Revacycle processing technology of spur bevel gears
Spur bevel gears are widely used in the design of automotive differentials and other applications. In high-volume production, rotary tools are used to cut spur bevel gears, and this cutting process for bevel gears is shown in Figure 1.
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Most gear circle drawing cutting processes are formed by a continuously rotating tool continuously cutting at a uniform speed. Tool blades extending radially outward from the cutter head have concave edges creating a convex profile on the gear teeth. During the cutting process, the workpiece remains stationary, while the tool is moved by the cam in a straight line along the surface of the gear, substantially parallel to its root line. This movement makes it possible to create a straight tooth base, and the desired tooth profile is created by the combined action of the tool movement and the shape of the blade. Cutting machines do not have depth feed, and effective feed is obtained by making each insert longer than the insert before it.
The complete tool includes three inserts: roughing, semi-finishing and finishing. One rotation of the tool completes the machining of each tooth slot, and the indexing of the work is completed in the time gap between the last tool and the first tool rotation. Figure 2 shows the position of the circular broaching tool at the start of the cut. As the cutter rotates counterclockwise, the gradually increasing length of the cutter head comes into contact with the work gear until the tooth root of the gear.
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Figure 3a shows a lateral view of the tooth space enlarged to full depth. Each chip cut extends the full width of the groove, except for the allowance to be machined. Figure 3b is an axial view of the same tooth, showing the iron filings extending over the entire tooth length. In the first part of the rough cut, the tool is fed from Oc1 to Oc2 at the feed rate Fe, and then held from Oc2 to full tooth depth.
The rough cut teeth do not have the proper taper, which is essentially correct along the diagonal in Figure 3b. But the portion of the tooth surface on the right side of this line toward the large end of the tooth still has a considerable margin that must be removed prior to finishing. This requires semi-finishing inserts for machining, and the tool center at this stage is from Oc2 to Oc3.
The finishing phase is done when the tool center returns from Oc3 to Oc4 at a uniform speed. The finishing blades are given the appropriate tooth profile to produce the correct tooth profile and correct drum shape on the tooth profile of the gear. The blade cutting at both ends of the tooth gap is slightly wider, which is necessary for the correct taper, so that the ends of the teeth can be drummed and the tooth surface can be partially loaded. The resulting finished tooth flank consists of a series of inclined cutting paths similar to that shown in Figure 3C. In general, each different specification of gear requires a different tool. Figure 4 shows a close-up of a Gleason machine using the circular drawing method to cut spur bevel gears.
For manufacturing processes that are too deep to be completed in one cut, separate roughing and finishing processes are combined, with different tools and machine tools for different processes. The tools and cutting cycles are similar to the above with slight differences. This roughing tool has no semi-finishing or finishing inserts and no translation of the roughing tool. However, the finishing tool is in the machining of the finished product, and the semi-finishing blade cutting is performed during the first translation, and the finishing allowance correction is performed after the first translation.
As mentioned earlier, the tool that completes the entire machining consists of three inserts: roughing, semi-finishing, and finishing (Figure 5). Revacure inserts are profiled at the time of manufacture, so only the rake face is ground after use. During regrinding, the blade spacing, the plane angle of the rake face and the surface finish of the rake face must be strictly controlled. In addition, in order to achieve the required product consistency, when new parts are assembled on the cutter head, the accuracy of the positioning key positions, and the accuracy of the tightening bolts are very necessary.
This paper describes a new concept for enveloping cutting of spur bevel gears. When cutting spur bevel gears, enveloping circular cutters can also be used for cutting (Figure 6). When machining bevel gear teeth, the enveloping circular cutter head rotates around its axis of rotation. The workpiece to be machined rotates around an axis Ofr, which intersects at right angles to the rotation axis Oc2 of the cutter head. The rotation of the cutter head about its axis and the feed rate of the cutter vary over time. The required value of the workpiece gear rotational feed rate, as well as the required position of the center of rotation, can be expressed by the design parameters of the enveloping roller and the tool of the bevel gear being machined.
The rough tooth cutting of the cutter head completes most of the workpiece allowance. In the rough tooth segment of the enveloping gear cutter, the tooth height of the cutting teeth gradually increases from the first rough edge to the last tooth. The chips cut by the coarse teeth are approximately rectangular in cross section, which makes the chips curl easily. There is no chip interference between adjacent rough teeth, which increases the tool life of the rough teeth.
The coarse teeth are followed by the semi-fine teeth that wrap the gear cutting disc. Semi-finishing teeth remove a limited portion of the blank from the backlash of the bevel gear blank. The main purpose of semi-finishing teeth is to leave material and an evenly distributed allowance for finishing teeth. The main function of the finishing tooth is to generate the final required tooth surface, and the precision of the finishing tooth shape directly determines the level of the tooth shape precision of the final product.
For automatic loading and indexing, the enveloping circular gear cutter head is determined by the time it takes to rotate between the last tooth for finishing and the first tooth for roughing. In the roughing and semi-finishing parts, the rotation of the tool and the rotation of the gear blank are simultaneous, so that when the tool passes the angle
Indicates the angle of the roughing and semi-finishing parts of cutting, and the workpiece gear rotation angle corresponds to the roughing and semi-finishing cycles of bevel gear machining. In the finishing part of the cutter, the rotation angle and the time pattern through the rotation angle are similar to those just discussed. When the tool rotates by a certain angle, the workpiece also rotates by the corresponding angle.
Given the known geometry of the spur gear tooth flank, and its kinematics, as discussed previously, it is possible to shape the entire tooth enveloping the round cutter head. The use of elements from the envelope theory is decisive during gear machining. The roughing and semi-roughing cutting edges envelop the cutting teeth of the gear tool, moving inward, creating the gear tool.
The transverse cutting edges of the finishing teeth of the enveloping gear cutting tool are located within the generating surface T. The generated surface T of the tool is tangent to the tooth surface G of the bevel gear at every moment of the cutting gear. After this determination, the generating surface T is used to analytically describe the final tooth surface finishing cutting edge and clearance of the enveloping gear cutting tool.
The generated surface of the enveloping gear cutting cutter head is also important for the shaping of roughing and semi-finishing inserts. The cutting edges of the roughing teeth decrease inwardly with respect to the developing plane T by a distance tsr. This distance tsr is equal to the cutting thickness of the semi-finishing tool. Thus, the cutting edge of the roughing insert is within a surface that is offset in distance from the generating surface T of the enveloping gear cut. Similarly, the cutting edge of the semi-roughing blade is within a surface that is offset by a distance from the generating face Tf of the finishing enveloping gear cut. Here, tf represents the portion removed by dressing the blade of the tool.
Through the above brief discussion, the importance of the curved surface T to the shaping of the enveloping gear cutting tool is revealed. In the case under consideration, the generation surface T of the tool can be determined in the following way. Consider machining the flanks of bevel gears using the enveloping method. Position vector [1] of the flank point of the bevel gear:
When machining bevel gears, the enveloping gear cutting tool rotates in the longitudinal direction of the gear. The rotation of the tool around its axis of rotation and the feed action of the tool in units of feed are interrelated. During the roughing period, the time of rotation and offset corresponds to the angle through which the cutting tool travels over a distance. This represents the angle on the roughing section of the tool, and represents the distance between two subsequent positions, as well as the axis of rotation of the enveloping gear cutting tool.
As just discussed, rotation and translation are performed in a similar manner in the fine-cutting part of the tool. When the tool passes through a certain angle and it moves over a certain distance, what is expressed here is the angle on the finished part of the tool, and the distance between two subsequent positions and the axis of rotation of the enveloping gear cutting tool. Analytical representation of bevel gear tooth flank machining and the kinematic relationship of enveloping gear cutting, through machining, the equations of the two parts of the gear tool generation surface can be deduced.
The blade of the enveloping gear cutter only needs to be ground on the rake face for continued use during manufacture. During the resharpening process, the blade spacing, rake face plane angle and front surface finish must all be strictly controlled. In addition, when the new blade is assembled on the cutter head, the cleanliness of the assembly, the accuracy of the positioning key position and the strict control of the tightening bolt tension are the basic conditions for obtaining a good cutting tooth surface.
The concept of enveloping cutting spur bevel gears can be extended to the production of spur and helical gears. For this purpose, an enveloping gear cutting cutter head can be used (Fig. 7). Gear blanks remain unclear during cutting. The bevel gear cutting tool rotates around its axis of rotation, as shown in FIG. 7 . All the cutting teeth of the gear tool are subdivided into sections. The rough teeth of the enveloping gear tool remove most of the material from the gullet of the blank, and the tooth height of the cutting teeth increases from the first piece of the roughing insert to the last cutting edge in the rough cutting portion of the tool teeth. The chips cut by the coarse teeth are approximately rectangular in cross section, which makes the chips curl easily. There is no chip interference between adjacent rough teeth, which increases the tool life of the rough teeth.
Rough teeth are followed by semi-finished teeth, which remove a limited portion of the gap width of the gear blank. The main purpose of semi-finishing teeth is to make the allowance of finishing teeth evenly distributed. The flank of the finished gear is produced by the finishing teeth, and the precision of the finishing teeth directly affects the precision of the gear. For automatic loading and indexing, the enveloping circular gear cutter head is determined by the time it takes to rotate between the last tooth for finishing and the first tooth for roughing. The finishing teeth of the enveloping gear cutter are identical to those of the inner disc cutter. The cutting edges of the roughing and semi-finishing cutters of the enveloping gear tool move inward, causing the gear tool generating body to move inward.
It is convenient to use the plane as the rake face of the enveloping circular gear cutting tool. The rake face can be rotated through the axis of rotation of the enveloping gear cutter (in which case the outside angle is zero), or it can be offset at a distance from the axis (the outside rake angle is positive). For precision, the flank surface of the tool grinds only the rake face.
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Most gear circle drawing cutting processes are formed by a continuously rotating tool continuously cutting at a uniform speed. Tool blades extending radially outward from the cutter head have concave edges creating a convex profile on the gear teeth. During the cutting process, the workpiece remains stationary, while the tool is moved by the cam in a straight line along the surface of the gear, substantially parallel to its root line. This movement makes it possible to create a straight tooth base, and the desired tooth profile is created by the combined action of the tool movement and the shape of the blade. Cutting machines do not have depth feed, and effective feed is obtained by making each insert longer than the insert before it.
The complete tool includes three inserts: roughing, semi-finishing and finishing. One rotation of the tool completes the machining of each tooth slot, and the indexing of the work is completed in the time gap between the last tool and the first tool rotation. Figure 2 shows the position of the circular broaching tool at the start of the cut. As the cutter rotates counterclockwise, the gradually increasing length of the cutter head comes into contact with the work gear until the tooth root of the gear.
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Figure 3a shows a lateral view of the tooth space enlarged to full depth. Each chip cut extends the full width of the groove, except for the allowance to be machined. Figure 3b is an axial view of the same tooth, showing the iron filings extending over the entire tooth length. In the first part of the rough cut, the tool is fed from Oc1 to Oc2 at the feed rate Fe, and then held from Oc2 to full tooth depth.
The rough cut teeth do not have the proper taper, which is essentially correct along the diagonal in Figure 3b. But the portion of the tooth surface on the right side of this line toward the large end of the tooth still has a considerable margin that must be removed prior to finishing. This requires semi-finishing inserts for machining, and the tool center at this stage is from Oc2 to Oc3.
The finishing phase is done when the tool center returns from Oc3 to Oc4 at a uniform speed. The finishing blades are given the appropriate tooth profile to produce the correct tooth profile and correct drum shape on the tooth profile of the gear. The blade cutting at both ends of the tooth gap is slightly wider, which is necessary for the correct taper, so that the ends of the teeth can be drummed and the tooth surface can be partially loaded. The resulting finished tooth flank consists of a series of inclined cutting paths similar to that shown in Figure 3C. In general, each different specification of gear requires a different tool. Figure 4 shows a close-up of a Gleason machine using the circular drawing method to cut spur bevel gears.
For manufacturing processes that are too deep to be completed in one cut, separate roughing and finishing processes are combined, with different tools and machine tools for different processes. The tools and cutting cycles are similar to the above with slight differences. This roughing tool has no semi-finishing or finishing inserts and no translation of the roughing tool. However, the finishing tool is in the machining of the finished product, and the semi-finishing blade cutting is performed during the first translation, and the finishing allowance correction is performed after the first translation.
As mentioned earlier, the tool that completes the entire machining consists of three inserts: roughing, semi-finishing, and finishing (Figure 5). Revacure inserts are profiled at the time of manufacture, so only the rake face is ground after use. During regrinding, the blade spacing, the plane angle of the rake face and the surface finish of the rake face must be strictly controlled. In addition, in order to achieve the required product consistency, when new parts are assembled on the cutter head, the accuracy of the positioning key positions, and the accuracy of the tightening bolts are very necessary.
This paper describes a new concept for enveloping cutting of spur bevel gears. When cutting spur bevel gears, enveloping circular cutters can also be used for cutting (Figure 6). When machining bevel gear teeth, the enveloping circular cutter head rotates around its axis of rotation. The workpiece to be machined rotates around an axis Ofr, which intersects at right angles to the rotation axis Oc2 of the cutter head. The rotation of the cutter head about its axis and the feed rate of the cutter vary over time. The required value of the workpiece gear rotational feed rate, as well as the required position of the center of rotation, can be expressed by the design parameters of the enveloping roller and the tool of the bevel gear being machined.
The rough tooth cutting of the cutter head completes most of the workpiece allowance. In the rough tooth segment of the enveloping gear cutter, the tooth height of the cutting teeth gradually increases from the first rough edge to the last tooth. The chips cut by the coarse teeth are approximately rectangular in cross section, which makes the chips curl easily. There is no chip interference between adjacent rough teeth, which increases the tool life of the rough teeth.
The coarse teeth are followed by the semi-fine teeth that wrap the gear cutting disc. Semi-finishing teeth remove a limited portion of the blank from the backlash of the bevel gear blank. The main purpose of semi-finishing teeth is to leave material and an evenly distributed allowance for finishing teeth. The main function of the finishing tooth is to generate the final required tooth surface, and the precision of the finishing tooth shape directly determines the level of the tooth shape precision of the final product.
For automatic loading and indexing, the enveloping circular gear cutter head is determined by the time it takes to rotate between the last tooth for finishing and the first tooth for roughing. In the roughing and semi-finishing parts, the rotation of the tool and the rotation of the gear blank are simultaneous, so that when the tool passes the angle
Indicates the angle of the roughing and semi-finishing parts of cutting, and the workpiece gear rotation angle corresponds to the roughing and semi-finishing cycles of bevel gear machining. In the finishing part of the cutter, the rotation angle and the time pattern through the rotation angle are similar to those just discussed. When the tool rotates by a certain angle, the workpiece also rotates by the corresponding angle.
Given the known geometry of the spur gear tooth flank, and its kinematics, as discussed previously, it is possible to shape the entire tooth enveloping the round cutter head. The use of elements from the envelope theory is decisive during gear machining. The roughing and semi-roughing cutting edges envelop the cutting teeth of the gear tool, moving inward, creating the gear tool.
The transverse cutting edges of the finishing teeth of the enveloping gear cutting tool are located within the generating surface T. The generated surface T of the tool is tangent to the tooth surface G of the bevel gear at every moment of the cutting gear. After this determination, the generating surface T is used to analytically describe the final tooth surface finishing cutting edge and clearance of the enveloping gear cutting tool.
The generated surface of the enveloping gear cutting cutter head is also important for the shaping of roughing and semi-finishing inserts. The cutting edges of the roughing teeth decrease inwardly with respect to the developing plane T by a distance tsr. This distance tsr is equal to the cutting thickness of the semi-finishing tool. Thus, the cutting edge of the roughing insert is within a surface that is offset in distance from the generating surface T of the enveloping gear cut. Similarly, the cutting edge of the semi-roughing blade is within a surface that is offset by a distance from the generating face Tf of the finishing enveloping gear cut. Here, tf represents the portion removed by dressing the blade of the tool.
Through the above brief discussion, the importance of the curved surface T to the shaping of the enveloping gear cutting tool is revealed. In the case under consideration, the generation surface T of the tool can be determined in the following way. Consider machining the flanks of bevel gears using the enveloping method. Position vector [1] of the flank point of the bevel gear:
When machining bevel gears, the enveloping gear cutting tool rotates in the longitudinal direction of the gear. The rotation of the tool around its axis of rotation and the feed action of the tool in units of feed are interrelated. During the roughing period, the time of rotation and offset corresponds to the angle through which the cutting tool travels over a distance. This represents the angle on the roughing section of the tool, and represents the distance between two subsequent positions, as well as the axis of rotation of the enveloping gear cutting tool.
As just discussed, rotation and translation are performed in a similar manner in the fine-cutting part of the tool. When the tool passes through a certain angle and it moves over a certain distance, what is expressed here is the angle on the finished part of the tool, and the distance between two subsequent positions and the axis of rotation of the enveloping gear cutting tool. Analytical representation of bevel gear tooth flank machining and the kinematic relationship of enveloping gear cutting, through machining, the equations of the two parts of the gear tool generation surface can be deduced.
The blade of the enveloping gear cutter only needs to be ground on the rake face for continued use during manufacture. During the resharpening process, the blade spacing, rake face plane angle and front surface finish must all be strictly controlled. In addition, when the new blade is assembled on the cutter head, the cleanliness of the assembly, the accuracy of the positioning key position and the strict control of the tightening bolt tension are the basic conditions for obtaining a good cutting tooth surface.
The concept of enveloping cutting spur bevel gears can be extended to the production of spur and helical gears. For this purpose, an enveloping gear cutting cutter head can be used (Fig. 7). Gear blanks remain unclear during cutting. The bevel gear cutting tool rotates around its axis of rotation, as shown in FIG. 7 . All the cutting teeth of the gear tool are subdivided into sections. The rough teeth of the enveloping gear tool remove most of the material from the gullet of the blank, and the tooth height of the cutting teeth increases from the first piece of the roughing insert to the last cutting edge in the rough cutting portion of the tool teeth. The chips cut by the coarse teeth are approximately rectangular in cross section, which makes the chips curl easily. There is no chip interference between adjacent rough teeth, which increases the tool life of the rough teeth.
Rough teeth are followed by semi-finished teeth, which remove a limited portion of the gap width of the gear blank. The main purpose of semi-finishing teeth is to make the allowance of finishing teeth evenly distributed. The flank of the finished gear is produced by the finishing teeth, and the precision of the finishing teeth directly affects the precision of the gear. For automatic loading and indexing, the enveloping circular gear cutter head is determined by the time it takes to rotate between the last tooth for finishing and the first tooth for roughing. The finishing teeth of the enveloping gear cutter are identical to those of the inner disc cutter. The cutting edges of the roughing and semi-finishing cutters of the enveloping gear tool move inward, causing the gear tool generating body to move inward.
It is convenient to use the plane as the rake face of the enveloping circular gear cutting tool. The rake face can be rotated through the axis of rotation of the enveloping gear cutter (in which case the outside angle is zero), or it can be offset at a distance from the axis (the outside rake angle is positive). For precision, the flank surface of the tool grinds only the rake face.
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