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If the parameters of the gear meshing with the gear to be ground are unknown, for the sake of safety, the gear can be meshed with the rack to calculate, where 1' is: 1' = mt (z12sint-1sint). Where: mt - the end face modulus of the gear to be ground; z1 - the number of teeth of the gear to be ground; t - the pressure angle of the end face of the gear to be ground.
When the first trial grinding part detects the involute tooth profile accuracy, the length should be detected at the same time. It must be ensured that any working face is 1<1'. If the ground gear does not meet this condition, the involute length is easily insufficient.
1.2 The tooth root transition curve is not well connected. The step tooth root defect refers to the root geometry defect that is easy to occur in the grinding tooth production practice. In the manufacturing process, about 50 gears have bosses, some of which are asymmetrical on both sides of the root, one side of the boss is obvious, and one side has a better transition; some have a boss with a full tooth width, and the bosses occupy about the root 1/3. After grinding the tooth root to produce a grinding step, it will cause severe stress concentration, which greatly weakens the root bending fatigue, and the grinding step should be avoided during the manufacturing process.
1.3 The phenomenon of "over-grinding" the "over-grinding" crests or roots of the crest or root of about 30 occurs on the thin gears and on the large gears with deep grooves on the end faces.
1.4 Carburizing and quenching grinding tooth surface damage and tooth surface crack Carburizing and quenching gears are prone to tooth surface cracks, and the scrap rate is much higher than the soft tooth surface, which is one of the reasons for the high cost of hard tooth gears. Therefore, the production process specification should be detailed to minimize the loss of waste.
2 Causes and Solutions for Problems 2.1 Causes and Solutions for Insufficient Length of Involute (1) The design of the hob before grinding is unreasonable. The position at which the root point of the tooth is pre-machined using the pre-grinding hob depends on the length of the antenna. If the length of the antenna is increased, the position of the starting point of the undercut is moved up, and the length of the involute will be insufficient. It is assumed that the radius of curvature of the starting point of the pre-machined tooth cutting is 1 sink. To make the length of the involute line meet the requirements, it is necessary to ensure that 1 sinking <1'.
(2) The actual residual grinding margin is too large. If the actual grinding allowance is greater than the grinding allowance of the pre-grinding hob design, the depth of the pre-machining tooth profile will be reduced, causing the position of the starting point of the cutting to move up, resulting in insufficient length of the involute, so leaving the grinding The quantity should be consistent with the design.
(3) The gear grinding machine is not properly adjusted. For the tapered grinding wheel type grinding machine, the insufficient adjustment depth of the grinding wheel will result in insufficient length of the involute, so the adjustment depth of the grinding wheel should be guaranteed to be 1<1′; for the butterfly double-sided grinding wheel grinding machine 0o grinding, mainly because If the length of the exhibition is insufficient, the length of the involute is insufficient, and 1<1' should be guaranteed when calculating the length of the exhibition.
(4) Heat treatment deformation. After the carburizing and quenching of the gear, deformation will inevitably occur, resulting in unequal curvature radius 1 of the starting point of the involute of each tooth. Therefore, it must be ensured that any working tooth surface 1<1' can guarantee the length of the involute.
2.2 Reasons and solutions for the poor connection of the tooth root transition curve (1) The design of the hob before grinding is unreasonable. The height of the horn of the pre-grinding hob should be the sum of the one-side grinding allowance and the depth of the undercut. If the depth of the cutting depth is too small, the pre-machining tooth depth will be too shallow, so that the teeth are made when grinding. The roots create steps. In order to ensure that no steps are generated when grinding the teeth, the root cutting amount H' ≤ (0.015mn 0.1) should be made, where mn is the gear modulus.
(2) The actual residual grinding margin is too large. The actual grinding allowance cannot be greater than the amount of protrusion of the hob used, otherwise a boss is created. In order to prevent the actual grinding allowance from being too large, the specific common normal line size and tolerance should be given during the rough rolling. The general process requires that the common normal line size of the pre-grinding hobbing should be 0.44 mm.
(3) Heat treatment deformation will also result in a bad tooth root transition curve, resulting in a step. After grinding the teeth, the fitter uses a small spherical grinding wheel to grind the roots into a transitional smooth curve.
The main reason and solution for "over-grinding" the crest or root is that the main cause of "over-grinding" the crest or root is that the heat treatment deforms too much or reverses deformation. Due to uneven cooling during heat treatment, the carburized and quenched gears are severely swollen above the underside, and are tapered, or the ends of the gear shaft are swollen or even reduced in a drum shape. Under normal circumstances, the outer diameter of the gear should be 1 ‰ to 2 ‰, and the tooth expansion should be within 0.4 。.
The solution to the problem is to ensure that the anti-deformation amount of the process and the tooth tip clearance of the pre-grinding hob fully satisfy the normal deformation. For the abnormally deformed carburizing and quenching gear, the outer circle dimensions of the gear ends can be measured during the finishing process after quenching. If it is larger than the drawing requirements, the fine teeth are rounded to the requirements.
Causes and solutions for carburizing and quenching of tooth surface damage and tooth surface cracking 2.4.1 Effect of heat treatment (1) Effect of retained austenite: Retained austenite during grinding will be hot due to grinding wheel grinding The change with pressure, accompanied by surface tempering and grinding cracks, so the amount of retained austenite should be controlled within 30 (mass fraction).
(2) Influence of carburized layer concentration: The concentration of carburized layer is too high, and it is easy to form wind head carbide or excessive free carbide in the layer structure. Due to the extremely hard material, local overheating may occur during grinding. Prone and surface tempering. Therefore, the surface carbon concentration should be controlled within the range of 0.75 to 0.95 (mass fraction).
(3) The effect of decarburization: When heat treatment, the surface or environmental protection will produce surface oxidation, so that a thin decarburization layer will be formed on the tooth surface, which will cause the grinding wheel to overload or overheat, resulting in surface tempering.
(4) The effect of tempering: Under the premise of ensuring the hardness, the tempering temperature is as high as possible, and the tempering time is as long as possible, so that the plasticity of the carburized hardened surface can be improved, and the residual stress can be balanced or reduced. Improve the distribution of surface stress, reduce the probability of occurrence of grinding cracks, and improve the grinding efficiency.
(5) Effect of heat treatment deformation: If the heat treatment deformation is too large, and the grinding operation is not started at the maximum radial runout of the ring gear, the grinding allowance removed at these points for each grinding will be no Normal, resulting in burns and cracks. The amount of deformation can be reduced by pretreatment measures to refine and homogenize the tooth blank structure and reduce deformation during carburizing and quenching.
Effect of Grinding Conditions The grinding speed of the grinding wheel is very high when grinding the teeth. The contact area between the grinding wheel and the gear teeth is small, and the generated heat may form a high temperature in the contact area, resulting in damage to the grinding teeth.
(1) Influence of grinding tooth allowance: Excessive grinding heat is generated due to excessive grinding tooth allowance, which leads to grinding tooth damage, so the grinding tooth allowance should be reduced as much as possible.
(2) Influence of grinding wheel: The hardness of carburizing steel is high, the sand is easy to be blunt, in order to avoid sand blunt and generate a lot of grinding heat, the hardness of the grinding wheel should be soft, so that the blunt sand can fall off in time, keep the grinding wheel sharp. On the premise of ensuring the roughness of the tooth surface, it is advisable to select a coarser-grained grinding wheel to achieve a higher removal ratio; to make the grinding wheel cool enough, and to keep the coolant pure and to control the temperature of the coolant.
The problems that have occurred in the processing of the carburized and hardened hardened gears have attracted the attention of the gear manufacturing industry at home and abroad. This paper studies and analyzes the causes of these problems, and proposes corresponding solutions, which has certain guiding significance for improving gear manufacturing quality and technical level.
When the first trial grinding part detects the involute tooth profile accuracy, the length should be detected at the same time. It must be ensured that any working face is 1<1'. If the ground gear does not meet this condition, the involute length is easily insufficient.
1.2 The tooth root transition curve is not well connected. The step tooth root defect refers to the root geometry defect that is easy to occur in the grinding tooth production practice. In the manufacturing process, about 50 gears have bosses, some of which are asymmetrical on both sides of the root, one side of the boss is obvious, and one side has a better transition; some have a boss with a full tooth width, and the bosses occupy about the root 1/3. After grinding the tooth root to produce a grinding step, it will cause severe stress concentration, which greatly weakens the root bending fatigue, and the grinding step should be avoided during the manufacturing process.
1.3 The phenomenon of "over-grinding" the "over-grinding" crests or roots of the crest or root of about 30 occurs on the thin gears and on the large gears with deep grooves on the end faces.
1.4 Carburizing and quenching grinding tooth surface damage and tooth surface crack Carburizing and quenching gears are prone to tooth surface cracks, and the scrap rate is much higher than the soft tooth surface, which is one of the reasons for the high cost of hard tooth gears. Therefore, the production process specification should be detailed to minimize the loss of waste.
2 Causes and Solutions for Problems 2.1 Causes and Solutions for Insufficient Length of Involute (1) The design of the hob before grinding is unreasonable. The position at which the root point of the tooth is pre-machined using the pre-grinding hob depends on the length of the antenna. If the length of the antenna is increased, the position of the starting point of the undercut is moved up, and the length of the involute will be insufficient. It is assumed that the radius of curvature of the starting point of the pre-machined tooth cutting is 1 sink. To make the length of the involute line meet the requirements, it is necessary to ensure that 1 sinking <1'.
(2) The actual residual grinding margin is too large. If the actual grinding allowance is greater than the grinding allowance of the pre-grinding hob design, the depth of the pre-machining tooth profile will be reduced, causing the position of the starting point of the cutting to move up, resulting in insufficient length of the involute, so leaving the grinding The quantity should be consistent with the design.
(3) The gear grinding machine is not properly adjusted. For the tapered grinding wheel type grinding machine, the insufficient adjustment depth of the grinding wheel will result in insufficient length of the involute, so the adjustment depth of the grinding wheel should be guaranteed to be 1<1′; for the butterfly double-sided grinding wheel grinding machine 0o grinding, mainly because If the length of the exhibition is insufficient, the length of the involute is insufficient, and 1<1' should be guaranteed when calculating the length of the exhibition.
(4) Heat treatment deformation. After the carburizing and quenching of the gear, deformation will inevitably occur, resulting in unequal curvature radius 1 of the starting point of the involute of each tooth. Therefore, it must be ensured that any working tooth surface 1<1' can guarantee the length of the involute.
2.2 Reasons and solutions for the poor connection of the tooth root transition curve (1) The design of the hob before grinding is unreasonable. The height of the horn of the pre-grinding hob should be the sum of the one-side grinding allowance and the depth of the undercut. If the depth of the cutting depth is too small, the pre-machining tooth depth will be too shallow, so that the teeth are made when grinding. The roots create steps. In order to ensure that no steps are generated when grinding the teeth, the root cutting amount H' ≤ (0.015mn 0.1) should be made, where mn is the gear modulus.
(2) The actual residual grinding margin is too large. The actual grinding allowance cannot be greater than the amount of protrusion of the hob used, otherwise a boss is created. In order to prevent the actual grinding allowance from being too large, the specific common normal line size and tolerance should be given during the rough rolling. The general process requires that the common normal line size of the pre-grinding hobbing should be 0.44 mm.
(3) Heat treatment deformation will also result in a bad tooth root transition curve, resulting in a step. After grinding the teeth, the fitter uses a small spherical grinding wheel to grind the roots into a transitional smooth curve.
The main reason and solution for "over-grinding" the crest or root is that the main cause of "over-grinding" the crest or root is that the heat treatment deforms too much or reverses deformation. Due to uneven cooling during heat treatment, the carburized and quenched gears are severely swollen above the underside, and are tapered, or the ends of the gear shaft are swollen or even reduced in a drum shape. Under normal circumstances, the outer diameter of the gear should be 1 ‰ to 2 ‰, and the tooth expansion should be within 0.4 。.
The solution to the problem is to ensure that the anti-deformation amount of the process and the tooth tip clearance of the pre-grinding hob fully satisfy the normal deformation. For the abnormally deformed carburizing and quenching gear, the outer circle dimensions of the gear ends can be measured during the finishing process after quenching. If it is larger than the drawing requirements, the fine teeth are rounded to the requirements.
Causes and solutions for carburizing and quenching of tooth surface damage and tooth surface cracking 2.4.1 Effect of heat treatment (1) Effect of retained austenite: Retained austenite during grinding will be hot due to grinding wheel grinding The change with pressure, accompanied by surface tempering and grinding cracks, so the amount of retained austenite should be controlled within 30 (mass fraction).
(2) Influence of carburized layer concentration: The concentration of carburized layer is too high, and it is easy to form wind head carbide or excessive free carbide in the layer structure. Due to the extremely hard material, local overheating may occur during grinding. Prone and surface tempering. Therefore, the surface carbon concentration should be controlled within the range of 0.75 to 0.95 (mass fraction).
(3) The effect of decarburization: When heat treatment, the surface or environmental protection will produce surface oxidation, so that a thin decarburization layer will be formed on the tooth surface, which will cause the grinding wheel to overload or overheat, resulting in surface tempering.
(4) The effect of tempering: Under the premise of ensuring the hardness, the tempering temperature is as high as possible, and the tempering time is as long as possible, so that the plasticity of the carburized hardened surface can be improved, and the residual stress can be balanced or reduced. Improve the distribution of surface stress, reduce the probability of occurrence of grinding cracks, and improve the grinding efficiency.
(5) Effect of heat treatment deformation: If the heat treatment deformation is too large, and the grinding operation is not started at the maximum radial runout of the ring gear, the grinding allowance removed at these points for each grinding will be no Normal, resulting in burns and cracks. The amount of deformation can be reduced by pretreatment measures to refine and homogenize the tooth blank structure and reduce deformation during carburizing and quenching.
Effect of Grinding Conditions The grinding speed of the grinding wheel is very high when grinding the teeth. The contact area between the grinding wheel and the gear teeth is small, and the generated heat may form a high temperature in the contact area, resulting in damage to the grinding teeth.
(1) Influence of grinding tooth allowance: Excessive grinding heat is generated due to excessive grinding tooth allowance, which leads to grinding tooth damage, so the grinding tooth allowance should be reduced as much as possible.
(2) Influence of grinding wheel: The hardness of carburizing steel is high, the sand is easy to be blunt, in order to avoid sand blunt and generate a lot of grinding heat, the hardness of the grinding wheel should be soft, so that the blunt sand can fall off in time, keep the grinding wheel sharp. On the premise of ensuring the roughness of the tooth surface, it is advisable to select a coarser-grained grinding wheel to achieve a higher removal ratio; to make the grinding wheel cool enough, and to keep the coolant pure and to control the temperature of the coolant.
The problems that have occurred in the processing of the carburized and hardened hardened gears have attracted the attention of the gear manufacturing industry at home and abroad. This paper studies and analyzes the causes of these problems, and proposes corresponding solutions, which has certain guiding significance for improving gear manufacturing quality and technical level.
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