GB1592208A - Collapsible cores for the manufacture of moulded components - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO COLLAPSIBLE CORES FOR THE MANUFACTURE OF MOULDED COMPONENTS (71) We, GEYER, WERKZEUGBAU GMBH & CO. KG formerly known as GEYER & CO., of Konigsberger Strasse 11 D-5889 Ludenscheid, Germany, a German Kommanditgesellschaft, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a collapsible core usable, for example, for the manufacture of moulded components. In particular the invention relates to a collapsible core comprising an elongate core member, for example a core pin, and a segmented casing whose segments are arranged to move axially of the. pin and also radially from an operative moulding state to a state in which the moulded component can conveniently be removed.

Collapsible cores allow plastics components, for example, to be injection moulded, and such components can be manufactured with internal screw threads, nozzles, internal cavities, grooves, notches, apertures and undercuts. The outer surfaces of the segmented casing determine, in the moulding state, the shape of the inner wall of the component. If the inner wall has undercuts, the outer diameter of the casing must be reduced to allow removal of the component after moulding. Separation of the component from known collapsible cores is often incomplete.

In accordance with the present invention there is provided a collapsible core comprising an elongate core member surrounded by a segmented casing whose segments are arranged to move axially and radially of the core member, wherein the outer surface of the core member comprises two groups of surface portions of which the surface portions of one group are stepped, and the surface portions of the second group are conical, the surface portions of the one group alternating in circumferentially with the surface portions, of the second group, and wherein the segmented casing comprises two groups of segments, the segments of a first of the groups having stepped inner surfaces extending parallel to the longitudinal axis of the core and being mounted for sliding on respective ones of the stepped surface portions of the core member, and the segments of the second of the groups having conical inner surfaces arranged to co-operate with an be guided by respective ones of the conical surface portions of the core member.

The collapsible core of the present invention allows manufacture of components with rounded or rectangular cross-sections, for example, which also may have complex undercuts.

Only a small number of slidable segments are required, and different ones may be used with the same core member to provide collapsible cores for producing mouldings of different diameters, or other lateral dimension. The slidable segments are moved radially inwards towards each other by their movement axially of the core member, so that long undercuts can be produced in a moulded component, and the undercuts can be of any required shape, for example rounded or angular. No burrs are formed- on the finished article, which can be produced to a high degree of accuracy.

The synchronisation of the slidable segments minimizes wear and tear of the core and thus lengthens its lifetime.

Large equipment is not required in order to set up the core for operation; its assembly is simple and cheap, and there is no restriction due to the core construction on the maximum lateral dimension of a component to be produced.

The elongate core member, conveniently formed as a pin, allows a cooling bore to be provided and to extent to its free end, adjacent the core region at which formation of the component takes place.

By appropriate choice of material, the collapsible core can be used for thermoplastic manufacture, duroplastic manufacture, metal die casting, and for piercing and stamping.

Since no additional connections are required to the core, it can be used with almost any form of injection moulding apparatus.

An embodiment of an expansible core for the manufacture of injection moulded components, constructed in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure la is an elevational, cross-sectional view along the line W-W of Figures 1b and 1c, of an embodiment of a core constructed in accordance with the invention and the injection moulding operative state; Figure ib is an axial end view in the direction of arrow Y of Figure la; Figure ic is a cross-sectional view along line X-X of Figure la; Figures 2a, 2b and 2c are views similar to Figures la, 1b and 1c respectively, showing the core of Figures la to 1c in an intermediate position; and Figures 3a, 3b and 3c are views similar to Figures la, 1b and 1c respectively, showing the core of Figures la to 1c in the inoperative, moulded article demounting, state.

The illustrated collapsible core includes an elongate core member in the form of a core pin 1 and two groups of segments in the form of lateral or flanking sides 2 and 3 arranged around the core pin. All of the lateral slides belonging to the same group are of identical structure. The illustrated embodiment has three slides in each group.

Each of the lateral slides 2 alternates with successive lateral slides 3, around the circumference of core pin 1.

At one of its ends, core pin 1 is shaped to constitute a connecting part 11 for making a connection with a stationary part of a moulding tool 5. At the free end of connecting part 11, a thread 12 is provided. A central cooling bore 13 passes through substantially the entire core pin 1 from the outer end face of part 11 to the region of the opposite end face of part 11 to the region of the opposite end face of core pin 1.

At its free end, directed away from connecting part 11, each lateral slide 2 is provided with an extension 24 whose outer surfaces 25 defines the inner wall of the injection moulding cavity which is to be formed by the core. In the illustrated embodiment the outer surface 25 is provided with parallel grooves.

At a point spaced from extension 24, each lateral slide 2 is provided with a part 26 of an annular collar by which the axial movement of the lateral slides 2 within the moulding tool is effected.

Each lateral slide 3 is also provided with an extension 34 at its free end directed away from part 11, the outer surface 35 of this extension conforming to the shape of the inner wall of the injection moulding cavity to be established. At a point spaced from the outer surface 35 each lateral slide 3 is also provided with a part 36 of the annular collar. Parts 26 and 36 form the complete annular collar. This collar is provided to effect the axial movement of the lateral slides 2 and 3 within the moulding tool.

The core pin 1 is provided, subsequent to the connecting part 11, with three outer surface portions 14 which are reduced in their distance from the core axis in a stepwise manner as they succeed each other towards the free end of the core pin 1. The outer surface portions 14 are equispaced about the circumference of core pin 1. Each outer surface portion 14 has a sloped step 18 near the free end of core pin 1 and extends essentially over the entire length of core pin 1, with the exception of the region defined by part 11. Between each two succeeding outer surface portions 14 there is provided an outer surface portion 15 which slopes uniformly inwardly toward the free end of core pin 1. Each outer surface portion 15 is provided in its centre with the dovetail mortise 17 which extends in the axial direction. Each surface portion 15 extends axially essentially over half of the length of core pin 1, beginning at its free end, and excluding part 11. In the region between the lower ends of the outer surface portions 15 and the start of the connecting part 11, the core pin is made circular without any particular features.

The lateral slides 2 sliding along the stepped outer surface portions 14 of the core pin 1 are provided with axially parallel inner surfaces 28 which are interrupted by steps 29. These lateral slides have their axially parallel inner surfaces 28 held in contact with the outer surface 14 of the core pin 1 by means of at least two helical springs 23 which enclose the lateral slides 2 in the area of their end faces. One of the helical springs 23 is provided in collar 26. The helical springs 23 are preferably double helixes.

Each lateral slide 2 has a cross-sectional shape which is essentially a truncated circular sector.

The lateral slides 3 which slide along the conical outer surface portions 15 of core pin 1 and are guided in grooves 17, each have a sloping inner surface 38. Each lateral slide 3 with its sloping inner surface 38 has a substantially rectangular cross section. The side walls 39 of each lateral slide 3 are parallel to the adjacent side walls 27 of the two lateral slides 2 between which it is disposed, side walls 27 defining parts of the cross sectional shape of the sector of a circle of their associated slides 2 and being spaced from walls 39 in the moulding state of Figures 6a to 6c. Each lateral slide 3 is guided in the groove 17 of its associated outer surface portion 15 by means of the dovetail tenon 33.

Each one of the axially parallel outer surface portions 14 of the core pin 1 is provided with a sloping step 18 located at a distance from the free end, i.e. the end remote from part 11, ofthe core pin equal to the effective length of the mould core. The effective length of the mould core corresponds to the distance to which the core is inserted into the part being moulded. Each one of the lateral slides 2 is provided with two sloping steps 29 located at respective distances from the free end of the core pin which are equal to one end and three times the effective length of the mould core.

In toto, this embodiment has three lateral slides 2 and three lateral slides 3. When seen from the top, i.e. as shown in Figure 16, the core pin 1 therefore has at its free end substantially the shape of a regular hexagon in which a groove 17 is provided in every alternate face and the intervening faces are flat.

In the operative moulding state i.e. the state shown in Figure 1, all the extensions 24 and 34 form the mould core for producing an internal wall in the moulded part.

The collapsible core illustrated operates as follows: the mould is opened and slide guide plates (not illustrated) are moved together with stripping plate upwardly in the axial direction as shown in Figures la and 2a. The slide guide plates are screwed or otherwise secured together and can only travel a limited distance. Since the core pin 1 is firmly secured to a stationary base plate (also not illustrated), the lateral slides 2 and 3 which have been carried along via collar 26, 36 also traverse the limited distance.

The core opening movement of the lateral slides 2 and 3 initially causes the lateral slides 2 to be moved parallel to the axis of core pin 1 on the outer surface portions 14, while the lateral slides 3 are moved axially and radially inwardly on the sloping outer surface portions 15. This movement is continued until the rear edge of the portions of slides 2 and 3 which define the recess formed by the core in the moulded part is substantially flush with the frontal end face of the core pin 1, which position is shown in Figures la, 1b and 1c. In this position the lateral slides 3 have been moved inwardly to such an extent that the moulded part is released from lateral slides 3. A further axial movement of lateral slides 3 is not required or intended. However, lateral slides 2 continue to move further in the axial direction. This axial movement is continued until that step 29 of each lateral slide 2 which is closer to collar part 26 has reached the level of step 18 in the associated outer surface portion 14 of core pin 1. When this position has been reached, the helical springs 23 press the lateral slides 2 radially inwardly as shown in Figures 2a, 2b and 2c.

The moulded part is thus completely free of the mould core and can be withdrawn from the collapsible core with the aid of the associated stripping plate.

As long as the lateral slides 3 have not reached their innermost radial position, which they reach by travelling along outer surface portions 15, the lateral slides 2 cannot be pressed inwardly since both groups of lateral slides 2 and 3 contact one another via adjacent edge surfaces in the region of mould surfaces 25 and 35. Only after the lateral slides 3 have reached the above-mentioned innermost position can lateral slides 2 move radially inwardly during their further axial movement.

In the inoperative state, the two groups of lateral slides need not have the same axial position with respect to the core pin.

Rather, the lateral slides 2 with the stepped inner surfaces can be moved axially beyond the lateral slides 3 with the sloping inner surfaces. For this reason, and in order to realise greater radial movement for the lateral slides with sloping inner surfaces, it is of advantage for the lateral slides 2 with the stepped inner surfaces to be longer than those with the sloping inner surfaces. For example the former could extend along practically the entire length, the latter only over half the length, of the core pin.

Upon return of the moulding tool to its starting position, the lateral slides 2 and 3 slide back along the core pin 1 to their starting positions. A new injection moulding process can then be initiated. Here it is of advantage to arrange the moulding tool as a multiplate tool, i.e. to provide it with a plurality of collapsible cores.

WHAT WE CLAIM IS: 1. A collapsible core comprising an elongate core member surrounded by a segmented casing whose segments are arranged to move axially and radially of the core member, wherein the outer surface of the core member comprises two groups of surface portions of which the surface portions of one group are stepped and the surface portions of the second group are conical, the surface portions of one group alternating circumferentially with the surface portions of the second group, and wherein the segmented casing comprises two groups of segments, the segments of a first of the groups having stepped inner

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. parallel to the adjacent side walls 27 of the two lateral slides 2 between which it is disposed, side walls 27 defining parts of the cross sectional shape of the sector of a circle of their associated slides 2 and being spaced from walls 39 in the moulding state of Figures 6a to 6c. Each lateral slide 3 is guided in the groove 17 of its associated outer surface portion 15 by means of the dovetail tenon 33. Each one of the axially parallel outer surface portions 14 of the core pin 1 is provided with a sloping step 18 located at a distance from the free end, i.e. the end remote from part 11, ofthe core pin equal to the effective length of the mould core. The effective length of the mould core corresponds to the distance to which the core is inserted into the part being moulded. Each one of the lateral slides 2 is provided with two sloping steps 29 located at respective distances from the free end of the core pin which are equal to one end and three times the effective length of the mould core. In toto, this embodiment has three lateral slides 2 and three lateral slides 3. When seen from the top, i.e. as shown in Figure 16, the core pin 1 therefore has at its free end substantially the shape of a regular hexagon in which a groove 17 is provided in every alternate face and the intervening faces are flat. In the operative moulding state i.e. the state shown in Figure 1, all the extensions 24 and 34 form the mould core for producing an internal wall in the moulded part. The collapsible core illustrated operates as follows: the mould is opened and slide guide plates (not illustrated) are moved together with stripping plate upwardly in the axial direction as shown in Figures la and 2a. The slide guide plates are screwed or otherwise secured together and can only travel a limited distance. Since the core pin 1 is firmly secured to a stationary base plate (also not illustrated), the lateral slides 2 and 3 which have been carried along via collar 26, 36 also traverse the limited distance. The core opening movement of the lateral slides 2 and 3 initially causes the lateral slides 2 to be moved parallel to the axis of core pin 1 on the outer surface portions 14, while the lateral slides 3 are moved axially and radially inwardly on the sloping outer surface portions 15. This movement is continued until the rear edge of the portions of slides 2 and 3 which define the recess formed by the core in the moulded part is substantially flush with the frontal end face of the core pin 1, which position is shown in Figures la, 1b and 1c. In this position the lateral slides 3 have been moved inwardly to such an extent that the moulded part is released from lateral slides 3. A further axial movement of lateral slides 3 is not required or intended. However, lateral slides 2 continue to move further in the axial direction. This axial movement is continued until that step 29 of each lateral slide 2 which is closer to collar part 26 has reached the level of step 18 in the associated outer surface portion 14 of core pin 1. When this position has been reached, the helical springs 23 press the lateral slides 2 radially inwardly as shown in Figures 2a, 2b and 2c. The moulded part is thus completely free of the mould core and can be withdrawn from the collapsible core with the aid of the associated stripping plate. As long as the lateral slides 3 have not reached their innermost radial position, which they reach by travelling along outer surface portions 15, the lateral slides 2 cannot be pressed inwardly since both groups of lateral slides 2 and 3 contact one another via adjacent edge surfaces in the region of mould surfaces 25 and 35. Only after the lateral slides 3 have reached the above-mentioned innermost position can lateral slides 2 move radially inwardly during their further axial movement. In the inoperative state, the two groups of lateral slides need not have the same axial position with respect to the core pin. Rather, the lateral slides 2 with the stepped inner surfaces can be moved axially beyond the lateral slides 3 with the sloping inner surfaces. For this reason, and in order to realise greater radial movement for the lateral slides with sloping inner surfaces, it is of advantage for the lateral slides 2 with the stepped inner surfaces to be longer than those with the sloping inner surfaces. For example the former could extend along practically the entire length, the latter only over half the length, of the core pin. Upon return of the moulding tool to its starting position, the lateral slides 2 and 3 slide back along the core pin 1 to their starting positions. A new injection moulding process can then be initiated. Here it is of advantage to arrange the moulding tool as a multiplate tool, i.e. to provide it with a plurality of collapsible cores. WHAT WE CLAIM IS:

1. A collapsible core comprising an elongate core member surrounded by a segmented casing whose segments are arranged to move axially and radially of the core member, wherein the outer surface of the core member comprises two groups of surface portions of which the surface portions of one group are stepped and the surface portions of the second group are conical, the surface portions of one group alternating circumferentially with the surface portions of the second group, and wherein the segmented casing comprises two groups of segments, the segments of a first of the groups having stepped inner

surfaces extending parallel to the longitudinal axis of the core and being mounted for sliding on respective ones of the stepped surface portions of the core member, and the segments of the second of the groups having conical inner surfaces arranged to co-operate with and be guided by respective ones of the conical surface portions of the core member.

2. A collapsible core according to claim 1, wherein the slidable segments of the first group are spring biassed towards the core member.

3. A collapsible core according to claim 1, wherein the spring biassing is provided by two springs mounted within each said slidable segment adjacent respective ends thereof.

4. A collapsible core according to any of claims 1 to 3, wherein the slidable segments of the second group are guided within grooves extending along the core member.

5. A collapsible core according to claim 4, wherein the grooves are of substantially dovetailed cross-section.

6. A collapsible core according to any of claims 1 to 5, wherein the slidable segments of the second group are of substantially rectangular cross-section.

7. A collapsible core according to claim 6, wherein the slidable segments of the first group have a cross-section that is substantially that of a sector of a circle sector whose side faces extend parallel to the side faces of the rectangular slidable segments of the second group.

8. A collapsible core according to any of claims 1 to 7, wherein the slidable segments have an extension at their free ends, the outer surface of the extension being arranged for engagement with the inner surface of the article to be produced by the core.

9. A collapsible core according to any of claims 1 to 8, wherein the slidable segments of the first group are shorter in the axial direction than the slidable segments of the first group.

10. A collapsible core according to any of claims 1 to 9, wherein the free end surface of the core pin is of a substantially regular hexagon shape.

11. A collapsible core according to any preceding claim, wherein each of the stepped portions of the outer surface of the core member has a sloping step spaced from the free end of the core member by a distance substantially equal to the length of the article to be produced by the core.

12. A collapsible core according to claim 11, wherein each slidable segment of the first group has a step arranged to engage one of the sloping steps, the step being spaced from the free end of its associated slidable segment by between one and three times the length of the article to be produced by the core.

13. A collapsible core according to any preceding claim, wherein each of the slidable segments has a portion extending radially outwards thereof remote from the free end of the core member, by means of which the segments are axially movable relative to the core member.

14. A collapsible core according to any preceding claim, wherein each of said groups comprises three segments.

15. A collapsible core according to any preceding claim, wherein the core member has a cooling bore extending therewithin.

16. A collapsible core substantially as hereinbefore described with reference to the accompanying drawings.