Grinding wheel capable of preventing workpiece end face cracks in high-speed grinding process and preparation method of grinding wheel

Abstract

The invention discloses a grinding wheel capable of preventing workpiece end face cracks in the high-speed grinding process and a preparation method thereof, and belongs to the field of grinding wheel manufacturing and grinding machining. According to the method, randomly-distributed micro holes (200-500 microns) are formed in the two end faces of the grinding wheel through laser, a high-fraction binding agent (23-28%) is used in the formula of the grinding wheel, and micron-sized small holes (5-10 microns) are formed in the binding agent to increase convective heat transfer of a cooling medium, so that more heat is taken away by the cooling medium, and then grinding cracks of the end faces are prevented. The high binding agent mass ratio increases the wrapping holding force of the binding agent on the CBN abrasive, reduces the falling of the abrasive, and improves the durability of the grinding wheel. The micro holes adsorb moisture through the capillary action in the grinding process, the millimeter holes can form cooling water flow channels, the cooling effect is good in the mode of combining laser drilling and the micrometer holes of the binding agent, the grinding performance of the grinding wheel is not weakened, and therefore the dressing frequency of the grinding wheel is reduced, and the service life of the grinding wheel is prolonged.

Description

Technical Field

[0001] The invention belongs to the field of grinding wheel manufacturing and grinding processing, and particularly relates to a grinding wheel for preventing end face cracks of a workpiece during high-speed grinding and a preparation method thereof. Background Art

[0002] Ceramic CBN grinding wheels have been widely used in the field of grinding processing due to their excellent properties such as stable chemical properties, good sharpness, long service life, and good precision retention. They are especially suitable for high-speed grinding conditions. The grinding process is a macroscopic manifestation of the interference cutting of countless single abrasive particles with the workpiece. The process is extremely complex, and most of the grinding power consumed in the grinding process is converted into heat energy. For grinding processing, about 10% of the heat flows into the grinding chips, and about 55%-90% of the heat flows into the ground workpiece. After entering the workpiece, this heat accumulates in the grinding contact area to form an instantaneous high temperature, causing residual stress on the workpiece surface, and even grinding cracks. This phenomenon is called grinding cracks. Grinding cracks on the workpiece surface will greatly affect the fatigue strength and service life of the workpiece. From the perspective of grinding wheel manufacturing, there are currently two main methods to prevent grinding cracks: ① Slotting the outer cylindrical end face of the grinding wheel to allow coolant to enter the grinding contact area to take away a large amount of heat load, thereby reducing the grinding surface temperature of the workpiece and preventing tempering cracks and quenching cracks. Although this method is effective, the wear of the grinding wheel after slotting will increase in high-speed scenarios, resulting in a reduced service life. In addition, the microscopic abrasive particles that fall off abnormally from the edge after violent impact can easily enter the grinding contact area and cause scratches on the workpiece surface. ② By adding a certain amount of pore-forming agent to the grinding wheel formula, the pore size formed by the pore-forming agent is small and irregular, which is difficult to control, and the effect cannot be guaranteed. It also affects the original formula ratio, which can easily cause instability during the use of the grinding wheel. Summary of the invention

[0003] In order to solve the problem of end face grinding cracks in the current high-speed grinding process, the present invention adopts a conventional ceramic CBN crankshaft grinding wheel formula, wherein the binder mass ratio is usually 15-22%, and the hole making method is usually natural hole making and adding floating beads or hollow balls with the same size as the abrasive, and the hole size is 100-200 μm or more. The present invention provides a grinding wheel for preventing end face cracks in the high-speed grinding process and a preparation method thereof. A high portion of binder (23-28%) is used in the grinding wheel formula, and micron-level small holes (5-10 μm) are made in the binder. The two end faces of the grinding wheel are laser-punched with randomly distributed micro holes (200-500 μm) to increase the convective heat exchange of the cooling medium, so that the cooling medium takes away more heat, thereby preventing end face grinding cracks. Compared with the conventional method, the high binder mass ratio increases the wrapping and holding force of the binder on the CBN abrasive, reduces the shedding of the abrasive, and improves the durability of the grinding wheel. In order to avoid burn cracks, cooling is achieved by combining micron holes in the binder with millimeter holes punched by laser. The micron holes absorb moisture by capillary action during grinding, and the millimeter holes can form cooling water flow channels. The combination of laser drilling and micron holes in the binder has a good cooling effect and does not weaken 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 cracks on the end face of a workpiece during high-speed grinding. A perforated area is correspondingly provided on the abrasive layer at both end faces of the grinding wheel. The perforated area is an annular 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. A plurality of small holes are distributed in the perforated area.

[0005] Furthermore, the diameter of the grinding wheel is 500mm-700mm, the diameter of the small holes is 0.2-0.5mm, the total area of ​​the small holes accounts for 3%-10% of the area of ​​the punching area; the small holes do not overlap each other and the distance b between the holes is 0.5mm-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 this condition, the depth of the small hole is 5mm-7mm.

[0007] The punching area is an annular area on the outer edge of the end surface 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 circle with the fuzzy randomly generated data point as the center and r3 as the radius completely within the target area.

[0009] (2) To prevent the life of the grinding wheel 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 small holes in the target area. After multiple experiments, it was found that when the diameter of the grinding wheel is 500 mm to 700 mm, the value range of q is 3% to 10%;

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

[0011] Specifically, the coordinate position of the center of the small hole is obtained by the following process:

[0012] In order to reduce the amount of calculation and improve the calculation speed, a local model of the end face of the grinding wheel layer is established, such as Figure 2 As shown, the annular area to be laser punched is divided into t parts, and the center angle of each part is (α2-α1), then t is a positive integer, and one of the fan ring areas is taken as the target area. The target area is set as ADQM, AD is the local arc length of the outer circle of the end face of the grinding wheel layer, and the radius corresponding to the arc is r2, MQ is the local arc length of the inner circle of the end face of the grinding wheel layer, and the radius corresponding to the arc is r1, the radius of the small hole is r3, and the center angle interval corresponding to the target area is θ∈[α1,α2]. O1-X1Y1 is the rectangular coordinate system where the target area is located. The center of the target area is taken as the origin O1, and the axis of symmetry between the straight line AM and the straight line DQ is taken as the Y1 axis to establish a rectangular coordinate system, which is recorded as O1-X1Y1; the target area ADQM can be expressed by the mathematical equation as follows:

[0013]

[0014] Wherein: a is the distance between the center of the small hole in the annular area and point O1, (x1, y1) is the coordinates of the center of the small hole in the target area, (x0, y0) is the coordinates of the center of the target area, which is (0, 0) in this invention.

[0015] To ensure that the full circle with the fuzzy randomly generated data point as the center and r3 as the radius is completely within the target area ADQM, it is necessary to ensure that the circle generated at the extreme position point is located at the boundary point of the target area ADQM. From the right figure, it can be seen that F, G, J, and K are the extreme position points. Then, the circle with F, G, J, and K as the center and r3 as the radius is tangent to the boundary line of the target area ADQM;

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

[0017] Next, the coordinates of the random points in the point-taking area need to be solved. Since the diameter of the small hole in the present invention is relatively small, about 0.2-0.5 mm, the point-taking area can be approximately expressed in the form of a mathematical equation in the coordinate system O2-X2Y2 as follows:

[0018]

[0019] Where: r4 is the distance from any point in the point-taking area to the origin O2, which can be considered as a random radius factor in the point-taking area ranging from r4∈[(r1+r3-|O1O2|),(r2-r3-|O1O2|)]; θ is a random angle factor in the point-taking area ranging from θ∈[α1,α2], and (x2,y2) are the coordinates of a random point in the point-taking area; is the coordinate origin in O2-X2Y2, which is taken as (0,0).

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

[0021] First, it can be seen from the figure that the area S1 of the target area ADQM is:

[0022]

[0023] Assuming that the area of ​​the small hole S2 accounts for q of the area of ​​the target area ADQM, the total area of ​​the small holes is

[0024]

[0025] So the number of holes is:

[0026]

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

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

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

[0030] θ=α1+[α2-α1]rand(1) (7)

[0031] Therefore, substituting (6) and (7) into the point-taking area equation (2) yields:

[0032] like Figure 3 As shown, using Matlab software, we first use the rand(1) function to generate the coordinates of the first random point in the interval [0,1]. Substituting them into formulas (6) and (7) we can get the values ​​of the random radius factor r4 and the random angle factor θ. Substituting r4 and θ into formula (2) we can get the corresponding coordinate point 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 hole margin clearance factor, which can adjust the hole distance), the second random point meets the constraint requirements, the random point is retained, and the next random point is regenerated to continue the calculation; if d1<(2r3+b), the second random point does not meet the constraint requirements, the random point is not retained, and the next random point is regenerated to continue the calculation.

[0033] Similarly, when generating the jth random point, it is necessary to determine the set of all center distances h(d1, d2, d3...d j-1 ), If h≥(2r3+b) (where b is the clearance between holes), the jth random point meets the constraint requirements, the random point is retained, and the next random point is regenerated to continue the calculation. If h<(2r3+b), the jth random point does not meet the constraint requirements, the random point is not retained, and the next random point is regenerated to continue the calculation until j=N, at which time the coordinates of the N random points in the point-taking area have been obtained.

[0034] Since the coordinates of the N random points in the point-taking area are in O2-X2Y2, and the laser drilling is programmed with the point coordinates in the coordinate system O1-X1Y1, it is necessary to convert the coordinates of the N random points in O2-X2Y2 to O1-X1Y1:

[0035]

[0036] Since the target area ADQM is one of the t parts of the annular area, if you want to calculate the random points in the entire annular area, you need to rotate the random points in the local area t-1 times. The coordinates of the points after each rotation are:

[0037]

[0038] The finished grinding wheel is placed on a laser drilling machine, and micro-holes of the same size are processed on the upper and lower ends of the grinding wheel layer according to the random distribution method, so as to obtain a ceramic CBN grinding wheel that can prevent the end surface cracks of the workpiece during high-speed grinding. Figure 4 shown.

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

[0040] Mixing: In terms of mass percentage, the abrasive layer is composed of: 50-70% CBN abrasive, 23-28% ceramic binder, 2-15% pore former, and 5-8% wetting agent. Take the raw materials in proportion and mix them thoroughly to obtain a mixture;

[0041] Pressing and molding: putting the mixed material in the previous step into a mold of corresponding specifications and pressing and molding to obtain abrasive layer blank segments of specified sizes;

[0042] Drying; drying and dehydration according to the corresponding drying curve;

[0043] Sintering: Place the formed and dried grinding wheel segments in an oven and perform sintering strengthening according to the corresponding sintering curve to obtain CBN grinding wheel abrasive layer segments;

[0044] Bonding: Use bonding glue to bond the sintered CBN grinding wheel abrasive layer segments to the corresponding outer circle of the substrate one by one 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 in the drilling area, and perform laser drilling on the end face of the effective grinding area of ​​the abrasive layer. After drilling, turn the grinding wheel over, align it, and then drill the hole on the other end face of the abrasive layer.

[0046] The position coordinates of the holes are determined by a local fuzzy random distribution method in the fixed area of ​​the end face. The position 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, in terms of mass ratio, the composition of the ceramic binder is: SiO2 53.5% to 55.5%, Al2O3 8% to 11%, TiO2 0.1% to 0.12%, CaO 0.6% to 0.7%, MgO 2.2% to 3.2%, Na2O 3.5% to 3.8%, K2O 0.8% to 1.3%, B2O3 19% to 21%, ZrO2 0.03% to 0.05%, BaO 1.3% to 1.7%, and ZnO 1.63 to 7.5%.

[0048] Furthermore, the CBN abrasive is single crystal cubic boron nitride or polycrystalline cubic boron nitride or a mixture of the two in any proportion. The pore-forming agent is a nano-scale carbonate that can decompose at high temperature to produce gas, and the carbonate is one or more of calcium carbonate, potassium carbonate, magnesium carbonate, etc. The wetting agent is a dextrin solution with a concentration of 10 to 30 wt%.

[0049] Beneficial effects of the present invention:

[0050] 1. The grinding wheel involved in the invention has great advantages in formula ratio, better wear resistance, good self-sharpening property and improved service life.

[0051] 2. The invention adopts a laser drilling method on the side, which can effectively increase the convective heat exchange in the grinding contact area, reduce the heat flowing into the workpiece, and effectively prevent the crack phenomenon on the side.

[0052] 3. The invention drills holes on the side of the grinding wheel layer. The holes have a certain distribution space and no connected holes are generated. The overall mechanical strength of the grinding wheel is not damaged. The hole size is small, which is comparable to the particle size of the abrasive. From a microscopic structure, it has no effect on the formula structure of the grinding wheel and does not weaken the grinding performance of the grinding wheel. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0055] Figure 3 This is the calculation flow chart of 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 distribution diagram of the centers of random holes in the O2-X2Y2 coordinate system of the grinding wheel of Example 1 obtained after calculation;

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

[0059] Figure 7 The random hole distribution diagram in the punched annular area of ​​the grinding wheel in Example 1 obtained after calculation;

[0060] Figure 8 This is a partial enlarged view of the random hole distribution in the punched annular area of ​​the grinding wheel of Example 1 obtained after calculation;

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

[0062] Fig.10 This is a microscopic morphology of the grinding wheel obtained in Example 1;

[0063] Fig.11 The fluorescence method is used to detect the side grinding cracks after the workpiece is processed by the traditional grinding wheel and the grinding wheel of Example 1. DETAILED DESCRIPTION

[0064] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0065] Comparative Example 1

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

[0067] Mixing: In terms of mass percentage, the raw material composition of the grinding wheel 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%, MgO2.8%, Na2O 3.5%, K2O 1.1%, B2O3 20%, ZrO2 0.05%, BaO 1.5%, and ZnO 6.61%; the CBN abrasive is: cubic boron nitride, with a particle size of 100 / 120. The wetting agent is: a 20wt% corn dextrin aqueous solution. Take the abrasive, ceramic binder, and wetting agent in proportion, place the above mixture in a special mixer, rotate at 50 rpm, and mix for 1.5 hours to ensure the uniformity of the mixture.

[0068] Pressing and molding: Divide the mixed material in the previous step into preset fractions, put them into a special mold of corresponding specifications, and press them according to the corresponding molding process to obtain a grinding wheel segment of a specified size; the molding process adopted in the present invention is: cold pressing method, 15MPa pressing, and holding pressure for 20 seconds.

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

[0070] Sintering: placing the formed and dried grinding wheel segment in an oven, sintering and strengthening according to the corresponding sintering process to obtain a high-strength CBN grinding wheel segment; the sintering curve adopted by the present invention is: heating from room temperature to 400°C at a rate of 15°C / min and keeping at 400°C for 3 hours, heating from 400°C to 980°C at a rate of 10°C / min, keeping at 980°C for 2.5 hours, and cooling to room temperature with the furnace.

[0071] Bonding: Use high-strength double-ratio mixed adhesive to bond the sintered grinding wheel segments to the corresponding outer circle of the substrate one by one, put them into an oven and heat them from room temperature to 50°C at a rate of 100°C / min and keep them at 50°C for 4 hours for curing to obtain a traditional ceramic bond CBN grinding wheel.

[0072] Example 1

[0073] A grinding wheel for preventing end face cracks of workpieces during high-speed grinding, model: 14LL1R, specifications: outer diameter 675mm×base thickness 32mm×inner hole 127mm×end face ring width 12.5mm×abrasive layer thickness 36mm, used in the British Landis double-wheel follower crankshaft grinder to process crankshafts of automotive internal combustion engines. The specific preparation process is as follows:

[0074] Mixing: In terms of mass ratio, the raw materials of the abrasive layer are composed of: CBN abrasive 62%, ceramic binder 24.5%, pore former 7.5%, wetting agent 6%; in terms of mass percentage, the composition of the ceramic binder is: SiO2 54.5%, Al2O3 9.2%, TiO20.12%, CaO 0.62%, MgO 2.8%, Na2O 3.5%, K2O 1.1%, B2O3 20%, ZrO2 0.05%, BaO1.5%, ZnO6.61%; CBN abrasive is: cubic boron nitride, with a particle size of 100 / 120. The pore former is: calcium carbonate powder with a particle size of 1 micron. The wetting agent is: a 20wt% corn dextrin aqueous solution. Take abrasive, ceramic binder, pore former and wetting agent in proportion, place the above mixture in a special mixer, rotate at 50 rpm, mix for 1.5 hours to ensure the uniformity of the mixture.

[0075] Pressing and molding: Divide the mixture of the previous step into a preset number of portions, put them into a special mold of corresponding specifications, and press them according to the corresponding molding process to obtain abrasive layer blank segments of specified sizes; the molding process adopted in this embodiment is: cold pressing method, 15MPa pressing, and holding pressure for 20 seconds.

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

[0077] Sintering: placing the formed and dried grinding wheel segments in an oven, sintering and strengthening according to the corresponding sintering process, and obtaining high-strength CBN grinding wheel abrasive layer segments; the sintering curve adopted by the present invention is: heating from room temperature to 400°C at a rate of 15°C / min and keeping at 400°C for 3 hours, heating from 400°C to 980°C at a rate of 10°C / min, keeping at 980°C for 2.5 hours, and cooling to room temperature with the furnace.

[0078] Bonding: Use adhesive (epoxy resin glue, purchased from Shanghai Huitian New Materials Co., Ltd.) to bond the sintered abrasive layer segments to the corresponding outer circle of the substrate one by one, put them into an oven, heat them from room temperature to 50°C at a rate of 100°C / min, and keep them at 50°C for 4 hours for curing to obtain the finished CBN grinding wheel. Its microscopic three-dimensional morphology is shown in Fig.10 As shown: The figure shows that the ceramic binder has the characteristics of melting flow, connecting and wrapping the CBN particle abrasive. The larger holes visible in the organization are naturally formed by ceramic CBN. Dense small holes with a size of 5 to 10 microns can be seen on the surface of the binder.

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

[0080] Table 1. The present invention selects the following parameter table as known design parameters:

[0081]

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

[0083]

[0084] From the formula of the number of copies t, we can get:

[0085] From the straight-line distance formula of the origin O1 and O2, we can get:

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

[0087]

[0088]

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

[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 in the interval The random number in can be expressed as follows using formula (7):

[0093]

[0094] In Matlab software, we first use the rand(1) function to generate the first random number in the interval [0,1]. Substituting it into the above formula, we can get the values ​​of the random radius factor r4 and the random angle factor θ. Substituting r4 and θ into formula (2) x2 and y2, we can get the corresponding coordinate points. When generating the second random point coordinates When Is it true? If true, the coordinates of the second random point If the result is qualified, the coordinates of the third random point will be generated. Otherwise, the second random point will be regenerated and the judgment will continue. When the coordinates of the third random point are generated When Are they both true? If true, the coordinates of the third random point (x 23 ,y 23 ) is qualified, the coordinates of the 4th random point are generated, otherwise, the 3rd random point is regenerated to continue the judgment; and so on until the coordinates of the 29th random point are calculated. The calculated coordinates of the 29 hole centers are shown in Table 3 below:

[0095] Table 3.

[0096]

[0097]

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

[0099] because Figure 5 The coordinates of the 29 circle centers shown are Figure 2 The point area O2 is represented in the X2Y2 coordinate system, and the punching operation needs to be Figure 2 The coordinates of the 29 circle centers are transformed from the O2-X2Y2 coordinate system to the O1-X1Y1 coordinate system. From formula (8), we know that

[0100]

[0101] Substituting the 29 center coordinate points into the above formula one by one, the coordinate system can be converted to O1-X1Y1. 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 shown.

[0106] The coordinates of the random points in the target area need to be rotated 89 times. From formula (9), when the first rotation calculation is performed, that is, when k=1, the calculation formula is:

[0107]

[0108] Substitute the above 29 points into the above formula one by one: the 29 coordinate points after the first rotation can be obtained as shown in Table 5 below:

[0109] Table 5.

[0110] Quantity <![CDATA[x i 'Coordinate value]]> <![CDATA[y i 'Coordinate value]]> Quantity <![CDATA[x i 'Coordinate value]]> <![CDATA[y i 'Coordinate value]]> 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 area after 89 rotation calculations of random points in the target area is as follows: Figure 7 As shown, the local enlarged picture is as follows Figure 8 shown.

[0112] The above random point coordinates 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 turned 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 the traditional grinding wheel, under the same dressing and grinding processing parameters (Table 6), the roundness and straightness form and position tolerances are consistent, the grinding wheel roughness and beat are improved, the grinding wheel dressing frequency is increased by 4 times, and the grinding wheel life is increased by 4 times, which is greatly improved (see Table 7).

[0113] Table 6 Grinding wheel processing parameters

[0114]

[0115] Table 7 Comparison of grinding effect of crankshaft machined by grinding wheel

[0116]

[0117] The fluorescence method was used to detect grinding cracks on the sides of the third workpiece ground by the conventional grinding wheel and the 12th workpiece ground by the grinding wheel of the present application. Fig.11 As shown, there is no crack on the side of the 12th workpiece ground by the grinding wheel of the present application, while cracks appear on the side of the 3rd workpiece ground by the conventional grinding wheel.

[0118] The grinding wheel formula design method involved in the present invention adopts a structure of high-fraction binder and forming holes in the binder bridge, and has excellent characteristics such as good self-sharpening and good wear resistance.

[0119] The invention adopts a method of randomly punching micro holes on the end surface to effectively increase the convection heat transfer in the grinding contact zone, which is of great significance to improving the grinding cracks on the surface of the workpiece.

Claims

1. A grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding, characterized in that: A perforated area is provided on the abrasive layer at both end surfaces of the grinding wheel. The perforated area is an annular 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. A number of small holes are distributed in the perforated area.

2. The grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to claim 1, characterized in that: The diameter of the grinding wheel is 500 mm to 700 mm, the diameter of the small hole is 0.2 to 0.5 mm, and the total area of ​​the small hole accounts for 3% to 10% of the area of ​​the punching area; The small holes do not overlap each other and the distance b between the holes is 0.5 mm to 2 mm.

3. The grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to claim 1 or 2, characterized in that: The small holes are 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.

4. The grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to claim 3, characterized in that: The coordinate position of the center of the small hole is obtained by the following process: (1) Divide the annular area to be laser punched into t parts, and the center angle of each part is (α2-α1), then t is a positive integer, and one of the fan ring areas is taken as the target area. The radius of the small hole is r3. The number of small holes in the target area is calculated according to the proportion of the total area of ​​the small holes in the target area q and the area of ​​the target area S1. The central angle interval corresponding to the target area is θ∈[α1,α2]. The center of the target area is taken as the origin O1, and the symmetry axis of the two straight sides is taken as the Y1 axis. A rectangular coordinate system is established, which is recorded as O1-X1Y1; (2) Find the limit position point of the target area to form a fan ring point area. Take the intersection of the two straight sides of the point area on the Y1 axis as the origin O2, and the symmetry axis of the two straight sides of the point area as the Y2 axis. The Y2 axis and the Y1 axis coincide with each other. Establish a rectangular coordinate system, recorded as O2-X2Y2, where the straight-line distance between the origins O1 and O2 is: (3) Using Matlab software and the rand function, the coordinates of N random points are generated in the point-taking area; (4) Use equation (8) to transform the coordinates of N random points in O2-X2Y2 to O1-X1Y1; but (5) The random point in the sector ring area is rotated t-1 times to obtain a random point in the entire ring area; the coordinate point after each rotation is obtained according to equation (9):

5. The grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to claim 4, characterized in that: In step (1), the radius of the arc length outside the target area is r2, the radius of the arc length inside the target area is r1, and the mathematical equation of the target area is: a is the distance between the center of the small hole in the annular area and point O1, (x1, y1) is the coordinate of the center of the small hole in the target area, and (x0, y0) is the coordinate of the center of the target area, which is taken as (0, 0).

6. The method for preparing a grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to claim 4, characterized in that: In step (2), a circle with the extreme position point as the center and r3 as the radius is tangent to the boundary line of the target area; In the coordinate system O2-X2Y2, the point area can be approximately expressed in the form of a mathematical equation as follows: Where: r4 is the distance from any point in the point-taking area to the origin O2, is the random radius factor in the point-taking area ranging from r4∈[(r1+r3-|O1O2|),(r2-r3-|O1O2|)], θ is the random angle factor in the point-taking area ranging from θ∈[α1,α2], (x2,y2) are the coordinates of a random point in the point-taking area; is the coordinate origin in O2-X2Y2, which is taken as (0,0).

7. The method for preparing a grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to claim 6, characterized in that: In step (3), the rand function is used to generate random numbers in the specified interval. For the random radius factor r4 in the interval r4∈[(r1+r3-|O1O2|),(r2-r3-|O1O2|)], the random number is: r4=(r1+r3-|O1O2|)+(r2-2r3-r1)·rand(1) (6) For the random angle factor θ, the random number in the interval [α1, α2] is: θ=α1+[α2-α1]·rand(1) (7) Using Matlab software, we first use the rand function to generate the coordinates of the first random point in the interval [0,1]. Substituting them into formulas (6) and (7) we can get the values ​​of the random radius factor r4 and the random angle factor θ. Substituting r4 and θ into formula (2) we can get the corresponding coordinate point (x 21 ,y 21 ), when generating the second random point coordinate (x 22 ,y 22 ), it is necessary to determine the center distance between the second point and the first point If d1≥(2r3+b), the second random point meets the constraint requirements, the random point is retained, and the next random point is regenerated to continue the calculation; if d1<(2r3+b), the second random point does not meet the constraint requirements, the random point is not retained, and the next random point is regenerated to continue the calculation; Similarly, when generating the jth random point, it is necessary to determine the set of all center distances h(d1, d2, d3...d j-1 ), j=2,3,4…N, if h≥(2r3+b), the jth random point meets the constraint requirements, the random point is retained, and the next random point is regenerated to continue the calculation; if h<(2r3+b), the jth random point does not meet the constraint requirements, the random point is not retained, and the next random point is regenerated to continue the calculation until j=N.

8. The method for preparing a grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to any one of claims 1 to 7, characterized in that: The process is as follows: The abrasive layer is composed of 50-70% CBN abrasive, 23-28% ceramic binder, 2-15% pore former and 5-8% wetting agent in percentage by mass. The raw materials are taken in proportion and fully mixed to obtain a mixture. The mixture is put into a mold of corresponding specifications and pressed to obtain abrasive layer blank segments of specified sizes. The abrasive layer blank segments are dried and dehydrated and then sintered to obtain CBN grinding wheel abrasive layer segments. The sintered CBN grinding wheel abrasive layer segments are bonded to the outer circle of the corresponding substrate one by one by using adhesive to obtain a finished CBN grinding wheel. The abrasive layer punching area and the position of the small holes in the punching area are determined, and laser drilling is performed on the end face of the effective grinding area of ​​the abrasive layer. After the drilling is completed, the grinding wheel is turned over, aligned, and then the hole on the other end face of the abrasive layer is drilled.

9. The method for preparing a grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to claim 8, characterized in that: In terms of mass ratio, the composition of the ceramic binder is: SiO2 53.5%~55.5%, Al2O3 8%~11%, TiO20.1%~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%.

10. The method for preparing a grinding wheel for preventing end surface cracks of a workpiece during high-speed grinding according to claim 8, characterized in that: The CBN abrasive is one of single crystal cubic boron nitride and polycrystalline cubic boron nitride or a mixture of two of them in any proportion; the pore-forming agent is one of calcium carbonate, potassium carbonate and magnesium carbonate or a mixture of two or more of them in any proportion; and the wetting agent is dextrin liquid with a concentration of 10-30wt%.

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