US20130273816A1

US20130273816A1 - Automatic polishing device for surface finishing of complex-curved-profile parts

Info

Publication number: US20130273816A1
Application number: US13/794,665
Authority: US
Inventors: Kwok Fung KAN; Ji Chen; Jian Chao HE; Chun Zhang
Original assignee: Nano and Advanced Materials Institute Ltd
Current assignee: Nano and Advanced Materials Institute Ltd
Priority date: 2012-04-13
Filing date: 2013-03-11
Publication date: 2013-10-17
Also published as: CN103372806A; CN103372806B

Abstract

The present invention discloses an automatic polishing device and the method of using the device for the surface finishing of a workpiece such as complex-curved-profile parts. Automatic polishing is performed by mounting the workpiece on an apparatus which enables different orientations along multiple axes and immerging the workpiece in a controlled flow of abrasive slurry. The device of the present invention provides a uniform finish on free form surface. It is also precise, low cost, non-destructive, and non-polluting.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from the U.S. provisional application Ser. No. 61/686,852 filed on Apr. 13, 2012, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to an automatic polishing device, in particular, to a flow-based polishing device for the surface finishing of complex-curved-profile parts.

TECHNICAL BACKGROUND

Polishing is an essential process of creating a smooth and shiny surface by using mechanical or chemical reaction and it has been employed by manufacturing industry for centuries. Comparing with hand-polishing, the process using automated polishing machines, such as those used for polishing semiconductor wafers and for polishing fine optics, are more efficient. However, the use of these automated polishing machines is restricted to those parts with surface profiles in regular shape. Therefore, hand-polishing is still widely used in a number of industries (e.g., watch, jewelry, mould and die, etc.) as in many circumstances, the surface profiles of the polishing parts are not in regular shape as those of semiconductor wafers or optical lenses. Most of the existing automated polishing machines just could not be applied to the complex-curved-profile parts, such as small watch parts and jewelry parts that are made of metal or metal alloy, jade stone, ivory, and ceramics, etc. There are considerable needs to develop an efficient automated polishing technique yet with the flexibility as skilled hands. Moreover, the machine-based polishing technique would yield a more uniform and reliable polishing effect comparing to those done by hand-polishing. It is believed that hand-polishing can reach the best surface roughness of R>0.1 μm, while machine-based polishing can reduce the surface roughness by one order of magnitude. This is essential, for example, for the mould-and-die industry which requires a precise surface treatment of molding-tool-steel.
Many prior arts have attempted to overcome the difficulties of surface finishing of complex-curved-profile parts. U.S. Pat. No. 6,171,175 has disclosed a hand polishing method using conventional grinding, lapping, honing techniques, or an automatic polishing method with improved adaptive mechanical tools but none of these methods can give enough precision at acceptable efficiency. Computer programmed robotic polishing (European Pat. No. EP1935564), magnetorheological polishing (U.S. Pat. No. 5,449,313), or ion beam machining (US Patent Application Pub. No. 20070227878) possess high precision but the capital cost is too high. The flow-based machining, e.g., abrasive flow machining (U.S. Pat. No. 4,936,057), magnetic abrasive finishing (U.S. Pat. No. 4,175,930), fluid jet polishing (U.S. Pat. No. 7,455,573), can balance the requirements of precision and cost but only working for hard workpieces with strength against the flow force. The chemical polishing (U.S. Pat. No. 4,826,563), electrochemical polishing (U.S. Pat. No. 4,740,280), and plasma-electrolytic polishing (US Patent Application Pub. No. 20100200424) provide a solution of precise, gentle and low-cost surface finishing. However, the treatment and disposal of used chemicals and waste water are troublesome. Such wet-polishing processes involving chemical reactions are restricted due to environmental regulations in many circumstances. The disclosure of these cited references and their entirety are incorporated herein by reference.
There is a need for a new polishing means which is low-cost, environmental-friendly, precise, gentle and suitable for various types of workpiece including complex-curved-profile parts.

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide an alternate polishing device. The device includes a bath of controlled flow of abrasive slurry, at least one apparatus for mounting at least one workpiece with which its orientation varies along multi-axes, and at least one container containing the abrasive slurry. The device of the present invention provides a uniform finish on a free form surface. It is also precise, low cost, non-destructive, and non-polluting. The at least one apparatus for mounting the at least one workpiece includes a first rotary stage which can be a one-axis, two-axis, or three-axis rotary stage and is immerged inside flow of abrasive slurry during operation of the device. The first rotary stage is automatically adjustable such that the orientation of the mounted workpiece varies in a controlled manner. The abrasive slurry comprises a plurality of abrasive particles and a carrying liquid which is driven by a liquid pump. Optionally, the abrasive slurry includes a plurality of abrasive particles which is pre-mixed with a plurality of elastic polymer particles and the carrying liquid. Alternatively, a plurality of relatively smaller abrasive particles can be pre-coated on the surface of a relatively larger elastic polymer particle. The relatively larger elastic polymer particle may further include a magnetic core to facilitate the flow of the abrasive slurry driven by a plurality of magnetic bars situated under the container. Depending on the shape of the workpiece, the device of the present invention may be further modified to include a second rotary stage for driving the rotation of the first rotary stage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of the device having a circular container for holding an abrasive slurry and a three-axis rotary stage for mounting a workpiece to be polished. Abrasive flow is driven by a liquid pump.

FIG. 2 is a schematic diagram of another embodiment of the device having a circular container for holding an abrasive slurry and a three-axis rotary stage for mounting a workpiece to be polished. The abrasive slurry contains magnetic particles and abrasive flow is driven by electromagnetic force. The inset shows the structure of the magnetic abrasive slurry.

FIG. 3 is a schematic diagram of a further embodiment of the device having a cylindrical container for holding an abrasive slurry and a two-axis rotary stage for mounting a workpiece to be polished. The relative movement between the abrasive slurry and the workpiece is achieved by rotating the cylindrical container.

FIG. 4 is a schematic diagram of other embodiment of the device having a fixed (non-rotatable) cylindrical container for holding an abrasive slurry and a first one-axis rotary stage for mounting a workpiece. The relative movement between the abrasive slurry and the workpiece is achieved by rotating the first rotary stage inside the cylindrical container with a second rotary stage outside of the cylindrical container.

FIG. 5 shows the surface roughness of a steel work piece before and after polishing using the method in one of the embodiments illustrated in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an exemplary embodiment of the present invention. The automatic polishing device in this embodiment comprises a circular container 11 containing an abrasive slurry 12 which comprises a plurality of abrasive particles and a carrying liquid driven by a liquid pump 13, wherein the liquid pump 13 drives the abrasive slurry to form abrasive slurry flow 12 in the circular container 11. A workpiece 15 to be polished is mounted in a three-axis rotary stage 16 immerged inside the abrasive slurry flow 12. The orientation of the workpiece 15 varies in a controlled manner by the three-axis rotary stage 16 capable of automatic adjustment to facilitate a gentle and uniform surface finish of the workpiece 15. In one example, the workpiece 15 is a complex-curved-profile aluminum article at dimension of less than 50(L)×50(W)×50(H)mm³. It is immerged in the abrasive slurry 12 containing 600 mesh silicon carbide (SiC) abrasive particles, other polymers such as silicone-based elastic polymer, and a carrying liquid. The abrasive slurry flow 12 is driven by the liquid pump 13 inside the circular container 11. The circular container 11 is made of plastic and the inner diameter of the container 11 is 200 mm and the outer diameter is 400 mm and the height is 400 mm. Comparing with containers of other shapes (e.g., the cylindrical container), the circular container 11 confines the flow of the abrasive slurry 12 in a circular track at relatively constant speed ranging from 0.3-3.0 m/s. The relative movement between the abrasive slurry 12 and the workpiece 15 yields an adaptive polishing of a curved surface. In the meantime, with the automatic three-axis rotary stage 16, the orientation of the workpiece 15 slowly varies along three axes periodically at the rate of ˜one cycle per minute, so that a uniform surface polishing can be achieved. In such operation, the as-cut workpiece 15 can reach a mirror-like shinning surface in 30-60 min.
FIG. 2 illustrates another embodiment of the present invention having a circular container 21 for holding a magnetic abrasive slurry 22 and a three-axis rotary stage 23 for mounting a workpiece 24 to be polished. The magnetic abrasive slurry 22 in this embodiment comprises a plurality of elastic polymer particles of about 1 mm in size. Each of the elastic polymer particles has a magnetic core inside the particle and a plurality of abrasive particles of about 1-100 μm in size which are pre-coated on the surface of the elastic polymer particle. The magnetic abrasive slurry 22 in this embodiment flowing inside the circular container 21 is driven by a plurality of magnets on a magnetic board 25 driven by a motor 26 for rotating under the circular container 21. The workpiece 24 to be polished is mounted in the three-axis rotary stage 23 immerged inside the magnetic abrasive slurry flow 22. The orientation of the workpiece 24 varies in a controlled manner by the three-axis rotary stage 23 capable of automatic adjustment to facilitate a gentle and uniform surface finish of the workpiece 24. In one example, the workpiece 24 is a complex-curved-profile steel article at the dimension of less than 50(L)×50(W)×50(H)mm³. It is immerged in the magnetic abrasive slurry 22 comprising silicone-based elastic polymer particles of about 1 mm in size. Each of the elastic polymer particles has a magnetic core of specially-treated magnetic stainless steel of 0.3 mm(D)×1 mm(L) pin inside the particle. A plurality of SiC abrasive particles of about 1-100 μm in size which are pre-coated or glue-mixed on the surface of the elastic polymer particle. The magnetic abrasive slurry 22 in such is flowing inside the circular container 21, driven by a plurality of magnets rotating under the circular container 21 or a plurality of electromagnets under the circular container 21 alternating the electromagnetic field inside the circular container 21. The circular container 21 is made of plastic and the inner diameter of the container 21 is 200 mm and the outer diameter is 400 mm and the height is 400 mm. The circular container 21 confines the flow of the magnetic abrasive slurry 22 in a circular track and the magnetic abrasive slurry 22 flow driven by the magnetic force runs as fast as 30 Hz. Moreover, it automatically switches direction between clockwise and counter-clockwise once a minute with pre-setting. The relative movement between such magnetic abrasive flow and the workpiece 24 yields an efficient polishing of curved surface. In the meantime, with the automatic three-axis rotary stage 23, the orientation of the workpiece 24 slowly varies along three axes periodically at the rate of ˜one cycle per minute, so that a uniform surface polishing can be achieved. In such operation, the use of carrying liquid in abrasive slurry is optional. That is, the polishing process can be achieved with a ‘dry flow’ of the magnetic-abrasive-polymer particles. In certain embodiments, this is convenient that the workpiece 24 needs not to be in contacted with water or oil. Depending on the size and surface complexity, the as-cut workpiece 24 can reach a mirror-like shinning surface in 30-60 min with this method. FIG. 5 shows the surface profile of a steel workpiece sample treated as such measured with Alpha Step from Tencor Instruments. As a direct readout from the Instrument, the surface roughness (Ra) improves from 3.7 μm to 0.1 μm after the said polishing treatment.
FIG. 3 illustrates a further embodiment of the present invention. An abrasive slurry 31 in this embodiment comprises a plurality of abrasive particles which are pre-mixed with a plurality of elastic polymer particles and a carrying liquid. The abrasive slurry 31 is held in a cylindrical container 32 which is about 400 mm in diameter and rotatable, as such, the abrasive slurry 31 rotates together with the rotating cylindrical container 32 driven by a rotating stage 33 connected to the bottom of the cylindrical container 32. The rotating stage 33 is further driven by a motor 34. The workpiece 35 to be polished is mounted in a two-axis rotary stage 36 immerged inside the abrasive slurry flow and about 100-150 mm away from the rotating axis at the centre of the cylindrical container 32. The orientation of the workpiece 35 varies in a controlled manner by the two-axis rotary stage 36 capable of automatic adjustment to facilitate a gentle and uniform surface finish of the workpiece 35. In one example, the workpiece 35 is a mammoth task figure at the dimension of less than 50(L)×50(W)×50(H)mm³.The abrasive slurry 31 contains 1200 mesh Al₂O₃abrasive particles and silicone-based elastic polymer particles and an oil-based carrying liquid. The abrasive slurry 31 is held in the stainless steel cylindrical container 32 at the diameter of 400 mm and the height of 400 mm. The abrasive slurry 31 rotates together with the rotating cylindrical container 32 driven by a rotating stage 33 connected to the bottom of the cylindrical container 32 at the rate of 60-600 rpm. The workpiece 35 is mounted in the two-axis rotary stage 36 immerged inside the abrasive slurry flow at about 100-150 mm away from the rotating axis at the centre of the cylindrical container 32. Such arrangement results in a relative movement between the abrasive slurry 31 and the workpiece 35 at the linear speed of 1-10 m/s. With the relatively fine and soft abrasive slurry 31 used, the rotation provides a gentle polishing on a complex-curved surface of relatively soft material. For the workpiece 35 such as a mammoth task figure, only the outline along the vertical axis of the figure needs to be polished. The bottom surface to support the figure is flat and treated with other means. In this special case, the multi-axis rotary stage that mounts the workpiece 35 can be simplified as the two-axis rotary stage 36, and the figure to be polished is mounted with vertical axis along with one of the rotary axis as shown in the FIG. 3. With the automatic two-axis rotary stage 36, the orientation of the workpiece 35 slowly varies along two axes periodically at the rate of ˜one cycle per minute, so that a uniform surface polishing can be achieved. Depending on the finest or color effect required, the polishing process of such a delicate workpiece 35 takes about 1-10 hours.
FIG. 4 illustrates other embodiment of the present invention. An abrasive slurry 41 in this embodiment comprises a plurality of abrasive particles of about 1-100 μm in size which are pre-coated on the surface of each of the elastic polymer particles of about 100-1000 μm in size. The abrasive slurry 41 is held in a fixed (non-rotatable) cylindrical container 42 of about 400 mm in diameter. A workpiece 43 (e.g., a patterned stainless steel sheet) to be polished is mounted in a one-axis rotary stage 44 immerged inside the abrasive slurry 41 flow and about 100-150 mm away from the central axis of the fixed cylindrical container 42. The first rotary stage 44 is further mounted on a second rotary stage 45 rotating along the central axis of the fixed cylindrical container 42. The second rotary stage 45 is driven by a motor 46. While the orientation of the workpiece 43 varies in a controlled manner by the first rotary stage 44 capable of automatic adjustment, the relative movement between the abrasive slurry 41 and the workpiece 43 is driven by the second rotary stage 45, and as such a gentle and uniform surface finish of the workpiece is achieved. In one example, the abrasive slurry 41 comprised silicone-based elastic polymer particles of about 100-1000 μm in size. A plurality of SiC abrasive particles of about 1-100 μm in size are pre-coated or glue-mixed on the surface of the elastic polymer particle. The abrasive slurry 41 is held in the fixed (non-rotatable) stainless steel cylindrical container 42 at the diameter of 400 mm and the height of 400 mm. The workpiece 43 is a patterned stainless steel sheet of the size of 100(L)×50(W)×0.5(H)mm³. The typical dimensions of the through-patterns (holes and lines) on the sheet are ranging from 0.5-5 mm, and it requires smooth lines and edges at-finish on both sides of the sheet. In order to polish the through-patterns of the stainless steel sheet, the abrasive slurry 41 must flow across the sheet, passing through the patterns at appropriate force that does not deform the 0.5 mm-thick sheet. In this specific embodiment, the rotary stage that mounts the sample can be simplified as the one-axis rotary stage 44. In the setup, the workpiece 43 is mounted in the first one-axis rotary stage 44 so that the center line along longitude direction of the sheet is aligned with the rotary axis of the one-axis rotary stage 44. It rotates slowly along this axis at the rate of ˜one cycle per minute to provide a uniform operation. On the other hand, the first rotary stage 44 is further mounted on the second rotary stage 45, which is driven by the motor 46 and suspends on top of the container 42. The second rotary stage 45 rotates along the central axis of the cylindrical container such that the workpiece 43 is immerged inside the abrasive slurry 41 at about 100-150 mm away from the central axis. While the second rotary stage 45 rotates at the rate of 60-600 rpm, the workpiece 43 further rotates in the abrasive slurry 41 along the central axis at the linear speed of 1-10 m/s, in addition to the foresaid slow rotation driven by the first rotary stage 44. While the relative movement between the abrasive slurry 41 and the workpiece 43 is governed by the fast rotation driven by the second rotary stage 45, the orientation of the workpiece 43 is controlled by the slow rotation driven by the first rotary stage 44. Even though stainless steel is a hard material, the deburing process of the pattern edges can be achieved in this operation within one hour duration.
If desired, the different functions discussed herein may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the above-described functions/embodiments may be optional or may be combined.
For example, the abrasive slurry might be composed of:

- (a) abrasive particles and carrying liquid; or
- (b) abrasive particles and elastic polymer particles; or
- (c) abrasive particles and elastic polymer particles and carrying liquid; or
- (d) abrasive particles and magnetic particles; or
- (e) abrasive particles and magnetic particles and carrying liquid; or
- (f) abrasive particles and magnetic particles and elastic polymer particles; or
- (g) abrasive particle and magnetic particles and elastic polymer particles and carrying liquid; and the abrasive particles are not limited to SiC or Al₂O₃particles as mentioned in the above descriptions.

In terms of industrial applications, the container and the rotary stage can be readily scaled up to meet the needs in various applications. Multiple containers engaged with single or multiple driving forces and multiple rotary stages for mounting multiple workpieces in each container can be applied.
Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described embodiments and/or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims.
It is also noted herein that while the above describes exemplary embodiments of the invention, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

INDUSTRIAL APPLICABILITY

The present invention is useful for polishing both regular and irregular shaped objects in a fully automated polishing process to replace the conventional manual polishing or partially automated polishing process. The setup of the automatic polishing device is flexible and the composition of the abrasive slurry flow could also be modified to suit different shapes and size of the workpiece. The multi-axis rotary stage of the mounting apparatus in the present invention also enables different orientations of the movement of the workpiece along different axes during the automatic adjustment.

Claims

What we claim:

1. An automatic polishing device for the surface finishing of a workpiece comprising

at least one container for holding an abrasive slurry;

one or more driving apparatuses for controlling the relative movement between said abrasive slurry and the workpiece in said abrasive slurry; and

one or more mounting apparatuses for mounting at least one workpiece inside said abrasive slurry,

wherein said one or more mounting apparatuses automatically adjust the orientation of said at least one workpiece along one or more axes in a controlled manner.

2. The device of claim 1, wherein said abrasive slurry comprises one or more of

a plurality of abrasive particles, a carrying liquid, a plurality of elastic polymer particles, and/or a plurality of magnetic particles.

3. The device of claim 1, wherein said abrasive slurry is magnetic or non-magnetic.

4. The device of claim 2, wherein said abrasive particles are silicon carbide (SiC) and/or aluminum oxide (Al₂O₃).

5. The device of claim 1, wherein said one or more driving apparatuses provides a controlled driving force for controlling the relative movement between said abrasive slurry and said at least one workpiece in said abrasive slurry by exerting mechanical force, electromagnetic force, or a combination of both mechanical and electromagnetic forces.

6. The device of claim 1, wherein said one or more driving apparatuses comprises one or more of liquid pumps, magnetic boards, rotating stages and/or rotary stages.

7. The device of claim 1, wherein said relative movement is carried out by

immerging said at least one workpiece in a flow of said abrasive slurry or by moving said at least one workpiece in a static abrasive slurry.

8. The device of claim 1, wherein said orientation of said at least one workpiece varies along one axis, two axes, or three axes.

9. The device of claim 1, wherein said at least one container is circular; said one or more driving apparatuses is a liquid pump; said one or more mounting apparatuses comprises a three-axis rotary stage to enable the orientation of said at least one workpiece along three different axes in a controlled manner; said abrasive slurry comprises a plurality of abrasive particles and a carrying liquid driven by said liquid pump to create a flow of said abrasive slurry.

10. The device of claim 1, wherein said at least one container is circular; said driving apparatus is a magnetic board situated below said container; said one or more mounting apparatuses comprises a three-axis rotary stage to enable the orientation of said at least one workpiece along three different axes in a controlled manner; said abrasive slurry comprises a plurality of abrasive particles, a plurality of elastic polymer particles and a plurality of magnetic particles, and wherein said abrasive particles of about 1-100 μm are pre-coated on each of said elastic polymer particles of about 1 mm while said magnetic particles are embedded into the core of each of said elastic polymer particles.

11. The device of claim 1, wherein said at least one container is cylindrical and rotatable with a diameter of about 400 mm; said one or more driving apparatuses is a rotating stage connected to the bottom of said container; said one or more mounting apparatuses comprises a two-axis rotary stage to enable the orientation of said at least one workpiece along two different axes in a controlled manner and is situated about 100-150 mm away from the rotating axis at the centre of said at least one container; said abrasive slurry comprises a plurality of abrasive particles, a plurality of elastic polymer particles and a carrying liquid, and wherein said abrasive particles are pre-mixed with said elastic polymer particles.

12. The device of claim 1, wherein said at least one container is cylindrical and non-rotatable; said one or more driving apparatuses comprises a second rotary stage; said one or more mounting apparatuses comprises a first rotary stage capable of moving said at least one workpiece mounted on said mounting apparatuses along one axis in a controlled manner which is situated about 100-150 mm away from the central axis of said container, and the distal end of said first rotary stage is further connected to said second rotary stage; said abrasive slurry comprises a plurality of abrasive particles of about 1-100 μm, a plurality of elastic polymer particles of about 100-1000 μm, and a carrying liquid, and wherein said plurality of abrasive particles are pre-coated on the surface of each of said elastic polymer particles.

13. A workpiece polished by the device of claim 1 comprises complex-curved-profile parts, irregular shaped article, and/or regular shaped article, wherein said workpiece is made of metal or non-metal material.