EPT 221ENGINEERING DESIGN

FORMULATING A DESIGN PROBLEM

Objectives of this lecture

• Describe the overall process of formulating a design problem

• Describe and use sources of product and customer information

• Prepare an engineering design specification• Understand and implement various design

methods: objective trees, pairwise comparison chart, quality function deployment (house of quality)

Defining the Problem:Problem Statement

• Need - an expression of dissatisfaction with the current situation.

• Goal - a brief, general, and ideal response to the need statement.

Need: There is too much damage to automobiles in low-speed frontal collisions.

Goal: Design an improved front bumper.

Need vs Goal

• Need: Childproof pill bottles are too difficult for people with arthritis to open.

• 4 possible goals:• Design a childproof pill bottle that is easier to open

• Design a childproof pill container that is easier to open

• Design a childproof system for dispensing pills• Design a childproof system for dispensing medication

Moregeneral

Objectives • Objectives

- quantifiable expectations of performance measurable- E.g.:

Objectives for design of automobile front bumperi. The bumper should be inexpensive.ii. The bumper should not be significantly damaged in the collision.iii. Other parts of the car should not be significantly damaged in the collision.iv. The bumper should be easily recyclable.v. The car should still be operative after collision

• Specify the performance measures for each objective and identify the units of measurement.

• Include all relevant performance characteristics ( behaviour, performance) without referring to any design parameters.

Objectives, their Bases for Measurement, and their Units of Measures

Objectives Basis for Measurement Units

1. Inexpensive Unit manufacturing cost for a production run of 50,000

Dollars

2. No significant damage to bumper

Distance bumper is pushed into body

Inches

3. No significant damage to other parts

Repair cost Dollars

4. Easily recyclable Amount of aluminum lb.

5. Retain maneuverability Turning radius ft.

6. Retain braking capability Braking distance ft.

Constraints • Constraints

- define the permissible condition of design features and the permissible range of the design and performance parameters.- three general forms:

– Yes-no constraints: represent conditions that either exist or do not exist.E.g.: the doors must open and shut.

– Equality constraints: specifies that some characteristics of the design must take on a specified value, with no leeway for variations from that value.E.g.: in order to prevent over-riding bumpers in collisions between automobiles, the bumpers should be installed 18” up from the ground.

– Inequality constraints: requires some characteristics of the design to be greater than, or less than, some specified values.

• One-sided inequality constraints: requires some characteristics of the design to be greater than, or less than, some specified value.E.g.: the weight of the bumper cannot exceed 50 lb.

• Two-sided inequality constraints: requires that a design/ performance characteristics be greater than one specified value and less than another specified value. E.g. the mounting brackets on the bumper must be between 8.0” and 12.5” from the centre so they match with the brackets attached to the automobile frame

Example

Assignment

Describe a reasonable set of objectives (including performance measures and units) and constraints (please identify each type of constraints) for the design of either (i) an electric pencil sharpeneror(ii) a flashlightDue on the 1st August 2008. Pass up during class hours.

The Process of Problem Formulation

4 primary activities in the process of formulating a design problem:

1. Seeking information• surveys, studies. • objective - to get detailed understanding of the customer, his or

her specific needs, and the competition.2. Interpreting

• detailing the specific requirements of the part, assembly, or product, desired performance targets, necessary constraints, evaluation criteria.

3. Gaining consensus• team members discuss data interpretations, revising this

conclusions, reporting data source, resolve conflicts.• prepare preliminary engineering design specification.

4. Obtaining management approval design review meeting, memorandum, technical report

Seeking Information

• Gather, examine, evaluate information regarding – customer requirements – company requirements – engineering characteristics – constraints – customer satisfaction

Customer and Company Requirements

• What product functions are desired • How well the functions are performed• The operating environment that the

product is subjected to• Marketing • Manufacturing• Financial concerns

Company requirements

Customerrequirements

Customer Requirements

• Product functions desired

• How well functions are performed

• Operating environment

• Value = benefits/ costs

• So, if benefits , so value , customer satisfaction

Customer Requirements….continued

• Function and Performance Functions / Importance Engineering characteristics (units, limits) Performance Targets Satisfactions

• Operating environment Air temp., humidity, pressure Contaminants Shock, vibration

• Safety• Economics • Geometric Limitations• Maintenance • Repair

• Retirement • Reliability• Robustness• Pollution• Ease of use• Human factors • Appearance

Example

• Motorcycle design: Customer requirements– Function / performance:

• start engine quickly,• support rider(s) comfortably, …

– Operating road shock wet, cold, high altitude

– Other• maintenance intervals• fuel economy

Company Requirements• Marketing

knowing who are the customers and consumers individual, group, business, government agency

Purchasing procedures, evaluation criteria of different customers Time to market understanding what the competition is and what it will be doing

during the time it takes to get the product to the market Advertising resources, annual volume that is to be produced and sold.

• Manufacturing Purchasing, fabrication, assembly, warehousing, distribution. Expected annual production volume (number of units to be made).

• Financing concerns Estimate of the capital expenditures necessary to purchase and install

manufacturing equipment or modify existing facilities. Projection of sale revenues, expenses, profits, return on investment. To determine whether to continue or terminate the project

• Others Patents, legal & voluntary regulations, standards, codes.

Example

• Motorcycle design: Company requirements– Marketing:

• need product in 24 months, • sale price competitive

– Manufacturing 5,000 units per year use existing manufacturing plant

– Financial• $300,000 R&D budget

Engineering Characteristics

• measures that quantify how well a product performs each requirement.

• Can be used to impartially assess how well an existing product satisfies its customer requirements.

• Assess how well a new product might perform • engineering requirements to measure these

characteristics• Characteristics a means to establish requirement• Requirement a desirable or necessary target value for

an engineering characteristics• Has appropriate units and limits

Engineering Characteristics, Units and Limits

Constraints

• Restrictions on function or form. • Maximum or minimum performance limits

relating to the desired functions or sub-functions.• Specific limitations regarding shape, size,

configuration, materials, or manufacturing processes. design parameters

• Explicit vs implicit (not directly expressed) constraints

• Feasible design – when a part (or product) satisfies all the constraints unfeasible design

Customer Satisfaction • Customer decide what a good or excellent design is not the

designer• Try establish qualitative and quantitative levels of satisfaction • Qualitative measures not satisfied, somewhat satisfied,

moderately satisfied• Quantitative measures express customer satisfaction in

numerical form/values• Graphing can be used to provide satisfaction values as a function

of a performance variable Customer satisfaction curve: 3 categories:

1. more-is-better, 2. target-value-is-better (i.e., nominal-is-better), 3. less-is-better

Qualitative and quantitative measures

Graphing

Less-is-better

Target-value-is-better

More-is-better

Information Sources

• Surveys – customer feedback system service reports, customer support reports, warranty claims

• Market Studies by trade associations/ government agencies

• Literature reference handbooks, technical journals, periodicals, electronic sources, internet

• Focus Groups a group of customers gather in one locations to discuss a product

• Observation Studies done by company representatives/ consultants

• Benchmark Studies assessments of competitive products

Engineering Design Specification (EDS)

• A single document that captures the whole team’s understanding of the specific details of design problems.

• Includes information of: Customer requirements Company requirements Engineering characteristics Constraints Customer satisfaction

• Equivalent to preparing a ‘statement of the problem’ that we find in general problem solving methods

• Also known as Product Design Specification• Work-in-progress, dynamic in nature• NOT the same as Product Specification (PS)

Printed information about the finished product usually given to the customer in the owner’s manual or ‘instructions’ sheet.

• The process of writing the EDS establishes a team consensus on the important customer and company requirements.

Engineering Design Specification Template

Cover pageTitle StakeholderDate

Introduction Design problem description Intended/unintended usesSpecial features

Customer requirements Functional performanceOperating environmentSafetyEconomic Geometric limitationsMaintenanceRepair

RetirementReliability RobustnessPollutionEase of useHuman factorsAppearance

Company requirementsMarketingManufacturingFinancialOther

AppendicesSite visit dataSales/ marketing dataHouse of quality