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PowerPoint to accompany

Krar • Gill • Smid

Technology of Machine Tools6th Edition

Operating Conditions

and Tool Life Unit 30

30-2

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

30-3

Operating Conditions

• Three operating variables influence metal-removal rate and tool life– Cutting speed– Feed rate– Depth of cut

30-4

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

30-5

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

30-6

Reduction in Tool Life

Operating Conditions

CUTTINGSPEED + 50%

FEEDRATE + 50%

DEPTH OFCUT + 50%

90% 60% 15%

30-7

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

30-8

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

30-9

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

30-10

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