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Operating Conditions and Tool Life. Unit 30. Objectives. Describe the effect of cutting conditions on cutting-tool life Explain the effect of cutting conditions on metal-removal rates State the advantages of new cutting-tool materials
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Objectives • Describe the effect of cutting conditions on cutting-tool life • Explain the effect of cutting conditions on metal-removal rates • State the advantages of new cutting-tool materials • Calculate the economic performance and cost analysis for a machining operation
Operating Conditions • Three operating variables influence metal-removal rate and tool life • Cutting speed • Feed rate • Depth of cut
Depth of Cut, Feed Rate, and Cutting Speed • Metal-removal rate (MRR) • Rate which metal removed from unfinished part • Measured in cubic inches or cubic centimeters per minute • Change accordingly with each variable (cutting speed, feed, and depth of cut) • Difference can be proven by test piece on lathe
Effects of Changing Operating Conditions • Minimum depth of lathe cut • 10 times rate of feed • After testing variable and effect on tool life • Changes in depth of cut have least effect • Changes in feed rate have greater effect than depth-of-cut changes • Changes in cutting speed of any material have greater effect than either depth-of-cut or feed-rate changes
Reduction in Tool Life Operating Conditions CUTTING SPEED + 50% FEED RATE + 50% DEPTH OF CUT + 50% 90% 60% 15%
General Operating Condition Rules • Proper cutting speed most critical factor to consider establishing optimum conditions • Too slow: Fewer parts produced, built-up edge • Too fast: Tool breaks down quickly • Optimum cutting speed should balance metal-removal rate and cutting-tool life • Choose heaviest depth of cut and feed rate possible
Factors Affecting Production Rate • Inadequate horsepower • Limits metal-removal rate • Surface finish requirements • May limit feed rate • Machine rigidity • May not be sufficient to withstand cutting forces, feed rate and depth of cut • Rigidity of part being machines • May limit depth of cut
Economic Performance • Many factors considered for true cost • Most important factor affecting metal-removal rate is type of cutting tool used • Two factors considered for total machining cost equation • Cost of using cutting tool • Price of cutting tool
Cost of Using the Tool • Ability of cutting tool to remove stock determines production rate and amount of labor to produce part • Tool's ability to remove stock governed by number of times tool must be reconditioned or replaced • Rate cutting tool wears influences how often tool removed and replaced • Tool must be reconditioned and stored in inventory affecting total machining cost