Homework Solutions – Chapter 12
1. Is it possible to achieve zero inventories? Why or why not?
In reality, zero inventories are a challenging, if not impossible, goal for most organizations. The
concept is theoretical because the ideal production unit is one. Nothing is made until the customer
expresses an unmet need for the product. In reality, inventories will always exist due to the timing
between the expressed need and the actual delivery of the completed unit(s). There are inventories in
transit. Some safety stock is necessary to buffer against demand and supply uncertainty. Some order
batching is necessary when multiple variants of the same product are made. Nevertheless, this goal
aids in understanding of the lean concepts, and remains a reference point to continually remember in
the on-going improvement process.
2. Explain the relationship between quality and productivity under the lean operations philosophy.
Under JIT, quality and productivity are key and equal partners. As quality improves, so does
productivity, as only good units are assembled. No work is wasted on preparing inferior quality
items. Both are necessary in the lean philosophy.
3. Briefly explain the difference between a “push system”, “pull system”, and “team system” for
manufacturing. What are some of the pro’s and con’s of each system?
Push System: Every worker maximizes own output, making as many products as possible.
Pro’s and con’s: Focuses on keeping individual operators and workstations busy rather than efficient
use of materials; Volumes of defective work may be produced; Throughput time will increase as
work-in-process increases (Little’s Law); Line bottlenecks and inventories of unfinished products will
occur; Hard to respond to special orders and order changes due to long throughput time
Pull System: Production line is controlled by the last operation
Pro’s and con’s: Controls maximum WIP and eliminates WIP accumulating at bottlenecks; Keeps
materials busy not operators so operators work only when there is a signal to produce; If a problem
arises, there is no slack in the system; Throughput time and WIP are decreasedso there is faster
reaction to defects and less opportunity to create defects
Team System: Group of cross-trained workers has overlapping responsibility
Pro’s and con’s: Cross-training and team efforts reduces WIP or the bottleneck concept; Most
efficient use of both materials and labor; Cross training means one worker can step out if a problem
arises; Higher process responsibility and ownership; Cross training can be costly