How to dress a grinding wheel

Abstract

Disclosed herein is a method of dressing a grinding wheel, the method comprising providing a dressing roller and a grinding wheel, the dressing roller comprising a hub and a plurality of polycrystalline diamond (PCD) segments mounted about a periphery of the hub, each PCD segment having a pair of generally radially extending side faces and an end face extending generally circumferentially between the side faces, the method comprising the steps of: a. rotating the dressing roller and / or the grinding wheel; and b. engaging an outer periphery of the dressing roller with an outer periphery of the grinding wheel, the speed ratio q between the dressing roller and the grinding wheel being greater than or equal to 1000 rpm. d is less than 0 or greater than +1, and a rake surface is located on one of the sides of each PCD segment and a corresponding flank surface is located on an end face.

Description

[Technical field]

[0001] The present disclosure relates to a method of dressing a grinding wheel with a dressing roller having polycrystalline diamond (PCD) segments, particularly but not exclusively for imparting a fir tree profile to the base of a nickel alloy turbine blade. [Background technology]

[0002] Dressing is generally understood to mean the mechanical shaping of a rotating grinding wheel, where a dressing roller is held against or applied to the working surface of the grinding wheel, producing a controlled wear on the grinding wheel so that the latter operates in a perfectly accurate manner when rotating. Furthermore, a defined profile can be produced on the working surface of the grinding wheel in a corresponding manner. A further purpose of dressing is to produce a defined surface roughness. When the workpiece is ground, the grinding wheel is often intended to produce a defined roughness on its surface. The degree of this roughness depends on the manner in which the dressing step of the grinding wheel was carried out.

[0003] Creep-feed grinding techniques are characterized by lower workpiece speeds (table speeds) and higher depths of cut. Typically, very soft, ultra-high porosity aluminum oxide wheels are used to minimize heat. An example is shown in Figure 1. One drawback is that these wheels need to be continuously dressed to keep the wheel shape within tolerances. Typically, electroplated diamond dressers are also used in creep-feed grinding applications. An example is shown in Figure 2.

[0004] Dressing is extremely important to creep feed grinding because it keeps the grinding wheel open and free cutting. The method of using the diamond roll dresser has a large effect on the quality and efficiency of the creep grinding process.

[0005] The rotation speed and direction of the diamond roll have a crucial effect on creep feed grinding. d =V Dresser / V Grinding ) means that the dresser roll and the grinding wheel are moving in the same direction at the contact point. For example, q d When q is +0.8, it means that the peripheral speed of the dresser is 80% of the peripheral speed of the grinding wheel. d If q is negative, it means that the dresser roll and the grinding wheel are moving in different directions at the contact point. d If is between 0 and 1, this is called the "fracturing" dressing mode or "synchronous dressing", and q d If is negative or greater than 1, this is called "cut" dressing mode or "asynchronous dressing". The relative linear velocity (RLV) is the difference between both linear velocities (see Figure 3). The RLV is the sum of both linear velocities (see Figure 4).

[0006] The main dressing operation parameters used in creep feed grinding with diamond roll dresser are as follows, as shown in Figure 3: d (V Grinding ,V Dresser ), RLV(V Grinding ,V Dresser ) and a r where a r is the feed rate.

[0007] Diamond grit wears by both ductile and brittle mechanisms. Positive q d For low values ​​of q (high RLV), the grit undergoes ductile fracture and a wear flat is formed at the tip of the grit (see Figure 5a). The wear flat is produced by a combination of mechanical wear and a hot flash. d When the value of q is high (low RLV), the grit fails in a brittle fracture mode. The extent of failure is q d It increases with increasing temperature and goes from “microfracture” to “macrofracture” at larger fracture scales (see Figures 5b and 5c, respectively).

[0008] q d As q approaches +1, the forces become increasingly compressive, leading to large-scale diamond fracture, or "macrofracturing" (see Figure 5c). d Negative values ​​of RLV, resulting in very high values ​​of RLV, lead to severe blunting of the grit (ductile fracture) and flattening of the wheel, a condition that causes thermal damage to the workpiece.

[0009] Therefore, the optimum condition is typically in the range of +0.85 and +0.5, where the grinding wheel grit breaks by "microfracture". Figure 6 shows the effect of the dressing and grinding forces of the electroplated grit on the effective surface roughness of the grinding wheel. d This shows a typical effect of

[0010] Previous studies in the field introduced the interference angle (δ) to indicate the severity of the dressing (see Eq. 1). This parameter describes the relationship between the feed rate, the dresser and the grinding wheel peripheral speed. The study showed that a larger interference angle results in less dressing energy and a higher probability of grit breakage. On the other hand, a smaller interference angle flattens the grit and requires more dressing energy. It was also found that the interference angle affects the grinding performance. It was observed that a larger interference angle reduces the grinding force and increases the workpiece surface roughness. The opposite trend was observed for a smaller interference angle. Thus, a balance between the dressing parameters (see q above) is needed to achieve optimal grinding performance. d ranges from +0.5 to +0.85). JPEG2025507203000002.jpg13170 formula 1 Here, a r is the feed rate and D is the wheel diameter.

[0011] a r If we assume that is constant, q d The relationship between and RLS is shown in Figure 7.

[0012] Polycrystalline diamond (PCD) blades offer an improvement over existing electroplated diamond roll dresser technology. PCD blades are also referred to as "abrasive segments." An example of a PCD-based diamond roll dresser is provided in GB2574492. PCD is an example of an ultrahard material (also referred to as ultraabrasive or ultrahard material) that comprises a mass of diamond particles that are substantially intergrown, forming a skeletal mass that defines interstices between the diamond particles. PCD materials typically comprise at least about 80 vol.% diamond, and are conventionally produced by subjecting an agglomerate of diamond particles to temperatures of at least about 1,200°C at ultrahigh pressures, e.g., greater than about 5 GPa.

[0013] For grit sizes between 20 and 100 mesh (typical for electroplated wheels), the number of grits on the wheel surface per unit length, Nl, is O(10 0 ~10 1 ) order of magnitude. For PCD blades, assuming the maximum and minimum amounts of blades are within the range of 24 and 117 based on previous work by the applicant, Nl corresponds to the number of blades per unit length, and is O(10 -2 ~10 1 ) order of q d The optimum value of is influenced by many parameters, one of which is Nl. Therefore, the wear mechanism of the grinding wheel and dresser, and therefore the tool life, are related to δ and Nl.

[0014] The use of PCD blades requires a different approach than current technology, electroplated grit. The value of δ can be adjusted to the same value used for electroplated diamond rolls, but the depth of cut per blade (dr=a), which is a measure of cutting aggressiveness, is reduced. r / Nl) can be an order of magnitude larger. In this case, the operation of the PCD dresser must be changed to improve tool life. Summary of the Invention [Problem to be solved by the invention]

[0015] It is an object of the present invention to provide optimized dressing conditions for a rotary abrasive machining tool comprising multiple PCD abrasive segments. [Means for solving the problem]

[0016] According to the present invention, there is provided a method of dressing a grinding wheel, the method comprising providing a dressing roller and a grinding wheel, the dressing roller including a hub and a plurality of polycrystalline diamond (PCD) segments mounted about a periphery of the hub, each PCD segment having a pair of generally radially extending side faces and an end face extending generally circumferentially between the side faces, the method comprising: a. rotating a dressing roller and / or a grinding wheel; b. engaging an outer periphery of a dressing roller with an outer periphery of a grinding wheel, the speed ratio qd between the dressing roller and the grinding wheel being less than 0 or greater than +1, such that a rake surface is located on one of the sides of each PCD segment and a corresponding flank surface is located on an end face; Includes.

[0017] Preferred and / or optional features of the invention are set out in the dependent claims.

[0018] The invention will now be described by way of example with reference to the accompanying drawings, in which: FIG. [Brief description of the drawings]

[0019] [Figure 1] 1 shows an example of a prior art aluminum oxide grinding wheel. [Diagram 2] FIG. 1 illustrates an example of a prior art electroplated diamond roll dresser used in creepfeed grinding applications. [Diagram 3] FIG. 1 is a schematic diagram showing the conditions between the grinding wheel and the dressing roller when operating at a positive speed ratio qd. [Figure 4]FIG. 1 is a schematic diagram showing the condition between the grinding wheel and the dressing roller when operating at a negative speed ratio qd. [Diagram 5] Figure 5a is a high resolution image showing the ductile and brittle mechanisms of grit wear, showing a wear flat, Figure 5b is a high resolution image showing the ductile and brittle mechanisms of grit wear, showing microfracture, and Figure 5c is a high resolution image showing the ductile and brittle mechanisms of grit wear, showing microfracture. [Figure 6] FIG. 13 is a schematic diagram illustrating the effect of qd on the dressing and grinding forces and the effective grinding wheel surface roughness. [Figure 7] 2 is two graphs showing the relationship between RLS and qd. [Figure 8] FIG. 1 is a perspective view of an example of a rotary abrasive tool used in the present invention. [Figure 9] FIG. 9 is an end view of the tool of FIG. 8. [Figure 10] FIG. 9 is a front view of the tool of FIG. 8. [Figure 11] FIG. 11 is a cross-sectional view taken along line AA in FIG. [Figure 12] FIG. 12 is an enlarged view of Enclosure Zone D in FIG. 11, with the enlarged zone drawn at a scale of 1.5:1. [Figure 13] FIG. 12 is an enlarged view of Enclosure Zone B in FIG. 11, with the enlarged zone drawn at a scale of 1.5:1. [Figure 14] FIG. 9 is a partial perspective view of the tool of FIG. 8. [Figure 15] FIG. 9 is a cross-sectional view through the tool of FIG. 8. [Figure 16] FIG. 9 is a close-up partial perspective view of an abrasive segment mounted to the hub of the tool of FIG. 8. [Figure 17] FIG. 9 is a front perspective view of the hub of FIG. 8. [Figure 18] FIG. 9 is a rear perspective view of the hub of FIG. 8. [Figure 19] FIG. 9 is a perspective view of an individual abrasive segment of FIG. 8. [Figure 20] FIG. 20 is a side view of the abrasive segment of FIG. 19. [Figure 21]FIG. 9 is a cross-sectional view through the tool of FIG. 8 when the spring pin is installed. [Figure 22] 1 is a graph showing the relationship between the thickness (in millimeters, mm) of an individual abrasive segment and the number of abrasive segments (referred to in the graph as "blades") required. [Figure 23] Figure 23a is a schematic diagram showing the flank and rake faces of an abrasive segment when operating in a crushing mode, and Figure 23b is a graph showing the corresponding values ​​of qd. [Figure 24] Figure 24a is an image showing spalling at the top of a PCD blade when operated in spallation mode, and Figure 24b is a schematic showing the direction of the associated velocity vectors. [Diagram 25] Figure 25a is a schematic diagram showing the flank and rake faces of an abrasive segment when operating in cutting mode, and Figure 25b is a graph showing the corresponding values ​​of qd. [Figure 26] Figure 26a is an image showing the wear on the top of a PCD blade when operating in cutting mode, and Figure 26b is a schematic showing the direction of the associated velocity vectors. [Figure 27] FIG. 1 is a schematic diagram showing how the interference angle (δ) can be changed by changing qd and ar. [Figure 28] FIG. 1 is a schematic diagram comparing the average grit protrusion (h), a characteristic of an electroplated diamond dresser, with a PCD blade. [Figure 29] 13 is a heat map showing the relationship between δ=f(ar,qd) and RLV for an initial single PCD blade test. [Diagram 30] FIG. 1 is a heat map showing the varying levels of surface roughness when the PCD blade is operating in cutting mode within the preferred ranges of ar and RLV, i.e., ar is within the range of 0.001-0.006 μm / rev and RLV is within the range of 4-20 m / s. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Examples of rotary abrasive tools

[0021] 8-21, a rotary abrasive machining tool is generally designated 100. For purposes of the present invention, the rotary abrasive machining tool 100 is configured as a dressing roller. The rotary abrasive machining tool 100 includes a hub 102 having a plurality of axially extending radial slots 104 at its periphery and a plurality of abrasive segments 106 disposed within the radial slots. Each abrasive segment has a body 108 for mounting the abrasive segment to the hub and further includes an abrasive edge 110. Each abrasive segment is individually secured to the hub using a pin element 112 that extends at least partially through the abrasive segment and / or at least partially through the hub adjacent the abrasive segment.

[0022] The pin element extends axially partially through the abrasive segment and partially through the hub adjacent the abrasive segment.

[0023] The hub is an annular body with a central aperture 114 for mounting to a rotating shaft of a rotary dressing machine (not shown). The general shape of the hub resembles a pipe flange, having a ring portion 116 and a raised surface 118 on one side, best seen in FIG. 15. The hub has first and second opposed major shank surfaces 120, 122 (see FIGS. 17 and 18). An outer circumferential surface 124 connecting the first and second major shank surfaces generally tapers radially inward from one side to the other.

[0024] The slots extend axially between a first major axial surface and a second major axial surface. The slots also extend radially into the hub, thereby defining a series of supports 126 between the slots. Each slot has an adjacent support. Each support is generally L-shaped having a radially extending first support leg portion 128 and an axially extending second support leg portion 130. The first support leg portion is shorter than the second support leg portion. The first support leg portion is located adjacent the first major axial surface and the second support leg portion terminates at the second major axial surface.

[0025] A first pin recess 132 (see FIG. 14) for partially receiving a pin element extends along the longitudinal extent of each support. The first pin recess has a semicircular side cross-section and is intended to form a complete, i.e. full circle, when aligned with another pin recess having a semicircular side cross-section, as will be described in more detail below.

[0026] Each abrasive segment is also generally L-shaped, as best seen in FIG. 19. As such, the abrasive segment comprises a first segment leg portion 134 extending from a second segment leg portion 136. The first segment leg portion is shorter than the second segment leg portion. The first segment leg portion extends at an angle X relative to the second segment leg portion, the angle X being in the range of 75 degrees to 100 degrees. The angle X is measured between the outer surfaces of the first segment leg portion and the second segment leg portion, as shown in FIG. 20. Preferably, the angle X is about 80 degrees.

[0027] Due to the L-shape configuration, the resulting rotary abrasive machining tool is particularly well suited for machining fir-tree profiles. The L-shape helps minimize the amount of material required by the abrasive segment in the machining operation. This is especially important when expensive ultra-hard materials like PCD are required for maximum wear resistance and long life.

[0028] Each abrasive segment is inserted into a slot between two supports. When it reaches its final position, the first segment leg aligns with the first support leg of the hub and the second segment leg aligns with the second support leg. The L-shaped configuration of the supports helps minimize the mass of the hub and provides support only where it is needed.

[0029] As shown in Figures 19 and 20, the abrasive segment further comprises a nesting surface 138 intermediate the outer surface of the first segment leg portion and the second segment leg portion. The nesting surface is important to maximize the amount of abrasive segments that can be removed from the blank 140 during manufacture. Typically, the blank is a disk of abrasive material such as PCD backed with a carbide layer. In determining the appropriate nesting configuration, the introduction of the nesting surface increases the amount of abrasive segments that can be stacked on the blank compared to stacking abrasive segments that do not have a nesting surface. The nesting surface extends from the outer surface of the second segment leg portion at an angle Y in the range of 30 to 50 degrees, as shown in Figure 20. Preferably, the angle Y is about 45 degrees.

[0030] In the hubs of Figures 8-16, the quantity of slots and corresponding abrasive segments is 80. This quantity was determined by considering factors such as the target volume of the wheel to be machined by the tool, the rotation speed and the feed rate. There are also geometric constraints to consider, such as the minimum spacing between abrasive segments (e.g. 15 mm) and / or the radial thickness of the support (e.g. 0.75 mm).

[0031] The amount of abrasive segments required is related to the total thickness l of each abrasive segment and the diameter D of the hub. From experiments, the relationship between the amount of abrasive segments, the thickness of the abrasive segments, and the diameter of the hub has been empirically understood and can be determined by the following two equations: JPEG2025507203000003.jpg1042 JPEG2025507203000004.jpg1038

[0032] In fact, if the hub is tapered (as in the first example), the diameter used is actually the diameter measured to the minimum height of the profile ground edge. For non-tapered hubs, it is much easier to specify the diameter dimension.

[0033] For example, in the graph of Figure 22, when l = 1 mm, D = 150 mm, the amount of abrasive segments required for the hub is between the maximum value shown by line Lmax and the minimum value shown by line Lmin. It is possible to use an amount of abrasive segments outside of these two lines Lmin and Lmax, but at some point, you will have a life span and the number of wheels that can be machined by the tool.

[0034] For completeness, the illustrative rotary abrasive tool has a total abrasive segment thickness of about 3 mm and a hub diameter of about 140 mm. This gives a working range of 24 to 117 abrasive segments number that can be used, with 80 chosen as an example. Preferably, the segment thickness is in the range of 1 to 4 mm.

[0035] A second pin recess 142 having a semicircular side cross section extends along the longitudinal extent of the sharpening segment. In the final position described above, the second pin recess of the sharpening segment aligns with the first pin recess of the adjacent support, together forming a hole 144 having a circular side cross section. When a pin element is inserted into this hole, the sharpening element is secured in the slot (see FIG. 21). The sharpening element can be removed from the hub by simply pulling out the pin element. The pin element is a spring pin 146 (also called a slotted spring tension pin), made, for example, from galvanized spring steel. The spring pin is elongated and, in the uncompressed state, comprises a single coil 150 with an open gap 152. When compressed, as occurs when the spring pin is driven into the hole created by the aligned first and second pin recesses, the spring pin reduces in diameter and, due to its inherent spring bias, tries to return to its uncompressed state. This behavior allows the spring pin to function as a fastener between the sharpening segment and the hub. In the compressed state, the spring pin gap is aligned with the surfaces of the abrasive segment and support.

[0036] Briefly referring again to FIG. 20, the abrasive edge forms part of the second segment leg portion. In the final position, the abrasive edge projects radially beyond the second support leg portion in order to function as intended. The abrasive edge has a profile that is molded into the second segment leg, for example by means of laser machining. This profiling operation is preferably performed after the abrasive segments are placed in situ in their respective slots, as described in GB 2574492, so that typical profiles of the abrasive segments before and after profiling are shown at P and Q, respectively. Profile P is essentially artificial and dashed, depicting the profile at a particular point in time. Finally, profile Q is (one of) the desired profiles to be imparted to, for example, the wheel. In practice, the desired profile can be molded into the abrasive edge at any depth between lines P and Q. The depth of the abrasive between lines P and Q can therefore also be considered as a re-sharpening allowance.

[0037] A flange 154, also known as a backing plate, is mounted coaxially on the hub relative to the first major axis plane (see FIG. 15). The flange is secured in place using a number of screws 156 and threaded holes 158 in the hub spaced from the abrasive segments. The flange helps prevent axial movement of the abrasive segments under harsh operating conditions. Optionally, the flange is an annular plate having a patterned surface (not shown). The patterned surface on or in the flange engages a corresponding pattern on the hub in a mating arrangement. The cooperating pattern minimizes relative rotation between the hub and the flange. Typically, the pattern is a series of recesses and / or protrusions. An example is shown in FIG. 18, which includes a pair of inscribed arcuate recesses 160. The rotary abrasive machining tool can be configured as a grinding wheel, a rotary dressing tool, or other similar forms of machining tool. As mentioned above, rotary abrasive tools are particularly useful for dressing grinding wheels having complex shaped profiles, such as fir tree profiles.

[0038] Operating conditions of PCD blades

[0039] q d Depending on the value of , the flank and rake faces of the tool are different. d <0 and q d ≥ 1) is ideal for PCD dressers (see Figures 25 and 26). Due to the velocity vector direction and the rake surface at the top of the blade, the crushing mode (i.e., 0 d <1), severe spalling occurs on the flank surface. Therefore, this condition should be avoided for PCD dressers.

[0040] Based on Eq. 1, q d and a r By changing , the interference angle (δ) can be changed. Therefore, if the same value is required for a PCD dresser (compared to an electroplated wheel), q d and a r (See Figure 27.) In the case of an electroplated diamond dresser, a r The value of is constrained by the average grit protrusion (h) (typically 0.5-1 μm / rev) (see Figure 28). However, in the case of PCD dressers, the prescribed edge characteristics of the PCD cutter limit a r Any feasible value can be considered (eg, 1 to 10 μm / rev).

[0041] The wear rate of a PCD dresser is a function of several parameters: RLV and Nl.

[0042] In the blade unit test, The relationship between JPEG2025507203000005.jpg625 and RLV is shown in Figure 27.

[0043] For any given quantity of PCD segments intended for use in a rotary abrasive machining tool, a heat map can be created, such as that shown in Figures 29 and 30. The heat map in Figure 29 shows that for an RLV of, say, about 12 m / s, a feed rate of a r ​The heat map in Fig. 30 shows that the feed rate a needs to be kept above 0.002 mm / rev to minimize the surface roughness at the same RLV. r Thus, using the two heat maps in combination with each other, it is clear that for any given amount of PCD segments, the RLV and feed rate a r is optimal for the wear rate and surface roughness.

[0044] In a preferred embodiment, the dressing roller is driven at a feed rate (a r ), the feed rate per PCD segment (in absolute terms) ranges between one-fortieth (i.e., 0.025) and one-fifth (0.2), in other words, from 0.2 to 0.025. As a first example, if the quantity of PCD segments is 80 and the feed rate is 3 μm / rev, then the feed rate per PCD segment is 3 / 80=0.0375. As a second example, if the quantity of PCD segments is 30 and the feed rate is 6 μm / rev, then the feed rate per PCD segment is 6 / 30=0.2.

[0045] Preferably, the feed rate (a r ) is in the range of 0.001 to 0.006 mm / rev, and preferably, the RLV is q d <0 is in the range of 10-30m / s, and q d >1 is in the range of 2-10 m / s. Within these ranges, the amount of PCD segments can be iterated and further optimized to potentially reduce the amount of PCD segments, thereby reducing the overall cost of the rotary abrasive tool.

[0046] Although the present invention has been particularly shown and described with reference to embodiments, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the scope of the invention as defined by the appended claims. [Explanation of symbols]

[0047] 100 Rotary abrasive tools 102 Hub 104 Radial Slot 106 Polishing Segment 154 Flange

Claims

1. 1. A method of dressing a grinding wheel, comprising: providing a dressing roller and a grinding wheel, the dressing roller comprising a hub and a plurality of polycrystalline diamond (PCD) segments mounted about a periphery of the hub, each PCD segment having a pair of generally radially extending side surfaces and an end face extending generally circumferentially between the side surfaces; The method further comprising: a. rotating the dressing roller and / or the grinding wheel; b. engaging the outer periphery of the dressing roller with the outer periphery of the grinding wheel, the speed ratio between the dressing roller and the grinding wheel being q d is less than 0 or greater than +1, a rake surface being located on one of the side surfaces of each of the PCD segments and a corresponding flank surface being located on the end surface; A method comprising:

2. The dressing roller has a feed speed (a r 2. The method of claim 1, wherein the feed rate per PCD segment is between 1 / 40 and 1 / 5.

3. The method of claim 2 , wherein the feed rate per PCD segment is between 40 times slower and 10 times slower.

4. The feed speed of the dressing roller (a r 4. The method according to claim 1, wherein the rotational speed is in the range of 0.001 to 0.010 mm / rev.

5. The method according to claim 4, wherein the feed rate of the dressing roller is in the range of 0.001 to 0.006 mm / rev.

6. The method according to claim 4 or 5, wherein the feed rate is in the range of 0.002 to 0.005 mm / rev.

7. The relative linear velocity (RLV) of the dressing roller is q d 7. The method according to claim 1, wherein the velocity is in the range of 10 to 30 m / s at <0.

8. The relative linear velocity (RLV) of the dressing roller is q d The method according to any one of claims 1 to 7, wherein the velocity is in the range of 2 to 10 m / s at >0.

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