Patent Application
20220032425
The invention proceeds from a method for the surface processing of a component by flow grinding, comprising the following steps:
Flow grinding processes are processing processes in which a surface to be processed is flooded by a fluid carrier material containing grinding particles, in particular a liquid containing grinding particles. The grinding particles contained in the fluid carrier material strike the surface of the component to be processed during the flooding operation, as a result of which the corresponding surface is abraded by erosion in that the grinding particles remove material from the component upon impact. Depending on the geometry, in particular the form and size distribution of the grinding particles, a very fine processing of the surfaces and in particular also a treatment of very fine structures is possible in this case. When the fluid carrier material is a liquid, the flow grinding process is also referred to as a hydroerosive process or a hydroerosive grinding process. Flow grinding processes can be used for example to treat the surfaces of 3D-printed components of metal, ceramic and/or plastic that have a surface roughness of between 50 and 500 μm. These surface roughnesses bring about undesired effects when the corresponding components are being used, for example fouling or increased loss of pressure. In order to be able to maintain the exact geometry within the error tolerances after the grinding process, the geometry of the component must optionally be modified already in the case of the production process, in particular during production by a 3D-printing process, and it has to be possible to adjust the grinding process in a precise and controlled manner.
WO 2014/000954 A1 discloses, for example, chamfering bores on injection nozzles in injection valves for internal combustion engines by a hydroerosive process, in order in this way to abrade sharp-edged transitions at the very small bores, through which the fuel is injected into the internal combustion engine at high pressure. For the process, a liquid containing grinding particles flows through the injection nozzle. For a uniform flow through the bore in the injection nozzle and thus a uniform chamfering of the edges, a hollow body is introduced into the injection valve and the liquid containing grinding particles is conducted through the internal flow duct formed in the hollow body and an external flow duct formed between the hollow body and the inner wall of the injection valve. Here, for a uniform result, it is possible to use different liquids containing grinding particles that flow through the internal and external flow ducts, and/or to pass the liquid containing grinding particles through the internal and the external flow duct at different flow velocities or pressures.
A mathematical simulation of hydroerosive grinding is described, for example, in P. A. Rizkalla, Development of a Hydroerosion Model using a Semi-Empirical Method Coupled with an Euler-Euler Approach, Dissertation, Royal Melbourne Institute of Technology, University of Melbourne, November 2007, pages 36 to 44.
The known method is disadvantageous in that, in the case of non-planar surfaces to be processed, what can occur is a flow separation which results in cavitation and thus undesired removal of material, and therefore can lead to damage to the surface to be processed and a mathematical simulation of the grinding is complicated.
It is therefore an object of the present invention to provide a method in which the surfaces of the component that are to be processed are not damaged and the mathematical simulations of which are less complicated.
The object is achieved by a method for the surface processing of a component by flow grinding, comprising the following steps:
By the rounding of the blank at positions at which, during flooding, the flow direction of the fluid carrier material containing the grinding particles changes and by attaching additional material at positions at which a flow separation occurs on the finished component, the situation is prevented in which, as a result of the processing of the surface with the fluid carrier material containing the grinding particles, material is removed in an uncontrolled manner by cavitation on account of the flow separation and associated backflows, and the component being damaged as a result.
The fluid carrier material which contains the grinding particles is for example water, oil or a highly viscous grease, i.e. a grease having a viscosity in the range of from 100 to 1 000 000 Pa·s, in particular having a viscosity in the range of from 1000 to 200 000 Pa·s, at the processing temperature. It is particularly preferred if the fluid carrier material is oil, in particular a hydraulic oil. The proportion of the grinding particles in the fluid carrier material is preferably in the range of from 1 to 80% by volume, in particular in the range of from 2 to 60% by volume. When a liquid is used as fluid carrier material, for example water or oil, the proportion of the grinding particles is preferably in the range of from 1 to 50% by volume, more preferably in the range of from 1 to 20% by volume and in particular in the range of from 1 to 5% by volume, and, when using a highly viscous grease as fluid carrier material, the proportion of the grinding particles is preferably in the range of from 20 to 80% by volume and in particular in the range of from 40 to 60% by volume.
The material used for the grinding particles depends on the material of the component to be processed. When the component is composed of a metal or a ceramic, grinding particles of boron carbide or diamond are preferably used. In the case of a component composed of a plastic, suitable in particular are grinding particles of boron carbide, diamond, sand or silicon. The form and the size of the grinding particles also depend on the material of the component that is to be processed and on the desired surface finish, in particular the desired surface roughness, and the size of the structure to be processed. Suitable forms for the grinding particles are in particular sharp-edged particles, for example crushed particles. Suitable grinding particles preferably have a size distribution of 1 to 1000 μm and in particular a size distribution of 1 to 10 μm when using oil and 10 μm to 1000 μm when using grease.
For processing by flow grinding, firstly the component is introduced into a duct through which the fluid carrier material containing the grinding particles flows. When the intention is to process external surfaces of the component, the component is introduced into the duct such that the fluid carrier material containing the grinding particles can flood the surfaces. When processing internal surfaces, for example bores, the component is connected to the duct such that the fluid carrier material containing the grinding particles flows through the openings, for example bores, to be processed, but does not come into contact with surfaces which are not intended to be processed. For the grinding of bores, for example, suitable connections can be provided on the component, via which connections the fluid carrier material containing the grinding particles is supplied and flows back out of the component.
In order to prevent a flow separation and thus an undesired removal of material by cavitation at the positions at which, during flooding, the flow direction of the fluid carrier material containing the grinding particles changes, the blank is rounded at the positions at which, during flooding, the flow direction of the fluid carrier material containing the grinding particles changes with a radius which corresponds to 0.1 to 2.5 times the mean spacing between the surface over which flow passes and the opposite wall of the duct through which the fluid carrier material containing the grinding particles flows. It is preferable if the blank is rounded at the positions at which, during flooding, the flow direction of the fluid carrier material containing the grinding particles changes with a radius which corresponds to 0.25 to 1.5 times and in particular 0.5 times the mean spacing between the surface over which flow passes and the opposite wall of the duct through which the fluid carrier material containing the grinding particles flows.
In this context, the mean spacing can for example be determined numerically. It is preferable, however, if the mean spacing is the mean value of the minimum spacing between the surface over which flow passes and the opposite wall and the maximum spacing between the surface over which flow passes and the opposite wall. In this case, the minimum spacing and the maximum spacing can both lie upstream of the change in the flow direction or both lie downstream of the change in the flow direction, or one of the two spacings lies upstream of the change in the flow direction and the other of the two spacings lies downstream of the flow direction. In particular in the case of a duct through which flow passes which comprises a change in direction, it is possible for example that the duct has a first hydraulic diameter upstream of the change in direction and a second hydraulic diameter downstream of the change in direction. In this respect, the first hydraulic diameter can be smaller than the second hydraulic diameter, or the first hydraulic diameter is larger than the second hydraulic diameter.
Here, the hydraulic diameter is calculated as follows:
where Dh is the hydraulic diameter, U is the circumference and A is the cross-sectional area of the duct though which flow passes.
A change in the flow direction of the fluid carrier material containing the grinding particles results, for example, when a duct, into which the blank is introduced and through which the fluid carrier material containing the grinding particles flows in order to process the external surfaces of the blank, has a curvature or a bend and the blank to be processed is positioned in the region of the curvature or the bend. Furthermore, a change in the flow direction also results when the blank contains a duct and this duct has a curvature or a bend, and the intention is to process the walls which bound the duct by the flow grinding method. In this case, the fluid carrier material containing the grinding particles flows through the duct in the blank.
When the intention is to process external surfaces of the blank by the flow grinding process, the blank is customarily positioned in a duct which runs in a straight line without a bend or curvature and without a constriction or widening. In order to prevent in this case the situation in which material is removed in an uncontrolled manner by cavitation on account of flow separation, additional material is attached at positions at which a flow separation occurs on the finished component. In the case of a component having a rotationally symmetrical projection surface exposed to the flow, the additional material on the side facing the flow has a surface which is inclined and runs concavely in the flow direction with respect to a central axis of the duct in which the fluid carrier material containing the grinding particles flows.
In this context, “on the side facing the flow” means the side over which the fluid carrier material containing the flow particles flows.
A component having a rotationally symmetrical projection surface exposed to the flow is, for example, a sphere. Any other component which exhibits a circular face in the flow direction of the fluid carrier material containing the grinding particles also has a rotationally symmetrical projection surface exposed to the flow. Such a component can for example also have the form of a droplet, the component in this case being exposed to the flow at the hemispherical end of the droplet.
In order to prevent a flow separation, the inclined and concavely running surface of the additionally applied material has a curvature with a radius in the range of from 1 to 5 times the diameter of the rotationally symmetrical projection surface. The inclined and concavely running surface of the additionally applied material further preferably has a curvature with a radius in the range of from 1.5 to 3 times the diameter of the rotationally symmetrical projection surface, for example a curvature with a radius which corresponds to two times the diameter of the rotationally symmetrical projection surface.
When the projection surface exposed to the flow is not rotationally symmetrical, the additional material, which is attached at positions at which a flow separation occurs on the finished component, on the side facing the flow has a surface which is inclined and runs concavely in the flow direction with respect to a central plane running parallel to the flow direction of the fluid carrier material containing the grinding particles. Also in this case, the surface which is inclined and concave with respect to the central plane running parallel to the flow direction of the fluid carrier material containing the grinding particles prevents a flow separation from occurring, which leads to cavitation and thus uncontrolled removal of material.
It is particularly advantageous when the surface of the additional material that is inclined and runs concavely with respect to the central plane running parallel to the flow direction of the fluid carrier material containing the grinding particles has a curvature with a radius in the range of from 2 to 10 times the maximum perpendicular spacing from the central plane running parallel to the flow direction of the fluid carrier material containing the grinding particles to the edge of the non-rotationally symmetrical projection surface. It is particularly preferable if the curvature of the inclined and concavely running surface has a radius in the range of from 3 to 6 times the maximum perpendicular spacing from the central plane running parallel to the flow direction of the fluid carrier material containing the grinding particles to the edge of the non-rotationally symmetrical projection surface, for example a radius which corresponds to four times the maximum perpendicular spacing from the central plane running parallel to the flow direction of the fluid carrier material containing the grinding particles to the edge of the non-rotationally symmetrical projection surface.
In this context, “central” means that the intersecting line of the plane running parallel to the flow direction of the fluid carrier material containing the grinding particles and having the non-rotationally symmetrical projection surface runs in the center of the projection surface. In the case of an axially symmetrical projection surface, the intersecting line of the plane running parallel to the flow direction of the fluid carrier material containing the grinding particles and having the non-rotationally symmetrical projection surface forms the axis of symmetry of the non-rotationally symmetrical projection surface.
Components having a non-rotationally symmetrical projection surface are, for example, tubes, shafts or spindles, the external surface of which is to be processed by the flow grinding method. The tubes, shafts or spindles can have any desired cross-sectional form here, a round cross section being particularly suitable for processing by the flow grinding method. The tube to be processed, the shaft to be processed or the spindle to be processed is placed, in this case transversely to the flow direction of the fluid carrier material containing the grinding particles, is placed into the duct through which the fluid carrier material containing the grinding particles is conducted, with the result that the projection surface of the tube, the shaft or the spindle that is exposed to the flow is a rectangle, the length of which corresponds to the length of the tube, the shaft or the spindle and the height of which corresponds to the diameter of the tube, the shaft or the spindle. The central plane running parallel to the flow direction of the fluid carrier material containing the grinding particles extends preferably parallel to the length of the rectangle and intersects the projection surface at half the height. In this case, the radius of the curvature of the inclined and concave surface thus corresponds to 2 to 10 times the radius of the tube, the shaft or the spindle.
After the surface has been processed by the flow grinding, the additionally applied material has to be removed in order to obtain the desired component. For this purpose, it is possible for example to increase the flow velocity of the fluid carrier material containing the grinding particles and thus to abrade the material in a targeted manner. In this respect, it should be ensured that the velocity is not increased too greatly, in order to prevent uncontrolled removal of the additionally applied material.
When the intention is not to process the external surface of the blank, but rather a duct within the blank, in the case of a surface over which flow passes that forms a wall of the duct in which the duct comprises a change in direction, material which has in the center a convexly running surface and outwardly a concavely running surface is preferably applied to the wall of the duct which is exposed to the flow of the fluid carrier material containing the grinding particles on account of the change in direction of the duct.
The additionally applied material on the side which is exposed to the flow of the fluid carrier material containing the grinding particles prevents the situation in which a depression is introduced into the wall of the duct by the flow grinding. The surface which runs convexly in the center and runs outwardly concavely assists the deflection of the fluid carrier material containing the grinding particles and prevents in particular uncontrolled removal of material by cavitation. The material applied to the wall is thus removed in a controlled manner by the flow grinding process, with the result that it is possible to prevent damage to the wall of the duct in a simple manner.
It is preferable if the convexly running surface has a curvature with a radius in the range of from 0.5 to 5 times the hydraulic diameter of the duct. The curvature particularly preferably has a radius in the range of from 0.5 to 2 times the hydraulic diameter of the duct, for example one times the hydraulic diameter of the duct. The maximum thickness of the applied material corresponds preferably to 0.1 to 0.75 times the hydraulic diameter of the duct, in particular 0.4 to 0.6 times, for example 0.5 times.
The outwardly concavely running surface of the applied material preferably has a curvature with a radius in the range of from 0.5 to 5 times the hydraulic diameter of the duct. The outwardly concavely running surface particularly preferably has a curvature with a radius in the range of from 1 to 3 times, for example two times, the hydraulic diameter of the duct.
When the duct has a different hydraulic diameter upstream of the change in direction than downstream of the change in direction, the hydraulic diameter on which the radius of the concave curvature of the applied material and the radius of the convex curvature of the applied material are based is the hydraulic diameter of the duct downstream of the change in direction.
When the duct has a widening in which the duct increases in size from a region with a first hydraulic diameter to a region with a second hydraulic diameter, that is to say that the second hydraulic diameter is greater than the first hydraulic diameter, in which a transition portion of the wall of the duct between the region with the first hydraulic diameter and the region with the second hydraulic diameter has an angle of between 7° and 90°, in particular between 45° and 90°, with respect to the main flow direction, it is possible for cavitation and thus an uncontrolled removal of material to occur both at the transition portion and in the region with the second hydraulic diameter when flow passes through the duct in the direction from the region with the first hydraulic diameter to the region with the second hydraulic diameter. In the case of an inverse flow direction, cavitation with associated uncontrolled removal of material can correspondingly occur in the transition region and the region which then adjoins it in the flow direction and has the first hydraulic diameter.
In order to prevent this uncontrolled removal of material, it is preferred when, in the case of a surface over which flow passes that forms a wall of a duct, in which the duct has a widening in which the duct increases in size from a region with a first hydraulic diameter to a region with a second hydraulic diameter, in which a transition portion of the wall of the duct between the region with the first hydraulic diameter and the region with the second hydraulic diameter has an angle of between 7° and 90°, in particular between 45° and 90°, with respect to the main flow direction, in which the surface over which flow passes runs convexly at the transition from the region with the first hydraulic diameter to the transition portion and runs concavely at the transition from the transition portion to the region with the second hydraulic diameter. The transition from the transition portion to the region with the second hydraulic diameter can however also have an angle.
As a result of the convex course at the transition from the region with the first hydraulic diameter to the transition portion, a flow separation at the transition from the region with
the first hydraulic diameter to the transition portion is prevented or at least greatly reduced, with the result that an uncontrolled removal of material on account of the associated cavitation can be prevented or restricted.
The surface running convexly at the transition from the region with the first hydraulic diameter to the transition portion preferably has a curvature with a radius in the range of from 0.05 to 2.5 times the hydraulic diameter of the duct upstream of the widening. The surface running convexly at the transition from the region with the first hydraulic diameter to the transition portion preferably has a curvature with a radius in the range of from 0.25 to 1 times, for example 0.375 times, the hydraulic diameter of the duct upstream of the widening.
The surface running concavely at the transition from the transition portion to the region with the second hydraulic diameter preferably has a curvature with a radius in the range of from 0.05 to 2.5 times the hydraulic diameter of the duct upstream of the widening. The curvature of the surface running concavely at the transition from the transition portion to the region with the second hydraulic diameter particularly preferably has a radius in the range of from 0.25 to 1 times, for example 0.375 times, the hydraulic diameter of the duct upstream of the widening.
The blank which is processed by the flow grinding process can be produced by a variety of production methods. By way of example, the blank can be produced by a casting process. It is also possible to produce the blank by a machining process. However, the blank is particularly preferably produced by an additive production process, for example 3D printing.
Examples of the invention are illustrated in the figures and explained in more detail in the following description.
In the figures:
A blank 1 having a surface 3, which is intended to be processed by flow grinding, is introduced for this purpose into a suitable duct, through which a fluid carrier material containing grinding particles flows. In order to prevent a flow separation, additional material 5 is attached to the blank 1 on the side facing away from the flow. The additional material 5 has on the side 7 facing the flow a surface 11 which is inclined and runs concavely in the flow direction with respect to a central plane 9, which runs parallel to the flow direction 25 of the fluid carrier material containing the grinding particles.
The blank 1 illustrated in
When the blank is not a cylinder but rather is a sphere, it has a rotationally symmetrical projection surface, in this case the additional material on the side facing the flow having a surface which runs concavely and in an inclined manner in the flow direction 25 with respect to a central axis. The central axis runs in this case in a manner corresponding to the central plane 9 through the center point of the sphere and parallel to the flow direction 25 of the fluid carrier material containing the grinding particles.
In the case of a cylindrical blank 1, the surface 11 which is inclined and runs concavely with respect to the central plane 9 preferably has a curvature with a radius 13 which corresponds to 2 to 10 times the maximum perpendicular spacing from the central plane 9 to the edge of the non-rotationally symmetrical projection surface, that is to say it corresponds to 2 to 10 times the radius 15 of the cylindrical blank 1. Correspondingly, in the case of a spherical blank 1, the surface which is inclined and runs concavely with respect to the central axis has a curvature with a radius 13 which corresponds to 1 to 5 times the diameter of the spherical blank 1, that is to say 2 to 10 times the radius of the spherical blank 1.
The radius 13 of the curvature of the surface 11 which runs concavely and in an inclined manner particularly preferably amounts to 3 to 6 times the maximum perpendicular spacing from the central plane 9 to the edge of the non-rotationally symmetrical projection surface and/or the radius 15 of the rotationally symmetrical projection surface, for example, as illustrated in
The surface running concavely and in an inclined manner of the additionally applied material is preferably inclined such that the central plane 9, in the case of a blank 1 with a non-rotationally symmetrical projection surface in the flow direction 25, or the central axis, in the case of a blank 1 with a rotationally symmetrical projection surface in the flow direction, is a tangent of the inclined and concavely running surface 11.
In the case of a blank 1 in which the central plane 9 is a plane of symmetry, the additional material 5 is also attached symmetrically with respect to the central plane 9, with the result that the additional material 5 on both sides of the central plane 9 has an inclined and concavely running surface 11 which ends tangentially with respect to the central plane 9. In the case of a blank 1 with a projection surface which is rotationally symmetrical in the flow direction, the additional material 5 is preferably likewise rotationally symmetrically attached to the blank 1. In the case of a non-rotationally symmetrical projection surface, which in the flow direction 25 is also not axially symmetrical with respect to the intersecting line with the central plane 9, the additional material is preferably applied such that the radius of the curvature on both sides of the central plane 9 is different, such that the central plane 9 on both sides and at the same position in the flow direction of the fluid carrier material containing the grinding particles forms a tangent to the surface running in a curved and inclined manner.
The duct 17 illustrated in
Additional material 5, which has in the center a convexly running surface 27 and outwardly a concavely running surface 29, is applied to the wall 23 of the duct 17 which is exposed to the flow of the fluid carrier material containing the grinding particles, the flow direction of which is labeled by an arrow 25, on account of the change in direction of the duct.
The convexly running surface 27 preferably has a curvature with a radius 31 which is in the range of from 0.5 to 5 times the hydraulic diameter. The radius 31 of the curvature of the convexly running surface 27 particularly preferably amounts to 0.5 to 2 times the hydraulic diameter of the duct 17. When, as illustrated here, the duct 17 has a first hydraulic diameter 19 upstream of the change in direction and a second hydraulic diameter 21 downstream of the change in direction, the hydraulic diameter on which the size of the radius 31 is based is the second hydraulic diameter 21. The radius 31 of the curvature of the convexly running surface particularly preferably amounts to one times the second hydraulic diameter 21, as illustrated here.
The concavely running surface 29 preferably has a curvature with a radius 33 which is in the range of from 0.5 to 5 times the hydraulic diameter of the duct 17. The radius 33 particularly preferably amounts to 1 to 3 times the hydraulic diameter of the duct 17. Like for the radius 31 of the curvature of the convexly running surface 27, the hydraulic diameter on which the radius 33 of the curvature of the concavely running surface 29 is based is the second hydraulic diameter 21. The radius 33 of the curvature of the convexly running surface 27 in particular amounts to two times the second hydraulic diameter 21, as illustrated here.
The thickness of the applied additional material 5 has a maximum thickness, which corresponds to 0.2 to 0.75 times the hydraulic diameter of the duct 17. The thickness of the applied additional material 5 particularly preferably corresponds to 0.5 times the hydraulic diameter of the duct 17, the hydraulic diameter on which the thickness of the applied additional material 5 is based also being the second hydraulic diameter here.
The wall 37 is rounded on the side which is opposite the wall which is exposed to the flow of the fluid carrier material containing the grinding particles on account of the change in direction of the duct and at which a flow separation can result on account of the change in direction of the duct 17. The radius 39 with which the wall 37 is rounded preferably corresponds to 0.1 to 2.5 times the hydraulic diameter of the duct 17, in which the hydraulic diameter of the duct 17 in the case of a duct with a first hydraulic diameter 19 upstream of the change in direction and a second hydraulic diameter 21 downstream of the change in direction the average hydraulic diameter is used. In this respect, the arithmetic mean value is used, that is to say the average hydraulic diameter is calculated from the sum of the first hydraulic diameter 19 and the second hydraulic diameter 21 divided by 2. The radius 39 particularly preferably corresponds to 0.25 to one times the average hydraulic diameter and in particular 0.5 times the average hydraulic diameter.
A duct 41 through which flow passes and which has a widening 43 has a first region 45 with a first hydraulic diameter 47 and a second region 49 with a second hydraulic diameter 51. In this case, the second hydraulic diameter 51 is greater than the first hydraulic diameter 47. At the widening 43, the duct 41 through which flow passes has a transition portion 53, in which the wall of the duct 41 has an angle of between 45° and 90° with respect to the flow direction 25. In the embodiment illustrated here, the wall of the duct 41 transition portion has an angle of 90° with respect to the flow direction 25.
In order to prevent a flow separation at the widening 43, that surface of the duct 41 over which flow passes runs convexly at the transition from the first region 45 to the transition portion 53.
The surface 55, which runs convexly at the transition from the first region 45 to the transition portion 53, preferably has a curvature with a radius 57 in the range of from 0.05 to 2.5 times the hydraulic diameter of the duct upstream of the widening 43, that is to say of the first hydraulic diameter 47 in the first region 45. The surface 55, which runs convexly at the transition from the first region 45 to the transition portion 53, particularly preferably has a curvature with a radius 57 which corresponds to 0.25 to 1 times the first hydraulic diameter, for example, as illustrated here, 0.375 times the first hydraulic diameter 47 in the first region 45.
The transition from the transition portion 53 to the second region 49 can have an angle, for example a right angle in the case of a wall of the transition portion 53 which has an angle of 90° with respect to the flow direction 25, or else, as illustrated here, can run concavely.
When the surface in the transition from the transition portion 53 to the second region 49 runs concavely, said surface preferably has a curvature with a radius 59, which corresponds to 0.05 to 2.5 times the first hydraulic diameter 47 in the first region 45, that is to say the hydraulic diameter upstream of the widening 43. The curvature at the transition from the transition portion 53 particularly preferably has a radius 59 which corresponds to 0.25 to 1 times the first hydraulic diameter 47, for example, as illustrated here, 0.375 times the first hydraulic diameter, that is to say the hydraulic diameter upstream of the widening 43 in the first region 45.
As a result of the convex transition from the first region 45 to the transition portion 53 and the concave transition from the transition portion 53 to the second region 49, a flow separation at the widening 43 is prevented and in addition the occurrence of an undesired backflow, which can lead to cavitation and thus uncontrolled removal of material, is prevented.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18196196.2 | Sep 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/074929 | 9/18/2019 | WO | 00 |
