Machining Operations by Ed Red Objectives Introduce machining operations terminology

Variables: Th - part handling time Co (Cg) – operator (grinder’s) cost rate/min

Tm – machining time Ch – cost of part handling time

Tt – tool change time Cm – cost of machining time

np – number of parts cut by Ctc – cost of tool change time tool during tool life

Tc – cycle time per part Ct – cost per cutting edge

T – tool life Ctp = Ct/np - tool cost per part

• Maximum production rate - turning

• Total time per part produced (cycle time):
• Tc = Th + Tm + Tt/np
• where Tt/np is the tool change time per part.
• Consider a turning operation. The machining time is given by
• Tm =  D L/(v f)
• The number of parts cut per tool is given by
• np = T/Tm= f C(1/n)/( D L v(1/n -1) )

• Maximum production rate - turning

• Substituting, we get the total cutting time
• Tc = Th +  D L/(v f) + Tt[  D L v(1/n -1)/( f C(1/n) )]
• Minimizing cycle time (dTc/dv = 0 ) gives optimum (max) cutting speed and tool life:
• vmax = C/[(1 - n) Tt/n]n
• Tmax = (1 - n) Tt /n

• Minimum cost per unit - turning

• Cost of part handling time:
• Ch = CoTh
• Cost of machining time:
• Cm = CoTm
• Cost of tool change time:
• Ctc = CoTt /np

• Minimum cost per unit - turning

• Tool cost per part:
• Ctp = Ct /np
• Tooling cost per edge:
• Disposable inserts Ct = Pt /ne ne = num of edges/insert Pt = original cost of tool
• Single point grindable Ct = Pt /ng + Tg Cg “includes purchase price” ng = Num tool lives/tool Tg = time to grind tool

• Minimum cost per unit - turning

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