Patent Application
20180272604
This application is based upon and claims the benefit of priority from British Patent Application No. 1704676.4 filed 24 Mar. 2017, the entire contents of which are incorporated by reference.
The present disclosure relates to additive layer manufacturing methods and apparatus. More particularly, the present disclosure concerns a re-coater device (sometimes known as a “doctor blade”) for use in an additive layer manufacturing method.
Additive layer manufacturing (ALM) methods are known. Broadly, such methods involve selected regions within a fluid mass of material being processed across a number of sequential layers to cause local solidification of the material. The sequential layers are built up to form a three dimensional solid object within the fluid mass.
Additive layer manufacturing methods can be broadly divided into two groups. In a first group, material is deposited sequentially in patterned layers, the pattern of each layer representing a two dimensional cross section of a three dimensional shape of an object. As each layer is deposited atop a previous layer, a three dimensional object is built. Examples of this group of methods include; direct energy deposition (where focussed thermal energy is used to fuse materials as they are being deposited), material extrusion (where an extrusion head moves in a pattern selectively dispensing material through an orifice as it travels) and sheet lamination (where sheets of material already defining a two-dimensional pattern are bonded in sequence to build up the three dimensional object.)
In the second group, the process starts with a bulk mass which may, for example, be a bed of powdered material such as a ceramic, a ferrous alloy or a non-ferrous alloy, or a vat of liquid typically comprising a photopolymer. Regions within the mass are selectively treated, for example by melting, sintering, photochemical reaction or interaction with a chemical bonding agent, to solidify. However unlike with the first group, the untreated material remains in a layer as the next layer is formed. Surplus (untreated) material may be removed when the three dimensional build is complete, through it is also known for surplus material sometimes to be contained within cavities of the three-dimensional object.
Within the second group of ALM methods, a layer of untreated material may be deposited onto an already treated layer by dispersal from a hopper or by dipping the treated layer below the surface of the untreated material. For the three-dimensional shape to be properly controlled, the thickness and consistency of thickness of each layer to be treated must be carefully controlled. This is conventionally achieved by positioning a top surface a fixed distance from the tip of a “doctor blade” which is then skimmed across a top surface of the material to level out the top surface.
Various forms of doctor blade are known. In its simplest form the doctor blade is a straight-edged, rigid blade which is skimmed across the material surface gradually pushing away any excess from the newly added material layer. In a more advanced form, the straight edged, rigid blade may comprise a hollow through which a vacuum can be applied. The blade is positioned a small distance from the required top surface level. Rather than push material away, such a device sucks excess material into the hollow as it passes across the surface. In regions where there is insufficient material remaining at the top surface, the vacuum effect is arrested and material is drawn from the hollow back onto the surface. Where the material to be treated is viscous, there may be a waiting time between recoats while the viscous top surface drains and settles. In some cases highly viscous materials may not drain and settle resulting in the top surface rising above the desired height and a consequent, detrimental effect on the quality of the component.
The Applicant's previously filed European Patent Application no. EP17150873 describes a doctor blade which is configured to flex as it passes over a surface layer.
In accordance with the present disclosure there is provided an additive layer manufacturing apparatus comprising a doctor blade having a tip which, in use, is arranged proximal to a material layer to be recoated during an additive layer manufacturing method, the doctor blade having a cavity with an inlet and an outlet, the outlet located at the tip and the inlet connectable to an air supply whereby air can be directed through the cavity to the outlet and onto the material layer.
The air supply may be a compressed air supply. The apparatus may further include a flow control device adjustable to vary the velocity and or pressure of the directed air supply. The apparatus may further include a temperature control device for adjusting and or maintaining the temperature of the compressed air supply. The blade may include features downstream of the outlet configured to control and/or direct air exiting the outlet. Without limitation, such features may include a grid, one or more nozzles, differently directed channels or the like. In an option, the blade tip may be tapered to provide a converging or diverging outlet.
In some embodiments, multiple doctor blades are provided. In an option, individual blades of the multiple doctor blades may have a different configuration to others of the multiple doctor blades. Optionally multiple blades may have the same structure but air supply to each is individually controllable. For example, individual blades may have individual supply lines and any given supply line may include a flow control device which is adjustable independently of a flow control device in another supply line.
The doctor blade may be flexible. The doctor blade may have an associated flexible element arranged to follow the tip of the doctor blade across the material layer to be recoated. The flexible doctor blade or flexible element may be configured to flex when drawn across the material layer in a first direction but inflexible when drawn across the material layer in a second direction which is opposite to the first direction.
The apparatus may include a build platform in an X-Y plane and an indexing device for moving the blade in a direction Z, orthogonal to the X-Y plane. The apparatus may include a build platform in an X-Y plane and an indexing device for moving the build platform in a direction Z, orthogonal to the X-Y plane.
In some embodiments the additive layer manufacturing apparatus may include a vat for containing a liquid material from which a 3 dimensional product is to be built and a device for initiating polymerisation of molecules in the liquid material. The device for initiating polymerisation may comprise a focusable light source in the ultraviolet to visible region of the electromagnetic spectrum and a transport mechanism for moving the source across a section of the liquid.
In other embodiments the additive layer manufacturing apparatus may include a container for a powdered material from which a 3 dimensional product is to be built and a device for initiating fusion of the powder. The device for initiating fusion of the powder may, for example, be a laser or an electron beam.
Embodiments of the present disclosure will now be described with reference to the accompanying drawings in which:
As can be seen in
The doctor blade 7 can be swept across the surface 6 to level the mound 8, however, when the build is only a few layers thick, this sweeping motion has an associated risk of stressing the build with a consequence of possible structural damage to the body.
One solution to the problem of stresses resulting from the doctor blade is the vacuum doctor blade. An example is illustrated in
Turning to
Again, where the resin is highly viscous, there may be a considerable delay in the manufacture while the resin fills the dip 40.
As the blade passes over the mound, the air exiting the outlet forcibly spreads the mound 58 so as to smooth out the resin surface 56 into a flat surface more quickly than if the mound 58 were left to flow uninfluenced. This is illustrated in
Whilst the embodiment is directed to dissemination of a resin in a mound, it is to be appreciated that the doctor blade 57 and associated air supply 53 may also be used to fill efficiently a dip in a resin surface.
Whilst the embodiments are described in the context of vat photo-polymerisation based additive layer manufacturing methods, the apparatus of the present disclosure may be applied to other additive layer manufacturing methods, for example powder bed ALM.
It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the invention as defined by the accompanying claims. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1704676.4 | Mar 2017 | GB | national |
