Complexity Metrics for Design &

Manufacturability Analysis

Carlos Rodríguez-ToroCranfield University, UK

(Shaping the Complexity of a Design)

Outline of This Presentation

Designers’ Sandpit background.Manufacturing cost analysis – reasons for complexity measure.Past studies – survey review.Complexity analyses.Theoretical considerations.Final discussion – conclusions. Ongoing work.Questions and suggestions.

The Designers’ Sandpit

‘Assembly-oriented environment’ written in C++.Implements DFA as design evaluation tool.Incorporates methods for generation and evaluation of concept design ideas, manufacturing analysis, assembly planning and design advice.

Website: http://eng.hull.ac.uk/research/sandpit/

DFMA

Manufacturability

Functional Handling

Assembly

DFMA – Analysis Steps

Manufacturing Cost Estimation

Most factors can be measured, but geometry and topology are still subjective,Shape complexity affects manufacturing and assembly operations…

Relative Cost I deal P rocess Cost M aterial Cost

Volum e

W aste Coeffi cient

Cost of M aterial

To lerances

M aterial Su itability

Shape Com plexity

How to Measure Complexity?

Past Studies – Survey (1)

Definitions of complexity declare it as ... Abstract estimation, Context dependent, Information management, Associated with product flexibility and tendency

to product mistakes.

Conceptual definitions – design (geometry).Quantitative representations and mathematical models – manufacturing (systems complexity).

Past Studies – Survey (2)

Geometry. Computer graphics and FEA.

Topology. Feature recognition techniques, Group technology part codes.

Assembly analysis. Assembly sequence, Insertion trajectories, Gripping configuration, etc.

Specific Complexity Measures

Axiomatic design (Nam Suh, 1999).

Time independent (imaginary and real complexity). Time dependent (uncertainty of future events).

Systems complexity (Calinescu et al., 2000).

Entropic measures of information (amount of information required to predict state of the system).

Complexity and complicatedness. (Victor tang, 2001).

Function of number of parts and their interactions. Beneficial property, given reduction of

complicatedness.

Evaluating Shape Complexity

2D objects – shape similarity for image retrieval.

FEM – amount of volume transformed.

Statistical methods. Stochastic methods for part orientation

yield the measure of shape complexity.

Complexity in the Sandpit

DFA methodology – evaluation of manufacturing processes for each component.Part count reduction – minimises assembly operations, but increases component complexity (geometry).

Complexity Analysis Taxonomy

Com ponent Assem bly

Manufacturing Process Structural Sequence

GeometricShape

I nsertion, Alignmentand Handling

Critical Assembly Path,Parallel P rocessing

No of I nsertionOperations

Component Complexity

Manufacturing complexity. Geometric shape, Counterbalance part count

reduction.

Process complexity. Difficulty associated with

alignment, insertion and handling operations on individual parts.

DFA techniques provide a scoring system to evaluate these aspects.

Assembly Complexity

Structural complexity. Structural breakdown – implications in

ease of assembly (critical paths). Subassemblies – increase product

flexibility (parallel processing), but impact part tracking (mating conditions, storage and inspections).

Sequence complexity. Number of insertion operations is

proportional to the number of components.

Badly defined sequences incorporate unnecessary operations.

Theoretical Considerations

Complexity related to… Number of parts, Complexity of each part,

Part count vs. Part complexity (efficiency?)

Part Count Complexity

Assembly Cost

Optimum balance

Component cost

Overall complexity as the sum of component and assembly complexity.Is there a threshold value for the overall complexity?Spotted - Geometry as the common factor.

Overall Sandpit Requirements

Manufacturing cost estimation,Establish precise definitions of each type of complexity,Complexity metrics that can be used in conjunction with other metrics,Shape similarity comparison (for reduction of variance or enhancement of product flexibility)

Conclusions (1)

Complexity is a problem of semantics and interpretations are only relevant within the same context,Product design presents challenges for specific complexity metrics that need be comparable,

Conclusions (2)

The problem is the creation of methods and metrics for assessing the impact of design decisions on production (product design efficiency),Shape/geometry is a common factor amongst the different types of complexity of a product and fundamental for the manufacturing analysis.

Ongoing Work

Definition of precise geometric reasoning methodology for manufacturability analysis (algorithms),Definitions of units of measurement,Identification of hidden dependencies and additional factors to the problem of complexity metrics.