lacnhceTrrub f toiiataDhgeHs・tcudorP（Time）（10 thousand shots）SKD11SKH51SKH40SKD11＋TiCN coatingSKH51＋TiCN coatingSKH40＋TiCN coating●Estimated maintenance time：8 hours/time.●Work rate（%）＝Theoretical production time÷（Theoretical production time＋Maintenance time）●Unit punching cost ￥3，000／Estimated time※4：Take SKD11 as the standard.Quality control is applied according to the height limit of burr. And the height limit is assumed as 50μm （10% of the plate thickness）. With the increase of the height （Diagram1,2,3）, burrs will go beyond the limit. If no maintenance is applied, the punching shots that a set causes burrs between 50μm and 60μm are listed in Table 4. According to the comparison of punches with・without coating, the features are listed as follows. ・ For punches without coating, the punching shots of different materials don’t differ much. Because the height of burr exceeds the limit in the initial phase, the punch materials are not wearable （Drawing 5）. During the stationery phase, the difference of punch materials will appear gradually. ・ For punches with coating, the punching shots of different materials differ greatly. Because coating is applied on the surface, burrs are controlled well, and they will not exceed the limit even after the initial phase. On the other hand, the wearability of different punch materials is different. And during the stationary phase, burrs will exceed the limit when different punching shots are applied. Base on this, the work rate is available in continuous production. When 1 million, 2 million and 3 million are taken as standard amounts of continuous production, the punching cost can be figured out, and the cost variance is available when taking SKD11 as standard. For the coating punches that can bring more punching shots, maintenance cost can be reduced, and the production amount （cost variance） is increased. Compared to cost variance, the cost of coating is much cheaper, and this can be used as the standard for punch selection. Visible difference between No difference between punch materialsWear at the initial phasepunch materials ShotsStationary phaseConsiderationTable 4 Punching shots of a batchType of punchSKD11SKH51SKH40SKD11＋TiCN coatingSKH51＋TiCN coatingSKH40＋TiCN coatingProduction amount 1 millionType of punchProduction Work rate 70% 70% 70%100%100%100%time808080565656 ShotsMachining timeComparison※4 27 31 33120140160151718677889Standard1.11.24.45.25.9Table 5 The improvement of work rate and stamping costProduction amount 2 millioncostStamping Cost variance240,000Standard240,000 0240,000 0168,000－72,000168,000－72,000168,000－72,000Work rate66%70%70%93%93%93%Drawing 5 The relationship between height of burr and punch materialProduction Stamping costtime167159159119119119Cost varianceWork rate65%70%70%91%91%95%501,000Standard477,000－ 24,000477,000－ 24,000357,000－144,000357,000－144,000357,000－144,000Production amount 3 millionProduction time255239239183183175costStamping Cost variance765,000Standard717,000－ 48,000717,000－ 48,000549,000－216,000549,000－216,000525,000－240,0001115
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