WO2013136096A1

WO2013136096A1 - Additive manufacturing

Info

Publication number: WO2013136096A1
Application number: PCT/GB2013/050687
Authority: WO
Inventors: Oana Roxana GHITA
Original assignee: University Of Exeter
Priority date: 2012-03-16
Filing date: 2013-03-18
Publication date: 2013-09-19

Abstract

An additive manufacturing method comprising depositing a product material to form a first product layer (5a), undertaking a fusing operation to form reinforcing regions (15a) within the first product layer, and depositing and undertaking a fusing operation on at least one further product layer (5b) to form a multilayered product integrally formed with reinforcing regions (15a, 15b).

Description

Additive Manufacturing

This invention relates to an additive manufacturing method and to a product manufactured thereby.

Additive manufacturing processes have been known for some time. Initially they were used primarily in the manufacture of one-off prototypes, although more recently the processes and techniques, and materials used, have been adapted to allow the manufacturing of final products.

A number of additive manufacturing processes are known. For example, one technique involves depositing a thin layer of material, in powder form, upon a support table and selectively fusing the parts of the layer which are to form part of the product. Subsequently, a further layer of material is deposited upon the previously deposited layer and the fusing process is repeated. These steps are repeated a number of times until a desired product has been formed.

Whilst this is one additive manufacturing technique, a number of other techniques are known, such as 3D printing, liquid vat stereo lithography, and layered material deposition processes.

These techniques all involve building up a final product in a series of layers. The material used can include a range of polymer materials, metals, graphite and wax-like materials.

As the final product is built up in the form of a series of layers, one disadvantage with the use of these techniques is that there is a risk of layers failing to satisfactorily bond or fuse to adjacent layers of the product, with the result that the final product may be of reduced strength. As a result, there are applications in which it may be thought that products manufactured using an additive manufacturing technique may be unsuitable for use.

In order to counter this, it is known to incorporate within the material reinforcing fibres. Typically, these fibres are of relatively short length as the use of longer fibres may interfere with the operation of the additive manufacturing process. Whilst the provision of such reinforcing fibres may serve to strengthen or reinforce a final product to some degree, the mechanisms by which the materials are deposited, in use, will tend to result in the fibres being approximately aligned in the direction in which the layer of material extends, rather than being arranged with a random orientation. As a result, the degree of reinforcement provided thereby is limited. In particular, reinforcement between layers is limited.

By way of example, where a powder bed manufacturing process is used, each material layer is typically deposited by the use of a wiper or roller to substantially uniformly spread the material to form a uniform thickness thin layer. The action of using a wiper or roller to distribute the material is thought to result in reinforcing fibres located within the material tending to extend in approximately the direction in which the roller or wiper is moved. It is an object of the invention to provide an additive manufacturing method whereby a product can be manufactured in which at least some of the disadvantages discussed hereinbefore are overcome or are of reduced effect.

According to the present invention there is provided an additive manufacturing method comprising depositing a product material to form a first product layer, undertaking a fusing operation to form reinforcing regions within the first product layer, and depositing and undertaking a fusing operation on at least one further product layer to form a multilayered product integrally formed with reinforcing regions. The reinforcing regions of adjacent layers may be bonded or fused to one another.

The product material may be of a type in which heating thereof to a first temperature, and subsequent cooling, results in the formation of regions of the layer with a first structure, and heating thereof to a second, higher temperature, and subsequent cooling thereof, results in the formation of regions of the layer with a second structure. The first and second structures may comprise different crystal structures and/or different super molecular orders. The first and second structures may both comprise crystalline or semicrystalline structures or, alternatively, the first structure may be amorphous whilst the second structure is crystalline or semicrystalline. It will be appreciated that by appropriate control over the melting or sintering operations, the temperatures to which various of parts of the layer are exposed can be controlled with the result that material with the first structure is present in some parts of the layer whilst material with the second structure is present elsewhere.

Material of one of the first and second structures may form the majority of the material of the final product, the material of the other of the structures forming reinforcing regions extending within the material. If desired, the reinforcing regions formed in one of the layers may bond with the reinforcing regions of adjacent layers, thereby strengthening the bond between the adjacent layers, and so enhancing the strength of the overall product.

It will be appreciated that by appropriate control over the melting or sintering process, the reinforcing regions may be formed where desired within the product, thus some parts of the product may, if desired, contain more reinforcing regions that other. Furthermore, the directions in which the reinforcement formed by the reinforcing regions extends may be controlled as desired.

The different regions may be formed by controlling a laser used to perform the fusing operation in such a manner that parts of the layer are heated to a different temperature to other parts of the layer. This may be achieved, by way of example, by varying the intensity or power of the laser, or by controlling the manner in which the laser output is scanned over the laser, for example reducing the scan speed in areas to be heated to a higher temperature, increasing the scan speed where a lower temperature is required. Alternatively, repeated heating may be used to raise the temperature of parts of the layer.

In an alternative arrangement, the product material may comprise a substantially uniform blend of a material with a relatively high melting point and a material with a relatively low melting point, the fusing operation heating the product material to a temperature sufficiently high to cause melting of the low melting point material but low enough to cause sintering or fusing of the high melting point material, but avoiding complete melting thereof. It is thought that the lower melting point material within a matrix of higher melting point material serves to reinforce the higher melting point material, thus forming reinforcing regions within the product. The materials are preferably polymers, conveniently selected from the same polymer family, for example they may be selected from PEK, PEEK and PEKK (all poly aryl ether ketones) or from PA6, PA6.6, PA12 or PA11 (all polyamides).

In one arrangement, the blend may comprise a blend of PEEK and PEK. In such an arrangement, the PEK forms the relatively high melting point material, having a melting point of 365°C, the PEEK with a melting point of 335°C forming the relatively low melting point material.

Such arrangements provide good reinforcement and good bonding between the matrix material and the reinforcing regions.

The additive manufacturing process is conveniently a powder bed process. However, this need not always be the case and the invention may also applicable to arrangements in which other additive manufacturing processes are used.

The invention further relates to an additive manufacturing method in which a material is deposited in layers, and a reinforcement extends across a boundary between adjacent layers. The reinforcement may take the form of a reinforcing region of one layer bonded to a reinforcing region of an adjacent layer.

The invention further relates to a product manufactured according to the method outlined hereinbefore.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 illustrates the manufacture of a product in accordance with one embodiment of the invention;

Figures 2 and 3 illustrate variants to the arrangement of Figure 1 ;

Figure 4 is a view illustrating an alternative arrangement; and Figure 5 is a graph illustrating the effect of increasing heating.

Referring firstly to Figure 1 , a powder bed type additive manufacturing apparatus is illustrated. The apparatus comprises a support table 20 which is capable of being incrementally raised and lowered. A delivery device 30 is arranged to deliver uniform thickness layers 5a, 5b of powder material to the table 20, when desired, the thickness of each layer 5a, 5b being determined by the size of the increments by which the table 20 can be lowered. A laser-based heating device 40 is operable to heat the material of the layers 5a, 5b. The heating operation is undertaken by scanning the laser beam output from the device 40 over selected parts of each layer 5a, 5b to raise the temperature of the selected parts of each layer 5a, 5b. The manner in which the laser beam output is scanned could involve physically moving the laser relative to the table 20. However, it will generally be more convenient for the laser and table 20 to both be fixed during the scanning operation, and for the laser beam output to be scanned over the layers 5a, 5b by adjustment of the positions of suitable optical devices such as mirrors or other reflectors.

In use, the table 20 initially occupies a raised position, and the delivery device 30 is operated to deliver the first layer 5a of powder material thereto. The powder is of a material having a number of possible crystal structures, heating of the powder to a first, relatively low temperature, and subsequent cooling resulting in the material adopting a first crystal structure, and heating thereof to a second, higher temperature, and subsequent cooling, resulting in the material adopting a second crystal structure. The material may comprise a suitable polymer or thermoplastic material such as nylon.

The heating device 40 is operated to heat selected parts 10a, 15a of the layer 5a to raise the temperature of the material thereof, melting or partially melting the material and thereby allowing the powder material thereof to fuse to form a solid. Parts 17a of the layer 5a which will not form part of the final product are not significantly heated. The parts 15a are heated to a higher temperature than the parts 10a with the result that the crystal structure of the parts 15a in the end product is different to that of the parts 10a, the parts 15a forming reinforcing regions 15 extending through the parts 10a.

The manner in which the heating device 40 is controlled to achieve selective heating of just the desired parts of the layer 5a, and to control the temperature in such a manner as to result in the formation of the different structures may take a range of forms. For example, during the heating process the laser output power may be varied, increasing the power when the parts 15a are being heated, and reducing it when the parts 10a are being heated. Alternatively, the intensity may be controlled to achieve the desired heating pattern. A further alternative may be to keep the power output and intensity substantially constant and instead vary the scan speed such that the regions 15a are irradiated for longer than the regions 10a. Furthermore, the selected heating pattern could be achieved by repeatedly heating the regions where a relatively high temperature is required. The various techniques may be used in combination, if required. Regardless as to how the different temperatures are achieved, the device 40 is conveniently computer controlled, both in relation to the selection of which parts of each layer to heat and in relation to the temperature to heat each region to. Conveniently, a single computer program undertakes all of this control. Figure 5 illustrates that the use of increased laser power (and hence increased temperature if the other parameters are held constant) results in the formation of materials of enhanced resilience, being capable of withstanding increased loads, and hence undergoing increased elongation, prior to failure. Where the powder material is nylon, the process may result in the formation of, for example, regions 15a of nylon-6 and regions 10a of nylon-6,6.

After heating the various parts of the layer 5a to the desired temperatures, the table 20 is lowered by an increment and a fresh powder layer 5b is deposited over the layer 5a by the device 30. The heating operation is then repeated, heating the selected parts of the layer 5b to the desired temperatures to form the regions 10b, 15b, 17b. The process of lowering the table 20, applying powder layers thereto and heating the selected parts of the powder layers is repeated until the complete product has been built up, at which point the product can be removed from the table 20 and cleaned to remove the powder from the unheated regions 17 therefrom.

In the arrangement shown in Figure 1 , the regions 15a, 15b form the reinforcing regions 15 in the final product, and they are orientated such that the regions 15a can bond to the regions 15b, forming continuous reinforcing regions 15 extending across the boundaries between the layers, enhancing the strength of the final product. It will be appreciated that the number and density of the reinforcing regions 15 can be selected by appropriate control over the heating operation.

Whilst in the arrangement of Figure 1 the reinforcing regions 15 each extend perpendicularly to the table 20, this need not always be the case. By appropriate selection of the parts of the layers 5a, 5b which will form the regions 15a, 15b, it will be appreciated that the reinforcing regions 15 may be angled relative to the table (for example as shown in Figure 2), or may extend parallel to the table 20 (for example as shown in Figure 3). It will be appreciated that these options are merely examples and that a wide range of alternatives are possible without departing from the scope of the invention. Furthermore, there is no need for all of the reinforcing regions 15 to extend in the same direction as one another, or to be of a uniform size. It is envisaged that the reinforcing regions 15 may take the form of threads or fibres extending through the final product, but this need not be the case and they may take a wide range of other forms.

Figure 4 illustrates an alternative to the arrangements described hereinbefore. In the arrangement of Figure 4, like those of Figures 1 to 3, layers 5a, 5b of a powder material are deposited, in turn, upon a table 20 by a device 30, and selected parts thereof are heated by a device 40. Unlike the arrangements of Figures 1 to 3, however, the powder material takes the form of a blend of a material having a relatively high melting point and a material having a relatively low melting point. By way of example, the relatively high melting point material may comprise PEK with a melting point of 365°C, and the relatively low melting point material may comprise PEEK with a melting point of 335°C.

Whilst PEEK and PEK are used in this arrangement, it will be appreciated that other materials could be used. The materials are preferably polymers, conveniently selected from the same polymer family as one another. For example, they could all be poly aryl ether ketones (such as PEEK, PEK and PEKK) or polyamides (such as PA6, PA6.6, PA12 or PA11).

During the heating operation, the device 40 is controlled in such a manner that the parts 10a, 10b of each layer 5a, 5b which are to form part of the final product are heated, whilst the parts 17a, 17b thereof which are not to form part of the final product are not heated. The parts 10a, 10b are heated substantially uniformly to a temperature sufficiently high to cause melting of the relatively low melting point material, but sufficiently low that the relatively high melting point material is not melted but rather sinters or fuses to form the desired product. The melting of the relatively low melting point material results in enhanced binding of the particles of the relatively high melting point material to one another and so serves to form reinforced regions 15 within the product, enhancing the strength thereof. Relatively little shrinkage occurs as only part of the material is fully molten. The end product can be of relatively low density and thus light in weight. Depending upon material selection, recycling of the end product may be relatively simple.

It will be appreciated that in the arrangement of Figure 4, provided the powder blend is thoroughly mixed, and the heating operation achieves uniform heating of the desired parts of each layer 5, the reinforced regions 15 will be substantially uniformly distributed within the final product.

In any of the arrangements described hereinbefore, recycling of the products may be relatively straightforward as there is no need to remove or process reinforcing fibres such as carbon fibres or glass fibres.

In the arrangements described hereinbefore, where the reinforcing regions are of crystalline or semicrystalline form, it will be appreciated that the reinforcing regions are of relatively high Young's modulus and thus provide a strong, resilient reinforcement to the product.

Whilst the manufacturing methods described hereinbefore are all powder bed type additive manufacturing methods, it will be appreciated that the invention may be applied to other forms of additive manufacturing process including, for example, 3D printing techniques, material deposition techniques or liquid vat stereo lithography techniques in which deposited materials may be heated during or after deposition to achieve the formation of reinforcing regions therein. Different heating techniques, including electron beam melting, may be used if desired. Furthermore, whilst certain specific materials have been mentioned hereinbefore, it will be appreciated that these are merely examples and that the techniques may be used with a range of other materials. Whilst specific embodiments of the invention are described hereinbefore, it will be appreciated that a wide range of modifications and alterations may be made thereto without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS:

1. An additive manufacturing method comprising depositing a product material to form a first product layer, undertaking a fusing operation to form reinforcing regions within the first product layer, and depositing and undertaking a fusing operation on at least one further product layer to form a multilayered product integrally formed with reinforcing regions.

2. A method according to Claim 1 , where the product material is of a type in which heating thereof to a first temperature, and subsequent cooling, results in the formation of regions of the layer with a first structure, and heating thereof to a second, higher temperature, and subsequent cooling thereof, results in the formation of regions of the layer with a second structure.

3. A method according to Claim 2, wherein the first and second structures comprise different crystal structures and/or different super molecular orders.

4. A method according to Claim 3, wherein the first and second structures both comprise crystalline or semicrystalline structures.

5. A method according to Claim 3, wherein the first structure is an amorphous form and the second structure is crystalline or semicrystalline.

6. A method according to any of Claims 2 to 5, wherein material of one of the first and second structures forms the majority of the material of the final product, the material of the other of the structures forming the reinforcing regions extending within the material.

7. A method according to any of the preceding claims, wherein the reinforcing regions within one of the layers bond with the reinforcing regions of adjacent layers.

8. A method according to any of the preceding claims, wherein the different regions are formed by controlling a laser used to perform the fusing operation in such a manner that parts of the layer are heated to a different temperature to other parts of the layer.

9. A method according to Claim 8, wherein the laser is controlled to vary the intensity or power thereof, or to varying scanning speed, dwell time and/or repetition to control heating of the regions of each layer.

10. A method according to Claim 1 , wherein the product material comprises a substantially uniform blend of a material with a relatively high melting point and a material with a relatively low melting point, the fusing operation heating the product material to a temperature sufficiently high to cause melting of the low melting point material but low enough to cause fusing of the high melting point material, but avoiding complete melting thereof.

1 1. A method according to any of the preceding claims, wherein the method is a powder bed process.

12. An additive manufacturing method in which a material is deposited in layers, and a reinforcement extends across a boundary between adjacent layers.

13. A method according to Claim 12, wherein the reinforcement takes the form of a reinforcing region of one layer bonded to a reinforcing region of an adjacent layer.

14. A product manufactured according to the method of any of the preceding claims.