What decisions need to be made for a good layout?
Material handling equipment Capacity and space requirements Environment and aesthetics Flows of information Cost of moving between various work areas
What is a job shop process flow structure?
Absolutely unique products are made under the usage of standard tools in very low quantities
What does being process-focused mean?
A form of production in which workstations are grouped according to type of process performed and equipment
What is a flow shop (line layout)?
A lot of the same products are made using assembly lines
What is a dominant product flow?
(almost) all items follow through the workstations according to the same sequence
What does being product focused mean?
A form of production processing organization in which workstations are organized according to the type of product being produced
What is a batch flow production system?
A mixed approach between job shop and line layout
What is a minimum-makespan general job-shop scheduling problem(JSSP)?
A set of n jobs, which are to be processed on a set of m machines, Each job needs to be processed according to a predefined sequence of machines, and for each job and machine combination the processing time is known
What is the makespan?
TIme it takes to complete all jobs
What is a dispatching rule based heuristic?
Heuristic that aims to construct a schedule based on the earliest start time principle
What is the shortest processing time (SPT)?
Tie breaker that says that the shortest job should be completed first
What do MAT & JAT mean in the dispatching rule based heuristic?
Machien available time & Job available time
What are alternative dispatching rules?
Random : pick random job in queue
First come, first serve: jobs are processed in order they arrive
Shortest processing time: Pick job which is done fastest
Earliest due date: Prioritize job that has earliest due date
Critical ratio: time until job is due/total shop time remaining–>pick lowest
Slack time = time until job is due-total shop time remaining –>pick lowest
Slack time per remaining per operation: slack time divided by number of operations remaining –>pick lowest
What is a precedence diagram?
Diagram which displays which tasks need to be performed in which order
What is the production rate of an assembly?
Number of units that the line produces per time unit
What is the cycle time?
The time required to output one unit
What is the takt time?
The reciprocal of the desired production rate, maximum feasible cycle time
What is the idle time of an assembly line?
Total time that the workstations are not occupied during a production cycle
What is the efficiency of an assembly line?
Total time that the workstations are not occupied over total production maximum time
What is theoretical minimum number of workstations (L)?
Lower bound regarding the optimal number of workstations
L = (sum of job times)/T, where T is take time
What kind of priority coefficients can be chosen for an assembly line heuristic?
Longest task time: choose task with highest task time
Most following task time: choose task with most number of following tasks
Ranked positional weight: Choose task with highest total time of tasks following it, including itself
Shortest task time: choose task with lowest task time
Least number of following task: Choose task with lowest number of following tasks
COmputer Method of Sequencing Operations for Assembly Lines (COMSOAL): Randomly chooses operations, performs this often and chooses best one
What are some examples of additional difficulties in simple assembly line balancing problem?
- Do not balance, but re-balance
- Workstations have identities
- Cannot eliminate workstations
- Need to equalize loads
- Multiple operators
- Multiple-operator operations
- Multiple products
