A Synthesis of Decision Models for Tool Management in Automated Manufacturing

1

• A Synthesis of Decision Models for Tool
  Management in Automated Manufacturing

2
Scope of the Paper

• Evaluates tool management approaches
• Identifies operational tradeoffs
• Analyzes models developed to address management
  decisions involving tooling

• Accounts for 25 to 30 of both fixed and
  variable costs of production in automated
  manufacturing

3
Management Decisions Involve

• Selecting optimal machining parameters
• Most economic processing rate for a particular
  operation
• Loading of tools and jobs on machines
• Determination of optimal tool-mix inventories
  needed for a particular production schedule

4
Tool Management Requires

• A design strategy

• A planning strategy

To coordinate tooling inventory, tool tracking,
tool loading/unloading

• A scheduling strategy

To ensure that the appropriate tools are
available in the right time in the right
quantities
To account for tool availability and tool changes

• A control strategy

• A tool monitoring strategy

To coordinate tool transfers between machines and
tool cribs
To identify and react to unexpected tool wear and
breakage
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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 stockouts and setup delays

• Improvements in part and routing flexibility

• Better tracking and cost accountability of tooling

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Order Delivery Schedule
Process Planning and Part Programming
Tool Requirements Planning
Master Production Planning
Capacity Requirements Planning
Machine Grouping
Scheduling
Tool Inventory Control
Machine Loading
Machine Sequencing
Tool Allocation to Machines
Tool Placement in Magazine
Process Monitoring
Individual Tool Monitoring
Tool Replacement
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Tool Specific Issues
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Number and types of tools
• Tool speed rates
• Tool feed rates
• Technology used to monitor and control machining
  and tooling conditions

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Tool Specific Issues
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL
More critical in automated manufacturing than
manual operations because of

• Level of integration necessary between the
  various production functions
• Greater capital and time involved in developing
  hardware, software and technical support for
  automated manufacturing

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TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL
Tool Specific Issues
Spindle speed
Depth of cut
Feed rate
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TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL
Tool Specific Issues

• Major tool management concerns
• Tool life
• Cutting tool economics
• Tool standardization
• Information requirements

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1-Tool Life
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Useful life depends on
• Machining environment (speed, feed rate)
• Material composition of the part and the tool
• Depth of the cut

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1-Tool Life
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL
Expected tool life

• Taylor
• VTn k
• Extended tool life equation
• VtC/dxfy

Emprical constants (depends on m/c conditions
and material composition)
Cutting speed
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2-Cutting Tool Economics
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Economic tool life optimal time interval between
  planned tool replacements.
• Tradeoff
• As machine speed increases, tooling
• expenses rise exponentially
• vs
• Throughput rates increases
• Machine speed should be controlled

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2-Cutting Tool Economics
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Cooks formula

Y(YonG)/(n1)
Y mean tool usage cost Yoinitial cost of the
tool n number of times a tool is reground G
cost of a single regrind
Economic tool life is found where Y is minimized
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2-Cutting Tool Economics
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Objectives include Production rate, profit rate,
  variable cost, surface roughness.
• Decision variables Speed, feed rate, spindle
  revolution rate.
• Multiple shallow cuts vs fewer deeper cuts
• More realistic cases tool life is treated as a
  random variable

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2-Cutting Tool Economics
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Using same tool for a mixture of part
• types
• Minimizes the of tool changes
• Minimizes the of tools required
• Increases part routing flexibility

However, existing tool life models are unable to
provide reliable predictions of tool life under
these conditions
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3-Tool Standardization
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• 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 and improved system reliability

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4-Information requirements
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Common tool management database
• Data record should be linked to vendors, part
  types, machines
• Extensive information requirements both for
  planning and monitoring tooling

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4-Information requirements
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Tools must be monitored for wear to permit
  planning for replacement and regrinding.
• Continuous monitoring Adaptive control to adjust
  m/c speed and feed rates appropriately
• Off-line monitoring Increase non-productive m/c
  times and may result in workpiece damage.

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4-Information requirements
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Sophisticated information systems to
• coordinate delivery of the proper tools to
  specific m/cs in time
• provide location information
• correlate the of tools needed for the quantity
  of parts to be produced
• offer acceptable substitutes when needed

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4-Information requirements
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• 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 at the Machine Level
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Loading and placing a set of tools in the
  machines magazine
• Determining the part input sequences to meet
  certain magazine constraints
• Establishing tool replacement strategies

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Tool Management at the Machine Level
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL
Tool Change Arm
Tool Magazine
Stored Tools
Active Tool
Part
Work table
Empty Storage Slot
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1-Equipment Selection
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Specifications of a tool magazine and an
• automatic tool changer include
• Tool storage capacity
• Type of accessing system
• Whether tool loading is manual or automatic
• Tool standards used
• Maximum tool diameter, length, weight

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2-Sequencing on a Flexible Machine
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Total number of tools required is usually larger
  than the available magazine storage capacity

Required tool may be absent and a tool change
must occur before that operation can begin
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2-Sequencing on a Flexible Machine
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Objectives include
• Min of group tool change instances
• Min of individual tool changes
• Min tool setup, tool replacement and
  
• m/c times

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3-Tool Placement in a Magazine
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Many tools of various sizes
• Placement of individual tools determine magazine
  capacity (large tools)
• Weight balancing
• Tool search time

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3-Tool Placement in a Magazine
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• One copy of each tool to save magazine capacity
  or multiple copies because of short life or often
  use
• Open research question Determination of the
  optimal of copies of each tool

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4-Tool Replacement
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Tool replacement strategy is two-fold
• When to replace a particular tool due to wear
  or failure
• Which additional tools to change early, given a
  tool change must take place.

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4-Tool Replacement
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Non-bottleneck machines Tool change may not
  result in lost system throughput
• Bottleneck machines Change several tools early
  when one tool fails.

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System Management
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

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

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1-Master Production Planning
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Effective planning models must take into
• account
• Tool magazine sizes
• Tool commonalities
• Tool changing times
• Tool lives

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1-Master Production Planning
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Tool management issues are particularly
• visible in
• Part type selection
• Machine grouping
• Loading problems

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1-Master Production Planning
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• 1- Part-Type Selection
• Two approaches
• Batching approach Partition the part types into
  batches, machine each batch individually, change
  all the tools
• Flexible approach Select the part type to be
  produced next, machine according to ratios that
  balance the workload

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1-Master Production Planning
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Flexible approach
• More frequent tool changes but the time to change
  tools is much less
• More uniform utilization of machines and setup
  personnel
• Decreased order leadtime and increased
  productivity
• More duplicate tooling and more sophisticated
  tool transport system

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TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL
1-Master Production Planning

• 2- Machine Grouping and Loading
• Machine grouping problem Partition machines into
  groups so that each machine in a group is tooled
  to be able to perform same set of operations
• Loading problem Allocate the operations and
  required tools among the machine groups subject
  to technological and capacity constraints

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TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL
1-Master Production Planning

• 2- Machine Grouping and Loading
• Can be considered jointly, separately or
  iteratively
• Many studies in the literature

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TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL
1-Master Production Planning

• 3- Manual vs Automatic Tool Handling
• Tool transporters requires large investment in
  tools, magazines, setup and delivery system,
  causes additional scheduling problems
• Some setup time on the magazines is reduced
• No formal characterization of operational
  tradeoffs.

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2-Machine Sequencing and Process Monitoring
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Tools are resources that must be scheduled and
  controlled along with parts.
• Few scheduling models fully consider the
  implications of tooling constraints
• Machine, operation and routing flexibilities
  increases complexity of scheduling

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3-Process Planning for Economic Production Rates
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Improved scheduling performance can be based on a
  production rate/tool wear tradeoff
• Once a throughput target is set processing times
  can be manipulated to reduce cost and increase
  tool lives
• Slow down noncritical machines

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4- Spares Management
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Tool handling system
• Ability to substitute non-identical tools
• Need to provide alternate part routes
• of identical tools required
• Tool magazine capacities
• Tool life distributions
• Tool costs

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5- Tooling Inventory Management
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Operational flexibility requires many tool types
• At least 3 duplicate tools one in tool magazine,
  one as backup, one in preparation
• of types in storage increases over time
• Determination of the appropriate of tools to be
  purchased

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5- Tooling Inventory Management
TOOL LEVEL
MACHINE LEVEL
SYSTEM LEVEL

• Custom tools are more expensive but can shorten
  processing times
• Optimal reorder points and safety stock levels
  are not studied
• The tradeoff between tool availability,
  manufacturing capacity, tool reorder points and
  the overall investment in tooling stocks

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TOOL LEVEL
DESIGN
PLANNING
CONTROL
- Assignment of Tool Types to Operations
(2) - Economic Process Planning (21)
-Tool Life (13)
-Standardization of Tool Types (3) -Tool
Tracking Technology (3) -Tool Information
Requirements (5)
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SINGLE MACHINE LEVEL
DESIGN
PLANNING
CONTROL
-Tool Replacement Strategy Due to Expected
Tool Wear (5) -Sequencing Parts/
Scheduling Tools (8) -Sequencing Operations/
Assigning Tools to Slots (4)
-Tool Replacement Strategy Due to Actual
Wear (2) -Adaptive Control at One Machine (1)
-Monitoring and Control Technology
(0) -Tool Magazine Capacity (0) -Tool
Changing Technology (0)
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SYSTEM LEVEL
DESIGN
PLANNING
CONTROL
-Production Planning (2) -Part Type Selection
(7) -Cell Grouping Facility Loading
(14) -Tool Change Times and Detailed
Scheduling (6) -Processing Rate
Determination Bottleneck Control (6) -Spares
Levels (0) -Allocation of Spares (7) -Tool
Inventory Control (4)
-Adaptive Control Strategies (2)
-Number and Type of Machines (0) -Tool
Loading Handling Technology (0) -Loading
Duplicate Tools (0)
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• Questions?