Module 2: Production Management Flashcards
What are the definitions of:
- workstation
- routing
- order
- Throughput
- capacity
- work in process
- cycle time
- utilization
Workstation: a collection of one or more identical machines.
Routing: sequence of workstations needed to make a part.
Order: request from customer.
Throughput (TH): the average quantity of good (non-defective) parts
produced per unit time.
Capacity: an upper limit of the throughput
Work in Process (WIP): inventory between the start and endpoints of a
routing.
Cycle Time (CT): time between release of a job at the beginning of the
routing until it reaches an inventory point at the end of the routing.
Utilization: fraction of time a workstation is not idle for lack of parts
What is the Push and Pull method?
see docs
What is MRP, materials requirements planning.
see docs
What is JIT, just-in-time?
see docs
What is CONWIP?
What are the advantages of MRP and JIT?
Main Advantage of MRP over JIT:
MRP takes forecasts for end
product demand into account. In an environment in which
substantial variation of sales are anticipated (and can be
forecasted accurately), MRP has a substantial advantage.
Main Advantage of JIT over MRP:
JIT reduces inventories to a
minimum. In addition to saving direct inventory carrying costs,
there are substantial side benefits, such as improvement in quality
and plant efficiency.
What is the basic of MRP?
see docs
What is the explosion calculus??
The explosion calculus is a set of rules for converting the MPS to
requirement schedules for all sub-assemblies, components, and
raw materials necessary to produce the end item.
What are the basis operations comprising explosion calculus
There are two
basic operations comprising the explosion calculus:
- Time phasing: Requirements for lower level items must be shifted
backwards by the lead time required to produce the items - Multiplication: A multiplicative factor must be applied when more
than one sub-assembly is required for each higher level item.
What is the product structure diagram?
see docs
What is L4L method?
The simplest lot sizing scheme for MRP systems is lot-for-lot
(abbreviated L4L). This means that requirements are met on a
period by period basis as they arise in the explosion calculus.
However, more cost effective lot sizing plans are possible. These
would require knowledge of the cost of setting up for production
and the cost of holding each item.
What is the Lot Sizing Problem?
see docs
What is the Silver-Meal heuristic?
see docs
What is the Least Unit Cost?
see docs
What are the shortcomings of MRP?
Uncertainty. MRP ignores demand uncertainty, supply uncertainty, and
internal uncertainties that arise in the manufacturing process.
Capacity Planning. Basic MRP does not take capacity constraints into
account.
Lead Times Dependent on Lot Sizes. In MRP lead times are assumed
fixed, but they clearly depend on the size of the lot required.
Quality Problems. Defective items can destroy the linking of the levels
in an MRP system.
Order Pegging. A single component may be used in multiple end items,
and each lot must then be pegged to the appropriate item.
What is the mechanics of Kanban?
see dics
What are the advantages of JIT systems?
Advantages:
1 Decreases Inventory Costs
2 Improves Efficiency
3 Reveals quality problems
Disadvantages:
1 May result in increased worker idle time
2 May result in decreased throughput rate
What are the advantages and disavantages of JIT systems with Kanban implementation?
Advantages:
1 Efficient tracking of lots
2 Inexpensive implementation of JIT
3 Achieves desired level of WIP
Disadvantages:
1 Slow to react to changes in demand
2 Ignores predicted demand patterns
What are :
- bottleneck rate
- raw process time
- critical WIP
Bottleneck rate (rb): rate of the workstation having the highest
long-term utilization (i.e. the bottleneck). It is an upper limit on TH
Raw process time (T0): the sum of the long-term average
process times of each workstation in the line. It is a lower limit on
CT. It is CT when there is no waiting, e.g. line is empty.
Critical WIP (W0): WIP level in which a line would achieve
maximum throughput (i.e. rb) with minimum cycle time (i.e. T0)
How can we assess whether a production line is performing well?
We will simulate a production line under two different
assumptions:
- Best-case
- Worst-case
We hold the WIP in the line constant over time (CONWIP
protocol).
What is the best-case performance ?
see docs
Best possible situation: A production line with minimum cycle time
and maximum throughput for each WIP level.
No randomness, no variability (perfectly balanced line).
Same conditions i.e. same rb and T0
What is Little’s Law?
Little’s Law: the fundamental relation between WIP, CT and TH
WIP = TH × CT
Insights:
- It is the “F = m × a” law for manufacturing systems
- Very generic as it doesn’t depend on variability, randomness. . .
- Simple and powerful
- You know two measures, you get the third for free
What is the worst-case performance?
see docs
- We seek maximum CT with minimum TH
- Any idea how to do that?
- NOTE: we need to keep the same rb and T0
- High variability: All items are moved from one workstation to the next together (batching), or variability in process times.
- Note that no randomness is introduced in the systemW
What are production lines with Stochastic Process time?
see docs
What is the motivation behind Cross-training in production systems>
