Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
PART STRUCTURE BUILT BY METAL POWDER BASED ADDED MANUFACTURING
Document Type and Number:
WIPO Patent Application WO/2012/131481
Kind Code:
A1
Abstract:
The invention provides a part structure (1) built by metal powder based added manufacturing, wherein a metal powder forming a metal powder bed resting on a base element (3) is selectively fused in a layer-by-layer fashion such as by selective laser melting, selective electron beam melting or selective ion beam melting. The part structure (1) comprises at least one individual part (2) and an auxiliary structure (4; 4, 5) attached to the at least one individual part (2) and to the base element (3). The auxiliary structure (4; 4, 5) is a grid-like structure comprising different types of grid elements including beam elements (4) and volume elements (5).

Inventors:
SPIERINGS ADRIAAN (CH)
LEVY GIDEON (CH)
Application Number:
PCT/IB2012/000636
Publication Date:
October 04, 2012
Filing Date:
March 29, 2012
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
INSPIRE AG IRPD (CH)
SPIERINGS ADRIAAN (CH)
LEVY GIDEON (CH)
International Classes:
B29C67/00; B22F3/105
Foreign References:
EP2022622A12009-02-11
US20090072447A12009-03-19
US5595703A1997-01-21
US6193923B12001-02-27
GB2458745A2009-10-07
Other References:
A.B. SPIERINGS: "Generative Verfahren bieten neue Chancen", SONDERDRUCK AUS TECHNISCHE RUNDSCHAU 2009, no. 12, 2009, XP002679183, Retrieved from the Internet [retrieved on 20120704]
SPIERINGS A ET AL: "Mit mehr Moeglichkeiten schneller ans Ziel", TECHNISCHE RUNDSCHAU, HALLWAG AG, CH, vol. 100, no. 4, 15 February 2008 (2008-02-15), pages 32 - 34, XP001510206, ISSN: 1023-0823
SANTOS E C ET AL: "Rapid manufacturing of metal components by laser forming", INTERNATIONAL JOURNAL OF MACHINE TOOLS AND MANUFACTURE, ELSEVIER, US, vol. 46, no. 12-13, 1 October 2006 (2006-10-01), pages 1459 - 1468, XP024902437, ISSN: 0890-6955, [retrieved on 20061001], DOI: 10.1016/J.IJMACHTOOLS.2005.09.005
ROCHUS ET AL: "New applications of rapid prototyping and rapid manufacturing (RP/RM) technologies for space instrumentation", ACTA ASTRONAUTICA, PERGAMON PRESS, ELMSFORD, GB, vol. 61, no. 1-6, 14 May 2007 (2007-05-14), pages 352 - 359, XP022078096, ISSN: 0094-5765, DOI: 10.1016/J.ACTAASTRO.2007.01.004
O. REHME, C. EMMELMANN: "Rapid manufacturing of lattice structures with Selective Laser Melting", PROC. OF SPIE, vol. 6107, 2006, XP002679184
J.-P. KRUTH, B. VANDENBROUCKE, J. VAN VAERENBERGH, P. MERCELIS: "BENCHMARKING OF DIFFERENT SLS/SLM PROCESSES AS RAPID MANUFACTURING TECHNIQUES", PROC. INT. CONF. POLYMERS & MOULDS, 2005, pages 1 - 7, XP002679185
Attorney, Agent or Firm:
KRUMPHOLZ, Erhard (Zürich, CH)
Download PDF:
Claims:
Claims

1. A part structure (1 ) built by metal powder based added manufacturing, wherein a metal powder forming a metal powder bed resting on a base element (3) is selectively fused in a layer-by-layer fashion such as by selective laser melting, selective electron beam melting or selective ion beam melting, said part structure (1 ) comprising at least one individual part (2) and an auxiliary structure (4; 4, 5) attached to the at least one individual part (2) and to the base element (3), characterized in that said auxiliary structure (4; 4, 5) is a grid-like structure comprising different types of grid elements including beam elements (4) and volume elements (5).

2. The part structure according to claim 1 , characterized in that said beam elements (4) include beam elements differing in beam length and in beam cross section.

3. The part structure according to claim 2, characterized in that at least some of said beam elements (4) are arranged in a tree-like fashion forming a tree-like portion of said grid-like structure.

4. The part structure according to any one of claims 1 to 3, characterized in that it comprises attachment elements (6) arranged between said at least one individual part (2) and said auxiliary structure (4; 4, 5) and/or arranged between said base element (3) and said auxiliary structure (4; 4, 5).

5. The part structure according to claim 4, characterized in that the attachment elements (6) comprise pre-defined breaking points.

6. The part structure according to any one of claims 1 to 5, characterized in that the volume elements (5) within said auxiliary structure (4, 5) are located adjacent to said at least one individual part (2).

7. The part structure according to claim 6, characterized in that attachment elements (6), preferably only attachment elements, are arranged between said at least one individual part (2) and said auxiliary structure (4, 5).

8. The part structure according to any one of claims 1 to 7, characterized in that the density of grid-elements in said grid-like structure increases as one approaches the at least one individual part (2) and, preferably, is greatest adjacent to said at least one individual part (2).

9. The part structure according to any one of claims 1 to 8, characterized in that the beam element (4) diameter is less than 4 mm.

10. The part structure according to any one of claims 1 to 9, characterized in that the beam element (4) is a hollow, tube-like element and, preferably, has a wall thickness of less than 45% of the beam element diameter.

11. The part structure according to any one of claims 1 to 10, characterized in that the cross-section of the beam elements (4) has a circular or polygonal shape.

12. The part structure according to any one of claims 5 to 11 , characterized in that the attachment elements (6; 6') comprise constrictions (6a) and/or porous regions pre-defining said breaking points.

13. The part structure according to any one of claims 1 to 12, characterized in that an angle formed between a part surface (2a) of the at least one individual part (2) and the horizontal plane (H) is between 0 and 60°.

14. The part structure according to any one of claims 1 to 13, characterized in that the beam elements (4) in the grid-like structure are arranged at angles greater than 45° to the horizontal plane (H).

15. The part structure according to any one of claims 1 to 14, characterized in that said different types of grid-elements are arranged as a mechanical support and heat removal structure between an overhanging part surface (2a) of the at least one part (2) and the horizontal plane (H).

Description:
Part structure built by metal powder based added manufacturing

The invention relates to a part structure built by metal powder based added

manufacturing. In order to build such a part structure, a metal powder forming a metal powder bed resting on a base element is selectively fused in a layer-by-layer fashion such as by selective laser melting, selective electron beam melting or selective ion beam melting. The resulting part structure comprises at least one individual part and an auxiliary structure attached to the at least one individual part and to the base element.

Background of the invention

Several additive manufacturing processes, such as Selective Laser Melting, Electron Beam Melting, Stereolithography, etc., need support structures in order to support the parts produced. There are different technical reasons for support structures, two important ones being:

• Mechanical support:

Stable positioning of the parts to be produced during the build process. This is of particular relevance for overhanging surfaces of a part to be produced.

• Heat sink:

Thermal processes (Selective Laser Melting, Electron Beam Melting) use a high energy beam in order to melt the raw material (powders). In order to guarantee a stable build process, the thermal energy has to flow away from the created melt-pool. Therefore, the support structure can act as a thermal heat sink, taking up this amount of energy.

Current support strategies, such as disclosed in US 5'595703, typically build only vertical support elements, such as thin walls, small volume elements, etc. In this way, the support structures may be standing on structures of the part itself. The removal of these support structures requires finishing operations of the upface-surfaces where the support structures are standing on the part. The single elements of existing volume support structures, as disclosed in US 5'595703, typically have the same cross section over nearly the whole height.

Summary of the invention

It is an object of the present invention to provide a part structure built by metal powder based added manufacturing, which part structure allows both efficient mechanical support of overhanging surfaces and efficient removal of heat during the build process.

To this end, the invention provides a part structure built by metal powder based added manufacturing, wherein a metal powder forming a metal powder bed resting on a base element is selectively fused in a layer-by-layer fashion such as by selective laser melting, selective electron beam melting or selective ion beam melting, and wherein the part structure comprises at least one individual part and an auxiliary structure attached to the at least one individual part and to the base element.

According to the invention, this auxiliary structure is a grid-like structure comprising different types of grid elements including beam elements and volume elements.

Preferably, the beam elements include beam elements differing in beam length and in beam cross section.

Preferably, at least some of said beam elements are arranged in a tree-like fashion forming a tree-like portion of the grid-like structure.

In a particularly preferred embodiment, the part structure comprises attachment elements arranged between the at least one individual part and the auxiliary structure and/or arranged between the base element and the auxiliary structure.

Preferably, the attachment elements comprise pre-defined breaking points.

Preferably, the volume elements within the auxiliary structure are located adjacent to the at least one individual part. In another preferred embodiment, attachment elements, preferably only attachment elements, are arranged between the at least one individual part and the auxiliary structure.

In yet another preferred embodiment, the density of grid-elements in the grid-like structure increases as one approaches the at least one individual part and, preferably, is greatest adjacent to the at least one individual part.

Preferably, the beam element diameter is less than 4 mm, the lower limit of the beam element diameter being determined by the metal type and particle size of the powder. The beam element may be a hollow, tube-like element and, preferably, may have a wall thickness of less than 45% of the beam element diameter, the lower limit of the wall thickness again being determined by the metal type and particle size of the powder. The cross-section of the beam elements may have a circular or polygonal shape.

In further preferred embodiment, the attachment elements comprise constrictions and/or porous regions pre-defining the breaking points.

Preferably, an angle formed between a part surface of the at least one individual part and the horizontal is between 0 and 60°. Preferably, the beam elements in the gridlike structure are arranged at angles greater than 45° to the horizontal.

Preferably, the above mentioned different types of grid-elements are arranged as a mechanical support and heat removal structure between an overhanging part surface and the horizontal.

The following technical and economical results are achieved by the part structure of the invention:

Technical results:

The support structures (auxiliary structures) act as a thermal sink for the surfaces that have to be built.

This result is achieved by the volume support structures in contrast to e.g. fine walls. The support structures are able to support different structural elements of a physical part. These elements can be classified as:

- Overhanging surfaces with an angle to the horizontal of 0° up to « 40°.

- Surfaces with an angle to the horizontal in the range of « 40° up to about 50°.

- Part edges with an angle to the horizontal of 0° up to « 60°.

- Internal holes with an axis to the horizontal in the range of 0° up to « 50° and diameters above * 5mm.

Easy removal of support structures is achieved by the attachment elements to the part and the base plate, respectively, being fine enough to be broken away manually. This is achieved by the special design of the attachment elements with predetermined breaking points.

In order to optimise the removal of the support structures from the base plate and the parts, the laser, during the build process, can be operated in continuous wave mode or in pulse mode. By adapting the pulse parameters (mean energy, pulse energy, pulse shape, frequency) the material parameters (hardness, density, heat

conductivity) can be designed according to the needs.

Economical results:

Easy removal of the part structure (part together auxiliary structure) from the base plate.

Easy removal of the support structures (auxiliary structures) from the part.

Few remaining structures of the original support on the parts / surfaces.

As far as possible, no support structures standing on upward facing surfaces

Good surface qualities.

Low volume of the support structures, thus minimising build time.

Brief description of the drawings

Fig. 1 indicates the situation of total energy introduced into the part structure and different types of energy flows within and out of the part structure.

Fig. 2 is a side view showing a first example of a part structure according to the invention. Fig. 3 is a side view showing a second example of a part structure according to the invention.

Fig. 4 is a side view showing a third example of a part structure according to the invention.

Fig. 5 is a perspective view showing a fourth example of a part structure according to the invention.

Fig. 6 is a side view showing a fifth example of a part structure according to the invention.

Fig. 7 is a side view showing a sixth example of a part structure according to the invention.

Fig. 8 is a side view showing a first detail of a part structure according to the invention.

Fig. 9 is a side view showing a second detail of a part structure according to the invention.

Detailed description of preferred embodiments of the invention

Preferably, volume elements serving as additional thermal heat sinks near the part surfaces / part structures are built ("part-near volume element"). The use of additional heat sinks (in addition to the heat sink function of the part being built) is optional, as for several types of part surfaces or part structures the supporting effect of grid-like structures itself can be sufficient.

The sizes of such part-near volume elements acting as heat sinks depend on the type, the orientation and the size of the part structures that need a support.

Relevant criteria for the design of the volume elements are the type of the part structures that need a support (part surfaces and edges with an angle to the horizontal, holes), the angle to the horizontal of the part structures or part surfaces, and the size of the part structures.

The design and the size of the part-near volume elements and support structures as well as their distances to the part could be estimated and optimized by the space- resolved solution of the heat equation.

Referring to the situation illustrated Fig. 1, we can write the following equation:

Q|_aser = QRadiation + Qpart + Qpowder + QlHeat sink + Qsupport structure

However, for practical reasons, standard design rules for the heat sinks for the different situations and part structures can be defined.

The heat sink structures can be described by several structural parameters, defining the shape / type of the heat sink, the size and the volume of the heat sink, or the distance of the heat sink to the part surface.

Thermal heat sinks can also be used for the stacking of parts. In this case, above an already built part, a horizontal volume plate is built, defining a new base plate for the more highly positioned next part, as shown in Fig. 7.

Below the heat sink, a tree-like grid structure holding the heat sink in place in the case where additional heat sinks are used, as shown in Figs. 2 and 5. This tree-like grid structure may also directly support part surfaces or part structures at regularly spaced or evenly distributed locations using specially designed attachment points, as shown in Fig. 4.

The size, shape and distribution of the single grid elements as well as the overall grid structure can be designed according to the need for a fast cooling down of the surface-near volume after scanning.

The grid-structure itself may consist of different types of grid-elements having different sizes / volumes. The grid shows - starting from the base plate - an evolutionary development regarding the shape, design and density of the beams, defining a tree-like grid structure, as shown in Fig 3.

The grid elements are standing only on the base plate and do not touch any part surface.

Exceptions:

Holes through the part with an angle to the horizontal of the axis < «45° and with a diameter > critical hole diameter, typically «7mm.

In the case where several parts are built upon another part, it may be necessary to use grid-structures standing on another part surface (stacking of parts), as shown in Figs. 6 and 7.

The density of the grid elements (beams) may change depending on the location within the grid. The closer to the part surface the narrower is the grid.

The shape of the beams can be a tube with a diameter <= 5 mm and a wall thickness starting from the smallest possible wall thickness up to 50% of the tube diameter (reaching a full cylinder), or a beam with polygonal cross-section with >= 3 edges, implemented as a tube or as a filled beam.

The support structures, consisting of volume- and grid-elements, can be built under different angles to the horizontal and are designed with respect to the technical requirements and restrictions of the build process (e.g. SLM). Typically, the angle to the horizontal of the structures will be > ¾45°.

The support structures can start to support the part structures at a specific height form the base plate, where the starting height depends on the orientation of the part surfaces that need a support.

Figs. 2 to 7 show some possible part structures built by metal powder based added manufacturing according to the invention. Fig. 2 is a side view showing a first example of a part structure 1 according to the invention. The part structure 1 comprises a part 2 with an overhanging part surface 2a, a grid-like auxiliary structure 4, 5 and attachment elements 6. The grid-like auxiliary structure 4, 5 comprises beam elements 4 of different lengths and volume elements 5 attached to them. The part 2 and the beam elements 4 are supported by and attached to a base plate 3. The volume elements 5 are attached to the beam elements 4 and to a part surface 2a of the part 2. Thus, part 2 is partially supported directly by the base element 3 and partially supported indirectly by the base element 3 via the grid-like auxiliary structure 4, 5.

The part surface 2a forms an angle of about 40° with respect to the horizontal plane H (base plate plane), thus constituting an overhanging part 2 with an auxiliary structure 4, 5 between the overhanging part surface 2a and the base plate 3. In addition to providing mechanical support for the overhanging part 2, the auxiliary structure 4, 5 provides conductive connections / pathways by its beam elements 4 for removing heat from the part 2 on the one hand and heat sinks by its volume elements 5 for receiving some of the heat removed from the part 2.

The beam elements 4 have different lengths and may be hollow, tube-like elements. Most of the beam elements extend along directions different from the vertical direction V. In contrast, the volume elements 5 are solid and may have different sizes. Each of the volume elements 5 has a large surface facing the part surface 2 and narrows towards an opposite end where the volume element 5 is attached to a beam element 4. The large surface of the volume element 5 is attached to the part surface 2a of the part 2 via a plurality of attachment elements 6. The narrow opposite end of the volume element 5 is attached to the beam element 4 via an attachment element 6.

The overhanging part surface 2a is support-free up to a height h form the horizontal plane H. Beyond that support-free height, the part 2 is mechanically supported and provided with an additional strong heat sink by the grid-like auxiliary structure 4, 5.

Fig. 3 is a side view showing a second example of a part structure 1 according to the invention. The part structure 1 comprises a part 2 with two overhanging part surfaces 2a, and a tree-like auxiliary structure 4 and attachment elements 6. The tree-like auxiliary structure 4 comprises only beam elements 4 of different lengths. In addition, volume elements 5 (see Fig. 2) could be included in the tree-like structure 4 in a manner similar to the example shown in Fig. 2. Only the beam elements 4 are supported by and attached to the base plate 3. Thus, part 2 is only supported indirectly by the base element 3 via the tree-like auxiliary structure 4.

Fig. 4 is a side view showing a third example of a part structure 1 according to the invention. This part structure 1 is similar to the part structure 1 shown in Fig. 2. The part structure 1 comprises a part 2 with an overhanging part surface 2a, a tree-like auxiliary structure 4 and attachment elements 6. The tree-like auxiliary structure 4 comprises only beam elements 4 of different lengths. The part 2 and the beam elements 4 are supported by and attached to the base plate 3. In addition, the beam elements 4 are attached to the part surface 2a of the part 2. Thus, part 2 is partially supported directly by the base element 3 and partially supported indirectly by the base element 3 via the tree-like auxiliary structure 4.

Again, as in Fig. 2, the overhanging part surface 2a is support-free up to a height h form the horizontal plane H. Beyond that support-free height, the part 2 is

mechanically supported and provided with an additional moderately strong heat sink by the tree-like auxiliary structure 4.

Fig. 5 is a perspective view showing a fourth example of a part structure 1 according to the invention. This part structure 1 is similar to the part structure 1 shown in Fig. 2. The part structure 1 comprises a part 2 with an overhanging part surface 2a, a gridlike auxiliary structure 4, 5 and attachment elements 6. The grid-like auxiliary structure 4, 5 comprises beam elements 4 of different lengths and one volume element 5 attached to them. The part 2 and the beam elements 4 are supported by and attached to a base plate 3. The volume element 5 is attached to the beam elements 4 and to a part edge 2b delimiting the part surface 2a of the part 2. Thus, part 2 is partially supported directly by the base element 3 and partially supported indirectly by the base element 3 via the grid-like auxiliary structure 4, 5. Fig. 6 is a side view showing a fifth example of a part structure 1 according to the invention. This part structure 1 allows two parts 2 to be arranged in a vertically spaced relationship, i.e. the two parts 2 can be arranged one on top of the other.

Each of the two parts 2 is supported by a tree-like auxiliary structure 4 comprising only beam elements 4 in a manner similar to the one shown in Fig. 3. In addition, some beam elements 4 extending between the two parts 2 provide additional mechanical stability and a thermal pathway between the two parts 2. Thus, the lower one of the two parts 2 may serve as a heat sink for the upper one of the two parts 2.

Fig. 7 is a side view showing a sixth example of a part structure 1 according to the invention. This part structure 1 is similar to the part structure 1 of Fig. 6. Again, this part structure 1 allows two parts 2 to be arranged in a vertically spaced relationship, i.e. the two parts 2 can be arranged one on top of the other.

Each of the two parts 2 is supported by a tree-like auxiliary structure 4 comprising only beam elements 4 in a manner similar to the one shown in Fig. 3. In addition, a second base plate 3 extending horizontally between the two parts 2 provides additional mechanical stability and an additional heat sink. A lower group of beam elements 4 extend between the lower one of the two parts 2 and the second base plate 3, and an upper group of beam elements 4 extend between the upper one of the two parts 2 and the second base plate 3, thus contributing to the additional mechanical stability and providing a thermal pathway between the two parts 2. Thus, the second base plate 3 and the lower one of the two parts 2 may serve as a heat sink for the upper one of the two parts 2.

Fig. 8 is a side view showing a first detail of a part structure 1 according to the invention. Three types of attachment elements 6 extending between a part 2 and a heat sink 5 are shown. The first type of attachment element 6 is a tetrahedron-like or pyramid-like element with one constriction 6a at the narrowing top of the tetrahedron / pyramid. The second type of attachment element 6 is a double-tetrahedron-like or double-pyramid-like element again with one constriction 6a where the narrowing tops / ends of the tetrahedron / pyramid meet. The third type of attachment element 6 is a cylinder-like element. Instead of a constriction, it may have a porous region somewhere along its cylinder axis. Both the constrictions 6a and the porous region constitute pre-defined breaking points of the attachment elements 6.

Fig. 9 is a side view showing a second detail of a part structure according to the invention. An angled attachment element 6' is shown which comprises a first attachment element portion 6b and a second attachment element portion 6c. The bigger attachment element portion 6b is attached to the base plate 3 via a first constriction 6a. The smaller attachment element portion 6c is angularly attached to the bigger attachment element portion 6b and is attached to the part 2 via a second constriction 6a.

The attachment elements 6 are specially designed structures, which are used to connect a heat sink volume element 5 or a mechanical support beam 4 with a part surface 2a or part edge 2b.

They are designed with regard to the following aspects:

There is a pre-defined breaking point at the attachment element structure that allows an easy removal of the support structure (heat sink, grid structure) from the part 2. The breaking points can be near the heat sink 5 or between the heat sink 5 and the part 2. As a result, after removal, the remaining material from the attachment element structure on the part surface 2a is as low as possible/thus reducing the finishing work needed.

The attachment structures already act as small heat sinks, able to take up more energy as a single, small wall or a small beam. Therefore, the attachment elements 6 need to be already a small volume element.

The number, shape, size and distribution of the attachment elements 6 on the part surfaces 2a are dependent on the orientation and the size of the part surfaces 2a or part edges 2b that need a support (angle to the horizontal).

The specially designed attachment structures can also be used to optimize the direct connection of the beams of the grid with the heat sink.

In the above part structures 1 , the laser parameters are adjusted for an easier removal from the base plate 3 and the part 2, respectively. Especially a pulsed laser beam with tailored parameters (frequency, pulse energy, pulse shape, mean power) can be used to adjust the hardness of the material, the porosity and the resulting heat conductivity of the part structures 1.