Additive manufacturing

Abstract

A method of additive manufacturing metallic components, the method includes: forming a component in a layer by layer process, the component being formed integrally with at least one non-perforated support structure to be separated from the component after the layer by layer process, the support structure being formed with at least one wall that is non-perforated; and wherein after completion of the layer by layer process, the method includes exposing the component and support structure to at least one thermal pulse so as to weaken, or break, the interface(s) between the support structure and component prior to removal of the support.

Claims

1. A method of additive manufacturing metallic components, the method comprising: forming a component in a layer-by-layer process, the component being formed integrally with at least one non-perforated support structure to be separated from the component after the layer-by-layer process, the support structure being formed with at least one wall that is non-perforated; and after completion of the layer-by-layer process, exposing the component and support structure to at least one thermal pulse so as to weaken, or break, an interface arranged between the support structure and component prior to removal of the support, wherein the support structure is formed with a bulk support member, and wherein the interface is formed by a plurality of interface support members for connecting the bulk support member to the component, wherein the width of the interface support members narrows from the bulk support member to the component, wherein the thermal pulse is at a temperature exceeding the melting point of the metallic material, wherein after mechanical removal of the support structure from the component, at least one further thermal pulse is applied to the separated component.

2. The method of claim 1, wherein the support structure is formed with a plurality of walls.

3. The method of claim 2, wherein a distance between each wall is at least 0.8 mm.

4. The method of claim 3, wherein a centre-to-centre distance between each wall is at least 0.8 mm.

5. The method of claim 1, wherein each of the walls is formed with a thickness of 0.1 mm or less.

6. The method according to claim 1, wherein each interface support member is formed with its narrowest width at the interface with the component.

7. The method according to claim 6, wherein each interface support member reaches its narrowest width at a predetermined distance away from the interface with the component, wherein the predetermined distance is between approximately 0.5 mm and approximately 2 mm away from the interface with the component.

8. The method according to claim 6, wherein the interface support members have a base length defined as the length of the interface between the bulk support member and the interface support member, and ratio of the base length to a height of the interface support member is equal to 1.5 or less.

9. The method according to claim 6, wherein: the component and support structure are formed on a baseplate; the support structure comprises an internal support structure arranged between two parts of the component and an external support structure arranged between the component and the baseplate, the internal support structure and the external support structure both comprising a bulk support member and a plurality of interface support members; the interface support members have a base length defined as the length of the interface between the bulk support member and the interface support member; the base length to height ratio of the interface support members of the internal support structure is between 0.55 and 0.75; and the base length to height ratio of the interface support members of the external support structure is between 1.2 and 1.4.

10. The method of claim 1, wherein the step of exposing the component and support structure to a thermal pulse comprises placing the component and support structure in a chamber, filling the chamber with a combustible gas mixture, allowing the gas mixture to surround the component and support structure and igniting the gas mixture.

11. The method of claim 10, wherein the thermal pulse is an explosive or pseudo-explosive combustion.

12. The method of claim 10, wherein the chamber is at an increased atmospheric pressure of 400 bar and a peak pressure during combustion reaches 2000 bar or more.

13. The method of claim 1, wherein a plurality of thermal pulses are applied to the separated metallic component.

14. The method of claim 1, wherein the surface of the metallic component is abrasively cleaned after the application of at least one thermal pulse to the separated metallic component.

15. The method of claim 1, wherein the additive manufacturing process comprises powder bed selective laser manufacturing.

16. The method of claim 1, wherein the step of exposing the component and support structure to at least one thermal pulse provides a peak temperature increase of at least between approximately 2000 C. and approximately 3500 C.

17. The method of claim 1, wherein the step of exposing the component and support structure to at least one thermal pulse comprises the thermal pulse having a duration between approximately 20 milliseconds and approximately 100 milliseconds.

18. A method of additive manufacturing metallic components, the method comprising: forming a component in a layer-by-layer process, the component being formed integrally with at least one support structure to be separated from the component after the layer-by-layer process, the support structure being formed with at least one wall having a thickness of 0.1 mm or less; and after completion of the layer-by-layer process, exposing the component and support structure to at least one thermal pulse so as to weaken, or break, an interface arranged between the support structure and component prior to removal of the support, wherein after mechanical removal of the support structure from the component, at least one further thermal pulse is applied to the separated component.

19. A method of additive manufacturing metallic components, the method comprising: forming a component in a layer-by-layer process, the component being formed integrally with at least one support structure to be separated from the component after the layer-by-layer process, the support structure being formed with a plurality of walls, wherein a distance between each wall is at least 0.8 mm; and after completion of the layer-by-layer process, exposing the component and support structure to at least one thermal pulse so as to weaken, or break, an interface arranged between the support structure and component prior to removal of the support, wherein after mechanical removal of the support structure from the component, at least one further thermal pulse is applied to the separated component.

20. The method of claim 19, wherein each of the plurality of walls is non-perforated.

21. The method of claim 19, wherein the plurality of walls are formed in a hatched arrangement.

22. The method according to claim 21, wherein the plurality of walls are formed in a hatched arrangement fragmented into discrete smaller hatched sub-arrangements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Specific embodiments of the invention will now be described in detail, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic representation of a part manufactured by a conventional additive manufacturing method;

(3) FIG. 2 shows example metal parts formed by additive manufacturing with support structures both present and removed;

(4) FIG. 3 shows a flow chart for the forming an additive manufactured component in accordance with embodiments of the invention;

(5) FIG. 4 show different arrangements of the wall(s) of the support structure;

(6) FIG. 5 show example interface support members; and

(7) FIG. 6 shows sample components A-G before and after a thermal pulse has been performed.

DETAILED DESCRIPTION OF INVENTION

(8) A schematic representation of a metal part 1 manufactured in an additive manufacturing method is shown in FIG. 1. The metal part is for example a casing and includes a cavity 1a within its body. The part 1 is formed by being built up on a layer-by-layer manner on a baseplate 4 in a manner which will be well known to those skilled in the art.

(9) A bulk support structure 2 is provided within the cavity 1a of the part 1. The bulk support is arranged to be built relatively quickly during the additive layer manufacture but to have sufficient strength to resist the loads from the part 1 and, for example to resists geometric distortion of the part 1. The skilled person will appreciate that the support 2 may have any convenient (optimised) form and could be a solid or for example a lattice or honeycomb structure.

(10) To ensure that the support 2 can be removed from the component 1 after manufacture it is provided with an interface 3 which forms a distinct break line between the support 2 and component 1. The interface may comprise a number of distinct, tooth like, interface members 3a, 3b, 3c which join the component 1 and support 2. It will be appreciated that the component 1, support 2 and interface 3 are all integrally formed on a layer-by-layer basis during the additive manufacturing process.

(11) Some example drawings are shown in FIG. 2 to illustrate the removal of a support structure 2 from a component 1 using the method in accordance with embodiments of the invention. It may be noted that the drawings show the support 2 both in situ, partially removed and after removal (with remnants of an interface 3 showing).

(12) The method in accordance with an embodiment of the invention is shown by the flow chart of FIG. 3. In the initial step 10 a component is built along with support structures by a known metallic additive manufacture process. A subsequent heat treatment 20 is applied to the part after removal from the additive layer manufacturing machine but with the part remaining attached to the baseplate to resist deformation. Alternatively or in addition to heat treatment step 20, a heat treatment step may be applied to the part after removal from the baseplate (e.g. between steps 50 and 60 mentioned below). This heat treatment is in a non-oxidising atmosphere (inert or vacuum) and is intended to reduce or minimise residual stresses.

(13) With the residual stresses reduced by the heat treatment process 20, the component may be processed 30 to remove it from the baseplate (but will still have associated support structure attached or embedded within it).

(14) After this removal the part and support structure are subjected to a thermal pulse process 40 to weaken the interfaces between the support and component. This thermal pulse is carried out in a sealed chamber at increased pressure. The chamber is filled with methane and air which is allowed to fully surround the component prior to ignition to provide extremely rapid and high temperature combustion (an explosive or pseudo explosive process). The thermal pulse may for example last approximately 20 milliseconds and result in an increase in temperature within the chamber of between 2500 C. and 3500 C. and a pressure spike of up to 2000 bar. The heat will strike the surfaces of the component and support structure but is of insufficient duration to cause bulk heating thereof. The thermal pulse step may for example be carried out using a conventional thermal deburring apparatus.

(15) The thermal pulse step 40 has been found to weaken the interface parts 3 of the support 2 but since it does not cause any bulk heating of the component 1 it does not cause any change in its material properties. In contrast the interface parts are assumed to have a greater thermal conductivity so experience more significant surface oxidation and/or vaporisation and/or melting during the thermal pulse. This has been found to have provide a significant weakening of the interface and aid removal of the support (in step 50 below).

(16) After the thermal pulse step 40, the support 50 is removed using any convenient mechanical processing step 50 (and the skilled person will appreciate that the particular mechanical process selected may depend upon several factors such as the material and geometry of the component and support).

(17) Once the support has been fully removed it is normal to apply a final abrasive cleaning step 70 such as abrasive blasting to remove any remaining remnants of the interface members 3 from the separated component 1. In accordance with an embodiment prior to such abrasive blasting the component may optionally be subjected to a further thermal pulse step 60. The thermal pulse step 60 may include the application of a plurality of thermal pulses.

(18) It has surprisingly been found that the application of this additional step 60 produces a greater reduction in final surface reduction. This appears to go directly against the teaching in the art since an advantage of utilising thermal pulses in known processes such as thermal deburring is that component surfaces should not be affected. When the method of an embodiment was applied to test pieces by the applicant it was found to demonstrate a reduced surface roughness (Ra measurement), measured using a surface profilometer following the subsequent abrasive blasting process 70, of at least 30% and typically 50% to 60%.

(19) Without being bound to any particular theory, the applicants believe that the reduction in surface roughness is a result of the residual high points of the interface (and for example high points of roughness on downward faces) being vaporised, oxidised or melted by the thermal pulse creating a selectivity to the process and thereby enabling a smoothing to take place. The surface oxide than results from the thermal process is then removed by abrasive blasting.

(20) Experiment

(21) An experiment was carried out to study how various manufacturing parameters of the support structure affect the effectiveness of the thermal pulse in weakening or removing the support structure.

(22) Samples A to G were built on an EOS M270 selective laser melting powder bed additive manufacturing machine (produced by EOS GmbH). The samples were formed using a nickel superalloy, Nimonic C263. This is a nickel alloy with high chromium content (approximately 20%). Samples A to G shown in FIG. 6.

(23) Samples A to G comprised a cross section of a tube and were formed on a baseplate. EOS supports (as are known in this field) were formed inside the tube (internal supports) and between the sample and the base plate (external supports). Each sample was 20 mm wide by 30 mm high with a hole of diameter 25 mm. Each sample was spaced from the baseplate by the outside supports to a minimum height of 10 mm above the baseplate.

(24) The external supports were spaced from the baseplate by a series of line supports 1 mm high that enabled powder to be removed from the support structures. Such line supports are described in UK patent GB2458745.

(25) The manufacturing parameters for the internal and external supports that were used for each sample are indicated in Table 1.

(26) TABLE-US-00001 TABLE 1 Sample A B C D E F G Internal supports x/y 0.8 0.8 0.8 0.8 0.8 0.8 0.8 spacing (mm) Hatching Wide Wide Narrow Narrow Narrow Wide Narrow teeth Hatching No No No No No Yes Yes teeth break- away Border Wide Wide Narrow Narrow Narrow Wide Narrow teeth Border No No No Yes No No No teeth breakaway Frag- Yes Yes Yes Yes Yes Yes Yes mentation Per- Yes No No Yes No Yes No forations DMA No No. No No Yes Yes Yes border wall External supports x/y 0.6 0.6 0.6 0.6 0.8 0.8 0.8 spacing (mm) Hatching Wide Wide Narrow Narrow Wide Narrow Narrow teeth Hatching No No No No No Yes Yes teeth breakaway Border Wide Wide Narrow Narrow Wide Narrow Narrow teeth Border Yes No No Yes Yes Yes Yes teeth breakaway Frag- No No No No No No No mentation Per- Yes No No Yes No Yes No forations DMA No No. No No Yes Yes Yes border wall

(27) The terminology used in Table 1 is from the Magics software produced by Materialise (of Leuven, Belgium) and is a de-facto industry standard.

(28) FIGS. 4(a)-(f) shows possible arrangements of the walls of the support structure. Each line represents a wall.

(29) The term x/y spacing refers to the distance between the walls. FIG. 4(a) shows a schematic of a support structure with an x/y spacing of 0.6 mm, and FIG. 4(b) shows a schematic of a support structure with an x/y spacing of 0.8 mm. A smaller spacing results in a higher density of walls.

(30) FIGS. 4(a), (b), (d), (e) and (d) show examples of hatching, which refers to a hatched (lattice) structure having walls criss-crossing at 90, with voids contained between the walls.

(31) Hatching may be fragmented into discrete blocks (FIGS. 4(d) and (f)) or continuous from border to border (FIGS. 4(a) and (b)). The fragmentation used in this experiment was 44, as shown in FIGS. 4(d)-(f).

(32) Sections of hatching may be surrounded by perimeter walls, referred to as borders in Table 1. Borders may be doubled (i.e. two perimeter walls), as shown in FIG. 4(f).

(33) The hatching and border wall thickness was set to approximately 0.1 mm and the x/y spacing between walls was set at 0.6 mm or 0.8 mm as indicated in Table 1.

(34) For some samples, the walls of the support structure contained perforations, whereas for other samples, the walls were solid, i.e. contained no perforations.

(35) Examples of interface support members, referred to as teeth in Table 1, are illustrated in FIG. 5. They are located at the extremities of the support structure, where the support structure meets the sample. In Table 1, wide refers to a base length to height ratio of 1.3 and narrow refers to a base length to height ratio of 0.65.

(36) FIG. 5 also shows an example of a breakaway. This refers to a narrowing of the teeth from the bulk support up to a predetermined distance d away from the component wall. In the experiment a distance of 0.1 mm was used for breakaways.

(37) The above-described support removal process was carried out on all the samples using a single blast of natural gas and air in a 1:1 ratio at 12 bar pressure.

(38) After the support removal process was carried out, the following observations were made:

(39) All sample surfaces and supports were visibly oxidised (burnt).

(40) There was no visible evidence of damage to the sample (or baseplate) other than surface oxidation.

(41) All supports had suffered structural damage, as desired.

(42) Some of the supports had visibly melted (molten metal blobs were observed loosely attached to the baseplate and sample walls). This indicates that the temperature of the supports reached at least about 1500 C.

(43) Consolidation/melting and bonding of supports was observed in high density areas.

(44) The external supports were found to have been less affected by the thermal pulse than the internal supports.

(45) The parts of the internal supports remaining after the thermal pulse (visible in FIG. 6) were loosely attached to the sample and could be removed easily with slight effort, e.g. with a fingernail. This is substantially different from unprocessed supports that require considerable physical effort and/or power tools to remove.

(46) The internal support for sample E performed best (i.e. was easiest to remove from the sample after the thermal pulse), based on a subjective judgement.

(47) Discussion of the Experimental Results

(48) The supports most affected by the thermal pulse were the internal supports. The external supports, while weakened, did not respond as well as the internal supports, particularly at the end nearest the baseplate.

(49) Without being bound by any theory it is suggested that the effectiveness of the thermal pulse in melting/vaporising supports is a function of the following.

(50) Low thermal mass supports, or elements of elements (e.g. teeth and breakaway) that can become hot enough to melt (or vaporise) due to the rapid rise in temperature of the surrounding gas and the poor thermal conductivity of the bulk material.

(51) It is postulated from observations of the samples that explosive forces have built up inside some of the support structures. Where perforations or line supports are present the support has largely remained, though it may have destructively melted. However, where pressure from the ignition of the fuel-air mix has built up, the support has been physically blown awayparticularly at its weakest point. It is therefore postulated that where the hot gases can dissipate more easily, the thermal pulse has less effect on the supports.

(52) In particular, at the baseplate end of the external supports the thermal pulse may dissipate more easily due to the line supports between the external supports and the baseplate.

(53) The thermal pulse process was less effective when the support structure has a higher density of walls (lower x/y spacing). It is postulated that having a higher density of walls allows less explosive gas mixture to infiltrate the support structure and/or makes the support structure stronger and more capable of withstanding the thermal pulse process. It is therefore suggested that to increase the effectiveness of the thermal pulse process, support structures having the thinnest walls with the largest x/y spacing required for their function as supports are used.

(54) The non-perforated+fragmented support structures showed the greatest dislodging from the sample after the thermal pulse process. It is postulated that non-perforated supports have better gas trapping compared to perforated supports which allow the explosive gas mixture to dissipate through the perforations.

(55) Based on observation after the thermal pulse treatment of the supports, there was a reduction of approximately 80% of the manual force needed for complete removal of the supports.

(56) The support removal process of this invention does not need to completely remove all supports to be of practical application. There is considerable benefit to substantially weakening the supports to ease their subsequent removal, particularly for thin-walled (e.g. 0.8 mm to 2 mm) components of high complexity with significant supports attached. In production, parts can get irreparably damaged in the conventional support removal process.

(57) Although the invention has been described above with reference to a preferred embodiment, 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. For example, there may be more than one thermal pulse to process step 40 and some (or all) interface members 3a, 3b, 3c may be completely broken by the thermal pulse process step 40. Indeed the complete breaking of all interface members would be idealthereby allowing the simplest possible removal of the support (including by gravity). A limiting factor to interface breaking by additional thermal pulses may be an undesirable bulk heating of the part or simply cost and timeat some point it may be more desirable to mechanically cut the support away (including by unconventional methods such as electro discharge machining). In all regards though the support is mechanically removed; a thermal pulse does not of itself remove the support.