Welcome to the Breakfast Workshop Series Develop

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Transcript Welcome to the Breakfast Workshop Series Develop

Cellular Manufacturing
Adapted from:
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Introduction to Cellular Manufacturing (CM)
• Product layouts (assembly lines, mass production one a few
products on the same line) is the most efficient of the basic
layout options
• Many products are not made in volumes that require a
product layout
• Cellular manufacturing (group technology) – forms families
of products that have common production requirements
• Locate machines, people, jigs, fixtures, drawings, measuring
equipment, material handling equipment together (focused
factory)
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Introduction to Cellular Manufacturing
• The cellular approach is to organize the entire manufacturing
process for particular or similar products into one group of
team members and machines known as a "Cell".
• These "cells" are arranged in a U-shaped layout to easily
facilitate a variety of operations.
• Parts or assemblies move one at a time (or in small batch
sizes).
• The parts are handed off from operation to operation without
opportunity to build up between operations.
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Introduction to Cellular Manufacturing
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Introduction to Cellular Manufacturing
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Introduction to Cellular Manufacturing
• Fast setup and quick changeovers are essential to Cellular
Manufacturing systems since production runs are shorter.
• Setup reduction principles are used to achieve one piece
flow and mixed model synchronization.
• All cells concentrate on eliminating waste.
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Empowered Employees in CM
• Goals and tracking charts are maintained and posted.
• Problems are solved through daily cell meetings and
problem solving teams.
• The inventory management system is a KANBAN Demand
Pull instead of a work order/kit picking system.
• Cells are responsible for planning, scheduling and
expediting directly with vendors.
• They establish and maintain a KANBAN system with the
vendors.
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Advanced CM
• The cell operates like an independent business with total
responsibility for quality, manufacturing and delivery of the
product to the customer.
• All cells have the resources within their organization to
accomplish their mission.
• The requirements are known and goals are established.
• Cell members are flexible and work in teams to accomplish
their goals including continuous improvement.
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Benefits of CM
• Common tooling required for many products (fewer setups)
• Tooling can be justified since many products require it (more
volume when products are grouped)
• Minimized material handling
• Simple production schedule
• Short cycle time
• Low WIP
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Benefits of CM
• Cross-training – employees operate several machines
• Minimized material handling costs – since no paperwork is
required and distance is small
• Employees accept more responsibility of supervision
(scheduling of parts within cell, scheduling of vacation,
purchasing of material, managing a budget)
• Simple flow pattern and reduced paperwork
• Buffers are small if batch size is small
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Disadvantages of CM
• Lower equipment utilization
• Increased set-up costs
• Less flexibility than functional departments
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Family Formation
• Various levels – macro and micro
• Macro – entire factories (focused factories) can specialize in
a particular type of part
• Micro – families can be based on similarities in part
geometry (group shafts, flat parts, gears, etc…), process
requirements (castings, forgings, sheet metal parts, heattreated parts, printed circuit boards)
• How are these groupings determined?
– Coding
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Finding Part Families
• Visual Inspection of physical parts or photographs to identify similarities.
• Coding and Classification of parts by examining design and/or
manufacturing attributes.
– OPITZ System
– MICLASS System
• Here a code is assigned to specific features of the part.
– Is the part cylindrical or prismatic ?
– Does it have threads?
– Does it have through slots?
– Does it require heat treatment?
• This requires a large initial time investment in coding and classifying all
parts.
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Finding Part Families
• Production Flow Analysis : Since the parts in a part family
have similar manufacturing processes, it is possible to
identify similar parts by studying the route sheets.
• Parts with similar routes can be grouped into families.
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Group Analysis
• To create part families and machine groups a part-machine
matrix is created.
• This is a 0-1 matrix in which a one signifies that a machine is
required for a given part.
• While creating this matrix the machine refers to a "type" of
machine.
• Thus, if there are 5 identical CNC lathes we will create one
row in the matrix for these lathes.
• Also, the number of times a part visits a machine is not
considered at this stage
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Group Analysis
• Once a the part-machine matrix is created, it is customary to
remove approximately 10% of the most heavily used
machines.
• Several copies of these machines are likely to be available
and thus it is always possible to split these machines
between different groups later.
• The remaining matrix is then inspected for part families.
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Group Analysis
• To identify the part-families the rows and columns are interchanged such
that a block-diagonal structure is obtained. There are several algorithms
that can be used to do this. A simple algorithm for this problem can be
described as follows:
– Pick any row and draw a horizontal line through it.
– For each 1 in the row that has been crossed once draw a vertical line
through the corresponding column.
– Pick each new column identified in the previous step. For each 1 in
the column that has been crossed once draw a horizontal line
through the row.
– Repeat this process until there are no singly-crossed 1s in the
matrix.
– Remove the rows and columns that have been crossed to form a
part family-machine group.
– Continue for the rest of the matrix
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Group Analysis
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Coding
• GT coding and classification schemes attempt to capture
design and manufacturing attributes such as the main
shape, size, features of the product, production quantity, and
material.
• A large number of GT coding schemes have been developed
for discrete machined parts including MICLASS, Opitz and
DCLASS
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Coding
• Code should contain information about:
• Part or assembly itself
• Manufacturing process (manufacturing engineering,
industrial engineering, tool engineering, scheduling, line
supervision, quality assurance, etc…)
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Coding Requirements
• Precise nonambiguous meaning, no double or triple
definitions for the same phrase
• Tightly structured and concise
• Easy to use
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Coding Options
• Codes can be chain or hierarchical
• Chain – each digit’s specific location is fixed for a particular
meaning
• Chain Example –
– First digit is reserved for the product type
– Second digit for material
– Digits 3-6 for part geometry
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Coding Options
• Chain Advantage – easy to learn
• Chain Disadvantage – requires more digits making it difficult
to handle manually and with low power computers (not as
big a problem today as the price of computers has dropped)
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Coding Options
• Hierarchical code – each code character depends on the
preceding one – a tree type structure
• Advantages – code can be sort since many branches can be
eliminated
• Disadvantages – difficult to learn
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Code Generation
• CM codes are typically generated manually or interactively
by answering a series of questions and applying appropriate
coding rules.
• However, this is a slow and inconsistent procedure which
inhibited the widespread use of CM.
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Opitz Coding Scheme
• Shah and Bhatnagar developed an automated CM coding
system based on the Opitz coding scheme for machined
parts.
• The system assigns pre-defined taxonomy codes for each
feature of its feature-based CAD system.
• The generic information captured by the taxonomy codes is
used to determine individual feature characteristics and the
relationships between features and the entire parts.
• The CM code generator uses the resulting feature
information and Opitz coding rules to generate the CM
codes.
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Using Codes
• Comparing the CM codes of two products is a quick and
efficient method for estimating product similarity in selected
attributes.
• CM codes can be used to search a database of products
and retrieve the designs and process plans of those
products which are similar to a given design
• To generate new process plans automatically using a
knowledge-based system
• To assess manufacturability of a product design
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Cell Layout
• Usually U, L or circular shaped
• Minimizes transportation distance for operators (human or
robotic)
• Encourages multiple machines per operator
• Most machines are automatic or semiautomatic, resulting in
considerable idle time
• In a job shop (functional layout) there is one operator for
each machine
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Supply Push
• Input availability triggers production or work
• Emphasis on “keeping busy” to maximize resource utilization
as long as there is work to be done
• Will synchronize supply with demand at each stage if:
– If all information (about product recipe, processing lead
times, and part inventories) is accurate
– If forecasts of finished goods are correct
– If there is no variability in processing
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Demand Pull
• Output need triggers production
• Each station produces only on demand from its customer
station
• Each station signals demand by picking up a part from its
input buffer
• The supplier station produces a new unit as a replacement
in the buffer
• Toyota formalized demand pull with cards called kanbans
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Kanbans
• Kanbans are attached to output flow units in the buffer
between customer and supplier processes
• Each card lists the following information:
– Customer process
– Supplier process
– Parts description
– Production quantity
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Kanbans
• As the customer withdraws output flow units from the buffer,
the attached kanban goes back to the supplier
• It signals an authorization for the supplier to produce the
listed quantity to be replaced in the buffer
• Upon producing the required quantity, the supplier returns
the output with an attached kanban to the buffer
• Kanbans control buffer inventory and provide information
and discipline to the supplier as to when and how much to
produce
• In the case of a process that handles multiple products, each
supplier station must also know what to produce
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Problem 2 - Test 2 Summer 2001
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Problem 2 - Test 2 Summer 2001
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Problem 2 - Test 2 Summer 2001
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Problem 2 - Test 2 Summer 2001
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Problem 2 - Test 2 Summer 2001
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Thus all parts require all machines and only cell is formed
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