Sustainability · FMEA is a methodology for determining all possible ways that components can fail and establishing the effect of failure on the system. FMEA analysis is routinely

3/6/2018

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Embodiment Design: Parametric Design

Chapter 8

Part II

1 Dieter/Schmidt, Engineering Design 5e.

©2013. The McGraw-Hill Companies

Embodiment Design in PDP



8.6 Parametric Design

What is parametric design?



Parametric Design

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In configuration design the emphasis was on starting with the product

architecture and then working out the best form of each component.

Qualitative reasoning about physical principles and manufacturing

processes played a major role.

In parametric design the attributes of components identified during

configuration design become the design variables for parametric design.

A design variable is an attribute of a part whose value is under the control

of the designer.

This aspect of design is much more analytical than conceptual or

configuration design.

The objective of parametric design is to set values for the design variables

that will produce the best possible design considering both performance

and cost.

Dieter/Schmidt, Engineering Design 5e.


Systematic Steps in Parametric Design

Step 1: Formulate the parametric design problem.

Step 2: Generate alternative designs.

Step 3: Analyze the alternative designs.

Step 4: Evaluate the results of the analyses.

Step 5: Refine/Optimize.



Parametric Design Example:

Helical Coil Compression Spring



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Details of the Spring



Design for Manufacturing(DFM) and

Design For Assembly(DFA)

It is imperative that during embodiment design decisions

concerning shape, dimensions, and tolerances should be

closely integrated with manufacturing and assembly

decisions.

This is achieved by having a member of the manufacturing

staff as part of the design team.

Generalized DFM and DFA guidelines have been developed.

Many companies have specific guidelines in their design

manuals.

The reason for the strong emphasis on DFM/DFA is the

realization by U.S. manufacturers in the 1980s that

manufacturing needs to be linked with design to produce

quality and cost-effective designs. 8 Dieter/Schmidt, Engineering Design 5e.


Failure Modes and Effect Analysis

(FMEA)

A failure is any aspect of the design or manufacturing

process that renders a component, assembly, or system

incapable of performing its intended function.

FMEA is a methodology for determining all possible ways

that components can fail and establishing the effect of

failure on the system.

FMEA analysis is routinely performed during embodiment

design.



Design for Reliability and Safety

Reliability is a measurement of the ability of a component

or system to operate without interruption of service or

failure in the service environment.

Durability is the amount of use that a person gets out of a

product before it deteriorates.(it is a measure of the

product lifetime)

Safety involves designing products that will not injure

people or damage property.

A safe design is one that instills confidence in the

customer and does not incur product liability costs.



Design for Quality and Robustness

Achieving a quality design places great emphasis on

understanding the needs and wants of the customer.

In the 1980s, there was the realization that the only way to

ensure quality products is to design quality into the product, as

opposed to the then-current thinking that quality products

were produced by careful inspection of the output of the

manufacturing process.

A robust design is one whose performance is insensitive to

variations in the manufacturing process by which it has been

made or in the environment in which it operates.

The methods used to achieve robustness are termed robust

design, which are mostly the work of Genichi Taguchi.



Embodiment Design: Dimensions and Tolerances

Chapter 8, Section 8.7

Part III



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Dimensions

Dimensions are used on engineering drawing to specify

size, location, and orientation of features of components.

Dimensions are as important as the geometric

information that is conveyed by the drawing.

Each drawing must contain the following information:

The size of each feature

The relative position between features

The required precision(tolerance) of sizing and positioning

features

The type of material, and how it should be processed to obtain

its expected mechanical properties.



Tolerances

A tolerances is the acceptable variation in the dimension.

Tolerances must be placed on a dimension or geometric

feature of a part to limit the permissible variations in size

because it is impossible to repeatedly manufacture a part

exactly to a given dimension.

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Tight

Tolerance

• Greater ease of interchangeability of parts

• Less play or chance of vibration

• Increased cost of manufacture

Loose

Tolerance

• Poorer system performance

• Easier to assemble components

• Reduced cost of manufacture



Proper Way of Dimensioning

15

Proper way to give dimensions for

size and features

Proper way to give dimensions for

location and orientation of features



Use of Section View



Courtesy of Professor Guangming Zhang, University of Maryland.

Eliminating of Redundant Dimension




Expressing Tolerances

Bilateral tolerance:

Balanced bilateral tolerance: 2.500 ± 0.005

Unbalanced bilateral tolerance: 2.500−0.030+0.070

Unilateral tolerance:

Variation is in only one direction:2.500 0.010+0.000



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Quality Control Chart



Issues with Parametric Design

There are generally two classes of issues in parametric

design associated with tolerances on parts when they

must be assembled together:

Fit: How closely the tolerances should be held when two

components fit together in an assembly.

Stackup: The situation where several parts must be assembled

together and interference occurs because the tolerances of the

individual parts overlap.



Fit example: Bearing and Shaft

Assembly



Fit

Clearance fits:

Both the maximum and minimum clearances are positive.

ANSI has established nine classes of clearance fits form RC1

(perceptible play) to RC9 (loose running fits).

Interference fits:

The shaft diameter is always larger than the hole diameter, so that

both the maximum and minimum clearance are negative.

ANSI has established five classes of interference fits from FN1

(light drive) to FN5 (heavy shrink).

Transition fits:

The maximum clearance is positive and the minimum clearance is

negative.

ANSI has established three classes of transition fits: LC, LT, LN. 22 Dieter/Schmidt, Engineering Design 5e.


Stackup

Tolerance stackup occurs when two or more parts must

be assembled in contact.

Stackup occurs from the cumulative effects of multiple

tolerances.

A stackup analysis typically is used to properly tolerance a

dimension that has not been given a tolerance or to find

the limits on a clearance (or interference) gap.



Eliminating of Redundant Dimension




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Worst-Case Tolerance Design

In the worst-case tolerance design scenario the

assumption is made that the dimension of each

component is at either its maximum or minimum limit of

the tolerance.

Example: using 2-D dimension chain



Finding Tolerance Stack Up using a 2-D

dimension chain



Wall snap ring sleeve washer

Determination of Basic Gap Dimension

and Its Tolerance



Statistical Tolerance Design

An important method used to determine assembly tolerances is

based on statistical interchangeability.

The method is based on the following additional assumptions:

The manufacturing process for making the components is in

control, with no parts going outside of the statistical control

limits.

The dimensions of the components produced by the

manufacturing process follow a normal or Gaussian frequency

distribution.

The components are randomly selected for the assembly process.

The product manufacturing system must be able to accept that a

small percentage of parts produced will not be able to be easily

assembled into the product.



Process Capability Index (𝐶𝑝)

The process capability index, (𝐶𝑝), is commonly used to

express the relationship between the tolerance range

specified for the component and the variability (i.e.

standard deviation, 𝜎) of the process that will make it.

𝐶𝑝 =𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝑝𝑟𝑜𝑐𝑒𝑠𝑠 𝑠𝑝𝑟𝑒𝑎𝑑

𝑎𝑐𝑡𝑢𝑎𝑙 𝑝𝑟𝑜𝑐𝑒𝑠𝑠 𝑠𝑝𝑟𝑒𝑎𝑑=𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒

3𝜎+3𝜎=𝑈𝑆𝐿−𝐿𝑆𝐿

6𝜎

A capable manufacturing process has Cp at least = 1.

The relationship between the standard deviation of a

dimension in an assembly of components and the standard

deviation of the dimensions in separate components is:

𝜎𝑎𝑠𝑠𝑒𝑚𝑏𝑙𝑦2 = 𝜎𝑖

2

𝑛

𝑖=1



Normal Distribution

30

𝑧 =𝑥 − 𝜇

𝜎



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Determination of Gap and Its Tolerance

Using Statistical Method



Determination of Variation Contribution

of Each Part in an Assembly



Advanced Tolerance Analysis

When many dimensions are involved, and the mechanism

is definitely three-dimensional, a system of tolerance charts

has been developed.

For tolerance analysis on three-dimensional problems,

specialized computer programs are almost mandatory.

Some of these are standalone software applications, but

most major CAD systems have packages to perform

tolerance analysis.

They also typically support the Geometric Dimensioning

and Tolerancing (GD&T) system.



Geometric Dimensioning and

Tolerancing (GD&T)

In engineering practice this and many other tolerance

issues are described and specified by a system of

Geometric Dimensioning and Tolerancing (GD&T) based on

ASME standard Y14.5–2009.

GD&T is a universal design language to precisely convey

design intent. (Refer to Figure 8.25)

Two important pieces of information in an engineering

drawing brought by GD&T:

it clearly defines the datum surfaces from which

dimensions are measured

it specifies a tolerance zone that must contain all points of

a geometric feature



Datum

Datums are theoretically perfect points, lines, and planes

that establish the origin from which the location of

geometric features of a part is determined.

A part has six degrees of freedom in space.

Depending on the complexity of the part shape there may

be up to three datums.

The primary datum, A, is usually a flat surface that

predominates in the attachment of the part with other

parts in the assembly.

One of the other datums, B or C, must be perpendicular

to the primary datum.



Datum Feature Identifiers



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Geometric Tolerances

Geometric tolerances can be defined for the following

characteristics of geometric features:

Form:

Flatness, straightness, circularity, cylindricity

Profile:

Line, surface

Orientation:

Parallelism, angularity

Location:

Position, concentricity

Runout:

Circular runout, total runout



Material Condition Modifiers

Maximum material condition (MMC) is the condition in

which an external feature like a shaft is at its largest

allowable by the size tolerance.

Least material condition (LMC) is the opposite of MMC,

that is, a shaft that is its smallest allowed by the size

tolerance or a hole at its largest allowable size.

Regardless of feature size (RFS) means that the tolerance

zone is the same no matter what the size of the feature.

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BONUS TOLERANCE: The increase in the tolerance zone with size

of the feature is usually called a bonus tolerance because it allows

extra flexibility in manufacturing.



Guidelines for Tolerance Design

Focus on the critical-to-quality dimensions that most affect fit and function.

For the noncritical dimensions, use a commercial tolerance recommended for the

production process of the components.

A possible alternative for handling a difficult tolerance problem might be to

redesign a component to move it to the noncritical classification.

A difficult problem with tolerance stackup often indicates that the design is over

constrained to cause undesirable interactions between the assembled components.

If tolerance stackup cannot be avoided, it often is possible to minimize its impact by

careful design of assembly fixtures.

Another approach is to use selective assembly where critical components are

sorted into narrow dimensional ranges before assembling mating components.

Make sure that you have the agreement from manufacturing that the product is

receiving components from a well-controlled process with the appropriate level of

process capability.

Consider carefully the establishment of the datum surfaces.



8.8 Industrial Design

How can we do industrial design?



Industrial Design

Industrial design, also often called just product design, is

concerned with the visual appearance of the product and

the way it interfaces with the customer.

Industrial design deals chiefly with the aspects of a

product that relate to the user:

Aesthetics appeal:

Aesthetics deal with the interaction of the product with the human

senses.

Ergonomics (usability):

This activity deals with the user interactions with the product and

making sure that it is easy to use and maintain.



Visual Aesthetics

Aesthetics relate to our emotions.

Since aesthetic emotions are spontaneous and develop

beneath our level of consciousness, they satisfy one of

our basic human needs.

Visual aesthetic values can be considered as a hierarchy of

human responses to visual stimuli.



Z. M. Lewalski, Product Esthetics, Design & Development Engineering Press, Carson City, NV.

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8.9 Human Factors Design

What is human factors design?



Human Factors Design

Human factors is the study of the interaction between people,

the products and systems they use, and the environments in

which they work and live.

This field also is described by the terms human factors

engineering and ergonomics.

Human factors design applies information about human

characteristics to the creation of objects, facilities, and

environments that people use.

Human factors expertise is found in industrial designers, who

focus on ease of use of products, and in industrial engineers,

who focus on design of production systems for productivity.



Human Physical Effort

Measurement of the physical effort that a man could

perform in the manual handling of materials (shoveling

coal) and supplies was one of the first studies made in

human factors engineering.

45

Correspondence Between Human Factors Characteristics & Product Performance



Sensory Input

The human senses of sight, touch, hearing, taste, and smell

are chiefly used for purposes of controlling devices or

systems.

In selecting visual displays remember that individuals differ

in their ability to see, so provide sufficient illumination.

Different types of visual displays differ in their ability to

provide on-off information, or exact values and rate of

change information.



Muscle Strength of Arm, Hand, Thumb



MIL-STD-1472F, p. 95.

Types of Visual Displays



Adapted from D. Ullman, The Mechanical Design Process, 4th ed., McGraw-Hill, New York,2010.

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Characteristics of Common Visual

Displays



Adapted from D. Ullman, The Mechanical Design Process, 4th ed., McGraw-Hill, New York, 2010.

User-Friendly Design

Simplify Tasks

Make the controls and their functions obvious

Make controls easy to use

Match the intentions of the human with the actions

required by the system

Use mapping

Displays should be clear, visible, large enough to ready

easily, and consistent in direction

Provide feedback

Utilize constraints to prevent incorrect action

Standardize



Reaction Time

The reaction time is the time to initiate a response when a

sensory signal has been received.

The reaction time is made up of several actions.

We receive information in the form of a sensory signal,

interpret it in the form of a set of choices, predict the

outcomes of each choice, evaluate the consequence of

each choice, and then select the best choice.



Anthropometric Data

Anthropometrics is the field of human factors that deals

with the measurements of the human body.



From FAA Human Factors Design Guide.

Design for Serviceability

Serviceability is concerned with the ease with which

maintenance can be performed on a product.

There are two general classes of maintenance:

Preventive maintenance is routine service required to

prevent operating failures, such as changing the oil in your

car.

Breakdown maintenance is the service that must take place

after some failure or decline in function has occurred.



Design for Packaging

Packaging is related to visual aesthetics because attractive,

distinctive product packaging is typically used to attract

customers and to identify product brands.

Packaging provides physical protection against mechanical

shock, vibration, and extreme temperatures in shipping

and storage.

Different packaging is required for liquids, gases and

powders than for solid objects.

A shipping package provides information about the

recipient, tracking information, instructions regarding

hazardous materials, and disposal.



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8.10 Life-Cycle Design

What is life-cycle design?



Life-Cycle Design

The worldwide concern over global warming coupled

with concerns over energy supply and stability have

moved design for the environment (DFE) to a top

consideration in design for all types of engineering

systems and consumer products.

The major issues of life-cycle design are:

Design for packaging and shipping

Design for serviceability and maintenance

Design for testability

Design for disposal



8.11 Prototyping and Testing

How can we do prototyping and testing?



Prototype & Model Testing Throughout

the Design Process

Phase Zero:

Product Concept Model

Conceptual Design:

Proof-of Concept Prototype

Embodiment Design:

Alpha-Prototype Testing

Detail Design:

Beta-Prototype Testing

Manufacturing:

Preproduction Prototype Testing



Rapid Prototyping

Create a CAD model

Convert the CAD model to

the STL file format

Slice the STL file into thin

layers

Make the prototype

Post processing:

Removing and cleaning any

support structures.



R. Noorani, Rapid Prototyping, John Wiley & Sons, New York, 2006, p. 37.

Rapid Prototyping by Stereolithography

(SL)



J. A. Schey, Introduction to Manufacturing Processes, 3rd ed., McGraw-Hill, New York, 2000.

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RP Processes

Stereolithography (SL):

This process uses a UV laser beam to build up layers of solid polymer by

scanning on the surface of a bath of photosensitive polymer.

Selective laser sintering (SLS):

This process was developed to use stronger, higher-melting-temperature

materials than polymers in the RP process.

Laminated Object Modeling (LOM):

This process is an older method that continues to have useful applications

because of the simplicity of the equipment that is needed.

Fused-Deposition Modeling (DFM):

This process is an example of several liquid-state deposition processes used to

make prototypes.

Three-dimensional Printing (3DP):

This process is a RP process that is based on the principle of the inkjet printer.



Student Made Prototypes

62

Injection Molded Part Paper Prototype Made by LOM

Plastic Prototype Made by DFM



Examples of Testing

Testing of design prototypes

Modeling and simulations

Testing for all mechanical and electrical modes of failure

Specialized tests on seals, or for thermal shock, vibration,

acceleration, or moisture resistance, as design dictates

Accelerated life testing.

Testing at the environmental limits

Human engineering and repair test

Safety and risk test

Built-in test and diagnostics

Manufacturing supplier qualification

Packaging



Statistical Design of Testing

The discipline of statistics has provided us with the tools

to do just that in the subject called Design of Experiments

(DoE).

Benefits from statistically designed experiments:

more information per experiment will be obtained than

with unplanned experimentation.

statistical design results in an organized approach to the

collection and analysis of information.



Classes of Statistically Designed

Experiments

Factorial designs:

Experiments in which all levels of each factor in an

experiment are combined with all levels of all other

factors.

Blocking designs:

Use techniques to remove the effect of background

variables from the experimental error.

Response surface designs:

Used to determine the empirical relation between the factors

(independent variables) and the response (performance

variable).



Different Behavior of Response y



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8.12 Design for X (DFX)

What is DFX?



Design for X (DFX)

The terminology to describe a design methodology

became known as Design for X, where X represents a

performance measure of design, as in:

Design for Manufacture (DFM) Chapter 13

Design for Assembly (DFA) Chapter 13.6

Design for the Environment (DFE) = Sustainability Chap 10

The development of the DFX methodologies was

accelerated by the growing emphasis on concurrent

engineering.

Today, design improvement goals are often labeled, “Design

for X,”



Steps of DFX Strategy

Determine the issue (X) targeted for consideration

Determine where to place your focus.

Identify methods for measuring the X characteristics and

techniques to improve them.

The DFX strategy is implemented by insisting the product

development team focus on the X and by using

parametric measurements and improvement techniques

as early in the design process as possible.



Documents

Sustainability · FMEA is a methodology for determining all possible ways that components can fail and establishing the effect of failure on the system. FMEA analysis is routinely