机电技术专业英语 教学课件 作者 徐起贺 张庆良pata b lesson Twelve.pptVIP

* 机电技术专业英语 Lesson Twelve Text Rake and Clearance Angles Figure B.6 represents the crosssection through simple metalcutting tool（the direction of cutting is relative, and is obtained either by moving the tool to the left, or the workpiece to the right）. The rake angle controls the chip formation, and is in turn governed by the mechanical properties of the material being cut. MetalCutting Tools Figure B.6 Metal cutting Lesson Twelve Chip Formation Research workers have classified chip formation into tear and shear. Tear involves compression of the workpiece material adjacent to the tool face, so that a crack runs ahead of the cutting tool, and towards the body of the workpiece. The chip is highly deformed, and the workpiece material is relatively underformed. Cutting takes place intermittently, and there is no movement of the workpiece material over the tool face. The Formation of Builtup Edge Builtup edge is associated with continuous chip formation, it is produced by the underside of the chip becoming elongated, and as a result of the combination of high temperature and pressure, some of the chip material becoming welded to the tool face. As cutting continues, the material piles up on the tool face, forming a dome over which the chip flows as it leaves the parent material. The chip movement and pressure cause the dome to become workhardened, so Lesson Twelve that particles of it break away, and become welded to the chip and to the body of the workpiece. As the dome breaks down, some of the tool material breaks away as well, causing a crater to be produced on the tool face. After the breakdown of the dome, the builtup edge forms again. Investigation into Metal Cutting A considerable amount of research work has been done on metal cutting, to study the formation of chips, the forces acting upon the tool, the best shape cutter for a specific job, the economics of tool life, etc. The forces acting upon a tool tip are measured b