Grinding wheel and its preparation method for preventing workpiece end face crack in high speed grinding process

Abstract

The application discloses a grinding wheel for preventing end face cracks of a workpiece in a high-speed grinding process and a preparation method thereof, and belongs to the field of grinding wheel manufacturing and grinding processing. The two end faces of the grinding wheel are provided with randomly distributed micro holes (200-500 microns) through laser marking, a high number of binders (23-28%) is used in the formula of the grinding wheel, and a method for forming micron-sized small holes (5-10 microns) in the binders is used to increase the convective heat transfer of the cooling medium, so that the cooling medium carries away more heat, thereby preventing end face grinding cracks. In the method, the high binder mass ratio increases the wrapping holding force of the binder on the CBN abrasive, reduces the falling of the abrasive and improves the durability of the grinding wheel. The micro holes adsorb moisture through capillary action during grinding, the millimeter holes can form a cooling water flow channel, the combination of laser marking and micron-sized small holes in the binder has good cooling effect, does not weaken the grinding performance of the grinding wheel itself, thereby reducing the dressing frequency of the grinding wheel and prolonging the service life of the grinding wheel.

Description

Technical Field

[0001] This invention belongs to the field of grinding wheel manufacturing and grinding, specifically relating to a grinding wheel for preventing workpiece end face cracks during high-speed grinding and its preparation method. Background Technology

[0002] Ceramic CBN grinding wheels are widely used in the grinding industry due to their excellent properties such as stable chemical properties, good sharpness, long service life, and good precision retention, especially suitable for high-speed grinding. The grinding process is a macroscopic manifestation of countless individual abrasive grains interfering with and cutting the workpiece; the process is extremely complex, and the vast majority of the grinding power consumed during grinding is converted into heat energy. In grinding, approximately 10% of the heat flows into the grinding chips, while approximately 55%-90% of the heat flows into the workpiece being ground. This heat accumulates in the grinding contact area, creating instantaneous high temperatures, causing residual stress on the workpiece surface, and even grinding cracks. This phenomenon is called grinding cracks, and grinding cracks on the workpiece surface significantly affect the workpiece's fatigue strength and service life. From the perspective of grinding wheel manufacturing, there are currently two main methods to prevent grinding cracks: ① Grooving the outer end face of the grinding wheel allows coolant to enter the grinding contact area, carrying away a large amount of heat load, thereby reducing the workpiece's grinding surface temperature and preventing tempering cracks and quenching cracks. While this method is effective, in high-speed scenarios, the wear of the grinding wheel will be accelerated after grooving, leading to a reduction in service life. Furthermore, micro-abrasive grains that abnormally detach from the edges after violent impacts can easily enter the grinding contact area, causing scratches on the workpiece surface. ② Adding a specific amount of pore-forming agent to the grinding wheel formulation is another method. However, the pores formed by the pore-forming agent are small and irregular in size, making them difficult to control and unreliable. It also affects the original formulation ratio, easily causing instability during the use of the grinding wheel. Summary of the Invention

[0003] This invention addresses the problem of end-face grinding cracks during high-speed grinding. Traditional ceramic CBN grinding wheel formulations for crankshafts typically use a binder mass ratio of 15-22%, and the pore-forming methods usually involve natural pore formation or the addition of float beads or hollow spheres of similar size to the abrasive grains, with pore sizes exceeding 100-200 μm. This invention provides a grinding wheel and its preparation method for preventing end-face cracks during high-speed grinding. The grinding wheel formulation uses a high binder mass ratio (23-28%) and creates micron-sized pores (5-10 μm) within the binder. Randomly distributed micro-pores (200-500 μm) are laser-drilled on both end faces of the grinding wheel to increase convective heat transfer in the cooling medium. This allows the cooling medium to remove more heat, thus preventing end-face grinding cracks. Compared to traditional methods, the high binder mass ratio increases the binder's holding force on the CBN abrasive, reducing abrasive grain shedding and improving the grinding wheel's durability. To avoid burn cracks, a cooling method combining bonded micro-pores and laser-drilled millimeter holes is used. The micro-pores adsorb moisture through capillary action during grinding, while the millimeter holes form cooling water channels. The combination of laser drilling and bonded micro-pores provides good cooling without weakening the grinding performance of the grinding wheel itself, thereby reducing the frequency of grinding wheel dressing and increasing the service life of the grinding wheel.

[0004] A grinding wheel for preventing workpiece end face cracks during high-speed grinding has a perforated area on the abrasive layer on both ends of the grinding wheel. The perforated area is a ring-shaped area on the effective grinding area of ​​the abrasive layer. The area of ​​the perforated area is less than or equal to the area of ​​the effective grinding area on the abrasive layer. Several small holes are distributed in the perforated area.

[0005] Furthermore, the diameter of the grinding wheel is 500mm to 700mm, the diameter of the small holes is 0.2 to 0.5mm, the total area of ​​the small holes accounts for 3% to 10% of the area of ​​the drilling area; the small holes do not overlap and the distance between the holes is 0.5mm to 2mm.

[0006] Furthermore, the small hole is made by laser drilling. During laser drilling, the power of the laser drilling equipment is 120-150W, the laser pulse width is 0.6-0.95, and the laser frequency is 60-70Hz. The depth of the small hole can be controlled by setting the laser drilling conditions. Under these conditions, the depth of the small hole is 5mm-7mm.

[0007] The drilling area is a ring-shaped region on the outer edge of the effective grinding area of ​​the abrasive layer, such as... Figure 1 As shown, the radius of the small hole is r3, and the position coordinates of the hole need to meet the following conditions:

[0008] (1) Make the whole circle with the fuzzy random data points as the center and r3 as the radius completely located within the target area.

[0009] (2) To prevent the grinding wheel life from being reduced due to an excessive number of holes, the number of holes is automatically adjusted by controlling the area ratio q of the total area of ​​the holes in the target area. After multiple experiments, it was found that when the grinding wheel diameter is 500mm to 700mm, the value of q is 3% to 10%.

[0010] (3) In order to ensure that the density of the holes is relatively uniform in the target area, the holes do not overlap and the distance between the holes is reasonably set. After multiple experiments, it was found that when the diameter of the grinding wheel is 500mm to 700mm, the value of b is 0.5mm to 2mm.

[0011] Specifically, the coordinates of the center of the hole are obtained through the following process:

[0012] To reduce computational load and improve computational speed, a local model of the grinding wheel layer end face is established, such as... Figure 2 As shown, the annular area requiring laser drilling is divided into t parts, with the center angle of each part being (α2-α1). t is a positive integer. One portion of the fan-shaped region is taken as the target region, denoted as ADQM. AD is the local arc length of the outer circle of the grinding wheel layer end face, with a radius of r2. MQ is the local arc length of the inner circle of the grinding wheel layer end face, with a radius of r1. The radius of the small hole is r3. The central angle interval corresponding to the target region is θ∈[α1,α2]. O1—X1Y1 is the rectangular coordinate system where the target region is located. The origin O1 is taken as the center of the target region, and the axis of symmetry between lines AM and DQ is taken as the Y1 axis. The target region ADQM can be expressed by the mathematical equation:

[0013]

[0014] In the formula: a is the distance between the center of the hole in the annular region and point O1, (x1,y1) is the coordinate of the center of the hole in the target region, and (x0,y0) is the coordinate of the center of the target region, which is (0,0) in this invention.

[0015] To ensure that the entire circle with a radius of r3, centered on a fuzzy randomly generated data point, lies entirely within the target region ADQM, it is necessary to ensure that the circle generated at the extreme position points lies at the boundary point of the target region ADQM. As shown in the right figure, F, G, J, and K are extreme position points. Therefore, the circle with F, G, J, and K as centers and r3 as radius is tangent to the boundary line of the target region ADQM.

[0016] Taking point F as an example, FG is the local arc length equidistant from the normal of the local arc length of the outer circle of the grinding wheel end face by r3, and the radius of this arc is (r2-r3). Similarly, JK is the local arc length equidistant from the normal of the local arc length of the inner circle of the grinding wheel end face by r3, and the radius of this arc is (r1+r3). When the generated random data point falls within FGKJ, the circle generated by this data point must be within the target area ADQM. Therefore, the area composed of the limit points F, G, K, and J is the point selection area. Taking the intersection of lines FJ and GK on the Y1 axis as the origin O2, and the axis of symmetry of lines FJ and GK as the Y2 axis, where the Y2 axis coincides with the Y1 axis, a rectangular coordinate system is established, denoted as O2—X2Y2, where the straight-line distance between the origins O1 and O2 is:

[0017] Next, we need to solve for the coordinates of the random points within the sampling area. Since the diameter of the small holes in this invention is relatively small, approximately 0.2–0.5 mm, the sampling area can be approximated in the coordinate system O2—X2Y2 using a mathematical equation as follows:

[0018]

[0019] In the formula: r4 is the distance from any point within the selected area to the origin O2, which can be considered as a random radius factor within the selected area where r4∈[(r1+r3-|O1O2|), (r2-r3-|O1O2|)]; θ is a random angle factor within the selected area where θ∈[α1,α2]; and (x2,y2) are the coordinates of a random point within the selected area. Let O2 be the origin of the coordinate system O2—X2Y2, and let it be (0,0).

[0020] To determine the random coordinates (x2, y2) of a point within the selected area, it is necessary to determine the values ​​of the random radius factor r4 and the random angle factor θ within their respective ranges in the equation, and then substitute them into the equation to obtain the coordinates of the point (x2, y2) in the coordinate system O2—X2Y2.

[0021] First, as shown in the figure, the area S1 of the target region ADQM is:

[0022]

[0023] Assuming the area S2 of the orifice accounts for q% of the area of ​​the target region ADQM, then the total area of ​​the orifice is...

[0024]

[0025] Therefore, the number of holes is:

[0026]

[0027] When determining the random factor, this application uses the rand function to generate random numbers within a specified interval. rand(1) represents a random number within the interval [0,1]. For the random radius factor r4, the random number within the interval r4∈[(r1+r3-|O1O2|), (r2-r3-|O1O2|)] is:

[0028] r4=(r1+r3-|O1O2|)+(r2-2r3-r1)rand(1) (6)

[0029] For a random angle factor θ in the interval [α1, α2], the random number is:

[0030] θ=α1+[α2-α1]rand(1) (7)

[0031] Therefore, substituting (6) and (7) into the equation (2) of the region of origin, we can obtain:

[0032] like Figure 3 As shown, using MATLAB software, the first random point coordinates are generated in the interval [0,1] using the rand(1) function. Substituting these coordinates into formulas (6) and (7) yields the values ​​of the random radius factor r4 and the random angle factor θ. Substituting r4 and θ into formula (2) yields the corresponding coordinates. When generating the coordinates of the second random point, it is necessary to determine the center distance between the second point and the first point. If d1≥(2r3+b) (where b is the set gap factor between holes, which can be adjusted), then the second random point meets the constraint requirements, and the random point is retained. The next random point is regenerated and the calculation continues. If d1<(2r3+b), then the second random point does not meet the constraint requirements, and the random point is not retained. The next random point is regenerated and the calculation continues.

[0033] Similarly, when generating the j-th random point, it is necessary to determine the set of center distances h(d1, d2, d3, ..., dn) between the j-th point and the previous (j-1) points. j-1 ), If h ≥ (2r³ + b) (where b is the clearance margin between holes), then the j-th random point meets the constraint requirements, and the random point is retained. The next random point is regenerated and the calculation continues. If h < (2r³ + b), then the j-th random point does not meet the constraint requirements, and the random point is not retained. The next random point is regenerated and the calculation continues until j = N. At this point, the coordinates of N random points within the sampling area have been obtained.

[0034] Since the coordinates of the N random points within the sampling area are in the O2—X2Y2 coordinate system, while laser drilling is programmed using the O1—X1Y1 coordinate system, it is necessary to transform the coordinates of the N random points in the O2—X2Y2 coordinate system to the O1—X1Y1 coordinate system:

[0035]

[0036] Since the target region ADQM is one part of a ring-shaped region divided into t parts, to calculate the random points within the entire ring-shaped region, the random points within the local region need to be rotated t-1 times. The coordinates of the points after each rotation are:

[0037]

[0038] A finished grinding wheel is placed on a laser drilling machine, and microholes of uniform size are machined on the upper and lower end faces of the grinding wheel using a random distribution method. This results in a ceramic CBN grinding wheel that can prevent workpiece end face cracks during high-speed grinding. Figure 4 As shown.

[0039] A method for preparing a grinding wheel to prevent workpiece end face cracks during high-speed grinding, the process is as follows:

[0040] Mixing: By mass percentage, the abrasive layer composition is: 50-70% CBN abrasive, 23-28% ceramic binder, 2-15% pore-forming agent, and 5-8% wetting agent; take each raw material according to the proportion and mix them thoroughly to obtain the mixture;

[0041] Compression molding: The mixture from the previous step is placed into a mold of the corresponding specifications and pressed to obtain abrasive layer blanks of the specified size;

[0042] Drying; remove moisture by drying according to the corresponding drying curve;

[0043] Sintering: The shaped and dried grinding wheel segments are placed in an oven and sintered according to the corresponding sintering curve to obtain CBN grinding wheel abrasive layer segments;

[0044] Bonding: Using adhesive, the sintered CBN grinding wheel abrasive layer segments are bonded one by one to the outer circle of the corresponding substrate to obtain the finished CBN grinding wheel;

[0045] Laser drilling: Determine the drilling area of ​​the abrasive layer and the position of the small holes within the drilling area. Perform laser drilling on the end face of the effective grinding area of ​​the abrasive layer. After drilling, flip the grinding wheel, align it, and then drill the hole on the other end face of the abrasive layer.

[0046] The positional distribution of the holes within the fixed area on the end face is determined by a local fuzzy random distribution method. The positional coordinates of the holes are obtained by an algorithm designed by the tool software. The diameter of the holes is 0.2 to 0.5 mm.

[0047] Furthermore, by mass ratio, the ceramic binder comprises: SiO2 53.5%–55.5%, Al2O3 8%–11%, TiO2 0.1%–0.12%, CaO 0.6%–0.7%, MgO 2.2%–3.2%, Na2O 3.5%–3.8%, K2O 0.8%–1.3%, B2O3 19%–21%, ZrO2 0.03%–0.05%, BaO 1.3%–1.7%, and ZnO 1.63%–7.5%.

[0048] Furthermore, the CBN abrasive is cubic boron nitride single crystal or polycrystalline cubic boron nitride, or a mixture of both in any proportion. The pore-forming agent is a nano-sized, high-temperature decomposable carbonate that produces gas; the carbonate is one or more of calcium carbonate, potassium carbonate, magnesium carbonate, etc. The wetting agent is a 10–30 wt% concentration of dextrin solution.

[0049] The beneficial effects of this invention are:

[0050] 1. The grinding wheel involved in this invention has a significant advantage in terms of formula ratio, resulting in better wear resistance, better self-sharpening properties, and improved service life.

[0051] 2. The invention employs a side-mounted laser drilling method, which can effectively increase convective heat transfer in the grinding contact area, reduce the heat flowing into the workpiece, and effectively prevent side cracking.

[0052] 3. The invention drills holes on the side of the grinding wheel layer. The holes have a certain distribution space and do not create interconnected holes. This does not cause a loss in the overall mechanical strength of the grinding wheel. The hole size is small and comparable to the particle size of the abrasive. From a microscopic perspective, it has no impact on the formulation structure of the grinding wheel and does not weaken the grinding performance of the grinding wheel. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the drilling area of ​​the grinding wheel;

[0054] Figure 2 A schematic diagram showing the local fan-shaped region ADQM as the target region when establishing a local model of the grinding wheel layer end face;

[0055] Figure 3 A flowchart for calculating the coordinates of the small hole during laser drilling;

[0056] Figure 4 This is a schematic diagram of the grinding wheel structure after drilling;

[0057] Figure 5 The diagram shows the distribution of random hole centers in the O2-X2Y2 coordinate system, obtained after calculation of the grinding wheel in Example 1.

[0058] Figure 6The diagram shows the random hole distribution in the O1-X1Y1 coordinate system, obtained after calculation of the grinding wheel in Example 1.

[0059] Figure 7 This is a diagram showing the random hole distribution in the annular region of the grinding wheel, calculated according to Example 1.

[0060] Figure 8 This is a magnified view of the random hole distribution in the annular region of the grinding wheel in Example 1, calculated after the experiment.

[0061] Figure 9 Schematic diagram of the grinding wheel drilling area in the embodiment;

[0062] Figure 10 The image shows the microstructure of the grinding wheel obtained in Example 1.

[0063] Figure 11 The fluorescence method was used to detect grinding cracks on the side surfaces of workpieces after machining with conventional grinding wheels and the grinding wheel of Example 1. Detailed Implementation

[0064] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0065] Comparative Example 1

[0066] The traditional crankshaft grinding wheel, model 14LL1R, has the following specifications: outer diameter 675mm × base thickness 32mm × inner diameter 127mm × end face ring width 12.5mm × abrasive layer thickness 36mm. The specific manufacturing process is as follows:

[0067] Mixing: By mass percentage, the grinding wheel raw material composition is: 80% CBN abrasive, 14% ceramic binder, and 6% wetting agent; the mass ratio of the ceramic binder is: SiO2 54.5%, Al2O3 9.2%, TiO2 0.12%, CaO 0.62%, MgO 2.8%, Na2O 3.5%, K2O 1.1%, B2O3 20%, ZrO2 0.05%, BaO 1.5%, ZnO 6.61%; the CBN abrasive is cubic boron nitride with a particle size of 100 / 120. The wetting agent is a 20wt% aqueous solution of corn dextrin. Take the abrasive, ceramic binder, and wetting agent according to the proportions, place the mixture in a dedicated mixer, and mix at 50 rpm for 1.5 hours to ensure uniformity of the mixture.

[0068] Compression molding: The mixture from the previous step is divided into a preset fraction and placed into a special mold of the corresponding specification. It is then pressed according to the corresponding molding process to obtain grinding wheel segments of the specified size. The molding process adopted in this invention is: cold pressing, pressing at 15MPa, and holding pressure for 20 seconds.

[0069] Drying: The drying curve is as follows: the temperature is increased from room temperature to 40℃ at a rate of 5℃ / min and held at 40℃ for 20 hours, then increased from 40℃ to 60℃ at a rate of 10℃ / min and held at 60℃ for 12 hours, and then cooled to room temperature in the furnace.

[0070] Sintering: The shaped and dried grinding wheel segments are placed in an oven and sintered and strengthened according to the corresponding sintering process to obtain high-strength CBN grinding wheel segments. The sintering curve used in this invention is as follows: the temperature is increased from room temperature to 400℃ at a rate of 15℃ / min and held at 400℃ for 3 hours, the temperature is increased from 400℃ to 980℃ at a rate of 10℃ / min and held at 980℃ for 2.5 hours, and then cooled to room temperature in the furnace.

[0071] Bonding: Using a high-strength, two-ratio mixed adhesive, the sintered grinding wheel segments are bonded one by one to the outer circle of the corresponding substrate. The segments are then placed in an oven and heated from room temperature to 50°C at a rate of 100°C / min, and held at 50°C for 4 hours to cure, thus obtaining a traditional ceramic bonded CBN grinding wheel.

[0072] Example 1

[0073] A grinding wheel, model 14LL1R, designed to prevent workpiece end-face cracks during high-speed grinding, has the following specifications: outer diameter 675mm × base thickness 32mm × inner diameter 127mm × end-face ring width 12.5mm × abrasive layer thickness 36mm. It is used on a Landis dual-wheel follower crankshaft grinding machine in the UK for machining crankshafts of automotive internal combustion engines. The specific manufacturing process is as follows:

[0074] Mixing: By mass ratio, the abrasive layer raw material composition is: 62% CBN abrasive, 24.5% ceramic binder, 7.5% pore-forming agent, and 6% wetting agent; by mass percentage, the ceramic binder composition is: 54.5% SiO2, 9.2% Al2O3, 0.12% TiO2, 0.62% CaO, 2.8% MgO, 3.5% Na2O, 1.1% K2O, 20% B2O3, 0.05% ZrO2, 1.5% BaO, and 6.61% ZnO; the CBN abrasive is cubic boron nitride with a particle size of 100 / 120. The pore-forming agent is calcium carbonate powder with a particle size of 1 micrometer. The wetting agent is a 20wt% aqueous solution of corn dextrin. Take the abrasive, ceramic binder, pore-forming agent and wetting agent according to the specified proportions, place the mixture in a special mixer, rotate at 50 rpm, and mix for 1.5 hours to ensure the uniformity of the mixture.

[0075] Compression molding: Divide the mixture from the previous step into a preset number of portions, put them into a special mold of the corresponding specifications, and press them according to the corresponding molding process to obtain abrasive layer blanks of the specified size; The molding process used in this embodiment is: cold pressing, pressing at 15MPa, and holding pressure for 20 seconds.

[0076] Drying: The drying curve is as follows: the temperature is increased from room temperature to 40℃ at a rate of 5℃ / min and held at 40℃ for 20 hours, then increased from 40℃ to 60℃ at a rate of 10℃ / min and held at 60℃ for 12 hours, and then cooled to room temperature in the furnace.

[0077] Sintering: The shaped and dried grinding wheel segments are placed in an oven and sintered and strengthened according to the corresponding sintering process to obtain high-strength CBN grinding wheel abrasive layer segments; The sintering curve used in this invention is as follows: heating from room temperature to 400℃ at a rate of 15℃ / min and holding at 400℃ for 3 hours, heating from 400℃ to 980℃ at a rate of 10℃ / min and holding at 980℃ for 2.5 hours, and then cooling to room temperature in the furnace.

[0078] Bonding: Using adhesive (epoxy resin, purchased from Shanghai Huitian New Materials Co., Ltd.), the sintered abrasive layer segments were bonded one by one to the corresponding outer diameter of the substrate. The substrate was then placed in an oven and heated from room temperature to 50°C at a rate of 100°C / min, and held at 50°C for 4 hours for curing, resulting in the finished CBN grinding wheel. Its microscopic three-dimensional morphology is as follows: Figure 10 As shown in the figure: The ceramic binder exhibits molten flow characteristics, connecting and encapsulating CBN abrasive particles. Large pores are visible in the structure, which are naturally formed by the ceramic CBN. Dense small pores with a size of 5-10 micrometers are visible on the surface of the binder.

[0079] Laser drilling: The drilling method of this invention is laser drilling, which is performed on a laser drilling machine. The operation can be adjusted according to the working conditions. In this embodiment, laser drilling is performed under the conditions of 150W laser power, 0.48 pulse width, and 70Hz frequency, effectively reducing damage to the grinding wheel layer. The area for laser drilling of this specification of grinding wheel is as follows: Figure 9 As shown.

[0080] Table 1. The following parameter table is selected as the known design parameters in this invention:

[0081]

[0082] According to formulas (3), (4), and (5), we can obtain:

[0083]

[0084] From the formula for the number of parts t, we can obtain:

[0085] From the formula for the straight-line distance between the origin O1 and O2, we can obtain:

[0086] Table 2. The parameters calculated from the design parameters are shown in the following table:

[0087]

[0088]

[0089] From formula (2), we know that the random radius factor r4 is a random number within the interval [320.0866, 324.5866], which can be expressed by formula (6):

[0090] r4 = 320.0866 + 4.5·rand(1)

[0091] rand(1) represents a random number in the interval [0,1].

[0092] The random angle factor θ is an interval The random number within can be expressed by formula (7):

[0093]

[0094] In MATLAB software, the rand(1) function is first used to generate the first random number in the interval [0,1]. Substituting this into the above formula, the values ​​of the random radius factor r4 and the random angle factor θ can be obtained. Substituting r4 and θ into formula (2) x2 and y2, the corresponding coordinate points can be obtained. When the second random point coordinates are generated At that time, it is necessary to judge Does this hold true? If so, what are the coordinates of the second random point? If the result is satisfactory, begin generating the coordinates of the third random point; otherwise, regenerate the second random point and continue the evaluation. When the coordinates of the third random point are generated... At that time, it is necessary to judge Do they all hold true simultaneously? If so, what are the coordinates of the third random point (x, y)? 23 ,y 23 If the result is satisfactory, the coordinates of the 4th random point are generated; otherwise, the 3rd random point is regenerated and the process continues until the coordinates of the 29th random point are calculated. The calculated coordinates of the centers of the 29 holes are shown in Table 3 below.

[0095] Table 3.

[0096]

[0097]

[0098] The distribution of the 29 random circle center coordinates in the sampling area is as follows: Figure 5 As shown.

[0099] because Figure 5 The coordinates of the 29 circle centers shown are in Figure 2 The point region is represented in the O2-X2Y2 coordinate system, while the drilling operation needs to be performed in the O2-X2Y2 coordinate system. Figure 2 The coordinates of the 29 center points are to be transformed from the O2-X2Y2 coordinate system to the O1-X1Y1 coordinate system, as shown in equation (8).

[0100]

[0101] Substituting the coordinates of the 29 center points into the above formula sequentially transforms the coordinates to the O1-X1Y1 coordinate system, and the results are shown in Table 4 below:

[0102] Table 4.

[0103]

[0104]

[0105] The distribution of the above 29 center coordinate points and circular holes in the target area is as follows: Figure 6 As shown.

[0106] The coordinates of random points in the target area still need to be calculated through 89 rotations. From equation (9), the calculation formula for the first rotation, i.e., when k=1, is:

[0107]

[0108] Substituting these 29 points into the formula above, we obtain the 29 coordinate points after the first rotation, as shown in Table 5 below.

[0109] Table 5.

[0110] 1 -22.6752 330.1938 16 -23.5342 326.7034 2 -13.7173 327.4678 17 -29.1842 329.9936 3 -29.1177 326.9756 18 -27.8383 327.9292 4 -33.3428 327.9919 19 -21.6590 328.7105 5 -32.5379 326.1372 20 -24.8893 330.3773 6 -26.4916 330.3494 21 -19.4367 328.1770 7 -25.1243 328.2141 22 -29.7174 328.5813 8 -16.6105 328.4519 23 -21.5582 327.2134 9 -31.3851 327.4779 24 -11.8805 330.0801 10 -14.6206 330.2660 25 -11.8341 327.2373 11 -26.4470 326.7609 26 -34.1801 329.6448 12 -32.0645 329.9602 27 -20.0206 329.9877 13 -15.3464 327.3262 28 -18.0636 327.2596 14 -13.3220 329.3401 29 -13.2393 331.0981 15 -17.5007 330.3101

[0111] Similarly, the distribution of the point set in the annular region after performing 89 rotations on random points in the target region is as follows: Figure 7 As shown, its enlarged partial view is as follows: Figure 8 As shown.

[0112] The coordinates of the random points above are imported into the laser drilling system to generate a CNC program to complete the drilling of the end face of the abrasive layer. After drilling, the grinding wheel is flipped over, aligned, and then the hole on the other end face of the abrasive layer is drilled. The grinding wheel manufactured by this method effectively prevents workpiece cracks. Compared with traditional grinding wheels, under the same dressing and grinding parameters (Table 6), the roundness and straightness form and position tolerances are kept consistent, the grinding wheel roughness and cycle time are improved, the grinding wheel dressing frequency is increased by 4 times, and the grinding wheel life is increased by 4 times, resulting in a significant improvement (see Table 7).

[0113] Table 6 Grinding parameters

[0114]

[0115] Table 7 Comparison of grinding effects of crankshafts processed by grinding wheels

[0116]

[0117] Grinding cracks were detected on the sides of the third workpiece ground by conventional grinding wheel and the twelfth workpiece ground by the grinding wheel of this application using fluorescence method. Figure 11 As shown, the side of the 12th workpiece ground by the grinding wheel of this application has no cracks, while the side of the 3rd workpiece ground by the conventional grinding wheel has cracks.

[0118] The grinding wheel formulation design method involved in this invention adopts a high-particulate binder and a structure with holes in the binder bridge, which has excellent properties such as good self-sharpening and good wear resistance.

[0119] The present invention employs a method of randomly drilling micro-holes on the end face, which can effectively increase convective heat transfer in the grinding contact area and is of great significance for improving grinding cracks on the workpiece surface.

Claims

1. A grinding wheel for preventing cracks on the end face of a workpiece during high-speed grinding, characterized in that, A perforated area is provided on the abrasive layer at both ends of the grinding wheel. The perforated area is a ring-shaped area on the effective grinding area of ​​the abrasive layer. The area of ​​the perforated area is less than or equal to the area of ​​the effective grinding area on the abrasive layer. Several small holes are made in the perforated area by laser drilling. The diameter of the grinding wheel is 500mm~700mm, the diameter of the small holes is 0.2~0.5mm, and the total area of ​​the small holes accounts for 3%~10% of the area of ​​the perforated area. The small holes do not overlap and the distance between the holes is 0.5mm~2mm. The depth of the small holes is 5~7mm, and no interconnected holes are generated. By mass percentage, the composition of the abrasive layer is: 50~70% CBN abrasive, 23~28% ceramic binder, 2~15% pore-forming agent, and 5~8% wetting agent. Micron-sized small holes with a pore diameter of 5~10μm are formed in the binder.

2. The grinding wheel for preventing workpiece end face cracks during high-speed grinding according to claim 1, characterized in that, When performing laser drilling, the power of the laser drilling equipment is 120~150 W, the laser pulse width is 0.6~0.95, and the laser frequency is 60~70 Hz.

3. The grinding wheel for preventing workpiece end face cracks during high-speed grinding according to claim 2, characterized in that, The coordinates of the center of the small hole are obtained through the following process: (1) Divide the annular area that needs to be laser-drilled into... Each portion corresponds to a central angle of 1 / 2. , This represents the starting angle of the fan-ring region. Let be the termination angle of the fan-ring region, then t is a positive integer, and one portion of the fan-shaped region is taken as the target region, with the radius of the small hole being... Based on the proportion q of the total area of ​​the pinholes in the target area and the area of ​​the target area... Calculate the number N of holes within the target area, and the corresponding central angle interval of the target area is: With the center of the target area as the origin O1 and the axis of symmetry of the two straight sides as the Y1 axis, establish a rectangular coordinate system, denoted as O1—X1Y1; (2) Find the extreme position points of the target area to form a fan-shaped point-taking area. Take the intersection of the two straight sides of the point-taking area on the Y1 axis as the origin O2, and the axis of symmetry of the two straight sides of the point-taking area as the Y2 axis, where the Y2 axis coincides with the Y1 axis. Establish a rectangular coordinate system, denoted as O2—X2Y2, where the straight-line distance between the origins O1 and O2 is: ; (3) Using MATLAB software, the rand function is used to generate the coordinates of N random points within the sampling area; (4) Use equation (8) to transform the coordinates of N random points in O2—X2Y2 to O1—X1Y1; but (8) (5) Random points in the fan-ring region are processed -1 rotations yield random points within the entire annular region; the coordinates of the points after each rotation are obtained according to equation (9): (9)。 4. The grinding wheel for preventing workpiece end face cracks during high-speed grinding according to claim 3, characterized in that, In step (1), the radius of the outer arc of the target area is... The radius of the arc length within the target area is The mathematical equation for the target region is: (1) The distance between the center of the small hole within the annular region and point O1. The coordinates of the center of the holes within the target area are given. Let the coordinates of the center of the target region be , and let them be . , The range of the sampling area is within The random angle factor, for the random angle factor In the interval The random number is: (7)。 5. The grinding wheel for preventing workpiece end face cracks during high-speed grinding according to claim 4, characterized in that, In step (2), the extreme position point is taken as the center of the circle. A circle with radius is tangent to the boundary line of the target region; In the coordinate system O2—X2Y2, the region of points can be approximately represented by a mathematical equation as follows: (2) In the formula: Let O2 be the distance from any point within the selected area to the origin O2, and let O2 be the distance within the selected area. The random radius factor, The coordinates of a random point within the sampling area; Let O2 be the origin of the coordinate system O2—X2Y2, and let it be (0,0).

6. The grinding wheel for preventing workpiece end face cracks during high-speed grinding according to claim 5, characterized in that, In step (3), the rand function is used to generate random numbers within a specified interval, and the random radius factor is... In the interval The random number is: (6) Using MATLAB software, the first random point coordinates are generated in the interval [0,1] using the rand function. Substituting these coordinates into formulas (6) and (7) yields the random radius factor. Random angle factor The value will , Substituting into formula (2) yields the corresponding coordinate points. When the coordinates of the second random point are generated When doing this, it is necessary to determine the center distance between the second point and the first point. ,like If the second random point satisfies the constraint requirements, this random point is retained, and the next random point is generated to continue the calculation. If the second random point does not meet the constraint requirements, the random point is not retained, and the next random point is generated to continue the calculation. Similarly, when the first... When the nth random point is selected, it is necessary to determine the nth random point. The point and the previous The set of all center distances of points , ,like Then the first If a random point satisfies the constraints, that random point is retained, and a new random point is generated to continue the calculation. Then the first If a random point does not meet the constraints, that random point is not retained; a new random point is generated, and the calculation continues until... until.

7. The method for preparing a grinding wheel to prevent workpiece end face cracks during high-speed grinding according to any one of claims 1 to 6, characterized in that, The process is as follows: Take the raw materials in proportion and mix them thoroughly to obtain a mixture; put the mixture into a mold of the corresponding specification and press it into shape to obtain abrasive layer blanks of the specified size; after drying and removing water from the abrasive layer blanks, sinter them to obtain CBN grinding wheel abrasive layer blocks; use adhesive to bond the sintered CBN grinding wheel abrasive layer blocks one by one to the outer circle of the corresponding substrate to obtain the finished CBN grinding wheel; determine the drilling area of ​​the abrasive layer and the position of the small holes in the drilling area, and perform laser drilling on the end face of the effective grinding area of ​​the abrasive layer. After drilling, flip the grinding wheel, align it, and then drill holes on the other end face of the abrasive layer.

8. The method for preparing a grinding wheel to prevent workpiece end face cracks during high-speed grinding according to claim 7, characterized in that, The ceramic binder, by mass ratio, comprises: SiO2 53.5%~55.5%, Al2O3 8%~11%, TiO2 0.1%~0.12%, CaO 0.6%~0.7%, MgO 2.2%~3.2%, Na2O 3.5%~3.8%, K2O 0.8%~1.3%, B2O3 19%~21%, ZrO2 0.03%~0.05%, BaO 1.3%~1.7%, and ZnO 1.63%~7.5%.

9. The method for preparing a grinding wheel to prevent workpiece end face cracks during high-speed grinding according to claim 7, characterized in that, The CBN abrasive is one or a mixture of two of monocrystalline cubic boron nitride and polycrystalline cubic boron nitride in any proportion; the pore-forming agent is one or a mixture of more than two of calcium carbonate, potassium carbonate and magnesium carbonate in any proportion; and the wetting agent is a dextrin solution with a concentration of 10-30 wt%.

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