1、STD.AGMA bFTM2-ENGL L77b 0687575 000LiLib b7 m 96FTM2 The New Way of Manufacturing Bevel and Hypoid Gears in a Continuous Process by: Dr. Hermann J. Stadtfeld, The Gleason Works TECHNICAL PAPER STDmAGMA SbFTM2-ENGL L99b W Clb87575 OO11847 513 = The New Way of Manufacturing Bevel and Hypoid Gears in
2、a Continuous Process Dr. Hermann J. Stadtfeld, The Gleason Works The statements and opinions contained herein are those of the author and should not be construed as an official action or opinion of the American Gear Manufacturers Association. Abstract Much attention has been paid to face hobbing in
3、the last decade. The CNC technology made a quantum step in this period which was beneficial especially for the continuous bevel gear cutting process. Paraiiel to the CNC technology a new method of face hobbing was subsequently developed and is introduced today as the different and new way of face bo
4、bbing. The basis is a new gear theoreticai approach to design the blank geometry, the ease off and the tooth contact. The tools are different in design than reguiar Cutting blades an enable a high economical procedure of roughing and finishing in one chucking. The process kinematic was completely re
5、designed, benefitting from the he form concept of todays cutting machines. All the aspects of precision, flexibiiity and economy made the new face hobbing also popular for the gearbox manufacturer and jobber. The paper explains the theoretid background and the important tool and process details. Cop
6、yright O 1996 American Gear Manufacturers Association 1500 King Street, Suite 201 Alexandria, Viginia, 22314 October, 1996 ISBN: 1-55589-669-3 STD-AGHA bFTfl2-ENGL 1996 m Ob87575 0004848 45T m The New Way of Manufacturing Bevel and Hypoid Gears in a Continuous Process Dr. Hermann J. Stadtfeld Vice P
7、resident Research 8 Development The Gleason Works, Rochester, New York i. Introduction In 1920 James E. Gleason and Arthur L. Steward received a patent on a method and the machine to cut face hobbed gears using face cutter heads. Todays machining processes for face hobbing are still based on this 80
8、 year old idea. Until 20 years ago only face milling, (single indexing method) was used for the tens of thousands of gears produced daily in the automotive industry. Face hobbing (continuous indexing) was only used by a few gearbox manufacturers. Even the advanced continuous methods were always 1 O
9、years behind the single indexing process in their innovative steps like controlled flank crowning or non-generating of the ring gears. More attention has been paid to face hobbing in the last decade. The CNC technology made a quantum step especially for the continuous method. Parallel to the CNC tec
10、hnology a new method of face hobbing was subsequently developed and today is introduced as the different and new way of face hobbing. different in design than regular cutter heads and enabic .-I highly economical procedure of roughing and finishing . chucking. The process kinematic was complets ; re
11、designed, benefiting from the free form concept todays cutting machines. If lapping is not sufficient or desired as a finish? process, a skiving operation with carbide tools can k? applied. The skiving uses identical machines and CU% heads, the only dtfference being that the blade sticks ai. from sp
12、ecial ultra fine grain carbide. The new method - even supported by the fast, numerically contra!;. building of cutter heads to a high accuracy. All the aspects of precision, flexibility and economy mat: the new face hobbing also popular for the gearbr manufacturer and jobber. This paper explains t!
13、I; theoretical background and the important tool a if process details. The basis is a new gear theoreticai approach to design the blanks, the ease off and contact. The tools are -1 - STD.AGMA SbFTM2-ENLL 1996 m Ob87575 0004849 39b m 2. Face Hobbing, a Continuous Bevel Gear Cutting Method The continu
14、ous indexing method requires a second rotational coupling (electronic gear box) between the cutter head rotation and the workpiece rotation. For this reason the method is also called three axis process. Figure 1 shows the orientation of the blade groups on a cutter head (right side of figure). On th
15、e left side of Figure 1, the single indexing method for comparison is shown l. Face Milling Method Face Hobbing Method I outside biade -+ :*,I ,. -_.- 6. cutter rotation _/- -.-_- - Figure 1: Configuration and motions of single indexing versus continuous indexing 3. Advantages of Face Hobbing t The
16、epicyclical shape of the flank in the face-width direction makes a face hobbed gearset less sensitive to bending of the pinion shaft and deflection of the gear housing. Those deflections in most cases cause a misalignment of the spiral angles between pinion and gear where the reaction of the contact
17、 is a length movement toward the heel. For an epicyclicai function, the spiral angle increases more between toe and heel compared to a circular function. The curvature radius is smaller at the heel than at the toe. The relative movement between pinion and gear flank provides the higher radius of cur
18、vature of the pinion flank to contact the lower radius of curvature of the gear flank (drive side), which counteracts the movement of the contact from center to heel. The profile movement of the contact under deflections or misalignment caused by tolerances follows about the same rules as for face m
19、illed gears. Wrong adjustment of the backlash was detected to have a sensitive impact to the rolling sound and the contact. This has to do with the relatively long bias in contact pattern which is commonly applied to face hobbed gears (Figure 2, lower graphic). Using the same amount of length crowni
20、ng and some amount of profile crowning delivers a “natural“ kind of bias in for face hobbed gears with the appearance of a longer contact. This has to be compared (Figure 2, upper graphic). However, the adjustment of the backlash gets simplified by the fact that face hobbing is a completing operatio
21、n with proper tooth thickness without stock Each blade group Of a IAC cutter head has Only two with the short high bias bearing of a faCe milled gear blades, one outer blade and one inner blade. While one blade group passes through a slot, the work gear rotates in the counter direction of the cutter
22、. This relative motion produces an epicyclical function along the face width of the work gear. After the blade group leaves the slot, the trials. next blade group enters the next slot. The ratio between the cutter head and the gear must be the number of teeth of the work divided by the number of sta
23、rts (blade groups) of the cutter head. In the generation process, the roll motion is used as cutting feed. This roll is very slow compared with the face milling process. Since face hobbing takes chips on tooth after tooth in about the same roll position, the roll motion can be slower (by the number
24、of teeth of the work gear), and still have about the same cutting time as face milling. . Face hobbed gearsets deliver generating flats which are optimally suited for an efficient lapping process with a quality result. The contact lines and the generating flats of face hobbed flanks have a significa
25、ntly different angular position. Lapping compound is pumped through the contact area of face hobbed gears. In addition to a reduction in lapping time on face hobbed gears versus face milled gears, also a non-wavy surface finish is developed; although the generation marks are higher in peak to peak m
26、agnitude than the comparable marks of a face milled gear. Figure 3 shows the contact lines between pinion and gear as thin single lines. The generation flat for face milling is shown as double line which matches the contact lines from shape and angle. -2- STD-AGMA 7bFTM2-ENGL L77b 111 Ob87575 OOOY85
27、0 O08 = * Figure 3 displays a face hobbing generating flat as a long double line which intersects the contact lines under an angle of about 25“. The resulting surface structure of generation flats after lapping may act as oil pockets and pump oil through the contact even in critical operating condit
28、ions, where the oil film is wiped-off from a face milled flank pair. This, together with the forgiveness in the case of high load deflections, can explain the good behavior of face milled gears in extreme situations. Face hobbing is very flexible and universal. It is used in the generated method, wh
29、ere pinion and gear flanks are formed in the generation process and in the FORMATE method. The ring gear member is produced by plunging in and the pinion is generated with a special tilted cutter head. Both generated and non-generated pairs are available as spiral bevel gears orwith a hypoid offset.
30、 Single indexing philosophy coast side Ease - On Continuous indexing philosophy contactpattern root 133 toe heel root Figure 2: Typical results of tooth contact analysis, face milling (top) and face hobbing (bottom) Figure 3: Contact lines and generating marks, face milling and face hobbing -3- STD-
31、AGHA SbFTM2-ENGL 297b W Ob87575 0004852 T44 Drive 4. Design and Analysis coast The Gleason face hobbing, of course, is based on a uniform tooth depth. This simplifies the design calculation dramatically because of the conjugate surface pairs of pinion and gear flanks and provides, together with the
32、epicyclical tooth . length-form the advantages of face hobbed gearsets. The differences between the uniform tooth depth and the tapered tooth depth is visualized in Figure 4. The areas, like undercut and sharp topland do not appear as critical in face hobbing as they would in face milling, using a u
33、niform depth tooth. However, undercut influences in face hobbed pinions are very usual and accepted. To prevent sharp pinion toplands a secondary face angle is employed if necessary 2. The basic design calculation employs cutter head tilt to produce length crowning and uses curved blade profiles to
34、get profile crowning. In addition, cutter head tiit is used to match a pinion with a non-generated gear and to develop a flank twisting or mesh crowning, which is needed to realize the desired displacement characteristic of a gear set. Figure 5 shows the results of a TCA and Ease Off calculation usi
35、ng cutter head tilt and curved blades. The contact bearing in Figure 5 has a common bias in orientation and the Ease Off shows usual crowning values for a pick up truck size face hobbed gear set. Ease On , Drive Heel Tooth Contact Analysis TW Heel TOe Motion Graph Toe TIA Figure 5: Tooth contact ana
36、lysis results of a face hobbing gearset Figure 4: Uniform depth tooth compared and tapered In addition to the optimization abilities of the cutter head tilt the Gleason face hobbing method allows operation depth tooth The calculation for face hobbing allows use of the same features as are available
37、for face milling. A calculation of the tooth contact analysis (TCA) is standard as is the undercut calculation, the loaded tooth contact analysis (LTCA) and the finite element stress calculation. Also for optimizations and corrections, tools like coordinate measurement of real gears compared with th
38、eoretical flank surfaces and correction with Gleason G-AGE offer unlimited possibilities. with all the higher order motions that a CNC free-fonn machine offers. The Ease Off optimization with interactive software gives the opportunity to change and modify each point of the Ease Off. The mathematics
39、working in the background superimposes all available motions to realize the desired correction. This utilization of free-form machine motions is called Universal Motion Concept (UMC). These motions are roll position dependent, using a continuous change of the tilt angle, cutter eccentricity and mach
40、ine root angle. With the face hobbing process of -4- STD-AGHA SbFTM2-ENGL L9Sb D Ob87575 0004852 980 = 1 the past, fine tuning of gear sets with the intent of noise the cutter body and outer ring. Figure 6 shows how the reduction, was almost more difficult than in the face milling method. A reason w
41、as the limited number of freedoms “to catch the last micron“. With the higher order motions, an entire variety of freedom is available to apply to the face hobbing method. dovetail is arranged around the cutter body, integrated into the webs. The outer ring is designed from two pieces which are conn
42、ected with one bolt at each web. The internal dovetail is machined oversize relative to the outer dovetail. The amount of oversize is exactly defined to create a sufficient compression in the dovetail clamp to prevent slipping of the outer ring in all operating conditions. 5. Face Hobbing Cutter Hea
43、d The Gleason Face Hobbing method uses TRIAC cutter heads with stick blades. Todays cutter heads are completely redesigned tools of the second generation. The outer ring of an older style cutter is welded to the webs of cutter body; which presents a number of disadvantages. Welding causes stresses w
44、hich are relatively high due to the complicated slot design of cutter heads. Since cutter body and outer ring are both from case-hardened steel and welded together, extreme stress is created during cutting in this critical parts. Figure 6: New TRIAC cutter head body with ring shaped dovetail The int
45、ernal stresses caused from the welding operation become reduced during the cutting of gears. On the one hand, this leads to a reduction of the position accuracy of the blade slots; one the other hand, it causes a high danger of creating cracks along the welding between cutter body and outer ring. Cr
46、acks can appear especially in cases of overload or other disturbances. The new cutter head design which is presented in this paper, has a ring-shaped dovetail combination between Figure 7: Two part outer clamp ring The amount of compression is limited to a value which does not deliver any buckling o
47、f the webs. Figure 7 shows the two parts of the outer ring with the internal dovetail. The connection between the outer ring and the cutter body provides an excellent dampening behavior which guarantees a smooth and quiet cutting operation as well as an improved surface finish of the produced gears.
48、 In comparison to an old style cutter, the new TRIAC cutter head has an outer ring with an increased width of 150%. The conventional blade clamp block cannot be used anymore due to the increased width of the ring. The use of two damp screws per cutter blade is not acceptable because it leads to incr
49、eased cutter building times and less runout precision of the cutting edges. The solution to the blade clamping problem is the use of a newly developed clamp block design. This clamp block is shaped like a leaf spring (Figure 8, bottom). The clamp screw contacts the arched block somewhat asymmetrically (not shown in Figure 8) which provides a higher clamp pressure towards the front of the cutter head. Torquing of the clamp screw is finished when the arched clamp block reaches a straight shape. At this very -5- STD-AGHA SbFTH2-ENGL L
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