GB2617595A

GB2617595A - Adaptive lifting of build platform for additive manufacturing

Info

Publication number: GB2617595A
Application number: GB2205500.8A
Authority: GB
Inventors: Robert Catt Steven
Original assignee: Thales Holdings UK PLC
Current assignee: Thales Holdings UK PLC
Priority date: 2022-04-13
Filing date: 2022-04-13
Publication date: 2023-10-18
Also published as: GB202205500D0

Abstract

An additive manufacturing method and device which provide a rotation between a build platform 110 and window 130 to reduce the vacuum forces imparted on a product 170 during manufacture; this reduces the likelihood of build failure and allows a wider variety of product designs to be manufactured. An additive manufacturing apparatus comprises a build platform for supporting a product being manufactured, a window configured to allow light to pass, a light source 160 for selectively curing resin located between the build platform and the window to form cured resin connected to the build platform; and one or more actuators 114 configured to adjust the separation and to provide relative rotation between the build platform and the window. The relative rotation may be about at least one axis that runs parallel to the window and/or build platform to tilt or pivot the platform/window. A computer implemented method for controlling an additive manufacturing process is further provided.

Description

Adaptive Lifting of Build Platform for Additive Manufacturing TECHNICAL FIELD The present disclosure relates to additive manufacturing methods and devices. In particular, but without limitation, this disclosure relates to improved vat photopolymerization methods and devices.

BACKGROUND

Additive manufacturing is a manufacturing process where a product is manufactured by adding material, usually layer by layer, over time. This is in contrast to subtractive manufacturing where a product may be manufactured by removing material from solid raw material (e.g. through milling, drilling, etc.) Vat photopolymerisation is a group of additive manufacturing processes where a liquid feedstock (typically a UV curable resin) within a vat is selectively cured via an energy source (typically a laser or an array of LEDs). The energy source is used to selectively cure areas of the feedstock to form a part (or product).

There are a number of different methods of vat photopolymerisation. These methods can generally be split into two groups. In a first group the energy source is located above the vat and is focused on the top surface (air/resin boundary) of the resin (e.g. stereolithography, SLA). In a second group, the energy source is located below or to the side of the vat and the energy source passes through a "window" (or "membrane") in the container holding the resin before curing a selected area (e.g. digital light processing, DLP).

After each layer has been cured the build platform upon which the product is secured is lifted away from the window to allow additional resin to flow into the void that is created so that a further layer can be cured.

SUMMARY

Embodiments described herein provide an improved additive manufacturing method and an improved additive manufacturing device which provide a rotation between a build platform and window to reduce the vacuum forces imparted on a product during manufacture. This reduces the likelihood of build failure and allows a wider variety of product designs to be manufactured.

According to a first aspect there is provided a computer-implemented method for controlling an additive manufacturing process. The additive manufacturing apparatus comprises a build platform for supporting a product being additively manufactured from resin within a curing region of the additive manufacturing apparatus, a window positioned on an opposite side of the curing region from the build platform, a light source configured to selectively cure resin within the curing region through the window for additively manufacturing the product, and one or more actuators configured to adjust a separation between the build platform and the window and to provide relative rotation between the build platform and the window. The method comprising controlling the additive manufacturing apparatus over one or more curing steps. Each curing step comprises: curing a selected region of resin between the build platform and the window using the light source when the build platform and window are at a first orientation relative to each other to form cured resin connected to the build platform; rotating at least one of the window or the build platform away from the other to open a gap between at least a peripheral section of the cured resin and the window to allow resin to begin to flow between the window and the cured resin; and moving at least one of the window or the build platform to increase a separation between the window and the cured section of resin and return the window and build platform to the first orientation.

By rotating at least one of the build platform or the window away from the other, a seal between the build platform and window may be broken whilst imparting a reduced force to the cured resin relative to alternative methods that do not introduce such a rotation.

Accordingly, the rotation step reduces the forces exerted on the cured resin (the product) during manufacture, reducing the likelihood of build failure.

At least one of the build platform or window may be rotated. This means that the build platform may be rotated, the window may be rotated, or both the build platform and window may be rotated. Similarly, at least one of the build platform or window may be moved (e.g. moved linearly) to increase separation. This means that the build platform may be moved, the window may be moved, or both the build platform and window may be moved. Component or set of components (e.g. the build platform and/or window) that are rotated need not be the same as the component or set of components that are moved to increase the separation.

Increasing separation may include linear motion (e.g. along a direction perpendicular to the window and/or build platform). Relative rotation may be about at least one axis that does not run perpendicular to the window or build platform (e.g. that runs parallel to the window or build platform). The light for curing need not be within the visible range of light. That is, the light may be any form of electromagnetic radiation (e.g. ultraviolet light or infrared light). The first orientation may be the window and build platform being parallel to each other.

Moving the at least one of the window or the build platform may comprise: performing a first movement to increase the separation between the window and the cured resin to a first separation to allow resin to flow between the window and the cured resin; reorienting the window and build platform to return the window and build platform to the first orientation; and performing a second movement to reduce the separation between the window and the cured resin to a second separation, wherein the second separation is smaller than the first separation.

The reorienting of the window and build platform may be performed during one or both of the first movement and the second movement. Alternatively, the reorienting of the window may be performed before or after the first movement.

The one or more actuators may be configured to provide relative rotation between the build platform and window about at least one axis that runs parallel to one or both of the window or the build platform when in the first orientation (e.g. when parallel to each other).

The one or more actuators may be configured to provide relative rotation between the build platform and window about a plurality of axes that run parallel to one or both of the window or the build platform when in the first orientation. The method may comprise selecting an axis from the plurality of axes for use in rotating at least one of the window or the build platform away from the other based on a shape of the cured resin. An axis may be selected for each curing step. The axis may be selected to maximise a distance between a pivot point of rotation and the peripheral section of the cured resin during rotation.

The build platform and window may be parallel to each other in the first orientation. The first orientation may be independent of separation between the build platform and window and relative rotation of the build platform and window about an axis running perpendicular to the build platform and/or window.

The speed of rotation may be increased as that at least one of the window or the build platform is rotated away from the other.

The at least one of the window or build platform may be rotated away from the other over a plurality of rotation steps. A step size may increase over the plurality of rotation steps. Alternatively or in addition, each rotation step may be at least partially reciprocal such that it includes an inverse rotation along at least a portion of the rotation step.

The one or more actuators may be controlled to limit a force applied to the cured resin during rotation and/or movement to be less than a maximum allowable force for the cured resin. The maximum allowable force for the cured resin may be based on one or more of: a shape of the cured resin, mechanical properties of the cured resin and mechanical properties of the resin.

For brevity, in the context of this invention the use of the term "cured resin" at a stage during the manufacture of a part relates to resin in its cured and partially cured state.

The use of the term cured resin in relation to finished/final parts relates to a resin that has also typically been exposed to an additional curing cycle, this state is also known as "fully cured".

The mechanical properties of the resin may relate to uncured resin and may include viscosity and density of the uncured resin. The shape of the cured resin may include a cross-section of an interface between the cured resin and the build platform, a cross-section of an interface between the cured resin and the window and/or a cross-section of a narrowest part of the cured resin.

According to a further aspect there is provided an additive manufacturing apparatus comprising: a build platform for supporting a product being additively manufactured; a window configured to allow light to pass; a light source for selectively curing resin located between the build platform and the window through the window to form cured resin connected to the build platform; and one or more actuators. The one or more actuators are configured to adjust a separation between the build platform and the window and to provide relative rotation between the build platform and the window such that at least one of the window or the build platform can be rotated away from the other by the one or more actuators to open a gap between at least a peripheral section of the cured resin and the window to allow resin to begin to flow between the window and cured resin.

The one or more actuators may comprise: at least one actuator configured to move one of the build platform or the window to provide relative motion between the build platform and the window along a direction perpendicular to at least one of the window or the build platform; and at least one rotary actuator configured to rotate one of the build platform or the window to provide relative rotation between the build platform and window about an axis parallel to at least one of the window or the build platform.

The one or more actuators may comprise a plurality of linear actuators that are pivotally mounted to one of the window and the build plate to allow for both linear and rotational movement. Alternatively, the one or more actuators may comprise at least one linear actuator configured to adjust the separation between build platform and the window and at least one rotary actuator configured to provide relative rotation between the build platform and the window.

The additive manufacturing apparatus may comprise one or more processors configured to control the additive manufacturing apparatus in order to perform any of the methods described herein.

According to an embodiment there is provided a computer program comprising computer executable instructions that, when executed by a processor, cause the processor to control an additive manufacturing apparatus according to any of the methods described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Arrangements of the present invention will be understood and appreciated more fully from the following detailed description, made by way of example only and taken in conjunction with drawings in which: FIG. 1 shows a schematic diagram of an additive manufacturing apparatus; FIG. 2 is a schematic diagram of an additive manufacturing apparatus according to an embodiment at a first step in a manufacturing process; FIG. 3 is a schematic diagram of the additive manufacturing apparatus of FIG. 2 in a second step in the manufacturing process; FIG. 4 is a schematic diagram of the additive manufacturing apparatus of FIG. 2 in a third step in the manufacturing process; FIG. 5 is a schematic diagram of the additive manufacturing apparatus of FIG. 2 in a fourth step in the manufacturing process; FIG. 6 is a schematic diagram of the additive manufacturing apparatus 100 of FIG. 2 in a fifth step in the manufacturing process; FIG. 7 shows an additive manufacturing method according to an embodiment; FIG. 8 shows a further method of additive manufacturing according to an embodiment; and FIG. 9 shows a computing device for controlling an additive manufacturing device according to an embodiment.

DETAILED DESCRIPTION

Vat polymerization involves a part being manufactured over a number of curing steps. One method of vat photopolymerization locates a light source (a source of electromagnetic radiation, such as ultraviolet light) below or to the side of the part and emits light through a window within the vat.

Where the resin is cured through a window, often an engineer or user has to pay close attention during the manufacturing process to ensure that the resin is cured in the correct place, such that it does not adhere/bond to the window and such that the build platform can be lifted without causing part failure.

After each curing step, the part is moved away from the window to allow additional resin to flow into the gap between the part and the window to allow another curing step to be performed. Build failures (e.g. interlayer adhesion or build platform adhesion failures) often occur due to the reaction loads placed on the part during this lifting step.

The embodiments described herein adapt the process of moving the build platform (or window) to reduce reaction loads on the part to reduce the likelihood of build failures.

This also enables more viscous resins/mixes to be used and a wider variety of designs of parts to be manufactured (e.g. designs with larger cross sections).

FIG. 1 is a schematic diagram of an additive manufacturing apparatus 100. A build platform 110 is positioned above a housing 120. A window 130 is positioned within the housing 120, opposite to the build platform 110. The window 130 is parallel to the build platform 110, with both being positioned parallel to the horizontal plane, in use. The housing 120 is open on an upper side such that the window 130 and upper side of the housing define an open container (a vat) for containing resin 140. The upper opening in the vat is larger than the cross-section of the build platform 110 such that the build platform 110 may be moved in and out of the vat along a direction perpendicular to the build platform 110 (a vertical direction) via one or more linear actuators.

A light source 160 is positioned on the opposite side of the window to the resin 140/build platform 110. The light source 160 may be any appropriate source of electromagnetic radiation, such as a laser or a light projector, for curing the resin 140. The light emitted by the light source need not be visible light, and may relate to any frequency of electromagnetic radiation.

When manufacturing a product or part 170, the build platform 110 is lowered into the resin 140. A space is left between the bottom of the part 170 (or the build platform 110, where no part 170 is present) to maintain a polymerization zone 180 containing uncured resin. The energy source 160 is then directed to selectively cure a region of the polymerisation zone 180 to add a layer to the product 170.

The product 170 may be connected to the build platform 110 via supports 190. In addition, or alternatively, the product 170 may be directly connected to the build platform via the adhesion of the cured resin. Any supports 190 that are formed are also formed from cured resin in a similar manner to the product 170.

After each curing step, the build platform is moved away from the window 130 to allow additional resin to flow (or be mechanically agitated) into the gap between the part 170 and the window 130 ready for curing at the next step. In this manner, a product 170 is built up in layers through multiple steps of curing.

The selected areas that are cured at each curing step are defined by an electronic file which defines the shape of the slices/layers that are cured. The whole process is controlled by a processor (not shown) within the additive manufacturing device. The details of the software and computer processing is discussed further below.

Accordingly, a product can be built up, layer by layer, through multiple curing steps, where the build platform is moved linearly away from the window after each curing step.

Having said this, there are a number of problems that can occur when moving the build platform between curing steps.

Firstly, a vacuum effect can result in the part being broken or separated from the build platform. The resins used in these processes are reasonably viscous (e.g. in comparison to water). This, in combination with the shape of the product being manufactured (e.g. build layer/void aspect ratio) can result in significant forces being exerted on the part as the build platform is moved.

The layer thickness of each build layer can be very small, typically 5-60pm. The build layer is parallel to the window and, with many processes, very close to the window, typically equal or less than the layer thickness. Hence, the initial gap that the resin needs to flow black into can be very thin. As the build layer is a cross section of the part being made, which changes with each part/design/orientation, many designs require printing a large cross sectional area (when compared to the layer height), which results in a void being produced with a wide, long and very thin aspect ratio.

The void described above needs to be refilled with liquid resin (which can be viscose) such that further build layers can be cured. This can be achieved by lifting/pulling the build platform away from the window to allow resin to refill the gap, and then moving the build platform back towards the window to locate the part ready for a further curing stage (e.g. so that the part is separated from the window by a suitable distance ready for the next layer to be cured). In this case, the axis of travel is perpendicular to the window/build platform. This lifting/pulling results in a local area of low pressure/vacuum that begins the pull of the resin into this void.

The combination of the rate/magnitude of perpendicular pull, the narrow aspect ratio and the viscosity of the resin dictates the magnitude of this low pressure, and hence also the magnitude of the forces applied to the newly printed layers between this void and the build platform.

The strength of the above vacuum effect can be influenced by the composition of the resin (e.g. the presence of fillers, powders or particles). Some applications/materials suspend fillers, powers or particles in the resin. These fillers further increase the viscosity of the resin. These fillers can also settle within the vat, further restricting the initial flow of resin onto the void. These factors increase the vacuum effect applied on the part being manufactured.

The manufacturing process can fail in a variety of ways, including build platform adhesion failure, interlayer adhesion failure or structural failure in the part being manufactured.

Build platform adhesion failure results from a failure between the part and the build platform. Additive manufacturing processes are "additive" rather than "subtractive". Hence, the initial layers that are deposited are adhered to a substrate of some kind (in this case, the build platform or a substrate mounted onto the build platform). The level of achievable or tailored adherence required depends on a number of factors (e.g. the removal method, the cross-section of the part being adhered to the substrate, whether the substrate will become part of the final product, whether the substrate is to be reused, achievable bond strength, etc.). Build platform adhesion failures occur where the part is separated (e.g. delaminated) from the substrate. This can occur due to one or more factors (e.g. vacuum effect, part shrinkage, etc.) Interlayer adhesion failure occurs when different cured layers within the part separate from each other. This is similar to build platform adhesion, but in this instance the part material is present on both sides of this interface. The cross section of a given bond area changes based on the design. Accordingly, the likelihood of interlayer adhesion failure can depend on the cross-section of the product (e.g. a minimum cross section along its height). Interlayer adhesion failure is also based on the bond strength between layers (e.g. based on the resin being used and the method of curing).

More general structural failures in the product may also occur. Vat photopolymerization is able to produce very complex and intricate designs. These designs can vary in cross section with thinner lattice structures supporting larger cross sections later in the build. Where this is the case for a design, a build failure can occur through the design breaking at a structurally weak section (e.g. a point with a narrow cross-section).

All of these build failures can be caused by strong vacuum forces applied as the build platform is moved linearly away from the window.

Build failures can be overcome by limiting design freedoms and limiting the cross section of the parts that can be successfully printed via these processes. This is acceptable for some general applications, but is not always possible, depending on the specific requirements of the product. Some more complicated applications require printing features that contain large aspect ratios and/or printing with highly viscous resins (e.g. resins that are also filled with a powder). These factors can lead to numerous Interlayer adhesion or build platform adhesion failures.

Given the above, there is a need for an improved additive manufacturing method that is able to reduce the forces imparted on a part being manufactured in order to reduce the likelihood of build failure and increase the design freedom (e.g. with regard to geometries and types of resins) when producing a product.

To solve the above problem, an improved additive manufacturing process according to an embodiment firstly lifts one side/corner of the build platform away from the window (e.g. through a rotation about at least one axis parallel to the window/build platform) before moving the whole platform away from the window. This reduces the forces exerted on the part as the build platform is moved. Alternatively, instead of rotating and/or moving the build platform, the window may be rotated and/or moved. Accordingly, the methodology described herein implements a relative rotation of one or both of the build platform and window before the build platform and/or window are linearly moved away from each other.

Accordingly, in addition to lifting the build plate away from the window, along an axis perpendicular to the window, this solution minimises the vacuum effect by introducing steps 1 and 3 below: 1. first, lifting/moving one side of the build platform away from the window to allow/initiate reflow of the resin between the part and the window (rotation of the build plate about an axis parallel to the build platform/window), then 2. moving the build platform away, along the z axis (axis perpendicular to the window), then 3. rotating the build platform back such that it is parallel to the window, then 4. moving the build platform back towards the window, along the z axis, ready for the next layer to be cured.

By introducing a rotation of the build platform, the vacuum effect and reaction loads applied to the part during the build are reduced. This rotation only needs to be small to bias the side of the void where the reflow begins.

In light of the above, this rotation can be achieved via a small-scale, conventional, mechanical actuator setup. Either as a conventional actuated floating surface with multiple degrees of freedom or a conventional single actuator/hinge setup with 1 degree for freedom.

The method introduces at least one additional degree of freedom (DOF) between the build platform and the window in order to reduce loads applied to the part during the build. This could either be applied by rotating the build platform as describe above or rotating the window.

In one embodiment a rotary actuator may be mounted between the build platform and the z-axis mounting bracket of the additive manufacturing machine (where the z-axis is perpendicular to the window, e.g. defining a vertical axis of the machine). For instance, this could be retrofitted to a conventional vat photopolymerization machine.

In a further embodiment a rotary actuator may be mounted to the window/vat of the additive manufacturing machine, such that the window rotates away from the build platform.

Whilst one actuator is discussed above, additional rotary actuators may be included to provide additional degrees of freedom (additional axes of rotation).

The actuator(s) for providing rotational movement may be mounted at point of manufacture or as aftermarket modifications to previously manufactured additive manufacturing machines.

In addition or alternatively to providing one or more rotary actuators, rotary movement may be provided through the build platform being mounted on multiple, independently operable linear actuators with the inclusion of a rotary connection (e.g. a pivot, a hinge or gimbal). For instance a set of linear actuators may be provided, with each being pivotally connected to the build plate. This allows both for linear motion and rotation. Furthermore, where three or more actuators are provided, this can allow rotations around multiple different axes.

Each axis of rotation may be located at one edge of the build platform/window or outside an extent of the build platform/window. This ensures that the window and platform are not forced into one another at one side during the rotation.

Whilst the above method performs moves the build platform away along the z axis (step 2) before then rotating the build platform back such that it is parallel to the window (step 3), the order of these steps may be reversed. That is, the build platform may be rotated back to parallel to the window before the build platform is moved away from the window along the z axis. In this scenario, even though the platform is rotated back to parallel before increasing the separation, the vacuum forces are still reduced relative to methods that do not include a rotation. This is because the highest vacuum forces are before any reflow of resin. The rotation allows resin to begin flowing back beneath the part. Even when the platform is rotated back to parallel before it is moved away from the window, some resin is retained beneath the part. This can be through one or both of compression of the resin and flexibility in the window. Accordingly, even when separation is only increased after the platform has returned to parallel, the vacuum forces are still reduced by the reflow that has begun due to the rotation.

FIG. 2 is a schematic diagram of an additive manufacturing apparatus 100 according to an embodiment at a first step in a manufacturing process. The apparatus is much like the system of FIG. 1. Like features are represented by the same reference numerals.

For brevity, only the differences will be described. The build platform is mounted to allow both rotation and linear movement. In this case, the build platform is mounted to multiple linear actuators 114, with each linear actuator 114 being connected to the build platform 110 via a pivotal connection 112 (such as a pivot, a hinge, or a gimbal).

FIG. 2 shows a step in the manufacturing of part 170 after a layer of resin has been cured. As shown, a lower layer of the part 170 has been cured such that the part is nearly in contact with the window 130.

FIG. 3 is a schematic diagram of the additive manufacturing apparatus 100 of FIG. 2 in a second step in the manufacturing process. At this point, the build platform 110 has been rotated away from the window. That is, a lateral section of the built portion has been moved away from the window. This causes a rotation around an axis that runs parallel to the window. In this case, the rotation is caused by one of the linear actuators 114 moving the lateral section away from the window, but this could equally be implemented through a rotary actuator.

FIG. 4 is a schematic diagram of the additive manufacturing apparatus 100 of FIG. 2 in a third step in the manufacturing process. At this point, the build platform 110 has been moved linearly away from the window 130. This movement is along a direction perpendicular to the window. This movement fully separates the part 170 and the window 130.

FIG. 5 is a schematic diagram of the additive manufacturing apparatus 100 of FIG. 2 in a fourth step in the manufacturing process. At this point, the build platform 110 has been rotated back to be parallel with the window 130.

FIG. 6 is a schematic diagram of the additive manufacturing apparatus 100 of FIG. 2 in a fifth step in the manufacturing process. At this point, the build platform 110 is moved back towards the window 130 to position the part 170 ready for curing. The part 170 may be positioned a predetermined distance away from the window 130 (e.g. as defined by the layer thickness of the additive manufacturing process). Following this point, the additive manufacturing apparatus may cure a further layer of resin 140 onto the part 170.

Whilst the steps shown in FIGs. 4, 5 and 6 are shown as separate steps, they may be combined. For instance, the build platform 110 may be rotated back to its original orientation (e.g. parallel to the window 130) whilst also being moved towards the window ready for the next curing step (e.g. to position the part 170 a predefined distance from the window 130). Alternatively, the build platform 110 may be rotated back to its original orientation as it is being moved away from the window 130. By reorienting the platform at the same time as changing the separation, the overall time taken to reposition the platform is reduced. Given that each build can include thousands of layers, even a small reduction in the time between curing steps can greatly reduce the time to build a product.

FIG. 7 shows an additive manufacturing method 200 according to an embodiment. This relates to one curing step in an overall process for manufacturing a product. This method may be implemented on a system such as that shown in FIG. 2.

A selected region of resin is cured between the build platform and the window 210. The light source is shone on the resin over the selected region when the build platform and window are at a first orientation relative to each other (e.g. parallel to each other) to form cured resin connected to the build platform. The connection to the build platform may be a direct connection (e.g. the newly cured resin may be in direct connection to the build platform) or may be an indirect connection (e.g. via one or more previously cured layers of resin that are connected to the build platform). In the first orientation the window and build platform may be parallel to each other. At this stage, the window and build platform may be separated by a predefined gap. The predefined gap may be dependent on (e.g. equal to) the layer thickness of the product (the thickness of the newly cured region).

After the curing step, at least one of the window or the build platform is rotated away from the other 220. This opens a gap between at least a peripheral section of the cured resin and the window to allow resin to begin to flow between the window and the cured resin. The rotation may be about an axis that is parallel to one or both of the build platform and window (e.g. when in the first orientation). By rotating the window and/or build platform, rather than moving them linearly, the forces exerted on the cured resin (and, by extension, the part being constructed) are reduced, and therefore the likelihood of part failure during manufacture is reduced.

At least one of the window or the build platform is then moved to increase a separation between the window and the cured section of resin and return the window and build platform to the first orientation 230. This step may involve both a linear movement and a rotation. Linear movement may be started before the rotation is started. Step 230 may position the cured resin a predetermined distance from the window. This predetermined distance may be based on (e.g. equal to) the layer thickness.

Whilst the build platform and window are returned to the first orientation (e.g. to parallel to each other), this orientation need not be fixed in all rotational degrees of freedom. For instance, the first orientation may be fixed around one or more axes running parallel to one or both of the build platform and window, but may not be fixed with regard to one or more axes running perpendicular to one or both of the window or the build platform. Accordingly, whist the window and build platform are returned to the first orientation (e.g. parallel), they may have been rotated about one or more axes that run perpendicular to one or both of the window or the build platform. That is, whilst the present method relates to rotating the build platform and/or window around an axis that runs parallel to one or both of the window or the build platform, this may also include a rotation about an axis running perpendicular to one or both of the window or build platform.

Furthermore, step 230 may involve moving the build platform and/or window apart and then moving the window and/or build platform back towards each other. That is, the separation between the window and the build platform may first be increased to a first separation and may then be reduced to a second separation. The rotation may be performed between these two movement steps or performed during one or both of the movement steps.

FIG. 8 shows a further method 200 of additive manufacturing according to an embodiment. This method broadly matches that of FIG. 7; however, additional sub-steps are shown as part of step 230.

As part of the movement and rotation step 230, a first movement is performed to increase the separation between the window and the cured resin to a first separation 232. This allows further resin to flow between the window and the cured resin. The first separation may be larger than the layer thickness for the cured resin (e.g. the first movement may more than double the separation between the build platform and window).

The window and build platform are reoriented to return the window and build platform to the first orientation 234. As discussed above, this may involve a rotation about one or more axes running parallel to one or both of the build platform and/or window.

Furthermore, in the first orientation the build platform and window may be parallel to each other.

A second movement is performed following the first movement to reduce the separation between the window and the cured resin to a second separation 246. The second separation is smaller than the first separation. The second separation may be equal to the layer thickness for the next layer of resin to be cured at a next curing step.

By implementing multiple curing steps (as shown in FIGs. 7 and 8), a product may be built up through many layers of cured resin.

Whilst FIG. 8 shows the reorientation step 234 being performed between the first and movement step 232 and the second movement step 236, the reorientation may be performed during one or both of these movement steps, provided that the build platform and window are not returned to the first orientation before the first movement is started.

Alternatively, the reorientation step 234 may be performed before the first movement step 232. That is, the window and build platform may be reoriented to return the window and build platform to the first orientation before the first movement is started to increase the separation between the window and the cured resin to the first separation.

At least one of the build platform or window being rotated may mean that the window may be rotated, the build platform may be rotated or both the window and build platform may be rotated. At least one of the build platform or window being moved may mean that the window may be moved, the build platform may be moved, or both the build platform and the window may be moved. A different one or combination of the window and build platform may be rotated to the one or combination of the window and build platform that is moved. Furthermore, movement as described herein means a movement including at least a component of linear movement (e.g. that moves the whole object along a particular direction).

As discussed above, at least one of build platform and window is rotated away from the other before they are fully separated from each other. Performing a rotation to move a peripheral portion away before moving the whole part away from the window reduces the vacuum forces exerted on the part. This in turn reduces the likelihood of the part breaking during manufacture.

In addition to the above, or alternatively, the force(s) applied to move and/or rotate the build platform and/or window may be limited to avoid breakage of the part being manufactured. For instance the force of retraction for separating the part (the cured resin) from the window may be limited to be less than a maximum force for the product.

The force to separate the part from the window (the force of retraction) to enable/encourage resin to flow into the polymerisation zone varies with a number of load factors: F, = loads relating to properties of the resin (density, particulates, viscosity, temperature, elapsed shelf life, etc.); Ff = loads relating to flow of the resin into a void (shape of entry, functional properties of the surfaces, etc.); Ks = aspects or factors that are influenced by the speed of retraction; FA= loads relating to the area of the void (the volume and aspect ratio of the void to fill with resin); Fb = loads relating to inadvertent bonding between the part and the window; and Fe= loads relating to a volume of resin being trapped in a cavity. Based on the above, the total force of retraction (FR) is: FR = F Not influence by retraction speed + Ks Fin f luenced by retraction speed =la + KsIErFiFAF, In contrast, the maximum allowable load is the maximum force that can be applied to a part of support structure/interface without part failure. This varies with a number of factors: = knock down factor for the yield strength of the cured resin, given that the part/support is partially cured at the point where the force of retraction is applied; Ks = conventional stress concentrations factors (holes, sharp corners, changes in cross section, etc.); LP= maximum load (force and induced torque) that can be applied to the partly built part if the material was fully cured; Ls = maximum load that can be applied to the partly built support structure; Pi= maximum stress that can be applied to the interface of the partly built support structure; and Ai = interfacing area of the partly built support structure These factors vary depending on the material being cured (the mechanical properties of the cured resin) and the shape of the product being built, including any support structures. For instance, a tall, thin part may be able to withstand a lower torque than a short, wide part. Furthermore, any overhanging sections or narrower sections will reduce the overall force that can be exerted on the part.

Given the above, the maximum allowable load (Lmax) is: Lmax = Kc Min[LP, L5, Linter f ace] = K, min[K,Lp, Ls, PiAii As the force of retraction must be less than the maximum allowable load: FR < Lmax 1Fb KsIF,-FrFAF, < K, min [KsLp, Ls, PEAJ This defines a limitation on the forces that the one or more actuators can exert on the part during rotation/movement. Accordingly, the one or more actuators may be controlled so that they do not exert more than the maximum allowable load on the part. Where the one or more actuators are electric actuators (e.g. electric motors), this may include limiting the voltage applied to the one or more actuators.

The one or more actuators may be controlled to provide rotation over a plurality of steps.

Each step may include a rotation of a set amount, with pauses in rotation between each step. Stepped rotation can simplify the control (relative to continuous rotation) and can limit the forces exerted on the part at each step of rotation. In addition, stepped rotation allows resin to flow into the gap between the part and the window after each step of rotation. The steps may increase in size as the overall angle or rotation increases. This is because the highest forces will be exerted at the start of the rotation, when the suction and bonding between the part and the window is highest. For similar reasons, the speed of rotation may be increased over the extent of the rotation. This variable speed may be applied regardless of whether the rotation is continuous or stepped.

In addition, the rotation may be implemented reciprocally, through a pulsed rotation/vibration in order to assist in the displacement of resin between the part and the window. The pulsed rotation/vibration may be about multiple axes of rotation. The axes of rotation may be alternated between each pulse.

In addition, where the additive manufacturing device is configured to provide rotation around multiple axes of rotation, the axis of rotation applied to the part (e.g. at each curing step) may be selected depending on the shape of the part manufactured so far and/or the shape of the most recently cured layer of resin.

For instance, the additive manufacturing device may be configured to provide rotation around two axes of rotation that run parallel to the window or build plate, wherein the two axes of rotation are perpendicular to each other. Based on this, the additive manufacturing device may impart a rotation about any axis of rotation (that is parallel to the window or build plate) through a combination of rotations about one or both of these two axes. This could be implemented through two rotary actuators, or three pivotally mounted linear actuators, for example.

An axis of rotation may be selected for a given part based on the overall shape of the part that has been manufactured so far and/or based on the cross-section of the most recently cured layer of resin. This axis of rotation may remain constant throughout the printing process of the part, or may be selected for each curing step (e.g. based on the cross-section of the most recently cured layer). The axis of rotation may be selected to maximise the distance from the axis of rotation to the far edge (peripheral section) of the cured part (relative to the axis of rotation). This maximises the displacement for each degree of rotation whilst minimizing the suction force applied during the rotation.

Additive manufacturing processes typically fabricate components based on three-dimensional (3D) information, for example a three-dimensional computer model (or design file), of the component.

Accordingly, examples described herein not only include methods of manufacturing products or components via additive manufacturing, but also computer software, firmware or hardware for controlling the manufacture of such products via additive manufacturing.

The structure of one or more parts of the product may be represented digitally in the form of a design file. A design file, or computer aided design (CAD) file, is a configuration file that encodes one or more of the surface or volumetric configuration of the shape of the product. That is, a design file represents the geometrical arrangement or shape of the product.

Design files can take any now known or later developed file format. For example, design files may be in the Stereolithography or "Standard Tessellation Language" (.stl) format which was created for stereolithography CAD programs of 3D Systems, or the Additive Manufacturing File (.amf) format, which is an American Society of Mechanical Engineers (ASME) standard that is an extensible markup-language (XML) based format designed to allow any CAD software to describe the shape and composition of any three-dimensional object to be fabricated on any additive manufacturing printer.

Further examples of design file formats include AutoCAD (.dwg) files, Blender (.blend) files, Parasolid (.x_t) files, 3D Manufacturing Format (.3mf) files, Autodesk (3ds) files, Collada (.dae) files and Wavefront (.obj) files, although many other file formats exist.

Design files can be produced using modelling (e.g. CAD modelling) software and/or through scanning the surface of a product to measure the surface configuration of the product.

Once obtained, a design file may be converted into a set of computer executable instructions that, once executed by a processer, cause the processor to control an additive manufacturing apparatus to produce a product according to the geometrical arrangement specified in the design file. The conversion may convert the design file into slices or layers that are to be formed sequentially by the additive manufacturing apparatus. The instructions (otherwise known as geometric code or "G-code") may be calibrated to the specific additive manufacturing apparatus and may specify the precise location and amount of material that is to be formed at each stage in the manufacturing process.

As discussed above, the formation of the product may be through curing resin over one or more curing steps. The instructions may define one or more rotations to be performed between each curing step, as described herein.

The code or instructions may be translated between different formats, converted into a set of data signals and transmitted, received as a set of data signals and converted to code, stored, etc., as necessary. The instructions may be an input to the additive manufacturing system and may come from a part designer, an intellectual property (IP) provider, a design company, the operator or owner of the additive manufacturing system, or from other sources. An additive manufacturing system may execute the instructions to fabricate the product using any of the technologies or methods disclosed herein.

Design files or computer executable instructions may be stored in a (transitory or non-transitory) computer readable storage medium (e.g., memory, storage system, etc.) storing code, or computer readable instructions, representative of the product to be produced. As noted, the code or computer readable instructions defining the product that can be used to physically generate the object, upon execution of the code or instructions by an additive manufacturing system. For example, the instructions may include a precisely defined 3D model of the product and can be generated from any of a large variety of well-known computer aided design (CAD) software systems such as AutoCAD®, TurboCAD®, DesignCAD 3D Max, etc. Alternatively, a model or prototype of the component may be scanned to determine the three-dimensional information of the component.

Accordingly, by controlling an additive manufacturing apparatus according to the computer executable instructions, the additive manufacturing apparatus can be instructed to print out one or more parts of a product. These can be printed either in assembled or unassembled form. For instance, different sections of the product may be printed separately (as a kit of unassembled parts) and then subsequently assembled.

Alternatively, the different parts may be printed in assembled form.

In light of the above, embodiments include methods of manufacture via additive manufacturing. This includes the steps of obtaining a design file representing the product and instructing an additive manufacturing apparatus to manufacture the product in assembled or unassembled form according to the design file. The additive manufacturing apparatus may include a processor that is configured to automatically convert the design file into computer executable instructions for controlling the manufacture of the product. In these embodiments, the design file itself can automatically cause the production of the product once input into the additive manufacturing device. Accordingly, in this embodiment, the design file itself may be considered computer executable instructions that cause the additive manufacturing apparatus to manufacture the product. Alternatively, the design file may be converted into instructions by an external computing system, with the resulting computer executable instructions being provided to the additive manufacturing device.

Although additive manufacturing technology is described herein as enabling fabrication of complex objects by building objects point-by-point, layer-by-layer, typically in a vertical direction, other methods of fabrication are possible and within the scope of the present subject matter.

FIG. 9 shows a computing device for controlling an additive manufacturing device according to an embodiment. This computing device 500 may be integrated within the additive manufacturing device, or may be external to the additive manufacturing device but communicatively connected to the additive manufacturing device.

The computing device 500 includes a bus 510, a processor 520, a memory 530, a persistent storage device 540, an Input/Output (I/O) interface 550, and a network interface 560.

The bus 510 interconnects the components of the computing device 500. The bus may be any circuitry suitable for interconnecting the components of the computing device 500. For example, the bus 510 may be an internal bus located on a computer motherboard of the computing device 500 or may be a global bus of a system on a chip (SoC).

The processor 520 is a processing device configured to perform computer-executable instructions loaded from the memory 530. Prior to and/or during the performance of computer-executable instructions, the processor may load computer-executable instructions over the bus from the memory 530 into one or more caches and/or one or more registers of the processor. The processor 520 may be a central processing unit with a suitable computer architecture, e.g. an x86-64 or ARM architecture. The processor 520 may include or alternatively be specialized hardware adapted for application-specific operations.

The memory 530 is configured to store instructions and data for utilization by the processor 520. The memory 530 may be a non-transitory volatile memory device, such as a random access memory (RAM) device. In response to one or more operations by the processor, instructions and/or data may be loaded into the memory 530 from the persistent storage device 540 over the bus, in preparation for one or more operations by the processor utilising these instructions and/or data.

The persistent storage device 540 is a non-transitory non-volatile storage device, such as a flash memory, a solid state disk (SSD), or a hard disk drive (HDD). A non-volatile storage device maintains data stored on the storage device after power has been lost. The persistent storage device 540 may have a significantly greater access latency and lower bandwidth than the memory 530, e.g. it may take significantly longer to read and write data to/from the persistent storage device 540 than to/from the memory 530. However, the persistent storage 540 may have a significantly greater storage capacity than the memory 530.

The I/O interface 550 facilitates connections between the computing device and external peripherals (e.g. the additive manufacturing device). The I/O interface 550 may receive signals from a given external peripheral, e.g. a keyboard or mouse, convert them into a format intelligible by the processor 520 and relay them onto the bus for processing by the processor 520. The I/O interface 550 may also receive signals from the processor 520 and/or data from the memory 530, convert them into a format intelligible by a given external peripheral, e.g. a printer or display, and relay them to the given external peripheral.

The network interface 560 facilitates connections between the computing device and one or more other computing devices over a network. For example, the network interface 560 may be an Ethernet network interface, a Wi-Fi network interface, or a cellular network interface.

Given the above, the design and manufacture of implementations of the subject matter and the operations described in this specification can be realized using digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. For instance, hardware may include processors, microprocessors, electronic circuitry, electronic components, integrated circuits, etc. Implementations of the subject matter described in this specification can be realized using one or more computer programs, i.e., one or more modules of computer program instructions, encoded on computer storage medium for execution by, or to control the operation of, data processing apparatus. Alternatively or in addition, the program instructions can be encoded on an artificially-generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus. A computer storage medium can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate physical components or media (e.g., multiple CDs, disks, or other storage devices). Accordingly, embodiments may include transitory or non-transitory computer readable media storing computer-executable code.

While certain arrangements have been described, the arrangements have been presented by way of example only, and are not intended to limit the scope of protection. The inventive concepts described herein may be implemented in a variety of other forms.

In addition, various omissions, substitutions and changes to the specific implementations described herein may be made without departing from the scope of protection defined in the following claims.

Claims

CLAIMS1. A computer-implemented method for controlling an additive manufacturing process, the additive manufacturing apparatus comprising a build platform for supporting a product being additively manufactured from resin within a curing region of the additive manufacturing apparatus, a window positioned on an opposite side of the curing region from the build platform, a light source configured to selectively cure resin within the curing region through the window for additively manufacturing the product, and one or more actuators configured to adjust a separation between the build platform and the window and to provide relative rotation between the build platform and the window, the method comprising controlling the additive manufacturing apparatus over one or more curing steps, wherein each curing step comprises: curing a selected region of resin between the build platform and the window using the light source when the build platform and window are at a first orientation relative to each other to form cured resin connected to the build platform; rotating at least one of the window or the build platform away from the other to open a gap between at least a peripheral section of the cured resin and the window to allow resin to begin to flow between the window and the cured resin; and moving at least one of the window or the build platform to increase a separation between the window and the cured section of resin and return the window and build platform to the first orientation.
2. The method of claim 1 wherein moving the at least one of the window or the build platform comprises: performing a first movement to increase the separation between the window and the cured resin to a first separation to allow resin to flow between the window and the cured resin; reorienting the window and build platform to return the window and build platform to the first orientation; and performing a second movement to reduce the separation between the window and the cured resin to a second separation, wherein the second separation is smaller than the first separation.
3. The method of claim 2 wherein the reorienting of the window and build platform is performed during one or both of the first movement and the second movement.
4. The method of any preceding claim wherein the one or more actuators are configured to provide relative rotation between the build platform and window about at least one axis that runs parallel to one or both of the window or the build platform when in the first orientation.
5. The method of any preceding claim wherein the one or more actuators are configured to provide relative rotation between the build platform and window about a plurality of axes that run parallel to one or both of the window or the build platform when in the first orientation, and wherein the method comprises selecting an axis from the plurality of axes for use in rotating at least one of the window or the build platform away from the other based on a shape of the cured resin.
The method of claim 5 wherein an axis is selected for each curing step.
7. The method of claim 5 or claim 6 wherein the axis is selected to maximise a distance between a pivot point of rotation and the peripheral section of the cured resin during rotation.
8. The method of any preceding claim wherein the build platform and window are parallel to each other in the first orientation.
9. The method of any preceding claim wherein the speed of rotation is increased as that at least one of the window or the build platform is rotated away from the other. 25
10. The method of any preceding claim wherein the at least one of the window or build platform is rotated away from the other over a plurality of rotation steps, wherein: a step size increases over the plurality of rotation steps; and/or each rotation step is at least partially reciprocal such that it includes an inverse rotation along at least a portion of the rotation step.
11. The method of any preceding claim wherein the one or more actuators are controlled to limit a force applied to the cured resin during rotation and/or movement to be less than a maximum allowable force for the cured resin.
12. The method of claim 11 wherein the maximum allowable force for the cured resin is based on one or more of: a shape of the cured resin, mechanical properties of the cured resin and mechanical properties of the resin.
13. An additive manufacturing apparatus comprising: a build platform for supporting a product being additively manufactured; a window configured to allow light to pass; a light source for selectively curing resin located between the build platform and the window through the window to form cured resin connected to the build platform; and one or more actuators configured to adjust a separation between the build platform and the window and to provide relative rotation between the build platform and the window such that at least one of the window or the build platform can be rotated away from the other by the one or more actuators to open a gap between at least a peripheral section of the cured resin and the window to allow resin to begin to flow between the window and cured resin.
14. The additive manufacturing apparatus of claim 13 wherein the one or more actuators comprise: at least one actuator configured to move one of the build platform or the window to provide relative motion between the build platform and the window along a direction perpendicular to at least one of the window or the build platform; and at least one rotary actuator configured to rotate one of the build platform or the window to provide relative rotation between the build platform and window about an axis parallel to at least one of the window or the build platform.
15. The additive manufacturing apparatus of claim 13 wherein the one or more actuators comprise: a plurality of linear actuators that are pivotally mounted to one of the window and the build plate to allow for both linear and rotational movement.
16. The additive manufacturing apparatus of any of claims 13-15 further comprising one or more processors configured to control the additive manufacturing apparatus in order to perform the method of any of claims 1-12.
17. A computer program comprising computer executable instructions that, when executed by a processor, cause the processor to control an additive manufacturing apparatus according to the method of any of claims 1-12.