Powered removal for element formed by powder bed fusion additive manufacturing processes

A method for forming a part includes: forming a first portion of the part at a first level; forming a second portion of the part at a second level; wherein forming the first and second portions includes exposing the first and second levels to a sintering process and portions of the first and second levels to an electron beam; causing a magnetorheological (MR) fluid to move into a passage inside the first and second portions; exposing the first and second portions to a magnetic field causing motion of particles in the MR fluid to move and break up sintered material in the passage; and removing some or all of the sintered material in the passage.

BACKGROUND OF THE INVENTION

This invention relates forming elements or parts and, more particularly, to a method of removing power from parts formed by powder bed fusion.

Powder bed fusion (PBF) methods use either a laser or electron beam to melt and fuse material powder together. Electron beam melting (EBM) is a particular example of a PBF method and is a type of additive manufacturing (AM) for metal parts. In particular, it is a powder bed fusion technique process where an electron beam is used to melt metal powder layer by layer in a vacuum to form a product. One unique aspect of EBM additive manufacturing is that non-melted particles, i.e. those particles not utilized in the final part, are sintered together. The sintering process binds the non-melted particles together providing additional mechanical strength during the build process. The sintered particle is very difficult to remove from more complex structures, particularly those that contain internal features such passages or blind holes. Another type of PBF utilizes a laser. Powder is not sintered but complex geometries may still exist that include unfused powder.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a method for forming a part is disclosed. The method includes: forming a first portion of the part at a first level; forming a second portion of the part at a second level; wherein forming the first and second portions includes exposing the first and second levels to a sintering process and portions of the first and second levels to an electron beam; causing a magnetorheological (MR) fluid to move into a passage inside the first and second portions; exposing the first and second portions to a magnetic field causing motion of particles in the MR fluid to move and break up sintered material in the passage; and removing some or all of the sintered material in the passage.

In another aspect, a method for forming a part is disclosed. This method includes: forming a first portion of the part at a first level; forming a second portion of the part at a second level; wherein forming the first and second portions includes exposing the first and second levels to a sintering process and portions of the first and second levels to an electron beam; forming a wire in the passage formed inside the first and second portions by exposing a portion of the passage to the electron beam; causing a magnetorheological (MR) fluid to move into a passage inside the first and second portions; and applying a current to the wire which creates a magnetic field causing motion of particles in the MR fluid to move and break up sintered material in the passage; and removing some or all of the sintered material in the passage.

DETAILED DESCRIPTION OF THE INVENTION

As briefly described above, it is very difficult to remove the dense, sintered powder after completion of the build. Parts with internal features such as passages within a housing have to be specially processed in order to remove dense powder. Powder removal is a step that, for complex parts, will add cost to an additively built part. Embodiments disclosed herein may provide a more efficient or economical solution to removing the dense power.

The methods disclosed herein may expedite and minimize the amount of time required for powder removal from PBF (including EBM and laser PBF) manufactured parts. In one embodiment, a magnetorheological (MR) fluid or a ferrofluids is caused to infiltrate sintered or semi-sintered residual powder within, for example, a passage or other portion of an AM component. A vacuum may pull the fluid through the passage in one embodiment or another external force may be used to the push the fluid push the fluid through the powder. An external magnetic field may then be applied to the passageway or component at large. The magnetic field may cause particles (e.g., ferromagnetic or ferrimagnetic particles) in the fluid to become aligned which, in turn, causes an application of a shear stress to the sintered or semi-sintered particles. The applied shear stress and increase in viscosity should be enough to mechanically fracture the particles thereby allowing to fall or flow out of a channel or passageway. In some instance, the process may need to be repeated several times depending upon its ability to infiltrate the sintered or semi-sintered powder material. For example, an alternating magnetic field may be applied to cause repetitive shear stresses.

In one embodiment, a powder removal element (e.g., a wire) is formed in an internal passageway of the part itself while the part is being formed. Application of a current to the wire will cause a magnetic field as described above. The current can be constant or could be varying (i.e. be an A.C. current) to create a time varying (e.g., rotating) magnetic field to increase the movement of the particles. Further, additional cleaning elements may be provided on an end of the powder removal element to mechanically pull the powder out after the current has been applied.

FIG. 1is an example of part1that is formed by PBF shown in a cut-away side view. While the following describes an EBM process, the removal methods are applicable to all PBF created pieces where powder needs to be removed from internal passages. The part1includes first and second portions2,4separated by an internal passage6. As the part1is formed, metallic power is first layered down and then sintered. The portions of the part1that are to become part of the final product are then exposed to an electron beam to convert the sintered powder to a fused dense metal object. However, the portions of the part that are not exposed to the electron beam are still sintered, just not fully fused by the electron beam.

In the example inFIG. 1, the passage6may be filled with sintered or partially sintered material8. That is, the portions2,4are metal pieces formed by exposing the sintered powder to an electron beam to form the fully fused metal. Portions that are not exposed remain as partially fused/sintered material as illustrated by sintered material8. Removal of this material to open, for example, passage6may be difficult, especially when the passage is not a straight or varies in size.

FIG. 2shows an example of a system20according to one embodiment. The system includes a fluid source21. The fluid source contains a liquid that contains that includes ferromagnetic or ferrimagnetic particles therein. Thus, the fluid may be an MR fluid in one embodiment. The system20also includes a vacuum22. The vacuum22is arranged such that it causes fluid from the fluid source21to enter the passageway6formed in the part1. As discussed above, the passageway6may include sintered or partially sintered material.

FIGS. 3A and 3Bshow an example of a passageway6containing sintered material8after an MR fluid has been drawn into it. InFIGS. 3A and 3Bthe fluid itself is not shown but the magnetic particles10contained therein are.

InFIG. 3A, a magnetic field has not been applied. InFIG. 3B, a magnetic field is/has been applied. As illustrated inFIG. 3B, the particles will line up generally along the magnetic flux lines12. The movement of the generally random location of the particles10inFIG. 3Ato the more uniform lines14following the flux lines12cause shear in the material8and, as such, break it up and make it easier to remove. In one embodiment, the vacuum22(FIG. 2) may be above to remove the material8after the magnetic field has been applied.

InFIG. 2, the source of the magnetic field is general shown as field source23. Any type of field source may be used. In one embodiment, the field source23is a magnetic field generated by permanent magnets (Fe—Nd—B magnets for example). Another field source may be an electromagnet.

In another embodiment, a wire may be formed in the passage way. The same process may be applied above to any of the embodiments below that include a wire. Also, rather than or in addition to the magnetic field being applied by an external source (e.g., field source23), the magnetic field may be formed by a current passing through the wire. The current may be D.C. or A.C.

FIG. 4is an example of part100that is formed by PBF shown in a cut-away side view. While the following describes an EBM process, the removal methods are applicable to all PBF created pieces where powder needs to be removed from internal passages. The part100includes first and second portions102,104separated by an internal passage106. As the part100is formed, metallic power is first layered down and then sintered. The portions of the part100that are to become part of the final product are then exposed to an electron beam to convert the sintered powder to a hard metal object. However, the portions of the part that are not exposed to the electron beam are still sintered, just not fully fused by the electron beam.

In the example inFIG. 4, the passage106may be filled with sintered material108. That is, the portions102,104are metal pieces formed by exposing the sintered powder to an electron beam to form the fully hardened metal. Portions that are not exposed remain as partially fused sintered material as illustrated by sintered material108. Removal of this material to open, for example, passage106may be difficult, especially when the passage is not a straight or varies in size. According to one embodiment, as the part100is being formed, a wire110is formed through the passage106. The wire110is formed in the same manner as the portions102,104. That is, as each level of the part100is formed, a small portion of the otherwise sintered only section (e.g., material108) is exposed to the electron beam to form a continuous wire110through it.

FIG. 5shows a top view of the part taken along line A-A fromFIG. 1. The portions102,104have been exposed to the electron beam to fully fused powder particles. So too has the wire110. Thus, portions102,104and wire110are in the same state of processing and are fully fused metal. The passage106is shown as including sintered material108that has not been exposed to an electron beam. This is the material that needs to be removed in order to allow material to pass through passage106. For example, if the part100is a manifold, passage106would need material108removed in order to allow fluids to pass through it.

With reference toFIG. 4, in one embodiment, the wire110may be coupled to a current source112. The current source112may be either A.C, or D.C. in one embodiment. After the fluid has been pulled into the material108(as described in relation toFIG. 2above), the current is applied to the wire106and this, as above, causes the particles10in the piece to align and shear the material108to make it easier to remove.

FIG. 6shows yet another embodiment. In this embodiment, the passage106is formed to include wire110a cleaning element120. The cleaning element120is formed of the same material as the wire in one embodiment. As the wire110is removed (direction C) the cleaning element120may aid in powder removal. The particular shape of the cleaning element120may be varied from that shown inFIG. 6. Also, more cleaning elements120may be provided. In general, the cleaning element120has a larger cross-section than the wire110. In another embodiment, one or more optional additional cleaning elements140may be added to the wire110. One or more of the additional elements140may be of a different size or shape than cleaning element120.

In yet another embodiment, and as shown inFIG. 7, nested cleaning elements220may be provided. Each element (e.g.,220a,220b) may be attached to an individual wire110a,110b, respectively. As illustrated, a first cleaning element220ais attached to a first wire110aand a second cleaning element220bis attached to a second cleaning element220b. In this configuration, the first wire110apasses through a hole or other passage way (e.g., notch240) formed in the second cleaning element220b. This allows the second cleaning element220bto be removed before the first cleaning element220a. In this manner, a first amount of powder may be removed and then a second amount (assuming that the second cleaning element220bis smaller than the first cleaning element220a). In on embodiment, the wires110a.110bmay run through different channels to allow them both to work in the illustrated channel106and then to work in different channels as they are removed.

FIG. 8shows a method according to one embodiment. A block800a plan for a part is received. The plan may, for example, be a representation of the part or it may be CAD model of the part. A block802, the part is formed. Forming the part includes layering down metallic power and then fusing it. The portions of the part that are to become part of the final product are then exposed to an electron beam to convert the sintered powder to a fused metal object. However, the portions of the part that are not exposed to the electron beam are still sintered, just not fully fused by the electron beam. At block804an MR fluid is pulled or pushed through an internal passageway of the part such that it invades the internal passageway. At block806, the part, including the MR fluid, is exposed to a magnetic field. The application of the field causes sintered material to experience a shear stress and makes it easier to remove (block808) as its structure is broken due to the stress.

FIG. 9shows a method according to one embodiment where a wire is used to provide the magnetic field. The method includes several optional steps that may or may not be needed depending on the particular wire/cleaning element combination chosen.

At block900a plan for part is received. The plan may, for example, be a representation of the part or it may be CAD model of the part. In some cases, one or more wires are added to the plan at block902. The additional wires are added such that they will be formed in an interior passage(s) of the part. At block904optional cleaning elements are added to the plan. At block906the part, including the wire(s)/optional cleaning element(s), is formed. The part and the wires are formed using electron beam manufacturing as described above. At block907an MR fluid is pulled or pushed through an internal passageway of the part such that it invades the internal passageway.

At block908a signal is applied to the wires. This signal causes sintered powder to break up or otherwise become easier to remove is it causes motion of the MR particles. At block610the wire (or wires) is removed.