Hakan Gultekin1 A Synthesis of Decision Models for Tool Management in Automated Manufacturing.

Hakan Gultekin 1

A Synthesis of Decision Models for Tool Management in Automated Manufacturing

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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

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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

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Tool Management Requires

A tool monitoring strategy:

To coordinate tooling inventory, tool tracking, tool loading/unloadingTo ensure that the appropriate tools are available in the right time in the right quantitiesTo account for tool availability and tool changesTo coordinate tool transfers between machines and tool cribsTo identify and react to unexpected tool wear and breakage

A control strategy:

A scheduling strategy:

A planning strategy:

A design strategy:

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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

Better tracking and cost accountability of tooling

Due to minimizing number and types of required toolsDue to reduced tools’ stockoutsand setup delays

Increase in productivity

Reduction in production costs

Improvements in part and routing flexibility

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Order Delivery Schedule

Process Planning andPart Programming

Machine Sequencing

Scheduling

Machine Grouping

Capacity Requirements Planning

Tool Requirements Planning

Master Production Planning

Process MonitoringIndividual Tool Monitoring

Tool Placement in Magazine

Tool Allocation to Machines

Machine Loading

Tool Inventory Control

Tool Replacement

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Tool Specific Issues

Number and types of tools Tool speed rates Tool feed rates Technology used to monitor and control

machining and tooling conditions

TOOL LEVEL MACHINE LEVEL SYSTEM LEVEL

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Level of integration necessary between the various production functions

Greater capital and time involved in developing hardware, software and technical support for automated manufacturing


More critical in automated manufacturingthan manual operations because of:


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Spindle speed Depth of cut

Feed rate

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



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1-Tool Life

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

Taylor:

VTn = k

Extended tool life equation:

Vt=C/dxfy

Expected tool life

Cutting speed Emprical constants (depends on m/c conditions andmaterial composition)

Cutting speed fora given tool life

Depth of cut

Feed rate

Empirical constants


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2-Cutting Tool Economics

Economic tool life: optimal time interval between planned tool replacements.

Tradeoff:As machine speed increases, tooling

expenses rise exponentiallyvs

Throughput rates increases Machine speed should be controlled


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Cook’s formula:

Y=(Yo+nG)/(n+1)

Y: mean tool usage costYo=initial cost of the tooln: number of times a tool is regroundG: cost of a single regrind

Economic tool life is found where Y is minimized


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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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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

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

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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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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Sophisticated information systems to: coordinate delivery of the proper tools to

specific m/c’s 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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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

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

ToolMagazine

Work table

Part

Stored Tools

Empty Storage Slot

Active Tool

Tool Change Arm


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1-Equipment Selection

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

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

Required tool may be absent and a toolchange must occur before that operation can begin


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2-Sequencing on a Flexible Machine

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

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

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 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

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

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


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1-Master Production Planning

Effective planning models must take into

account: Tool magazine sizes Tool commonalities Tool changing times Tool lives


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Tool management issues are particularly

visible in: Part type selection Machine grouping Loading problems


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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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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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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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2- Machine Grouping and Loading Can be considered jointly, separately or

iteratively Many studies in the literature



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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

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

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 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

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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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


5- Tooling Inventory Management

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TOOL LEVELDESIGN PLANNING CONTROL

-Standardization of Tool Types (3)

-Tool Tracking Technology (3)

-Tool Information Requirements (5)

- Assignment of Tool Types to Operations (2)

- Economic Process Planning (21)

-Tool Life (13)

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SINGLE MACHINE LEVELDESIGN PLANNING CONTROL

-Monitoring and Control Technology (0)

-Tool Magazine Capacity (0)

-Tool Changing Technology (0)

-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)

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SYSTEM LEVELDESIGN PLANNING CONTROL

-Number and Type of Machines (0)

-Tool Loading & Handling Technology (0)

-Loading Duplicate Tools (0)

-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)

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Questions?

Hakan Gultekin1 A Synthesis of Decision Models for Tool Management in Automated Manufacturing.

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