Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B37/00—Lapping machines or devices; Accessories
  • B24B37/11—Lapping tools
  • B24B37/20—Lapping pads for working plane surfaces
  • B24B37/26—Lapping pads for working plane surfaces characterised by the shape of the lapping pad surface, e.g. grooved
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B37/00—Lapping machines or devices; Accessories
  • B24B37/11—Lapping tools
  • B24B37/20—Lapping pads for working plane surfaces
  • B24B37/24—Lapping pads for working plane surfaces characterised by the composition or properties of the pad materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B37/00—Lapping machines or devices; Accessories
  • B24B37/11—Lapping tools
  • B24B37/12—Lapping plates for working plane surfaces
  • B24B37/16—Lapping plates for working plane surfaces characterised by the shape of the lapping plate surface, e.g. grooved
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/005—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used during pre- or after-treatment

Definitions

• the invention relates to a device for pre-polishing a ductile metallic material that has previously been cut.
• the invention also relates to a method for preparing a ductile metallic material for polishing, in which the pre-polishing operation is carried out with such a device.
• a metallic material especially a ductile metallic material, exhibits significant surface deformations of material that must be corrected before polishing operations take place.
• Pre-polishing primarily involves removing surface material sufficiently to correct defects caused by cutting. However, it also aims to achieve optimal surface roughness to prepare the material for the polishing operation.
• the pre-polishing of ductile metal materials is commonly carried out using a series of abrasive papers, progressing from the coarsest to the finest grit. These operations are time-consuming and require significant quantities of abrasive paper.
• the invention therefore relates to a pre-polishing device for ductile metallic materials that eliminates the need for abrasive paper and ensures both a sufficient material removal rate and a surface roughness suitable for the subsequent polishing operation.
• the aim is to reduce deformation caused by cutting while simultaneously removing sufficient material.
• the invention relates to a pre-polishing device for a ductile metal part to be prepared for polishing, which device comprises a working surface on which the part to be prepared is intended to be applied, and which is made of a plurality of hollow parts independent of each other and delimited by partitions whose flat upper walls form the active pre-polishing zone intended to be in direct contact with the part to be prepared during the pre-polishing operation, the partitions having a substantially constant height before use of the device, characterized in that the surface of the active pre-polishing zone represents between 45 and 55% of said working surface, in that it is based on resin mixed with an abrasive diamond powder.
• the invention also relates to a method of preparing a part for polishing which is essentially characterized in that after the cutting operation, a pre-polishing operation is carried out with the device as previously defined.
• the part to be polished is made of aluminum alloy.
• it is a copper-aluminum alloy.
• the part to be polished can also be made of copper alloys such as brass (CuZn36), bronze (CuSn8), and cupronickel (CuNi14Al2).
• the ductile metal part has a yield strength between 250 and 800 MPa and an elongation at break between 8 and 50%.
• FIG. 1 schematically represents a plan view of an example embodiment of the pre-polishing device of the invention in the form of a disc;
• FIG. 2a There figure 2a schematically represents a detail of the figure 1 according to arrow A of the Figure 1;
• Fig. 2b There figure 2b is a micrograph of a detail of the figure 1 according to arrow A of the figure 1 .
• FIG. 3 There figure 3 schematically represents a cross-sectional view along arrow III-III of the figure 2 ;
• FIG. 4 is a graph illustrating the material removal rate as a function of pre-polishing conditions for earlier art pre-polishings carried out with abrasive paper of different grits, for pre-polishings forming counter-examples made with pre-polishing discs of different kinds, and for pre-polishing according to the device of the invention;
• FIG. 5 There figure 5 is a graph illustrating the surface roughness Ra for each pre-polishing condition shown on the figure 4 ;
• FIG. 6 There figure 6 is a graph illustrating the surface roughness Rz for each pre-polishing condition shown on the figure 4 ;
• FIG. 7 is a graph illustrating the material removal rate at each cycle of the protocol as a function of the load-bearing rate of the pre-polishing device comprising diamond abrasive powder, of which the device of the invention;
• FIG. 8 [Fig. 9 ] THE figures 8 and 9 are graphs illustrating the surface roughness Ra and Rz of the part respectively as a function of the bearing capacity of the pre-polishing device comprising diamond abrasive powder, of which the device of the invention;
• FIG. 10 is a graph illustrating the evolution of the pressure applied to the part as a function of the bearing capacity of the pre-polishing device comprising diamond abrasive powder, of which the device of the invention;
• FIG. 11 is a graph illustrating the material removal rate at each cycle of the protocol as a function of the size of the diamond particles in the diamond powder mixed with the resin of the device of the invention
• FIG. 12 [ Fig. 13 ]
• FIG. 12 and 13 are graphs illustrating the surface roughness Ra and Rz of the part respectively as a function of the size of the diamond particles in the diamond powder mixed with the resin of the device of the invention;
• FIG. 14 is a graph illustrating the material removal rate at each cycle of the protocol as a function of the concentration of diamond particles in the thickness of the working surface of the device of the invention
• FIG. 15 [Fig. 16 ] THE Figures 15 and 16 are graphs illustrating the surface roughness Ra and Rz respectively of the part as a function of the concentration of diamond particles in the thickness of the working surface of the device of the invention.
• the pre-polishing device of the invention is described structurally with reference to the Figures 1 to 3 .
• FIG. 1 shows an example of an embodiment of the pre-polishing device according to the invention which is in the form of a disc whose substantially flat surface, called the working surface, intended to be applied against the ductile metal part to be pre-polished, comprises a plurality of hollow parts 1 which are delimited from each other by partitions 2.
• the hollow parts 1 here have substantially the shape of a square, the hollow parts, as well as the partitions, being preferably regularly distributed over the surface of the disc according to the invention.
• the disc is rotated and the parts to be polished are also rotated at a lower speed, and applied to the surface of the disc with a certain pressure.
• the partitions 2 are defined by a flat upper wall 3 and two side walls 4 and 5.
• partitions 2 have a height h which is preferably uniform across the entire surface of the disc, in order to ensure even pre-polishing of the parts to be polished. This depth h also defines the depth of each recessed section 1.
• This height h is advantageously between approximately 0.05 and 15 millimeters and, preferably, between 0.05 and 10 millimeters.
• the thickness of the partitions 2 or the dimension z of the upper face 3 of the partitions is advantageous for the thickness of the partitions 2 or the dimension z of the upper face 3 of the partitions to be between 0.5 and 15 millimeters, preferably between 1 and 2 millimeters, to contribute to the efficiency of material removal when using the disc.
• the recessed parts have a generally rectangular shape with a length x between 1 and 5 millimeters, preferably between 2 and 4 millimeters, and a width y less than the length x and also between 1 and 5 millimeters, preferably between 2 and 4 millimeters.
• the draft angle ⁇ , between the upper wall 3 of the partition 2 and a lateral wall 4 or 5, be less than 90. This is due to the fact that the disk is advantageously obtained by molding.
• this angle not be less than 75, so that the active area of the disk, consisting of all the upper walls of the partitions 2, is not significantly altered when the disk undergoes wear, after prolonged use.
• the invention is of course not limited to the shape of the hollow parts 1 and the partitions 2 which is illustrated in the figures.
• the recessed parts 1 can have any geometric shape, including polygonal and for example rectangular or hexagonal, or a rounded shape, such as a round or oval shape.
• the surface of the pre-polishing device according to the invention can also correspond to the negative or positive relief of a fabric, in particular of the satin or taffeta type.
• the invention is also not limited to a pre-polishing device in the form of a disc with a flat surface.
• the disc can have a concave or convex surface.
• the device can also be cylindrical, with the pre-polishing working surface being either the external or internal surface of the cylinder.
• the device according to the invention is a surface of revolution whose axis of revolution is the axis of rotation of the device on the pre-polishing machine on which it is used.
• the recessed parts and partitions be distributed regularly on any curve defining a plane perpendicular to the axis of revolution of the device and whose points are all equidistant from the axis of revolution.
• the pre-polishing disc is advantageously obtained by molding a synthetic resin mixed with a diamond abrasive powder, the specific characteristics of which will be described later.
• a diamond abrasive powder the specific characteristics of which will be described later.
• one or more additional metallic powders may be incorporated.
• the mold has the shape of the desired counterpart, in order to obtain the required recesses and partitions.
• a mold will have domes.
• the mold may consist of a negative reproduction of a grid whose voids represent the partitions, and to which a plate is attached to block them.
• the pre-polishing device has specific characteristics attached to the active pre-polishing zone.
• this active pre-polishing zone formed by the flat upper walls 3 of the partitions 2, represents between 45 and 55%, preferably 50%, of the working surface, which is defined as comprising the recessed parts 1 and the partitions 2. Furthermore, this active pre-polishing zone is made of resin mixed with a single abrasive diamond powder. Advantageously, the average size of the diamond particles in the abrasive powder is between 25 and 50 micrometers. For manufacturing convenience, a pre-polishing device in which the entire working surface (recessed parts 1 and upper walls 2 of the partitions) exhibits these properties is preferred. However, within the scope of the invention, what is essential is that the active pre-polishing zone in direct contact with the material to be pre-polished exhibits these properties.
• the pre-polishing device is advantageously applied to ductile metallic materials which deform easily under the pressure exerted by conventional discs during the pre-polishing operation, such as aluminum alloys or copper alloys.
• the ductile character of metallic materials suitable for use with the device of the invention is defined by an elastic limit between 250 and 800 MPa and an elongation at break between 8 and 50%.
• the polishing machine used is marketed under the name Masterlam 3.0 by the company LAMPLAN.
• Six samples are positioned on a central pressure sample holder with six sample receiving cavities.
• the six samples have on their underside a surface made of EN AW-2017A copper aluminum alloy with the formula AlCu4MgSi commonly used in the automotive and aerospace industries and which has been previously cut.
• the EN AW-2017A alloy is heat-treated under T3 conditions to achieve a minimum yield strength of 250 MPa and an elongation at break of at least 10% as specified by EN 754-2.
• the EN AW-2017A alloy thus treated exhibits a yield strength between 416 and 449 MPa and an elongation at break between 10 and 11.5%.
• the chemical composition of the EN AW-2017A alloy comprises, by weight: 0.2% ⁇ Si ⁇ 0.8%, Fe ⁇ 0.7%, 3.5% ⁇ Cu ⁇ 4.5%, 0.4% ⁇ Mn ⁇ 1%, 0.4% ⁇ Mg ⁇ 1%, Cr ⁇ 0.1%, Zn ⁇ 0.25%, Ti+Zr ⁇ 0.25%, other ⁇ 0.05%, the remainder being aluminium.
• the pre-polishing disc to be tested is installed on a rotating platform after being dressed for about 30 seconds using an abrasive dressing stone to remove the layer of resin that covers the diamond particles.
• the lubricant used is water, the functions of which are to remove abrasion debris, to cool and to lubricate the treated surface.
• Ra Surface roughness
• Roughness Rz expressed in microns ( ⁇ m) corresponds to the measurement of the difference between the highest peak and the lowest trough in the five-line sampling length. It indicates the maximum profile height. Also, the lower the Rz value, the smoother the surface.
• the goal in polishing, and more specifically pre-polishing, is to achieve both a sufficient material removal rate to simplify the subsequent polishing operation and the lowest possible surface roughness.
• the aim is to substantially reduce deformations resulting from cutting while removing sufficient material. It is defined that the material removal rate should preferably be greater than 0.9 g/min and that the surface roughness Ra should be less than 0.4 ⁇ m, preferably less than 0.3 ⁇ m, so that the metal surface is adequately prepared for polishing.
• polyester resin discs mixed with silicon carbide give material removal rates that are too low, equal to or less than 0.7 g/min.
• F240 and F600 aluminum oxide mixed resin discs are insufficient in terms of material removal rate.
• the material removal rate is too low (0.3575 and 0.378 g/min respectively).
• the surface roughness obtained with a load factor of 50% is surprising since it does not follow the evolution of the roughness for the load factors of 6.1%, 15% and 25% in that, in addition to the fact that the roughness predictably decreases, at least for the first and second cycles, with the increase in the load factor, the surface roughnesses Ra and Rz for the load factors of 15% and 25% are close after each of the cycles, whereas the surface roughness of Ra and Rz for the load factor of 50% is significantly lower.
• a load-bearing capacity of 50% thus allows us to benefit from the best ratio of material removal rate to surface roughness, even though this advantageous surface roughness could not be deduced from the surface roughnesses obtained for load-bearing capacities of 15% and 25%.
• the load-bearing rate between 45 and 55%, and more particularly 50%, has also been highlighted as enabling optimal surface pressure during pre-polishing by the pre-polishing machine.
• the pressure was evaluated according to the bearing rate of the disc for three central forces applied on the sample holder against the plate during pre-polishing of 120 Newton (reference 6), 180 Newton (reference 7) and 240 Newton (reference 8) respectively.
• Pressure Central force / (Sample surface area x Support bearing capacity) the load-bearing capacity of the support corresponding to the surface of the active pre-polishing zone, i.e. the surface constituted by the upper face 3 of the partitions.
• the material removal rate is directly related to the applied pressure. It has been observed that beyond a 55% bearing capacity, the pressure difference between two different central pressures decreases. Therefore, there is no particular advantage to exceeding a 55% bearing capacity, given that the material removal rate will be reduced and the size of the hollow sections will become too small to adequately evacuate the water that removes the produced metal debris.
• the results relating to roughness show a certain proportionality with respect to the sizes of the diamonds tested. This is not the case for the material removal rate, since the results obtained are higher for a diamond particle size of 35-37 ⁇ m than could be predicted by considering only the ratio between the sizes of the particles tested.
• the invention further relates to a method for preparing a ductile metal part for pre-polishing without the use of abrasive paper.
• the method comprises, after cutting, a single pre-polishing step using a device as previously described.
• the part is then ready for polishing using conventional methods.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)

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Citations (4)

• 2024
  • 2024-04-22 EP EP24315207.1A patent/EP4640370A1/de active Pending

Patent Citations (4)

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