03_Design of Production Systems Flashcards
What is a Work System?
- smallest organizational unit of the production system
Examples for Master Data
- capacity info
- bill of materials
- process plans
Examples for Transaction Data
- demand data
- volumes, due dates
Examples for Feedback
- quality produced
- due date adherence
3 types of production systems
- Job Shop
- Manufacturing Cells
- Flow Shop
Job Shop
Functional Layout
- spatial concentration of similar work systems
Flow Shop
Object layout, uniform material flow
- arrangement of work systems according to the work flow
Cellular manufacturing
Object Layout, production-dependant material flow
arrangement of product families to machine groups
Production Segment
sybsystem of the production system that is organized according to specific layout type
Job Shop
Characteristics
- more flexible
- high workload fluctuation
- low production vol
- low division of labout
- high product variety
Flow Shop Characteristics
- more efficient [assembly line sequence]
- low workload fluctuation
- low product variety
- high division of labout
- high production vols
Cellular Manufacturing
Characteristics
- medium workload fluctuation, production volume, product variety, division of labour
- often combinations of layout types to leverage benefits of both systems
Pros for Job Shop
3 items
- flexibility
- low monotony of work
- investment (automation) is low
Suitable for one-of-a-kin and small series appications
Facility layout planning
(determining in-plant locations)
- grid division of the floor space
- distance measure: mostly rectangular along the in-plant traffic lanes
Note:
- Aerial vs. rectangular distance
Objective of Factory Layout
Job Shop
- Minimization of the entire proxy criterion
- proxy defined as product of transport of quantity and transport distance summed up over all types of goods
Greedy Method
(Construction Heuristic)
5 Steps
Job Shop
- determine object i’ with heaviest transport relation from/to all other objects
- assign i’ to a grid square at center of floor space
- determine yet unassigned object i’’‘ which shows strongest transport relations from/to already assigned objects
- assign i’’ to grid square closest to already assigned objects so that proxy criterion between i’’ and to the already assigned objects is minimized
- if all obects are assigned STOP
Types of Line Production
Flow Shop
- Unpaced Lines: Sequential Layout
-
Paced Lines:
1. Discrete material flow: Transfer lines
2. Continuous Material Flow: Flow Lines - open vs closed stations
Tranportation Systems
Flow Shop 3 items
- Continuously moving conveyor (e.g. automotive final assembly lines) conveyer belt
- Synchronous transport (e.g. automated transfer lines)
- Asynchronous transport (e.g. manual lines)
Cycle Time C
+ Calculation
Flow Shop - Single product line
- time it takes to complete one task
- maximum duratin per work station
- including producing and wait stages
**C = T / X **
X = production volume e.g 30 pieces
T = effective operation time e.g. 360 min per day
C = 360 min / 30 = 12 min / piece
Determine the theoretical minimal # of work stations given total assembly time
Job Shop - single-product line
M = 𝜏 / C
- where x is the smallest integer number
- lower bound for # of workstations
- 𝜏 = ∑ of the task times of all work stations
Up to which lower limit could the cycle time C be reduced?
Minimum cycle time
- choose highest task time among work stations
What is the utilization p if the theoretical minimal number of work stations M = 4 could be realized?
What is the ulization p if M=5 work stations have to be set up?
𝜏 = 46 min total assembly time
C - 12 min cycle time
**p = 𝜏 / M*C **
e.g. 46 min / 4 workstations * 12 min = 95.8% line utilization
Popular Priority Rules
when selecting assignments of feasible tasks to stations
Flow Shop
- maximum standard time
- maximum # of immediate Successors
- maximum total number of successors
- position weight
- etc.
Throughput rate of 6 products / h
Calculate Cylce Time C
Flow Shop - Single product line balancing
6 units / h = 6/60 min
-> 10 min / unit
C = 10min
What to do when assigning tasks to work station and there is a tie in priority value and no tie-breaker?
Flow Shop - single-product line balancing
- most likely task with lowest task number
Line balancing for a mixed model assembly line
Flow Shop - mixed model balancing
- variants of basic product types e.g. size (clothing), optional equipment (automotive), colours, technical performance (electrical devices)
- different product variants are manufactured on same line
- no changeovers between different product variants are necessary
- product variants differ in task sequences and task times
How to balance mixed-model assembly line
Flow Shop
- generate hybrid with task times corresponding to variant-specific task times
- use the demand ratios of the variants as weighting factors
- priority rule for the precedence relationship e.g. max # of all successors
Ranked positional weight technique
mixed-model assemblu line
- priority rule based procedure for determining next task to be assigned to work station
- e.g. ∑ of all task times of the succeeding tasks + task itself
3 types of infeasibilities when assigning product variants to
Mixed-model Assembly Line
-
Task-casued infeasibility
- single task takes longer than cycle time C
- e.g 14 min for task 2 > C=13 -
Variant-Caused Infeasibility
- variant total task time exceeds capacity
- e.g. 35, 31, 54 min < 4 * 13 = 52min -
Assignemnt-caused Infeasibility
- combination of tasks > cycle time
- you can live with infeasibilities with smart sequencing if average workload overall stations and product variants = cycle time
Cellular Manufacturing
In depth Characteristics
- spatial consolidation of limited # of working systems or machines
- product families based on similarity of machine requirements
- machine groups with respect to specific product family
- based on machine-product incidence matrix
Cons or Cellular Manufacturing
- **challenging process
- may have to replicate machines in several cells**
- monotony of work
- investment (automation)
- generation of product families and machine groups
- capacity utilization
Types of Production Centers
Cellular Manufacturing
1. Machining center - single machine
2. Machining Center - multiple machines
2.1. Flexible manufacturing system (highly automated)
2.2. Manufacturing Cell: low cost as not automataed and manually moved
Method for generating product families and machine groups
Cellular Manufacturing
Binary Sorting
- aim to generate block-diagonal-structure
- sort row first -> sort column
What to do with tasks that are in the wrong machine / product group after the binary sorting?
Cellular Manufacturing
- **calculate additional costs of transporting the production volumes or buying a a new machine **
- if smaller transport
- if bigger buy an additional machine to avoid transportation costs
