[PPT]Cellular Manufacturing · Web viewTitle Cellular Manufacturing Author Christian Hicks Last...

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© Dr. C.Hicks, MMM EngineeringUniversity of Newcastle upon Tyne

Manufacturing Systems II

Chris [email protected]

http://www.staff.ncl.ac.uk/chris.hicks

mailto:[email protected]

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Topics

• Group Technology (Cellular Manufacture)

• Inventory Management• Material Requirements Planning• Just-in-Time Manufacture

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Cellular Manufacturing

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References• Apple J.M. (1977) Plant Layout and

Material Handling, Wiley, New York.• Askin G.G & Standridge C.R. (1993)

Modelling and Analysis of Manufacturing Systems, John WileyISBN 0-471-57369-8

• Black J.T. (1991) “The Design of a Factory with a Future”, McGraw-Hill, New York, ISBN 0-07-005550-5

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References (cont.)• Burbidge J.L. (1978)

Principles of Production ControlMacDonald and Evans, EnglandISBN 0-7121-1676

• Gallagher C.C. and Knight W.A. (1986) Group Technology Production Methods

in ManufactureE. Horwood, England ISBN 0-471-08755-6

• Hyde W.F. (1981)Data Analysis for Database DesignMarcel Dekker IncISBN 8247-1407-0

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Manufacturing Layout• Process (functional) layout, like

resources placed together.• Group (cellular) layout, resources to

produce like products placed together.

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Scientific Management• F.W.Taylor 1907• Division of labour - functional

specialism• Separation of “doing” and “thinking”• Workers should have exact instructions• Working methods should be

standardised• Specialisation led to functional layouts

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Process Layout• Like machines placed together• Labour demarcation / common skills• Robust wrt machine breakdown• Common jigs / fixtures etc.• Sometimes high utilisation• Components travel large distances• High work in progress• Long lead times• Poor throughput efficiency• Often hard to control

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Group Technology (Cellular Manufacturing)

• Group Technology is a manufacturing philosophy with far reaching implications.

• The basic concept is to identify and bring together similar parts and processes to take advantage of all the similarities which exist during all stages of design and manufacture.

• A cellular manufacturing system is a manufacturing system based upon groups of processes, people and machines to produce a specific family of products with similar manufacturing characteristics (Apple 1977).

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Cellular Manufacturing• Can be viewed as an attempt to obtain the

advantages of flow line systems in previously process based, job shop environments.

• First developed in the Soviet Union in 1930s by Mitrofanov.

• Early examples referred to as Group Technology.• Promoted by government in 1960s, but very little

take up.• In 1978, Burbidge asked “What happened to

Group Technology?”• Involves the standardisation of design and

process plans.

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Group (Cellular) Layout• Product focused layout.• Components travel small distances.• Prospect of low work in progress.• Prospect of shorter lead times.• Reduced set-up times.• Design - variety reduction, increased

standardisation, easier drawing retrieval.

• Control simplified and easier to delegate.

• Local storage of tooling.

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Group (Cellular) Layout• Flexible labour required.• Sometimes lower resource utilisation

due to resource duplication.• Organisation should be focused upon

the group e.g. planning, control, labour reporting, accounting, performance incentives etc.

• Often implemented as a component of JIT with team working, SPC, Quality, TPM etc.

• Worker empowerment is important - need people to be dedicated to team success. Cell members should assist decision making.

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Characteristics of Successful Groups

Characteristic Description

Team Specified team of workersProducts Specified set of products & no othersFacilities Dedicated machines / equipmentGroup layout Dedicated spaceTarget Common group goal for periodIndependence Groups can reach goals

independentlySize Typically 6-15 workers

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1 10 100 1,000 10,000Part Variety

(Number of different parts per hour)

1

10

100

1,000

Volume

FRED

High

Low

Job Shop

Transfer lines

Dedicated flow lines

Cells

FMS

Adapted from Black (1991)

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Implementation of Cellular Manufacturing

• Grouping - identifying which machines to put into each cell.

• Cell / layout design - identifying where to put to place machines.

• Justification• Human issues

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Types of Problem

• Brown field problem - existing layout, transport, building and infrastructure should be taken into account.

• Green field problem - designers are free to select processes, machines, transport, layout, building and infrastructure.

• Brown field problems are more constrained, whilst green field problems offer more design choice.

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Grouping Methods• “Eyeballing”• Classification of parts• Product Flow Analysis• Cluster Analysis

– Matrix methods (e.g. King 1980)– Similarity Coefficient methods

• Layout generation without groupingBeware:• Different methods can give different

answers• There may not be clear clusters• Cellular manufacturing not always

appropriate

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Classification of Parts

• Based upon coding.• Many schemes available.• Basic idea is to classify according to

geometry, similar shapes require similar processes.

• Grouping codes together is synonymous with grouping together like parts.

• Very prevalent in 1960s and 70s.• Many schemes aimed at particular

sectors.

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Coding issues• Part / component population

– inclusive should cover all parts.– flexible should deal with future parts

/ modifications.– should discriminate between parts

with different values for key attributes.

• Code detail - too much and the code becomes cumbersome - too little and it becomes useless.

• Code structure - hierarchical (monocode), chain (polycode) or hybrid.

• Digital representation - numeric, alphabetical, combined.

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Product Flow Analysis

• Developed by Jack Burbidge (1979).• Uses process routings.• Components with similar routings

identified.Three stages• Factory flow analysis.• Group analysis• Line analysis(See Askin and Standridge p177-179)

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Factory Flow Analysis

• Link together processes (e.g. machining, welding, pressing) and subprocesses (turning, milling, boring) used by a significant number of parts.

• Large departments are formed by combining all related processes.

• These are essentially independent plants that manufacture dissimilar products.

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Group Analysis

• Breaks down departments into smaller units that are easier to administer and control.

• The objective is to assign machines to groups so as to minimise the amount of material flow between the groups.

• Small inexpensive machines are ignored, since they can be replicated if necessary.

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Group Analysis• Construct a list of parts that require

each machine. The machine with fewest part types is the key machine.

• A subgroup is formed from all the parts that need this machine plus all the other machines required to make the parts.

• A check is then made to see if the subgroup can be subdivided.

• If any machine is used by just one part it can be termed “exceptional” and may be removed.

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Group Analysis

• Subgroups with the greatest number of common machine types may be combined to get groups of the desired size.

• The combination rule reduces the number of extra machines required and makes it easier to balance machine loads.

• Each group must be assigned sufficient machines and staff to produce its assigned parts.

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Process Plan Example

PartsMachine 1 2 3 4 5 6 7 8A 1 1 1B 1 1 1C 1 1 1 1D 1 1 1 1E 1 1F 1 1

(Askin and Standridge 1993)

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Applying GroupingSteps1. Identify a key machine. Either E or F.

Create a subgroup to D,E and F.2. Check for subgroup division. All parts

visit F and so subgroup cannot be subdivided. Only part 7 visits machine D so it is exceptional and is removed.

1. Identify an new key machine for remaining 6 parts. A is the new key machine with subgroup A,B,C producing parts 1,2 & 3.

2. Subgroup division - C only used for part 3, therefore exceptional and can be removed.

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Applying Grouping

1. Identify next key machine. Only parts 4,5, & 6 remain as well as machines C and D.

2. All parts use all machines - no subdivision possible.

3. Cell designer can now recombine the three subgroups into a set of workable groups of desired size.

4. The final solution must provide adequate machine resources in each group for the assigned parts. If exceptional parts exist, or if groups are not self contained, then plans must be made for transport.

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Rank Order Clustering

PartsM/C 1 3 4 7 2 5 6 8 ValueA 1 1 1 200E 1 1 17C 1 1 1 1 102F 1 1 17D 1 1 1 1 54B 1 1 1 2002N-k 128 64 32 16 8 4 2 1

1. Evaluate binary value of each row.2. Swap rows over to get them in rank order.

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PartsM/C 1 3 4 7 2 5 6 8 ValueA 1 1 1 200B 1 1 1 200C 1 1 1 1 102D 1 1 1 1 54E 1 1 17F 1 1 172N-k 128 64 32 16 8 4 2 1

Next apply same method to the columns

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PartsM/C 1 3 4 7 2 5 6 8 2M-k

A 1 1 1 32B 1 1 1 16C 1 1 1 1 8D 1 1 1 1 4E 1 1 2F 1 1 1Tot 48 56 12 7 48 12 12 3

M = number of machines, k number of rows

Next swap over columns to get in rank order.

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PartsM/C 3 1 2 4 5 6 7 8 2M-k

A 1 1 1 32B 1 1 1 16C 1 1 1 1 8D 1 1 1 1 4E 1 1 2F 1 1 1Tot 56 48 48 12 12 12 7 3

ROC has got a solution close to a block diagonal structure. The process can be repeated iteratively until a stable solution isfound.

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Consider a pair of machines I,j,

ni = number of parts visiting machine i

nj = number of parts visiting machine j

nij = number of parts visiting i and j.

Define similarity coefficient as:

sij = max(nij/ni,nij/nj)

Values near 1 denote high levels of interaction.

Values near 0 denote little or no interaction.

Similarity Coefficients

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Similarity Coefficients

1

654

32

S ij = m ax(n ij/n i, n ij/n j)

S 2,5 = m ax(2 /3 , 2 /2)

S 2,5 = 1

Machine 1 2 3 4 5 6 7 8A 1 1 1B 1 1 1C 1 1 1 1D 1 1 1 1E 1 1F 1 1

M/Cs A B C D E FA ---- 1 0.33 0 0 0B 1 ---- 0.33 0 0 0C 0.33 0.33 ---- 0.75 0 0D 0 0 0.75 ---- 0.5 0.5E 0 0 0 0.5 ---- 1F 0 0 0 0.5 1 ----

Initial similarity coefficient Sij

(Askin and Standridge 1993)

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Clustering• We start with 6 clusters, one for each

machine.• With a threshold of T = 1 machines A

and B can be grouped. Likewise E and F.

• There are several methods for updating similarity coefficients between newly formed clusters and existing clusters.

• The single linkage approach uses the maximum Sij for any machine i in the first cluster and any machine j in the second cluster. Therefore any single pair of machines can cause groups to be combined

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Updating Similarity Coefficients (Using Single Linkage)

MachinesM/CsAB C D EFAB ------ 0.33 0 0C 0.33 ------ 0.75 0D 0 0.75 ------ 0.5EF 0 0 0.5 ------

Updated similarity coefficient Sij

Next consider the highest value of Tpossible. This gives the cluster CD atT = 0.75.The coefficients then need to be updatedagain.

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Dendogram

1

0.75

0.5

0.25

0

A B C D E F

M A C H IN E S

4 G roups

3 G roups

2 G roups

1 G roups

Sim

i lar it

y C

o eff i

c ien

t Th r

e sh o

ld

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Variety ReductionBasic principle: always use common

designs and components wherever possible.

• Modular design.• Standardisation.• Redundant features.• Can base upon geometric series.• Imperial / metric series.• Reduced estimated & work planning.• Simplified stock control.• Less problems with spares.

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Variety Reduction

• May use slightly more expensive parts than necessary.

• Increases the volume of production of items.

• Reduced planning / jigs and fixtures etc.

• Reduced lead times.

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Product Family Analysis

There are a number of different ways of identifying part families. The following factors should always be considered:

• How wide is the range of components?• How static is workload?• What changes are anticipated?• Is Group Technology aimed purely at

manufacturing or is standardisation and modularisation of design a major issue?

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Manufacturing Layout

• Concerned with the relative location of major physical manufacturing resources.

• A resource may be a machine, department, assembly line etc.

• A block plan can be produced that shows the relative positioning of resources.

• Evaluation criteria are required such as minimising transport costs, distance travelled etc.

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Approaches• Many methods are based upon a static

deterministic modelling approach.• Dynamic effects may be “guessed” by

trying out a variety of scenarios.• Dynamic and stochastic effects may be

evaluated by simulation.• A premium may be placed upon

favourable attributes– Flexibility dealing with changes in

design, demand etc.– Modularity the ability to change the

system by adding or removing component parts to meet major changes in demand.

– Reliability– Maintainability

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Line Layout

D D D

Departments

Material Flow

Single Line, single row layout

D D D

Departments

D D D

Single line, double row layout

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Spine Layout

Materials Products

• Spine is central core for traffic.• Secondary aisles for traffic into departments• Each department has input /output storage areas along the spine.• Point of use storage reduces material flow.

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Material

Loop Structure

Circular Structure

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Layout Configurations

• Eli Goldratt I, V, U, W• I layouts have linear flow with no

direction changes, empty pallets may go in reverse direction.

• V and U lines have more direction changes but may help with empty pallets.

• Rectilinear layouts may restrict operators from working multiple machines.

• Circular layouts may enable operators to work multiple machines.

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Analysing Flow• Sting diagrams provide a very quick

way to identify the pattern of flow.• Look at performance measures:

– Distance travelled per component;– Material handling costs %;– Material handling time %;– Load / unload times;– Number of direction changes;– Number of moves per day;– Many, many more.

• Looking at performance measures enables alternative layouts to be evaluated.

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Measures of Performance

• Resource Measures:– Resource utilisation;– Productivity.

• Inventory:– work in progress;– queues.

• Product:– lead times;– delivery performance;– Quality.

• Financial, overhead recovery v.s. ABC costing.

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Creating Layouts• If there is a dominant flow, such as all

parts going from department 1-> 2 -> 3 then the layout should reflect this.

• At the other extreme, if the flow between departments is uniformly distributed, then any arrangement may be equally good.

• However, most problems will lie between the extremes of dominant and equal flow.

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Systematic Layout Planning

1. Data collection.2. Flow analysis.3 Qualitative considerations.4. Relationship diagram.5. Space requirements.6. Space availability.7. Space relationship diagram.8. Modifying considerations and

limitations.9. Evaluation.

(Muther 1973)

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1. Data Collection• Products to be produced & volumes.• Routing, Bill of Materials, parts lists.• Resources for production, layout &

geometrical information.• Timing information - set-up, processing

& transfer durations.• Data determines loads & resource

utilisation.• Quantity & variety determine

appropriate layout type.• A Product-Quantity chart, which is a

Pareto analysis of product importance can be used to determine items that justify their own lines or families of parts that justify a cell.

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Product-Quantity Chart

1 2 3 4 ... NProduct

Quantity

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2. Flow Analysis• Operation process charts determine

movement showing major operations, inspections, moves and storage.

• Process charts, similar to operation process charts, but more detail.

• Flow diagrams.• Flow data can be summarised in From-

To charts (like mileage charts in maps)– Volumes– Distance travelled*– Costs*

• String diagrams.

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Operation Process Chart

1010Thread,cut-off &chamfer

Face bottom

20 20

3030

40 40

SSA1 50

60SA1

A1

BaseHandle

Deburr

Inspect

Degrease

Knob

Rod

Face top

Drill 3 boltholes

Drill pinhole

Ream pinhole

Inspect

60 Inspect

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Process Chart Symbols

D

Operation

Transportation

Inspection

Delay

Storage

Combined activity

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Flow Diagram

Process chartsymbols

Material flow

Facility layout

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3. Qualitative Considerations

1. Offices2. Foreman3. Q/C4. Store5. Tool rm

A5

Rating

Reason

Code Reason1 Material flow2 Convenience34

RatingA Absolutely essentialE Especially importantI ImportantO Ordinary closenessU UnimportantX undesireable

REL Chart

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4. Relationship Diagram• Combines quantitative and qualitative

relationship data.• Provides a mechanism for visualising

relationships.

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5. Space Requirements

• Departmental space requirements need to be estimated.

• May have standards that define space requirement for each machine type.

• Can work from current space needs.• Can determine space requirement by

considering tasks performed, tooling, access, flow of materials etc.

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6. Space Availability

• Need to accommodate machines, material handling equipment, people, energy transmission, drainage, air lines, communications etc.

• If an existing facility is to be used, the available space and constraints need to be accurately defined.

• In the case of new facilities there are financial and often planning constraints.Need to consider possibility of future changes in demand or use.

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7. Space Relationship Diagram

• Represents departments with templates that are proportional in size to space requirements.

• Templates can be rearranged to find improved solutions.

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(a)

(b)

a) Relationship Diagramb) Space Relationship Diagram

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8. Modifying Considerations and Limitations

• Steps 1-7 have not taken into account implementation details.

• Site specific or operations specific conditions may require adjustments to the layout.

• Need to consider:– Utilities, power, heating, light,

drainage compressed air etc.– Structural limitations, load-bearing

capacity of floors, ceiling heights, columns.

– Location of external connections e.g. roads.

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9. Evaluation

• Several alternatives should be considered.

• Drawings, flow diagrams etc form the basis of assessment of advantages and disadvantages of each.

• Costs / benefits can be attributed to each alternative.

• Quality of flow can be evaluated.• Flexibility, maintainability, expandability

safety and ease of operations should be reviewed.

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Computerised Layout Planning

• Improvement algorithms are based upon an initial layout. They generate improvements by rearrangement. Suitable for brown field sites. Examples CRAFT (Armour & Buffa 1963)

• Construction algorithms start with a blank shop floor and add machines to it. Suitable for green field sites. Example: ALDEP (Seehof & Evans 1967), CORELP (Parsaei et al 1987), SHAPE (Hassan et al 1986).

• Hybrid algorithms include both construction and improvement algorithms.

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Computerised Relative Allocation of Facilities (CRAFT)

• Creates layouts by exchanging machine pairs and then evaluating the layout.

• When all pairs of exchanges have been completed, the exchange with the best evaluation is chosen and a new layout in generated.

• This process is repeated until no improvement can be made through exchanges.

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Automated Layout Design Program (ALDEP)

• A machine is randomly selected and added to the layout.

• The closeness of all the remaining machines to it is calculated. The “closest” machine is added. This is repeated until all machines have been placed.

• Once a machine has been placed, it is fixed. This makes it difficult to find good solutions.

• Often use an improvement algorithm to improve layout produced.

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Construction Algorithm Differences

• Method for election of next machine and its placement.

• Evaluation of the relationship between machines already located and the selected machine (e.g. by using different definitions of similarity coefficient).

• How the layout is represented.

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Synthetic Machine Concept

• A group of machines form a synthetic machine.

• Resource hierarchy flattened.• Framework to assist delegated

responsibility.• Local planning, control and work

organisation.• Concerned only with cell inputs and

outputs.

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Types of Cell• Highly automated - conveyers, robot

handling, Flexible Manufacturing Systems (FMS).

• Semi-automated - some automated material handling.

• Simple cells without automated material handling.

• Work grouped on a single machine using a multi-functional machine tool.

NOTE: Need to find an appropriate mix for given production volumes. Increasing automation normally increases overheads and reduces flexibility.

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Supporting Techniques

• Statistical process control.• Quality Circles.• Team working.• Empowerment.• Visible performance measures.• Total preventative maintenance.• Single minute exchange of dies.• Simple machine concept.

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Case Study 1

• World class automotive components supplier.

• Adopted lean manufacturing practices yet productivity still 50% of Japanese sister plant.

WHY?

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Findings

• Layout - rectilinear v.s clusters.• Supervision of resources.• Smallest machine concept.• Flexible resource variable.• Cost of capital and accounting

philosophies.

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Case Study 2

• SME supplier of orthotics (surgical appliances).

• Very long delivery.• High work in progress.How can situation be improved?

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Solution• Business process analysis:

– Non physical processes;– Physical processes .

• Target queuing by streamlining processes or increasing capacity.

Result:• Lead time 14 weeks to 4;• Cash flow improved by £300k on £2M

turnover.

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Other Key Issues

Batch sizes• Set-up• Machining• TransferEffect on other measures of performance.

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Hints

• Look at the material flow• Try to simplify• Think about removing in-process

inventory• Think about the operators• Consider other layout constraints

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Inventory Management

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Inventory

• Money invested in materials3 Types of inventory• Raw materials• Work in progress• Finished goods

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Advantages of Inventory

• Raw materials offset lead time• Work in progress offsets disturbances

in the production system and may help keep resource utilisation high

• Finished goods stocks enable fast delivery

• Economic order quantity methods claim to claim

• People feel busy• Process “decoupling”

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Inventory: Disadvantages

• Expensive to keep– Interest on capital– Storage costs

• Adverse effect on cash flow and liquidity

• Risk of obsolescence• Lack of flexibility• Masks problems with manufacturing

system• Difficult to control

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Types of Demand

• Independent– Demand for an item is independent

of the demand for another item• Dependant

– Demand for an item is linked to the demand for another item

– Product structure defines dependencies

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Inventory Control

“The activities and techniques of maintaining stock items at desired levels, whether they are raw materials, work in progress or finished products”

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Inventory Control Decisions

• How many? – (lot size or order quantity

• When– timing or order point

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Independent Demand• Fixed order quantity (FOQ) systems

order a predetermined quantity of items when stock levels drop below a predetermined level e.g. 2 bin system

• Economic order quantity systems aim to minimise the combination of ordering and carrying costs. They make a number of assumptions:– annual demand can be estimated– demand is uniform– no quantity discounts

• Ignores the costs associated with stock outs

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Dependent Demand• Demand for one item linked to the

demand for another• Producing an assembly causes

dependent demand for all the components that go into the assembly

• Assembling a car requires one windscreen, 5 wheels, one engine etc.

• One engine requires one crankshaft, one cylinder head etc.

• One cylinder head requires ….

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Product Structure

A

B C

Simple Product Structure

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Product StructureA

B Dc

E F

G H

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Material Requirements Planning

• Method for planning dependent demand

• Requirement for subassemblies and components based upon requirements for end items and product structure

• Takes into account current stocks of each item to calculate net requirements

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Material Requirements Planning

MRPStocks Product Structure

End Item Requirements

Net Requirements

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ABC Classification

Break items into 3 groups:• A - the items that represent 75% of

value and 20% volume• B - the items that represent 20% value

and 30% volume• C - the items that represent 5% value

and 50% volumeThis approach is based uponParieto analysis

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Just-in-Time

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Just-in-Time

• Approach to achieve excellence in manufacturing

• Minimise waste: anything that adds cost but not value

• Just the correct quantity• at just the right quality• at just the right time• in the right place

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Push Scheduling

Manufacturing Systems

Inventory

“PUSH”

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Kanban

• Japanese word for card• One card• Two card

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One Card Kanban

MC1 MC2

Machine 1 operatesat a constant rate

StockArea

Kanban

Item + Kanban

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Two Card Kanban

MC1 MC2

StockArea

“C” Kanban

Item + Kanban

“P” Kanban

Item

“P” Production Kanban“C” Conveyance Kanban

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Pull scheduling

Manufacturing System

1 345 2

PULL

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