WO2020126212A1

WO2020126212A1 - Noise absorbing jacket made in a 3d printing process

Info

Publication number: WO2020126212A1
Application number: PCT/EP2019/080746
Authority: WO
Inventors: Saeed Davoudabadi FARAHANI
Original assignee: Danfoss A/S
Priority date: 2018-12-20
Filing date: 2019-11-08
Publication date: 2020-06-25

Abstract

Noise generating devices in residential and industrial applications can be silenced by way of 3D printed noise dampeners. A noise reducing jacket intended for being mounted fully or partly around a noise generating device is characterized in that the noise reducing jacket comprises a wall and a chamber, wherein the wall consists of 3D printed powder material which has been sintered, and the chamber is filled with 3D printer powder material which is not sintered. A noise reducing jacket and a method for 3D printing such jacket is disclosed. In one embodiment of the invention the noise reducing jacket is applied to a refrigerant expansion valve.

Description

NOISE ABSORBING JACKET MADE IN A 3D PRINTING PROCESS

FIELD OF THE INVENTION

The present invention relates to the area of reduction or cancellation of noise generated by a noise generating device such as pipes, actuators, pumps, electrical motors or valves. Such noise can be a nuisance in industrial and residential areas alike.

BACKGROUND OF THE INVENTION

It is well known to add noise reduction jackets to devices such as pumps and valves which become noise generators because of the flowing liquid that is throttled or boosted by the valve. A typical solution is to provide a jacket or shell made in flexible foam having good noise absorption properties, and then wrap the jacket around the noisy device. The jacket is often made in two halves, wherein each half has a depression that corresponds to the shape of the noise generating device. Mating the two halves with the device in the middle then isolates and dampens the noise. Solutions like this is known from heating and cooling installations. Expansion valves in refrigeration systems are frequently a source of noise.

A drawback with these flexible foam jackets is that they are bulky and takes up a large space. This can be a problem in a narrow space with many pipe fittings. Further, some jackets do not fully cope with the noise level and has a poor dampening performance. Based on these drawbacks the present invention suggests a noise reduction jacket which is improved both in acoustic dampening performance and reduced in size.

DESCRIPTION OF THE INVENTION

The problem described is solved with a noise reducing jacket intended for being mounted fully or partly around a noise generating device where the noise reducing jacket comprises a wall and a chamber and the wall consists of 3D printed powder material which has been sintered, and the chamber is filled with 3D printer powder material which is not sintered .

More specifically the noise reducing jacket has in one of its surfaces a depression which has a shape or form that essentially matches the shape or form of the noise generating device. The device is so to speak nested inside the noise reducing jacket which surrounds either the whole noise generating device or only a part of it. That surface of the jacket that has the shape depression is the interfacing wall between the device and a chamber inside the jacket which chamber is filled with unused, i .e. un-sintered, 3D printer powder. The technical effect of this design of a noise jacket, frequently called a muffler, is that an improved reduction of the amplitude of the noise is obtained due to good absorption characteristics of the un sintered, i .e. unbonded, particles of the 3D printer powder. Noise reduction of 10 to 20 dB can be achieved with this design. This approach for generating a noise jacket is surprising because normally only the sintered parts plays a role in 3D printing, and the un-sintered 3D powder is normally quickly removed as waste, having no role at all in the final product. Contrary to this the current invention specifically makes use of the un-sintered powder.

The noise reducing jacket is preferably made in one material . The sintered powder material and the non-sintered powder material are of the same type, for example polyamide. The technical effect of having the same type of 3D printer material for the wall and the chamber is that manufacturing is easy as one does not need one material for the wall and another material as powder for absorbing noise. The jacket can be made in one go. Even though the material used for the wall and the chamber is the same the amount of powder used can be varied. Thus, for the wall one density of powder can be used and for the chamber another density. An average grain size of the powder is between 50-100 micrometer. By varying the size, shape and/or density of the absorption powder changed noise absorption

characteristics can be achieved. It is especially preferred if the absorption powder consists of inhomogenous particles i .e. particles that have a spherical shape mixed with particles that are e.g . pyramidical or longitudinal in shape. An inhomogeneous absorption powder as described is assumed by the applicant to provide a better noise dampening than if the powder consists of only spherically shaped particles. A preferred density range of the 3D printer powder in the chamber giving good noise absorption characteristics is between 0,2 gram/cm³ and 3,0 gram/cm³. The density can be varied from jacket to jacket and customized according to the specific frequency profile of the noise generating device.

Alternatively, the density can be varied inside the chamber over the length of the chamber. The wall of the noise reducing jacket preferably delimits and encloses the chamber, hereby keeping the powder in place. The chamber with un-sintered 3D printer powder is fully surrounded in all three dimensions by the wall . The advantage of this feature is that the powder will not spill out of the jacket. The chamber may also contain small sub chambers or sections, which each are delimited by a wall and contains un-sintered powder. In this way the noise is not only absorbed by the un-sintered powder but it is also trapped and circulating in the small chambers.

An air noise trap structure can be fitted to the wall delimiting the chamber. The noise trap structure is free of un-sintered 3D printer powder material and has walls and cavities causing sound waves to reflect thus reducing noise from the noise generating device. The noise trap structure contains cavities which allows the sound waves to circulate and to lose energy. The cavities are in open communication with each other hereby enabling the sound waves to travel from one cavity through the air to the next cavity, impinging on a wall in the cavity and being depleted of energy. The cavities can have the same size or different sizes or can be in the shape of meandering channels with a number of bendings along the channel length.

In a particularly preferred embodiment parts of the noise trap structure are shaped as teeth extending from an open air-filled channel. A multiple number of teeth are placed side by side and connected to the open air-filled channel. Each two teeth define together by their walls a cavity outside the noise trap structure. This cavity enhances the noise reduction.

By having two dampening elements in the noise reducing jacket, namely the chamber with powder and the noise trap, a particularly good noise reduction is obtained. First the noise has to pass through the first chamber holding the powder which absorbs energy from the progressing sound wave. After leaving the first chamber holding the powder the reduced sound wave will meet the hollow noise trap structure which reduces the amplitude of the sound wave even further. The noise trap structure is preferably also closed by a wall in the same way as the chamber holding the un-sintered powder. With a combined structure as described the noise reducing jacket performs both noise absorption, namely primarily via the powder, and noise isolation via the closed hollow noise trap structure. The sound absorption part with the un-sintered powder can be clamped directly onto the noise generating device, and the hollow noise trap structure being mounted on top of it, being in intimate wall-to-wall contact with the sound absorption part. Alternatively, the order of the two can be interchanged, i.e. the hollow noise trap structure being the first contact to the noise generating device. When printing the noise trap structure with a 3D Multi Jet Fusion process an inexpensive nylon powder (PA12) can be used. This powder does not have particularly good acoustic absorption properties, but it is cheap and when used in a jacket with a noise trap the noise trap will compensate for the lowered acoustic absorption properties of the powder. Thus, the jacket can be manufactured in a low cost material but exhibit good sound isolation and dampening characteristics. In some embodiments the noise isolation can be improved even further by having a vacuum in the volume of the hollow noise trap structure.

The noise reducing jacket consisting of the powder filled absorption chamber and the hollow noise trap structure is preferably made as a monolithic component, the monolithic component consisting of the same type of 3D printer material and one or more walls of the hollow noise trap structure being sintered to the wall of the chamber. The noise trap structure could be a discrete component clamped on to the chamber containing powder but it is preferred to have a jacket integrating the chamber and the structure having a seamless transgression from the powder filled chamber to hollow noise trap structure. Having a monolithic structure made simultaneously in the same 3D printing process is an advantage because it saves time in manufacture and gives a better noise reduction. No leaks for sound waves. Monolithic here means a structure that can be handled as a one-piece jacket to be mounted on the noise generating device. Advantageously the jacket can be made of two halves sharing a common hinge, but as the three components (two halves, one hinge) are mechanically connected the jacket is defined a monolith.

The noise reducing jacket comprises in one of its surfaces a contoured depression that mate with parts of a refrigerant expansion valve such as the main housing of the expansion valve, an inlet pipe and an outlet pipe. The main housing of the expansion valve holds in its inside the valve orifices where the noise is generated. Therefore noise encapsulation of the main housing is important.

The present invention also relates to a method of manufacturing a noise reducing jacket for encapsulating a noise generating device. The jacket comprises noise dampening material and a wall and is characterized in that the jacket is manufactured in a 3D Selective Laser Sintering process (SLS) or in a 3D Multi Jet Fusion process (MJF) using 3D printer powder material where the wall is made by sintering only parts of the powder material, and the noise dampening material consisting of un-sintered powder material. The wall is the wall that surrounds or defines the perimeter of the jacket. Preferably the powder material used for the wall and as dampening material is of the same type, so that the printing process can be made in one go. The inventive noise jacket design is obtained by either of two direct 3D printing processes. A direct 3D print process is a method where the desired object is printed instantly by the 3D printer as opposed to indirect printing, where the desired object is first printed as a mold and then finalized after injection of material into the mold and then curing the object.

More specifically the method of manufacturing a noise reducing jacket according to the invention when using Selective Laser Sintering printing comprises the following steps:

A) distributing first layers of powder on a powder bed, said layer covering an area corresponding to a wall of the jacket

B) laser sintering the first layers

C) distributing second layers of powder on top of the first sintered layers

D) sintering only the wall parts of the second layers, leaving other parts of the second layers un-sintered and keeping the un-sintered powder material inside a chamber delimited by the sintered wall parts

E) repeating steps C) and D) until the desired height or volume of the jacket is reached and

F) distributing third layers of powder on top of the second layers and sintering the third layers.

The area of step A) essentially matches the area intended for a surface or an outer wall of the jacket. This sintered area will be one of the sides of the jacket. The wall parts being sintered in step D) are the essentially vertically extending wall parts which are typically, but not always, orthogonal to the wall of step A). The wall parts grow incrementally in height with each step E.

Using the Multi Jet Fusion process the method according to the invention comprises these steps:

B) spraying a fusion agent on the first layers of powder

C) sintering the first layers of powder by increasing the temperature of the powder and fusion agent material

D) distributing second layers of powder on top of the sintered first layers

E) spraying a fusion agent material only on the wall parts of the second layers

F) sintering the fusion agent sprayed wall parts of the second layers, leaving other parts of the second layers un-sintered and keeping the un-sintered powder material inside the chamber delimited by the sintered wall parts

G) repeating steps D) to F) until the desired height or volume of the jacket is reached and

FI) distributing third layers of powder on top of the second layers and sintering the third layers after applying a fusion agent on them.

Step C) involves fusing the combination of powder and fusion agent into a hardened wall. During the printing process the temperature of the reaction chamber is set to 165°C, just below the melting temperature of the powder. A heating lamp will, when ignited, generate the extra 20°C to reach the melting and fusion temperature.

Preferably, the inventive method includes the 3D printing of an additional noise dampening element, a noise trap structure, on top of the absorption chamber. The 3D printing process is thus continued with fourth layers on top of the third layers, the fourth layers essentially orthogonal to the third layers and being sintered in wall parts only, and a fifth layer being fully sintered, where after powder material from un-sintered fourth layers are removed from the jacket. The fourth and fifth layers define a volume which acts as noise trap. This volume must be hollow, i .e. free of printer powder. Removal of the unused powder is done via holes in the wall of the noise trap part, i .e. that part which is made by the fourth layers.

The powder can be removed by gravitational force simply placing the jacket upside down and then let the powder run out. Alternatively, an additional hole can be made and an air gun or a vacuum pump can be used blowing or sucking through the volume. The powder can be recycled. In some embodiments the hole will be closed with a rubber cap. The first, second, third, fourth and fifth layers each typically are in the range of 1 to 1000 layers but fully depending on the intended size of the noise reducing jacket. Thus, the first layers which form the bottom on the bed of the printing plate can be made of 20 layers each 0, 1 mm height, thus reaching a thickness of the first layers of 2 millimeters. In general the wall thickness of the jacket must be in a range that it is flexible enough to be mounted on the noise generating device. Typically, the wall thickness is in the range of 0,5 to 5 millimeters, 2,5 millimeters being typical . Some walls can be made thinner than others : the wall facing the noise generating device is thinner than the distal wall of the jacket. Structural flexibility is achieved by choosing a proper 3D powder polymer. For the MJF process PA12 nylon powder can be used and for the SLS process PA2201 is useable.

An advantageous design of the jacket includes a space-maker creating an airgap between the jacket wall facing the body of the device and the body of the device itself. Such an air gap acts as a further noise trap. The space-maker can be built into the surface of the device by means of one or more dimples extending from the surface. Alternatively and preferred the space-maker is a part of the jacket wall facing the device and formed in the 3D printing process. By making an airgap a further dampening of the noise is obtained.

The 3D printers described here are in a well-known manner controlled by a control unit using a software program containing the design and instructions for 3D printing the inventive noise absorption jacket.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the accompanying drawings in which

Figure la-lc show the steps in the manufacturing of a noise reduction jacket according to the invention Figure 2 is a flow chart of the SLS manufacturing process according to the invention

Figure 3 is a cut away view of an embodiment of a noise jacket according to the invention

Figure 4a shows an expansion valve encapsulated by a noise jacket according to the invention and Figure 4b shows a prior art refrigerant expansion valve

DETAILED DESCRIPTION OF THE DRAWINGS

Figure la shows the principle of a well-known SLS 3D printer. A recoater 1 distributes first layers of polymeric powder 2 onto a bed 4 and a laser beam 5 then via heat sinters the particles of the powder. The black arrow shows the direction of movement of recoater and laser, here by example from right to left. The particles are hereby fused with each other.

The bed is lowered a little, and the recoater 1 places a new layer of powder. In Figure lb is shown the gist of the invention. After the first layers of powder material was sintered only parts of the second layers 7 are sintered, other parts 9 are left un-sintered . As seen in Figure lb the vertical walls 8 are sintered, but in between the two vertical walls 8 the 3D printer powder is left untouched . After reaching the desired height third layers 11 are distributed on top of the second layers and then sintered . In Figure 1C a finished jacket 10 is shown, here simplified as a rectangle. The powder 9 which is not sintered is fully enclosed inside the walls 8 of the cube. When this jacket is put in contact with a noise generating device then the sound waves will pass through the wall and meet millions of particles. These particles absorb the energy from the noise waves and will hence make it difficult for the waves to propagate unhindered. The result is that the waves lose a lot of energy and hence, once leaving the noise reducing jacket, has lost a lot of energy.

Figure 2 is a flow chart of a printing method according to the invention where a 3D SLS printer is used. After starting the 3D printer in step 100 the 3D printer will in step 200 start printing a noise absorption chamber which uses un-sintered 3D powder material. The printer distributes first layers of 3D printer powder on the printing bed. In step 300 a laser will radiate those portions only which are intended to be hardened . A sintering will happen in those areas and the printer powder will lose its powder state. In other areas of the first layers where no sintering is desired the laser beam is set to OFF and the 3D printing powder will remain untouched and in powder form. The steps in 200 and 300 will be repeated until the desired shape or height of the noise reducing jacket is reached, generating a "Yes" in question box 400. In step 500 the last layers of the jacket are sintered, hereby closing chamber 22 and enclosing the loose powder in chamber 22. In case a noise trap volume is desired to be added to the sound absorption chamber the 3D printing can continue and a "Yes" will be answered in question box 600. In step 700 a noise trap is printed on top of the absorption chamber. Before finishing the noise reduction jacket, the volume inside the noise trap just printed will be emptied in step 800. All un-sintered powder is removed. In 900 the method for manufacturing the noise reduction jacket is finished. A corresponding flow chart could be made for the MJF 3D printing process. Here steps 300 and 500 would be replaced by a fusion agent/glue spraying and heating lamp sintering techniques (baking).

Figure 3 is a cut away view of an embodiment of a noise reducing jacket 20 according to the invention. The noise jacket is mounted around a noise generating device 21. The jacket 20 comprises a chamber 22 which has a wall 23. This wall forms a closed perimeter and creates a cavity which is filled with 3D printer un-sintered powder 24. The wall 23 is as already described manufactured in a 3D SLS process but could as well be made in an MJF process. The wall is sintered by laser and the powder 24 is left un-sintered, i.e. is left in its original powder state. An auxiliary inner wall 25 can be built-in in order to reinforce the chamber structurally, but in general it should be avoided to create sound short circuits that allow the sound wave and vibrations to travel unhindered through noise absorption chamber 22. This is one of the advantages by manufacturing the jacket in polymer. If 3D printing the jacket in metal (Selective Laser Melting, SLM) supports or lattices will be needed for structural strength and this lowers the noise reduction efficiency of the jacket. In this embodiment of the invention a grain size of polyamide (PA) of 40-60 micrometers is used. The sound jacket functions in the following way. Sound waves (illustrated by arrows) emanate from the surface 35 of the noise generating source and pass through the inner wall 34 of the chamber 22, i.e. the wall that is facing the surface of the noise generating device. In the embodiment shown the chamber 22 is a cylindrical structure fully surrounding the noise generating device. Once the sound waves pass through wall 34 they encounter the un- sintered 3D printed powder. This powder is present as millions of particles. When the sound waves hit a powder particle this particle will be set to oscillate or changed in oscillating frequency. During this interaction the sound waves loses energy, hence having a lower amplitude and lower noise level. The chamber 22 is shown as a cylindrical body with an inner cavity filled with powder, it can of course have many different geometries adapted to the shape of the noise generating device.

Staying with figure 3 an additional noise reducing element is added to the chamber 22, namely the noise trap 26. This is a hollow structure with an outer wall 27 defining the outer perimeter of the noise trap. In one embodiment of the invention the bottom wall part 36 is the same wall as the outer wall part 37 of the chamber 22. Preferably noise reducing jacket 20 is 3D printed on top of wall 23, hereby creating a monolithic noise reducing jacket. The noise trap 26 is 3D printed in SLS or MJF method as already described, but the un-sintered powder is removed from the noise trap volume after printing, for example through a hole 32. The noise trap exhibits six sound dampeners, here each in the shape of tooth 38, each sound dampener designed for trapping those sound waves that have escaped the absorption chamber 22. By providing small and larger rooms with sharp edges the sound waves will reflect back and forth on the inner walls of the sound dampeners and loose energy and annihilate each other. The reflections are in this embodiment created by having a narrow passage 29 widening up to a broader room 30. A common open channel 28 between the wall 36 and the passages 29 is free of walls and connects the teeth with each other. 3D printing in polymer material gives good design possibilities and the noise trap can be made customized to the noise pattern and frequency from the noise generating device. Many noise cancelling geometries can be designed. The tooth shape 38 however has been found to be particularly well suited to lower noise because it creates a cavity 33 in-between two teeth . This cavity is created outside of the air trap structure and is in contact with ambient air. The improved technical effect in placing two teeth side by side to each other, creating an inversed tooth or hammer shape like profile, is that sound waves escaping from parts of the wall 27 will be entrapped again in the cavity 33. Only escape is a narrow channel between two neighboring heads of teeth 38. Noise trap 26 is in Figure 3 shown with open cavities 33. These cavities can in one embodiment be fully closed by letting wall 27 be straight and unbroken and connecting tooth 38 with the next tooth and closing cavity 33. In this way noise trap 26 has a smooth outer surface wall 27 preventing dust from settling inside cavity 33. Cavities 33 will then be closed air tunnels encircling the noise generating device.

The noise reducing jacket shown in figure 3 can be a one-piece monolith, for example a cylinder slided over the noise generating source, or a two-piece monolith, where the two pieces are mechanically connected through a hinge. The noise trap 26 is preferably manufactured integrally with chamber 22 but can in principle be mounted on cavity 22 later if the noise is not dampened sufficiently by chamber 22 alone. Noise trap 26 can be made in plastic or metal .

Figure 4b shows a traditional refrigerant expansion valve 40a with a brass housing 41, an inlet pipe 42 and an outlet pipe 43. The refrigerant medium is a two-phase refrigerant changing in a known manner between being in a gas phase and in a liquid phase. The phase shift of the liquid happens inside the expansion valve and causes audible noise. In figure 4a a noise reducing jacket 44 is mounted around the main body of the brass housing .

Expansion valve 40 now has a jacket 44 which according to the invention comprises an absorption chamber 22a close to the main body and a noise trap 38a. The jacket has a shape depression 45 on the side facing the housing 41 of the expansion valve. The shape depression corresponds to a widening portion of the housing 41. Preferably jacket 44 is made with a hinge (not shown) connecting two parts of jacket 44 hereby enabling the jacket to be closed in a sealing manner around the expansion valve. In one embodiment a small airgap is desired between jacket 44 and brass housing 41, hereby obtaining a further noise trap. The air gap is for example made by a protruding nose (a space-maker) (not shown in the figure) between brass housing 41 and the inner surface of jacket 44 facing the brass housing. A considerably quieter expansion valve is obtained.

Claims

Patent claims:

1. A noise reducing jacket (10,20,44) for being mounted fully or partly around a noise generating device (21,40) characterized in that the noise reducing jacket comprises a wall (23) and a chamber (22,22a), wherein the wall consists of 3D printer powder material which has been sintered (1,8,11), and the chamber is filled with 3D printer powder material (9) which is not sintered wherein a noise trap structure (26) is fitted to the wall delimiting the chamber (22), said noise trap structure is free of un-sintered 3D powder material and has walls (27) and cavities (30,33) causing sound waves to reflect thus reducing noise from the noise generating device.

2. A noise reducing jacket according to claim 1 wherein the sintered powder material (2) and the non-sintered powder material (9) are of the same type, preferably polyamid.

3. A noise reducing jacket according to claims 1 or 2 above wherein the wall (8,23) delimits and encloses the chamber (22,22a), hereby keeping the powder (9) in place.

4. A noise reducing jacket according to claim 3 wherein the jacket is a monolithic

component (40), the monolithic component consisting of one type of 3D printer material and one or more walls (37) of the noise trap structure (26) being sintered to the wall (36) of the chamber (22) .

5. A noise reducing jacket according to claim 3 wherein the noise trap structure (26) is a discrete component clamped on to the wall (37) of the chamber containing powder.

6. A noise reducing jacket according to claim 4 or 5 wherein the noise trap structure (26) has an open channel (28) communicating with a multiple of teeth (38) extending from said channel, the teeth having a first diameter (29) smaller than a second diameter (30) and a cavity (33) placed in-between two teeth.

7. A noise reducing jacket according to claim 4 or 5 wherein the noise trap structure (26) comprises cavities (28, 29, 30) being in open communication with each other.

8. A noise reducing jacket according to any of claims 1 to 7 wherein the noise trap

structure (26) has a hole (32) for the removal of un-sintered powder.

9. A noise reducing jacket according to claims 1 to 8 wherein the jacket comprises cavities that mate with a refrigeration expansion valve and has a chamber for a main housing (41) of the expansion valve and for an inlet pipe (42) and an outlet pipe (43).

10. Method of manufacturing a noise reducing jacket (10,20,44) for encapsulating a noise generating device (21,40), said jacket comprising noise dampening material and a wall characterized in that the jacket is manufactured in a 3D Selective Laser Sintering process (SLS) using polymeric powder material where the wall (8,23) is made by sintering only parts (8,300) of the powder material, and the noise dampening material consists of un-sintered powder material (9), the Selective Laser Sintering printing process involving the following steps:

A) distributing first layers (2) of powder on a powder bed (4), said layers covering an area corresponding to an area of a wall (8) of the jacket (10,20,40a, 200)

B) laser sintering the first layers

C) distributing second layers (7) of powder on top of the first layers

D) sintering only the wall parts (8) of the second layers (7), leaving other parts of the second layers un-sintered and keeping the un-sintered powder material (9) inside the chamber delimited by the sintered wall parts (300)

E) repeating steps C) and D) until the desired height or volume of the jacket is reached (400) and

F) distributing third layers (11) of powder on top of the second layers and sintering said third layers (500).

11. Method of manufacturing a noise reducing jacket (10,20,44) for encapsulating a noise generating device (21,40), said jacket comprising noise dampening material and a wall characterized in that the jacket is manufactured in a 3D Multi Jet Fusion process (MJF) using polymeric powder material where the wall (8,23) is made by sintering only parts (8,300) of the powder material, and the noise dampening material consists of un sintered powder material (9), the Multi Jet Fusion Process (MJF) involving the following steps:

A) distributing first layers (2) of powder on a powder bed (4), said layers covering an area corresponding to an area of a wall (8) of the jacket (10, 20, 40a, 200)

B) spraying a fusion agent material on the first layers of powder

D) distributing second layers (7) of powder on top of the first layers E) spraying a fusion agent material on the wall parts of the second layers

F) sintering only the wall parts of the second layers, leaving other parts of the second layers un-sintered and keeping the un-sintered powder material (9) inside the chamber delimited by the sintered wall parts

FI) distributing third layers (11) of powder on top of the second layers and sintering the third layers after applying a fusion agent on them.

12. A method according to claim 10 or 11 wherein the 3D printing process is continued with fourth layers (700) on top of the third layers, the fourth layers being sintered in wall parts only, and a fifth layer being fully sintered (700), where after powder material from un-sintered fourth layers are removed (800) from the jacket.