1、01FTM1Carbide Hobbing Case Studyby: Y. Kotlyar, Bodine Electric CompanyTECHNICAL PAPERAmerican Gear ManufacturersAssociationCarbide Hobbing Case StudyYefim Kotlyar, Bodine Electric CompanyThestatementsandopinionscontainedhereinarethoseoftheauthorandshouldnotbeconstruedasanofficialactionoropinion of
2、the American Gear Manufacturers Association.AbstractIn todays global economy, there is more and more pressure from the developing counties to produce gearsat agreaterefficiently and atalower cost. Carbidehobbing seemsas oneof thetechnological innovationsthat could give both theproductivity thus furt
3、her increasing cycle times and reducing productivity. On average, there was less than one setup per machine per day. The inexpensive conventional off-the-shelf “square” hobs had to be re-sharpened quite frequently, thus disrupting production flow. Lean manufacturing stresses the importance of JIT ma
4、nufacturing and continuous reduction of WIP. This leads to smaller lot sizes and greater setup frequency per day. 4 In summary, we had an abundance of opportunities. Quality improvements Process capability improvements Further tightening of the tolerances to produce a higher quality product Producti
5、vity improvements Reduce cycle times and increase production with the same number of people Reduce setup time Reduce process debugging time Cost improvements Cost reductions as a result of productivity improvements Lower cutting tool cost per gear or keeping it the same as HSS Reduction in rework co
6、st Additional Capacity Skiving Capabilities Reduction in outsourcing 2. Considerations for new technology We couldve benefited by improving the process in small incremental changes. Some examples are reworking the machines, buying better cutting tools, improving the fixtures, buying better blanks, a
7、nd even stressing greater control of our processes. These wouldve all brought some semblance of success. Nonetheless, we felt that we needed drastic, rather than incremental, improvement to bring the process under control and achieve cost reduction. This is why we decided to blow up everything, inve
8、stigate new carbide hobbing technology, and bring a new spirit into the factory. At the same time, we wanted to bring in technology that would work from the onset. We wanted to be conservative in our estimates; making sure that there would not be excessive process debugging. So we decided that a tes
9、t would be the ideal first step into a successful implementation of new carbide hobbing technology. 3. Hobbing Test Test Objectives. To learn more about potential challenges To understand the pros and cons of carbide hobbing as applicable to our pitch and size ranges To have the process debugged pri
10、or to purchasing the machine To specify the machine acceptance criteria based on challenges experienced during testing To compare machine suppliers To start a process of developing carbide hobbing support systems We anticipated a need for a better engineering support systems as well as a simpler, mo
11、re disciplined, process monitoring system that would give us a reliable feedback. We knew that after the major investment, the flat gear cell would be scrutinized under a microscope. Test Findings what was the best coating for our application; what was the optimum wear; what were the sharpening nuan
12、ces (i.e. edge preparation); when was the right time to strip the coating and was it possible; what was the hob life and tool cost per gear; and was there any predictability in carbide hobbing? NDP ODToothed length # gashes # startsAxial Pitch LA# cutting edgesHandTypeCurrent Total/Sharpening88964 6
13、25Material SupplierOrigin al coatingTotal Accum. # gears20 1.875 2.650 12 1 0.157 1.61 142 LHFinish Non-TopTarget Total/Sharpening35591 250 Carbide KGPHCTFurura TiAlN12127Hobbing Start Hobbing End Material Removal Hob SharpeningDateSetup Person Gear # DateSetup PersonNo. Gears madeDamage NoteGear fa
14、ceNo of teethHelix AnglePer Setup, inchPer sharpening, inchInch per Cutting edgeDate SentCompany NameTooth thickness beforeTooth thickness afterNew CoatingDate Received10/25/99 1103 26300026 10/26/99 1103 765 0.503 38 18.18 15391 15391 10811/1/99 2331 26301180 11/01/99 2331 78 0.505 48 18.18 1990 17
15、381 12211/5/99 2331 26300026 11/05/99 1103 768 0.503 38 18.18 15451 32832 23111/30/99 2331 26300026 12/02/99 2331 782 0.503 38 18.18 15733 48565 34112/2/99 2331 26301180 12/02/99 Walter 246 0.505 48 18.18 6276 54841 385 12/8/99 GPHCT2 0.272 0.265 TiAlN 12/23/992/9/00 1130 26301180 02/09/00 1130 238
16、0.505 48 18.18 6072 6072 433/28/00 1130 26330828 03/28/00 1130 104 0.605 54 16.27 3539 9612 684/24/00 1103 26300026 04/24/00 1130 770 0.503 38 18.18 15491 25103 1764/29/00 2331 26330136 04/29/00 2331 296 0.505 48 18.18 7552 32655 2295/11/00 1130 26300026 05/11/00 1130 724 0.503 38 18.18 14566 47221
17、3325/17/00 1130 26300026 05/18/00 1103 720 0.503 38 18.18 14485 61707 4336/6/00 1103 26300026 06/06/00 WALTER 724 0.503 38 18.18 14566 76273 5367/5/00 walter 26330136 07/05/00 walter 288 0.505 48 18.18 7348 83621 5877/8/00 walter 26300026 07/08/00 2331 748 0.503 38 18.18 15049 98669 6937/24/00 2331
18、26300026 07/24/00 1620 720 0.503 38 18.18 14485 113155 795 7/27/00 GCT2 0.263 0.248 TiAlN 08/11/0010/30/00 dan 26300026 10/30/00 Walter 486 0.503 38 18.18 9778 9778 6911/10/00 dan 26300026 11/10/00 Walter 490 0.503 38 18.18 9858 19636 13811/16/00 dan 26330136 11/16/00 dan 236 0.505 48 18.18 6021 256
19、57 18011/22/00 dan 26300026 11/27/00 Walter 964 0.503 38 18.18 19394 45052 31612/12/00 walter 26300026 12/13/00 dan 484 0.503 38 18.18 9737 54789 3852/12/01 2331 26300045 02/12/01 Walter 214 0.299 32 28.35 2327 57116 4013/8/01 dan 26301180 03/08/01 Walter 994 0.505 48 18.18 25361 82477 5793/12/01 da
20、n 26300026 03/12/2001walter 150 0.503 38 18.18 3018 85494 6013/12/01 walter 26301143 03/12/01 walter 112 0.505 48 21.03 2909 88403 6213/12/01 walter 26300027 03/12/01 Walter 26 0.503 40 21.03 560 88964 62510 Here is an example of one of the many challenges that we experienced. Coating fractures can
21、contribute to poor hob performance. Coating on the illustration is breaking away from the tool. Close inspection within these areas exhibit multiple coating layers that chipped on the outer surface, while the lower coating layers have remained intact. Layer Buildup. Each coating is approximately .00
22、04”. Top layer is AlNite coating, a single layer of TiAlN. Two layers of Futura coating, each 27 to 35 alternating sub layers of Titanium Nitride (TiN) and Titanium Aluminum Nitride (TiAlN). Yellow lines between layers is TiN. Light colored substrate is near the bottom. We have yet to find overall c
23、onsistency in hob performance. Although, the greatest performance factor is probably how people use the hobs, other contributing factors are sharpening, coating quality, and the ability of the coating layers to stick to the previous layer. Toothed length # gashes# startsAxial Pitch LA# c utting edge
24、sHandTypeCurrent Total/S harpening47916 217MaterialSupplierNote: Serial # 003O riginal coatingTotal A ccum. # gears2.625 12 1 0.112 1.13 221 RHFinish TopTarget Total/S harpening55174 250Carbide KGPHCT OKFutura TiAlN15781Start Hobbing End Material Removal Hob SharpeningGear # DateSetup PersonNo. Gear
25、s madeDamage NoteGear faceNo of te e thHelix AnglePer Setup, inc hPer sharpening, inchInch per Cutting edgeDate SentCompany NameTooth thic kness beforeTooth thic kness afterNew CoatingDate Received26300067 10/26/99 1620 434 0.177 45 0 3457 3457 1626300078 10/27/99 1103 144 0.465 42 0 2812 6269 28263
26、00065 1/10/00 2331 768 0.538 52 0 21486 27755 12626322005 1/15/00 2331 1083 0.185 35 0 7012 34767 15826300069 1/17/00 2331 304 0.177 41 0 2206 36973 16826300066 1/24/00 2331 650 0.177 47 0 5407 42381 19226300078 1/27/00 1130 148 0.465 42 0 2890 45271 20526300018 1/27/00 1620 414 0.148 52 22 3431 487
27、02 22126300024 1/28/00 2331 360 0.299 55 19 6278 54981 24926300071 2/3/00 1130 318 0.177 35 0 1970 56951 25826322005 2/28/00 2331 720 0.185 35 0 4662 61613 27926300023 3/9/00 2331 1100 0.299 52 22 18418 80031 36326300024 3/9/00 2331 366 0.299 55 19 6383 86414 39226300018 3/9/00 1620 408 0.148 52 22
28、3381 89795 407 3/22/00 GPHC 0.261 0.256 TiAlN 4/6/0026300065 5/16/00 1130 384 0.538 52 0 10743 10743 4926300069 5/16/00 walter 434 0.177 41 0 3150 13892 6326300065 6/1/00 walter 388 0.538 52 0 10855 24747 11226300065 6/8/00 walter 384 0.538 52 0 10743 35490 16126322005 6/14/00 JERRY 742 0.185 35 0 4
29、804 40294 18326300065 6/26/00 2331 400 0.538 52 0 11190 51485 233 6/26/00 GPHC 0.256 0.247 TiAlN 7/14/0026300078 8/1/00 2331 288 0.465 42 0 5625 5625 2526300023 9/11/00 walter 726 0.299 52 22 12156 17780 8126300066 9/12/00 DAN 216 0.177 47 0 1797 19577 8926322005 9/21/00 walter 724 0.185 35 0 4688 2
30、4265 11026300066 9/27/00 walter 222 0.177 47 0 1847 26112 11826300078 10/2/00 DAN 576 0.465 42 0 11249 37361 169 10/10/20 GCTC3 0.247 0.242 TiAlN 2/13/0126322005 2/28/01 walter 366 0.185 35 0 2370 2370 1126300065 3/5/01 walter 484 0.538 52 0 13540 15910 7226322005 3/14/01 DAN 366 0.185 35 0 2370 182
31、80 8326322005 3/16/01 walter 752 0.185 35 0 4869 23149 10511 Every single carbide hob has a history worksheet. Currently, we have over 80 carbide hobs that service our Flat Gear Cell. Every time the hob is used, the setup people record the date, the gear number, and the number of gears hobbed. The r
32、est of the worksheet is calculated automatically. One of the important characteristics is material removal per hob cutting edge. Hob Length Significance. In addition to changing the hob material to carbide, we introduced longer hobs. This further improved the cutting tool cost per gear and reduced d
33、owntime caused by hob changes; since longer hobs make more gears per sharpening. Conventional thinking implies that the improvement would be proportional to the hob length increase. However, in reality, the improvement is proportional to the shifting increase. The graphs show the load and wear distr
34、ibution on short and longer hobs. Short hobs may have little or no shifting length available. Frequently, a small hob length increase can result in hob performance improvements many fold. Cutting Tools Cost Reduction. A conservative estimate of per gear tooling cost reduction is close to three fold.
35、 Hob Cost Per One Gear$0.000$0.050$0.100$0.150$0.200Carbide hobs HSS hobsSharpen. costInitial cost12 5. Support Systems To understand and to maintain the carbide hobbing process, our company introduced a system for monitoring process performance. A setup database was created to include all process d
36、ocumentation; such as fixture, cutting tools, gear parameters, cutting conditions, cycle time and other necessary setup information. For every setup, the database query creates a single sheet of paper with the latest setup information. The original tooling has been expanded to process over180 differ
37、ent parts numbers. Machine part programs are backed up periodically. Fixture and automation change parts are stored in a clearly marked storage area adjacent to the machine. As was mentioned before, every hob has a worksheet with a history of usage, sharpening, and recoating. Performance monitoring
38、production/value-added efficiency Visual scheduling Production monitoring from cell inception. Total Production010002000300040005000600012-Jun19-Jun26-Jun3-Jul 10-Jul17-Jul24-Jul31-Jul7-Aug14-Aug21-AugWeeksTime Allocation0%10%20%30%40%50%60%70%80%90%100%12-Jun19-Jun26-Jun3-Jul 10-Jul17-Jul24-Jul31-J
39、ul7-Aug14-Aug21-AugWeeksNon-Value Added TimeSetup TimeValue Added Time13 6. Improvements Summary Productivity improvements. Major productivity improvements were realized due to three times (3X) higher speed capabilities of carbide hobs. Other factors contributing to the productivity improvements wer
40、e setup time reduction, a CNC control hob travels, more consistent setups & cycle times, a drastic reduction in process debugging time for lead/ involute/runout problems, and precise calculations of hobbing cycles & goal setting. Despite all of the challenges with carbide hobs, the productivity impr
41、ovement made it possible for us to replace (4) machines. In addition, we increased production by in-sourcing all gear hobbing and skiving, with a $280,000 annual volume. Tool cost improvements. Annual Tool Cost Comparison$0$20,000$40,000$60,000Carbide hobs HSS hobsSharpen. costInitial cost2630012626
42、30002626300023263001292632200326300020New Cycle timeCurrent Cy0.000.200.400.600.801.001.201.401.60Hobbing Cycle Time, Minutes14 Annual Scrap$0$10,000$20,000$30,000$40,000$50,000$60,000CNC GearManufacturingMechanicalPinionManufacturingQuality Improvement. Prorated Annual Scrap Saving was $47,000 as c
43、ompared with three mechanical pinion cells using old machines, HSS cutting tools and producing approximately the same amount of parts. Other cost improvements resulted from process capability improvements. The six sigma process variation became smaller than the tolerance due to improving upon all of
44、 the process variables: new machines that were statistically evaluated for the process capability during the runoff, AA quality cutting tools, precision fixtures, better quality blanks, ISO compliant quality systems, and having setup and cutting parameter consistency. The improvements in the process
45、 capability made it possible to reduce the inspection and rework expenses. In closing, the investment into new carbide hobbing technology made us look under the microscope and improve upon other contributing factors that lead to successful gear manufacturing. These are fixtures, machines, cutting tools, blanks, and quality systems. The results are better quality gears at a lower cost. Acknowledgement. The author would like to express his gratitude to Mark Ryba and Paul Ruff for their editing help. 6Sigma
