Patent Application
20220389277
3-D printing processes generally result in part bodies having a rough surface finish. As used herein, the term “3-D printed” refers to an additive manufacturing process (e.g., laser sintering or powder jet printing) in which layers of powder particles (e.g., metal powder particles) are sequentially deposited.
In many cases, 3-D printed metal bodies have complex shapes with internal surfaces that make them poor candidates for abrasive surface finishing techniques. Accordingly, chemical-etching has been considered. However, this technique has limitations such as the tendency of the etchant to etch deeply into surface pores, rather than just etching raised portions of the surface. Electropolishing is also a possibility, but is generally not suitable for finishing internal surfaces and rounded corners. As a result, good smoothness is difficult to impossible using current methods.
The present disclosure overcomes the above deficiency of etching methods, and provides a method capable of finishing metal surfaces that have improved smoothness as compared to prior etching methods of surface finishing.
An abrasive solution for finishing a metal part is provided. The abrasive solution includes abrasive particles suspended in a solution. The abrasive particles are configured to abrade a surface of the metal part. The abrasive particles are substantially non-responsive to a magnetic field. The abrasive solution also includes magnetic particles suspended in the solution. The magnetic particles are configured to respond to a magnetic field by aggregating together such that a local flow pattern of the solution changes in response to the aggregated magnetic particles.
Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale.
Metal additive manufacturing technologies now exist that are capable of producing components in many of the widely used engineering alloys, including stainless steels, cobalt-chrome alloys, titanium alloys; most notably Ti-6A1-4V, nickel based super alloys and aluminum alloys. These parts are manufactured without many of the constraints of traditional machining/casting methods. Complex geometry to enable weight reduction, performance improvement and combining parts into single assemblies are possible through additive manufacturing techniques.
Due to the method involved, rapid prototyping methods such as laser powder sintering and powder jet printing (following by sintering) result in sintered metal bodies having a sintered metallic surface comprising sintered metal powder particles and crevices (and/or peaks). Details concerning laser sintering can be found in, for example, U.S. Pat. No. 4,938,816 (Beaman et al.); U.S. Pat. No. 5,155,324 (Deckhard et al.); and U.S. Pat. No. 5,733,497 (McAlea). Details concerning powder jet printing techniques can be found, for example, in U.S. Pat. No. 5,340,656 (Sachs et al.); U.S. Pat. No. 6,403,002 B1 (van der Geest); and U. S. Pat. Appl. Publ. No. 2018/0126515 (Franke et al.).
However, the geometrical complexity available can cause a ‘line of sight’ problem whereby it is difficult for a conventional coated or bonded abrasive to access all surfaces to be finished. Accordingly there is a growth in the adoption of ‘mass finishing’ techniques for finishing metal additive manufactured components, such as vibratory finishing, for example. However, with complex parts, these techniques are best for external surfaces, and are likely to miss hard-to-reach areas such as recesses and internal channels. These processes cannot be targeted to finish a particular surface and can over-finish some areas to achieve the required properties of another area.
A finishing option is desired for surface finishing of the complex surface or internal geometries to improve the mechanical properties, particularly fatigue rates. The finishing option should be able to target specific areas for necessary finishing without over-finishing other areas.
Different systems and methods for finishing these surfaces have been attempted. For example, an abrasive liquid with magnetically responsive abrasive particles can be forced to move past a printed part using movement of a magnetic field. Alternatively, the viscosity of a magnetically responsive fluid can be increased in order to increase the cut rate of abrasive particles passing over a part surface.
Magneto-rheological finishing (MRF) is generally used in industry for the precision polishing of optical components. This technique uses a high concentration of magnetic iron within an oil formulation. The fluid is then controlled in real time using the magnetic field to control the material removal rate. In the current field of Magneto-Rheological Finishing (MRF) the magnetic component (typically iron) is suspended in the fluid in a high proportion and acts as part of the fluid. The iron particles may be less than 10 μm or up to 500 μm.
Embodiments described herein, in contrast, cause removal of magnetic particles from an abrasive suspension, using the magnet. The magnetic particles are gathered together in a position dictated by placement of the magnet. The shape formed causes disruption to the flow of an abrasive fluid pumped through a vessel used for finishing. By manipulating part orientation, the form of the gathered iron particles, and fluid velocity, a targeted stream of abrasive fluid can be directed against a specified part geometry, allowing for targeted finishing.
Therefore, it is important to have systems and methods that can facilitate finishing of parts 100 and 150 to remove surface roughness 120. Because of the difficulty for traditional systems and methods to maneuver around part portions 102, get into internal spaces 110 and through apertures 152, new systems and methods for targeted finishing are needed.
While parts 100 and 150 are shown, other exemplary metal components needing finishing include medical devices (e.g., artificial joints), architectural and/or ornamental castings, engine components parts, turbine blades, propellers. Additionally, while systems and methods described herein may be particularly useful for metal parts with complex geometries, it is also envisioned that they may be useful for any part with a metal surface needing finishing.
Abrasive fluid 230 also contains magnetic particles in suspension. In the presence of a magnet 240, the magnetic particles come together to form a magnetic guide vane 220 that alters the flow behavior of abrasive fluid 230 through pipe 202. While a physical magnet 240 is illustrated as positioned outside of, but parallel to a direction of flow within a pipe, other configurations are also expressly contemplated. For example, an electromagnetic field may be used instead of magnet 240. Additionally, magnet 240 may be positioned differently. For example, magnet 240 may be configured to move along a surface of pipe 202, causing magnetic guide vane 220 to dynamically change shapes. Additionally, magnet 240 could be built into pipe 202. Other configurations are also envisioned.
The shape and size of magnetic guide vane 220 is affected by a number of factors. The quantity of magnetic particles in suspension within abrasive fluid 230 affects the amount of magnetic material available to form magnetic guide vane 220. Additionally, size and placement of magnet 240 can affect the shape that magnetic guide vane 220 forms within pipe 202 by altering the magnetic field position and strength. The flow rate of the abrasive suspension can also change the shape of magnetic guide vane 220.
Magnetic guide vane 220 causes the flow behavior of abrasive fluid 230 to change, such that it is directed to a local area 222 on metal part 210 for focused abrasive activity. Altering the position, size and shape of magnetic guide vane 220 causes a position of localized polishing area 222 to change. Controlling how a position of magnet 240 changes along the surface of pipe 202, and the strength of the resulting magnetic field, for example by moving magnet 240 closer to, or further from, the surface of pipe 202, allows for predictable movement of local area 222 for targeted finishing of the surface of metal part 210. While
For example, 3D printed parts have an associated CAD file, STL file, or other design file used for designing and printing the part. Based on such a file, it is expressly contemplated that system 200 can incorporate an automated process for modulating one or more magnets 240 such that the entire structure of part 210 can be evenly finished. For example, a geometry file can be used to predict fluid flow using computational fluid dynamic techniques. This could be done automatically, for example, based on a received design file for part 210 and an intended position of part 210 with system 200.
While magnets 490 and 496 are illustrated as stationary magnets, it is contemplated that, in some embodiments, they are configured to move during a finishing operation. If magnets 490, 496 move during a finishing operation, flow 472 of abrasive fluid 470 can be targeted toward different surfaces of metal part 480. Additionally, while only two magnets 490, 496 are illustrated, it is also envisioned that, in some embodiments, more than two magnets are present, such as three, four, five or more. Further, while magnets are illustrated, it is also expressly contemplated that a magnetic field can be generated using other suitable mechanisms, such as electromagnetic technology.
Abrasive solution 600 also includes abrasive particles 610. Abrasive particles 610 may include crushed particles 612, precisely shaped particles 614, or other particles 616 such as formed particles, platey particles, agglomerates of particles, or other suitable abrasive particles. In some embodiments, a mixture of different abrasive particle types may be used, such as both crushed 612 and precisely shaped particles 614. Different sizes of particles may also be used in different embodiments, based on the finishing operation being conducted.
As used herein, the term “shaped abrasive particle,” means an abrasive particle with at least a portion of the abrasive particle having a predetermined shape that is replicated from a mold cavity used to form the shaped precursor abrasive particle. Except in the case of abrasive shards (e.g. as described in US Patent Application Publication Nos. 2009/0169816 and 2009/0165394), the shaped abrasive particle will generally have a predetermined geometric shape that substantially replicates the mold cavity that was used to form the shaped abrasive particle. Shaped abrasive particle as used herein excludes abrasive particles obtained by a mechanical crushing operation. Suitable examples for geometric shapes having at least one vertex include polygons (including equilateral, equiangular, star-shaped, regular and irregular polygons), lens-shapes, lune-shapes, circular shapes, semicircular shapes, oval shapes, circular sectors, circular segments, drop-shapes and hypocycloids (for example super elliptical shapes).
Geometric shapes are also intended to include regular or irregular polygons or stars wherein one or more edges (parts of the perimeter of the face) can be arcuate (either of towards the inside or towards the outside, with the first alternative being preferred). Hence, for the purposes of this invention, triangular shapes also include three-sided polygons wherein one or more of the edges (parts of the perimeter of the face) can be arcuate, i.e., the definition of triangular extends to spherical triangles and the definition of quadrilaterals extends to superellipses. The second side may have (and preferably is) a second face. The second face may have a perimeter of a second geometric shape.
Shaped abrasive particles also include abrasive particles comprising faces with different shapes, for example on different faces of the abrasive particle. Some embodiments include shaped abrasive particles with different shaped opposing sides. The different shapes may include, for example, differences in surface area of two opposing sides, or different polygonal shapes of two opposing sides.
The shaped abrasive particles are typically selected to have an edge length in a range of at least about 0.001 mm, or at least about 0.01 mm, or at least about 0.1 mm, or at least about 1 mm, or longer, based on the geometry of the part to be finished.
The term “platey crushed abrasive particle”, which refers to a crushed abrasive particle resembling a platelet and/or flake that is characterized by a thickness that is less than the width and length. For example, the thickness may be less than ½, ⅓, ¼, ⅕, ⅙, 1/7, ⅛, 1/9, or even less than 1/10 of the length and/or width. Likewise, the width may be less than ½, ⅓, ¼, ⅕, ⅙, 1/7, ⅛, 1/9, or even less than 1/10 of the length.
Abrasive solution 600 also includes magnetic particles 620. Magnetic particles 620 are in suspension in abrasive solution 600, in one embodiment. Magnetic particles 620 can be a variety of sizes, such as nano iron, iron filings, as well as mixtures of different sized particles. Magnetic particles 620 are iron-based 622, in one embodiment. In another embodiment, magnetic particles 620 contain cobalt 624. However, other magnetic particles 628 may also be used, such as magnetite (Fe3O4), Sendust, or NdFeB powder, for example. Magnetic particles 620 may include particles coated with a layer of material, in one embodiment. In another embodiment, magnetic particles 620 are formed from substantially all magnetic material.
Abrasive solution 600 may also include a chemical additive 630. For example, finishing may be accomplished faster if a corrosive element is present. For example, a strong basic compound 632, or a strong acidic compound 634 may be present. In one embodiment, calcium hydroxide is present in the abrasive solution. However, other chemical additives 632 may also be used. In some embodiments, the chemical additive is a mineral acid (or base). Exemplary acids include: mineral acids such as, for example, hydrochloric acid, perchloric acid, sulfuric acid, nitric acid (an oxidizing acid), phosphoric acid, aqua regia; and organic acids such as, for example, oxalic acid, methanesulfonic acid, triflic acid, citric acid and acetic acid. Citric acid may be particularly useful in chemical mechanical polishing applications on an iron workpiece because it selectively attacks rust without substantially affecting an iron base. Combinations of acids and different dilutions of acids (e.g., with water) may also be used. Exemplary basic compounds include, alkali metal hydroxides, and alkali metal metasilicates. Calcium hydroxide could be used in one embodiment. Other chemical additives may also be used. In embodiments where a gas is evolved from an additive-caused reaction, a system using abrasive solution 600 may need to be able to vent or separate the evolved gas from the stream.
Abrasive solution 600 may also have other additives 640, in some embodiments. For example, it may be helpful for a particular finishing operation if abrasive solution 600 is more or less viscous than solvent 602. A rheological additive 642 may be added to change the rheology of solution 600, such as fumed silica, laponite, bentonite, organically modified clays or other suitable additives. Other additives 648 may also be present in abrasive solution 600, such as a rust inhibitor for an aqueous solution 600 with iron particles.
Abrasive solution 600 may be provided as part of a kit for finishing a metal part. In one embodiment, solvent 602 is provided as part of the kit. Abrasive particles 610 may be provided in a kit in solvent 602 or may be provided separately. Magnetic particles 620 may be provided in a kit in solvent 602 or may be provided separately. Potential additives may be provided as part of a kit, in one embodiment, as part of solvent 602 or separately. A kit may also be provided, for example, based on known temperature conditions for a finishing operation.
While a single magnet is illustrated in
It is also expressly contemplated that movement of magnet 730 may be accomplished both manually, for example by a user visually monitoring the finishing operation, or by a controller. Additionally, in some embodiments, magnet 730 is controlled semi-autonomously, based on both user input and an automated routine. A controller may create a finishing routine to control movement of magnet 730 and/or part 720 based on known specifications of part 720. A user may edit the created routine, or add on to the created routine, based on how rough a part is following manufacturing for example, or based on other criteria. The routine may take into account computational fluid dynamics concerning part 720, vessel 702, and properties of abrasive solution 710 such as viscosity and solid loading, for example.
In step 810 a part is provided for finishing. The part may be a metal part. It may be a sintered metal part or a non-sintered metal part. The part may be formed from an additive manufacturing method, as indicated in block 812, or from another method, as indicated in block 822. The part may be mounted within a finishing system, in some embodiments. The mount may maintain the part in a stationary position within a finishing vessel, in one embodiment, or may allow for part to be rotated or moved. Rotation or movement of a part within a finishing vessel may be controlled, in one embodiment, or the part may be mounted such that at least some free movement is allowed.
In step 820 an abrasive solution is provided. The abrasive solution may contain magnetic particles in suspension in addition to abrasive particles. The abrasive particles may be crushed particles, formed abrasive particles, shaped abrasive particles, platey abrasive particles or another suitable abrasive particle.
The abrasive solution may also have a chemical additive. For example, in one embodiment, an aqueous abrasive solution may contain a strong base, such as calcium hydroxide, which may have a corrosive effect on a metal part and aid in finishing. However, in another embodiment, an aqueous abrasive solution contains a strong acid. However, weak acidic or basic compounds may be useful for some embodiments.
Additionally, a rheological additive may be present, in some embodiments. For example, a higher viscosity abrasive solution may be needed for a particular finishing operation, so an additive may be provided in one embodiment that increases the viscosity of the abrasive solution.
The abrasive solution may be provided in a continuous flow operation such that it flows past, over and/or through the metal part, as indicated in block 822. In another embodiment, the abrasive solution could be provided in a batch operation, as indicated in block 824, for example in a vessel with an agitation mechanism that causes flow of the abrasive solution around a part mounted within the batch vessel. However, other configurations are also envisioned, as indicated in block 826.
In step 830, a magnetic field is provided. The magnetic field can be provided by one or more magnets placed outside a vessel, as indicated in block 832. In another embodiment, an electromagnetic field is generated, as indicated in block 834. The generated magnetic force acts on the magnetic particles within an abrasive solution, causing them to aggregate within a finishing vessel, for example along an interior surface. The aggregated magnetic particles change the flow pattern of the abrasive solution within the vessel. Controlling the position and strength of the magnetic field allows for targeted finishing of a metal part.
In step 840, the magnetic field is modulated. Modulation can include manual adjustments of a magnetic field, as indicated in block 852, for example adjusting a strength of the magnetic field, as indicated in block 842, a position of the magnetic field, as indicated in block 844, or other changes, as indicated in block 846, such as adding or removing a magnetic field source. In another embodiment, modulating includes automatically altering the magnetic field, for example by changing a strength 842, position 844, or number of magnetic field sources, such that magnetic guide vanes formed within a vessel also change, forcing an abrasive fluid flow to change. The automatic modulation may be driven, in one embodiment, by known specifications of a part being finished, for example provided by a STL file used to print the part, a CAD file related to the part, or another specification format. Modulation may continue until the part is finished, in one embodiment.
Use of method 800 may allow for surfaces of the part that would be difficult for an abrasive solution to access to be identified and targeted.
In step 910 part specifications are provided. For parts printed using additive manufacturing techniques, a stereolithography file (STL file) is used to provide instructions for a printer. An STL file provides a description for a triangulated surface. However, while systems and methods described herein refer to an STL file 902, other files used for additive manufacturing 906, either known now or future developed, may also be used in method 900. Additionally, any other suitable computer aided design (CAD) file 904 may also be used.
In step 920 surfaces requiring finishing are identified. Additive manufacturing, or other manufacturing techniques, can result in a part with a surface that has undesired roughness. A roughness level 912 of the part surface is identified. The part may have an even roughness across an entire surface, or may have some areas with more or less roughness. In some embodiments finishing occurs unevenly, such that rougher areas are finished without over-finishing occurring on less rough areas. Surfaces needing finishing may be identified manually, as indicated in block 914, for example by a user so indicating. However, it is also envisioned that roughness can be determined automatically, as indicated in block 916. for example by scanning a metal part and comparing it to a CAD file. Other roughness identification methods may also be used, as indicated in block 918. For example, optical measurement techniques such as laser or projected light may be used. Additionally, surface profiling may be used. An X-ray scan may also be used to determine roughness.
In step 930, a finish routine is determined. Determining a finishing routine may include retrieving a pre-set finishing routine based on an identified part, in one embodiment. In another embodiment, a finishing routine is dynamically determined based on an identified part and detected surface roughness. Determining a finishing route may include determining, based on finishing needs of a metal part, position and strength of one or more magnetic fields with respect to a finishing vessel during a finishing operation. For example, a first and second magnet may have a first and second position, at a second time at a first time and may move to a third and fourth position, respectively, at a second time such that, at the first time, a first area of a metal part is targeted for finishing and, at the second time, a second area is targeted. However, while two magnets are discussed, it is also expressly contemplated that only one magnet, or more than two magnets, may be used in different embodiments. Additionally, magnetic fields may be generated by electromagnetic systems instead of naturally magnetic material. Determining a finishing routine may also include consideration of the composition of an abrasive finishing solution. For example, an amount of magnetic material in suspension will affect the size of magnetic guide vanes that can be created. And the rheology of the abrasive solution will affect fluid flow. Additionally, a type, size and amount of abrasive particles will affect how quickly a part surface is abraded, as will the presence of a corrosive agent.
Determining a finishing routine can be done manually, as indicated in block 932, for example by a user positioning magnets to direct an abrasive fluid flow toward an area needing targeted finishing. Determining a finishing routine can also be done automatically, as indicated in block 934. Other methods can also be used, as indicated in block 936, such as a partially autonomous determination of magnet placement over time.
A finishing routine can be determined using computational fluid dynamics (CFD) analysis based on known specifications of a part, the abrasive fluid and the finishing vessel, as indicated in block 922. It may also be determined using machine learning, in some embodiments, such that a controller can adjust a finishing routine based on past changes made by a user to similar parts, as indicated in block 924. Other computer-aided methods may also be used, as indicated in block 926.
In step 940, a part is mounted for finishing. Mounting may include mounting the part in a fixed position for an entire finishing operation. In another embodiment, mounting includes moving the part with respect to a finishing vessel such that different surfaces can be more easily targeted.
In step 950, a finishing sequence is applied. The finishing sequence may include application of an abrasive fluid, as indicated in block 952. The abrasive fluid may be applied in a continuous flow, or in a batch vessel with the mounted part. The abrasive fluid may contain any or all of abrasive particles, magnetic particles, chemical or other additives. Applying the finishing sequence may also include applying a magnetic force to a finishing vessel such that magnetic particles in the abrasive fluid are agglomerated within the finishing vessel, as indicated in block 954. Applying the finishing sequence may also include other steps such as pretreatment, a cleaning rinse, adjusting a mount, changing an abrasive fluid, or other suitable steps.
Systems and methods described herein can be used for finishing metal components. Such metal components may be manufactured in a variety of ways including, but not limited to, additive manufacturing or 3D printing techniques. Additionally, while systems and methods described herein may be particularly useful for parts with internal or complex geometry, they may also be useful for other components, including those that have uneven finishing requirements. Systems and methods described herein may allow for targeted finishing of areas with a greater roughness without over-finishing areas that are less rough.
While systems described herein may be useful for accomplishing methods described herein, the methods described herein may be useful with other system configurations, in some embodiments. The methods described herein may also include other steps that are not discussed in detail. Further, while the methods are described with respect to a particular sequence, it is also contemplated that at least some steps can be accomplished in orders other than those illustrated, where appropriate.
Additionally, while the methods described herein may be useful in understanding the systems illustrated, it is also envisioned that systems may be used differently than as described in the methods. Additionally, while the systems illustrate particular components, it is also understood that more, or fewer, components may be present where appropriate.
Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight.
Finishing of an additively manufactured part which is fixtured within a pipe through which an abrasive solution is pumped. The abrasive solution comprises 0.1 molar concentration solution of Potassium Hydroxide (KOH) in water (as sold by Sigma Aldrich, UK) with P500 semi-friable aluminium oxide, such as “BFRPL,” which is commercially available from Imerys Minerals. The weight percent of each component are shown in the table below. The iron was obtained from Sigma Aldrich. The percent of iron is dependent on the volume of the guide vanes which will be formed. There should be an excess of iron in suspension such that the iron in the system is not all consumed in the formed guide vanes.
In the control case the abrasive fluid would flow around an additively manufactured part, with the flow paths and shear on surfaces defined by the external geometry of the part and orientation to the flowing abrasive fluid, using the control set up of
In
Magnets with different strengths can be used to direct all the abrasive fluid past one side of the part. In
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/059902 | 10/21/2020 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 62926830 | Oct 2019 | US |
