Additive manufacturing machines produce three dimensional (3D) objects by building up layers of material. Some additive manufacturing machines are commonly referred to as “3D printers”. 3D printers and other additive manufacturing machines make it possible to convert a CAD (computer aided design) model or other digital representation of an object into the physical object. The model data may be processed into layers, each defining that part of a layer or layers of build material to be formed into the object.
In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. It is to be understood that features of the various examples described herein may be combined, in part or whole, with each other, unless specifically noted otherwise.
The descriptions and examples provided herein can be applied to various additive manufacturing technologies, environments, and materials to form a three dimensional (3D) object based on data of a 3D object model. Various technologies can differ in the way layers are deposited and fused, or otherwise solidified, to create a build object, as well as in the materials that are employed in each process.
In an example additive manufacturing process, a build material and a printing agent can be deposited and heated in layers to form a build object. An example additive manufacturing technology can dispense a build material and spread the build material onto a build surface to form a layer of build material. The build surface can be a surface of a platen or underlying build layers of build material on a platen within a build chamber, for example. The example additive manufacturing technology can dispense a suitable printing agent in a desired pattern onto the layer of build material and then expose the build material and the printing agent to an energy source, such as a thermal energy source for fusing. Sintering, or full thermal fusing, can be employed to fuse small grains of build material, e.g., powders. Sintering typically involves heating the build material to melt and fuse the particles together to form a solid object.
In some additive manufacturing technologies, the layer of build material may be formed using a roller or a recoater. A printhead may be used to dispense a printing agent, such as a fusing agent or a binder agent, on a formed layer of build material. The recoater and printhead may be carried on a moving carriage system. The moving carriage system may comprise, in different examples, either a single carriage or multiple carriages. A build material dispensing assembly can be mounted to the moving carriage system to dispense and spread build material to form a layer of build material. A printhead can be employed to selectively dispense fusing agent, or another kind of printing agent, and can be mounted to the moving carriage system. A thermal energy source can also be mounted to the carriage system and moved across the build surface. The energy source can generate heat that is absorbed by fusing energy absorbing components of the printing agent to sinter, melt, fuse, or otherwise coalesce the patterned build material. In some examples, the energy source can apply a heating energy, to heat the build material to a pre-fusing temperature, and a fusing energy, to fuse the build material where the printing agent has been applied. Thermal, infrared, or ultraviolet energy can be used, for example, to heat and fuse the material. The patterned build material can solidify and form an object layer, or a cross-section, of a desired build object. The process is repeated layer by layer to complete the 3D build object.
In an example additive manufacturing process using selective laser sintering (SLS) technology, a layer of build material is formed and a thermal heat source, such as a laser, is used to selectively heat and fuse portions of the layer of the build material in a build pattern. With SLS technology, the patterned build material can melt and solidify to form an object layer, or a cross-section, of a desired build object. The process is repeated layer by layer to complete the three dimensional (3D) build object.
Build material can be a powder-based type of build material and the printing agent can be an energy absorbing liquid that can be applied to the build material, for example. Build material can include plastic, ceramic, and metal powders, and powder-like material, for example. In some examples, build material can be formed from, or may include, short fibers that may, for example, have been cut into short lengths from long strands or threads of material. Other types of build materials can also be acceptable.
In one example, the build material dose can be dispensed onto a dose plate prior to being spread onto the build surface. The build material dose can be dispensed onto a dose plate adjacent the build surface to assist with control of the dose. For example, dispensing the build material onto a dose plate prior to the build material being spread onto the build surface can assist with controlling the temperature of the build material prior to the build material being spread onto the build surface. Control of the build material temperature at the dose plate can result in control of variations in thermal profile of the build material layer during spreading of the build material dose over the build surface to mitigate, or control, the effects of convection, conduction or other thermal variations in the build chamber during the build process that can cause over or under fusing of build parts, resulting in part defects and material property variations. It is desirable to monitor and control the build material dose temperature during the build process to reduce thermal variations, resulting in improved material properties and reducing part defects.
The temperature of the build material in the build chamber can be cooler (e.g., have thermal roll off) on the front and back sides of the build chamber, the front and back sides being parallel to the scanning axis, for example. Thermal roll off can occur when cooler temperatures influence warmer temperatures, such as at the edges of heated object layer surrounded by cooler ambient air. In 3D printing, thermal roll off can occur at each build layer in the build chamber. The thermal roll off can be due to several factors such as thermal roll off of the scanning thermic source, conduction of heat into the chamber walls and convective losses due to air currents in the build chamber. Reducing thermal variations, such as thermal roll off on the front and back side areas of the build chamber, can provide a more thermally uniform build area, increase the size of the buildable area, reduce defects in part quality, reduce dimensional inaccuracy, reduce material property defects, and reduce color variation in the build parts.
In one example, heating element 14 can be thermally coupled to dose plate 12. In one example, heating element 14 is disposed along bottom surface 28 of dose plate 21. Heating element 14 can selectively heat each zone 12. In one example, heating element 14 can include a resistive heater. Heating element 14 can heat dose plate 12 and build material 24 disposed on dose plate 12 (see, e.g.,
Sensor 16 can detect a thermal energy or a temperature of each of the at least two zones 20a . . . x at or around dose plate 12. In one example, sensor 16 can be disposed within additive manufacturing machine 10 as appropriate to sense each of first and second thermal energies of first and second zones 20a, 20b, respectively. For example, sensor 16 can be mounted on, or adjacent to, dose plate 12 to sense the temperature of each zone 20a, 20b. One or a plurality of sensors 16 can be employed as appropriate to sense the temperature at each of the at least two zones 20a . . . x. In one example, a separate sensor 16 can be included to sense the temperature of each of the at least two zones 20a . . . x independently. In another example, more than one sensor 16 is included for each of the at least two zones 20a . . . x. In one example, sensor(s) 16 can detect thermal energy or temperature of build material 24 on dose plate 12. In one example, sensor 16 can include an infrared camera. In another example, sensor 16 can include a thermocouple. In one example, sensor 16 can sense a thermal energy or temperature of each of the at least two zones 20a . . . x and communicate the sensed thermal energy or temperature of each of the at least two zones 20a . . . x to controller 18.
Controller 18 can control power to, and thus, energy emitted by heating element 14. Controller 18 can independently adjust energy levels emitted by heating element 14 at each of the at least two zones 20a . . . x based on the thermal energy sensed, or detected by, sensor(s) 16 in each of the at least two zones 20a . . . x. In one example, controller 18 can be employed as a closed loop control system to control the temperature of build material 24 disposed along dose plate 12 at each of the at least two zones 20a . . . x during the build process. In one example, controller 18 can command a target temperature for each of the at least two zones 20a . . . x. Controller 18 can apply power to heating element 14 at each of the at least two zones 20a . . . x to adjust the temperature of each of the at least two zones 20a . . . x to the target temperature for each of the at least two zones 20a . . . x independent of each of the other at least two zones 20a . . . x. Controller 18 can adjust the thermal energy emitted by heating element 14 at each of the at least two zones 20a . . . x independent from the adjacent, or other, zones 20a . . . x based on thermal energy or temperature detected by sensor 16 for each of the at least two zones 20a . . . x, respectively, and transmitted to controller 18. In one example, when target temperature is achieved in the respective zone of the at least two zones 20a . . . x, power to heating element 14 at the respective zone of the at least two zones 20a . . . x can be terminated. In one example, controller 18 controls heating element 14 by switching heating element 14 on-and-off at each of the at least two zones 20a . . . x, respectively, to independently adjust the energy emitted by heating element 14 at each of the at least two zones 20a . . . x. Controller 18 can adjust power level of heating element 14 for each dose of build material 24 disposed on dose plate 12. In one example, controller 18 can adjust power level of heating element 14 based on a dose mass of build material 24 dispensed onto dose plate 12.
In one example, dose plate 112 can be formed as a single contiguous conductive plate. In one example, dose plate 112 can includes grooves 138, or recesses, between adjacent regions 134 of dose plate 112, extending at least partially through a thickness of dose plate 112 between top surface 126 and bottom surface 128. In one example, grooves 138 extending between adjacent regions 134 of dose plate 112 can aid in control of thermal transfer between regions 134 of respective zones 120. In one example, an insulation 140 can be disposed in grooves 138 to assist with control of thermal transfer between regions 134 and associated zones 120. In one example, insulation 140 is disposed between adjacent regions 134 to inhibit, prevent, or reduce thermal bleed, or cross-over, between adjacent regions 134. Insulation 140 can be formed as strips and disposed within grooves 138, for example. In one example, an insulation layer 142 can also be formed as a sheet and disposed along bottom surface 128 of dose plate 112 and heating element 114 to maintain heat emitted from heating element 114 at or along dose plate 112. Insulation layer 142 can extend partially or fully across heat element 114 and/or bottom surface 128 of dose plate 112. Insulation 140 and insulation layer 142 can be formed of mica, asbestos, ceramic or any other suitable insulation material.
In one example, heating element 114 includes independently controlled portions to independently heat each of the at least two zones 120a . . . x to a different temperature concurrently. In one example, heating element 114 includes individual heating devices 136a . . . x to independently supply heat to each of the at least two regions 134a . . . x of dose plate 112. For example, heating element 114 can include heating devices 136a-c useful to selectively heat each zone 120a-c. In one example, each heating device 136a-c of heating element 114 can be independently associated with and thermally coupled to a specific region 134a-c, or area, of dose plate 112 and, correspondingly, a portion of build material (not shown) disposed onto the respective region 136a-c of dose plate 112. For example, heating element 114 can have first heating device 136a thermally coupled to a first region 134a of dose plate 112 to selectively heat first region 134a to a first thermal energy level or temperature, a second heating device 136b thermally coupled at a second region 134b of dose plate 112 to heat second region 134b of dose plate 112 to a second thermal energy level or temperature, etc. In one example, first and second heating devices 136a, 136b can heat first and second regions 134a, 134b to first and second thermal energy levels (or temperatures), respectively, concurrently.
Although three zones 120a-c are illustrated in
Prior to beginning the build process, build material 24 can be dispensed onto dose plate 312,412 at a lower temperature than desired during the build process. For example, dose plate 312, 412 and/or build material 24 can be maintained at room temperature prior to the build process. In one example, heating element 314 can heat dose plate 312 and build material 24 residing on dose plate 312 prior to build material 24 being spread onto build surface 506. In another example, heating element 414 can heat dose plate 412 and dose plate 412 can, in turn, transfer heat from heating element 414 to build material 24 residing on dose plate 412 prior to build material 24 being spread onto build surface 506.
With additional reference to the top view of a dose plate 512 and build surface 506 illustrated in
Although specific examples have been illustrated and described herein, a variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.
Filing Document | Filing Date | Country | Kind |
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PCT/US2018/015760 | 1/29/2018 | WO | 00 |