Transcript Chapter 6 Batching & Flow Interruptions Setup Times & EOQ

Chapter 6
Batching & Flow Interruptions
Setup Times & EOQ
The Cost Minimizing Order Quantity
Cost
C(Q)
Q
The Impact of Set-ups on Capacity
Production cycle
Batch of 12
Production cycle
Batch of 60
Batch of 120
Batch of 300
60
120
180
240
300
Time
[minutes]
Produce steer supports (1 box holds 12 units = 12 scooters)
Set-up from ribs to steer support
Produce ribs (1 box holds 24 units = 12 scooters)
Set-up from steer support to ribs
Process Analysis with Batching
Capacity calculation changes:
Batch Size
Capacity given batch size 
Setup time  Batch size  Time per unit
Note: Capacity increases with batch size…
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
1/p
10
50
90
130
170
210
250
290
330
370
410
450
490
530
570
610
650
Capacity
Batch Size
… and so does inventory (and thus flow time)
•Common in low volume manufacturing (including a lot of high-tech)
• Also: transportation, education / training
• Creates an inherent mismatch between demand and supply
Batch Flow Operations Carry a Lot of Inventory
Production with large batches
Production with small batches
Cycle
Inventory
Cycle
Inventory
ISedan
Produce Sedan
IWagon
Produce Station wagon
ISedan
Beginning of
Month
End of
Month
IWagon
Beginning of
Month
Movie theater vs. a room full of DVD players
SMED (Single minute exchange of die): reduce set-up times
End of
Month
6.1
Metal window boxes are manufactured in two process
steps: stamping and assembly. Each window box is made of 3
pieces: base A and two side Bs. These parts are fabricated by
a stamping machine with a setup time of 2 hours whenever
switching between the two part types. Once the machine is
set up, the activity time for part A is one minute and for part B
is 30 seconds. The current rotation is 360 As to 720 Bs.
Completed parts move from stamping to assembly once a
batch is complete. At assembly, one A, two Bs and some
purchased parts are required per finished unit. Each product
requires 27 minutes of labor to assemble; there are 12
workers in assembly; there is sufficient demand to sell every
box produced.
What’s the capacity at stamping?
What should the batch size be?
6.3
Consider the following batch-flow process consisting of 3
process steps performed by 3 machines. Work is processed in
batches at each step. Before a batch is processed at a step,
the machine must be set up during which it is unable to
produce. Each machine has a dedicated setup operator.
What is the capacity of step 1 if the batch size is 35?
For what batch sizes is step 1 (2,3) the bottleneck?
Step 1
Step 2
Step 3
Activity Time
Activity Time
Activity Time
0.25 min/part
0.20 min/part
0.15 min/part
Setup Time 30 min
Setup Time 20 min
Setup Time 45 min