Patent Application
20190184643
This application claims priority to United Kingdom (GB) patent application 1720886.9, filed Dec. 14, 2017, the entire contents of which are hereby incorporated by reference.
The present invention relates to a blank grown by an additive layer manufacturing process, and a method of producing and post-processing the same.
Additive layer manufacturing (ALM) is a growing technology in the field of engineering due to its ability to easily manufacture complex parts. However, due to the manufacturing process of coalescing particles to form an ALM part, significant post-processing is necessary to remove loose and semi-coalesced material before the manufactured part can be used in a final product.
Post-processing of ALM parts typically requires the use of air hoses and brushes to remove loose material, and metallic tools to remove semi-coalesced material from the ALM part. Air hoses and brushes can only remove loose dust and so metallic tools, such as drill bits, are required to remove semi-coalesced material from the ALM part. The metallic tools need to be accurately located and are unwieldy. Post-processing can be especially difficult where small features are blocked with semi-coalesced material. Small features are typically difficult to access and often require significant amounts of user skill to removed semi-coalesced powder in these regions, which adds to manufacturing process time.
Furthermore, the material of the traditional tools used for the removing semi-coalesced material is typically mismatched from that of the ALM part. Therefore, since one of either the tool or the ALM part is typically harder than the other, the process of removing semi-coalesced material from the ALM part can also cause damage to either the ALM part or the tool.
It is therefore desirable to provide a means for removing semi-coalesced material from an ALM part that is both capable of accessing difficult to reach features and that also minimises any damage to the ALM part and/or the tool during use.
A first aspect of the invention provides a blank comprising a part, a tool, and a connection member connecting the tool to the part. The part, the tool and the connection member are integrally formed as a single piece of build material. The connection member can be broken or cut to disconnect the tool from the part. After the tool has been disconnected from the part, the tool can be used to mechanically remove surface build material from the surface of the part.
A second aspect of the invention provides a method of manufacturing and post-processing a part, the method comprising growing a blank by an additive layer manufacturing process with a build material, the blank comprising a part, a tool, and a connection member connecting the tool to the part. The part, the tool and the connection member are integrally formed by the additive layer manufacturing process as a single piece of the build material. The connection member is broken or cut to disconnect the tool from the part. After the tool has been disconnected from the part, the tool is used to mechanically remove surface build material from the surface of the part.
The tool is used to remove the surface build material mechanically, by motion of the tool, rather than using a non-mechanical method such as blowing air at the part. Typically the tool is used to mechanically remove the surface build material from the surface of the part by bringing the tool into contact with a surface of the part and then moving the tool in contact with the surface of the part, for instance by rotating and/or reciprocating the tool. This motion of the tool mechanically removes the surface build material from the surface of the part, for instance by a scraping, reaming or polishing action.
A third aspect of the invention provides a computer file containing instructions for growing a blank according to the first aspect of the invention by a process of additive layer manufacturing.
Preferably the part has a feature (such as a hole, channel, passageway, recess or corner) with an interior surface; and the tool is grown inside the feature. Growing the tool inside such a female or inaccessible feature enables the tool to be “bespoke”—in other words of a suitable size and shape to access all areas of the interior surface.
Optionally the blank has a clearance between the tool and the interior surface of the feature, so that no part of the tool is in contact with the interior surface of the feature, at least until the post-processing stage when the tool is used to remove the surface build material. The tool is grown inside the feature with no part of the tool in contact with the interior surface of the feature, which prevents the tool from coalescing to the interior surface during the additive layer manufacturing process.
The tool may be grown entirely within the feature, or more preferably it has a first (or proximal) portion which is grown outside the feature and a second (or distal) portion which is grown inside the feature. The unwanted surface build material is removed from the interior surface of the feature by the second portion of the tool. The first portion protrudes from the feature making it easy to grip with pliers or a similar device.
Optionally the tool extends to a tool tip at a distal end of the tool, and the tool tip is inside the feature. Preferably the tool tip is brought into contact with the interior surface of the feature, and then the tool tip is used to mechanically remove the surface build material from the interior surface of the feature during the post-processing stage.
Optionally a clearance is provided between the tool tip and the interior surface of the feature, so that the tool tip is not in contact with the interior surface of the feature, at least until the post-processing stage.
Optionally the connection member is not located within the feature. This makes the connection member more easily accessible to be cut.
Optionally the connection member has a minimum cross-sectional area A1, the tool has a minimum cross-sectional area A2, and the area A1 is less than the area A2. This relatively small cross-sectional area makes the connection member easy to break or cut.
The part, the tool and the connection member are integrally formed as a single piece of the same build material. The build material may be a metal, a thermosetting polymer, a thermoplastic polymer, or any other suitable build material.
Optionally the surface build material which is mechanically removed by the tool is un-coalesced material (such as loose or un-coalesced powder) and/or semi-coalesced material (such as semi-coalesced powder). In this case, the part may include coalesced material, along with unwanted un-coalesced and/or semi-coalesced material which forms the surface of the part. Alternatively the surface build material which is mechanically removed by the tool may be fully coalesced material, which is removed to polish or otherwise improve a surface finish of the part.
In one embodiment the tool comprises a smooth rod. In other embodiments the tool comprises a shaft with protrusions or recesses on its outer surface, which may be helical or non-helical. These increase the surface area of the shaft and create features which can help to dislodge material.
In a preferred embodiment the tool comprises a shaft with a helical recess on its outer surface. Such a spiral shaft can be rotated to transport the surface material by an auguring action after it has been removed by the tool from the surface of the part. The groove may be formed by helical flutes or threads, for example.
Optionally the blank is grown by forming a series of layers of the build material, for instance in the form of a powder such as a metallic powder or a thermoplastic polymer powder. The build material is selectively coalesced layer-by-layer during the formation of the series of layers so that at least some of the layers have a first area of coalesced build material, a second area of un-coalesced build material, and semi-coalesced build material between the first and second areas. The un-coalesced build material is then removed to leave the coalesced build material and the semi-coalesced material which together constitute the blank. In this case the surface build material removed from the surface of the part by the tool may be semi-coalesced build material.
Alternatively the blank may be grown by selectively curing a liquid build material such as a thermosetting resin. In this case the surface build material removed from the surface of the part by the tool may be semi-cured resin.
Preferably the build material is selectively coalesced by heating, for instance with a laser-beam or electron-beam.
Optionally the tool supports a weight of the part during the additive manufacturing process.
Embodiments of the invention will now be described with reference to the accompanying drawings, in which:
A laser head 24 then scans over the powder layer, and a laser beam from the head is turned on and off to selective coalesce the powder by melting or sintering the powder in a desired pattern. Movement of the laser head 24 and modulation of the laser beam is determined by a Computer Aided Design (CAD) model of the desired profile and layout of the blank. The laser head 24 is controlled by a computer numeric controller (CNC) 25 connected to a memory 26. The memory 26 contains a computer file 26 containing data defining the CAD model for a blank. The CNC 25 is programmed to actuate the laser head 24 so that the laser beam selectively coalesces the desired areas of each respective powder layer as determined by the data in the file 26.
After the initial layer has been selectively coalesced, the CNC 25 commands a substrate actuator 27 to move the substrate 23 down by a small distance (typically of the order of 0.1 mm) to prepare for growth of the next layer. After a pause for the melted powder to solidify, the roller 22 rolls another layer of powder over substrate 23 in preparation for coalescing. Thus as the process proceeds, a first area of coalesced powder 28 is grown, along with a second area of un-coalesced loose powder 29. Semi-coalesced material (not shown) is also formed between the first and second areas 28, 29 when powder becomes slightly heated, but not sufficiently heated to fully coalesce, as the laser beam passes close by. The semi-coalesced powder becomes loosely adhered to the coalesced powder. Both the loose un-coalesced powder 29 and the semi-coalesced powder must be removed from the blank in post-processing.
A blank 30 according to an embodiment of the present invention is shown in
The blank 30 comprises a tool 32 and a connection member 33 which are integrally formed with the part 31 by the ALM process shown in
The connection member 33 is connected at one end to the external surface 35 of the part 31 outside the channel 34, and at its other end to the protruding proximal portion 32a of the tool 32. The connection member 33 is not located within the channel 34, making it easy to access by a cutting tool 40 as shown in
The blank 30 has a clearance between the rod 32b and the interior surface 34a,b of the channel, so that no part of the tool is grown in contact with the interior surface 34a,b. More specifically, once the un-coalesced powder has been removed then a full clearance is provided between the tool tip 34c and the base 34a of the channel; and full clearance is also provided between the cylindrical side of the rod 32b and the cylindrical side wall 34b of the channel This full clearance prevents the tool from coalescing to the interior surface 34a,b during the ALM process.
For a channel 34 with a diameter of 3 mm, the diameter of the rod 32b is limited to no more than 1 mm, so as to leave at least 1 mm clearance on each side.
The proximal portion 32a of the tool 32 typically has a diameter of about 5 mm, to enable it to be easily gripped by pliers 50 as shown in
A method of manufacturing and post-processing the blank 30 will now be described with reference to
A first build stage involves the manufacture of the blank 30 using an additive layer manufacturing process, such as the one described in
In a first post-processing stage, the un-coalesced powder is removed to leave the blank formed from coalesced powder and semi-coalesced powder as shown in
Next the connection member 33 is cut or broken to release the tool 32 from the part 31, in this case by cutting it with hand cutters 40 as shown in
The connection member 33 has a minimum cross-sectional area that is significantly smaller than that of the tool 32, to make it easy to cut or break. In this case the connection member 33 has a cylindrical shape with a radius R1 (which is typically of the order of 0.25 mm) and cross-sectional area π(R1)2=A1, and the rod 32b has a cylindrical shape with a radius R2 (of the order of 0.5 mm to a few cm) and cross-sectional area π(R2)2=A2. The cross-sectional area A1 of the connection member 33 is less than the cross-sectional area A2 of the rod by a factor of about 4-10.
After the tool 32 has been disconnected from the part 31 as shown in
The dislodged semi-coalesced powder is then removed from the channel in the same manner as the un-coalesced powder in the first post-processing stage described above.
Since the rod 32b is built within the channel 34, it is able to easily access the full length of the channel that would otherwise be difficult to reach with conventional tooling.
Also, since the tool 32 is created for the bespoke purpose of removing semi-coalesced material from a particular region of a specific part 31, this method also gives the opportunity to design and build specific tooling for a particular job, instead of relying on a select set of available tools, and the tool can be custom built to a specific size, shape and quantity rather than the nominal available sizes provided by a tool manufacturer.
Furthermore, since the tool 32 is integrally formed with the part 31, the tool 32 is formed from the precisely the same build material as the part 31, in this case powdered Titanium. Therefore, the tool 32 is strong enough to remove the semi-coalesced material, but not so strong as to damage the part. This also has the added benefit of enabling the tool to be recycled along with the other waste build material.
A blank and post-processing method according to an alternative embodiment of the present invention is shown in
The blank of
The maximum diameter of the shaft 63 is wider than the diameter of the cylindrical rod 32b, the maximum diameter of the shaft 63 typically being about 2 mm for a 3 mm diameter channel 34 leaving a reduced clearance of about 0.5 mm rather than 1 mm This reduced clearance is acceptable, since the recess 64 results in a reduced surface area which could potentially adhere to the part.
The tool of
In the embodiments of
The smooth cylindrical rod 32b potentially compresses powder at the bottom of the channel, but the spiral shaft 63 of
A variety of other blanks are illustrated in
The tool 72 has a cylindrical shaft 72a and an enlarged conical or wedge-shaped distal portion 72b which tapers to a sharp tip 72c. The distal portion 72b is grown within the feature 74, with the angle of taper of the distal portion 72b matching the angle of the walls 74a so the sharp tip 72c can fit into the sharp corner 74b to remove semi-coalesced powder.
The connection member 33 of
In this case the tool 82 has a curved rod 82b which is grown within a curved channel 84. The rod 82b and the channel 84 have the same curvature so that the clearance remains constant along the length of the curved rod. The curved rod 82b is moved with a reciprocating motion with substantially no rotation to dislodge the semi-coalesced powder.
Each tool 102-105 has a proximal portion 102a, 103a, 104a, 105a and a spiral shaft 102b,103b,104b,105b with a helical recess on its outer surface. Each shaft 102b-105b is grown within a respective one of the channels 94-97.
During post-processing, the connection member 93a is cut to release the tool assembly 101 from the part 91, then the linking members 93b-d are cut or broken to separate the tools 102-105 from each other before they are used to clear semi-coalesced powder from the channels 94-97.
Although each of the shafts 102b-105b illustrated in
In the embodiments described above, the shaft of the (or each) tool has an outer surface which is either smooth and cylindrical, or formed with a helical recess which provides an auguring action as well as creating features (such as the edge of the recess) which can help dislodge material, for instance by a scraping action. In other embodiments, the shaft of the tool may be formed with non-helical recesses (such as circular pits or annular grooves) or protrusions (such as raised bumps, hoops or axial ridges) on its outer surface. Although these recess or protrusions do not provide an auguring action, they do increase the surface area of the shaft and create features which can help dislodge material.
In the embodiments described above, the blank is formed by a so-called “powder-bed” ALM process shown in
The blanks shown in
Where the word or appears this is to be construed to mean ‘and/or’ such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination.
Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1720886.9 | Dec 2017 | GB | national |
