WO2020219048A1

WO2020219048A1 - Conditioning build material for additive manufacturing

Info

Publication number: WO2020219048A1
Application number: PCT/US2019/029084
Authority: WO
Inventors: Pol FORNOS MARTINEZ; Maria del Carmen QUEROL ESPARCH; Maria de las Mercedes BLANCO ROLLAN
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2019-04-25
Filing date: 2019-04-25
Publication date: 2020-10-29

Abstract

A method comprising depositing successive layers of powdered build material in an additive manufacturing system to form a bed of build material and applying energy to each layer of powdered build material after each layer has been deposited to condition each layer of powdered build material, thereby forming a bed of powdered conditioned build material.

Description

CONDITIONING BUILD MATERIAL FOR ADDITIVE MANUFACTURING

BACKGROUND

[0001] Polymer materials have different melting temperatures depending on the composition of the polymer or its method of manufacture. More particularly, some polymers have a wide temperature range across which melting takes place. Polymer material that has undergone a thermal conditioning or annealing process may exhibit a narrower melting temperature range and an increased melting temperature than polymer which has not been conditioned in this manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Figure 1 is an example of a method that may be used to condition a build material in an additive manufacturing system.

[0003] Figure 2 is an example of a method that may be carried out using a 3D printer to anneal a build material.

[0004] Figure 3 is an example of a non-transitory computer readable medium coupled to a processor and an additive manufacturing system.

DETAILED DESCRIPTION

[0005] Annealing of polymers may involve applying energy to a polymeric material in the form of heat. Semi-crystalline polymeric material is heated to a temperature below its melting point and then allowed to cool. The temperature to which the polymeric material is heated may also be above the polymer’s glass transition temperature. Heating a semi-crystalline polymer in this manner may relieve internal stresses present in the polymer structure following its manufacture or fabrication. The annealing process may also change the crystal structure or the degree of crystallinity of a polymer whilst promoting the formation of additional polymeric crosslinks in some circumstances. As explained above, annealing a previously unannealed polymer may result in a narrowing of the polymer’s melting temperature range and an increase in its melting temperature. [0006] Polymers are one of many build materials suitable for the formation of a 3D object using an additive manufacturing system such as a 3D printer. Some of the polymeric build materials that impart desirable properties to a finished printed 3D object may possess a wide melting temperature range which in turn may pose challenges when these materials are used for fabrication of a 3D object. A polymer with a wide melting temperature range may limit an additive manufacturing system’s capability to maintain thermal control of said polymer during the build process. Polymers may therefore be subjected to a thermal conditioning process, such as annealing, prior to their use for the formation of a 3D object. The consistency and quality of a 3D building process may be improved by using a conditioned polymer for construction. Semi-crystalline polymeric materials that may be suitable for conditioning using an additive manufacturing apparatus include polyamides, polypropylenes, polyethylene treaphthalates, and combinations thereof. In an example, a polymeric build material may comprise polypropylene. The build material may be in the form of a powder. A powdered build material may comprise powders, spheres, granules, pellets, fibres, platelets, particles of irregular shape, hollow particles, and combinations thereof. In some examples the powder may be formed from, or may include, short fibres that may, for example, have been cut into short lengths from long strands or threads of material. In other examples, the powder may be formed from, or may include, substantially spherical particles. In yet other examples, the powder may be formed from, or may include particles of irregular shape.

[0007] Additive manufacturing systems may utilise powdered build materials for the formation of 3D objects. In operation, one or more powdered build materials may be deposited on a build surface of an additive manufacturing system and then fused to form a desired 3D object. The powdered build materials may be provided to end users having already undergone thermal conditioning during the manufacturing process. The end user is therefore provided with an annealed product that may be used immediately in a printing device. However, thermal treatment of material on a large scale may increase the cost of manufacture and the increased cost of manufacture may be passed on to the end user in the form of an increased cost of the build material at point of sale. The total cost of ownership may therefore be reduced for an end user if they are able to obtain unconditioned or unannealed build material, which may be referred to as fresh build material or virgin build material, at a reduced cost and then perform the thermal conditioning process using an additive manufacturing system.

[0008] Figure 1 shows an example of a method 100 that may be used to condition a build material. The method may comprise depositing successive layers of powdered build material in an additive manufacturing system to form a bed of build material 101 and applying energy to each layer of powdered build material after each layer has been deposited to condition each layer of powdered build material, thereby forming a bed of powdered conditioned build material 102. As the additive manufacturing system is not being used to fabricate a 3D object and is annealing the powdered build material, no portion of the deposited powdered build material is fused by the applied energy. In effect, all of the deposited build material will remain in the form of a powder after energy is applied to each layer of powdered build material constituting the conditioned material bed. The conditioned powdered build material may subsequently be transferred in whole or in part to a powder storage medium from where it may be utilised for the production of a 3D object using the additive manufacturing apparatus. The conditioned powdered build material may be used substantially immediately after conditioning or may instead be stored in the storage medium and used in the formation of a 3D object some time later.

[0009] The conditioning of the build material may be wholly, or in part, performed automatically by an additive manufacturing apparatus in response to a user selecting a mode of operation on the additive manufacturing system. In an example, the depositing of successive layers and the applying energy to each layer are performed by the additive manufacturing system without further user input in response to a user selecting a material conditioning mode on the additive manufacturing system.

[0010] Energy, in the form of heat, may be applied to the build material via heating elements, thermal lamps or other heating means forming part of the additive manufacturing apparatus. Some additive manufacturing systems include independent warming and fusing heating components. In such additive manufacturing apparatus, the warming heating component is intended to warm the build material, whereas the fusing heating component is intended to fuse or melt the build material during formation of a 3D object. In an example, the heat energy to condition the build material may be applied to the build material using the fusing heating component. In another example, the heat energy to condition the build material may be applied to the build material using the warming heating component. In yet another example, the heat energy to condition the build material may be applied to the build material via both the warming and the fusing heating elements. The melting point of the unconditioned and conditioned build material may be known prior to carrying out the conditioning process, thereby allowing the amount of energy applied to each layer of powdered build material to be selected and controlled to heat the build material to a temperature below its melting point. In an example, the energy E to heat a build material to a sufficient temperature may be calculated using a build material’s heat capacity C, the mass of build material to be heated M _Uiid, the increase of material temperature DT and the efficiency of heat transfer from the heating component of the additive manufacturing system to the build material K. The energy may therefore be calculated using the formula:

E = C x Mbuiid x DT x K

The powdered build material will not melt or fuse during the conditioning process provided temperature control is achieved, and consequently the build material will remain wholly in the form of powder following application of energy to each layer of powdered build material. The melting behaviour of a build material may be characterised by a melting curve with a peak designating the material’s melting point. The melting curve and melting point of a material may be determined via differential scanning calorimetry (DSC). The build material may be heated to a temperature below the lower temperature range of the material’s melting curve to prevent the melting of the material during the annealing process. In an example, a powdered build material may be heated to between 30 °C and 2 °C below its melting point. In another example, a powdered build material may be heated to between 20 °C and 5 °C below its melting point. In yet another example, a powdered build material may be heated to between 10 °C and 8 °C below its melting point. In a further example, a powdered build material may be heated to between 20 °C and 15 °C of its melting point. The amount of energy to be applied to the unconditioned powdered build material will depend upon the volume and dimensions of the bulk material to be annealed, the particle size of the powdered material, the heat capacity of the build material, the efficiency of energy transfer to the material, and the increase in temperature of build material to carry out the annealing process. The temperature to which the build material must be heated to carry out the annealing process will depend upon the melting point and melting curve of the material which may in turn be influenced by the chemical structure of the build material and presence of any additives or impurities in the build material. In an example, a polypropylene powder build material may have a melting point of 140 °C with a melting curve extending ±15 °C from the melting point peak. In this example, the powdered polypropylene build material may be heated to between 120 °C and 125 °C to perform the annealing process.

[0011] The thickness of each deposited layer of powdered build material will be of a thickness to allow sufficient energy to transfer throughout each layer of build material such that the entire thickness of a build material layer is suitably conditioned without causing the material in closest proximity to the 3D printer’s heating component to be heated beyond its melting point. Consequently, each layer of powdered build material may be heated to within a desired temperature range to promote conditioning prior to the deposition of the next successive layer of build material. The entirety of each layer of build material may be heated to one consistent temperature, or different regions of each layer may be brought to different temperatures suffice that all material is suitably conditioned and no material is provided sufficient energy to melt. In an example, an additive manufacturing system may deposit layers of the maximum possible thickness such that sufficient heat energy may still penetrate the entirety of the layer to allow the entire layer to be annealed. In this example, the additive manufacturing system may operate at the highest available speed of material deposition to maximise material throughput.

[0012] In use, an additive manufacturing system will deposit a layer of at least partially unconditioned build material. The layer of at least partially unconditioned build material will then be subjected to heat energy to condition the layer. Additional layers of build material may then be deposited on top of the layers of conditioned build material and the layers individually conditioned until a desired quantity of conditioned build material is obtained by a user. As previously described, each layer of powdered build material deposited in the additive manufacturing system will remain in the form of a powder throughout the conditioning process. Each layer of deposited powdered build material may be substantially the same thickness as each other layer of deposited powdered build material or each layer of deposited build material may be of a different thickness to at least one other layer of deposited build material, suffice that each layer is of sufficient thickness to ensure that energy may be applied to the additional layer to cause conditioning without melting the layer. For example, where a precise quantity of additional conditioned build material is desired, the next of the successive layers of build material deposited in the additive manufacturing apparatus may be of reduced thickness when compared to a previously deposited layer of build material to provide a combined conditioned powder bed formed by the combined layers that matches the desired quantity of conditioned build material sought by the user.

[0013] As the use of unconditioned build material may contribute to quality issues during the formation of a 3D object and, as the method of conditioning the build material is intended to prepare unconditioned build material for a 3D printing process, no agents such as fusing agents or detailing agents are added during the conditioning process. The addition of fusing or detailing agents may result in the fusing of the powder and the unintended formation of a 3D object which would prevent the fused volume of powder from being conditioned and re used for 3D object fabrication. Fused build material may be unsuitable for use in the production of a 3D object and the fusing or melting of material may prevent the entire bed of conditioned build material from being transferred into a storage medium for use in the construction of a 3D object. Consequently, the methods and examples provided maintain the build material in wholly powdered form throughout the conditioning process such that all of the powder deposited during the conditioning process may be subsequently used for formation of a 3D object.

[0014] The powdered build material deposited to form each layer of build material may be formed entirely from unconditioned build material or may comprise both unconditioned and previously conditioned build material. Repeated conditioning of polymeric build materials will typically impart no adverse effects upon the characteristics of the materials. Repeated conditioning processes may further narrow the melting point range of a material or increase the melting point of that material if earlier conditioning processes had not been sufficient to completely condition the material. In effect, a mixture of unconditioned and conditioned material may be conditioned together to yield a layer of conditioned build material.

[0015] An example of a method 200 that may be carried out using an additive manufacturing system such as a 3D printing apparatus is shown in Figure 2. The method may comprise selecting an annealing mode 201 in a 3D printing apparatus which causes the 3D printing apparatus to perform operations 210. The operations may comprise depositing a first layer of powdered build material on a receiving surface of a platform of the 3D printing apparatus 21 1 , applying energy to the first layer of powdered build material to form a bed of annealed powdered build material 212, depositing a second layer of powdered build material on the bed of annealed powdered build material 213, and applying energy to the second layer of powdered build material to increase the thickness of the bed of annealed powdered build material 214. The bed of annealed build material formed in the 3D printing apparatus may then be transferred to a storage medium 220.

[0016] The layers of powdered build material may be deposited across the entire surface area of the receiving surface of the platform of the 3D printing apparatus or may be deposited across part of the surface area of the receiving surface of the platform. The platform of the 3D printing apparatus may be at least partially enclosed by one or more walls to form a bed of powder in the 3D printing apparatus. The deposited powdered build material may be formed of unannealed powdered build material or a mixture of previously annealed and unannealed build material. In an example, the deposited powdered build material may comprise 100% unannealed build material. In another example, the deposited build material may comprise up to 50% of unannealed build material. In a further example, the deposited powdered build material may comprise up to 30% unannealed build material. In yet another example, the deposited powdered build material may comprise up to 20% unannealed build material. Once deposited, annealed and transferred to the storage medium, at least part of the annealed powdered build material in the storage medium may be used in the building or fabrication of a 3D object using the 3D printing apparatus.

[0017] The method may further comprise determining the quantity of annealed powdered build material present in a build unit and comparing the quantity of annealed powdered build material present in the build unit with the quantity of annealed powdered build material to complete a build job. In an example, the build unit may be removable from the 3D printing apparatus. In another example, the build unit may be a fixed component of the 3D printing apparatus. If the quantity of annealed powdered build material to complete a build job is greater than the quantity of annealed powdered build material in the build unit, the quantity of additional annealed powdered build material to complete the build job may be determined by subtracting the quantity of annealed powdered build material present in the build unit from the quantity of annealed powdered build material to complete a build job. Once the quantity of additional annealed powdered build material to complete a build job has been determined, the 3D printing apparatus may deposit and anneal additional successive layers of powdered build material until the quantity of additional annealed powdered build material has been produced. In an example, a user may fill a build unit with 100% fresh, virgin, or unannealed powdered build material from a storage tank containing fresh powdered build material. The build unit may then be used to condition or anneal the unconditioned powdered build material as previously described. The annealed build material may then be stored in a build unit or transferred to a storage tank containing conditioned or annealed powdered build material. An empty build unit may then be filled with annealed powdered build material or a mixture of annealed and unannealed powdered build material prior to the construction of a 3D object using the build material in the build unit.

[0018] The determination of the quantity of additional annealed powdered build material may be performed wholly or in part by the 3D printing apparatus. The determination of the quantity of additional annealed powdered build material may be performed prior to commencing a build job using the 3D printing apparatus to ensure that sufficient annealed powdered build material is present in the build unit to complete the entire job. The determination of the quantity of additional annealed powdered build material may also be performed throughout or during a build job. If insufficient annealed powdered build material is present in the build unit during a build job, the 3D printing apparatus may notify a user that additional annealed powdered build material is wanted and provide the option of selecting the annealing mode to produce the additional annealed powdered build material to complete the build job. In some circumstances, the 3D printing apparatus may automatically initiate an annealing process in response to determining that insufficient annealed powdered build material is present in the build unit to complete a current build job. In an example, the determination of the quantity of annealed powdered build material present in the build unit, the comparison of the quantity of annealed powdered build material to complete a build job and the calculation of the quantity of additional annealed powdered build material to complete the build job may be carried out by the 3D printing apparatus in response to the user selecting an annealing mode on the 3D printing apparatus. In another example, upon obtaining a quantity of fresh or unconditioned build material, a user may choose to anneal the quantity of fresh build material without planning for a particular build job. In this example, the user prepares the conditioned build material so that it is ready and available when a build job is to be started.

[0019] Figure 3 shows an example of a non-transient computer readable medium storing instructions that, when executed by a processor 301 communicably coupled to an additive manufacturing system 303, causes the additive manufacturing system 303 to perform an annealing operation. The annealing operation may comprise depositing a first layer of powdered build material on a receiving surface of a platform of the additive manufacturing system 310; annealing the first layer of powdered build material to form a bed of annealed powdered build material 31 1 ; depositing a second layer of powdered build material on the bed of annealed powdered build material 312; and annealing the second layer of powdered build material to increase the thickness of the bed of annealed powdered build material 313. The non-transient computer readable medium may be any electronic magnetic, optical or other physical storage device that stores executable instructions, sometimes referred to as a memory 302. Thus, the non-transient computer readable medium may be, for example, Random Access Memory (RAM), and Electrically-erasable Programmable read-Only Memory (EEPROM), a storage drive, an optical disc, and the like.

Claims

1. A method comprising:

depositing successive layers of powdered build material in an additive manufacturing system to form a bed of build material; and

applying energy to each layer of powdered build material after each layer has been deposited to condition each layer of powdered build material, thereby forming a bed of powdered conditioned build material;

wherein no portion of the deposited powdered build material is fused by the applied energy.

2. The method as claimed in claim 1 , wherein the depositing successive layers and the applying energy are performed by the additive manufacturing system in response to a user selecting a material conditioning mode in the additive manufacturing system.

3. The method as claimed in claim 1 , further comprising transferring the entire bed of conditioned powdered build material into a powder storage medium.

4. The method as claimed in claim 1 , wherein no agents are added to any of the successive layers of powdered build material during the conditioning process.

5. The method as claimed in claim 1 , wherein the energy is heat energy.

6. The method as claimed in claim 1 , wherein the powdered build material comprises polypropylene.

7. The method as claimed in claim 1 , wherein the powdered build material comprises a mixture of unconditioned powdered build material and previously conditioned powdered build material.

8. A method comprising:

selecting an annealing mode in a 3D printing apparatus which causes the 3D printing apparatus to perform operations comprising:

depositing a first layer of powdered build material on a receiving surface of a platform of the 3D printing apparatus; applying energy to the first layer of powdered build material to form a bed of annealed powdered build material;

depositing a second layer of powdered build material on the bed of annealed powdered build material; and

applying energy to the second layer of powdered build material to increase the thickness of the bed of annealed powdered build material;

and transferring the bed of annealed build material formed in the 3D printing apparatus to a storage medium.

9. The method as claimed in claim 8, wherein the layers of powdered build material are deposited across the whole surface area of the receiving surface of the platform of the 3D printing apparatus.

10. The method as claimed in claim 8, further comprising:

determining the quantity of annealed powdered build material present in a build unit;

comparing the quantity of annealed powdered build material present in the build unit with the quantity of annealed powdered build material to complete a build job; calculating the quantity of any additional annealed powdered build material to complete the build job.

11. The method as claimed in claim 10, further comprising depositing and annealing additional successive layers of powdered build material to obtain the additional powdered build material to complete the build job.

12. The method as claimed in claim 1 1 , wherein the selection of the annealing mode causes the 3D printing apparatus to perform the determining, the comparing, the calculating and the depositing and annealing additional successive layers of powdered build material.

13. The method as claimed in claim 8, wherein the deposited powdered build material comprises a mixture of previously annealed and unannelaed build material.

14. The method as claimed in claim 8, further comprising utilising at least part of the annealed build material in the storage medium to build a 3D object using the 3D printing apparatus.

15. A non-transient computer readable medium storing instructions that, when executed by a processor communicably coupled to an additive manufacturing system, causes the additive manufacturing system to perform an annealing operation comprising:

depositing a first layer of powdered build material on a receiving surface of a platform of the additive manufacturing system;

annealing the first layer of powdered build material to form a bed of annealed powdered build material;

annealing the second layer of powdered build material to increase the thickness of the bed of annealed powdered build material.