WO2022023848A1

WO2022023848A1 - Method of abrading a workpiece

Info

Publication number: WO2022023848A1
Application number: PCT/IB2021/056159
Authority: WO
Inventors: Polly H. R. Keen
Original assignee: 3M Innovative Properties Company
Priority date: 2020-07-30
Filing date: 2021-07-08
Publication date: 2022-02-03

Abstract

A method of abrading a surface of a workpiece comprises providing a vessel containing loose abrasive bodies, loose resilient foam bodies, and at least a portion of the workpiece. At least most of the loose abrasive bodies have a maximum dimension of 3 centimeters. At least most of the loose abrasive bodies have a maximum dimension of 0.1 to 3 centimeters. The vessel is then agitated with sufficient energy such that at least some of the loose abrasive bodies contact and abrade at least a portion of the surface of the workpiece.

Description

METHOD OF ABRADING A WORKPIECE

TECHNICAL FIELD

The present disclosure broadly relates to abrasives and methods of abrading.

BACKGROUND

Additive manufacturing of metals, polymers, composites and ceramics for both prototyping and manufacturing has increased in importance in recent years. Additive manufacturing methods such as, for example, Direct Metal Laser Sintering (DMLS) often produce parts with unacceptable surface roughness for the parts’ intended function. Most users require post-processing techniques to reduce the roughness of the surface of the part before use. Examples of such post-processing steps include vibratory finishing and abrasive flow machining. In vibratory finishing, abrasive media are agitated and abrade the surface of a workpiece to smooth its surface.

SUMMARY

Quite unexpectedly, the present inventor discovered that under certain conditions, adding resilient foam bodies to abrasive particles can substantially increase their efficiency. Moreover, in many cases, the resilient foam bodies, which can originate as manufacturing scrap, can be used with multiple batches of loose abrasive bodies recycled when the abrasive particles wear down.

Accordingly, in one aspect, the present disclosure provides a method of abrading a surface of a workpiece, the method comprising: providing a vessel containing: loose abrasive bodies, wherein at least most of the loose abrasive bodies have a maximum dimension of 3 centimeters; loose resilient foam bodies wherein at least most of the loose resilient foam bodies have a maximum dimension of 0.1 to 3 centimeters; and at least a portion of the workpiece; and agitating the vessel with sufficient energy such that at least some of the loose abrasive bodies contact and abrade at least a portion of the surface of the workpiece.

As used herein:

The term "vessel" refers to a hollow or concave container used for holding liquids or other contents.

Features and advantages of the present disclosure will be further understood upon consideration of the detailed description as well as the appended claims.

DETAILED DESCRIPTION

In an exemplary method of abrading a surface of a workpiece, the method comprises the steps of providing a vessel containing loose abrasive bodies, loose resilient foam bodies, and at least a portion of the workpiece, and then agitating the vessel with sufficient energy such that at least some of the loose abrasive bodies contact and abrade at least a portion of the surface of the workpiece.

Methods according to the present disclosure may be carried out using a vibratory system that includes a vessel having an interior processing chamber. The vessel can be reclosable and/or have at least one opening through which a portion of a workpiece may extend into the interior processing chamber. The system may further include an actuator (e.g., a mechanical actuator) capable of vibrating the sealed vessel. Preferably, a control module controls the actuator such that the sealed vessel vibrates under resonant or near-resonant conditions (e.g., resonant acoustic conditions) throughout the surface modification process. Use of vibrationally resonant conditions ensures high efficiency use of the supplied energy.

Commercially available mixing devices capable of accomplishing the above are marketed by Resodyn Acoustic Mixers, Butte, Montana. Laboratory-scale devices include LabRAM I and LabRAM II controlled batch mixers. Large scale devices are marketed under the trade designations OmniRAM,

RAM5, and RAM 55. These devices typically operate at resonant vibrational frequencies of from 20 to up to < 1 kHz, preferably 40 to 100 hertz, more preferably 40 to 80 hertz, and more preferably 55-65 hertz, although this is not a requirement. The vibrating mixers are also characterized by actuator displacements that are on the order of 0.5 inch (1.3 cm), that may be accompanied by an acceleration g-force, where g =

9.8 m/s , of at least 20-g, 30-g, 40-g, 50-g, or even at least 60-g, although this is not a requirement. Further details concerning 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.).

The vessel may be capable of retaining any volume of material, and may be partially or completely filled with loose abrasive bodies and loose resilient foam bodies. In either case, there should be sufficient mobility of the loose abrasive bodies and the and loose resilient foam bodies and/or the workpiece so that there is relative motion between the bodies and workpiece during agitation. In some embodiments, the loose abrasive bodies and loose resilient foam bodies collectively fill at least 10 volume percent, at least 20 volume percent, at least 30 volume percent, at least 40 volume percent, or even at least 50 volume percent of the maximum retaining capacity (i.e., excluding overflow) of the vessel. In some embodiments, including any of those mentioned in the preceding sentence, the loose abrasive bodies and the loose resilient foam bodies may collectively fill less than 90 volume percent, less than 80 volume percent, or less than 70 volume percent of the maximum retaining capacity of the vessel. Lesser and greater amounts of the loose abrasive bodies may also be used. Typically, the greater the mass of each loose abrasive body, the less important the percentage fill of the vessel, although this is not a requirement.

On a volume basis, the loose abrasive bodies may collectively constitute up to 20, 30, 40, 50, 60,

70, or 80 percent of the volume of the interior chamber, for example. However, in typical use the working bodies may collectively constitute from 5 to 35 percent of the volume of the interior chamber, although lesser and greater amounts may also be used. In some embodiments, in addition to the workpiece, the loose abrasive bodies, and the loose resilient foam bodies, the vessel may further contain additional items, if desired. In other embodiments, the vessel may be free of such additional items.

Any suitable means to agitate the vessel and hence also the loose abrasive bodies and loose resilient foam bodies may be used, including, for example, shaking, vibrating, and/or tumbling. Motion of the vessel may comprise linear, arcuate, elliptical, or random oscillations, for example. In some preferred embodiments, the motion comprises linear reciprocating motion. The process of abrading the workpiece may be batch-wise or continuous.

In practice, the loose abrasive bodies, the loose resilient foam bodies, and the workpiece(s) are disposed within the vessel. The workpiece(s) may be loose within the vessel or fixed in a given position relative to the vessel (e.g., mounted to a wall of the vessel or extending into the interior processing chamber). The latter configurations may be desirable in instances where selective modification 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, so that collisions between the workpiece and the vessel walls are prevented.

The loose abrasive bodies may be smooth or rough, regular in shape or irregularly shaped so that sharp-edged particles can cut away brittle surface deposits; however, this is not a requirement. For example, in some embodiments, the loose abrasive bodies may be spherical. Loose abrasive bodies useful for the methods of the present disclosure may include any abrasive bodies that are useful for abrasive blasting (commonly termed "sandblasting") or vibratory tumbling. There are several variants of the process using various media. Some are highly abrasive, whereas others are milder.

The abrasive bodies (which can be abrasive particles) may comprise crashed abrasive bodies and/or shaped abrasive bodies. The abrasive bodies can comprise a ceramic abrasive material. Useful abrasive materials include, for example, fused aluminum oxide, heat treated aluminum oxide, white fused aluminum oxide, ceramic aluminum oxide materials such as those commercially available as 3M CERAMIC ABRASIVE GRAIN from 3M Company of St. Paul, Minnesota, black silicon carbide, green silicon carbide, titanium diboride, boron carbide, tungsten carbide, titanium carbide, cubic boron nitride, garnet, fused alumina zirconia, sol-gel derived ceramics (e.g., alumina ceramics doped with chromia, ceria, zirconia, titania, silica, and/or tin oxide), silica (e.g., quartz, glass beads, glass bubbles and glass fibers), feldspar, or flint. Examples of sol-gel derived crashed ceramic particles can be found in U.S. Pat. Nos.

4,314,827 (Leitheiser et al.), 4,623,364 (Cottringer et ah); 4,744,802 (Schwabel), 4,770,671 (Monroe et ah); and 4,881,951 (Monroe et al.). Further details concerning methods of making sol-gel-derived abrasive bodies can be found in, for example, U.S. Pat. Nos. 4,314,827 (Leitheiser), 5,152,917 (Pieper et ah), 5,213,591 (Celikkaya et ah), 5,435,816 (Spurgeon et al.), 5,672,097 (Hoopman et ah), 5,946,991 (Hoopman et al.), 5,975,987 (Hoopman et al.), and 6,129,540 (Hoopman et al.), and in U.S. Pubh Pat. Appln. Nos. 2009/0165394 Al (Culler et ah) and 2009/0169816 Al (Erickson et ah).

The abrasive bodies may be shaped (e.g., precisely-shaped) or random (e.g., crashed and/or platey). Shaped abrasive bodies and precisely-shaped abrasive bodies may be prepared by a molding process using sol-gel technology as described, for example, in U.S. Pat. Nos. 5,201,916 (Berg), 5,366,523 (Rowenhorst (Re 35,570)), 5,984,988 (Berg), 8,142,531 (Adefris et al.), and U.S. Patent No. 8,764,865 (Boden et al.).

Exemplary shapes of abrasive bodies include crushed, pyramids (e.g., 3-, 4-, 5-, or 6-sided pyramids), truncated pyramids (e.g., 3-, 4-, 5-, or 6-sided truncated pyramids), cones, truncated cones, rods (e.g., cylindrical, vermiform), spheres, and prisms (e.g., 3-, 4-, 5-, or 6-sided prisms). In some embodiments (e.g., truncated pyramids and prisms), the ceramic particles respectively comprise platelets having two opposed major facets connected to each other by a plurality of side facets.

In some embodiments, the ceramic particles preferably comprise crushed abrasive particles having an aspect ratio of at least 1.73, at least 2, at least 3, at least 5, or even at least 10.

Preferably, ceramic particles used in practice of the present disclosure have a core hardness of at least 6, at least 7, at least 8, or at least 15 GPa.

Further details concerning ceramic particles suitable for use as abrasive bodies and methods for their preparation can be found, for example, in U.S. Pat. Nos. 8,142,531 (Adefris et al.), 8,142,891 (Culler et al.), and 8,142,532 (Erickson et al.), and in U.S. Pat. Appl. Publ. Nos. 2012/0227333 (Adefris et al.), 2013/0040537 (Schwabel et al.), and 2013/0125477 (Adefris).

Usually, the abrasive bodies range in diameter from 0.01 millimeter (mm) to as large as 3 cm, preferably from 0.05 mm to 1 cm, more preferably 0.05 to 500 mm; however, this is not a requirement. In some embodiments, the abrasive bodies (e.g., abrasive particles) may be sized according to an abrasives industry specified nominal grade. Abrasive particles graded according to abrasive industry accepted grading standards specify the particle size distribution for each nominal grade within numerical limits. Such industry accepted grading standards (i.e., abrasives industry specified nominal grade) include those known as the American National Standards Institute, Inc. (ANSI) standards, Federation of European Producers of Abrasive Products (FEPA) standards, and Japanese Industrial Standard (JIS) standards.

ANSI grade designations (i.e., specified nominal grades) may 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. JIS grade designations include JIS8, JIS12, JIS16, JIS24, JIS36, JIS 46, JIS 54, JIS 60, JIS 80, JIS 100, JIS 150, JIS 180, JIS 220, JIS 240, JIS 280, JIS 320, JIS 360, JIS 400, JIS 600, JIS 800, JIS 1000, JIS 1500, JIS 2500, JIS 4000, JIS 6000, JIS8000, JIS 10000, JIS 20000, and JIS 30000.

Alternatively, abrasive bodies can be graded to a nominal screened grade using U.S. A. Standard Test Sieves conforming to ASTM E-l 1 "Standard Specification for Wire Cloth and Sieves for Testing Purposes." ASTM E-l 1 proscribes the requirements for the design and construction of testing sieves using a medium of woven wire cloth mounted in a frame for the classification of materials according to a designated particle size. A typical designation may be represented as -18+20 meaning that the abrasive particles through a test sieve meeting ASTM E-l 1 specifications for the number 18 sieve and are retained on a test sieve meeting ASTM E-l 1 specifications for the number 20 sieve. In one embodiment, the abrasive bodies have a particle size such that most of the particles pass through an 18 mesh test sieve and can be retained on a 20, 25, 30, 35, 40, 45, or 50 mesh test sieve. In various embodiments of the disclosure, the abrasive bodies can have a nominal screened 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.

While not required for practice of aspects of the present disclosure; in some embodiments, it may be desirable to provide the loose abrasive bodies according to a predetermined specific size distribution (e.g., monomodal or polymodal) and/or compositional specifications. It may also be desirable to provide the loose abrasive bodies as random shapes or specified shapes.

Optionally, the vessel (e.g., if sealed), may contain a fluid such as, for example, water. The fluid may contain optional additives such as, for example, surfactant, defoamer, or in the case of abrasive bodies an etchant (e.g., an alkali metal hydroxide).

The loose resilient foam bodies may have any shape and size which may be the same as, or different from, one another. For example, they may be randomly shaped, shaped as prisms (e.g., square prisms, rectangular prisms, trigonal prisms, hexagonal prisms). In some embodiments, the loose resilient foam bodies have a maximum dimension of 0.25 to 3 centimeters (cm) preferably 0.5 to 1.5 cm; although this is not a requirement.

The resilient foam may have lesser or greater resilience. Exemplary types of foams include silicone foams, polyurethane foams, and latex foams. Useful foams may have open or closed cell structure. Resilient foams are widely available from commercial sources. It is also possible to use recycled and/or scrap foam in the method of the present disclosure.

Mixtures of two or more types, compositions, shapes, and/or sizes of the loose abrasive bodies and/or the loose resilient foam bodies may be used.

The workpiece may be any object, typically fabricated, where abrading of the workpiece surface is desired. Examples include camshafts, crankshafts, and turbine blades. Exemplary workpieces include metal components (e.g., which may be sintered metal parts manufactured by rapid prototyping/3 -D printing). Examples of workpiece materials include metal and metal alloys (e.g., aluminum and mild steel), exotic metal alloys, ceramics, glass, wood, wood-like materials, composites, painted surfaces, plastics, reinforced plastics, stone, and/or combinations thereof. The workpiece may be flat or have a shape or contour associated with it.

Objects and advantages of this disclosure are further illustrated by the following non-limiting examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure. EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.

A LabRAM Resonant Acoustic mixer from Resodyn Corporation, Butte, Montana was used. The machine, which was equipped with a sealed mixing vessel, was ran at 100% intensity in the auto frequency mode for 15 mins (2 x 7.5 min segments).

The mass of the workpiece was measured before processing. The workpiece was placed in a polypropylene container with 55 mm internal height and 80 mm internal diameter along with the loose abrasive grains and foam pieces (if present), and the container was sealed with a lid.

COMPARATIVE EXAMPLE A

Alumina regular tetrahedrons (100 grams, 0.20 millimeters edge length, prepared as described in U.S. Pat. Appl. Publ. No. 2020/0199425 A1 (Rodriguez et al.), paragraph [0110]) were placed in the mixing vessel with a machined aluminum alloy (Grade BS EN 755 6082-T6) 16 mm x 3 mm x 50 mm workpiece. After running the LabRAM acoustic mixer for 7.5 minutes, a mass loss of 0.001 grams from the workpiece was observed, which increased to 0.002 grams after an additional 7.5 minutes (15 minutes total).

EXAMPLE 1

The procedure of Comparative Example A was repeated, except that 5 grams of polyurethane foam corresponding to the foam backing found in 3M Flexible Foam Abrasive Discs marketed by 3M Company, cut into 50 mm x 1 cm x 1 cm pieces, was also added to the mixing vessel with the workpiece and abrasive particles. After running the LabRam acoustic mixer for 7.5 minutes, a mass loss of 0.012 g from the workpiece was observed, which increased to 0.018 grams after and additional 7.5 minutes (15 minutes total). It can be seen that an increase in mass loss of more than 8 times resulted from addition of minor amounts of foam to the mixing vessel.

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 portions of the incorporated references and this application, the information in this application shall control. The preceding description, given in order 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

What is claimed is:

1. A method of abrading a surface of a workpiece, the method comprising: providing a vessel containing: loose abrasive bodies, wherein at least most of the loose abrasive bodies have a maximum dimension 3 centimeters loose resilient foam bodies wherein at least most of the loose resilient foam bodies have a maximum dimension of 0.1 to 3 centimeters; and at least a portion of the workpiece; and agitating the vessel with sufficient energy such that at least some of the loose abrasive bodies contact and abrade at least a portion of the surface of the workpiece.

2. The method of claim 1, wherein the vessel has a maximum retaining capacity, and wherein the loose abrasive bodies and the loose resilient foam bodies combined have a total volume that is at least 25 percent of the maximum retaining capacity of the vessel.

3. The method of claim 1, wherein the vessel has a maximum retaining capacity, and wherein the loose abrasive bodies and the loose resilient foam bodies combined have a total volume that is at least 50 percent of the maximum retaining capacity of the vessel.

4. The method of any of claims 1 to 3, wherein the vessel is agitated by linear displacement.

5. The method of any of claims 1 to 4, wherein the method is continuous.

6. The method of any of claims 1 to 5, wherein the workpiece comprises metal.

7. The method of any of claims 1 to 5, wherein the workpiece comprises plastic.