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					Computer Aided Manufacturing


          Machining Operations
•   10 < n < 1000
•   workholding
•   toolholding
•   Feeds and speeds
•   Cutting conventions
•   Machine Types
•   Tolerancing
•   Surface Finish
Computer Aided Manufacturing


             Variety vs Quantity

     Prototyping
     & tooling



                      machining


                                      automation

    1        10      100       1000   10000   100000
Computer Aided Manufacturing


How much time is spent actually
     machining a part?
Computer Aided Manufacturing


                Process Layout
Computer Aided Manufacturing


        Mill-Turn example part




Example part with turned, milled, and drilled features
Computer Aided Manufacturing


                      Mill-Turn




 (1) Turn smaller diameter, (2) mill flat with part in
 programmed angular positions, four positions for square
 cross section; (3) drill hole with part in programmed
 angular position, and (4) cutoff of the machined piece
Computer Aided Manufacturing


              Feeds and Speeds
 Computer Aided Manufacturing


                Machinist Handbook:
                 Aggressive Cuts
The cardinal principle is to always use the maximum feed that conditions will permit.
Avoid, if possible, using a feed that is less than 0.001 inch per tooth because such low feeds
reduce the tool life of the cutter. When milling hard materials with small-diameter end
mills, such small feeds may be necessary, but otherwise use as much feed as possible.
Harder materials in general will require lower feeds than softer materials. The width and
the depth of cut also affect the feeds. Wider and deeper cuts must be fed somewhat more
slowly than narrow and shallow cuts. A slower feed rate will result in a better surface
finish; however, always use the heaviest feed that will produce the surface finish desired.
Fine chips produced by fine feeds are dangerous when milling magnesium because
spontaneous combustion can occur. Thus, when milling magnesium, a fast feed that will
produce a relatively thick chip should be used.
Computer Aided Manufacturing


          Stainless: Tough Stuff!
Cutting stainless steel produces a work-hardened layer on the
surface that has been cut. Thus, when milling this material, the feed
should be large enough to allow each cutting edge on the cutter to
penetrate below the work-hardened layer produced by the previous
cutting edge.
Computer Aided Manufacturing


     Taylors Tool Life Equation
The first comprehensive tool life data were reported by F.W. Taylor
in 1907, and his work has been the basis for later studies. Taylor
showed that the relationship between cutting speed and tool
life can be expressed empirically by:
VTn = C where:
V = cutting speed, in feet per minute
T = tool life, in minutes
C = a constant depending on work material, tool material, and other
machine variables. Numerically it is the cutting speed which would
give 1 minute of tool life.
n = a constant depending on work and tool material.
Computer Aided Manufacturing

This equation predicts that when plotted on log-log scales, there is a
linear relationship between tool life and cutting speed. The
exponent n has values ranging from 0.125 for high speed steel
(HSS) tools, to 0.70 for ceramic tools.

http://web.archive.org/web/20061130091912/http://www.manufactu
ringcenter.com/online_book/chap_3.pdf

				
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posted:3/26/2011
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