Determine a weekly production output of the shop and b whether this represents the weekly plant capacity... Manufacturing Lead Time A certain part is produced in batch sizes of 100 uni
Trang 1Vi du tham khao:
CACTI
A small machine shop has two machines and works 40 hr/wk During a week
of interest, four batches of parts were processed through these machines Batch quantities, batch times, and operation sequences for the parts are given
in the table below Determine (a) weekly production output of the shop and
(b) whether this represents the weekly plant capacity
A 25 pe/hr 12 hr 30 pc/hr 10 hr
Trang 2Loi giai tham khao:
(a) To determine the weekly production output, the fj; values are determined
as follows, given 40 hr per week: fi, = 12/40 = 0.30, fig = 20/40 = 0.50, hha = 10/40 = 0.25, fac = 24/40 = 0.60, and fon = 6/40 = 0.15 The fraction of idle time on machine 1 is = 8/40 = 0.20 Noting that part A has
2 operations in its operation sequence and the other parts have 1, the hourly production rate of parts completed in the plant is given by Equation (3.13):
Roph = ost + 0.5(10) + one") + 0.6(7.5) + 0.15(20) = 20 pc/hr
Weekly production output ®%„„„ = 40(20) = 800 pc/wk
(b) Machine 2 is operating the full 40 hr/wk Given the part mix in the problem, machine 2 is the bottleneck in the plant, and so the 800 pc/wk represents plant
capacity: PC,, = 800 pc/wk
Comment: Machine 1 is only operating 32 hr/wk, so it might be in- ferred from the situation that the production of part B could be increased by
80 units (8 hr < 10 pc/hr) to achieve a plant capacity of 880 pc/wk The question
is whether there would be a demand for those 80 additional units of part B
Cau 2:
Vi du tham khao:
EXAMPLE 3.3 Manufacturing Lead Time
A certain part is produced in batch sizes of 100 units The batches must be routed through five operations to complete the processing of the parts Average setup time is 3.0 hr/batch, and average operation time is 6.0 min/pc Average nonoperation time is 7.5 hr for each operation Determine the manufacturing lead time to complete one batch, assuming the plant runs
8 hr/ day, 5 days/wk
Solution: Given T,,, = 3.0hr and T,, = 7.5 hr, the manufacturing lead time for this
batch is computed from Equation (3.20), where the symbol j refers to the fact that only one part style is being considered
MLT, = 5(3.0 + 100(6.0/60) + 7.5) = 5(20.5) = 102.5 hr
At 8 hr/day, this amounts to 102.5/8 = 12.81 days
Trang 3Công thức áp dụng để giải câu a:
® Manufacturing lead time (MLT): the total time required to process a given part or product through the plant, including any time due to delays, parts being moved between operations, time spent in queues, and so on
MLT, =
MLT; = manufacturing lead time for a batch of part or product j, min;
Tu = setup time for operation i on part or product j, min
Q; = quantity of part or product jin the batch
T,, = cycle time for operation i on part or product j, min/pc
Throw = NONOperation time associated with operation ¡, min
Công thức áp dụng để giải câu b:
= R,; = production rate of machine i when processing part
J, pc/hr
= |; = average production time for part j on machine /, min/pc
= | = setup time for part j on machine ¡, min/batch
= Q = batch quantity of part j, pc/batch
Trang 4i nn ct
Vi du tham khao:
3.5 Manual versus Automated Production
Two production methods are being compared, one manual and the other automated The manual method produces 10 pc/hr and requires one worker
at $15.00/hr Fixed cost of the manual method is $5,000/yr The automated method produces 25 pc/hr, has a fixed cost of $55,000/yr, and a variable cost of
$4.50/hr Determine the break-even point for the two methods; that is, deter-
mine the annual production quantity at which the two methods have the same annual cost Ignore the costs of materials used in the two methods
Loi giai tham khao:
2.4 Manufacturing cost om
FC;
Method 2:
TC, = FC, + VC{Q) automated
TC, = FC, + VC\(Q)
FC,
Solution: The variable cost of the manual method is C, = ($15.00/hr) /(10 pe/hr) ——
= $1.50/pe
Annual cost of the manual method is TC,, = 5,000 + 1.500
The variable cost of the automated method is C, = ($4.50/hr) /(25 pe/hr)
= $0.18/pe
Annual cost of the automated method is TC, = 55,000 + 0.18Q
At the break-even point TC,, = TC,:
5,000 + 1.50Q = 55,000 + 0.180 1.500 — 0.18Q = 1.32Q = 55,000 — 5,000 = 50,000 1.32Q = 50,000Q = 50,000/1.32 = 37,879 pc Comment: It is of interest to note that the manual method operating
one shift (8 hr), 250 days per year would produce 8(250)(10) = 20,000 pc/yr,
which is less than the break-even quantity of 37,879 pc On the other hand,
the automated method, operating under the same conditions, would produce
8(250)(25) = 50,000 pc, well above the break-even point.
Trang 5Cau 4:
Vi du tham khao:
EXAMPLE 10.1 Determining Number of Vehicles in an AGVS
Consider the AGVS layout in Figure 10.14 Vehicles travel counterclock- wise around the loop to deliver loads from the load station to the unload sta-
tion Loading time at the load station = 0.75 min, and unloading time at the
unload station = 0.50 min, The following performance parameters are given:
vehicle speed = 50m/min, availability = 0.95, and _ traffic factor = 0.90
Operator efficiency does not apply, so E,, = 1.0 Determine (a) travel dis- tances loaded and empty, (b) ideal delivery cycle time, and (c) number of vehicles required to satisfy the delivery demand if a total of 40 deliveries per hour must be completed by the AGVS
Loi giam tham khao:
(a) Ignoring effects of slightly shorter distances around the curves at corners
of the loop, the values of Ly, and L, are readily determined from the layout to
be 110 m and 80 m, respectively
(b) Ideal cycle time per delivery per vehicle is given by Equation (10.1):
110 80
de 0.75 + “Sp + 0.50 + 55 = 5.05 min (c) To determine the number of vehicles required to make 40 deliveries/hr,
compute the workload of the AGVS and the available time per hour per
vehicle:
WL = 40(5.05) = 202 min/hr
AT = 60(0.95) (0.90) (1.0) = 51.3 min/hr per vehicle Therefore, the number of vehicles required is
202
no = 5, 3 = 3.94 vehicles
This value should be rounded up to 4 vehicles, since the number of vehicles
‘must be an integer.