Patent Application
20200262152
This invention concerns apparatus and methods for in-process monitoring in laser solidification apparatus and, in particular, apparatus and methods for capturing sensor data collected through an optical train of an optical scanner of a laser solidification apparatus, such as a powder bed fusion apparatus.
Laser solidification apparatus produce parts through layer-by-layer solidification of a flowable material. There are various laser solidification methods, including material bed systems, such as selective laser melting (SLM), selective laser sintering (SLS) and stereolithography systems.
In selective laser melting, a powder layer is deposited on a powder bed in a build chamber and a laser beam is scanned across portions of the powder layer that correspond to a cross-section (slice) of the object being constructed. The laser beam melts or sinters the powder to form a solidified layer. After selective solidification of a layer, the powder bed is lowered by a thickness of the newly solidified layer and a further layer of powder is spread over the surface and solidified, as required. In a single build, more than one object can be built, the parts spaced apart in the powder bed.
The laser beam is typically scanned over the powder bed using an optical scanner comprising a pair of tilting mirrors, each rotated under the control of a galvanometer. Transducers are arranged to measure a position of the mirrors/galvanometers for control of the mirror positions. In this way, a demand position can be achieved.
WO 2007/147221 A1 discloses a selective laser melting apparatus comprising a scanner for scanning the laser beam across the powder surface and a spatially resolved detector (e.g. a CCD or CMOS camera) or an integrated detector (e.g. a photodiode with a large active area) for capturing radiation emitted by a melt zone and transmitted through an optical system of the scanner.
WO 2015/040433 discloses a laser solidification apparatus comprising a spectrometer for detecting characteristic radiation emitted by plasma formed during solidification of the powder by the laser beam.
A problem with such systems is that alignment of the measurement device to be coaxial with the laser beam is required at the site of use and it is difficult and highly complex to change the measurement device, typically requiring an operator to breach a laser safe housing of the optical module.
According to a first aspect of the invention there is provided laser solidification apparatus for building objects by layerwise solidification of material, the laser solidification apparatus comprising a build platform for supporting the object and a material bed, an optical module comprising a movable guiding element for directing the laser beam to solidify material of the material bed, and a detector module comprising a sensor for detecting radiation emitted from the material bed and transmitted to the sensor by the movable guiding element of the optical module, wherein the detector module is removably mounted to the optical module.
In this way, the detector module may be removed from the laser solidification apparatus for cleaning, testing, maintenance or replacement without disassembling the optical module. In particular, the optical module may comprise an optical module housing containing the movable guiding element, the optical module housing having an outlet aperture therein though which the radiation emitted from the material bed is transmitted by the movable guiding element, and the detector module comprises a detector module housing containing the sensor, the detector module housing having a receiving aperture therein arranged for receiving radiation transmitted from the outlet aperture in the optical module housing when the detector module is mounted on the optical module.
One of the detector module and optical module may comprise a seal around the receiving aperture/outlet aperture for engaging with the other of the optical module and detector module so as to seal a transmission path for the radiation from the optical module to the detector module from dust and/or ambient light.
The optical module housing may comprise a filter for blocking light of a wavelength of the laser beam from passing out through the outlet aperture. This may allow the detector module to be removed safely without exposing an operator to potentially harmful laser light. The optical module housing and the detector module housing may be individually dust tight housings.
The optical module may comprise a controller comprising an interface arranged to be releasably coupled to an electronic output of the detector module such that the controller can receive sensor signals from the sensor of the detector module. The controller may be arranged to form data packets comprising control or measurement data sent to or generated by the optical module and sensor data based upon the sensor signals received from the detector module. The control data may comprise demand positions sent to the controller for setting a position of the movable guiding element. The controller may be further arranged to receive control data from a master controller of the laser solidification apparatus. The measurement data may comprise a position of the guiding element measured by a transducer and/or a measured parameter of the laser beam, such as laser modulation and/or laser beam intensity. The data packet may alternatively or additionally comprise sensor data based upon the sensor signals received from the detector module and an identifier, such as a time stamp, that can be used to associate the sensor data with control data and/or measurement data. The data packets may be as described in WO2017/085469. In this way, in use, sensor signals for the removable detector module are integrated into the control and reporting processes of the optical module and married up with corresponding data close to its source to minimise errors that could occur due to latency in data communications in the laser solidification apparatus.
The detector module and the optical module may comprise complimentary mounting formations for removably mounting the detector module on the optical module in a mounting position.
The detector module may further comprise an adjustment mechanism, such as a flexure, for adjusting a relative position of an optical axis of the sensor to the mounting position. The adjustment mechanism may comprise a translation optical mount in which an optical element, such as an objective lens, is mounted. Adjustment of a position of the optical element may adjust a position of the optical element relative to a mounting position of the detector module and therefore, a focal position of the radiation on the sensor, in use.
The complimentary mounting formations may be arranged for removably mounting the detector module on the optical module in a repeatable mounting position. The position of the detector module on the optical module may be sufficiently repeatable in successive mountings such that, once the sensor has been aligned with the optical axis of the laser beam, for example using the adjustment mechanism, the detector module can be removed and remounted on the optical module without requiring realignment of an optical axis of the sensor. The position may be repeatable within 100 micrometres or less, preferably 50 micrometres or less and most preferably within 10 micrometres or less. The complimentary mounting formations may form a kinematic or pseudo-kinematic mount.
The detector module may further comprise a removable cover attachable to the detector module to cover the receiving aperture. The cover may comprise mounting formations that cooperate with the same mounting formations used to attach the detector module to the optical module to attach the cover to the detector module.
According to a second aspect of the invention there is provided detector module for a laser solidification apparatus according to the first aspect of the invention, the detector module comprising a sensor for detecting radiation emitted from the material bed and transmitted to the sensor by the movable guiding element of the optical module, wherein the detector module is removably mountable to the optical module.
According to a third aspect of invention there is provided a detector module kit for a laser solidification apparatus according to the first aspect of the invention, the kit comprising a plurality of detector modules removably mountable to the laser solidification apparatus, each detector module of the plurality of detector modules comprising a sensor arranged for measuring a different property of the radiation emitted from the material bed and transmitted to the sensor by the movable guiding element of the optical module. For example, the different property may be different wavelength bands of the radiation, spatial or spectral dispersion of the radiation or an integrated intensity over a field of view.
The kit may allow an operator to select and mount a detector that is most appropriate for the selective laser solidification process that is to take place. For example, for the processing of different materials, different sensor setups may be required, such as setups arranged to detect light confined to wavelength bands characteristic for a particular material. Different ones of the detector modules may comprise different filters for filtering out different wavelengths of light. Furthermore, a detector module comprising a sensor for measuring spectral and/or spatial dispersion, such as a CCD or CMOS camera, may be used for the initial setup and/or maintenance of a laser solidification apparatus, such as an alignment of a plurality of lasers using the method as described in PCT/GB2017/051137, whereas an integrating sensor, such as a photodiode, may be used for in-process monitoring once the initial setup has been completed. A sensor for measuring spectral and/or spatial dispersion may be used for material development and/or development of a build of a part, whereas an integrating sensor may be used to monitor established builds after the development phase. In laser solidification processes, it is rare for a build to be successful on the first attempt and usually a plurality of development builds must be carried out to refine the process. During this development phase, additional information on the radiation may be beneficial. However, once a settled build process has been established, a detector module may be used for a different purpose, for example to check that the build stays within an acceptable process variation and for such purposes, an integrating detector may be sufficient.
According to a fourth aspect of the invention there is provided a method of assembling a laser solidification apparatus according to the first aspect of the invention, the method comprising mounting the detector module to the optical module and/or a test rig, aligning an optical axis of the sensor to a set alignment position when mounted on the optical module and/or a test rig, removing the detector module from the optical module and/or test rig for maintenance and/or transport, and (re)mounting the detector module on the optical module with the sensor in the set alignment position such that the detector module is ready for recording sensor signals during a laser solidification process.
Referring to
Layers of powder are formed as the workpiece 103 is built by lowering the platform 102 and spreading powder dispensed from dispensing apparatus 108 using wiper 109. For example, the dispensing apparatus 108 may be apparatus as described in WO2010/007396.
At least one laser module, in this embodiment laser module 105 generates a laser 118 for melting the powder 104. The laser 118 is directed as required by a corresponding optical module 157. The laser beam 118 enters the chamber 101 via a window 107. In this embodiment, the laser module 105 comprises a fibre laser, such as Nd YAG fibre laser. The laser beam enters the optical module 157 from above and is directed over the surface of the powder bed 104 by movable mirrors tiltable mirrors 150a, 150b (only one of which is shown in
Mounted around aperture 158 is a detector module connecting plate 159. The connecting plate 159 comprises four mounting formations in the form of slots 152a, 152b, 152c and 152d for receiving mounting formations in the form of pins 164a, 164b, 164c and 164d of the detector module 160, as described in more detail below.
A hood (not shown) fits over the optical components 150a, 150b, 155, 156 to provide a light tight and dust tight housing,
The optical module further comprises an integrated optical module control unit 180 having communication interfaces for communicating with master controller 140 and the detector module 160. In this embodiment, the interface is connected to an interface of the detector module 160 via a releasable cable 162.
The detector module 160 comprises at least one detector for detecting radiation transmitted to the detector module 160 from the optical module 157. In this embodiment, the detector is a photodetector 161 for detecting an integrated intensity of the transmitted light. However, in other embodiments the detector may alternatively or additionally comprise a further photodetector, a PSD, a CCD or CMOS camera and/or spectrometer.
The radiation enters the detector module via a receiving inlet of the detector module 160, in this embodiment in the form of an objective lens 163. As shown in
The detector module 160 is mounted onto the optical module 157 via four mounting pins 164a, 164b, 164c, 164d that fit into slots 152a, 152b, 152c, 152d on the optical module 157. Slots 152a and 152b have a first cross-sectional shape (as shown in
The detector module 160 is urged into this defined mounting position by a bolt 167 which engages with a surface of the connecting plate 159 to push the pins 164a, 164b, 164c, 164d into slots 152a, 152b, 152c, 152d.
A seal 168 is provided around the receiving aperture 163 and is arranged to engage with the connecting plate 159 to provide a dust tight and ambient light tight seal between the outlet aperture 158 of the optical module 157 and the receiving aperture 163 of the detector module 160.
A handle 165 is provided for an operator to grip when mounting and/or removing the detector module 160 from the optical module 157.
A master controller 140 is in communication with modules of the additive manufacturing apparatus, namely the laser module 105, optical module 157, build platform 102, dispensing apparatus 108, wiper 109 and controller 180. The controller 140 controls the modules based upon commands in a build file.
As described in WO2017/085469, sensor values generated by sensors in the optical module 157 and the detector module 160 are sent to controller 180 and each sensor value associated with a time stamp corresponding to a time at which the sensor value was generated. The optical module may comprise transducers for measuring a position of the tiltable mirrors 150a, 150b and these measured positions may be packaged together with the sensor values from the detector module 160 and a time stamp and delivered as a packet to the master controller 140, as described in pending UK patent application 1707807.2, which is incorporated herein by reference.
During an initial setup of the selective laser melting apparatus, the detector module 160 is aligned with the optical axis of the optical module 157 by mounting the detector module 160 on the optical module 160 or a test rig comprising corresponding mounting features and a position of the objective lens adjusted to centre collected radiation on the sensor in the detector module 160. If this is a first alignment after manufacture, the detector module 160 may be aligned at a manufacturing site and then removed for transport to a site at which the powder bed fusion apparatus will be used where it is then mounted onto/back onto the optical module 157 and realignment of the optics may not be required. In this way, a person skilled in the alignment of optics may not be required at the site of use. During use, it may become necessary to carry out maintenance of the detector module 160, for example cleaning dust and other dirt from surfaces of the detector module 160. To do this, the detector module 160 may be removed from the optical module 157 for cleaning and then remounted. Realignment of the optics upon remounting of the detector module 160 may not be required as the cooperating mounting formations 164a, 164b, 164c, 164d, 152a, 152b, 152c, 152d ensure that the detector module 160 is remounted in a mounting position which is sufficiently close to the mounting position in which the optics were aligned.
The optical module 257 comprises correspondingly shaped recesses 252a, 252b for receiving L-shaped mounting formations 264a and 264b. The L-shaped projections 246a and 264b comprise holes 290a, 290b therethrough for receiving bolts 267a, 267b, which engage with a threaded hole in the recess 252a, 252b. In this embodiment, hole 290a has approximately a square-shaped cross-section and the hole 290b has a pentagonal-shaped cross-section. An angled surface, in this embodiment at 45 degrees to the plane shown in
At a bottom of the optical module 257 are provided wedge-shaped projections 252c, 252d for engaging with angled surfaces 264c, 264d, the contact surfaces being perpendicular to the contact surfaces of the bolts 267a, 267b and holes 290a, 290b.
Accordingly, the mounting formations 264a, 264b, 264c, 264d, 252a, 252b, 252c, 252d define a mounting position of the detector module 260 such that the detector module 260 is returned to this mounting position on being removed from the optical module 257 and then remounted.
In one embodiment, a kit is provided comprising a plurality of the detector modules 160, 260, each detector module 160, 260 of the plurality comprising a different arrangement of sensors for detecting different properties of the radiation transmitted to the detector module 160, 260. In one embodiment, the plurality of detector modules comprises at least one first detector module 160, 260 comprising two photodetectors, one for detecting visible light and the second for detecting light in the infra-red spectrum, at least one second detector module comprising a position sensitive device (PSD) for detecting a position of the radiation transmitted to the detector module 160, 260 and at least one third detector module 160, 260 comprising a spectrometer for measuring an intensity of the radiation at a plurality of different wavelengths.
It will be understood that alterations and modifications can be made to the above-described embodiments without departing from the scope of the invention as defined herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1718596.8 | Nov 2017 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2018/053224 | 11/7/2018 | WO | 00 |
