Minimum Cost OR Component

Minimum Cost OR Component

Minimum Cost OR Component - The following costs are involved in metal cutting:

(i) Machining costs

(ii) Tool costs

(iii) Tool changing costs

(iv)Handling costs.

Finding the theoretical optimum point at which there is a balance of above mentioned four individual costs is the essence (metal cutting economics.

It can he seen that machining cost decreases with increasing calling speed.

Both the tool costs and the tool cutting costs are observed to increase, since tools are wearing out faster at the higher cutting speeds. The handling costs are independent of cutting speed.

Machining cost = C_o. t_m

There are two cost factors in this basic model (C_o, C_t) and three time factors (t m, t c, t h), in addition to the tool life factor. Each of these factors will be discussed briefly.

Operating Cost (C_o)

The operating cost equals the sum of the machine operator's rate plus appropriate overhead.

Tool Cost (C_t)

The tool cost is the cost of the insert price and a prorated cost per cutting edge of the complete tool holder and any other parts such as chip breakers, shim seats, clamps, screws, etc. If regrindable tooling is used, the tool cost is a function of the tool price, the total number of cutting edges in the life of the tool, the grinding time per cutting edge, the tool grinder's rate, and the tool room overhead rate.

Machining Time (t_m)

The machining time is the time in minutes that the tool is actually cutting. The time may be calculated by dividing the length of cut by the velocity with which the tool moves in the feeding direction:

t_m = L/f.N

L = the axial length of the cut

f= the feed ipm (inch per minute)

N = rpm.

Tool Changing Time (t_c)

The tool changing time is the complete cycle in minutes to remove a tool that has failed and replace it or index it, reset for size, and be ready for the next cut.

Handling Time (t_h)

The handling time is the time in minutes required to load and unload the workpiece from the machine. It includes the idle time and time necessary to advance and retract the tool.

Tool Life Factor

Tool life is taken from Taylor's equation, VTⁿ = C. The average tool life (T) in minutes per cutting edge is:

T = [C/V]^1/n.