WO2017059883A1

WO2017059883A1 - Fusing in additive manufacturing systems

Info

Publication number: WO2017059883A1
Application number: PCT/EP2015/072937
Authority: WO
Inventors: Xavier VILAJOSANA; Sebastia CORTES; Yngvar ROSSOW
Original assignee: Hewlett-Packard Development Company L.P.
Priority date: 2015-10-05
Filing date: 2015-10-05
Publication date: 2017-04-13

Abstract

A method of controlling a fusing sub-system in an additive manufacturing system. Image information is received, the received image information having been generated by a thermal imaging system in relation to a given fusing process. Positional information is received, the received positional information indicating the position of an axis carriage for the given fusing process. A power to be applied to one or more fusing lamps for the given fusing process is determined at least on the basis of the received image information and the received positional information. The power applied to the one or more fusing lamps is controlled according to the determination.

Description

FUSING IN ADDITIVE MANUFACTURING SYSTEMS BACKGROUND

[0001] Additive manufacturing systems that generate three-dimensional objects, including those commonly referred to as "3D printers", have been proposed as a potentially convenient way to produce three-dimensional objects. These systems may receive a definition of the three-dimensional object in the form of an object model. This object model is processed to instruct the system to produce the object using one or more material components. This may be performed on a layer- by- layer basis. The processing of the object model may vary based on the type of system and/or the production technology being implemented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Various features of the present disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate certain example features, and wherein:

[0003] Figure 1 is a schematic diagram showing components of an additive manufacturing system according to an example;

[0004] Figure 2 is a schematic illustration of a print bed area with an object printed with fusing agent and surrounded by detailing agent according to an example;

[0005] Figure 3 is a flowchart showing operations performed by a fusing controller in an additive manufacturing system according to an example;

[0006] Figure 4 is a flowchart showing a method 400 of controlling a fusing sub-system in an additive manufacturing system; and

[0007] Figure 5 is a schematic illustration of a processing device according to an example.

DETAILED DESCRIPTION

[0008] In the following description, for purposes of explanation, numerous specific details of certain examples are set forth. Reference in the specification to "an example" or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples.

[0009] Figure 1 shows an example 100 of an additive manufacturing system that uses an inkjet deposit mechanism 1 10 to print a plurality of liquid agents onto layers of a powdered (or slurry, paste, gel, etc.) substrate. Although the examples described herein may be applied to different types of additive manufacturing system, the example 100 of Figure 1 will be used for ease of reference to further explain some of the concepts disclosed herein. Other examples may be applied to one or more of selective laser sintering systems, stereo lithography systems, inkjet systems, fused deposition modelling systems, any three-dimensional printing system, inkjet deposition systems and laminated object manufacturing systems.

[0010] In Figure 1 , the inkjet deposit or print mechanism 1 10 implements a deposit mechanism. The deposit mechanism 1 10 in this example comprises four printheads, such as inkjet printheads, 1 15. Each printhead is adapted to deposit an agent onto a powdered polymer substrate 120. In particular, each printhead is arranged to deposit a particular agent upon defined areas within a plurality of successive substrate layers. An agent may for example act as a coalescing agent (e.g. an energy absorber or fusing agent or as a coalescing modifier. In Figure 1 the inkjet print mechanism 1 10 is communicatively coupled to a deposit controller 130. Further components, may be present but are not shown for clarity.

[0011] In Figure 1 , the additive manufacturing system comprises a substrate supply mechanism 150 to supply at least one substrate layer upon which the plurality of materials are deposited by the deposit mechanism 1 10. In this example, the substrate supply mechanism 150 comprises a powdered substrate supply mechanism to supply successive layers of substrate. Two layers are shown in Figure 1 : a first layer 120-L1 upon which a second layer 120-L2 has been deposited by the substrate supply mechanism 150. In certain cases, the substrate supply mechanism 150 is arranged to move relative to the platen 145 such that successive layers are deposited on top of each other. [0012] In the present example, the additive manufacturing system also comprises a fixing system 180 arranged to apply energy to form portions of the three- dimensional object from combinations of the agents and the powdered substrate. For example, Figure 1 shows a particular printhead 1 15 depositing a controlled amount of a fluid agent onto an addressable area of the second layer 120-L2 of powdered substrate. The fluid agent is absorbed by the powdered substrate and as such a drop of agent on an addressable area unit of the layer relates to a print resolution volumetric pixel (voxel) 160. Following application of the agent the fixing system 180 is arranged to fix or solidify the portion of the layer 160. In some examples, the fixing system 180 may apply energy uniformly to the whole layer. In some examples, portions of powder and coalescing agent may coalesce and solidify, whereas portions of powder alone (or powder and detailing agent) may not coalesce and solidify. In some examples, detailing agents may allow the properties of portions of powder to be modified (e.g. to have different properties depending on the nature of the agent).

[0013] In some examples, fixing system 180 comprises an energy source such as one or more ultra-violet or infra-red light sources, e.g. fusing lamps or lasers. In some examples, fixing system 180 comprises a fusing controller for controlling the fusing process, including controlling the power applied by a fusing energy source such as one or more fusing lamps or lasers. Figure 1 shows four print resolution voxels 170 that have been fixed in the first layer 120-L1 . As such, voxel 160 may be built on these previous voxels 170 to build a three-dimensional object. Lower layers of substrate may also provide support for overhanging fixed portions of a three- dimensional object, wherein at the end of production any unsolidified substrate is removed to reveal the completed object.

[0014] Figure 2 is a schematic illustration of a print-bed area 200 with an object printed with fusing agent 205 and surrounded by an agent 215. The fusing energy source (in this example fusing lamps 220A and 220B) is for example moved either along a scan axis or along a re-coater axis. In this example, fusing lamps 220A and 220B are attached to print carriage 210. [0015] In certain examples, the fusing process is carried out at different stages of the layer, usually after having printed with fusing agent a layer and before covering it with powder material. In some example, this process is carried out by one of the axis carriages, for example the re-coater carriage or the print carriage. Certain examples comprise a fusing energy source, for example in the form of one or more fusing lamps which are typically attached to the carriage (for example one at the front and the other at the back) and are able to deliver a large amount of energy in a short time period. The fusing lamps could for example be halogen lamps which are able to deliver power in the order of thousands of Watts. The main functionality of the fusing lamps is to melt and maintain the melting state during the phase change. This process is fundamental to obtain accurate printed part quality.

[0016] In known systems, power to fusing lamps is delivered using brute force, that is, acting like a switch. At the beginning of the carriage or recoater pass, the lamps are powered at 100% and all along the printbed they are kept in that state. This delivers excess energy to the printed part in most of the cases and excessively heats the non-printed powder producing so-called 'cake'.

[0017] Certain examples described herein relate to mechanisms for controlling and accurately delivering energy (not an excess of energy) to the part of the print- bed that is actually being printed without delivering energy to non-fusing agent covered parts. Certain examples do not affect the temperature of the (white) powder as this constrains selectivity and produces the 'cake' phenomena.

[0018] Certain examples involve accurately adjusting the energy delivered during the fusing process. This energy depends on the actual temperature of the print-bed and therefore uncontrolled or brute force energy delivery does not benefit the melting process. In that sense, certain examples described herein use thermal imaging information (for example from one or more thermo-cameras) to determine the amount of power that is to be delivered to the fusing lamps according to the current print-bed temperature just before the fusing process. So, in certain examples, when the part on the print-bed is relatively close to the melting temperature, the fusing lamps deliver a relatively low energy, whereas when the part on the print-bed is relatively far away from the melting temperature, the fusing lamps deliver a relatively high energy (e.g. almost full power).

[0019] Certain examples ensure that the fusing process is carried out in an optimal manner. That is, that material is melted with the right amount of energy without jeopardizing the selectivity by heating the raw powder when not needed or overheating the raw powder.

[0020] Certain examples comprise a mechanism by which fusing is controlled according to the current bed temperature and according to the layer being printed (or N last layers).

[0021] In some examples, at the beginning of a layer, and by using a carriage seeking function, that is, a functionality that informs the fusing system where in the bed the first drop of printing fluid (for example fusing agent, ink, etc.) will be dropped as well as the position of the last drop to be applied. Knowing this, the fusing subsystem can use the carriage encoder to monitor the position of the carriage and turn on the lamps when approaching the area to be melted. In some examples, the power to deliver to the fusing lamps is a function of the width and height of the part to be melted, since bigger and coarse parts tend to require less energy as they retain more heat.

[0022] In some examples, at the same time, the fusing controller is fed with the information from the thermo-camera. In some examples, using the image information from the pipeline, the temperature of the part being printed can be determined (for example by matching the thermo-camera pixels to the pixels of the image being printed in the current layer), that is the temperature of the area that is covered by fusing agent.

[0023] In some examples, using this information, the power to be applied can be determined according to the desired melt temperature and according to the current temperature of the fusing agent covered part.

[0024] Certain examples determine the power to be applied by expressing the power in a Proportional Integral Differentiation (PID) problem form such as expressed by the following equation: [0025] Power = Kd^*At + Ki^*Sum(Ti ..N-i)+Kd(T_N - T_N-i)/dt + Kw^*(partsurface)

[0026] The Kd^*At term in the above equation is a factor of the current error with respect to the target, i.e. a measure of how far away the current temperature is from the target temperature. This term is the 'Proportional' term in the PID problem form.

[0027] The Ki^*Sum(Ti..N-i) term in the above equation is a factor of the previous 'distances' from the target temperature, i.e. a measure of the inertia of the system to change its state. This term is the 'Integral' term in the PID problem form.

[0028] The Kd(TN - TN-i)/dt term in the above equation is a factor of the error variation, i.e. a measure of the error being reduced to reach the target temperature. This term is the 'Differentiation' term in the PID problem form.

[0029] The Kw^*(partsurface) term in the above equation is a factor of the area of the part (bigger parts retain more temperature than smaller parts).

[0030] Figure 3 is a flowchart showing operations performed by a fusing controller in an additive manufacturing system according to an example.

[0031] At block 310, image information is received from a thermal imaging camera. The received image information comprises image information associated with a given fusing process.

[0032] At block 320, on the basis of the received image information, the temperature of a part being printed in a given fusing process is estimated.

[0033] At block 330, positional information relating to an axis carriage is received. The received positional information indicates a current position of the axis carriage in the given fusing process.

[0034] At block 340, on the basis of at least the estimated temperature and the received positional information, a power to be applied to a fusing energy system for the given fusing process is determined.

[0035] According to an example, the fusing controller is configured to receive further image information from the thermal imaging camera, the received further image information comprising image information associated with a subsequent stage of the given fusing process. In this example, the fusing controller is configured to receive further positional information relating to the axis carriage, the received further positional information indicating a position of the axis carriage in the subsequent stage of the given fusing process. In this example, the fusing controller is configured to, on the basis of the received further image information, further estimate the temperature of the part being printed in the given fusing process. In this example, on the basis of at least the further estimated temperature and the received further positional information, the fusing controller is configured to dynamically determine an updated power to be applied to the fusing energy system for the subsequent stage of the given fusing process.

[0036] In some examples, the estimated temperature comprises the estimated temperature of a print-bed area for at least one layer of the part being printed in the given fusing process. In some examples, the estimated temperature comprises an average estimated temperature of a print-bed area for at least one layer of the part being printed in the given fusing process. In some examples, the estimated temperature comprises an average temperature of a whole part. In some examples, the estimated temperature comprises an average temperature of one or more portions of a part. In some examples, the estimated temperature comprises an average temperature of a layer of a part. In some examples, the estimated temperature comprises an average temperature of one or more portions of a layer of a part.

[0037] In a certain example, the fusing controller is configured to calculate a desired fusing agent melt temperature for the given fusing process. In this example, the power to be applied to the fusing energy system for the given fusing process is further determined on the basis of the desired fusing agent melt temperature.

[0038] In a certain example, the fusing controller is configured to calculate a desired fusing agent melt temperature for the given fusing process. In this example, the fusing controller is configured to determine a lower power to be applied to the fusing energy system for the given fusing process when the estimated temperature is closer to the calculated desired fusing agent melt temperature than when the estimated temperature is further away from the calculated desired fusing agent melt temperature.

[0039] In a certain example, the fusing controller is configured to determine a higher power to be applied to the fusing energy system for the given fusing process when the received positional information indicates that the current position of the axis carriage is closer to a position of the part being printed in the given fusing process than when the received positional information indicates that the current position of the axis carriage is further away from a position of the part being printed.

[0040] In a certain example, the received positional information comprises one or more of positional information associated with a position in the print-bed where a first part of fusing agent is to be applied, and positional information associated with a position in the print-bed where a last part of fusing agent is to be applied.

[0041] In a certain example, the fusing controller is configured to transmit a control signal representative of the determined power to the fusing energy system.

[0042] Figure 4 is a flowchart showing a method 400 of controlling a fusing sub-system in an additive manufacturing system.

[0043] At block 410, image information is received. The received image information was generated by a thermal imaging system in relation to a given fusing process.

[0044] At block 420, positional information is received. The received positional information indicates the position of an axis carriage for the given fusing process.

[0045] At block 430, determining, a power to be applied to one or more fusing lamps for the given fusing process is determined at least on the basis of the received image information and the received positional information.

[0046] At block 440, the power applied to the one or more fusing lamps is controlled according to the determination.

[0047] According to an example, further image information is received. The received image information is generated by the thermal imaging system in relation to a subsequent stage of the given fusing process. In this example, further positional information is received. The received further positional information indicates the position of the axis carriage in the subsequent stage of the given fusing process. In this example, an updated power to be applied to the one or more fusing lamps is further determined for the subsequent stage of the given fusing process on the basis of the received further image information and the received further positional information. In this example, the power applied to the one or more fusing lamps is dynamically controlled according to the further determination.

[0048] A certain example comprises calculating a desired fusing agent melt temperature for the given fusing process. In this example, the power to be applied to the one or more fusing lamps for the given fusing process is determined further on the basis of the desired fusing agent melt temperature.

[0049] According to an example, a desired fusing agent melt temperature for the given fusing process is calculated. In this example, the determining comprises determining a lower power to be applied to the one or more fusing lamps for the given fusing process when the estimated temperature is closer to the calculated desired fusing agent melt temperature than when the estimated temperature is further away from the calculated desired fusing agent melt temperature.

[0050] In an example, the determining comprises determining a higher power to be applied to the one or more fusing lamps for the given fusing process when the received positional information indicates that the current position of the axis carriage is closer to a position of a part being printed in the given fusing process than when the received positional information indicates that the current position of the axis carriage is further away from a position of the part being printed.

[0051] Certain system components and methods described herein may be implemented by way of machine readable instructions that are storable on a non- transitory storage medium. Figure 5 shows an example of a three-dimensional printing system or device 500 comprising at least one processor 510 arranged to retrieve data from a computer-readable storage medium 520. The computer- readable storage medium 520 comprises a set of computer-readable instructions 530 stored thereon. The at least one processor 510 is configured to load the instructions 530 into memory for processing. The instructions 530 are arranged to cause the at least one processor 510 to perform a series of actions.

[0052] Instruction 540 is arranged to estimate the temperature of a print-bed area for at least one layer of a part being printed in a given fusing process.

[0053] Instruction 550 is configured to cause the processer 510 to calculate the current position of an axis carriage in relation to the given fusing process.

[0054] Instruction 560 is then configured to cause the processer 510 to determine a power to be applied to one or more fusing lamps for the given fusing process at least on the basis of the estimated temperature and the calculated position.

[0055] Instruction 570 is lastly configured to cause the processer 510 to transmit a control signal representative of the determined power to a fusing lamp controller.

[0056] The non-transitory storage medium can be any media that can contain, store, or maintain programs and data for use by or in connection with an instruction execution system. Machine-readable media can comprise any one of many physical media such as, for example, electronic, magnetic, optical, electromagnetic, or semiconductor media. More specific examples of suitable machine-readable media include, but are not limited to, a hard drive, a random access memory (RAM), a readonly memory (ROM), an erasable programmable read-only memory, or a portable disc.

[0057] Certain examples improve the fusing process by enabling accurate part melting without jeopardizing powder selectivity and creating unnecessary cake.

[0058] Certain examples improve the fusing process by enabling optimal part melting as power delivered can be controlled according to the part type and current temperature.

[0059] Certain examples improve the overall printing process as precise energy delivery improves mechanical properties of the parts.

[0060] Certain examples improve the fusing process by overcoming issues associated with brute force energy delivery which creates strong peaks of current on the power line which can affect flick and harmonic regulations. [0061] The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive or to limit these principles to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.

Claims

1 . An additive manufacturing system, the system comprising a fusing controller, the fusing controller being configured to:

receive image information from a thermal imaging camera, the received image information comprising image information associated with a given fusing process; on the basis of the received image information, estimate the temperature of a part being printed in a given fusing process;

receive positional information relating to an axis carriage, the received positional information indicating a current position of the axis carriage in the given fusing process; and

on the basis of at least the estimated temperature and the received positional information, determine a power to be applied to a fusing energy system for the given fusing process.

2. The system of claim 1 , the fusing controller being configured to:

receive further image information from the thermal imaging camera, the received further image information comprising image information associated with a subsequent stage of the given fusing process;

receive further positional information relating to the axis carriage, the received further positional information indicating a position of the axis carriage in the subsequent stage of the given fusing process;

on the basis of the received further image information, further estimate the temperature of the part being printed in the given fusing process; and

on the basis of at least the further estimated temperature and the received further positional information, dynamically determine an updated power to be applied to the fusing energy system for the subsequent stage of the given fusing process.

3. The system of claim 1 , wherein the estimated temperature comprises the estimated temperature of a print-bed area for at least one layer of the part being printed in the given fusing process.

4. The system of claim 1 , wherein the fusing controller is configured to calculate a desired fusing agent melt temperature for the given fusing process, and wherein the power to be applied to the fusing energy system for the given fusing process is further determined on the basis of the desired fusing agent melt temperature.

5. The system of claim 1 :

wherein the fusing controller is configured to calculate a desired fusing agent melt temperature for the given fusing process, and

wherein the fusing controller is configured to determine a lower power to be applied to the fusing energy system for the given fusing process when the estimated temperature is closer to the calculated desired fusing agent melt temperature than when the estimated temperature is further away from the calculated desired fusing agent melt temperature.

6. The system of claim 1 , wherein the fusing controller is configured to determine a higher power to be applied to the fusing energy system for the given fusing process when the received positional information indicates that the current position of the axis carriage is closer to a position of the part being printed in the given fusing process than when the received positional information indicates that the current position of the axis carriage is further away from a position of the part being printed.

7. The system of claim 1 , wherein the received positional information comprises one or more of: positional information associated with a position in the print-bed where a first part of fusing agent is to be applied, and

positional information associated with a position in the print-bed where a last part of fusing agent is to be applied.

8. The system of claim 1 , wherein the fusing controller is configured to transmit a control signal representative of the determined power to the fusing energy system.

9. A method of controlling a fusing sub-system in an additive manufacturing system, the method comprising:

receiving image information, the received image information having been generated by a thermal imaging system in relation to a given fusing process;

receiving positional information, the received positional information indicating the position of an axis carriage for the given fusing process;

determining, at least on the basis of the received image information and the received positional information, a power to be applied to one or more fusing lamps for the given fusing process; and

controlling the power applied to the one or more fusing lamps according to the determination.

10. The method of claim 9, comprising:

receiving further image information, the received image information having been generated by the thermal imaging system in relation to a subsequent stage of the given fusing process;

receiving further positional information, the received further positional information indicating the position of the axis carriage in the subsequent stage of the given fusing process; on the basis of the received further image information and the received further positional information, further determining an updated power to be applied to the one or more fusing lamps for the subsequent stage of the given fusing process; and dynamically controlling the power applied to the one or more fusing lamps according to the further determination.

1 1 . The method of claim 9, comprising calculating a desired fusing agent melt temperature for the given fusing process,

wherein the power to be applied to the one or more fusing lamps for the given fusing process is determined further on the basis of the desired fusing agent melt temperature.

12. The method of claim 9, comprising calculating a desired fusing agent melt temperature for the given fusing process,

wherein the determining comprises determining a lower power to be applied to the one or more fusing lamps for the given fusing process when the estimated temperature is closer to the calculated desired fusing agent melt temperature than when the estimated temperature is further away from the calculated desired fusing agent melt temperature.

13. The method of claim 9, wherein the determining comprises determining a higher power to be applied to the one or more fusing lamps for the given fusing process when the received positional information indicates that the current position of the axis carriage is closer to a position of a part being printed in the given fusing process than when the received positional information indicates that the current position of the axis carriage is further away from a position of the part being printed.

14. The method of claim 9, wherein the received positional information comprises one or more of: positional information associated with a position in the print-bed where a first part of fusing agent is to be applied, and

15. A non-transitory computer-readable storage medium storing instructions that, if executed by a processor of a three-dimensional printing system, cause the processor to:

estimate the temperature of a print-bed area for at least one layer of a part being printed in a given fusing process;

calculate the current position of an axis carriage in relation to the given fusing process;

determine, at least on the basis of the estimated temperature and the calculated position, a power to be applied to one or more fusing lamps for the given fusing process; and

transmit a control signal representative of the determined power to a fusing lamp controller.