IE 131 Solutions for Problems due Jan 30 (Chs 2 and 3)
2.11
The normal time for a work cycle in a worker-machine system is 6.27 min. For setting the
standard time, the PFD allowance factor is 12%, and the machine allowance factor is 25%. The
work cycle includes manual elements totaling a normal time of 5.92 min, all but 0.65 min of
which are performed as internal elements. Determine (a) the standard time for the cycle and (b)
the daily output at standard performance. (c) During an 8-hour shift, the worker lost 39 min due
to personal time, rest breaks, and delays, and she produced 72 pieces. What was the worker’s
pace on the operator-controlled portion of the shift?
Solution
: (a) Machine time per cycle
T
m
= 6.27 – 0.65 = 5.62 min
Internal normal time
T
nwi
= 5.92 – 0.65 = 5.27 min
T
std
= 0.65(1.12) + Max{5.27(1.12), 5.62(1.25)} = 0.728 + 7.025 = 7.753 min
(b)
Q
std
= 8(60)/7.753 = 61.9 pc (if rounded, 62 pc)
(c) Time worked = 480 – 39 = 441 min
Given that
Q
= 72 pc, then total machine time = 72(5.62) = 404.64 min
Total worker-controlled time = 441 – 404.64 = 36.36 min
Given
T
nw
= 0.65 min, total worker-controlled time at normal pace = 72(0.65) = 46.8 min
P
w
= 46.8/36.36 = 1.287 = 128.7%
2.15
A new stamping plant must supply an automotive final assembly plant with stampings, and
the number of new stamping presses must be determined. Each press will be operated by one
worker. The plant will operate one 8-hour shift per day, five days per week, 50 weeks per year.
The plant must produce a total of 20,000,000 stampings annually. However, 400 different
stamping designs are required, in batch sizes of 5000 each, so each batch will be produced 10
times per year to minimize build-up of inventory. Each stamping takes 6 sec on average to
produce. Scrap rate averages 2% in this type of production. Before each batch, the press must be
set up, with a standard time per setup of 3.0 hours. Presses are 95% reliable (availability = 95%)
during production and 100% reliable during setup. Worker efficiency is expected to be 100%.
How many new stamping presses and operators will be required?
Solution
: Number of setups = 20,000,000/5,000 = 4,000 setups/yr
Setup workload
WL
su
= 4,000(3.0) = 12,000 hr/yr
Cycle time
T
c
= 6 sec = 0.1 min
Production workload
WL
p
= 20,000,000(0.1)/0.98(60) = 34,013.6 hr/yr
Available time for setup
AT
su
= 2,000(1.0) = 2,000 hr/yr per press
Available time for production
AT
p
= 2000(0.95) = 1900 hr/yr
n
=
w
= 34,013.6/1,900 + 12,000/2,000 = 17.9 + 6 = 23.9 rounded up to 24 presses and 24
operators
2.16
Solve the previous problem, except the plant will operate two 8-hour shifts instead of one.
(a) How much money would be saved if each press has an investment and installation cost of