ME 530 – Designing for Production

Dr. A. Tolga Bozdana

Assistant Professor

Mechanical Engineering

University of Gaziantep

Product Design for Manufacture and Assembly

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What is Design?

Sythesis involves the identification of design elements that comprise

the product, its decomposition into parts, and the combination of those

parts in the form of a workable and functional system.

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Analysis is decomposing the problem into manageable parts so that

we can understand how this design should perform under service, and

hence apply the appropriate disciplines of engineering to that design.

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A good design is the essence of engineering, which requires analysis

and synthesis.

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Design establishes and defines solutions to problems not solved

before, or new solutions to problems already solved in different ways.

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Constituents of Design

Compromise: balancing multiple and sometimes conflicting

requirements.

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Choice: making choices between many possible solutions at all

levels, from basic concepts to smallest detail of shape.

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Complexity: decisions on many variables and parameters.�

Creativity: creation of something that has not existed before or not

existed in the designer’s mind before.

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The “four C’s of design” are the constituents of a reliable design:�

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Detail DesignEmbodiment Design

Design Process

Product architecture

Arrangement of

physical elements to

carry out function

Configuration design

Preliminary selection

of materials and

manuf. processes,

Part modeling/sizing

Parametric design

Robust design,

Tolerances, Final

dimensions,

DFM/DFA

Detail design

Detailed

drawings and

specifications

Conceptual Design

Concept evaluation

Pugh concept

selection, Decision

matrices

Define problem

Problem statement,

Benchmarking,

QFD, PDS, Project

planning

Gather information

Internet, Patents,

Trade, Literature

Concept generation

Brainstorming,

Functional

decomposition,

Morphological chart

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Importance of Design

An extremely important issue during product design is the performance of

manufacturing system at all levels, from supply chain to production line.

This states that the product must be designed to fit the facility instead of

designing the manufacturing system around the product.

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Consequently, manufacturing companies (and solution providers) have

developed many design decision support tools that form the class of

Design for X (DFX) methodologies.

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Accurate predictions allow product development team to create superior

designs that perform satisfactorily in all ways. This reduces the number of

redesign iterations and the development costs.

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Making poor estimations leads to poor decisions and nonfeasible product

designs causing unforeseen problems and redesign of such products.

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Successful new product development requires the ability to predict the

life-cycle impacts at the early stages of the product development process.

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Concept of DFX Methodologies

Answering such questions requires information about product design,

manufacturing requirements, and production quantities along with

information about the manufacturing system that will create the product.

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How much inventory will be required to maintain superior customer

service in an international supply chain?

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How long will it take for the factory to complete customer orders?�

Does the production line have enough capacity to achieve the desired

production rate?

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It refers to methods that evaluate manufacturing system performance.�

Design for Production (DFP)

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Concept of DFX Methodologies

There are subsets of DFM based on manufacturing process (e.g. design

for casting, forging, sheet-metal forming, machining, welding, etc.) and

based on material type (e.g. design for metals, plastics, ceramics, etc.).

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It brings major benefits when used during the design of new generations

of products by concerning cost and difficulty of making.

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It is an approach for improving manufacturing productivity.�

Design for Manufacture / Manufacturability (DFM)

DFA works in conjunction with DFM to overcome design difficulties.�

For instance, ensuring that where a pin is to be fit into a hole that is only

slightly larger in diameter, then it is much easier if the end of the pin or

the entry to the hole (or both) are chamfered or finished with a radius.

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Once parts are manufactured, they need to be assembled into products

and subassemblies. DFA tackles the problems and issues at this stage.

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Design for Assembly (DFA)

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Concept of DFX Methodologies

Similar to DFM and DFA, DFP can also lead a product development

team to consider changing the product design to avoid problems or

improve profitability.

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On the other hand, DFP evaluates manufacturing system performance

at the production line, factory, or supply chain level.

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DFM and DFA evaluate the materials, the required manufacturing

processes, and the ease of assembly. In other words, they study the

feasibility and cost of manufacturing a product at the operation level.

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Like DFM and DFA, DFP is also related to the product's manufacture.�

DFP versus DFM / DFA

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Concept of DFX Methodologies

DFE can/should be involved at all stages of DFP, DFM, and DFA.�

Currently, environmental impact is considered in design along with

function, apperance, cost, quality, and other traditional design factors.

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DFE has become popular in recent years, and yet being considered as

a legal requirement for production of specific product systems.

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The most cost-effective way to improve the long-term environmental

condition of the earth is through early and high-priority concern for the

environment in product design, so called “green design”.

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Design for Environment (DFE)

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Material and Process Selection in Design

Design

Service conditions

Function

Cost

Materials

Properties

Availability

Cost

Processing

Equipment selection

Influence on properties

Cost

Business considerations�

Environmental profile�

Processing characteristics�

Performance characteristics�

General Criteria for Selection:

Selecting the best material is also connected with the processing of the material

into the finished part.

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An incorrectly chosen material can lead not only to failure of the part, but also to

unnecessary life-cycle cost.

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Performance Characteristics of Materials

The performance (i.e. functional

requirements) of a material is

expressed in terms of physical,

mechanical, thermal, electrical,

or chemical properties.

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Structural engineering materials

can be divided into main groups:

metals, ceramics, and polymers

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Sub-division leads to elastomers,

glasses, and composites.

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Finally, there is technology driving

class of electronic, magnetic, and

semiconductor materials.

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Chief characteristics of materials

and the relations between failure

modes and mechanical properties

are given on the next page.

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Performance Characteristics of Materials

Temperature sensitiveLow thermal conductivityHigh thermal conductivity

Electrically insulatingElectrically insulatingElectrically conducting

DurableBrittleTough

CompliantStiffStiff

WeakStrongStrong

PolymersCeramicsMetals

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Classification of Manufacturing Processes

Assembly processes: subassembly of finished products.8.

Polymer processing: injection molding, thermoforming, etc.4.

Heat and surface treatment processes: carburizing, nitriding, electroplating, etc.7.

Joining processes: welding, soldering, riveting, bolting, etc.6.

Powder processing: sintering, compaction, and so on.5.

Material removal or cutting (machining) processes: turning, milling, drilling, etc.3.

Deformation processes: forging, rolling, extrusion, etc.2.

Solidification (casting) processes: molten metal, plastic or glass casting1.

The common methods of material processing are as follows:

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Factors in Process Selection

Basic equation for the unit cost of a part is

depending upon the material, tooling and

labour costs.

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Consider the life cycle cost of the part

allowing for maintenance and disposal.

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The most important factor in selection of

manufacturing process and material.

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Cost of manufacture1.

n

C

n

CCC

LC

M ~++=

no. of parts produced per unit time

(the production rate)

ñ :

annual no. of parts producedn :

labour cost per unit timeCL :

capital cost of machinery and toolingCC :

material cost per unitCM :

The concept of flexibility in manufacturing (i.e. a process can be adapted to

produce different products or variations of the same product).

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The concept of an economical lot size (i.e. the break-even volume at which one

process with higher tooling costs becomes less expensive per unit than a process

with lower tooling costs).

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The minimum no. of pieces (volume) to justify the use of manufacturing process.�

Quantity of parts required2.

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Factors in Process Selection

Hence, candidate processes are detemined based on the complexity of the part.�

Many processes will not allow the manufacture of parts with undercuts.�

Parts can also be symmetrical or nonsymmetrical.�

Most mechanical parts have 3D shape although sheet-metal parts are simply 2D.�

The complexity of a part refers to its shape, size and type/number of features on it.�

Complexity3.

The next slide shows Prima selection matrix for material and process selection.�

Also, some materials may be too brittle for shaping by deformation processes while

others may be too reactive to have good weldability.

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For instance, the melting point of material determines applicable casting processes.�

Melting point, level of deformation resistance and ductility are the chief factors.�

Physical, mechanical and electrical properties of materials play an important role.�

Materials4.

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Prima Selection Matrix

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Factors in Process Selection (cont.)

Good dimensional accuracy and meeting tolerances in order to justify the use of

selected material and process for the manufacture of part for achieving required

functionality without incurring extra costs.

3.

Improved surface finish (i.e. lower surface roughness) of a part determines the

appearance, affects the assembly with other parts and increases its resistance

to corrosion, fatigue and wear.

2.

Freedom from internal defects (voids, porosity, micro cracks, segregation) and

external or surface defects (surface cracks, extreme roughness, discoloration).

1.

The quality of the part is defined by three aspects:�

Required quality of the part5.

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DFM and DFA Guidelines

DFM Guidelines

Utilise the special characteristics of processes (care about built-in causes or side effects).8.

Design multifunctional parts (e.g. a part may serve as a structural member and a spring).4.

Avoid or minimise the secondary operations (unless required for special/aesthetic purpose).7.

Avoid too tight tolerances (to reduce costs without deteriorating the functionality).6.

Design parts for the ease of fabrication (affects material selection).5.

Use common parts across product lines (use same materials, parts and subassemblies).3.

Standardise the components (to reduce costs and to enhance quality).2.

Minimise total number of parts (without making other parts too heavy or complex).1.

DFA Guidelines

Minimise assembly direction (design parts to be assembled from one direction).4.

Minimise handling in assembly (design parts so that assembly positions are easy to achieve).6.

Maximise compliance in assembly (adjust assembly forces required for non-identical parts).5.

Avoid separate fasteners (snap fits must be preferred wherever possible instead of screws).3.

Minimise the assembly surfaces (fewer surfaces need to prepared for assembly).2.

Minimise the total number of parts (part not need to be assembled is not required in design).1.