mec531 chapter 1_bibi

PART A:Mechanical Design Process

Dr. Bibi Intan Suraya Murat

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Introduction to Mechanical Design Process1. The Phase of Design2. Problem Identification and Definition3. Product Design Specification4. Concept Development, Evaluation and

Selection

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Reference:Dieter, G. Engineering Design – A Materials and Processing Approach, 4th Edition, McGraw Hill, 2009 Ulrich, K. and Eppinger, S. Product Design and Development, McGraw-Hill, 2000

What is design?

To formulate a plan for human satisfactionTo accommodate particular need based on problem

based solutionsExamples:1…….2…..3……To produce a product

The process of identifying and deeply understanding a problem or need, thinking creatively, using sound deci-sion-making processes to identify the best solution, and using project management and teamwork skills to drive the entire process, implement the solution, test it, and modify it.

What is Mechanical Engineering Design?

Design of a thing / system / product Integrates mathematics, basic sciences, engineering sci-

ences, economics and other subjects.Examples………………….1……….2……….3…….. Design sometimes begins when engineer recognizes a

need….. Specify Malaysia-based engineering problem…..

A design problem summaries what is undesirable in a particular situation, and the problem is considered solved when an improvement in the situation is achieved and

acceptable to all parties

Do you have the required skills? Yes? No?REMEMBER, there will always be limitations or

constraints during the project!Sometimes, great designs are invented, but have

been lost…..or failed to work…REMEMBER, presentation is a selling job!3 vital skills for a successful engineer: ->> ORAL, WRITTEN, GRAPHIC

Student Car Project

Chassis design Steering system Suspension system Braking system Power train Final competition……

Stage 1: First meeting1. Choose a leader2. List the team member 3. Please prepare yourself with these information (10 min-

utes class presentation):- Define the part / define job-scope- The working principle of the part- Elements / components / types involved for the

working part- Define the common problems with the part

Exercise 1

Think of a product….and thousands related questions from your boss / group’s members…

How does it begin? And what needs to be done?

The Phase of Design

7 Phases of Design Process

Phase I. Conceptual

Design

Phase II. Embodiment

Design

Phase III. Detail Design

Phase IV. Planning for Manufacture

Phase VII. Planning for Retirement

Phase VI. Planning for

Use

Phase V. Planning for Distribution

Define Problem

Parametric Design

Configuration Design

Product Architectur

e

Evaluation of

Concepts

Concept Generatio

n

Gather Informatio

n

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Phase 1

7 Phases Design Process

Phase I. Conceptual Design

Define Problem

Evaluation of Concepts

Concept Generation

Gather Information

• Most important steps in the engineering design process is identifying customer needs.

• The customer needs can be gained from:– Interviewing customers– Focus group– Customer survey– Customer complaints

• Tools to achieve this:– Benchmarking– QFD- Quality funtion deplyoment– PDS- Product Design Specifications

Identification of Customer Needs / Benchmarking

Question to Ponder• Who are my customer?• What does the customer want?• How can the product satisfy the customer while generating profit?• Which needs are critical? Which are secondary? How well are these needs being

currently met?• How do customers use existing products to meet these needs? What other products are

out in the market?• How do customers perceive current products relative to meeting their needs?• Why do customers use the existing products? Practical and/or emotional reasons?

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Benchmarking• Method for measuring company operation against the best company inside and outside of

the industries.• Select the product, process, or functional area that is to be benchmark.• Identify the performance metrics that will be measured and used for comparison.• Compare the best in class product or process with the in house equivalent using the

performance metrics.• Specified program and actions to meet an exceed the competition

QFD / House of Quality

3. Relationshipmatrix

2. How to satisfycustomer wants

(technical requirements)

4. Correlation matrix

6. C

om

peti

tive

ass

ess

men

t

7. Competitive

technicalevaluation

5. Target values

1. What the customer

Wants(customer

requirements)

Customer importance

ratings

Weighted rating

A planning and problem solving tool that is finding growing acceptance for translating customer requirements into engineering characteristics of a product.

3.1 importance ranking

1.1

cust

om

er

rati

ng

Trade off be-tween our ability

(2),

How we going to meet the customer

requirements?

What cus-tomer wants

from our product?

Intersect both (1) and (2) We com-

pare our-selves

with our competi-

tors, based on

(1)

Planned Tech. specs

We compare ourselves with our competitors,

based on (2)

Exercise 2

Think of the chosen product again (exercise 1), then write the QFD document for that product.

PDS

• Is a documented statement of what the product is to do.• List of customer needs and design specifications• A PDS specifies a problem not a solution.• It is dynamic rather than static – can be improved, changed to suit design

requirements.• Sometimes it defines the constraints/boundary of the design.• Design specifications to consider:

-- >> functional, safety, quality, manufacturing, economic, ergonomic, ecological, aesthetics, life-cycle

Example of PDS: 1. What do you want the product or process to be (goals)?2. What do you want the product or process to do

(functions)?3. What attributes might this new product/process have to

meet functional requirements (features)?4. What limitations must the design adhere to

(constraints/standards)?5. Generate an specification list with requirements,

functions, and features6. Financial requirements7. Social, political & legal requirement

Example PDS: Portable Winch Design Brief From internal market research, it has been decided that IWC need to design a general purpose winch to sell to the cable and pipe laying market sector. The winch should be portable but have mounting points for the end user. It is important that the winch sits within out current range of 'Excel General Purpose winches'. 1.0 Performance 1.1 Lift / lower a load of 2.5 tones (+/- 10%).1.2 Draw in cable in at a rate of 0.2 m/s.1.3 The winch drive should cut out when the load exceeds 10% of the specified load.1.4 Drive to stop lowering load when only 1.5 meters of cable remains on winch drum.1.5 Winch should operate with forward, reverse, stop and inch facility.1.6 Any braking system employed, should produce a braking torque of 150% the full load torque.1.7 Winch should have a manual device to control the brake release and load descent in the event of a power failure.1.8 In the event of the winch 'overrunning', a manual safety relay/braking device should operate within 1 second or before the load exceeds a speed of 3m/s.1.9 The product should be portable but with the option for permanent mounting.1.10 The product must use a portable power source, preferably a diesel engine.1.11 The weight of the product must be sufficient to aid the stability of the product.1.12 Efficiency of the unit should be high, preferably in the area of 20 - 30%.1.13 The drum should hold 50m of cable. 2.0 Environment 2.1 The winch drive and power unit should be power unit.2.2 The unit will be mainly used in European weather conditions. But we could expect sales of about 2% unit volume to the Far East.2.3 Temperature ranges:· -28 degree C – European· 12 - 44 degree C - Far East2.4 The product may experience humid conditions.2.5 Corrosion resistance may be considered by the use of special materials or surface protection methods.2.6 Any noise from the equipment should not exceed 95 dB at a distance of 1.0m.2.7 The winch will be stored in supplier’s warehouses before sales.

3.0 Target Product Cost 3.1 The product should have an end-user cost of £5500 within Britain.3.2 The cost of manufacture should be less than £2750.3.3 The cost of packaging and shipping should be no more than 15% of the manufacturing cost. 4.0 Competition 4.1 The winch will be operating against equivalent models which include the following companies:· Swansom - England· Oholom - Sweden· Winderhock - Germany 5.0 Standards and Specifications 5.1 Standards to be adhered to:· BS 5000 part 99 Motor Performance· BS 6105 and BSEN 20898(1) Bolts· BS 6322(2) & BS 4320 Nuts and washers· BS 7676 and BS 4517 Gears· BS 3019 Welding· BS 5989 Bearings· BS 2754 Electrical Insulation· BS 5646 pt4 Bearing Housing· BS 4235 Keys and Keyways· BS 7664 Painting· BS 1399 Seals 6.0 Testing 7.1 Testing is to be carried out on 5% of units.7.2 All cables should be tested to BS3621.

Exercise 3

Think of the chosen product again (exercise 1), then write the PDS document for that product.

Phase 1


Phase I. Conceptual Design

Define Problem


Concept Generation

Gather Information

• Information from Internet– Engineering URLs

• Patent Literature– Intellectual Property– Patents

• Handbook

Phase 1


Phase I. Conceptual

Design

Define Problem


Concept Generation

Gather Information

• Brainstorming

• Functional decomposition

• Morphological chart

Generating Design Concepts• Brainstorming

• Most common method used by design teams for generating ideas for design concepts in conceptual design.

• Think of all the possible limitations or shortcomings of the product.

• Functional decomposition (breakdown of functions)• Establish logical flow -describing the transformation

between the initial and final states of a system / device.

• Physical decomposition → separating the product or subassembly directly into its subsidiary subassemblies and components (output = physical decomposition block diagram).

• Functional decomposition → a general description of a device is refined into more specific arrangements of functions and subfunctions.

• Morphological chart• It is a table based on the function analysis• It is a visual aid used to come up with different ideas• Example: http://www.eng.fsu.edu/~

haik/design/idea_generation.htm

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http://www.eng.fsu.edu/~haik/design/idea_generation.htm

http://www.eng.fsu.edu/~haik/design/idea_generation.htm

1.3.2 Functional decomposition

Urban Car

Suspension system

Steering system

ChassisBraking system

Power train

1. Suspension system

1.1 Tires 1.2 Springs1.3 Shock absorbers

E.g.:

1. Physical decomposition

2. Developing Functional decomposition from the physical decomposition

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1.3.2 Functional decomposition

1.4 Linkage

1.1.1………??

1.2.1 Single coil…function??1.2.2 Air spring…..????

1.3.1 Mech damper1.3.2 Strut1.3.3 Absorber

1.4.1 Anti-sway bars…function???

1.3.3 Morphological chart

Morphological chart – Concept explanation

Exercise 4

Each team must develop a Functional Decomposition and Morphological Chart for the chosen product. Work out the most

detailed Functional Decomposition that you can. For FD, remember to stick to function and avoid defining form at this point!

Phase 1


Phase I. Conceptual

Design

Define Problem


Concept Generation

Gather Information

• How can a rough conceptual idea evaluated?• Absolute comparison – concept is

compared to a set of requirements• Relative comparison – concepts are

compared to each other

Tools to use:1.4.1 Comparison Based on Absolute Criteria

1.4. 2 Pugh’s Concept Selection Method

1.4.3 Weighted Decision Matrix

1.4.1 Comparison Based on Absolute Criteria

• Strongly dependent on the expertise of the design team.• Comparing the concepts to a series of absolute requirements

• Evaluation based on judgment of feasibility of the design• Overall evaluation:- definitely will not work- conditionally will work- yes it will work

• Evaluation based on assessment technology readiness• The technology used must be matured enough to be used in the product

without additional research needed.• Evaluation based on go/no-go screening of customer requirement

• Question back customer requirement either being addressed by concept or not

• Answer should range from (yes-go, maybe-go, no-no go).• If a concept has a few no-go responses, modify the concept rather

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1.4.2 Pugh Concept Selection Method

• This method compares each concept relative to a reference or datum concept.• Each criterion determines whether the concept is better than, poorer than or about the

same as the reference concept.• Steps in this Pugh concept selection method:

1. Choose the criteria by which the concepts will be evaluated- Can refer to QFD (House of Quality).

2. Formulate the decision matrix- Concepts on the row headings and criteria on the column headings.

3. Clarify the design concepts-Make sure every team member understand every developed concept.

4. Choose the datum concept- Choose a good concept, and mark as the datum concept. Concepts are

compared.5. Run the matrix

- Concept is compared to the datum for each criterion.- Use a three-level ratings, better (+), worse (-) or same (S).

6. Evaluate the ratings-Sum up the ratings.

7. Establish a new datum and rerun the matrix- Choose the best-rated concept as the DATUM.- Eliminate the lowest rating concepts.

8. Examine the selected concept for improvement opportunities- Objective: improve on the best existing.

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• In Pugh’s selection method one concept may turn out to be better than another concept.

• Do we know how apart how apart they really are?

• We may actually need more quantitative results to make a better selection.

• We need a way to rank ideas in a scaled manner…

• Rank the design criteria design criteria with a weighting factor. It is preferred to choose criteria that is measurable such that for each concept a numerical value can be considered against the criteria.

• Score each concept against each design criteria using a ratio scaleUse 5 point (0-4) scale when information regarding criteria is not very detailedUse 11 point (0-10) scale when criterion information is complete

• Multiply the scores for each concept for corresponding weighting factor of the criteria being considered.

• Add up the weighted ratings of concepts.

• Declare the concept with highest score, winner.

Weighted Decision Matrix

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E.g.: Crane hook Proposed concepts :

Concept 1 : Steel plates welded togetherConcept 2 : Steel plates riveted togetherConcept 3 : Cast-steel hook (monolithic)

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Step 1 – Identify the design criteria : Material cost Manufacturing cost Time to produce Durability Reliability Reparability

Step 2 – Determine the weighting factor for each design criteria Construct hierarchical objective tree

Example. Ref book: Dieter Objective tree for the design of a steel

crane hook.

Crane hook

Cost Quality in service

Mat. Cost

Manuf. Cost

Reparability Durability

Reliability

Time to produce

O1= 1.0

O11= 0.6 O12= 0.4

O111= 0.3

O112= 0.5

O113= 0.2

O121= 0.6

O122= 0.3

O123= 0.1

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Step 3: Determine the weighting factor for each of design

criteria.

Step 2: Determine the design criteria

The weights of in-dividual categories at each level of the

tree must add to 1.0

Design CriterionWeight factor

Units

Concept 1 Concept 2 Concept 3

Magnitude Score Rating Magnitude Score Rating Magnitude Score Rating

Mat cost 0.18 RM/kg 60 8 1.44 60 8 1.44 50 9 1.62

Manuf. Cost 0.3 RM 2500 7 2.1 2200 9 2.7 3000 4 1.2

Reparability 0.12 Experience Good 7 0.84 Excellent 9 1.08 Fair 5 0.6

Durability 0.24 Experience High 8 1.92 High 8 1.92 Good 6 1.44

Reliability 0.12 Experience Good 7 0.84 Excellent 9 1.08 Fair 5 0.6

Time to prod.

0.04 Hours 40 7 0.28 25 9 0.36 60 5 0.2

7.42 8.58 5.66

• Step 3 - Form the decision matrix

Step 4: Calculate the weighting factor. Multiply the weight as you go up

the chain.

Mat cost: 0.3 x 0.6 x 1.0 = 0.18

Step 5: Give the score based on the 0-10 (inade-quate-excellent)

list

Step 6: Total rat-ings


Design

Parametric Design


Product Architectur

e

• Preliminary Design.• Decisions are made in this design phase: strength,

material selection, size, shape, and spatial compatibility.

• Any major changes beyond this design phase become very expensive.

The Phase of Design


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• 3 major activities:1.Product architecture

• Arrangement of the physical functions• Dividing the overall system into subsystem module• How the physical components of the design are to be arranged and combined?

2.Configuration design• Preliminary selection of materials, modelings and sizing of parts• What features (e.g., holes, ribs, splines and curves) will be present and those

features are to be arranged in space relative to each other?3.Parametric design

• Involves the information on the part configuration and aims to establish its exact dimensions and tolerances

• Important aspect of parametric design is to examine the part, assembly and system for design robustness

Phase II

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Common Questions to Ask: Will it Work? Is it safe?

What function does it serve? Will it be made from scratch, bought in, or made

from a semi-finished material? How does it fit in with the rest of the design?

What development will be required? How long will it last?

How might it fail in practice?

• Embodiment Design: the process in which a structured development of the preferred concept is carried out

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Design

Parametric Design


Product Architectur

e

• Arrangement of the physical elements to carry out its required function.

• Relationship among the components in the product and the function the product performs.

• i.e. defining the building blocks of the product in terms of what they do and their interfaces

• Design for Human Factor• Creating user-friendly Design• 2 types:

• Integral architecture• Modular architecture

The Phase of Design


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Integral Architecture• The implementation of function uses only

one or few chunks.• Component perform multiple function: so

called ‘function sharing’• E.g., wrench, screw driver• 1 physical element save large number of

function• Changes made to any component tend to

propagate to other (or many physical elements)

• Often adopted when there is a constraint of weight, space or cost

Modular Architecture• The chunk implement only one or a few

function.• Accomplish overall function through

combination of building block/modules• Interaction between chunks are well defined• E.g., computer• Advantages:

• Components can be manufacture in higher quantity (reduce cost)

• Shortening product development cycles (mod. develops independently)

• Easier to evolve over time• To adapt to needs of different customers• To replaced components as they wear

out or used up

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Design for human factor• Designing something and considered the

interaction between human and product• Deals with the characteristics, abilities and

need of human and the interfaces between human and product technical

• Related with ergonomics and anthropometric data

• 4 ways human interact with a product:• as an occupant of workspace• as a power source (muscle power)• as a sensor (looking for warning light)• as a controller (control pedal)

Creating user-friendly design• Fit the product to the user’s physical

attributes and knowledge (from ergonomics and anthropometric data)

• Simplify tasks-straightforward• make the controls and their functions

obvious (place the control for function adjacent to the device)

• Provide feedback (sound or flashing dashboard light)

• Good displays (digital/analog)• Make controls easy to handle• Standardize (arrangement of brake and

clutch)• Anticipate human errors (provide warning or

emergency button)

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Design

Parametric Design


Product Architectur

e

• Establishing the shape and general dimensions of the components.

• Preliminary selection of materials, parts, sizing, etc

• Components include special purpose parts, standard parts, standard assemblies or modules.

• Develop from function.• Configuration depending on:

1. Available materials and production methods

2. Spatial constraints3. Product architecture

The Phase of Design


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Modeling• Represent physical appearance of the design

ideas• Engineers use model for thinking,

communicating, predicting, controlling, and training

• various types (e.g., scale models, prototype, equtions, CAD/CAE modeling)

Simulation• Model subject to various input or

environmental condition• To observe how they behave• Explore the result has might be obtained form

the real-world system• Manipulation of the model• Usually involves computer performance• E.g., prototype model, simulator

Analysis• Involves calculation form understanding of

mathematical and engineering fundamental• Ensuring the design concept are able and

reliable to performed and manufactured• Finite-element analysis solves wide range of

engineering problems area such as stress, thermal, flow, etc

• Several type of software (Nastran, Abacus, Lusas, Ansys)

• *However, understanding the fundamentals are important

Materials Selection• An important aspect of design for mechanical,

electrical, thermal, chemical or other application is selection of the best materials

• Systematic selection of the best material for a given application begins with properties and costs of candidate materials.

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Design

Parametric Design


Product Architectur

e

• Final Dimensions, Design for Manufacturing, Structural analyses

• Set the dimensions and tolerances in order to maximize quality and performance and minimize cost.

• Objective : to set values for the design variables that will produce the best possible design considering both performance and manufacturability.

• A few established method in designing to maximize performance and quality :

– FMEA (Ratings for severity, occurrence and detection of failure)– Design for reliability– Robust design– Design for Assembly (DFA)– Design for Manufacture (DFM)

The Phase of Design


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Failure Mode and Effect Analysis (FMEA)FMEA is designed to assist the engineer improve the quality and reliability of designProperly used FMEA provides the engineer several benefits such as:

• Improve product/process reliability and quality• Increase customer satisfaction• Early identification and elimination of potential product/failure modes• Prioritize product/process deficiencies• Capture engineering/organization knowledge• Emphasizes problem prevention• Documents risk and actions taken to reduce risk• Provide focus for improved testing and development• Minimizes late changes and associated cost• Catalyst for teamwork and idea exchange between functions.

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Design for Assembly (DFA)/Design for Manufacture (DFM)

Principle of DFA/DFM• Minimize part count• Use standardize part• Correct assembly tolerances

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Design for Assembly Guidelines Simplicity-minimize part number, part variety, simplify assembly sequences and component handling and insertion Standardize-On material usage Use the widest possible tolerance Choose material that suit function and production process Minimize non value added operations Team work Reduce number of parts Ensure that the remaining parts are easy to assemble

Design for Assembly Outcomes• Shorten product design time• Reduce assembly time• Simplify assembly process• Reduce total material cost• Improves quality and reduce defects• Reduce labour content

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Guidelines for Manual Assembly- Handling Divided into 2 areas:- Insertion and fastening

Design Guidelines for Insertion and Fastening Provide chamfers Provide clearance Standardize Design a part which can be locate before it is released

Design Guidelines for Part Handling• Avoid tangling part• Part should have end to end symmetry• Avoid part that stick together, small slippery and dangerous to the handler

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Factors that will affect handling

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Design feature that will help assembly process

Design to avoid adjustment during assembly

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Design concept that will provide easier access during assembly

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Design for Manufacture (DFM)

• Design for ease of manufacture of the collection of parts or product• More as a philosophy• It is a way of thinking that can be applied to component or product• DFM 3 key element

• Process selection• Reducing the number of process stages• Designing of the process

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Process Selection Analysis of material and processing methods for individual component based

on:- Tolerance requirement- Production volume- Component complexity requirement - Critical performance criteria

Reducing Process Stages• Eliminate unnecessary process stages through:• Component minimization• Elimination of finishing process• Combining processes

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Basic Principles of Designing for Economic Production Standard material and component Standardized design of product itself Liberal tolerance Design part so that many operation can be carried out without reposition it Simplicity

Surface symbol designation Surface roughness (um) Approximate relative cost %

Rough machine 250 100

Standard machining 125 200

Fine machining, rough ground 63 440

Very fine machining, grinding 32 720

Fine grinding shaving and honing 16 1400

Very fine grinding, shaving honing 8 2400

Lapping, burnishing polishing 2 4500

Relationship between relative cost and surface roughness

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Process Dimensional Tolerance(in) Approximate relative cost %

Rough machining ± 0.03 100

Standard machining ±0.005 200

Fine machining/ Rough grinding ±0.001 300

Very fine machining/ ordinary grinding ±0.0005 600

Fine grinding, shaving honing ±0.0002 1000

Lapping, burnishing, super honing ±0.00005 3000

Relationship between relative cost and dimensional tolerance

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Design of the Process• To ensure design of component will satisfy the specific production process• Exploit the benefits and limitation of the process• Design for machining• Design for casting• Design for injection moulding• Design for Powder Metallurgy

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Design for Machining Choose raw materials that will result in minimum component cost Try to design component that can be machined by one machine tool only Utilized standard pre shaped workpiece Avoid bent holes and dogleg Avoid internal feature for long components Provide base for work holding and references Employ standard machine features wherever possible Specify the widest tolerance and the roughest surface that will give the

required performance

The Phase of Design Process

Phase III. Detail Design

• Final Phase- Detail design• Waiting for final decision to be

manufacture• The design is brought to the stage of a

complete engineering description of a tested and producible product.

• Creation of final drawings and specifications• Any missing or incomplete information are

added → arrangement, form, dimensions, tolerances, surface properties, materials and manufacturing of each part

• Activities to be completed in the detail design phase (documentation):

– Detail engineering drawing.– Verification testing of prototype.– Assembly drawings and instruction, BOM.– A detailed product specification.– Decisions either to fabricate each part or to buy it– A detailed cost estimation.– A design review as a conclusion of the detail design phase before being passed to manufacturing.


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Phase III• Detail Design : the process in which the precise shape, dimension, and tolerances are specified,

the material selection is confirmed, and the method of manufacture is considered for every individual component of the product

• Detail Engineering Drawing - First task to be complete in detail design• Gives details of product specification in size and layout/views• Should also be understandable to production or customer• Drawing of each:

• Component• Subassembly• Assembly

• Information on details drawing include:• Standard views of orthogonal projection (top, front, side views)• Auxiliary views such as section, enlarge views or isometric views that aid in

visualizing the component and clarifying the details• Dimensions (Presented according to the standard)• Tolerances• Materials specification, and any special processing instructions• Manufacturing details; such as parting line location, draft angle, surface finish• Title block-with drawing title, scale, type of projection, name, logo, file location,

etc.

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NOTE: While many consider that the engineering design process ends with detail design, there are many issues that must be resolved before a product can be shipped

to the customer. These additional phases of design are often folded into what is called the product development process.

• Bill of Materials (BOM)• is a list of each individual component on the product• It lists the part description, quantity needed for a complete assembly, part number,

sources of the part and purchased order number• also lists the name of responsible person

The Phase of Design

Phase V: Planning for distributionPlanning for packaging, shipping, warehousing, and distribution of the product to the

customer.

Phase VI: Planning for useThe decisions made in phases I through III will determine such important factors as

ease of use, ease of maintenance, reliability, product safety, aesthetic appeal, economy of operation, and product durability.

Phase VII: Planning for product retirementAgain, decisions made in phases I through III must provide for safe disposal of the product when it reaches its useful life, or recycling of its materials or reuse or

remanufacture.

Phase IV: Planning for manufactureDesign of tooling and fixtures, designing the process sheet and the production line, planning the work schedules, the quality assurance system, and the system of

information flow.

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mec531 chapter 1_bibi

Documents

engineering design process

mechanical engineering

design problem summaries

phases design processphase

engineering sciences

retirement phase

entire process

conceptual designphase