16736164-Machining-Theory - 1 Curtin University of...

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Unformatted text preview: 1 Curtin University of Technology Department of Mechanical Engineering Industrial Technology 342 Machining Theory Overview A brief history of metal cutting process and its investigation can be found in ‘The Mechanics of Machining” by Armarego and Brown, researcher of tool performance which gave rise to the understanding of the cutting process started about the beginning of the 20 th Centaury. The principle cutting tool material used at this time was high carbon steel. However, tool steel was introduced in the early part of this centaury which vastly improved the performance of the cutting tools, enabling them to be used at higher cutting speeds and have a longer tool life. Today modern cutting tools have progress enormously increasing their cutting speeds and tool life, due to the materials being used and a better understanding of the cutting parameters. The tool parameters and the material that is being machined are all shown to have a significant influence on the tool tip temperature. This rise in tool tip temperature is shown to be the main cause of tool failure as it promotes the wear mechanisms in the tool material. The primary source of heat generation during the cutting operation is due to the shearing of the material, with a secondary source being due to friction as the chip passes over the tool face as shown in Figure 1. Figure 1: Primary source of heat generation during machining. The normal metal removal conditions for cutting tools used in the workshop is oblique machining as shown in Figure 2. this is a complex machining process due to the shape of the cutting edge which resulting in a complex analyse. 2 Figure.2: Oblique machining showing width of metal being removed. However, the cutting theory analysis normally considered by researchers is orthogonal machining, as this simplifies the cutting process as shown in Figure 3. For this reason, orthogonal theories will be used for the analysis of the machining process.. Figure 3: Orthogonal machining showing width of metal being removed. In orthogonal machining, the cutting edge of the tool is set perpendicular to the direction of the cutting, and parallel to the surface being machined as shown in Figure 4. Also, the tool must overlap the cutting surface such that the metal removal is only done on the primary surface. If the width of cut is very much larger than the depth of cut shown in Figure 2.5 t 1 < w , then the flow of the material approximates to that of plane strain, that is the flow is in two directions only. 3 Figure 4:Configulation for orthogonal cutting showing width of metal being removed w, chip thickness before cutting t 1 and chip thickness after cutting t 2 . Under certain conditions on the lathe the cutting processes can be considered approximately as orthogonal. These conditions are: the feed must be small relative to the depth of cut, making most of the cutting taking place in the direction of the feed, and the cutting on the nose of the tool will be negligible. Mikell P. Groover and the cutting on the nose of the tool will be negligible....
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16736164-Machining-Theory - 1 Curtin University of...

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