process models – cinderella among design models

Mechanical Engineering

Process models – Cinderella among design

modelsChris McMahon

Mechanical Engineering

Outline

Modelling in engineering design

Product models

Process and activity models

Exploiting process models

– Recording the outcome of design processes

– A framework for capture of engineering experience

– As a basis for design reuse

Questions

Mechanical Engineering

Modelling in Engineering Design

Modelling pervades engineering design

The output from the design process is a collection of models of the designed artefact

Models are used to allow designers to work with the artefact in the abstract

Models are used to allow analytical and computational techniques to be applied in the evaluation of the artefact

Models are used to assist in manufacture

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Models of the Designed Artefact

Engineering drawing picture here

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Models of the Designed Artefact

Engineering diagram picture here

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Models of the Designed Artefact

http://www.idtnet.co.uk/Idtweb_home1%20SR%20IR%20mirror%20CAD%20model.jpg here

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Models that Help to Work in the Abstract

http://www.hq.nasa.gov/office/pao/History/SP-4009/images/1-086.gif here

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Models that Help to Work in the Abstract

http://www.architecture.ca/firms/gearch/casaddledome/rendering.jpg here

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Models for Analytical Support

FE and CFD pictures here

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Models for Analytical Support

http://www.mfg.mtu.edu/cyberman/machtool/machtool/vibration/aniabsor.gif here

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Models for Analytical Support

http://www.itl.nist.gov/div898/handbook/apr/section1/apr166.htm here

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Models to Help Manufacture

Mould analysis picture here

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Models to Help Manufacture

Machining toolpath picture here

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The Historical Growth of Modelling

The growth of modelling is part of a general growth in the codification of design.

Codification is used to help cope with complexity, and as a means of exercising control over the manufacturing process

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Process Modelling

Process models are used to describe and assist in planning and monitoring the design process and design activities.

Process modelling is used

– To describe the overall process

– To describe activities, information flows etc.

– To help plan and manage the process

– To assist in standards development, training, knowledge management . . .

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High-level Models: Bombardier

Bombardier stage gate model here

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High-level Models: Airbus

Airbus stage gate model here

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DESIGN ACTIVITIES

• Clarify task• Elaborate the specification

• Identify essential problems• Establish function structures• Search for solution principles• Combine into concept variants• Evaluate against technical & economic criteria

• Develop preliminary layouts & form designs• Select best preliminary layouts• Refine against technical & economic criteria

• Optimise & complete form designs• Check for errors & cost effectiveness• Prepare preliminary parts list• Prepare preliminary production documents

• Finalise details• Complete detail drawings & production documents• Check all documents

DESIGN STAGE

SPECIFICATION

DEFINITIVELAYOUT

PRELIMINARYLAYOUT

TASK

DOCUMENTATION

SOLUTION

CONCEPT

DESIGN PHASE

TASKCLARIFICATION

CONCEPTUALDESIGN

DETAILDESIGN

EMBODIMENTDESIGN

TIM

E

UP

GR

AD

E &

IM

PR

OV

E

Pahl and Beitz Model

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Design Structure Matrix

Design structure matrix picture here

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Integrated Definition, IDEF

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Integrated Definition, IDEF

IDEF0 picture here

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IDEF0 in Standards

IDEF0 picture here

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Petri Nets; UML

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How May Process Models be Used?

Let us start with two simple examples:

– A conceptual phase design activity concept selection

E.g. selection of a drive mechanism

– A detail phase design activity analysis

E.g. fatigue analysis of an automotive part

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Concept Selection High Level

Selected concept

Selection methodology

Specification

Conceptgeneration

method

Function model

Product information

Designer

Concept selectionI

O

C

M

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Concept Selection Low(er) Level

Possibleconcepts

Selection methodologySpecification

Conceptgeneration

method

Functional model

Product information

Designer

Concept Generation

ChosenConceptConcept

Selection

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Design Analysis High Level

Estimated fatigue life

Analysis guidelines

Geometry

Load cases

Analyst

Fatigueanalysis

Materialsdata

Software&

workstation

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Design Analysis Low(er) Level

Stresses

Analysisguidelines

Analyst

Stressanalysis

Estimated fatigue lifeFatigue

lifeestimation

Geometry

Load cases

Materialsdata

Software &workstation

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Recording the Design Process

The design process is currently recorded through text documents that provide reports on the outcome of activities/processes – e.g. (for the two examples given) concept design report, analysis report

By using more formal representations of process outcomes it will be possible for the information-dependencies and decision-making in the design process to be traced.

– This will integrate product and process models.

– It might build on XLANG, XRL, WSDL, PSL etc.

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How Might This be Done? Document templates and mark-up may allow process outcomes

to be recorded in a straightforward manner, e.g.<ACTIVITY RECORD>

<ACTIVITY ID>Activity name</ACTIVITY ID>

<ACTIVITY METADATA> Metadata describing activity </ACTIVITY METADATA>

<SUMMARY> Activity summary </SUMMARY>

<INPUT> Reference to input – URI, metadata </INPUT>

:

<MECHANISM> Reference to mechanism – e.g. staff input</MECHANISM>

:

<CONTROL> Reference to control – URI, metadata </CONTROL>

:

<DESCRIPTION> Activity description and commentary – text </DESCRIPTION>

<OUTPUT> Reference to output – URI, metadata </OUTPUT>

:

<COMMENTARY> Commentary on output </COMMENTARY>

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XML Record of Analysis Process <ACTIVITY RECORD>

<ACTIVITY ID>Stress analysis</ACTIVITY ID>

<ACTIVITY METADATA> Metadata describing activity – component, project, date, etc</ACTIVITY METADATA>

<SUMMARY> Activity summary – objectives etc., and overall result </SUMMARY>

<INPUT> Reference to input – URI, metadata for CAD model, material and load case data </INPUT>

<CONTROL> Reference to control – URI, metadata for best practice advice </CONTROL>

<MECHANISM> Reference to mechanism – staff and software details </MECHANISM>

<DESCRIPTION> Activity description and commentary – text </DESCRIPTION>

<OUTPUT> Reference to output – FE output files and analysis summary data </OUTPUT>

<COMMENTARY> Commentary on output </COMMENTARY>

Combined with consistent metadata this may make it very much more straightforward to audit the design process.

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Capture of Engineering Experience

Process modelling provides a basis for accumulation of engineering knowledge:

– It provides a framework for representing understanding of the state of data, information and analytical relationships to be developed.

– It allows verification and validation feedback from comparison of experimental and analytical results

– It allows use of service experience to correct and update the understanding of the imprecision in engineering models, and to provide improved use case models for incorporation into future design processes.

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Activity as Transfer Function

Estimated stresses

Geometry

Load cases

Stress analysis

Materialsdata

Transfer function

What is the nature of the error between analytical and experimental transfer function?

is it explained by uncertainty in data?

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Categories of Evidence

Design knowledge may be categorised according to the extent to which comparison of analytical and experimental results are available

– Narrow or wide range of design parameters (e.g. one-off – narrow; mass production – wide)

– Narrow or wide range of load cases (i.e. do we understand the way this artefact can be loaded in use?)

– Point values or statistical variation in parameters and load cases

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Categories of Evidence

Direct evidence - evidence available for the specific design case. E.g. correlated analysis and experimental results for particular products

Indirect evidence - evidence is only available for related design cases and/or for parts of the process; evidence may be limited to qualitative evidence

– Evidence of performance of similar techniques using similar models

– Evidence of performance of parts of the process

– Evidence of satisfactory/unsatisfactory performance of actual artefacts – e.g. some designs are known to exhibit weaknesses.

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Design Reuse

At present we largely concentrate on reuse of components and concepts:

– E.g. part carry-over in automotive design; standardisation etc. – reduces inventory, tool costs etc.

– Reuse can involve systems, sub-assemblies, parts, features – but so far little effort on reuse of activities

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Design Reuse

Knowledge of process may assist with conventional design reuse:

– Using the “input information” for an activity assists in searching for outputs (case-based reasoning).

E.g motor selection based on motor application requirements

– Capture of the design history, rationale and intent may give more confidence in reusing components and sub-systems.

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Design Reuse

But in terms of engineering activity, is there more scope for reuse of the process information itself?

– Research in workflow modelling - standardisation of descriptions for reuse of workflow models.

– Can we extend that to the reuse of the information processing patterns in design activities?

– Example – INTEREST project Best Practice Adviser Assembled best practice advice giving general

advice, context-specific advice and examples, using a dynamic hypermedia approach and a repository of design advice and examples

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Web Browser

Web Server

BPA Assembler

BPA Page template

Dynamic BPA Page (XML or HTMLor DHTML)

Virtual Repository

BPA storageVirtual

Repository Database

JDBC

Internet - HTTP

3-tierArchitecture

Indexed

IINTEREST Approach

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INTEREST ProjectTopic Description

At this stage, one may choose to simplify and idealise the CAD geometry. For example, only take a half model into account due to the symmetry, and remove some unimportant small details. However, this step could be skipped if analysts choose to model the whole geometry instead.

General Information

General information for activity "Simplify and idealise CAD geometries"General information on "How to simplify geometries"General information on "How to take advantage of symmetry"

Context-specific information on its Geometric Features

How to simply the geometry of filletsHow to simplify the geometry of radii

Search results of the close matching algorithm

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Questions

Do process representations provide the opportunities that I have described, and do they work in an HCI context?

Do we need different fundamental modelling techniques for different process applications, or is there a “UPML”?

Can we integrate the representation of processes in general with the recording and representation of actual processes. Are different modelling methods necessary?

Does the model drive the design or does the design drive the model?

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Thank You for your attention

Contact me at:

Email: c.a.mcmahon@bath.ac.uk