GB2443170A

GB2443170A - Work piece holding system

Info

Publication number: GB2443170A
Application number: GB0621371A
Authority: GB
Inventors: Felim Patrick Mcneela; William Gerard Gaffney; Paul Michael Mulligan; Noel Gerrity; David Joseph Loughney
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-10-27
Filing date: 2006-10-27
Publication date: 2008-04-30
Anticipated expiration: 2026-10-27
Also published as: GB2443170B; GB0621371D0

Abstract

The invention provides a work piece holding system comprising a block 2 and a work piece 3 for use in the manufacture of injection moulds. The system has a locating means 5 for locating the block and work piece relative to one another as required. The locating means is slideably engageable between the work piece and the block and is provided at the centre of the block and work piece. The locating means is configured to enable the rotation of the work piece relative to the block to enable an accurate alignment of the two. Preferably the locating means is a dowel 7 provided in one of the work piece or block, which is provided in a steel insert 6 in the block.

Description

Work piece holding system

Field of the Invention

The present invention relates to a work piece holding system and in particular a work piece holding system for use in the manufacture of injection moulds.

Background

The method of manufacture of injection moulds includes taking a piece of steel in a raw blank state and precision machining it to tolerances of typically ± 0.005mm. A wide range of machining techniques may be used in the process, including turning, milling, surface grinding, cylindrical grinding, high speed machining, solid sink and wire electro discharge machining.

The conditions under which high volume injection moulds operate are extremely demanding and all steel inserts consequently require heat treatment to harden and temper the steels to meet the performance requirements of the process. This involves machining the work piece in its soft pre hardened state and subsequently finish machining it in its post hardened and tempered state.

The hardening process is often carried out by specialist sub contractors and involves heating the steels to temperatures exceeding 500 degrees Celsius.

Furthermore, before machining can commence it is necessary to establish the x, y and z datum's of a work piece. In one current approach, after clamping the work piece on a particular machine tool, the position of the work piece is established by using dial indicators in conjunction with the machine's axis scales (clocking up). However, this is a very time consuming operation and is also prone to human error. The time and investment in this operation is compounded since this operation has to repeated every time a work piece is to be machined.

Different work holding systems have been used. For example, in another approach Erowa (RIM), manufacture a work holding system in which a work piece is attached to a block by means of 2 x M6 screws. Referring to the prior art Fig. A, the block of this system comprises a brass block having a datum plate fixed to its underside and 4 locating apertures for establishing x and y datum's as well as 4 pads which provide a z datum. A centre clamping spigot is fixed to the block using an Ml 0 threaded hole on the centre of the block. The unit, (block, plate, and spigot with work piece attached) is then positioned on a receptive chuck, which is fixed in a set position on each machine. The spigot is then pulled back, clamping the unit in a fixed position on the 4 apertures and on the 4 pads. This arrangement provides an alternative to clocking up at each machining operation. After the work piece is machined in its soft state it must be removed from the block, It is then heat-treated. After heat treatment the work piece must be re-attached to the block and x, y ard z datums re-established.

This operation of relocation and re-attachment of the work piece to the block is clearly a time consuming and error prone operation. There is a further problem with existing systems in that they are often prone to misalignment due to distortion resulting from the heat treatment process.

There are therefore a number of problems with conventional work holding systems that need to be addressed.

Summary

These needs and others are addressed by a system in accordance with the invention which provides a work holding system comprising: a block and a work piece, the system having a locating means for locating the block and work piece relative to one another as required, wherein the locating means is slideably engageable between the work piece and the block and is provided at the centre of the block and work piece, and is configured to enable the rotation of the work piece relative to the block to enable an accurate alignment of the two.

The invention therefore provides a work holding system in accordance with claim 1. Advantageous embodiments are provided in the dependent claims thereto.

According to another aspect the invention provides a method for the post hardening set-up of a work holding system in accordance with the invention.

Brief Description Of The Drawings

The present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a perspective view of a work holding system in accordance with the invention; Figures 2, 3 and 4 are cross-sectional views of the components of the Figure 5 is a perspective view of the components of the work holding system of Fig.1.

Detailed Description Of The Drawings

Referring to the drawings a work holding system 1 comprises a block 2 and a work piece 3. The block 2 in this case comprises a central clamping spigot 4. The work holding system 1 further comprises a locating means 5.

The locating means 5 in this case, comprises a dowel locating means comprising a dowel hole 7 provided in the block 2, and a corresponding dowel hole is provided machined in the work piece 3, and a dowel 10 provided projecting from the block. Fixing pins 15 are provided to fix the block and work piece. In this case the pins project from the block and are received in corresponding fixing holes 1 6 provided in the work piece. In this case the fixing pins comprise screws. The fixing pins and holes are circumferentially located equispaced around the locating means.

The block 2 comprises a steel portion at the centre thereof, as shown and the block dowel hole 7 is formed in this steel portion. In this case, the block is of brass and a steel insert 6 is fitted to the centre of the block 2. The block dowel hole 7 is machined such that it is at the centre of the work holding system i.e. at the origin so that the dowel 10 is also located at the centre of the system.

Similarly the work piece dowel hole is centrally located on the work piece.

The locating means 5 enables the work piece to be located and relocated on the block as required. The work piece is located on the block by inserting the dowel 10 on the block into the dowel hole 11 in the work piece. The work piece is then rotated on the dowel and dial indicators are used to realign the axes. The work piece and block are then fixed to each other using the fixing pins 15.

While in this case the block is of brass and the locating means is provided on a steel insert which is fitted to the block, it will be appreciated that different portions of the block may be comprised of different suitable materials. It will be appreciated that work piece holding systems of various type are known and the invention provides in one embodiment a modification of such known systems.

While in this case the locating means comprises a dowel system it will be appreciated that a suitable alternative locati ng means may be provided.

The invention further provides a method for use of the work holding system. In particular the invention provides a method for the pre hardening and post hardening set-up of a work holding system in accordance with the invention including the following steps: a. providing a work holding system comprising a block and a corresponding work piece having a central locating means comprising a dowel locator b. assembling the work piece to the block c. conducting pre-hardening machining d. removing the work piece from the block e. heat treating the work piece f. fixing the work piece to the block using the central dowel and fixing pins g. rotating the work piece on the dowel and using dial indicators to realign axes.

Example 1:

The work holding system of example 1 comprises a block provided by the manufacturer Erowa (RIM), hereinafter referred to as the block 20. The block is described in detail above with reference to the prior art drawing Fig. A. The block 20 is modified in accordance with the process of the invention to provide a block and work holding system in accordance with the invention.

As noted above the block 20 is comprised of brass and comprises a central clamping spigot 4 and fixing pins 15 being provided to fix the block and work piece. In this case the pins 15 comprise M6 screws which project from the block and a received in corresponding holes 16 provided in the work piece.

A centrally located clamping spigot is fixed to the block using an M10 threaded hole fitted to the centre of the block 20 plugging the M10 hole. A single dowel hole 7 is formed in the steel inset to support the dowel 10. A corresponding dowel hole is formed in the work piece to receive the dowel 10.

The steel insert may be of any suitable steel material for example, a mild or tempered steel.

The method of the invention includes the following steps: -providing a work holding system comprising a block and work piece -providing in the work holding system a single centrally located 6mm dowel system -fitting a steel insert to the centre of the block 20 plugging the Ml 0 hole -machining a single 6mm dowel hole in the steel insert (this central hole is at xo and yo; in other words, the origin) -machining a corresponding 6mm dowel hole in the work piece prior to heat treatment along with the M6 fixing holes -assembling the work piece to the block 20 and conducting pre-hardening machining -removing the work piece from the block 20 -heat treating the work piece -fixing the work piece block using the 6mm central dowel and 2 x M6 fixings -rotating the work piece on the single dowel and using dial indicators to realign axes.

The system of the invention has advantages as follows: The central dowel and two fixing pin system and method provides for increased ease of use and increased accuracy in the task of fitting and refitting the work piece to the block.

The efficiency of the system is increased and the user-friendliness is similarly increased.

The method of the invention addresses the problem of the effects of distortion by the step of heat treating and provides means by which the post hardening setup is simplified.

The invention additionally provides a method for the modification of an 1 5 existing known work piece holder.

While in the embodiments described the block comprises a block of brass having a steel insert, it will be understood by the skilled person that suitable alternative may be used, for example, a block comprised of steel.

A further advantage of this system over existing blocks such as a block of brass is that location takes place on a steel insert, and not in the supplied brass block, making multiple uses possible with minimal wear to the location areas.

The steel insert of the system of the invention thus brings advantages of increased lifetime of the system. The steel is a hardened and tempered material which withstands wear and tear well. While units of material such as brass often show wear after one use, steel gives the user an order of magnitude improvement of 50-100 uses over that of a brass unit.

The system of the invention is designed to enable the user to perform the tasks of location and fixing separately by virtue of provision of separate independent components for locating and fixing. This provides the user with increased flexibility and ease of use. The locating system of the invention is highly user friendly, since it is possible for the user to slideably engage the component parts. The provision of a central locator in addition to circumferentially arranged locators increases ease of use by eliminating the effects of distortion or loss of alignment during heat treatment.

The use the central dowel locator has the advantage in the case when the work piece is hardened and the circuniferentially located locators may shift relative to one another, however, the centrally located dowel does not shift in orientation. This also has the further advantage of increased accuracy of alignment.

The words comprises/comprising when used in this specification are to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

Claims.

1. A work piece holding stem comprising: a block and a work piece for use in the manufacture of injection moulds, the system having a locating means for locating the block and work piece relative to one another as required, wherein the locating means is slideably engageable between the work piece and the block and is provided at the centre of the block and work piece, and is configured to enable the rotation of the work piece relative to the block to enable an accurate alignment of the two.

2. A work piece holding system as claimed in claim 1, wherein the locating means comprises a dowel provided in one of the work piece or block and a corresponding dowel hole provided in the other of the corresponding block or work piece.

3. A work piece holding system as claimed in claim 2 wherein the block comprises a steel insert and the dowel or dowel hole in the block is provided in said steel insert.

4. A work piece holding system as claimed in any preceding claim, further comprising fixing means configured to provide for a fixing of the work piece to the block once alignment is effected.

5. The work piece holding system as claimed in claim 4 wherein the fixing means comprises one or more fixing pins and corresponding holes for receiving the pins provided on the work piece and block.

6. A work piece holding system as claimed in claim 5 wherein the fixing pins and corresponding holes are located circumferentially around the locating means.

7. A work piece holding system as claimed in any of claims 5 or 6 wherein the fixing pins and corresponding holes are located equispaced around the locating means.

8. A work piece holding system as claimed many of claim 2 to 7 wherein the dowel is provided projecting from the block.

9. A work piece holding system as claimed in any preceding claim further comprising dial indicators for alignment of the work piece and block.

10. A work piece holding system as hereinbefore described with reference to the drawings.

S.' 11 A method of using the system of claims Ito 10 for the pre-hardening and post hardening set-up of a work piece comprising the following *:*::* steps: * S * * S. a. assembling the work piece to the block b. conducting pre-hardening machining c. removing the work piece from the block d. heat treating the work piece e. locating the work piece to the block using the locating means f. rotating the work piece on the locating means g. using dial indicators to realign axes, and h. fixing the work piece to the block using fixing means

10. A work piece holding system as claimed in any preceding claim configured to enable alignment of the work piece and block for both pre and post hardening set-ups.

11. A work piece holding system as claimed in any preceding claim configured to enable alignment of the work piece and block for an initial pre-hardening machining, and again after the work piece has been heat treated.

12. A work piece holding system as hereinbefore described with reference to the drawings.

13 A method for the pre-hardening and post hardening set-up of a work piece holding system as claimed in any of claims 1 to 12 comprising the following steps: a. assembling the work piece to the block b. conducting pre-hardening machining c. removing the work piece from the block d. heat treating the work piece e. locating the work piece to the block using the locating means f. rotang the work piece on the locating means g. using dial indicators to realign axes, and h. fixing the work piece to the block using fixing means 14. A method for the pre and post hardening set-up of a work piece holding system having a locating means comprising a central dowel locator comprising the following steps: a. assembling a work piece to a block b. conducting pre-hardening machining c. removing the work piece from the block d. heat treating the work piece e. locating the work piece to the block using the central dowel and fixing means f. rotating the work piece on the dowel and using dial indicators to realign axes g. fixing the work piece to the block using the fixing means Amendments to the claims have been filed as follows: Claims.

1. A work piece holding system comprising: a block and a work piece for use in the manufacture of injection moulds, the system having a locating means for locating the block and work piece relative to one another as required, wherein the locating means is slideably engageable between the work piece and the block and is provided at the centre of the block and work piece, and is configured to enable the rotation of the work piece relative to the block to enable an accurate alignment of the two, the locating means comprising a dowel provided in one of the work piece or block and a corresponding dowel hole provided in the other of the corresponding block or work piece; and wherein the block comprises a steel insert and wherein the dowel hole, for :... receiving said corresponding dowel in the block, is provided in said steel insert. * *

* ,. 15 2. A work piece holding system as claimed in claim 1, further comprising fixing means configured to provide for a fixing of the work piece to the block once alignment is effected. * I. * * * * **

3. The work piece holding system as claimed in claim 2 wherein the fixing means comprises one or more fixing pins and corresponding holes for receiving the pins provided on the work piece and block.

4. A work piece holding system as claimed in claim 3 wherein the fixing pins and corresponding holes are located circumferentially around the locating means.

5. A work piece holding system as claimed in any of claims 3 or 4 wherein the fixing pins and corresponding holes are located equispaced around the locating means.

6. A work piece holding system as claimed in any preceding claim wherein the dowel is provided projecting from the block.

7. A work piece holding system as claimed in any preceding claim further comprising dial indicators for alignment of the work piece and block.

8. A work piece holding system as claimed in any preceding claim configured to enable alignment of the work piece and block for both pre and post hardening set-ups.

9. A work piece holding system as claimed in any preceding claim configured to enable alignment of the work piece and block for an initial pre-hardening machining, and again after the work piece has been heat treated.