Field of technology

The presented solution concerns a structure adapted for attenuation of mechanical waves. The structure is manufactured by a layered 3D printing using a selective material deposition.

State of the art

The additive manufacturing technologies allow the fabrication of components with highly complex shapes due to the nature of the layer-by-layer approach. In case of metal additive manufacturing technologies, the powder bed fusion PBF process belongs to the most widespread. During the process, metal powder is spread over the build plate in a thin layer. The deposited powder is fused by means of laser or electron beam at the desired areas according to the digital data of the produced component. Fused areas in each layer correspond to the cross-section of the manufactured component’s shape in the given layer. After fusion of the layer is finished, the build plate is lowered according to the chosen layer thickness and a new layer of powder is deposited. Such procedure continues until the whole component is prepared. After the completion of the process, the unfused metallic powder surrounding the component is taken out and reused for another build job. Such a process is used for example in the document WO2012131481A1 .

Such structures may be used in many industrial fields and are used for a variety of applications. However, every application needs a specific approach. For example, in precise engineering, space engineering or many areas of mechanical engineering, structures that are suitable for attenuation mechanical waves are needed to reduce unwanted shocks of the system.

Summary of the invention

The above-mentioned disadvantages of the prior art are at least partially solved by a structure for attenuation of mechanical waves prepared by 3D printing of a combination of at least a first material and a second material. The acoustic impedances of the first material and the second material differ by at least 20 %. The structure comprises at least one structured area comprising at least two blocks of the first material separated by the second material. The structure solves the disadvantages of the prior art by effective attenuation of the mechanical waves propagating through the media, as at the interface of two different materials, a part of the wave is transmitted through the interface and the rest of the wave is reflected. The reflection increases with the difference in the acoustic impedances of the first material and the second material.

In a preferred embodiment the structure is comprised of a number of vertically or horizontally arranged layers wherein the layers are mutually offset in the direction of the propagating wave. This embodiment ensures more efficient attenuation of the propagated wave across the height of the structure.

In a preferred embodiment the structure is comprised of a number of vertically or horizontally arranged layers, wherein the thickness of the block is of at least two values. The values change in the direction of the propagating wave, wherein the values of thickness are alternating between the layers. This embodiment ensures that a single structured area may attenuate a broader range of wavelengths of the propagating mechanical wave.

In a preferred embodiment the blocks are V-shaped or saw-shaped. The angle of the tip of the V-shape or a “tooth” of the saw-shape is in the range of 10-150° and points in the direction of the propagating wave. Such structure ensures that a broader range of wavelengths is effectively attenuated when transmitted through the structured area. In a preferred embodiment the first material is an aluminum alloy, and the second material is a titanium alloy. In the following preferred embodiment the second material is a Ti-6AI-4V alloy. In another preferred embodiment the first material is a copper alloy, and the second material is a steel. In another preferred embodiment the first material is a copper or copper alloy and the second material is a zircon-ceramics or piezo-ceramics.

In a preferred embodiment the thickness of the block is in the range of 0,05-10 mm. Preferably, the thickness may increase incrementally or geometrically.

The above-mentioned disadvantages of the prior art are further at least partially solved by a method of manufacturing a structure for attenuation of mechanical waves. The method comprises the steps of:

- deposition of a layer of a first material and a second material in a powdered form. The powdered materials are deposited on a base plate.

- selective fusion of the deposited layer by an electron beam or a laser beam. The selective fusion is performed at an area corresponding to the cross section of a manufactured component.

- repetition of the previous two steps until obtaining the resulting shape of the manufactured component.

The drawbacks of the prior art are solved by that the second material is deposited in at least two blocks separated by the first material and by that the acoustic impedances of the first material and the second material differ by at least 20 %.

In a preferred embodiment the deposited layers are offset in the direction of the propagating wave. This embodiment ensures more efficient attenuation of the propagated wave across the height of the structure.

In a preferred embodiment the layers are deposited in such a way that the thickness of the block is of at least two values. The values change in the direction of the propagating wave, wherein the values of thickness are alternating between the layers. This embodiment ensures that a single structured area may attenuate a broader range of wavelengths of the propagating mechanical wave.

In a preferred embodiment the layers are deposited in such a way that the blocks are V-shaped or saw-shaped. The angle of the tip of the V-shape or a “tooth” of the sawshape is in the range of 10-150° and points in the direction of the propagating wave. Such structure ensures that a broader range of wavelengths is effectively attenuated when transmitted through the structured area.

In a preferred embodiment the first material is an aluminum alloy, and the second material is a titanium alloy. In the following preferred embodiment the second material is a Ti-6AI-4V alloy. In another preferred embodiment the first material is a copper alloy, and the second material is a steel.

In a preferred embodiment the layers are deposited in such a way that the thickness of the block is in the range of 0,05-10 mm. Preferably, the thickness may increase incrementally or geometrically.

Description of drawings

The summary of the invention is further explained on the basis of examples of its realization, which are described with the help of accompanying drawings, where: Figure 1 shows a schematic depiction of the system for manufacturing a structure for attenuation of mechanical waves.

Figure 2 shows a manufactured structure composed of the first material and the second material, wherein the interfaces between the materials are used for the attenuation of mechanical waves.

Figure 3 shows a manufactured structure having a plurality of blocks of the second material manufactured in a V-shape and separated by the first material.

Figure 4 shows possible alternations of layers of the first material and the second material.

Figure 5 shows a manufactured structure having a plurality of blocks of the second material manufactured in a V-shape and separated by the first material.

Figure 6 shows a cut-out manufactured structure having a plurality of blocks of the second material manufactured in a conical shape and separated by the first material. Figure 7 shows the attenuation of mechanical waves for planar structured areas.

Figure 8 shows the attenuation of mechanical waves for V-shape structured areas. Examples of embodiment of the invention

The invention will be further clarified by means of exemplary embodiments with reference to the respective drawings, which, however, have do not limit the scope of protection.

The structure 1. for attenuation of mechanical waves shown in the Fig. 1 , 2, and 3 comprises at least a first material 2 and a second material 3. The structure 1. is composed of a plurality of vertically arranged layers 6. The height of a single layer is in the range of 1 pm to 200 pm. The terms “vertical” and “horizontal” have only informational character intended to clarify the positional relationship between the components forming the claimed structure 1. and have no limiting nature for the scope of protection of the defined claims neither they define the orientation of the structure 1. with respect to its surroundings. The structure 1_ comprises at least one structured area 4 with at least two blocks 5 of the second material 3 separated by the first material 2. The thickness of the blocks 5 is in the range from 0,05 mm to 10 mm. The thickness of the block 5 may be constant along the whole height of the block 5, or it may be increased incrementally with each layer 6 of the structure 1_, or it may be alternating between at least two values in the neighboring layers 6, as seen on the Fig. 4c. Further, the blocks 5 forming the structured area 4 may be either all of the same thickness, or the thickness may increase incrementally between the neighboring blocks 5, or the thickness may be alternating between at least two values, or the thickness may increase geometrically between the neighboring blocks 5.

The blocks 5 forming the structured area 4 may be of various shapes, wherein the shape itself is chosen accordingly to the direction 100 of the propagating wave to be attenuated. In a single layer 6 or a cross section of the structure 1_, the single block 5 may be rectangular oriented with its longer side oriented across the direction 100 of the propagating wave, as seen in the Fig. 2, rectangular and skewed (rhomboidal), arched, V-shaped as seen in the Fig. 3 or 5, or saw-shaped, etc. In the case of a non-linear shape of the block 5, the arch or the tip is oriented in the direction 100 of the propagating wave. The of the tip 7 of either the V-shape or the saw-shape is in the range of 10-150°, preferably 60-120°. The resulting block 5 of the second material 3 can be that of a hollow cone, as seen in the Fig. 6, wherein the cross-section of the structure 1_ would then be V- shaped. Such shape of the block 5 and the structured area 4 provides attenuation in all directions.

In an exemplary embodiment of the invention the layers 6 are of the same shape resulting in a homogeneously shaped structured area 4.

In another exemplary embodiment, the layers 6 are offset in the direction 100 of the propagating wave. The blocks 5 comprised of offset layers 6 are then skewed in the direction 100 of the propagating wave, as can be seen in the Fig. 4b.

In an exemplary embodiment of the invention, the first material 2 and the second material 3 are selected so that their acoustic impedance acoustic impedances differ by at least 20 % without limiting which of the materials 2 or 3 has the higher value of the acoustic impedance.

In an exemplary embodiment of the invention, the pairs of the first material 2 and the second material 3 may be selected form the following non exhaustive list of possible materials: aluminum alloy and titanium alloy, wherein the titanium alloy is exemplarily a Ti-6AI-4V alloy; copper alloy and steel, wherein the steel is exemplarily a maraging steel, copper and copper alloy, wherein the copper alloy is exemplarily a copper alloy with either a zircon-ceramics or a piezo-ceramics.

The structure 1. is manufactured using the method of manufacturing a structure 1. for attenuation of mechanical waves comprising the steps of:

- deposition of a layer 5 of a first material 2 and a second material 3 in a form of a metal powder 10 on a base plate 8.

The powder dosing system 9 is adapted for dosing the powder 10 composed of at least the first material 2 and the second material 3 on the dedicated places on the base plate 8 by the movement of powder dispenser in X and Y direction over the whole build area using continual dosing according to the planned path or by singlepoint dosing according to a XY rasterized mesh. The dosing system 9 suitable for using is any of the following dosing systems 9: powder flow; powder flow forced by vibrations; powder flow forced by compressed gas; powder in carrier fluid forming droplets, where carrier fluid evaporates after deposition, or other. In such a way, the plurality of dispensers 11 (in the form of containers with nozzles or printheads, cartridges etc.) with different metal powders 10 selectively dose individual powders 10 on dedicated places until the whole area of single layer 5 is filled in chosen powder height (layer thickness). The smoothness of material transition in Z direction is driven by the layer thickness used while in XY directions it depends on the powder dosing resolution, size of the focused energy beam and material properties. Commonly the layer thickness may vary from 1 pm up to 200 pm. Maximum resolution of selective dosing system 9 may vary from tens of micrometres in case of droplet principle up to units of millimetres in case of nozzle dosing principle.

- selective fusion of the layer 6 using an electron beam 12 system or a laser beam 12 system, wherein the selective fusion is performed at an area corresponding to the cross-section of the manufactured component.

The focus spot of the beam 12 is usually in the range of tens of microns to about 100 pm. However, features in the range of 1 -10 pm are also achievable.

- repetition of the steps of deposition and selective fusion until obtaining the resulting shape of the manufactured component.

The second material 3 is deposited in at least two blocks 4 separated by the first material 2. The acoustic impedances of the first material 2 and the second material 3 differ by at least 20 %.

Another approach to the method of manufacturing the structure 1_ for attenuation of mechanical waves is to use one of the following methods: material jetting or vat photopolymerization 3D printing technologies which use photo sensitive polymers filled with ceramics or metal powders. Using a modified or dedicated 3D printer it is possible to deposit multiple materials in the form of liquid slurry of propolymer filled by metal or ceramic powder by multiple nozzles in case of material jetting technology by multiple vats in case of vat-photopolymerization technology.

The first material 2 and the second material 3 are deposited using the powder dosing system 9 which distributes the first material 2 and the second material 3 in a powder 10 form to the base plate 8. The materials 2, 3 are deposited in a single layer 6 either continually by rastering the dispenser in two perpendicular directions or by singlepoint dosing of the powder 10 to defined places. The processing parameters for single layer 5 need to contain at least two parameter sets with selected areas to apply, because each material typically has its optimal set of processing parameters different to other materials. The processing parameters are any of the following parameters: laser power, roster speed, layer 6 height, hatching speed, etc. Given layer 6 may be composed of either the first material 2, the second material 3 or the combination of both.

After the first layer 6 is deposited, selected areas of the layer 6 are irradiated either by an electron beam 12 system or by a laser beam 12 system of sufficient power. After irradiating, the selected areas of the layer 6 are melted and solidified. The selected areas of the solidified powder 10 correspond with their shape to the shape of the manufactured component of the structure 1_.

After the first layer 6 is selectively fused using the beam 12 system, the second layer 6 is deposited and selectively fused. This process is repeated until the desired shape of the structure 1. is obtained.

The layers 6 may be composed either solely by the first material 2, or the second material 3, or by their combination, or by their combination with at least one other material.

The layers 6 may alternate between the first material 2 and the second material 3 in order to create a structure 1. for attenuation of the mechanical waves. This alternating approach creates a structured area 4 comprising blocks 5 of the second material 3 separated by the first material 2.

In the Fig. 7, the results of simulations of the attenuation of the mechanical waves are shown for a structure 1. for attenuation of the mechanical waves, where the structure 1. comprises one structured area 4 comprising two blocks 5 of the second material 3 separated by the first material 2. The blocks 5 are planar and rectangular. In this exemplary embodiment, the first material 2 is the aluminium alloy of the elasticity module E=70,6e9 Pa, Poisson ratio v=0,345, density p=2700 Kg/m ³ with the speed of longitudinal elastic waves ci=5448 m/s. Corresponding mechanical impedance is then Z=13,8e6 kg/(m ² s). The second material 3 is the Ti6AI4V alloy of the elasticity module E=114,9e9 Pa, Poisson ratio v=0,34, density p=4500 Kg/m ³ with the speed of longitudinal elastic waves ci=5352 m/s. Corresponding mechanical impedance is then Z=22,7e6 kg/(m ² s). The characteristic frequency of the mechanical wave for this speed is about 5400 kHz. The thickness of the blocks 5 is 1 mm, wherein the thickness of the first material 2 separating the blocks 5 is 1 mm, which is roughly the wavelength of the wave with the frequency 5400 kHz. Simulations were made for waves with half the characteristic wavelength and double the characteristic wavelength.

In the Fig. 8, the results of simulations of the attenuation of the mechanical waves are shown for a structure 1. for attenuation of the mechanical waves, where the structure 1. comprises one structured area 4 comprising two blocks 5 of the second material 3 separated by the first material 2. The blocks 5 are V-shaped, wherein the V is directed in the direction 100 of the propagating wave. In this exemplary embodiment, the first material 2 is the aluminium alloy of the elasticity module E=70,6e9 Pa, Poisson ratio v=0,345, density p=2700 Kg/m ³ with the speed of longitudinal elastic waves ci=5448 m/s. The second material 3 is the Ti6AI4V alloy of the elasticity module E=114,9e9 Pa, Poisson ratio v=0,34, density p=4500 Kg/m ³ with the speed of longitudinal elastic waves ci=5352 m/s. The characteristic frequency of the mechanical wave for this speed is about 5400 kHz. The thickness of the blocks 5 is 1 mm, wherein the thickness of the first material 2 separating the blocks 5 is 1 mm, which is roughly the wavelength of the wave with the frequency 5400 kHz. Simulations were made for waves with half the characteristic wavelength and double the characteristic wavelength.

With the results above, the attenuative effect of the structure 1_ is obvious. The structure 1. provides best attenuation of mechanical waves with the thickness of the block 5 corresponding to the wavelength of the mechanical wave to be attenuated. The best results are thus achieved with scaling the thickness of the blocks 5 together with the thickness of the first material 2 separating the blocks 5 of the second material 3. As discussed in the exemplary embodiments, the thickness of the blocks 5 may increase incrementally to widen the range of wavelengths that can be attenuated by the structure 1.

The structure 1. may be used in a variety of applications depending on its resulting shape. A non-exhaustive list of possible applications is following: riffle butt, partial joint replacement, holder for an optical element of an optical system, holder for a sensing system, or holder for a satellite system.

In the context of the application, the mechanical attenuation of mechanical-stress waves is understood as:

1 ) the attenuation or decreasing of stress intensity measured as von Misses stress at the monitoring area concerning the initial/loading stress intensity at the applied area of the pulse/shock and

2) the attenuation of kinetic energy passing through the monitored area. The kinetic energy passing through the monitored area is measured by the time integration over the time range of interest from the kinetic energy included in the domain of interest - cumulative kinetic energy at the monitored area. Both types of attenuation can be observed in the stress wave propagation at a body made by multi-material 3D printing.

The attenuation of the stress wave and its intensity, measured by von Misses stress or cumulative kinetic energy at the monitored area, is influenced by the ratio of layer thickness h to the wavelength of the excited mechanical wave A. The wavelength A (in m) is generally controlled by the loading frequency f (in Hz) and wave speed of the materials (in m/s). The wavelength A can be estimated as A = c / f, where c is the wave speed of the elastic wave in m/s through the medium/layer; f is the frequency of the propagating wave in Hz. This frequency corresponds to the frequency of the excited pulse/shock. From that, the frequency range where attenuation of mechanical waves is observed, can be estimated. The attenuation effect of the structure 1. can be observed when the generated wavelength of the wave A is smaller than the thickness of layer h. Finally, the structure 1. can attenuate the wave with the frequency of pulse greater than a minimum value given as fmin = c / h, where the c is the wave speed in the second material (2).

For example, when considering the combination of Ti-AI materials, the wave speed longitudinal waves is about c=5400 m/s. The minimum thickness is considered to be 0,1 mm and the maximum 10 mm. From this follows that the range of frequencies for which it is possible to activate the attenuation effect in the 3D printed structure is from 500 kHz to 500 MHz.

Industrial applicability

The structure may be used in a variety of applications depending on its resulting shape. A non-exhaustive list of possible applications is following: a riffle butt, a part of human joint replacement, a holder for an optical element of an optical system, a holder for a sensing system, a holder for a satellite system, a rotary component in engine, a part of a damping system adapted to minimize engine vibrations, a part of a sensing system adapted to minimize mechanical waves in chosen frequency spectrum, a part of a system adapted to magnify mechanical waves in chosen frequency spectrum. List of reference marks

1 - structure

2 - first material

3 - second material 4 - structured area

5 - block

6 - layer

7 - tip

8 - base plate 9 - powder dosing system

10 - powder

11 - dispenser

12 - beam system