|Abstract or Summary
- This thesis is a study of certain costs relevant to the repair of
process line equipment. A specific production configuration is studied
through computer simulation and statistics. The significance of the
simulated costs are investigated and related to practical production
Costs relevant to the "permanent repair" of production equipment
on the single-channel of an n-one-n production configuration are examined.
A piece of equipment is assumed to be "permanently repaired"
if it is modified or replaced, thus halting the breakdowns previously
plaguing the machine. An n-one-n production configuration is a group
of process lines (multi-channel), each manufacturing the same product,
supplying a single process line (single-channel) with raw materials
which in turn are used to supply dependent multi-channel process lines
downstream with raw materials.
Costs deemed important to the permanent repair of single-channel
production equipment are:
1. the cost of breakdown repair,
2. the cost of single-channel idle time,
3. the cost of downstream multi-channel idle time due to single-channel
4. the cost of additional in-process inventory required to prevent
the costs of (2) and (3).
Computer simulation is used to analyze the impact of single-channel
breakdowns. The computer model simulates levels of single-channel
idle time, ranging from 50% to 15% to reveal the effects of
single-channel disrepair on the downstream multi-channel.
The application of the study is based on data from an aluminum
fabrication plant. The upstream multi-channel is where ingots are
cast out of molten aluminum, the single-channel is where these ingots
are rolled into coils, and the downstream multi-channel is where the
coils are fabricated into forms desired by customers, such as corrugated
metal or small widths of metal.
Two key costs are found to be most important to the permanent
repair decision: (1) the cost of single-channel idle time due to breakdowns,
and (2) the cost of repairing a breakdown each time it occurs.
These two costs comprise 84% of all expense resulting from breakdowns. In-process inventory is also very important to the operation of
the plant. Without it, downstream idle time would occur and millions
of dollars of sales would be lost due to order cancellations from delivery
Since every production system will have unique costs and individual
characteristics, the actual cost findings of this study are not
universally applicable. However, the methods used in deriving these
costs are applicable to other plants having an n-one-n production configuration.
The observations and techniques presented are a step
towards improved decision making in maintenance, a topic which
merits attention but has been partially ignored to date.