CN114502323A - Method for modifying the surface of a workpiece - Google Patents

Abstract

The present invention provides a method of modifying a surface of a workpiece, the method comprising providing a system comprising a sealed mixing vessel having an internal chamber in which the workpiece and a working body are housed. The sealed mixing vessel is then uniaxially vibrated at a frequency between 15 hz and 1khz and an amplitude between about 0.2cm and 3cm such that the working body impacts the surface of the workpiece. The method can be used for shot peening and abrasive finishing of a workpiece.

Description

Method for modifying the surface of a workpiece

Technical Field

The present disclosure broadly relates to a method for modifying a surface of a workpiece.

Background

Methods of modifying the surface of the workpiece include, for example, methods of dressing the surface of the workpiece and methods of hardening the surface of the workpiece.

With respect to molded parts (e.g., particularly cast metal parts), it is common practice to subject the workpiece to post-grinding machining to remove burrs, mold lines, and otherwise smooth the surface of the workpiece. Examples of such processes include vibrating and/or blasting with abrasive media (e.g., nut shells, ceramic particles, steel balls, or sand) propelled by a high velocity gas. In these processes, the unwanted raised surface features diminish over time.

Shot peening is similar to sand blasting except that it operates by a mechanism that is plastic rather than abrasive: each particle acts as a round head hammer. In practice, this means that less material is removed by the process and less dust is generated.

Shot peening, i.e., peening with shot particles (hereinafter referred to as "shot"), is a cold working method used to create a compressive residual stress layer and modify the mechanical properties of metal and composite materials. It requires impacting the metal surface with a shot (i.e., a round particle, typically made of, for example, metal, glass, or ceramic) with a force sufficient to cause plastic deformation. In machining, shot peening is used to strengthen and relieve stresses in parts such as steel automotive crankshafts and connecting rods. In construction, it provides a soft finish to the metal. Typically, in shot peening, a stream of shot is directed toward a workpiece.

Both abrasive dressing and shot peening can be manual, time consuming processes that can last for hours or days.

Disclosure of Invention

There remains a need for faster and improved methods of modifying the surface of a workpiece involving the impingement of particles such as sandblasting and shot-peening. Advantageously, the present disclosure provides for energy efficient and easy to perform rapid blasting and peening methods (e.g., without shot recirculation or manual guidance of the particle stream).

Accordingly, in one aspect, the present disclosure provides a method of modifying a surface of a workpiece, the method comprising:

providing a system comprising a sealed mixing vessel having an interior chamber containing a workpiece and a working body;

the sealed mixing vessel is uniaxially vibrated at a frequency between 15 hz and 1khz and an amplitude between about 0.2cm and 3cm such that the working body impacts the surface of the workpiece.

The features and advantages of the present disclosure will be further understood upon consideration of the detailed description and appended claims.

Detailed Description

Methods according to the present disclosure may be performed using a vibration system that includes a sealed mixing vessel having an internal processing chamber. The system may also include an actuator (e.g., a mechanical actuator) capable of vibrating the sealed mixing vessel. Preferably, the control module controls the actuator such that the sealed mixing vessel vibrates under resonant or near-resonant conditions (e.g., resonant acoustic conditions) throughout the surface modification process. The use of a vibrational resonance condition ensures efficient use of the supplied energy.

Commercially available mixing devices capable of accomplishing the above are sold by Resodyn Acoustic Mixers, Butte, Montana, of Batt, Montana, USA. The laboratory scale apparatus included LabRAM I and LabRAM II controlled batch mixers. Large scale devices are sold under the trade names OmniRAM, RAM5 and RAM 55. These devices typically operate at resonant vibration frequencies of from 20Hz up to 1kHz, preferably 40 to 100 Hz, more preferably 40 to 80 Hz, and more preferably 55 to 65 Hz, but this is not essential. The vibratory mixer is also characterized by an actuator displacement of about 0.5 inches (1.3cm), which may be accompanied by an accelerating g-force of at least 20-g, 30-g, 40-g, 50-g, or even at least 60-g, where g-9.8 m/s²But this is not essential. Further details regarding suitable resonant acoustic mixers can be found, for example, in U.S. Pat. Nos. 7,188,993(Howe et al) and 9,808,778(Farrar et al).

In practice, the working body and the workpiece are disposed within the internal chamber. The workpiece may be loose within the internal chamber or fixed in a given position relative to the sealed mixing vessel (e.g., mounted to a wall of the sealed mixing vessel). The latter configuration may be desirable where selective alteration of a portion of the workpiece surface is desired. The latter configuration may also be desirable if the workpiece has a large mass and/or is delicate, in order to prevent collisions between the workpiece and the container wall.

Advantageously, the working body springs open the sides and top of the sealed mixing container during vibration, so that the workpiece is bombarded from all angles.

Based on volume, the working bodies may together constitute, for example, up to 20%, 30%, 40%, 50%, 60%, 70%, or 80% of the volume of the internal chamber. However, in typical use, the working bodies may together constitute from 5% to 35% of the volume of the internal chamber, although smaller and larger amounts may also be used.

Useful working bodies may include grinding bodies and blasting bodies.

The abrasive body is generally irregular so that sharp particles can cut off brittle surface deposits; however, this is not essential. Abrasive bodies useful in the methods of the present disclosure may include any abrasive body useful for abrasive blasting (commonly referred to as "blasting") or vibratory tumbling. There are several variations of this method that use various media; some media are highly abrasive, while others are mild. Exemplary materials for the abrasive body may include sand, copper slag, nickel slag, coal slag, glass beads, plastic abrasives, cullet, silica, steel balls, steel shot, stainless steel balls, cutting steel wires, ground plastic, walnut shells, corncobs, alumina (including brown alumina, heat treated alumina, and white alumina), co-fused alumina-zirconia, ceramic alumina, green silicon carbide, black silicon carbide, chromia, zirconia, flint, cubic boron nitride, boron carbide, diamond, garnet, cubic boron nitride, chromia-based, diamond, garnet, sintered alpha alumina-based ceramics, as described, for example, in U.S. patent 4,314,827 (leithiser et al) and U.S. patents 4,770,671 and 4,881,951 (both issued to Monroe et al). Preferably, the abrasive body is an aggregate of the above-mentioned abrasive particles bonded, for example, by a polymer, ceramic, or metal.

Typically, the abrasive body has a diameter in the range of 0.01 millimeters (mm) to as large as 5mm, preferably 0.1mm to 5 mm; however, this is not essential. In some embodiments, the abrasive body can be sized according to an abrasives industry specified nominal grade.

Abrasive particles graded according to an abrasives industry recognized grading standard specify a particle size distribution for each nominal grade within numerical limits. Such industry-accepted grading standards (i.e., abrasives industry specified nominal grades) include standards known as the American National Standards Institute (ANSI) standard, the european union of abrasive products manufacturers (FEPA) standard, and the Japanese Industrial Standard (JIS).

ANSI grade designations (i.e., specified nominal grades) include: ANSI 4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI 36, ANSI 40, ANSI 50, ANSI 60, ANSI 80, ANSI 100, ANSI 120, ANSI 150, ANSI 180, ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI 360, ANSI 400, and ANSI 600. FEPA grade designations include: p8, P12, P16, P24, P36, P40, P50, P60, P80, P100, P120, P150, P180, P220, P320, P400, P500, P600, P800, P1000 and P1200. The JIS grade numbers include JIS8, JIS12, JIS16, JIS24, JIS36, JIS 46, JIS 54, JIS 60, JIS80, JIS 100, JIS 150, JIS 180, JIS 220, JIS 240, JIS 280, JIS 320, JIS 360, JIS 400, JIS 600, JIS800, JIS 1000, JIS 1500, JIS 2500, JIS 4000, JIS 6000, JIS8000, JIS 10000, JIS 20000, and JIS 30000.

Alternatively, the milling bodies may be graded to a nominal screening grade using a U.S. Standard test Sieve conforming to ASTM E-11 "Standard Specification for Sieve Cloth and Screen for Testing Purposes" (Standard Specification for Wire Cloth and Sieves for Testing Purposes). Astm e-11 specifies the design and construction requirements for a test screen that utilizes woven screen cloth mounted in a frame as a media to classify materials according to a specified particle size. A typical designation may be represented as-18 +20, meaning that the abrasive particles pass through a test sieve that meets ASTM E-11 specifications for 18 mesh screens, and remain on a test sieve that meets ASTM E-11 specifications for 20 mesh screens. In one embodiment, the abrasive body has a particle size such that: so that a majority of the particles pass through the 18 mesh test sieve and may be retained on the 20, 25, 30, 35, 40, 45 or 50 mesh test sieve. In various embodiments of the present disclosure, the abrasive body can have a nominal screening grade comprising: -18+20, -20+25, -25+30, -30+35, -35+40, -40+45, -45+50, -50+60, -60+70, -70+80, -80+100, -100+120, -120+140, -140+170, -170+200, -200+230, -230+270, -270+325, -325+400, -400+450, -450+500, or-500 + 635.

Optionally, the sealed mixing vessel may contain a fluid, such as water. The fluid may contain optional additives such as surfactants, defoamers, or in the case of abrasive bodies, etchants (e.g., alkali metal hydroxides).

Useful peening bodies can include any body known for peening. Examples include: spherical metal pellets (e.g., cast steel, iron steel, stainless steel, tungsten, molybdenum, tungsten, titanium, tantalum, cobalt-chromium, or cobalt), spherical ceramic/cermet beads (e.g., zirconia, alumina, silicon carbide, or tungsten/cobalt carbide), spherical glass beads, and modified (rounded) cutting wires (e.g., modified cutting wires). In some applications, the conditioned cutting wire shots may be preferred because they maintain their roundness when degraded, unlike cast shots, which tend to break into sharp pieces that may damage the workpiece. The tailored cut wire pellets may be five times longer than the cast pellets. Mixtures of two or more working body compositions, shapes and/or sizes may be used. Typically, the diameter of the blasting body is in the range of 0.1 millimetres (mm) to as much as 3.2mm, preferably 0.7mm to 1.2 mm; however, this is not essential.

Any blasting body useful for peening can be used in the practice of the present disclosure when blasting a surface-conditioned workpiece (e.g., deburred and/or smoothed). Exemplary useful blasting media include rounded metal (e.g., cast steel, stainless steel, molybdenum, tungsten, titanium, tantalum, cobalt-chromium, or cobalt) particles and modified filament patterns thereof, glass (e.g.,glass beads), ceramic particles (e.g., tungsten carbide, silicon carbide, titanium carbide, silicon carbide, and Zirshot ceramic media (60-70% ZrO)₂、28-33％SiO₂、<10％Al₂O₃Sold by SEPR Saint-Gobain ZirPro, Le pontte Cedex, France), and combinations thereof.

Peening can be advantageously performed on metal (e.g., including aluminum, steel forgings, and machine parts) workpieces. The effect of peening is a surface phenomenon, the depth of which is typically no more than several hundred microns, so it is generally only necessary that the surface of the workpiece be metallic in order to achieve a beneficial effect. However, in many cases, the entire workpiece may be metallic.

The method according to the present disclosure may be particularly beneficial for workpieces manufactured by powder jet or laser sintering additive manufacturing (3D printing) methods, as the working body and the workpiece may move freely within the sealed chamber, the working body (if small enough) may penetrate into an internal channel that is accessible from the workpiece surface and may not be easily accessible using other methods.

Examples

All parts, percentages, ratios, and the like in the examples and the remainder of the specification are by weight unless otherwise indicated.

The system used in all of the examples described below was a LabRAM resonant acoustic mixer from Raxodean Corporation of Batt, Montana, USA (Resodyn Corporation, button, Montana). Machines equipped with sealed mixing vessels run at 100% intensity in automatic frequency mode. Roughness measurements (Ra) were measured using a MarSurf PS 10 stylus profilometer and Sa roughness measurements were recorded using a MikroCAD surface metrology system.

Example 1

This example demonstrates an abrasive aluminum alloy with loose abrasive particles.

The workpieces were machined aluminum alloys (grade BS EN 7556082-T6), 16mm by 3mm by 50mm cubes. By hand scraping with P36-coated abrasivesRubbing the surface to produce an initial surface roughness R of 6.2 microns_a. The workpiece parts were placed in a polypropylene straight edge sealed cylindrical container having an internal height of 102mm and an internal diameter of 52 mm. P80 semi-brittle fused alumina BRFPL (175g, imperys, Paris, France) was placed in a container with the workpiece. The LabRAM was run in the automatic frequency mode at 100% intensity for 30 minutes. Thereafter, the surface roughness R of the workpiece_aIs 4.1 microns. During this processing period, the mass loss of the workpiece was 0.036 g.

Example 2

This example demonstrates an abrasive aluminum alloy with loose abrasive particles and a chemical etchant.

The workpieces were machined aluminum alloys (grade BS EN 7556082-T6), 16mm by 3mm by 50mm cubes. An initial surface roughness R of 7.1 microns was produced by manually scratching a workpiece with a P36 coated abrasive_a. The work piece was placed in a polypropylene straight edge sealed cylindrical container having an internal height of 102mm and an internal diameter of 52 mm. P80 semi-brittle fused alumina BRFPL (175g, english porcelain) was placed in the container along with the parts. 1M potassium hydroxide solution (75ml) was added to the vessel. The LabRAM was run in the automatic frequency mode at 100% intensity for 30 minutes. After 30 minutes of machining, the roughness R of the workpiece_aIs 5.1 microns. During this machining period, the mass loss of the workpiece was 0.094 g.

Example 3

This example demonstrates an abrasive aluminum alloy with abrasive agglomerates.

The workpieces were machined aluminum alloys (grade BS EN 7556082-T6), 16mm by 3mm by 50mm cubes. An initial surface roughness R of 5.1 microns was produced by manually scratching a workpiece with a P36 coated abrasive_a. The work piece was placed in a polypropylene sealed cylindrical container having an internal height of 55mm and an internal diameter of 80 mm. High quality ceramics were rapidly cut into Triangles (Premium Ceramic Fast Cutting Triangles) (75g, 2mm x 2mm, Kramer Industries, Piscataway, N.J., Piscataway, N.ew Jersey)) were placed in a container together with the work piece and 50g of water. The LabRAM was run in the automatic frequency mode at 100% intensity for 30 minutes. Thereafter, the surface roughness R of the workpiece_aIs 2.6 microns. During this processing period, the mass loss of the workpiece was 0.024 g.

Example 4

This example demonstrates an abrasive additive manufactured aluminum alloy with abrasive agglomerates.

The workpiece was an additive manufactured aluminum alloy (AlSi10Mg)20mm diameter tube with 2mm walls. The parts were printed by Direct Metal Laser Sintering (DMLS). Initial roughness R_aIs 4.7 microns. The work piece was placed in a polypropylene straight-sided three-wall sealed cylindrical container having an internal height of 84mm and an internal diameter of 60 mm. Abrasive agglomerates (200g, 720 micron cubes comprising P600 alumina FRPL pellets and a vitrified binder from 3M Company (Maplewood, Minnesota) of meprolid, mn) were placed in a container with the workpiece and 100g water. The LabRAM was run in the automatic frequency mode at 100% intensity for 30 minutes. Thereafter, the roughness R of the workpiece on the inner surface of the tube_a2.9 microns and the roughness of the workpiece on the outer surface of the tube was 2.4 microns. The mass loss of the workpiece was 0.010 g.

Example 5

This example demonstrates an abrasive additive manufacturing polymer with loose abrasive particles.

The workpiece was an additive manufactured FormLabs clear resin (methacrylate with photoinitiator) 20mm diameter tube with 2mm walls. Printing of a workpiece by means of a stereolithography technique (initial roughness S)_a51 microns). The work piece was placed in a polypropylene straight-sided three-wall sealed cylindrical container having an internal height of 84mm and an internal diameter of 60 mm. P120 semi-brittle fused alumina BRFPL (100g, english porcelain) was placed in a container along with the parts. The LabRAM was run in the automatic frequency mode at 100% intensity for 30 minutes. After that, the roughness S of the workpiece on the surface of the tube_aWas 2 microns (98% improvement). The mass loss of the workpiece was 0.18g (8% of the total initial mass).

Example 6

This example demonstrates the peening of an additive manufactured aluminum alloy (AlSi10 Mg).

The workpiece was an additive-fabricated aluminum alloy (AlSi10Mg)20mm diameter tube with a 2mm thick wall. Printing of parts by Direct Metal Laser Sintering (DMLS) method (initial roughness R)_a4.7 microns). The work piece was placed in a polypropylene straight-sided three-wall sealed cylindrical container having an internal height of 84mm and an internal diameter of 60 mm. Spherical zirconia grinding media (250g, 3mm diameter, Leichi, Haan, Germany) were placed in a vessel along with the work piece and 50g of water. The LabRAM was run in the automatic frequency mode at 100% intensity for 15 minutes. After that, the roughness R of the workpiece (both the inner and outer surface of the tube)_aIs 1.2 microns.

Example 7

This example demonstrates peening of an additively manufactured stainless steel workpiece.

The workpiece was an additive manufactured 17-4PH stainless steel pallet printed by DMLS within 3M company. After printing, the workpiece is not finished and its initial roughness R_aIs 11.7 microns. The work piece was then placed in a polypropylene sealed cylindrical container having an internal height of 55mm and an internal diameter of 80 mm. Stainless steel round pellets (100g, 2mm diameter, Cousins corporation of uk (CousinsUK)) were placed in a vessel together with the workpiece and 50g of water. The LabRAM was run in the automatic frequency mode at 100% intensity for a total of 60 minutes. Roughness R of the workpiece after 15 minutes of machining_aIs 2.9 microns. After 60 minutes, R_aIs 1.0 micron.

Example 8

This example demonstrates peening of an additively manufactured cobalt chromium alloy workpiece.

The workpiece was an additive manufactured cobalt chromium alloy (Co-Cr130)20mm diameter tube with 2mm walls printed by DMLS. Roughness R after printing_aIs 11.6 microns. The work piece was placed in a polypropylene sealed cylindrical container having an internal height of 55mm and an internal diameter of 80 mm. Mixing tungsten carbide spheres (100g, 1mm diameter, Sheffield, UK)Is placed in a container with a workpiece, together with 50g of water. The LabRAM was run in the automatic frequency mode at 100% intensity for 15 minutes. Then, R_aIs 3.0 microns.

Example 9

This example demonstrates peening of an additively manufactured titanium workpiece.

The workpiece was an additive manufactured titanium alloy (Ti6Al4V) rectangular tab (10 × 30 × 1mm) printed by DMLS. Initial roughness R after printing_aAnd is 6.9 microns. The work piece was placed in a polypropylene sealed cylindrical container having an internal height of 55mm and an internal diameter of 80 mm. Tungsten carbide spheres (120g, 3mm diameter, Bearing Warehouse Co., Ltd.) were placed in a container with a workpiece together with 50g of water. The LabRAM was run in the automatic frequency mode at 100% intensity for a total of 60 minutes. After 15 minutes, R_aIs 4.4 microns and after 60 minutes, R_aIs 2.2 microns.

Example 10

This example demonstrates the peening of a machined aluminum alloy (grade: BS EN 7556082-T6) workpiece.

The workpiece was a machined aluminum alloy (grade: BS EN 7556082-T6) 15.9mm by 3.2mm by 50mm cube. A roughness R of 7.5 microns was produced by manually scratching a workpiece with a P36 grade coated abrasive_a. The work pieces were placed in a polypropylene straight-sided thick-walled container (United States Plastic corp., Lima, Ohio) having an internal height of 84mm and an internal diameter of 60 mm. Spherical ceramic tumbling media (250g of 3mm K-Polish quality ceramic tumbling media, Claimer industries, Inc.) were placed in a vessel along with the work pieces. The LabRAM was run in the automatic frequency mode at 100% intensity for 30 minutes. Roughness R of the workpiece after 30 minutes of machining_aIs 1.8 microns. Before this process, the maximum compressive residual stress of the material surface was-100 MPa. After 30 minutes processing, the maximum compressive residual stress was-250 MPa. The depth of the compressive stress in the surface increases by 100 microns. The results are reported in table 1 below.

All cited references, patents, and patent applications in this application are incorporated by reference in a consistent manner. In the event of inconsistencies or contradictions between the incorporated reference parts and the present application, the information in the present application shall prevail. The preceding description, given to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims (14)

1. A method of modifying a surface of a workpiece, the method comprising:

providing a system comprising a sealed mixing vessel having an interior chamber containing the workpiece and a working body;

uniaxially vibrating the sealed mixing vessel at a frequency between 15 Hz and 1kHz and an amplitude between about 0.2cm and 3cm such that the working body impacts the surface of the workpiece.

2. The method of claim 1, wherein the workpiece is held in a fixed position relative to the sealed mixing vessel.

3. The method of claim 1, wherein the workpiece is constrained in 3 translational axes relative to the sealed mixing vessel, but is free to rotate about an axis of rotation.

4. A method according to any one of claims 1 to 3, wherein the frequency is at or near a resonant vibration frequency of the system.

5. The method of any of claims 1 to 4, wherein the surface of the workpiece is metallic.

6. The method of any of claims 1 to 4, wherein the surface of the workpiece is polymeric.

7. The method of any one of claims 1 to 6, wherein the working body comprises shot particles.

8. The method of any one of claims 1 to 6, wherein the working body comprises abrasive particles.

9. The method of any of claims 1-8, wherein the uniaxially vibrating the sealed mixing container imparts an acceleration force of at least 40 grams-force (9.8 millinewtons) to at least one of the workpiece and at least some of the working bodies.

10. A method according to any one of claims 1 to 9, wherein at least some of the working bodies are accelerated to a speed of at least one meter/second.

11. The method of any one of claims 1 to 10, wherein at least some of the working bodies have a mass of greater than 0.001 grams.

12. The method of any one of claims 1 to 11, wherein the internal chamber has a volume, and wherein a ratio of a total volume of the working body to the volume of the internal chamber is less than 0.8.

13. The method of any one of claims 1-12, wherein the interior chamber further comprises a fluid.

14. The method of claim 13, wherein the interior chamber further comprises an etchant for the workpiece.