Abrasive processing method

Abstract

The present invention provides an apparatus and method for processing a component surface by abrading the component surface using an abrasive surface. The apparatus comprises an abrasive surface which is rotatable about an axis extending parallel to said component surface. A support is provided for moving the abrasive surface or the component surface along a computer-generated toolpath and for applying a force between the abrasive surface and the component surface. The support increases the force between the abrasive surface and the component surface from a minimum force to a maximum force as the distance along the toolpath increases to maintain constant material removal from the component surface.

Claims

1. A method of processing a component surface by abrading the component surface using an abrasive surface, said method comprising: rotating said abrasive surface about an axis extending parallel to said component surface; moving said abrasive surface or said component surface along a computer generated toolpath whilst applying a force between said abrasive surface and said component surface; and modifying a feed rate of the component surface relative to the abrasive surface to control the amount of material removed from the component surface, wherein the force between the abrasive surface and the component surface is increased from a minimum force to a maximum force as the distance along the toolpath increases.

2. The method according to claim 1, wherein the force between the abrasive surface and the component surface is increased linearly from the minimum force to the maximum force as the distance along the toolpath increases.

3. The method according to claim 1, further comprising moving the abrasive surface or the component surface automatically by moving the abrasive surface or the component surface using a computer-controlled robotic arm.

4. The method according to claim 1, further comprising controlling the force between the abrasive surface and the component surface by a pneumatic, hydraulic, mechanical or electrical compliance force system.

5. The method according to claim 1, further comprising a first calibration step comprising establishing the minimum force by moving the abrasive surface relative to the surface of a plate formed of a material substantially identical to the component surface whilst urging the abrasive surface towards the plate surface using a first force and measuring the amount of material removed, if necessary, adjusting the first force until the amount of material removed falls within a desired range and using the first force or adjusted first force as the minimum force.

6. The method according to claim 5, further comprising a second calibration step comprising processing the plate surface by moving the abrasive surface relative to the plate surface along a toolpath whilst urging the abrasive surface towards the plate surface using the minimum force, detecting when the amount of material removal drops below the desired range and increasing the force by an amount necessary to increase the material removal to within the desired range, repeating the detecting and increasing steps until the tool path is complete and selecting the force in use at the end of the toolpath as the maximum force.

7. The method according to claim 1, wherein the abrasive surface is provided on a belt.

8. The method according to claim 1, wherein the component surface is a surface of an aerofoil for a gas turbine engine.

9. The method according to claim 1, wherein the component surface is a surface of an aerofoil for a gas turbine engine.

10. An apparatus for processing a component surface by abrading the component surface using an abrasive surface, said apparatus comprising: an abrasive surface, said surface being rotatable about an axis extending parallel to said component surface; a support for moving said abrasive surface or said component surface along a computer generated toolpath whilst applying a force between said abrasive surface and said component surface; and a controller for modifying a feed rate of the component surface relative to the abrasive surface to control the amount of material removed from the component surface, wherein said support is adapted to increase the force between the abrasive surface and the component surface from a minimum force to a maximum force as the distance along the toolpath increases.

11. The apparatus according to claim 10, wherein the support is a robotic arm.

12. The apparatus according to claim 10, wherein the support is adapted to linearly increase the force between the abrasive surface and the component surface from the minimum force to the maximum force as the distance along the toolpath increases.

13. The apparatus according to claim 10, wherein the abrasive surface is provided on a belt.

14. The apparatus according to claim 10, wherein the component surface is a surface of an aerofoil for a gas turbine engine.

15. A method of processing a component surface by abrading the component surface using an abrasive surface, said method comprising: rotating said abrasive surface about an axis extending parallel to said component surface; and moving said abrasive surface or said component surface along a computer generated toolpath whilst applying a force between said abrasive surface and said component surface, wherein the force between the abrasive surface and the component surface is increased linearly at a constant slope over an entire length of the toolpath from a minimum force at a first end of the toolpath to a maximum force at a second end of the toolpath.

16. The method according to claim 15, wherein the component surface is a surface of an aerofoil for a gas turbine engine.

17. An apparatus for processing a component surface by abrading the component surface using an abrasive surface, said apparatus comprising: an abrasive surface, said surface being rotatable about an axis extending parallel to said component surface; and a support for moving said abrasive surface or said component surface along a computer generated toolpath whilst applying a force between said abrasive surface and said component surface, wherein said support is adapted to linearly increase the force between the abrasive surface and the component surface at a constant slope over an entire length of the toolpath from a minimum force at a first end of the toolpath to a maximum force at a second end of the toolpath.

18. The apparatus according to claim 17, wherein the component surface is a surface of an aerofoil for a gas turbine engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

(2) FIG. 1 shows a graph of material removal against toolpath length, processing time and force.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES OF THE INVENTION

(3) FIG. 1 shows a graph of material removal (in mm) against toolpath length (in m), processing time (in minutes) and force (in N) for a VSM XK760X p80 belt (3500 mm long and 25 mm wide) running at a belt speed of 8.67 m/s.

(4) In order to establish an appropriate force profile for the desired material removal (in this case between 0.1 and 0.12 mm), a flat plate formed of an identical material to the component surface was prepared.

(5) The VSM belt having an abrasive surface was mounted on a force compliance control system (provided by PushCorp, Inc.) on a robotic arm and the abrasive surface was moved against the plate at a constant belt speed (8.67 m/s) and constant feed rate (64 mm/s). The amount of material removed was observed using an ultrasonic probe (although GOM or CMM could also be used). The force between the abrasive surface and plate was noted.

(6) If the material removal was too great, the process was repeated at a lower force. If the material removal was too little, the process was repeated at a higher force. In this way, an initial force of 75 N was determined as this gave the desired material removal.

(7) Next, the plate was processed with the abrasive surface moving along a toolpath and the amount of material removal was determined along the toolpath. When the amount of material removal dropped below the desired range, the amount of force applied by the robotic arm was increased by an amount sufficient to increase the amount of material removal to back within the desired range. In this case, it was found that an increase of 15 N was needed after just under 4 minutes of processing time (or after a toolpath length of just under 15 m).

(8) This process was carried out along the entire length of the toolpath (60 m in this case) and it was established that an increase of 15 N was needed at equally spaced intervals (just under 4 minutes processing time and just under 15 m of toolpath length).

(9) After a processing time of 15.6 minutes and a toolpath length of 60 m, the force was increased to 120 N.

(10) This information was used to calculate a linear profile for the force increase as follows:
Total distance traveled by belt=belt speed (m/s)time (s)=8115.12 m
Total force increase=Maximum forceminimum force=45 N
Change in force=45/8115.12=0.0055 N per every meter of belt contact

(11) This linear force profile was then used to process a component using the VSM belt at a belt speed of 8.67 m/s. The feed rate i.e. the speed at which the abrasive surface of the belt was moved over the component surface was varied throughout processing to take account of the material removal requirements. When an increase in material removal was required, the feed rate was reduced and when a decrease in material removal was required, the feed rate was increased.

(12) As shown above, using the linear force profile experimentally determined for the VSM belt at a feed rate of 64 mm gave a constant material removal of 0.1-0.12 mm. To double the material removal to 0.2-0.24, the feed rate would be reduced to 32 mm/s. To half the material removal to 0.05-0.06, the feed rate would be increased to 128 mm/s.

(13) Accordingly, the force between the abrasive surface and the component surface can be controlled to result in constant material removal rate and the feed rate can be controlled to control the amount of stock removed over the component surface.

(14) To take account of the fact that the force profile is calculated using a flat plate and the component surface is typically contoured, a nominal liner force profile is calculated for a flat plate and this is then applied to the contoured component surface. The material removal achieved with this nominal profile is observed and the gradient of the force profile is adjusted to take into account the observed material removal. For example, the minimum force may be increased and the maximum force decreased to decrease the gradient of the linear force profile.

(15) While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.