GB2438841A

GB2438841A - Fixture having heating means

Info

Publication number: GB2438841A
Application number: GB0611068A
Authority: GB
Inventors: Daniel Clark
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2006-06-06
Filing date: 2006-06-06
Publication date: 2007-12-12
Also published as: GB0611068D0

Abstract

A substrate 33 is clamped into a fixture 32 and material is deposited thereon to form a complex article 40. A series of recesses (36, Fig 3) are provided in the surface of the fixture 32 to allow argon gas to circulate beneath the substrate 33 and prevent stagnant air-rich pockets forming beneath the substrate 33. Heaters 41 are embedded in the fixture 32 and are located in the recesses. The heaters 41 are used to maintain the fixture 32 and associated clamping material at an elevated temperature more suitable for material deposition. Elevating the temperature of the fixture 32 prevents it acting as a heat sink and helps to establish process uniformity.

Description

A FIXTURE FOR HOLDING A COMPONENT

The present invention relates to a fixture for holding a component and in particular to a fixture capable of holding a substrate on which a complex components is formed from layers of deposited material.

It is known to produce metal work pieces by the deposition of a weld material onto a base plate. The weld material can be deposited by any one of a number of techniques including laser welding, electron beam welding, metal inert gas welding (MIG) or tungsten inert gas welding (TIG) . In MIG or TIG welding a welding torch is provided adjacent a base plate on which the work piece is to be produced. An electrode is provided within the weld torch such that when an electric current is passed therethrough an arc is formed between the weld torch electrode and the base plate. The arc generates heat allowing the welding to take place.

In the MIG process the electrode melts and forms a weld pool in the surface of the work piece. However in TIG welding the arc melts the material of the base plate and a consumable welding wire is fed into the weld pool to form the work piece.

The MIG and TIG welding processes have been used for building up features on conventionally manufactured components or substrates. However drawbacks have been encountered in producing such hybrid structures. For example the components need to be restrained by clamps, which act as heat sinks during the deposition process.

Distortion may occur as a result of the temperature difference between the substrate, clamps and deposited material. To control the amount of distortion, the substrate on which the weld material is deposited must be elevated in temperature. The substrate is preheated to prevent excessive or uneven heat-flow and help establish process uniformity. This is currently achieved by heating the substrate with an arc prior to depositing any material.

The present invention seeks to provide an improved fixture, which is capable of holding complex articles during manufacture and helps to establish process uniformity.

According to the present invention a fixture for holding a substrate on which an article is formed comprises a member having means for locating and holding the substrate on a face thereof and heating means being provided in the member adjacent to the substrate.

The heating means may be embedded in the member and/or located in an at least one recess in said face. Preferably the heating means are electrical and may be induction or radiant heaters or a combination thereof.

The recess may be circular and in one embodiment of the present invention a plurality of circular recesses are provided which are interconnected.

Additional heating means may be provided adjacent to the article to be formed. The additional heating means may be an annular radiant or induction coil. Preferably a structure is provided to support the additional heating means adjacent to the article to be formed by material deposition.

Preferably the article is formed by material deposition and the material is deposited in layers using a welding process.

The means for locating the substrate is at least one block mounted on the face. A plurality of blocks may be provided some of which translate relative to the face to hold the substrate thereon. Alternatively the means for holding the substrate are clamps.

The present invention will now be described with reference to the accompanying figures in which; Figure 1 is a schematic view of apparatus for forming a work piece by material deposition.

Figure 2 is a cross-sectional view of a heated fixture for attachment to the apparatus shown in figure 1.

Figure 3 is a plan view of the base plate of the fixture shown in figure 2.

Figure 4 shows an alternative fixture arrangement.

Figure 5 shows an additional annular heater for use with the fixtures in accordance with the present invention.

Referring to figure 1 apparatus (10) for forming an article (40) comprises a welding torch (12) attached to a computer controlled robot arm (14) . A table (16) is mounted on a pedestal (20), which rotates about base (23), as indicated by arrow B. The table (16) is also capable of pivotal movement in the direction of arrow A around shaft (21) to maintain an angle of 90 between the torch (12) and

the table (16)

A number of metal wires (22, 24) extend through the robot arm (14) from a supply in the form of a reel (not shown) . The wires (22, 24) are fed from the reel to the welding torch (12) such that the ends of the wires (22, 24) extend just below the tip of the welding torch (12) . The wires (22, 24) are manufactured from a suitable welding material such as titanium.

The apparatus also includes a supply of an inert gas, for example argon. The gas is supplied by a gas pipe (28), which extends through the robot arm (14) from a cylinder (26) to the welding torch (12) A computer (30) controls the movement of the table (16) and the robot arm (14) as well as controlling the supply of argon and feeding the metal wires (22 and 24) In operation the table (16) and the welding torch (12) are both connected to a supply of electricity. Argon gas is fed via the pipe (28) to form an argon shroud around the welding torch (12) . The argon gas between the wire electrodes (22,24) is ionised to create an electrical arc.

The wires (22, 24) are consumable as they act as both the arc initiator and also as the welding material.

A fixture (32), figure 2, is bolted onto the rotary table (16) . The fixture (32) has a base plate (34) onto which a substrate (33) is fastened. The substrate (33) is located against blocks (35) mounted on the upper surface of the base plate (34) . Some of the blocks (35) may translate relative to the base plate (34) to fasten the substrate (33) in position. Alternatively clamps (31), shown in figure 2, are used to fasten the substrate in position.

The upper surface of the base plate (34), on which the substrate is fastened, is also provided with a series of grooves (36) . In the embodiment shown in figure 3 the grooves (36) are in the form of concentric circles, which are interconnected at various radial positions (38) . The grooves (36) allow argon gas, supplied during the welding process, to circulate freely beneath the substrate (33) The circulation of the argon gas within the grooves (36) prevents stagnant air-rich pockets forming beneath the substrate (33) Electrical heating elements (41) are embedded in the base plate (34) . The heating elements (41) are embedded in the grooves (36) . The electrical heating elements (41) are switched on and off at different times in the material deposition process. In the preferred embodiment of the present invention the heating elements (41) are switched on to preheat the base plate (36) and are left on during the start of the deposition process. They are then switched off in the middle of the deposition cycle.

By embedding the heaters (41) in the fixture (32), the fixture (32) and associated blocks (35) and clamps (31) can be maintained at a temperature more suitable for material deposition. Elevating the temperature of the fixture (32) prevents it acting as a heat sink and helps to establish process uniformity.

Additional heating elements may also be incorporated.

In figure 2, a radiant heater (42) is located above the fixture (32) . The radiant coil (42) heats the article (40) being deposited. As an alternative to the radiant heater (42) an induction coil could be used to heat the deposited article (40) Figure 5 shows a heated ring (44) suitable for use with the fixtures (32) in accordance with the present invention. The ring (44) is supported from a frame (46) by adjustable cables (47) . Power is fed to the heater through the connections (48) and cooling water is fed to and from the annular ring in the direction of arrows A. The heaters (41 & 42) are used to prevent excessive or uneven heat flow during the material deposition process.

For process uniformity the base plate (34) and the substrate (33) are maintained at a temperature, which ensure steady heat-flow conditions throughout the material deposition process. To help achieve this the base plate (34) of the fixture (32) is manufactured from a material, which can be easily maintained at the temperature of the substrate (33) In the preferred embodiment of the present invention where titanium is being deposited onto a wrought, cast or previously deposited substrate of titanium, the base plate (34) is manufactured from either a heat resistant iron-nickel-chromium alloy or a super alloy.

It will be appreciated by one skilled in the art that the location of the heating elements (41 & 42) will depend upon the material and the shape of the component (40) being deposited.

Heaters (41 & 42) could either be positioned across the whole deposit footprint or could be used locally to accommodate any thermal variation resulting from a changing sectional geometry.

The heaters (41 & 42) could be arranged in an array and a sequenced heating pattern could be used in anticipation of the advancing heating profile of the deposition pool. This would make most efficient use of the preheating, limit overall heat input and counter residual stress build up.

The heater arrays may also be used to heat around the component (40) perimeter and counter the forces of expansion that tend to pull the component (40) out of position. This would help to achieve greater component accuracy.

High residual stresses are induced in the article (40) as it is deposited onto the substrate (33) . These residual stresses need to relieved and conventionally this is achieved by heat treatment following completion of the material deposition process. However the heating elements in the array could also be used to prolong the cooling cycle once the material deposition process is completed.

The post deposition stress relief would then occur whilst in the fixture (32) and would eliminate the need for a subsequent heat treatment process.

To achieve steady state heat flow thermal insulators may be used in the fixtures. Figure 4 shows an alternative fixture arrangement in which ceramic insulating pieces (49) are used as the thermal insulators. The ceramic insulting pieces (49) are not preheated themselves but restrict the rate of heat escape from the fixture (32) . The ceramic insulating pieces (49) are used to prevent excessive heat flow into other parts of the fixture (32) for example structural elements with maximum operating temperatures and mechanical manipulators relying on oil lubrication.

Claims

Claims: 1. A fixture for holding a substrate on which an article is

formed comprising a member having means for locating and holding the substrate on a face thereof and heating means being provided in the member adjacent to the substrate.

2. A fixture as claimed in claim 1 in which the heating means are electrical heating elements.

3. A fixture as claimed in claim 2 in which the electrical heating elements are radiant or induction heaters.

4. A fixture as claimed in any of claims 1-3 in which the heating elements are embedded in the fixture.

5. A fixture as claimed in any of claims 1-4 in which at least one recess is provided in the face of the fixture.

6. A fixture as claimed in claim 5 in which heating elements are located in the at least one recess.

7. A fixture as claimed in claim 5 or claim 6 in which the at least one recess is circular.

8. A fixture as claimed in claim 7 in which a plurality of circular recesses are provided in the face and are interconnected.

9. A fixture as claimed in any of claims 1-8 in which additional heating means are provided adjacent the article to be formed.

10. A fixture as claimed in claim 9 in which the additional heating means is a radiant heater.

11. A fixture as claimed in claim 9 in which the additional heating means is an induction coil.

12. A fixture as claimed in any of claims 9-11 in which a structure is provided to support the additional heating means adjacent the article to be deposited.

13. A fixture as claimed in any of claims 9-12 in which the additional heating means is annular.

14. A fixture as claimed in any preceding claim having a plurality of heating elements arranged in any array.

15. A fixture as claimed in claim 14 in which the array of heating elements extends around the periphery of the article being formed on the substrate.

16. A fixture as claimed in any preceding claim having thermally insulated pieces mounted therein.

17. A fixture as claimed in claim 16 in which the thermally insulated pieces are ceramic.

18. A fixture as claimed in any of claims 1-17 in which the means for locating the substrate is at least one block mounted on the face.

19. A fixture as claimed in claim 18 having a plurality of blocks at least some of which translate relative to the face to hold the substrate thereon.

20. A fixture as claimed in any preceding claim in which the means for holding the substrate are clamps.

21. A fixture as claimed in any preceding claim in which the article is formed by material deposition.

22. A fixture as hereinbefore described with reference to and as shown in figures 2-5.