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Patent Searching and Data


Title:
MATERIAL REMOVING UNIT
Document Type and Number:
WIPO Patent Application WO/2021/066790
Kind Code:
A1
Abstract:
A material removing unit for a three-dimensional (3D) printing system which comprises a housing coupleable to the 3D printing system,a number of air knives which are rotatably mounted inside the housing and a control unit. The control unit controls the rotation of the air knives such that they remove excess build material from a 3D object generated by the 3D printing system and from the inside of the housing.

Inventors:
DIOSDADO BORREGO, Jorge (Barcelona, Sant Cugat del Valles, ES)
CHANCLON FERNANDEZ, David (Barcelona, Sant Cugat del Valles, ES)
MURCIEGO RODRIGUEZ, Pablo Antonio (Barcelona, Sant Cugat del Valles, ES)
Application Number:
US2019/053764
Publication Date:
April 08, 2021
Filing Date:
September 30, 2019
Export Citation:
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Assignee:
HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P. (Spring, Texas, US)
International Classes:
B29C64/35; B29C64/379; B33Y40/20; B08B5/00
Attorney, Agent or Firm:
WOODWORTH, Jeffrey C. et al. (3390 East Harmony RoadMail Stop 3, Fort Collins Colorado, US)
Download PDF:
Claims:
WHAT IS CLAIMED IS:

1 . A material removing unit for a three-dimensional (3D) printing system com prising: a housing coupleable to the 3D printing system, a number of air knives which are rotatably mounted inside the hous ing, a control unit to control the rotation of the air knives such that the air knives are to remove excess build material from a 3D ob ject generated by the 3D printing system and from the inside of the housing.

2. The material removing unit according to claim 1 , wherein the housing comprises an opening which is arranged to face an opening in a housing of the 3D printing system when the ma terial removing unit is coupled to the 3D printing system; the housing of material removing unit and the housing of the 3D printing system form a sealed unit; the number of air knives remove excess build material from the 3D object which is placed within the sealed unit by applying an air flow.

3. The material removing unit according to claim 1 , wherein the housing of the material removing unit is to house the 3D object.

4. The material removing unit according to claim 1 , wherein the air knives are rotated by a driving system.

5. The material removing unit according to claim 1 , wherein the number of air knives are mounted orientable inside the housing of the material removing unit.

6. The material removing unit according to claim 2, wherein a second mate rial removing unit is sealed to the sealed unit, the second material remov ing unit comprising any or a combination of: a vibration mechanism to loosen excess build material from the 3D object; an air inlet and an air outlet to generate a laminar air flow to remove excess build material from the 3D object.

7. The material removing unit according to claim 1 , wherein at least two air knives extend parallel and spaced apart to each other over a length of the housing of the material removing unit.

8. The material removing unit according to claim 1 , further comprising an out let to exhaust and collect excess build material.

9. The material removing unit according to claim 1 , wherein the control unit is to control the pressure and mass flow of the air of the air knives.

10. Method to remove excess build material from a three-dimensional (3D) ob ject generated by a 3D printing system, comprising: removing excess build material with a number of air knives which are rotatably mounted inside a housing of a build material re moving unit coupleable to the 3D printing system from the 3D object and from the inside of the housing.

11 . The method according to claim 11 , further comprising coupling the build material removing unit to the 3D printing system such that an opening of the build material removing unit is arranged to face an opening of the 3D printing system; establishing a sealed unit of the housing of the material removing unit and housing of the 3D printing system; applying an air flow to the 3D object placed within the sealed unit.

12. The method according to claim 12, further comprising any or a combina tion of: vibrating the 3D object to loosen excess build material; applying a laminar air flow to the 3D object to remove excess build material

13. The method according to claim 12, further comprising rotating the number of air knives up to full turns thereby removing excess build material of the 3D object and cleaning the inside of the sealed unit.

Description:
MATERIAL REMOVING UNIT

BACKGROUND

[0001] The description is related to a three-dimensional (3D) printing sys tem. A 3D printer uses additive printing processes to make 3D objects from a digital 3D object model file. More particularly, the description is related to a material re moving unit for objects produced in a 3D printing system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Features of examples will be described, by way of example, in the following detailed description with reference to the accompanying drawings in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a pre viously described function may or may not be described in connection with other drawings in which they appear.

[0003] Non-limiting examples will now be described with reference to the accompanying drawings, in which:

[0004] Fig. 1 shows a front view of an example of a material removing unit coupleable to a 3D printing system.

[0005] Fig. 2 shows a side view of an example of the material removing unit coupleable to a 3D printing system.

[0006] Fig. 3 shows a bottom view of an example of the material removing unit coupleable to a 3D printing system.

[0007] Fig. 4 shows a front view of an example of the material removing unit coupled to a 3D printing system.

[0008] Fig. 5 shows a side view of an example of the material removing unit coupled to a 3D printing system. [0009] Fig. 6 shows an interior view of an example of the material removing unit coupled to a 3D printing system.

[0010] Fig. 7 shows another interior view of an example of the material re moving unit coupled to a 3D printing system.

[0011] Fig. 8 shows an example of the material removing unit coupled with a secondary material removing unit and a 3D printing system.

[0012] Fig. 9 shows a side view of an example of the material removing unit coupled with a secondary material removing unit and a 3D printing system.

[0013] Fig. 10 - Fig. 13 show examples of a material removing method of a material removing unit.

DETAILED DESCRIPTION

[0014] In some 3D printing systems, for example, a 3D object may be formed on a layer-by-layer basis where each layer is processed and combined with a subsequent layer until the 3D object is fully formed.

[0015] In various 3D printing systems, a 3D object being produced may be defined from a 3D object model file. Information in such a 3D object model file comprises 3D geometric information that describes the shape of the 3D model. The 3D geometric information in a 3D object model file may define solid portions of a 3D object to be printed or produced. To produce a 3D object from a 3D object model, the 3D model information may be processed to provide 2D planes or slices of the 3D model. Each 2D slice generally comprises an image and/or data that may define an area or areas of a layer of build material as being solid object areas where the build material is to be solidified during a 3D printing process.

[0016] In some powder-bed 3D printing systems a 2D slice of a 3D object model may be produced by spreading a thin layer of build material over a print bed in a build unit of the 3D printing system. This layer of build material is to selectively receive a functional agent such as a binding agent or a fusing agent. Conversely, areas of a build material layer that are not defined as object areas by a 2D slice comprise non-object areas where the build material is not to be solidified and will not receive a functional agent. The procedure of spreading build material and ap plying a functional agent is repeated until completion of the 3D object. In some systems, energy may be applied to cause coalescence or solidification of build material.

[0017] Within 3D printing systems, the term “build material” is to be gener ally understood as a physical substance that can be used to generate an object via 3D printing. Examples of such build material include sand, cements, ceramics, textiles, biomaterials, lactose powders, glass, resins, ceramics, plastics, polymers or metals. Examples of build material may also include a combination of a number of build materials. In some 3D printing systems, the build material is in powder form. In other 3D printing systems, the build material is in the form of paste mate rial, solid material, slurry material or liquid material.

[0018] In some 3D printing systems, the liquid functional agent may com prise a binding agent. The selective application of this binding agent, by for exam ple a printhead, causes the particles of the powdered material to solidify, generally after energy (such as heat or ultra-violet light) is applied. In one example, each layer of build material and binding agent is solidified immediately after printing by curing the binding agent. In another example, the contents of the build unit are heated to thermally cure the binder agent after printing is completed. After printing, or, as appropriate, after curing, a so-called cake is present in the build chamber which comprises the generated 3D objects as well as excess non-solidified powder material or artifacts which need to be removed. The excess powder may be the powder in each layer to which the binding agent has not been applied. The 3D objects may then be removed from the powder. The 3D objects may undergo a cleaning process before entering a sintering oven where final strength of the 3D objects is achieved by fusing the particles. In some 3D printing systems, the com position of the binder is based on the characteristics of the build material. In the following, binding agent and binder are used interchangeably.

[0019] The cleaning process avoids that residual parts or excess powder particles sinter together with the generated 3D object which would otherwise result in erroneous parts. The cleaning process may comprise a first, coarse cleaning, and a second, fine cleaning. The coarse cleaning may comprise removing a ma jority of powder material from around the generated 3D object. The fine cleaning may comprise removing the remaining material that may be in contact with a sur face of the 3D object.

[0020] The cleaning process may also comprise cleaning the inside of the housing of the 3D printing system where the 3D object was generated before real izing a new printing job to avoid undesired conglomeration with subsequent print ing orders, thereby reducing error probability of printed objects.

[0021] In the printing of metal parts by binding and curing using a binder agent, a generated object may have relatively low strength and so may be easily broken by an operator. Thus, reducing operator intervention in the material removal process may reduce the risk of an operator breaking the object. In some examples, the cleaning process is fully automated with low or no operator intervention at all. Also, direct exposure of person to build material is avoided which may otherwise involve enhanced safety measures.

[0022] Examples described herein allow unfused or unbound build material to be removed from a cake to provide a clean generated 3D object. This may be achieved by herein provided material removing unit and related methods.

[0023] Fig. 1 - 14 show a material removing unit or corresponding methods wherein like reference numerals correspond to the same components. Fig. 1 shows a front view of an example of a material removing unit 10. The material removing unit 10 comprises a housing 12 which is coupleable to a 3D printing sys tem. The material removing unit 10 further comprises a number of air knives 11 which are rotatably mounted inside the housing 12. Fig. 1 illustrates various rota tion angles of one air knife with corresponding air flows 18 in doted lines. The air knives 11 may be rotated to sweep the complete inside of the housing 12 with a directed air flow 18. In an example, the sweeping angle of the air knives 11 is aadjustable such as to direct the air flows 18 to different subareas of the inside of the housing. The housing 12 of the material removing unit 10 may be coupleable to the 3D printing system by a locking mechanism 13 of the housing 12.

[0024] The material removing unit 10 further comprises a control unit 16 which controls the rotation of the number of air knives 11 such that excess build material is removed from the generated 3D objects and also from the inside of the housing 12. The control unit may comprise a user interface 17 for allowing the user to modify operation of the material removing unit. In some examples, the control unit 16 may control pressure and mass flow of the air. Further, the rotation speed and sweeping angle of the air knives 11 may be controlled by the control unit 16. The control 16 unit may provide a number of preset cleaning programs to be se lected.

[0025] The material removing unit 10 may comprise a number of air knives 11. In examples described herein, a “number of air knives” may comprise a single air knife as well a plurality of air knives. Thus, the number of air knives may produce one air flow or a plurality of air flows as well as one air curtain or a plurality of air curtains in examples described herein. Hereafter, “excess build material” may com prise powder to be loosened from the generated 3D object. In some examples, the material removing unit 10 may be arranged to house a 3D object. In one example, the material removing unit 10 may be a container separate from the main compo nents of the 3D printing system. The main components of a 3D printing system may include a printer, a build unit and a processing station. The material removing unit may be coupleable to the build unit of the 3D printing system for secure trans fer of the generated 3D objects. The material removing unit 10 may be coupled in a way which also avoids spillage of excess build material during transfer. In some examples, the material removing system 10 may be arranged to automatically move the generated 3D objects from the 3D printing system to the material remov ing unit 10. In some examples, the material removing unit 10 may be operated independently from the 3D printing system. In some example, the material remov ing unit 10 may be decoupled from the 3D printing system upon receipt of the 3D object(s) with the excess material removing being carried out at a location separate from the 3D printing system. Decoupling the material removing unit 10 from the 3D printing system may comprise closing the material removing unit 10 such as to avoid spillage of excess build material.

[0026] In another example, the material removing unit 10 may be a further component of the 3D printing system. A locking mechanism 13 of the material re moving unit 10 ensures secure and reliable coupling to the 3D printing system. The material removal unit 10 may be arranged to automatically move the generated object within the 3D printing system to the material removing unit 10 after the object has been generated in a build bed of the 3D printing system. This may reduce operator intervention in the material removal process.

[0027] In some examples, the material removing unit 10 may have arrange ments for manual transport by a user. In other examples, the material removing unit 10 may have arrangements for machine-aided transport. The arrangements for machine-aided transport may be particularly helpful in automated production. [0028] Fig. 2 illustrates a side view of an example of the material removing unit 10. In some examples, the air knives 11 may extend parallel to and over the length of the housing 12 of the material removing unit 10.

[0029] In some examples, the air knives 11 are mounted rotatably inside the housing 12 of the material removing unit 10. A driving mechanism (not shown) may be configures to rotate the air knives 11 to remove excess build material from the generated 3D object and from the inside of the housing 12. The number of air knives 11 may be rotated such that different parts of the generated 3D objects are passed progressively. In other examples, the air knives are rotated to progressively clean the inside of the housing 12 of the material removing unit 10. In some exam ples, the air knives are rotated up to full turns.

[0030] In some examples, an air knife 11 is an air nozzle with a narrow and long slit arranged to generate an airflow by guiding air through the slit at defined pressure. The airflow leaves the slit at a predetermined exit air volume and velocity. In some examples, the air flow may resemble an air curtain with regular air flow over the length of the slit. In one example, the size of the slit may be modified to alter the air flow at defined pressure. The size of the slit may be modified by adding or removing shims to the slit. In some examples, the pressure of the air flow may amount to less than 10 bar.

[0031] In one example, the air knives 11 are mounted orientable in the inside of the housing 12 of the removing unit 10. The longitudinal axis of the air knives 11 may be oriented at a certain angle to one side of the housing 12 to remove excess build material from the generated 3D object. The longitudinal axis of the air knives 11 may be oriented at a certain angle to more than one side of the housing 12 to remove excess build material from the generated 3D object. In yet another exam ple, the air knives 11 may be mounted statically and the generated 3D objects are moved within the housing 12 of the material removing unit 10 to remove excess build material.

[0032] The number of air knives 11 may direct a corresponding number of air flows to cover the volume of the housing 12 of the material removing unit 10, thereby directing air to remove powder from different regions of the generated 3D object in the housing 12. This may permit the removal of excess build material without requiring human intervention.

[0033] In an example, the generated 3D objects may have complex shapes such that parts of the 3D object are concealed by other parts of the 3D object. Those parts may be partially reached by air that flows around the 3D object in a laminar manner. The air knives 11 may be arranged to enhance cleaning of such regions as they may be dynamically positioned within the three-dimensional space. In one example, the height of the air knives within the housing 12 may be modified. In another examples, the air knives may move progressively along the generated 3D objects. In yet another example, the air knives may rotate around their longitu dinal axis. In yet another example, all before mentioned positioning is applied.

[0034] In some examples, the number of air knives 11 directs a correspond ing number of curtains of air across a region of a generated 3D object and of the inside of the housing 12. In another example, the air knives 11 direct a correspond ing number of streams of air against a surface of a generated 3D object and of the inside of the housing 12. In some examples, the pressured air impinges on the 3D object and on the inside of the housing 12 with a perpendicular component.

[0035] In an example, the air knivesl 1 may apply plain air. In another exam ple, another gas or gaseous mixture may be applied by the air knives.

[0036] Fig. 3 shows a bottom view of an example of the material removing unit 10. The number of air knives 11 may extend parallel and spaced apart to each other over a length of the housing 12 of the material removing unit 10. In another example, the number of air knives 11 enclose an angle with the length of the hous ing 12 of the material removing unit 10. In yet another example, the air knives 11 may extend diagonally in the housing 12 of the material removing unit 10. Also, the height at which the air knives 11 are mounted within the housing 12 of the material removing unit 10 may be modified to the respective cleaning process.

[0037] In one example, the longitudinal axis of the number of air knives 11 may extend parallel to one side of the housing 12. In one example, the longitudinal axis of the number of air knives enclosed an angle with one side of the housing 12. In another example, the longitudinal axis of the number of air knives enclosed an angle with more than one side of the housing 12. In yet another example, the lon gitudinal axis of the number of air knives 11 may extend parallel to one side while being angular to one of two of the remaining sides of the housing 12.

[0038] In other examples, the control unit 16 may include a user interface 17 for allowing the user to configure operation of the material removing unit. In some examples, the user may select a subgroup of the number of air knives is to operate. In another example, the user may select a flow path from among a plural ity of possible flow paths of the number of air knives 11 . The control unit 16 may be modified to automatically operate a subgroup of the air knives 11 .

[0039] In some examples, the number of air knives 11 includes an elongated casing having an inlet for receiving air into the casing. The casing includes an elongated opening 14 that extends along the casing and allows air entering the casing through the inlet to exit the casing and to form a curtain of air. In some examples, the elongated casing is made from a piece of sheet metal bent to define a hollow region into which air is forced. The sheet metal may define an opening 14 along a length of the casing from which the air exits.

[0040] In some examples, the air knives 11 comprise an opening 14 to direct the air flow. In one example, the opening 14 may be a slit over the length of the air knives 11 . In another example, the opening 14 may comprise a plurality of holes over the length of the air knives 11 .

[0041] The air flow rate may be sufficient to loosen excess build material from the generated objects, whilst sufficiently low that abrasion of powder on the printed part of the object is reduced and the amount of powder entrained in the air is reduced. Metal powder is particularly abrasive and erosion of the generated 3D object by powder can impact on quality and tolerances of the generated 3D object.

[0042] In some examples, the housing 12 of the material removing unit 10 comprises an opening 15. The housing 12 may be arranged to face an opening in a housing of the 3D printing system. In other examples, the housing 12 of the ma terial removing unit may comprise an outlet (not shown) to exhaust and collect excess build material. In some examples, excess build material may be reused in another printing process.

[0043] Fig. 4 shows a front view of an example of the material removing unit

10 wherein the housing 12 of the material removing unit 10 is coupled to the hous ing 22 of the 3D printing system 20 such that the housings form a sealed unit 24. In one example, the opening 15 of the housing 12 of the material removing unit 10 may face an opening in the housing 22 of the 3D printing system 20. The locking mechanism 13 of the material removing unit is engaged with a counterpart 23 of the 3D printing system 20. In some examples, the sealed unit 24 may be a closed system which avoids any build material from leaking out. In some examples, the sealed unit may be a closed system comprising an outlet to exhaust excess build material.

[0044] In some examples, the 3D printing system includes a coater, a build unit with a build space or a build bed, a means for moving the build space or other components, a processing unit, a components station, a dosing device and a heat ing means. In some examples, the build unit may be removable from the 3D print ing system. In other examples, the build unit may be fixed to the 3D printing sys tem. In some examples, the build unit of the 3D printing system may comprise a lift to move the generated 3D object during printing and after completion.

[0045] Fig. 5 shows a side view of an example of the material removing unit coupled to a 3D printing system.

[0046] In some examples, excess build material may fall back into the build unit after removal. In other examples, excess build material may be collected out side the 3D printing system in a container connected to the 3D printing system.

[0047] Fig. 6 shows an interior view of an example of the material removing unit 10 coupled to a 3D printing system 20 such that the housings form a sealed unit 24. In one example, the number of air knives 11 is rotated simultaneously about the same angle such the air flow 18 of the number of air knives is in parallel. In another example, each of the number of air knives 11 is rotated at a given instant of time about a different angle such that they direct the air flows18 in different di rections. The air knives 11 may apply the air flow 18 on the generated 3D object 31 such that it also reaches interspaces. In some examples, the air flow 18 has a vertical component with respect to surface of the generated 3D objects 31 . The air knives 11 may also apply the air flow 18 on the inside of the housing 24 to remove excess build material.

[0048] In one example, the air knives 11 can be controlled to apply the air flow 18 to 3D objects positioned at different heights within the sealed unit 24. In one example, generated 3D objects 31 are positioned on a platform 33 within the 3D printing system 20. The platform 33 may be moved by a lift 34. Irrespective of the position of the platform 33 within the sealed unit 24, the air knives may be controlled to apply the air flow 18 to the generated 3D objects. In some examples, the platform 33 may be a meshed tray to allow removed build material to fall back into the 3D printing system.

[0049] Fig. 7 shows an interior view of a further example of the material re moving unit 10 coupled to a 3D printing system 20 such that the housings form a sealed unit 24. In this example, the generated 3D objects 31 are positioned on a platform 33 of the 3D printing system that is lifted into the material removing unit 10. The air knives 11 are controlled to apply the air flow 18 on the generated 3D objects now positioned within the housing 12 of the material removing unit 10.

[0050] In addition to the air knives 11 , the height of the platform 33 carrying the generated 3D objects may be controlled as well during the cleaning process.

[0051] In one example, the air knives 11 are rotated to clean the inside of the housing 12 of the material removing unit 10. In other examples, the air knives are rotated to clean the inside of the housing 22 of the 3D printing system 20. In one example, the air knives are rotated to clean the inside of the build unit of the 3D printing system 20.

[0052] Fig. 8 shows an example of the material removing unit 10 coupled with a secondary material removing unit 40 and a 3D printing system 20 such that the housings form a secondary sealed unit 45. The locking mechanism 13 of the material removing unit is now engaged with a locking mechanism 43 of the sec ondary material removing unit 40. A locking mechanism 43 of the secondary ma terial removing unit 40 is now engaged with a counterpart 23 of the 3D printing system 20.

[0053] In one example, the secondary material removing unit 40 may com prise a vibrating mechanism to loosen excess build material from the 3D object. The vibrating mechanism 41 may be arranged to vibrate the generated object, so that powder is loosened and falls away from the generated 3D object 31 . In an example, the vibrating mechanism 41 may be part of the locking mechanism 43 of the housing 42 of the secondary material removing unit 40. In an example, wherein the generated 3D objects are positioned on a platform 33 that is meshed, the loos ened powder may fall through the mesh when the object is vibrated and the loos ened powder may fall towards the bottom of the housing 22 of the 3D printing sys tem 20. The vibration mechanism may be suitable to vary the amplitude and/or frequency of the vibration. The control unit 16 may be suitable to control the am plitude and/or frequency of the vibration generated by the vibration mechanism.

[0054] In another example, the secondary material removing unit 40 may comprise a plurality of gas inlets and outlets 44 in the housing 42. A manifold of gas inlets and outlets 44 may be provided in a wall of the housing 42. The second ary material removing unit may comprise a plurality of manifolds on opposing walls of the housing 42. The gas inlets and outlets 44 may each comprise a valve, for example a pneumatic valve, for actuating the respective inlet or outlet. The plurality of gas inlets and outlets may be connectable, via the valves to a source of gas, for example air. The plurality of gas inlets and outlets may be connectable to a nega tive pressure source, for example a vacuum source. The valves may be arranged to control the gas inlets and outlets 44 such that each inlet and outlet 44 can se lectively act as an inlet or as an outlet or can be closed. The plurality of gas inlets and outlets in the housing may be are actuated to allow gas to flow through the housing.

[0055] In yet another example, the secondary material removing unit 40 may comprise both, a vibrating mechanism 41 and gas inlets and outlets 44. [0056] In one example of the secondary sealed unit 45, the air knives 11 are arranged to apply the air flow 18 on a generated 3D object positioned within the housing 12 of the material removing unit 10. In another example of the secondary sealed unit 45, the air knives 11 are arranged to apply the air flow 18 on a gener ated 3D object positioned within the housing 42 of the secondary material remov ing unit 40. In yet another example of the secondary sealed unit 45, the air knives 11 are arranged to apply the air flow 18 on a generated 3D object positioned within the housing 22 of the 3D printing system 20.

[0057] In one example, the air knives 11 are rotated to clean the inside of the of the secondary sealed unit 45.

[0058] In one example, the material removing unit 10 is coupled to the sec ondary material removing unit 40 such that they form a sealed unit. This sealed unit may be suitable to house generated 3D objects.

[0059] An example method 100 for coarse cleaning of a generated 3D ob ject is shown in Fig. 10. The method may be implemented by the material removing system 10 shown in figures 1 -9. Prior to the method 100, the 3D object may be generated in a 3D printing system 20 by a printing process. The 3D object may be an object formed through forming layers of fused powder, or may be formed by binding layers of metal powder and curing the bound layers. In some examples, the 3D object may be enclosed or surrounded by excess build material. In other examples, excess build material or artifacts may adhere on the 3D object. Such excess material may be removed from the generated 3D object by a number of air knives 11 in block 101 .

[0060] In one example, the air knives 11 are rotated for coarse cleaning of the generated 3D object 31 . In another example, the generated 3D objects 31 are moved relative to the air knives 11 for coarse cleaning.

[0061] Fig. 11 shows a further method 200 for removing build material from a generated 3D object. The method comprises coupling the material removing unit 10 to the 3D printing system 20. In some examples, the opening of the build mate rial unit 10 is arranged to face an opening of the 3D printing system 20 in block 201 . In some examples, the build material unit 10 may be coupled on top of the 3D printing system 20 such that a bottom opening of the material removing unit 10 and a top opening of the 3D printing 20 system are adjoining. In other examples, the material unit 10 may be coupled to one of the sides of the housing 22 of the 3D printing system 20 comprising an opening. A sealing connection between the hous ing of the material removing unit 10 and the housing of the 3D printing system 20 is established in block 202 such that they together form a sealed unit 24. Excess build material is removed from the 3D object by applying the air flow 18 on the 3D object which is positioned within the sealed unit 24.

[0062] In some examples, excess built material is collected in the 3D print ing system 20. In other examples, excess built material is exhausted through an outlet and collected outside the sealed unit 24. In some examples, the collected build material may be reused in a further printing process.

[0063] Fig. 12 shows a further method 300 for removing excess build mate rial. In addition to method 200 presented in Fig. 11 , the generated 3D object may be vibrated in an example to loosen excess build material from it in block 301 . In another example, laminar air flow may be applied to the 3D object to remove ex cess build material in block 302 in addition to method 200. In yet another example of method 300, the 3D object may be vibrated as well as to be exposed to a laminar air flow to remove excess build material in addition to the method 200.

[0064] Fig. 13 shows a further method 400 in which the air knives 11 are rotated up to full terms thereby removing excess build material of the generated 3D object as well as cleaning the inside of the sealed unit in block 401. The number air knives 11 may be rotated by a driving mechanism up to 360 degrees.

[0065] While the method, apparatus and related aspects have been de scribed with reference to certain examples, various modifications, changes, omis sions, and substitutions can be made without departing from the spirit of the pre sent disclosure. It is intended, therefore, that the method, apparatus and related aspects be limited by the scope of the following claims and their equivalents. [0066] It should be noted that the above-mentioned examples illustrate ra ther than limit what is described herein, and that those skilled in the art will be able to design many alternative implementations without departing from the scope of the appended claims. Features described in relation to one example may be com bined with features of another example.