Tool Wear And Failure Analysis
Tool Wear and Failure Mode - Figures show the development of tool wear for Tool A and Tool B respectively at various cutting speeds; 50, 60 and 70m/min. It was found that the tool wear rate for Tool B grow gradually when compared with Tool A. All the drills experienced a premature failure under 1 minute of cutting time. As a result, fewer holes were produced when using Tool A. Tool A experienced breakage when direct drilling after the 2nd hole at cutting speed of 60m/min. At 70m/min, rapidly breakage occurred after drill the 1st hole. Unlike Tool A, Tool B exhibited a lower tool wear rate as shown in Figures. It can be seen that initially the flank wear grew steadily and increased as drilling continues. Non-uniform flank wear and micro chipping
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The applications of special drill bits, step drilling, pilot hole, back- up plate and various non-traditional machining methods have been reviewed. The special drills show different level of the drilling thrust force varying with the feed rate. The special drill bits can be operated at larger feed rate (namely shorter cycle time) without delamination damage compared to the twist drill. The results well explain the wide acceptance of these tools in industry. The step drill and pilot hole reduce the central material removal, which particularly cancels the contribution of chisel edge to the thrust force in the case of a twist drill. The resulted reduction of drilling thrust therefore significantly avoids the delamination. The back-up plate supports the last laminae and prevents the deformations from leading to exit delaminations. The drilling process then allows for larger critical thrust force and can be operated at larger feed rate free of delamination damage. The non-traditional drilling methods reviewed in this article possess various characteristics. Waterjet in general makes holes fast and fine for medium to large diameter by contour cutting. The initial investment is however high. Ultrasonic machining provides very good quality, while its production rate can only be justified in multihole process. Laser cutting is satisfactory when the concerns of heat affected zone, release of particles and fumes are properly treated. EDM cuts an electrical conductor, while ECSM can handle non- conducting
The applications of special drill bits, step drilling, pilot hole, back- up plate and various non-traditional machining methods have been reviewed. The special drills show different level of the drilling thrust force varying with the feed rate. The special drill bits can be operated at larger feed rate (namely shorter cycle time) without delamination damage compared to the twist drill. The results well explain the wide acceptance of these tools in industry. The step drill and pilot hole reduce the central material removal, which particularly cancels the contribution of chisel edge to the thrust force in the case of a twist drill. The resulted reduction of drilling thrust therefore significantly avoids the delamination. The back-up plate supports the last laminae and prevents the deformations from leading to exit delaminations. The drilling process then allows for larger critical thrust force and can be operated at larger feed rate free of delamination damage. The non-traditional drilling methods reviewed in this article possess various characteristics. Waterjet in general makes holes fast and fine for medium to large diameter by contour cutting. The initial investment is however high. Ultrasonic machining provides very good quality, while its production rate can only be justified in multihole process. Laser cutting is satisfactory when the concerns of heat affected zone, release of particles and fumes are properly treated. EDM cuts an electrical conductor, while ECSM can handle non- conducting