Transfer Line Performance A machine tool builder submits a proposal for a 20-station transfer line to machine a certain component currently produced by conventional methods. The proposal states that the line will operate at a production rate of 50 pc/hr at 100% efficiency. On similar transfer lines

Question

Transfer Line Performance
A machine tool builder submits a proposal for a 20-station transfer line to machine a certain component currently produced by conventional methods.
The proposal states that the line will operate at a production rate of 50 pc/hr at 100% efficiency. On similar transfer lines, the probability of station breakdowns per cycle is equal for all stations: p = 0.005 breakdowns/cycle. It is also estimated that the average downtime per line stop will be 8.0 min. The starting casting that is to be machined on the line costs $3.00 per part. The line operates at a cost of $75.00/hr. The 20 cutting tools (one tool per station) last for 50 parts each, and average cost per tool is $2.00 per cutting edge. Determine (a) production rate, (b) line efficiency, and (c) cost per piece produced on the line.

Accepted Answer

(a) At 100% efficiency, the line produces 50 pc/hr. The reciprocal gives the unit time, or ideal cycle time per piece:

[latex]T_{c} = \frac{1}{50}= 0.02 hr/pc = 1.2 min[/latex]

With a station breakdown frequency p = 0.005, the frequency of line stops is
F = 20(0.005) = 0.10 breakdowns per cycle
Given an average downtime of 8.0 min, the average production time per piece is

[latex]T_{p} = T_{c} + FT_{d} = 1.2 + 0.10(8.0) = 1.2 + 0.8 = 2.0 min/pc[/latex]
Actual average production rate is the reciprocal of average production time per piece:

[latex]R_{p} = \frac{1}{2.0}= 0.500 pc/min =30.0 pc/hr[/latex]

(b) Line efficiency is the ratio of ideal cycle time to actual average production time:

[latex]E = \frac{1.2}{2.0}= 0.60 = 60 \%[/latex]

(c) Tooling cost per piece is [latex]C_{t} = (20 tools)(\$2/tool) / (50 parts) = \$ 0.80 /pc[/latex]
Now the unit cost can be calculated by Equation (16.14). The hourly rate of $75/hr to operate the line is equivalent to $1.25/min

[latex]C_{pc} = C_{m} + C_{o}T_{p} + C_{t}[/latex]

[latex]C_{pc} = 3.00 + 1.25(2.0) + 0.80 = \$ 6.30/pc[/latex]

Question 16.2: Transfer Line Performance A machine tool builder submits a p...

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