FixtureBased usefulness measure for hybrid process planning

1
Fixture-Based usefulness measure for hybrid
process planning
i-Design Lab.

• i-Design Lab.
• ?? 3?? ???

2
Abstract

• Hybrid process planning approach.
• Variant and generative PP while avoiding
  limitations.
• Identify existing design and process planning.
• Traditional geometric similarity measures are
  inadequate.
• New fixture-based usefulness measure.

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introduction

• Developing generative process planning for
  complex machined part is a difficult challenge.
• Less successful selecting the fixture needed to
  complete the PP.

To address this problem
Developing new hybrid approach to PP
4
introduction
This paper describes a new hybrid approach
Generative approach
Variant approach

• Better approach for creating a preliminary
  process plan.

• Very useful technique for completing the process
  plan.
• Adding the details like fixturing

Successful generative process planning approach
Variant fixture planning approach

5
introduction

• Background describes previous work
• Describes our hybrid process planning approach
• Defines the fixture planning problem
• Solve this problem
• Example
• Summarize

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Background

• PP describes the steps to manufacture a product.
• PP is subjective and time-consuming procedure.
• It requires extensive manufacturing knowledge
  about capabilities, tools, fixtures, materials,
  costs, and machine availability.
• CAPP automate many functions, reduce error, and
  process more quickly.

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Background
Variant approach
Generative approach
Synthesize a PP directly. Ideal process plan
Tools of choice. Commercially available.
Part mix changes. out-of-data PP.
Quite difficult Work in restricted Domain.
limitations
Hybrid process planning approaches.

• Attempt to exploit knowledge in existing plans
  while generating a process plan for a new design.
• Not yet developed comprehensive solutions.

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Background (Generative approach)
Its ideal but quite difficult to develop.

• Typical approach
• Feature-by-feature basis by retrieving processes
  from the manufacturing knowledge repository.
• Mant89,Kamb93, Gupt94a, Yue94
• Develop for various aspects of process planning.
• Difficulties arise form interaction (workpiece
  fixturing, process selection, process sequencing)
• As a result, most existing system work only in
  restricted domains.
• Part system Geel95
• Marketed commercially
• Not really achieved significant industrial use

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Background (Variant approach)

• Typically, VPP is based on the Group Technology
  coding schemes (DCLSSS, MICLASS, OPITZ)
• 1. captures a new products critical design and
  manufacturing attribute (GT code)
• 2. group products with similar GT code in to
  product families
• Variant approach proceeds as follows
• 1. New design D ? determines GT code
• 2. index into DB (P/D)
• 3. engineer modifies P
• 4. produce P

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Background (Variant approach)

• Another classifying designs use geometric
  properties of solid and CAD model.
• SUN95 described a similarity measure for
  solids based on properties of a boundary
  representation.
• ? not incorporate manufacturing considerations
• 2. Herr97, Sing97 developed plan-based design
  similarity measures
• ? mapping design attributes into process plan
  characteristics.
• ? its more accurate and more relevant to
  process planning

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Background (hybrid approach Variant hybrid)

• Park93 acquiring and storing knowledge as a
  schema (GPP), seeking schema with same features
• Mare94 capture the plan knowledge
• Lu98 case-based approach
• Robust hybrid approach must consider
• - feature interaction
• - precedence constraints
• - tolerances
• - other critical design information
• Must consider how to store, classify, and
  retrieve useful design and PP information

Existing hybrid approaches have limited
capabilities
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Background (fixture planning)
workpiece
Reference cutting tool
Hold
support
Locate

• In machining, an important part of PP is fixture
  planning
• Many different types of fixtures and fixture
  element
• Fixture has to satisfy stability, location,
  restraint, accessibility, cost
• Process planning and fixture planning
• Two problems Address separately, Effect on each
  other
• Research has focused on
• mathematical solution for locating and holding a
  part
• expert systems and computer-aided
  fixture-planning.

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Hybrid process planning

• Combine the best characteristics of both variant
  and GPP
• Avoid the worst limitations of each

Variant approach
Generative approach

• useful for completing the process plan.
• Adding the details like fixturing

• Better approach for creating a preliminary
  process plan.

• Previous paper Elin97
• This paper describe an approach that reflects our
  more recent idea.

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Hybrid process planning
Due to first designs complexity and additional
constraint
Almost any fixture can be used
Few fixture can be used
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Hybrid process planning

• Extends the generative approach Gupt94a
• Using that generative approach for process
  selection
• Variant procedure select fixtures, complete the
  process plan
• Feature-based representation
• Machining feature Volume resulting from a
  machining operation on one machine setup
• Represent a design as a collection of machining
  feature
• F-Rex feature extractorRegl97 identify the
  volumetric machining features
• These feature represent different possible
  machining operation

• Proposed design is a solid model.
• Information about available machining
  operations.

Assuming
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Hybrid process planning

• Repeat the following steps until promising
  feature-based model
• Generate a promising FBM from the feature set
• Generate promising operation plan for the FBM
• Estimate the achievable machining accuracy of
  operation plan
• Design fixture search the existing design and
  process contain fixture could be used for the new
  design ? modify the retrieved fixture
• Exit
• No promising operation plans were found failure
• Otherwise success
• Returning the operation plan best tradeoff
  among quality, cost, time

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Fixture selection

• Design a fixture for each setup
• Setup is a set of consecutive operations (same
  fixture)

Too much effort
Method used in the past
Calculating each fixtures feasibility
modification for infeasible fixture
search quickly
Search the existing designs for process plan that
contain fixtures that could be used for the new
designs process plan
Our approach
Database

• Designs process plan

• Sequence of setup
• Machining operation
• Fixture in each setup

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Fixture selection

• For each setup in the new designs process plan.
• Identify an existing setup whose fixture can be
  used for new setup.
• The old fixture modify, if necessary
• Verify the fixture
• - geometrically locate and constrain
  workpiece without cutting force
• - contact between part and fixture during
  machining operations.

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Fixture selection
D existing design P existing process plan S
existing setup
New process plan
D new design P incomplete process plan S
incomplete setup
Existing process plan
Find a D in D whose process plan contains a
setup S that uses a fixture that could be used
for S

• Usefulness measure should have following
  characteristics.
• The first setups fixture can be used for the
  second setup
• Process planner convey information precisely.

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Approach

• Three step approach for developing a
  fixture-based usefulness measure.

Define fixture usefulness measure
Fixture
characteristic
attribute
Setup
Planner
How well an existing fixture F can be used for
another setup S
Function
Define mapping
Relate the setup attributes to the fixture
characteristics.
Define usefulness measure
Usefulness measure
Usefulness of S1 for S2 , not necessarily
symmetric.
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Example

• Presented here illustrates the approach for
  defining a usefulness measure and is not intended
  to be a perfect measure.
• Fixture characteristics - six locating pins(1/2)
• Three on the bottom locating surface.
• Two on a side locating surface.
• One on a third locating surface.

Assume second locating surface is longer than
third locating surface.
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Example

• Fixture characteristics - three clamp(2/2)
• Top of the part.
• Side opposite second surface.
• Side opposite third surface.
• c1, c2, c3 vector-clamping location.
• k1, k2, k3 clamping force in -z, -y, -x.

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Example

• Setup Shs following nine attribute

Maximum cutting force
height
width
length
A h2 lt A h3
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Example - 1st approach

• Three step approach for developing a
  fixture-based usefulness measure.

Define fixture usefulness measure
Fixture
characteristic
attribute
Setup
Planner
How well an existing fixture F can be used for
another setup S
Function
Define mapping
Relate the setup attributes to the fixture
characteristics.
Define usefulness measure
Usefulness measure
Usefulness of S1 for S2 , not necessarily
symmetric.
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Example - 1st approach

• Fixture usefulness measure f ( F i , S h ) -
  (1/3)

Clamps position and force
Setups dimension and Maximum cutting force

• Without modifying Locating clamping point
• Without clamping force Because they are
  sufficient to withstand the cutting force

Fixture xy plane
Fixture coordinate workpiece coordinate
correspond
Fixture coordinate workpiece coordinate is
turned 180 degree
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Example - 1st approach

• Fixture usefulness measure f ( F i , S h ) -
  (2/3)

Clamps position and force
Setups dimension and Maximum cutting force

• Without modifying locating clamping point,
• Maximum increase clamping force

Fixture xy plane
Fixture coordinate workpiece coordinate
correspond
Fixture coordinate workpiece coordinate is
turned 180 degree
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Example - 1st approach

• Fixture usefulness measure f ( F i , S h ) -
  (3/3)

Clamps position and force
Setups dimension and Maximum cutting force

• Modify nine locating clamping points.
• By maximum distance in any dimension.

• These usefulness measure can be used to compare
  fixture relative to a given setup.
• F1 is most useful fixture for S h (without any
  change)
• F2 is more useful than F3 (change only camping
  force)
• If f ( F 4 , S h ) (2, 0.1 ?f) , its more
  useful than F 2 .
• If f ( F 5 , S h ) (3, 2?p) , its less
  useful than F 3 .

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Example - 2nd approach

• Three step approach for developing a
  fixture-based usefulness measure.

Define fixture usefulness measure
Fixture
characteristic
attribute
Setup
Planner
How well an existing fixture F can be used for
another setup S
Function
Define mapping
Relate the setup attributes to the fixture
characteristics.
Define usefulness measure
Usefulness measure
Usefulness of S1 for S2 , not necessarily
symmetric.
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Example - 2nd approach

• Mapping that correlate the setup attribute with
  fixture characteristics

The overall size of the fixture depends upon the
size of the workpiece
Fixture clamping forces have to be create enough
to withstand the cutting forces
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Example - 3th approach

• Three step approach for developing a
  fixture-based usefulness measure.

Define fixture usefulness measure
Fixture
characteristic
attribute
Setup
Planner
How well an existing fixture F can be used for
another setup S
Function
Define mapping
Relate the setup attributes to the fixture
characteristics.
Define usefulness measure
Usefulness measure
Usefulness of S1 for S2 , not necessarily
symmetric.
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Example - 3th approach

• Sh has the same size workpiece as setup Sk
• Experiences no greater cutting forces

old
new

• Sh has the same size workpiece as setup Sk
• The maximum cutting force in Sk is ?f greater
  than the

maximum cutting force in Sh

• Workpiece dimensions are different
• The maximum difference between the workpiece

dimension is ?p
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Example - 3th approach
f(S4,S0) (2, 0.1?f)
f(S1,S0) (1, 0)
f(S2,S0) (2, ?f)
f(S5,S0) (3, 2?p)
f(S3,S0) (3,?p)

• S 1 is most useful fixture for S 0 (without any
  change)
• S 2 is more useful than S3 (change only camping
  force)
• If f ( S 4 , S 0 ) (2, 0.1 ? f) , its more
  useful than S 2 .
• If f (S 5 , S 0 ) (3, 2?p) , its less useful
  than S 3 .

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Example
Length cutting force
L
H
H
W
X
-X
Y
-Y
L
Z
-Z
W
f(S1,S0) (1, 0)
f(S2,S0) (3, 3)
S1 more useful for S0 then S2
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Summary and conclusions

• Hybrid variant-generative process planning
  approach
• Generative planner is a better approach for
  creating a preliminary process plan.
• Variant approach is a very useful technique for
  completing the process plan.
• Describes an approach for defining a usefulness
  measure.
• Identify designs and process plans that have
  useful fixture.
• Usefulness approach could be applied to fixture
  planning in other domains.