03_Design of Production Systems Flashcards by isabel Wang

What is a Work System?

smallest organizational unit of the production system

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Examples for Master Data

capacity info
bill of materials
process plans

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Examples for Transaction Data

demand data
volumes, due dates

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Examples for Feedback

quality produced
due date adherence

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3 types of production systems

Job Shop
Manufacturing Cells
Flow Shop

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Job Shop

Functional Layout

spatial concentration of similar work systems

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Flow Shop

Object layout, uniform material flow

arrangement of work systems according to the work flow

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Cellular manufacturing

Object Layout, production-dependant material flow

arrangement of product families to machine groups

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Production Segment

sybsystem of the production system that is organized according to specific layout type

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Job Shop
Characteristics

more flexible
high workload fluctuation
low production vol
low division of labout
high product variety

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Flow Shop Characteristics

more efficient [assembly line sequence]
low workload fluctuation
low product variety
high division of labout
high production vols

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Cellular Manufacturing
Characteristics

medium workload fluctuation, production volume, product variety, division of labour
often combinations of layout types to leverage benefits of both systems

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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

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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

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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

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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

1. **Task-casued infeasibility** - single task takes longer than cycle time C - e.g 14 min for task 2 > C=13 2. **Variant-Caused Infeasibility** - variant total task time exceeds capacity - e.g. 35, 31, **54** min < 4 * 13 = 52min 3. **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