Cylindrical gear tooth profile processing method and processing plan
Non-cutting processes include hot-rolled gears, cold-rolled gears, precision forging, and powder metallurgy. Non-cutting machining has a series of advantages such as high productivity, low material consumption, and low cost, and has been widely used at present. However, due to its low processing accuracy, the process is not stable enough, especially when it is difficult to use the production batch hours, these shortcomings limit its use.
The tooth shape has cutting processing and has a good machining accuracy. At present, it is still the main processing method of the tooth shape. According to the principle of its processing can be divided into two kinds of forming and forming method.
The feature of the forming method is that the shape of the cutting edge of the tool used is the same as the shape of the wheel groove of the gear being cut, as shown in Figure 9-3. The method of forming the tooth profile using the forming principle includes: milling a tooth on a milling machine with a gear milling cutter, grinding a tooth with a forming wheel, pulling a tooth with a gear broach, and the like. Because these methods have indexing errors and installation errors of the tool, the machining accuracy is low. Generally, only gears with 9-10 precision can be machined. In addition, multiple discrete teeth are required during processing, and the productivity is also low. Therefore, it is mainly used for gears with low machining accuracy in single-piece small batch production and repair work.
The generative method is to apply the principle of gear meshing. The tooth profile formed by this method is the envelope of the tool's cutting edge motion path. Gears with different numbers of teeth can be machined with the same tool as long as the modulus and tooth angle are the same. The method of forming the tooth profile using the principle of development includes: hobbing, inserting, shaving, rake and grinding. Among them, shaved teeth, enamel teeth and grinding teeth belong to the finishing method of the tooth shape. The development method has a high processing accuracy and productivity, and has a good universality of tools, so it is widely used in production.
One, hobbing
(A) The principle and process characteristics of hobbing
Hobbing is the most productive and most widely used machining method in the tooth profile machining method. The principle of machining gears with a gear hob on a gear hobbing machine is equivalent to a pair of helical gears meshing forcibly without backlash, as shown in Figure 9-24. Hobbing has a good universality. It can process cylindrical gears as well as worm gears. It can not only machine involute tooth shapes, but also can process arc, cycloid and other tooth shapes; it can process large module gears, large Diameter gear.
Hobbing can directly process 8 to 9-level precision gears, and can also be used for rough machining and semi-finishing of gears of level 7 and above. The hobbing can achieve high movement accuracy, but the tooth surface is formed by enveloping the teeth of the hob, and the number of teeth participating in the cutting is limited. Therefore, the surface roughness of the tooth surface is relatively coarse. In order to improve the hobbing accuracy and tooth surface quality, rough hobbing should be separated.
(II) Analysis of hobbing process quality
1. Analysis of machining error affecting transmission accuracy
The main reason affecting the gear transmission accuracy is that the relative position and relative movement of the hob and the gear to be cut have changed during machining. The change in relative position (geometrical eccentricity) produces a radial error in the gear; the change in relative motion (motion eccentricity) produces a tangential error in the gear.
(1) Radial error of gears Gear radial error refers to the cumulative tolerance caused by the radial displacement of the gear teeth of the cutting gear due to the fact that the actual turning center of the gear blank does not coincide with the center of its reference hole when hobbing. , as shown in Figure 9-4.
The radial error of the gear can generally be reflected by measuring the radial runout ΔFr of the ring gear. The main reasons for gear radial error when cutting teeth are as follows:
1 When adjusting the fixture, the center of rotation of the spindle and the machine table does not coincide.
2 There is a gap between the reference hole of the gear tooth blank and the mandrel, which is biased to the side when clamping.
3 The reference end face is not well positioned. After clamping, the inner hole is eccentric with respect to the rotation center of the table.
(2) The tangential error of the gear The tangential error of the gear refers to the actual tooth profile displacement in the circumferential direction (tangential direction) relative to the theoretical position when hobbing, as shown in Figure 9-5. When the tangential displacement of the gear occurs, it can be reflected by measuring the normal normal length variation tolerance ΔFw.
The main cause of gear tangential errors when cutting teeth is caused by transmission chain transmission errors. Among the transmission elements of the gear transmission chain, the greatest impact on the transmission error is the indexing worm gear under the table. The indexing worm gear does not coincide with the rotation center of the table in the manufacturing and installation (motion eccentricity), so that the rotation error occurs in the rotation of the table, and is reproduced to the gear. Secondly, another important factor affecting the transmission error is the manufacturing and installation errors of the gear-to-turn gear. These errors are also transferred to the work table in a larger proportion.
2. Analysis of machining error affecting the smoothness of gear work
The main factors affecting the smoothness of the gear transmission work are the gear tooth error Δff and the base pitch deviation Δfpb. The tooth profile error causes transient changes in the gear ratio during meshing of each pair of gears; the base pitch deviation causes a sudden change in the gear ratio when the pair of teeth transitions into engagement with the other pair of teeth. Gear transmission generates noise and vibration due to instantaneous change and sudden change of transmission ratio, which affects the accuracy of work stability. When hobbing, the pitch deviation of the generated gear is small, and the error of the tooth profile is usually large. Discussed separately below.
(1) Tooth error
The tooth profile error is mainly caused by the manufacturing grinding error of the gear hob and the installation error of the hob, so it will be reflected on the tooth surface during each revolution of the hob. The common tooth form error has various forms as shown in Figure 9-6. Figure a shows that the tooth surface is out of edge, Figure b is the tooth profile asymmetry, Figure c is the tooth profile angle error, Figure d is the periodic error on the tooth face, and Figure e is the gear root cut.
Because the tooth surface of the gear deviates from the correct involute, the instantaneous transmission ratio in the gear transmission is not stable, which affects the work stability of the gear.
(2) When the base section limit deviation hobbing, the base section limit deviation of the gear is mainly affected by the deviation of the base section of the reel. The calculation formula of the hob base section is:
Pb0=pn0cosα0=pt0cosλ0cosα0≈pt0cosα0
Where: pb0 - hob base section;
Pn0 - hob normal tooth pitch;
Pt0 - axial pitch of hob;
Α0 - hob normal tooth angle;
λ0—The pitch angle of the hob indexing circle is generally small, so cos λ0 ≈1.
From the above equation, we can see that in order to reduce the deviation of the base section, the axial pitch and tooth angle error should be strictly controlled during the manufacture of the hob, and at the same time, the non-diameter of the rake face of the tooth that affects the tooth angle error and the axial pitch error The directional error is also controlled.
3. Analysis of machining error affecting gear contact accuracy
The contact condition of the gear tooth surface directly affects the uniformity of the load distribution in the gear transmission. When hobbing, the main factors that affect the contact accuracy in the direction of the tooth height are the tolerance of the tooth profile Δff and the limit deviation of the base section Δfpb. The main factor that affects the contact accuracy in the tooth width direction is the tooth tolerance ΔFβ. The main reasons for tooth-tooth tolerances:
(1) There is an error in parallelism between the guide rail of the hobbing machine tool holder and the axis of rotation of the table, as shown in Fig. 9-7.
(2) Gear blank clamping skew As the mandrel, the basic surface of the gear blank darts, and the two end surfaces of the washers are not parallel to each other, the gear blanks will be installed with a skew, which will result in a toothing error, as shown in Fig. 9-8.
(3) In addition to the influencing factors mentioned above, the error in the calculation of the differential gear of the machine tool will also affect the gear tooth error.
4. Ways to increase hobbing productivity
(1) High-speed hobbing
In recent years, China has begun to design and manufacture high-speed gear hobbing machines, while producing aluminum high-speed steel (MO5Al) hobs. The hobbing speed is increased from the general v=30 m/min to v=100 m/min or more, and the axial feed rate is f=1.38 mm/r to 2.6 mm/r, which increases the productivity by 25%.
The hobbing speed of foreign high-speed steel hobbers has been increased to 100 m/min to 150 m/min; carbide hob has been tested to more than 400 m/min. In short, high-speed hobbing has a certain development prospect.
(2) The use of multiple hobs can significantly increase productivity, but the machining accuracy is low and the tooth surfaces are rough, so they are mostly used for roughing. When the gear machining accuracy is required to be high, a large-diameter hob can be used to increase the number of cutter teeth participating in the exhibition movement and the roughness of the machined tooth surface is smaller.
(3) Improved hobbing processing method
a. Several pieces of machining will be processed on a mandrel with several tooth blanks in series, which can reduce the cutting and cutting time and loading and unloading time of each tooth blank by the hob.
b. There are two methods for cutting the blank into the blank using radial cut-in hobbing: radial cutting and axial cutting. Radial cut-in is shorter than axial cut stroke, saving cut-in time, especially for large-diameter hob hobbing.
c. The use of axial boring cutters and diagonal hob hobbing cutters involved in the cutting load varies, uneven wear, when the most loaded cutter teeth wear to a certain extent, the hob should move along the axial direction Distance (ie, axial boring tool) is continued after cutting to increase tool life.
Diagonal hobbing is the hob moving in the axial direction along the gear blank, and it also moves continuously along the axial direction of the hob cutter rod. The combination of the two movements makes the tooth surface form a diagonal tool mark, which not only reduces the tooth surface Roughness, and even wear of the tool, improve tool life and durability, as shown in Figure 9-9.
Second, the tooth
(I) Principle of pinching and movement
1. Principle of tooth insertion
From the principle analysis of the tooth insertion process, as shown in Figure 9-10, the shaper blade is equivalent to a pair of cylindrical gears whose axes are parallel to each other. The pinion cutter is essentially a gear with front and rear corners and a cutting edge.
2. The main movements of the pinions are:
(1) Up and down reciprocating motion of the cutting motion gear shaping cutter.
(2) The proper meshing relationship should be maintained between the toothed cutter and the workpiece. The pinion cutter reciprocates once. The arc length of the workpiece relative to the tool on the index circle is the circumferential feed amount during machining. Therefore, the engagement process between the tool and the workpiece is the circumferential feed process.
(3) Radial feed movement When inserting the tooth, it is gradually cut to the full tooth depth. The cutting tool should have radial feed fr.
(4) When the reciprocating motion of the knife is moved up and down, the cutting stroke is downward. In order to prevent the tool from scratching the machined tooth surface and reducing the wear of the tool teeth, the table brings the workpiece out of the cutting zone a certain distance (radial) as the cutting tool moves upwards. The worktable resumes its original position when it is working.
(B) the process characteristics of the pin
Compared with the hobbing and hobbing, the shaper has its own characteristics in terms of processing quality, productivity and application range.
1. The processing quality of the slotting tooth
(1) When the tooth profile accuracy of the pinion is higher than that of the hobbing tooth, the number of tangential lines forming the tooth profile envelope is only related to the number of chip pockets of the hob and the number of heads of the basic worm, and it cannot be changed by changing the processing conditions. Increase and decrease; but when inserting, the number of tangents forming the tooth profile envelope is determined by the size of the circumferential feed and can be selected. In addition, when the gear hob is manufactured, an approximately worm is used instead of the involute basic worm, which has a forming error. The tooth shape of the pinion cutter is relatively simple, and the accurate involute tooth shape can be obtained through high-precision grinding. So the spline can get higher tooth profile accuracy.
(2) The roughness of the tooth surface of the pinion is smaller than that of the hobbing. This is because when the hobbing is performed, the hob is intermittently cut in the direction of the teeth, forming a fish scale ripple as shown in Fig. 9-11a; The cutting of the cutting tool in the tooth direction is continuous, as shown in Fig. 9-11b. Therefore, the tooth surface roughness is smaller when inserting the teeth.(3) The movement accuracy of the pinion is worse than that of the hobbing. This is because the transmission chain of the gear shaping machine has one more tool worm gear pair than the hobbing machine, which means a part of the transmission error. In addition, one tooth of the pinion cutter cuts one tooth of the workpiece correspondingly. Therefore, the cumulative error of the cutting tooth itself must be reflected on the workpiece. When hobbing, because each tooth slot of the workpiece is machined out of the same 2 to 3 ring teeth of the hob, the cumulative error of the pitch of the hob does not affect the pitch accuracy of the processed gear, so the hobbing The movement accuracy is higher than the pinion.
(4) The error in the tooth orientation of the pinion is larger than the error in the tooth orientation when the tooth is larger than the hobbing tooth. The error in the parallelism between the axis of rotation of the spindle of the gear shaper and the axis of rotation of the table is mainly determined. Because the frequency of the reciprocating motion of the pinion cutter is high, the wear between the spindle and the sleeve is large, so the toothing error of the pinion is larger than that of the gear hobbing.
Therefore, in terms of machining accuracy, gears with low requirements for movement accuracy can be directly used for tooth profile finishing, while gears and shave gears with high requirements for movement accuracy (shaved teeth cannot improve movement accuracy), It is more advantageous to use hobbing.
2. The productivity of the pinion cuts the gear with a larger modulus, the pinion speed is restricted by the inertia of the reciprocating movement of the pinion cutter and the rigidity of the machine, and the cutting process has a lost time in the idle process, so the productivity is not as high as the hobbing. Only when gears with small modules, multiple teeth, and narrow tooth widths are used, the productivity of the pins is higher than that of hobbing. .
3. Rolling tooth range of application:
(1) Processing gears with shoulders and double or multiple gears with narrow sipes can only be used with pinions. This is because: When the cutting tool "cuts out" only a small amount of space is required, while the hobbing tool interferes with the large diameter part.
(2) Machining herringbone gears without hollow sipes, only using teeth;
(3) Internal gears can only be used for gear cutting.
(4) Machining the worm gear can only use hobbing.
(5) Processing helical gears, both of which are available. However, hobbing is more convenient. When inserting a helical gear, a spiral guide must be provided on the tool spindle of the gear shaper to provide the spiral motion of the pinion cutter, and a special helical tooth shaper is used, which is inconvenient.
(III) Ways to Improve the Productivity of Insertion
1. Increasing the circumferential feed can reduce the maneuvering time, but the circumferential feed amount is proportional to the knife amount during the idle stroke. Therefore, the tool issue of the tool must be solved.
2. The potential of the excavator bed increases the number of reciprocating strokes, using high-speed teeth.
Some gear shaping machines can reach 1200 to 1500 strokes/min per minute and up to 2500 strokes/min. Increased by 3 to 4 times than usual, the cutting speed is greatly improved, and at the same time, the maneuvering time required for the pinion can be reduced.
3. Improve the tool parameters, improve the durability of the pinion cutter, and give full play to the cutting performance of the pinion cutter. Such as the use of W18Cr4V cutting tool, the cutting speed can reach 60m/min; increase the rake angle to 15 degrees, the back angle to 9 degrees, can increase the durability of 3 times; in the rake face grinding 1 ~ 1.5 mm wide platform, It can also increase the durability by about 30%.
Third, shaved teeth
(A) shaving principle
Shave tooth machining is based on the principle of a pair of helical gears with different pitch angles. The shaving cutter intersects the axis space of the gear being cut at an angle, as shown in Fig. 9-12a. The shaving cutter is the drive wheel 1 and is cut. The gears are driven wheels 2 and their meshing is a free-formed movement with no backlash and double-sided meshing. In the meshing transmission, due to the existence of the axis crossing angle “φâ€, the relative slipping occurs along the tooth direction between the tooth surfaces. The slip speed vcut=(vt2-vt1) is the cutting speed of the shaving process. The tooth surface of the shaving cutter is slotted to form a cutting edge, and the machining allowance on the gear tooth surface is cut off by the slip speed. Due to the double-sided meshing, both sides of the shaving cutter can be machined, but because of the different cutting angles on both sides, one side is an acute angle, which has a strong cutting ability; the other side, an obtuse angle, has a weak cutting ability and is pressed and wiped. Light is dominant, so it has a greater impact on shaving quality. In order to obtain the same shaving conditions on both sides of the gear, the shaving cutter performs alternate forward and reverse movements during the shaving process.
Shaving machining requires the following types of motion:
1. The shaving cutter drives the high-speed positive and negative movements of the workpiece - the basic movement.
2. The workpiece reciprocates in the axial direction - so that the entire gear width can be shaved
3. The workpiece performs a radial feed motion each time it reciprocates - to remove the entire margin.
In summary, the shaving process is a free-formation movement in which the shaving cutter and the cut gear are closely meshed on both sides of the gear teeth to realize a fine cutting process, and the basic condition for realizing shaving is that the axis has a crossing angle. When the cross angle is zero, the cutting speed is zero and the shaving cutter has no cutting action on the workpiece.
(b) Shaved tooth characteristics
1. The shaved tooth processing accuracy is generally 6 to 7, and the surface roughness Ra is 0.8 to 0.4 μm, which is used for the finish machining of unquenched gears.
2. The productivity of shave-tooth processing is high. It usually takes 2 to 4 minutes to machine a medium-sized gear, which can increase productivity by more than 10 times compared to grinding teeth.
3. Since the shave tooth machining is free meshing, the machine tool does not show up into a motion transmission chain, so the machine tool structure is simple and the machine tool is easy to adjust.
(3) Several issues that should be paid attention to to ensure shaved tooth quality
1. Processing requirements for shaved gears
(1) Shave gear material requires uniform material density, no local defects, and toughness not to be too large, so as to avoid slippery boring and cutting and affect the surface roughness. The hardness of the gear before shaving is in the range of 22 to 32 HRC.
(2) Accuracy of shaved gear Since shaved teeth are "freely meshed" and there is no forced movement of the teeth, the uniformity of tooth distribution cannot be controlled. Due to the radial error of the shaved ring gear, the shaver can only perform shave-free cutting with the tooth profile farther from the center of rotation at the beginning of shave, and it becomes toothed with other teeth. Side clearance, but no shaving effect at this time. Continuous radial feed, other teeth gradually mesh with the teeth without backlash. As a result, the original radial runout of the ring gear is reduced, but the position of the tooth profile changes in a tangential direction and the amount of change in the length of the common normal line increases. Therefore, shave-tooth processing cannot correct the length variation of the normal. Although there is a strong ability to correct the radial runout of the ring gear, in order to avoid further changes in the length of the common normal during shaving due to excessive runout, the radial error of the shave gear must not be excessive. In addition, shaved teeth have a strong ability to correct other errors in gears.
According to the analysis, shaved teeth have relatively weak ability to correct errors in the first tolerance group. Therefore, it is required that the precision of the gear's movement before shaving cannot be lower than that after shave. In particular, the change in the length of the common normal line should be guaranteed before shaving. Accuracy can be one level lower than after shaving.
(3) The size of the remaining shave shave margin has a certain influence on the processing quality and productivity. Insufficient headroom, shaving errors and tooth surface defects can not be completely removed; excess margin, tool wear quickly, shaved tooth quality but worse. Table 9-5 refers to the available margins.
Table 9-5 Shaving allowance (mm)
Modulus
Shaving allowance
1 to 1.75
0.07
2 to 3
0.08
3.25 to 4
0.09
4 to 5
0.10
5.5 to 6
0.11
2. Selection of shaving cutters
The precision of the shaver is divided into three levels of A, B and C, and the gears with the precision of 6, 7, and 8 are processed respectively. The diameter of the indexing circle of the shaver has three kinds of modulus: 85 mm, 180 mm, 240 mm, of which 240 mm is most commonly used. There are three types of pitch helix angles: 5°, 10°, and 15°, of which 5° and 10° are the most widely used. 15° is mostly used for machining spur gears; 5° is used for machining helical gears and pinions in multiple gears. When shaving bevel gears, the shaft cross φ should not exceed 10° to 20°, otherwise the shaving effect is not good.
3. Shaved Tooth Error and Shave Tooth Profile Modification
Shaved gear teeth are sometimes recessed near the pitch circle, as shown in Figure 9-13, and are generally around 0.03 mm. The fewer gear teeth are shaved, the concave phenomenon is serious.
In order to eliminate the concave surface phenomenon after shave, shaving tooth profile can be modified. It needs a lot of experiment to finalize it. Special shave hobbing can also be used to shave teeth.
Fourth, tooth decay
The surface of gear teeth after quenching has scale, which affects the tooth surface roughness. The deformation of heat treatment also affects the accuracy of the gear. Since the workpiece has been hardened, in addition to grinding, machining can also be performed using rake teeth.
The principle of scraping teeth is similar to that of shaving teeth. The jaw wheel and the workpiece are similar to a pair of helical gears with no backlash. The relative sliding between the meshed parts and the application of a certain pressure between the tooth flanks are used for scraping.
The tooth movements are the same as shaving. That is to say, the jaw wheel drives the workpiece to rotate in positive and negative directions at high speed, the workpiece reciprocates in the axial direction and the workpiece moves in radial direction. The difference from shave teeth is that one radial advance to a predetermined position after driving starts, so the tooth surface pressure is larger at the beginning and then gradually decreases until the tooth decay ends when the pressure disappears.
The rubbing wheel is made of an abrasive (usually 80# to 180# grain of corundum) mixed with a raw material such as an epoxy resin and cast in an iron core. Cutters are a kind of finishing method after gear heat treatment.
Compared with shaved teeth, dental caries have the following process features:
(1) The rake wheel structure is similar to that of the grinding wheel, but the rake tooth speed is very low (usually 1 to 3 m/s). In addition to the finer grain size of the grinding wheel and the greater elasticity of the rake wheel, the rake tooth process is actually a kind of low-speed grinding. The comprehensive process of cutting, grinding and polishing.
(2) When tooth decay, tooth surface clearance has relative sliding along the tooth direction, there is also sliding along the tooth shape direction, so the tooth surface forms a complex mesh pattern, improves tooth surface quality, and its roughness can drop from Ra 1.6μm To Ra0.8-0.4μm.
(3) The elasticity of the caster wheel is relatively large, and the error correction of the front gear is not strong. Therefore, the accuracy of the reel wheel itself is not high, and the reel error is generally not reflected in the reel gear.
(4) The crucible wheel is mainly used to remove oxide scales and burrs on tooth surfaces after heat treatment. The residual amount of caries generally does not exceed 0.025mm, the reel speed is above 1000 r/min, and the longitudinal feed is 0.05 to 0.065mm/r.
(5) The productivity of the ç© wheel is very high, generally one minute, and it can be completed by three to five reciprocations.
Fifth, grinding teeth
Grinding is the most accurate method in tooth shape machining. It can grind unhardened gears as well as grind hardened gears. Grinding accuracy is 4 to 6, and tooth surface roughness is Ra0.8 to 0.2μm. It has strong correction ability to gear error and heat treatment deformation. It is mostly used for precision machining of hard tooth surface high-precision gears and gear cutters, shaving cutters and other gear cutters. Its disadvantage is low productivity and high processing costs, so it is suitable for small batch production.
(A) grinding teeth principle and method
According to the formation principle of the involute tooth surface, the tooth grinding method is divided into two types: profile method and generative method. The profile grinding method uses the formed grinding wheel to directly grind out the involute tooth profile. Currently, there are very few applications. The generating grinding tooth is to make the grinding wheel working face into two sides of the virtual rack and mesh the enveloping motion through the workpiece. The involute tooth surface of the gear.
Here are some common methods of tooth grinding:
1. Conical grinding wheel grinding teeth
Y7131 and Y7132 gear grinding machines are used for this kind of grinding method. They are generated by using the forcible meshing relationship between the hypothetical rack and the gear, as shown in Figure 9-14.
Since the gear has a certain width, in order to grind all the tooth surfaces, the grinding wheel must also reciprocate along the axial direction of the gear. The axial reciprocating motion and the generating motion combine to make the abrasive particles grind on the tooth surface, as shown in Fig. 9-15.
2. Double butterfly grinding teeth
Figure 9-16 shows a double butterfly grinding wheel.
The two butterfly grinding teeth form the two sides of the imaginary rack. The grinding wheel only rotates in-situ (n0) when grinding the tooth; the workpiece rotates (n) and reciprocates (v) accordingly, forming an exhibition movement. In order to grind the entire tooth width of the workpiece, the workpiece must also be slowly fed (f) along its axis. When the two sides of one tooth groove are finished, the workpiece rapidly exits the grinding wheel, and after the indexing, it enters the tooth surface processing of the next tooth groove position.
The above-mentioned generating movement can be realized by the mechanism shown in Fig. 9-16b. By means of the rolling disc steel strip mechanism composed of the slide 7 and the frame 2, the rolling disc 3 and the steel strip 4 in the figure, the coordinated motion of the workpiece's forward and backward rotation (n) and reciprocating movement (v) is realized. The slow feed of the workpiece (f) is completed by the movement of the table 1.
This tooth grinding method can achieve processing precision of up to 4 levels due to fewer transmission links for generating movements, small error in the drive chain (after the grinding wheel is worn out and compensated by an automatic compensation device) and high precision of tooth separation. However, because of the poor rigidity of the disc-shaped grinding wheel, the small depth of cut, and the low productivity, the processing cost is high, which is suitable for the high-precision machining of the internal and external meshing straight teeth and helical gears in small batch production.
(b) Measures to improve grinding accuracy and grinding efficiency
1. Measures to improve grinding accuracy
(1) Reasonable choice of grinding wheel
The grinding wheel material is white corundum (WA), and the hardness is soft and soft. The particle size is determined according to the shape of the grinding wheel used and the surface roughness requirements, and is generally selected within the range of 46# to 80#. For worm-type grinding wheels, the grain size should be selected slightly. Because of its rapid development, in order to ensure a lower surface roughness, the grain size should not be thicker. In addition, to ensure grinding accuracy, the grinding wheel must be precisely balanced.
(2) Improve machine tool accuracy
Mainly to improve the workpiece spindle rotation accuracy, such as the use of high-precision bearings, to improve the pitch accuracy of the index plate, and reduce its installation errors.
(3) Use reasonable process measures
Mainly include: According to the process specification, the gears are subjected to repeated qualitative treatment and tempering to eliminate the internal stress caused by residual stress and mechanical processing; the precision of the process reference is improved, and the clearance gap between the hole and the shaft is reduced for the workpiece. Eccentricity effect; Isolation of vibration source to prevent external disturbances; Room temperature remains stable when grinding teeth, and the temperature difference is not more than 1°C for every batch of gear grinding; For fine dressing of grinding wheel, the diamond used must be sharp, and so on.
2. Measures to improve tooth grinding efficiency
The increase in grinding efficiency is mainly to reduce the number of passes, shorten the length of the stroke and increase the amount of grinding. Commonly used measures are as follows:
(1) The grinding allowance should be uniform in order to effectively reduce the number of passes;
(2) Shorten the length of the span so as to shorten the grinding time. It can be used without rough grinding during rough machining;
(3) Adopt the air hole grinding wheel to increase the grinding amount.
Six, gear processing options
The choice of gear machining solution mainly depends on the gear's accuracy grade, production batch and heat treatment methods. Here are a few principles for the selection of gear machining solutions for reference:
1. For unhardened gears with accuracy of 8 and below, milling, hobbing or pinching can be used to directly meet the machining accuracy requirements.
2. For precision grade hardened gears with grades 8 and below, the precision must be increased by one stage before quenching. The machining scheme can be: roll (insert) tooth-tooth end machining-tooth surface hardening-correction bore.
3. For gears with 6 to 7 grades of non-hardened gears, the gear machining program: hobbing - shaving.
4. For the hardened gears with 6 to 7 grades of precision, there are generally two options for tooth profile machining:
(1) Shave - Honing program
Rolling (inserting) tooth-tooth end machining - shaving teeth - tooth surface hardening - correcting bores - tine teeth.
(2) grinding teeth program
Rolling (inserting) tooth-tooth end machining - tooth surface hardening - correcting bore - grinding teeth.
The shave-tank solution is highly productive and is widely used in mass production of gears with a precision of 7 stages. Grinding scheme has a low productivity and is generally used for gears with a grade of 6 or higher.
5. For gears with a precision of 5 or above, a gear grinding scheme is generally used.
6. For mass production, using a rolling (inserting) tooth-cold squeezing tooth machining scheme, a 7-level precision gear can be stably obtained.
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