1. Process models – Cinderella among design models
Chris McMahon

2. 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

3. 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

4. Models of the Designed Artefact
Engineering drawing picture here

5. Models of the Designed Artefact
Engineering diagram picture here

6. Models of the Designed Artefact
here

7. Models that Help to Work in the Abstract
here

8. Models that Help to Work in the Abstract
here

9. Models for Analytical Support
FE and CFD pictures here

10. Models for Analytical Support
here

11. Models for Analytical Support
here

12. Models to Help Manufacture
Mould analysis picture here

13. Models to Help Manufacture
Machining toolpath picture here

14. 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

15. 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 . . .

16. High-level Models: Bombardier
Bombardier stage gate model here

17. High-level Models: Airbus
Airbus stage gate model here

18. Pahl and Beitz Model DESIGN ACTIVITIES DESIGN STAGE DESIGN PHASE TIME•
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
DEFINITIVE
LAYOUT
PRELIMINARY
TASK
DOCUMENTATION
SOLUTION
CONCEPT
DESIGN PHASE
CLARIFICATION
CONCEPTUAL
DESIGN
DETAIL
EMBODIMENT
TIME
UPGRADE & IMPROVE
Pahl and Beitz Model

19. Design Structure Matrix
Design structure matrix picture here

20. Integrated Definition, IDEF

21. Integrated Definition, IDEF
IDEF0 picture here

22. IDEF0 in Standards
IDEF0 picture here

23. Petri Nets; UML

24. 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

25. Concept Selection High Level
Concept generation method
Specification
Selection methodology C
Function model
Concept selection
Selected concept I O
Product information M
Designer

26. Concept Selection Low(er) Level
Concept generation method
Selection methodology
Specification
Functional model
Possible concepts
Chosen Concept
Concept Generation
Concept Selection
Product information
Designer

27. Design Analysis High Level
Estimated fatigue life
Analysis guidelines
Geometry
Load cases
Analyst
Fatigue analysis
Materials data
Software & workstation

28. Design Analysis Low(er) Level
Analysis guidelines
Geometry
Estimated fatigue life
Fatigue life estimation
Stress analysis
Stresses
Materials data
Load cases
Analyst
Software & workstation

29. 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.

30. 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>

31. 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.

32. 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.

33. Activity as Transfer Function
What is the nature of the error between analytical and experimental transfer function?
is it explained by uncertainty in data?
Estimated stresses
Geometry
Load cases
Stress analysis
Materials data
Transfer function

34. 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

35. 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.

36. 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

37. 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.

38. 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

39. Virtual Repository Database
IINTEREST Approach
Web Browser
Internet - HTTP
Web Server
Dynamic BPA Page (XML or HTMLor DHTML)
3-tier
Architecture
BPA Assembler
BPA Page template
Virtual Repository
Indexed
JDBC
BPA storage
Virtual Repository Database

40. INTEREST Project Topic Description General Information
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 fillets How to simplify the geometry of radii
Search results of the close matching algorithm

41. 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?

42. Thank You for your attention Email: c.a.mcmahon@bath.ac.uk
Contact me at: