MSE407 Manufacturing Systems

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MSE407Manufacturing Systems
Chapter 12 Shop Floor Control Systems and
Extensions
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Agenda

• Weve made it! The end of the journey!!

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Learning Objectives

• End the course with a collection of relevant
  scheduling topics
• Hierarchical vs. heterarchical control and
  requirements for manufacturing execution systems
• Special topics for flow systems
• Line-balancing
• Lot-streaming
• Re-entrant flow scheduling
• Importance of tool management
• Issues associated with flexible manufacturing
  systems

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Shop Floor Control

• Enterprise information systems require data from
  the shop floor
• Purchasing and MRP - knowledge of inventory
  levels
• Marketing status of open work orders to respond
  to customer inquiries
• Accounting - input on worker activity to run
  payroll
• Industrial/Mfg Eng - labor data to develop time
  standards
• Schedulers - shop status of orders, workers,
  machines and tools to produce short-term schedules

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Shop Floor Control Functions

• Controls the execution of detailed tasks that
  define the short-term production schedule
• Planning
• Scheduling
• Converts production plan into detailed plan when
  each operation will be performed
• Communication protocol
• Network for informing and coordinating shop
  resources
• Accumulate data such as marketing, purchasing,
  accounting, scheduling, etc for higher level
  administrative and planning functions

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Definition of Shop Floor Control Systems (SFCS)

• Lowest level of production planning
• A system for controlling the manufacturing
  process from raw material to shipping
• Shop Floor Control Systems involve collaboration
  of every aspect of manufacturing to optimize
  productivity
• Basic focus of all approaches - WIP control

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Shop Floor Control System
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Shop Floor Control System Architecture

• Control System Architecture provides framework
  within which SFC must operate
• Architecture
• Linkages between components
• How they will interact
• Communication

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Hierarchical Control Systems Figure 12.1
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Heterarchical Control Systems

• Centralized scheduling
• Independent entities
• Well defined inter-relationships enables
  communication and cooperation
• Robust in short run to external changes
• Minimization of linkages
• Easier to change entities over time as system
  evolve

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Advancing Technology in Shop Floor Control Systems

• Real-Time Shop Management

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New Forms of Data Collection

• Bar Code Systems
• Digital Pictures
• Video Images
• CAD Drawings
• Graphs
• Scanned Items

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Benefits of a Properly Managed Shop Floor
Control System (SFCS)

• Higher Productivity
• Consistency Repeatability
• Paperless Work Management
• Ideal Production System
• Easier Integration
• Flexibility to accommodate new ideas and changes

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Common Shop Floor Control System Problems

• Inefficient processes
• Non-value added tasks
• Inefficient time management
• Difficulty with use of system
• Ineffective collection of data
• Human error

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Nascote Industries, Inc. Nashville IL

• Paint Company in Nashville IL
• Ineffective shop floor data collection
• Data stored on paper
• Filed by department and shift
• Obtaining data reports very difficult
• Lacking performance feedback
• Schedules distributed verbally or by hand
• Lost, outdated, misinterpreted schedules

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US Army Watervliet Arsenal

• The nation's oldest manufacturing arsenal
• America's sole manufacturing facility for large
  caliber cannon in volume
• Guns for the Army's main battlefield tank, the
  M1A1
• Located along the Hudson River at Albany
• Manual tool and gage control
• Delays in correct tool to the job
• 20 of schedules missed
• Interfacing three separate databases
• Generation of duplicate tooling
• Restricted traceability
• Labor intensive utilization

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Electrolabs Inc.Precision Metal Fabricator

• What they do
• Small production runs
• Sheet metal processing
• Metal layout to painting and silk screening
• Problem with their system
• Making sure that machine and tooling set-ups were
  done correctly and that parts were assembly
  efficiently

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Electrolabs SolutionImplementation of Real
Time System

• Use of digital cameras to take pictures of parts
  going through the production process
• Storing this information and forming a data
  collection base
• Helped workers to visual see and understand the
  assembly process
• Workers immediately know what tools and set-up to
  use
• Customers can view information for references

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Shop Floor Techniques Further Classification

• Low level scheduling
• Scheduling individual workstations (lot
  dispatching)
• Do not consider entire shop floor condition
• High level scheduling
• Regulate the daily production rate (lot release)
• Closed loop feedback
• Control-theoretic policies

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Some Low Level Policies

• Still commonly in use
• Static decisions
• Setting lot priorities
• Dispatching rules (FIFO, LIFO, etc.)
• Scheduling by critical resources
• Theory of Constraints
• These decisions are myopic, and not effective for
  fabrication with many small orders, dynamic
  product-mix, or critical due-dates

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High Level Policies

• Account for
• The information of other workstations
• Shifts in due-dates due to changes made by
  customers
• Make dynamic lot prioritization
• Requirements driven scheduling
• Hierarchical scheduling decisions in real-time

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Sample Shop Floor Control System Architecture
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Control-theoretic Approaches

• Aim at providing robustness with respect to
  uncertainty in the manufacturing system
• Fabrication uncertainties
• Machine breakdown
• Demand changes
• Changed due-dates
• Hedging policy Two-Boundary policy

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Hedging Policy
Periodic lot release
Hedging point control
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Loading rule

• Hedging point or inventory threshold
• Run at full load until threshold value reached
• Run at demand rate thereon
• Advantages
• Less backlogs during production start stage
• Reduced cycle times
• More control
• Problem
• Difficult to recover from breakdown if upstream
  machines are much faster

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Two-boundary (Flow Rate Control) Policy

• Simplified analysis and reduced data
• Workstation level analysis
• Hub-centered policy
• Objective and goal
• Minimizing the total inventory and surplus cost
• Decide the lot releases made to individual
  workstations

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Comparison With Other Policies

• WIP control, WIP-to-Bottleneck control, uniform
  loading (periodic release) policies are all being
  used
• Two-boundary policy gives best results
• Lowest WIP, surplus and backlog
• Lowest cycle times
• Highest throughput rates
• Most smooth performance
• Best performance under rapidly changing demand
  and uncertainty

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Design and Control of Flow Shop Systems

• Assembly Line Balancing
• Parallel Assembly Line
• Ranked position weight
• Random processing times and buffers
• Mixed-model releases
• Determining workstation spacing
• Lot-Streaming

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Assembly Line BalancingFigure 12.2

• Decision process of assigning tasks to
  workstations in a Serial Production System

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Parallel Assembly LineFigure 12.2
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Determining Workstation Spacing

• Deterministic, Single-Model Case
• Simple design
• Workstations placed along the line at a distance
  equal to the distance the line travels in a given
  time
• Asynchronous Case
• Requires more careful design
• Workstations must be separated by enough space to
  avoid the conflict of two adjacent workstations
• Desire to work on the same unit in the same space
  at the same time

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Lot-Streaming

• Advantages
• Using small transfer batches
• Significantly reduce throughput time
• Each transfer batch is moved to the next
  operation as soon as all units are completed
• Disadvantage
• Increase in frequency of material handling moves

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More on Design and Control of Flow Shop Systems

• Random Processing Times and Buffer
• No variation, Buffer not needed
• Mixed-Model Releases
• Runs asynchronously
• Flexible Flow Lines

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Re-Entrant Flow Lines

• Fluctuation Smoothing Policy for Mean Cycle Time
  (FSMCT)
• Minimizing the mean and standard deviation of
  cycle time
• Attempts to minimize mean flow time by reducing
  the inter-arrival time variability
• Queuing Theory
• Variability of inter-arrival times affects mean
  time at a work center

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MRP Used For Shop Floor Control

• Widely used for actual shop floor scheduling
• Approach
• Generates a start time for each order based on
  backward scheduling
• Assumes infinite capacity of resources
• Assumes an empty shop floor
• Hence, schedules generated cannot be be realized
  into practice
• Constant adjustment and correction in real-time
  necessary

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Manufacturing Execution Systems, MES

• Converting production plan into a set of tasks
  and monitoring those tasks
• Core Activities
• Interface to Production Planning System
• Work Order Management
• Workstation Management
• Tooling Management
• Labor Management and Effort Reporting
• Inventory Tracking and Traceability
• Material Handling

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Manufacturing Execution Systems, MES

• Core Activities, cont.
• Automated Data Collection and Management.
• Production Control and Exception Management.
• Maintenance Management.
• Quality Assurance.
• Supplier Interface.

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Enterprise Resource Planning (ERP) Systems

• The Key to Surviving in a Fast Paced Industry
• ERP is real time shop managing software
• Integrates with popular Windows accounting
  software
• Immediately provides work-in-progress reports and
  up-to-the-minute job history
• Allows a wide variation of information to be
  gathered
• Since the system is very versatile, it is useful
  to both small and large job shops

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Two-Boundary and Kanban

• Both limited (fixed) inventory policies
• Two-boundary policy more effective than Kanban in
  terms of lower WIP and cycle time
• Reasons-
• In Kanban, demand information transmitted only to
  adjacent workstation
• Kanban attempts to fill up inventory up to its
  fixed limit, causing more overall inventory than
  the control policy

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Tool Management Requires

• A design strategy
• To coordinate tooling inventory, tool tracking,
  tool loading/unloading
• A planning strategy
• To ensure that the appropriate tools are
  available in the right time in the right
  quantities
• A scheduling strategy
• To account for tool availability and tool changes
• A control strategy
• To coordinate tool transfers between machines and
  tool cribs
• A tool monitoring strategy
• To identify and react to unexpected tool wear and
  breakage

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Tool Management Classification

• Tool management can be classified into
• Tool-level
• Machine-level
• System-level issues
• Decisions at one level constrain those at lower
  levels
• Information from lower levels feeds back to
  higher level decisions

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Integration of Tool Management and Other Basic
Production Functions

• Reduction in production costs
• Due to minimizing number and types of required
  tools
• Increase in productivity
• Due to reduced tools stock outs and setup delays
• Improvements in part and routing flexibility
• Better tracking and cost accountability of
  tooling

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Tool Management Process
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Tool Standardization

• Hundreds of tool types and thousands of tools in
  inventory
• Done either by redesigning the part or process,
  or assigning more operations to similar tool
  types
• Substantial savings in
• Tool inventories
• Data management
• Improved system reliability

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Tool Information Requirements

• Common tool management database
• Data record should be linked to vendors, part
  types, machines
• Tools must be monitored for wear to permit
  planning for replacement
• Continuous monitoring
• Adaptive control to adjust machine speed and feed
  rates appropriately
• Off-line monitoring
• Increase non-productive times and may result in
  workpiece damage.

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Tool Information Requirements

• Sophisticated information systems to
• Coordinate delivery of the proper tools to
  specific work areas in time
• Provide location information
• Correlate the number of tools needed for the
  quantity of parts to be produced
• Offer acceptable substitutes when needed
• Bar-code labelling of tools or tool cabinets or
  memory chips are used to track tools and collect
  real time data

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Tool Management System

• Tooling issues arise in
• Production planning
• Scheduling
• Spare tool management
• Tool inventory management

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Tooling Inventory Management

• Operational flexibility requires many tool types
• At least 3 duplicate tools
• One in manufacturing area, one in tool crib as
  backup, one in preparation
• Number of types in storage increases over time
• Determination of appropriate number of tools to
  be purchased
• Custom tools are more expensive but can shorten
  processing times
• Optimal reorder points and safety stock levels
  are not studied
• Trade-off between tool availability,
  manufacturing capacity, reorder points and
  overall investment in tooling

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Flexible Manufacturing Systems, FMS

• Generally Consist Of
• Set of computer numerically controlled (CNC)
  machines
• Material handling system
• Economically attractive for mass production
• Used for low-variety, low volume parts
• When Using FMS, The Following Problems Must Be
  Solved
• Part type selection problem
• Production ratio problem
• Resource allocation problem
• Loading problem

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Summary

• Hierarchical vs. heterarchical control and
  requirements for manufacturing execution systems
• Special topics for flow systems
• Line-balancing
• Lot-streaming
• Re-entrant flow scheduling
• Importance of tool management
• Issues associated with flexible manufacturing
  systems

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Interactive Workshop (1 of 5)

• Shop Floor Control provides
• Data acquisition, planning, scheduling, and
  inventory control
• Data acquisition, planning, scheduling, and
  execution control
• Control of all that is happening on the shop
  floor
• A tool for management to watch what employees are
  doing

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Interactive Workshop (2 of 5)

• Heterarchical Control Systems
• Minimizes linkages that enable easier changes as
  system evolves
• Doesnt prepare for inevitable slippage
• Provides well defined inter-relationships that
  enable communication and cooperation
• Helps identify bottlenecks in a proposed schedule
  
• Both (a) and (c)
• Both (c) and (d)

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Interactive Workshop (3 of 5)

• Manufacturing Execution Systems
• Used to understand a sequence of steps or
  interrelationships of a process
• Focuses on bottlenecks for scheduling capacity
  planning
• Used to understand a sequence of steps or
  interrelationships of a product
• Converts production plan into a set of tasks and
  monitoring those tasks

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Interactive Workshop (4 of 5)

• High level scheduling technique
• Regulates the daily production rate (lot release)
• Schedules individual workstations (lot
  dispatching)
• Does not consider entire shop floor condition
• Schedules resources from one resource to the next

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Interactive Workshop (5 of 5)

• New forms of data collection include
• Bar Code Systems
• Digital Pictures
• Video Images
• All of the above

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Homework Assignment

• Page 511 problems
• 12.1
• 12.2
• 12.5
• Start preparing for final exam
• Chapters 7, 8, 9, 10, 11, 12
• Work on project paper presentation
• All teams ready by May 10, 2005
• Three teams on May 10, others on May 17

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Questions? Comments?