third wall portion 216 along a free edge thereof.

A further recessed wall 232 extends joins the first and second walls of the first and second wall portions 212,214 along their respective bottom edges. In this way the recessed wall forms a substantially"L"shaped groove 234 along a lower edge of the first and second wall portions.

A first rectangular boss 246 is formed on an upper portion of the first wall portion 212 and a second rectangular boss is formed on an upper portion of the second wall portion 212. cafter the casting is made, the metal from these surfaces, usually referred to as machining allowances, may be removed by machining (as shown by the dashed lines in Fig. 9) to allow for the fitting of bearing cheeks of a suitable material such as aluminium bronze.

Preferably, the pattern member 210 has a substantial cavity. For example, if there is no base web, a cavity will extend vertically from the lower edge of the vertical wall portions in a similar manner to that proposed for the pattern member 170 shown inn Fig. 7 and again this can act as a recess for a connecting tongue of an adjacent pattern member. The tongues 228,230 are optionally provided with one or more through holes 229, 231 which connect with the cavity. Similarly, the wall 222 is optionally provided with similar through holes 223 which connect with the cavity and can provide a through connection to a matching tongue of an adjacent pattern member.

The eighth pattern member 250 shown in Fig. 10 may be used to form a portion of a flat upper surface of a completed pattern and comprises a first, substantially horizontal, upper wall 252 and first, second, third and fourth substantially"L"shaped vertical walls 254,256,258,260 depending therefrom.

The"L"shaped walls 254,256,258,260 form an"X"shape when viewed from below. First, second, third and fourth quadrant walls 262,264,266,268 are disposed on the respective"L"shaped walls 254,256,258,260 and are located substantially parallel to the upper wall 252. An"X"shaped wall 270 is located between and across the"L"shaped walls 254,256,258,260 and is set back from free edges of the"L"shaped walls. In this way substantial cavities or recesses 272 are formed between the respective"L"shaped walls and the top wall. Where a tongue 274 is to be located between adjacent"L"shaped walls or between a quadrant wall 262,264,266,268 and the upper wall 252, a substantially vertical wall 276 is arranged to join the respective walls and the tongue is located on said vertical wall. The tongues 274 are optionally provided with one or more through holes which connect with the cavity. Similarly, the wall 270 is optionally provided with similar through holes which connect with the cavity and can provide a through connection to a matching tongue of an adjacent pattern member.

The casting pattern member 280 shown in Fig. 11 may be used to form a vertical inner rib junction of a completed pattern. The pattern member 280 comprises a first, substantiallv""shaped, horizontal upper wall 282, and first, second, third and fourth substantially"L"shaped vertical walls 284,286,288,290 depending from the edges thereof. A lower"X"shaped wall 292 is located between and across the"L"shaped walls and is set back from free edges of the"L"shaped walls. In this way substantial cavities or recesses 294 are formed between the respective walls. Tongues 296 are located on an upper surface of the upper wall.

The tongues 296 are optionally provided with one or more through holes which connect with the cavities. Similarly, the wall 292 is optionally provided with similar through holes which connect with the cavities and can provide a through connection to a matching tongue of an adjacent pattern member.

The pattern member 280 shown in Fig. 11 may be joined to the pattern member 250 shown in Fig. 10 by pushing members together in the general direction illustrated by arrow A in Fig. 11, this being the method normally applied to join all adjacent pattern members. Thus the pattern members may be assembled together in the manner of interlocking building blocks. To maintain the casting pattern members in position relative to one another the members may be joined together by applying adhesive to the casting pattern members, e. g. on the extending tongues, before joining the casting pattern members to one another.

Particular casting features, such as required for the lifting lug 30 shown in Fig. 1, may be left solid and assembled onto the pattern bv adhesive. Also some of the interlocking pattern members may be solid if the shape does not readily provide for a cavity or a cavity would weaken the pattern unduly. Where appropriate, supporting ribs or webs may extend partially or fully across cavities to provide appropriate support or stiffness.

When adjacent pattern members are assembled together, the cavities and recesses are closed by the tongues or abutting surface of the adjacent pattern member so that sand cannot enter, the casting taking up the shape of the outer, exposed, surface of the pattern. In this way the pattern has a smaller volume of expanded polystyrene than would be the case if the pattern members were formed from solid blocks of expanded polystyrene without the cavities.

There are a number of features normally associated with the lost foam method of casting which need particular care. For example, means need to be provided for the venting of the gassified polystyrene, not only to prevent voids in the casting but also to extract the gassified styrene produced during casting. furthermore, the polystyrene can leave an ash residue which has to be flushed away into a riser (an upstanding part of the pattern which is removed from the casting in the foundry. The reduced the volume of polystyrene helps to alleviate

these problems by reducing the volume of gas and ash. Where the cavities are interconnected by holes in the tongues and abutting end walls, the gas can escape rapidly through the pattern before the polystyrene is melted and gassified by the advancing molten metal, thereby further promoting the flushing away of the ash.

The various pattern members shown in Figs. 3 to 11 are preferably made by moulding to the required shape, e. g. by heat expansion of polystyrene pellets in a mould. This generally improves the surface finish, dimensional accuracy and surface strength of the pattern members. This can mean that features such as curves and corners that were previously only possible by finish machining of the casting can now be produced without the need for such finish machining. Also, the fillets that previously were produced by the use of masking tape can be easily generated as a feature of the standard pattern member. Furthermore, the accuracy of moulding can avoid the need to seal joints with masking tape.

Where production volumes are low relative to the cost of providing mould tools, it may be expedient to machine some of the pattern members from blocks of expanded polystyrene. This can be facilitated by using numerically controlled (N. C.) machine tools where the shape can be stored as data and thus readily reproduced. In any event, some features of the pattern member, e. g. the relief 13 shown in Fig. 1, would be required as a specific or one-off item to be assembled onto the assembly of standard pattern members bv adhesive or other means.

Fig. 12 illustrates a typical tongue and groove connection. Each groove in one part 300 may be considered to comprise upstanding walls 302,304 either side of a central valley 306. The upstanding walls have inner surfaces 308,310 which may be shaped, for example they may slope slightly (the slope being exaggerated in Fig. 12 for clarity) to form a keying surface with which side faces 312,314 of the tongues 315 in an adjacent part 316 may engage. The walls 302,304 will have

sufficient resilience to bend back allowing entry of the tongue 316, the walls subsequently closing over the tongue to hold the tongue within the walls of the groove 300. This resilience is improved if the pattern members are moulded to shape, the outer surface forming a skin where the individual polystyrene pellets expand against the walls of the mould and thus have a greater resilience than a machined surface where the expanded cells are cut to expose the foam. Fig. 12 also illustrates a through hole 317 in the tongue 315 to assist gas venting as described above.