Patent Publication Number: US-2019184643-A1

Title: Post-processing of additive layer manufactured part

Description:
CROSS RELATED APPLICATION 
     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. 
     FIELD OF THE INVENTION 
     The present invention relates to a blank grown by an additive layer manufacturing process, and a method of producing and post-processing the same. 
     BACKGROUND OF THE INVENTION 
     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. 
     SUMMARY OF THE INVENTION 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic view of an additive layer manufacturing system; 
         FIG. 2  is a schematic view of a blank according to an embodiment of the present invention; 
         FIGS. 3-5  illustrate a method of removing semi-coalesced material from the blank of  FIG. 2 ; 
         FIG. 6  is a schematic view of a blank according to an alternative embodiment of the present invention, with a spiral tool; 
         FIG. 7  illustrates a method of removing semi-coalesced material from the blank of  FIG. 6 ; 
         FIG. 8  is a schematic view of a blank according to a further alternative embodiment of the present invention, with a corner part; 
         FIG. 9  is a schematic view of a blank according to another alternative embodiment of the present invention, with a curved channel; 
         FIG. 10  is a schematic view of a blank according to another alternative embodiment of the present invention, with multiple tools; and 
         FIG. 11  shows an aircraft. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) 
       FIG. 1  illustrates a powder bed processing additive layer manufacturing (ALM) system for growing a blank. The system is “cold” in that the processing environment is at ambient temperature, and is not maintained at an elevated temperature. The system comprises a pair of feed containers  20 ,  21  containing metal powder such as Titanium powder. A roller  22  picks up powder from one of the feed containers (in the example of  FIG. 1 , the roller  22  is picking up powder from the right hand feed container  21 ) and rolls a thin, continuous layer of powder over a substrate  23 . In another embodiment (not shown) the layer of powder is spread over the substrate  23  by a rake rather than a roller. 
     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  FIG. 2 . The blank  30  comprises a part  31  corresponding to the desired final product of the ALM process. The part  31  has an exterior surface  35 , and a channel  34  with an interior surface comprising a base  34   a  and a cylindrical side wall  34   b.  Initially the channel  34  is filled with loose un-coalesced powder (not shown) which is removed from the channel  34  by inverting the blank  30  (so the un-coalesced powder falls out due to gravity) and/or by blowing compressed air into the channel Once this loose un-coalesced powder is removed, the interior surface  34   a,b  of the channel remains coated with semi-coalesced powder  36  which must also be removed. 
     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  FIG. 1 . So the part  31 , the tool  32  and the connection member  33  are integrally formed as a single piece of the same build material (in this case coalesced Titanium powder). The tool  32  has a proximal portion  32   a  which is grown outside the channel  34 , and a rod  32   b  which is grown inside the channel and extends to a tool tip  32   c  at a distal end of the tool. The proximal portion  32   a  protrudes from the channel making it easy to grip with pliers  50  or a similar device as shown in  FIG. 4 . 
     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  32   a  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  FIG. 3 . 
     The blank  30  has a clearance between the rod  32   b  and the interior surface  34   a,b  of the channel, so that no part of the tool is grown in contact with the interior surface  34   a,b . More specifically, once the un-coalesced powder has been removed then a full clearance is provided between the tool tip  34   c  and the base  34   a  of the channel; and full clearance is also provided between the cylindrical side of the rod  32   b  and the cylindrical side wall  34   b  of the channel This full clearance prevents the tool from coalescing to the interior surface  34   a,b  during the ALM process. 
     For a channel  34  with a diameter of 3 mm, the diameter of the rod  32   b  is limited to no more than 1 mm, so as to leave at least 1 mm clearance on each side. 
     The proximal portion  32   a  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  FIG. 4 . 
     A method of manufacturing and post-processing the blank  30  will now be described with reference to  FIGS. 2-5 . 
     A first build stage involves the manufacture of the blank  30  using an additive layer manufacturing process, such as the one described in  FIG. 1 . The CNC  25  uses only a single computer file, such as the file  26   a,  containing data defining a CAD model of the entire blank  30 , that is: the part  31 , the tool  32  and the connection member  33 . The use of only a single file  26   a  for the entire blank  30  helps to reduce build errors, and ensures that the rod  32  is accurately centred and aligned with the channel  34 , with full clearance. 
     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  FIG. 2 . This can be done by rotating and agitating the blank, or alternatively a brush or a compressed air hose may be used. 
     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  FIG. 3 . Alternatively the connection member  33  may be broken by gripping the tool  32  and twisting it. 
     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  32   b  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  FIG. 3 , the proximal portion  32   a  of the tool  32  is gripped by pliers  50 , or another hand tool, as shown in  FIG. 4 . The edge of the tip  32   c  of the rod is then brought into contact with the cylindrical side  34   b  of the channel, and moved by rotating and/or reciprocating the tool pliers  50  to mechanically dislodge the semi-coalesced powder  36 , for instance by a scraping or reaming action. Alternatively, the tool  32  may be reciprocated with its axis parallel with the cylindrical side of the channel  34   b  to mechanically remove the semi-coalesced powder  36  from the surface of the part. 
     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.  FIG. 5  gives an example—in this case the dislodged semi-coalesced powder  36  is removed by inverting the part  31  along with shaking and tapping the part  31 . Finally, the tool  32  may be recycled along with the material removed during post processing. 
     Since the rod  32   b  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  FIGS. 6 and 7 . 
     The blank of  FIGS. 6  is similar to the blank  30 , and identical features are given the same reference number and will not be described again. In this case the distal portion of the tool is a shaft  63  with a helical external recess  64 . The shaft  63  has a maximum diameter, and a minimum diameter coinciding with the recess  64 . 
     The maximum diameter of the shaft  63  is wider than the diameter of the cylindrical rod  32   b,  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  FIG. 6  is used in a similar way to the tool of  FIG. 4 , but it is also rotated within the channel by a tool  60  (or by twisting it between a pair of fingers) as shown in  FIG. 7 . This rotation has two functions: firstly the outer diameter of the shaft and the tip of the shaft  63  contact the part, and the rotation dislodges the semi-coalesced powder; and secondly the rotating helical recess  64  removes the dislodged semi-coalesced powder  36  from the channel by an auguring action indicated by vertical arrows in  FIG. 7 . The edges of the recess  64  can also dislodge the semi-coalesced powder  36  by a scraping action. 
     In the embodiments of  FIGS. 2 to 7 , the channel  34  is a “blind hole”, meaning that it does not extend through the entirety of the part  31 . The tool is sufficiently long that the tool tip  32   c  can be brought into contact with the base  34   a  of the channel  34  after the tool has been disconnected from the part. This enables the tool to access the full length of the channel  34  and remove surface build material from its base  34   a  by either a scraping, reaming or auguring action. 
     The smooth cylindrical rod  32   b  potentially compresses powder at the bottom of the channel, but the spiral shaft  63  of  FIG. 7  picks up such powder at the bottom of the channel and removes it by the auguring action. 
     A variety of other blanks are illustrated in  FIGS. 8-10 . 
       FIG. 8  shows a blank  70  with a part  71 , a tool  72  and a connection member  73 . The part  71  has a recess  74  with an interior surface formed by a pair of walls  74   a  which meet at a sharp internal corner  74   b.    
     The tool  72  has a cylindrical shaft  72   a  and an enlarged conical or wedge-shaped distal portion  72   b  which tapers to a sharp tip  72   c.  The distal portion  72   b  is grown within the feature  74 , with the angle of taper of the distal portion  72   b  matching the angle of the walls  74   a  so the sharp tip  72   c  can fit into the sharp corner  74   b  to remove semi-coalesced powder. 
     The connection member  33  of  FIG. 2  is located outside the channel  34 , but the connection member  73  of  FIG. 8  is located within the recess  74  and joined at each end to the walls  74   a.    
       FIG. 9  shows a blank  80  which is similar to the blank  30 , and identical features are given the same reference number and will not be described again. 
     In this case the tool  82  has a curved rod  82   b  which is grown within a curved channel  84 . The rod  82   b  and the channel  84  have the same curvature so that the clearance remains constant along the length of the curved rod. The curved rod  82   b  is moved with a reciprocating motion with substantially no rotation to dislodge the semi-coalesced powder. 
       FIG. 10  shows a blank  90  having a part  91  with four channels  94 , 95 , 96 , 97 , and a tool assembly  101  with four tools  102 , 103 , 104 , 105 . The tool assembly  101  is attached to the part  91  by a connection member  93   a,  and the four tools  102 - 105  are attached to each other by three linking members  93   b,    93   c,    93   d.  The part  91 , tools  102 - 105 , connection member  93   a  and linking members  93   b - d  are integrally formed as a single piece of build material. 
     Each tool  102 - 105  has a proximal portion  102   a,    103   a,    104   a,    105   a  and a spiral shaft  102   b , 103   b , 104   b , 105   b  with a helical recess on its outer surface. Each shaft  102   b - 105   b  is grown within a respective one of the channels  94 - 97 . 
     During post-processing, the connection member  93   a  is cut to release the tool assembly  101  from the part  91 , then the linking members  93   b - 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  102   b - 105   b  illustrated in  FIG. 10  are formed with helical recesses on their outer surface, they may be smooth cylindrical rods. In this case they can be reciprocated together to dislodge the semi-coalesced powder from the channels  94 - 97  without having to first break the linking members  93   b - d.    
     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  FIG. 1 , with a powdered build material. In an alternative embodiment of the invention, the blank may instead be grown from a liquid build material such as a thermosetting resin. In this case, the blank is grown on a substrate in a bath of the liquid build material. The substrate is immersed just below the liquid surface so there is a thin liquid layer above the substrate which is heated by a laser-beam or other heater to selectively cure the liquid. The substrate is then moved down slightly and another layer of liquid formed on top of the partially cured first layer. The process continues in a layer-by-layer fashion to build the blank. In this case the surface build material removed from the surface of the part by the tool will be semi-cured resin. 
     The blanks shown in  FIGS. 2-10  may have a variety of application, but one preferred application is to form part of the airframe of an aircraft.  FIG. 11  shows an aircraft  1  with an airframe comprising wings  2 ,  3  joined to a fuselage  4 , a vertical stabiliser  5  and a pair of horizontal stabilisers  6 . Various elements of the airframe  2 - 6  may be formed from a blank according to the present invention. In one example the fuselage may have a frame structure with nodes adhesively bonded to tubes, and the nodes are formed with channels for injecting adhesive to the bonding surface. Such nodes may be formed from a blank according to the present invention. 
     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.