EPT 221ENGINEERING DESIGNINTRODUCTION TO ENGINEERING DESIGN

Objectives of this Lecture

To define and describe what is engineering design. To differentiate between engineering design, engineering

science, and engineering analysis. To describe and explain the descriptive and prescriptive

engineering design process.

Definition of Engineering Design Definition 1(Engineering Design by Rudolph J. Eggert):

The set of decision-making processes and activities used to determine the form of an object given the functions desired by the customer.Definition 2 (Engineering Design by Rudolph J. Eggert): The organized, thoughtful development and testing of characteristics of new objects that have a particular configuration or perform some desired function(s) that meets our aims without violating any specified limitations.

Definition 3 (Engineering Design: A Project-Introduction by Patrick Little and Clive I. Dym) : The systematic, intelligent generation and evaluation of specifications for the artifacts whose form and function achieve stated objectives and satisfy specified constraints.

Definition 4 (Fundamentals of Engineering Design by Barry Hyman): The process of devising a system, component, or process to meet desired needs. It is a decision-making process (often iterative) in which the basic sciences and mathematics and engineering sciences are applied to convert resources optimally to meet a stated objective. i.e. ABET (Accreditation Board for Engineering and Technology) definition.

What is the common denominator of the three definitions?

Relationship between Form and Function

The form of an object usually depends on the function it performs.

Function: things the object is supposed to do.

Form: the shape/ geometry of the object/ artifact.

Engineering Science, Engineering Design, Engineering Analysis Engineering Science

- deals with applications of scientific principles and mathematical concepts for analyzing a wide variety of engineering problems such as: motion of an object, current in electric circuits, deflection of beams, temperature in fluids, and efficiency of engines.- a multidisciplinary program designed to integrate the sciences with areas of traditional engineering such as research, design and analysis fluid dynamics, solid mechanics, operations research, design, dynamical systems, bioengineering, solid-state devices, material sciences, electromagnetics, nanoscience, nanotechnology, energy, optics.

Engineering Design- form is the solution to a design problem- ill-structured and open-ended- 4 main stages: i. formulating

ii. generating iii. analyzing iv. evaluating

Engineering Analysis- predicts the behaviour/ function of an object, based on its given form, using analytical equations or experimental methods.- 3 main stages: i. formulating

ii. solving iii. checking

- predicted behaviour is the solution to an analysis problem.

Design Process

In line with the general strategy for tackling complex problems, the design process is split into a number of main phases, and each phase is then broken down into a number of steps. Methods are suggested to tackle each step.

Descriptive design process model attempts only to describe the elements of the design process

Prescriptive design process model prescribes what should be done during the design process

Descriptive Design Process Model

3-design phases Five-design phases

Prescriptive Design Process Model

5-design phases

5-Phases of Design

3 major benefits of this 5 phases of design:i. The team focus on the right sub-problem at the right time.

ii. The team efficiently gathers and process the right type of information.

iii. The teams focus on alternative methods pertinent to the phase.

(Problem) formulation: Understand the problem, not solving it. Explore design needs. Develop lists of objective design specifications.

Concept design: Synthesize a variety of candidate working principles/ concepts and their

abstract embodiments (sketches). Select one of the concepts for further development.

Configuration design: Generating a variety of configurations (geometry, size, weight, the

arrangement of components, etc). The design phase when alternative configurations are generated,

analyzed and evaluated.

Parametric Design: determining values for the controllable parameters, called design

variables (unknown during the configuration design phase). design variables deals with the form of a design i.e. shape,

configuration, size, material, and manufacturing process. redesign/ iterate.

Detail Design: Determine the remaining product specifications such as surface

finish, assembly procedures, etc. Fabricate and test critical parts. Prepare a complete package of manufacturing specifications i.e.

details and assembly drawings, etc.

Example:

Our customer owns and operates a custom-built machine tool used in her factory . The tool has a drive shaft that cannot be stopped other than by turning off the power and waiting about 90 seconds for the shaft to spin-down. The customer considers this a safety hazard and would like to actuate some device that would bring the shaft to a quicker stop. The shaft is 8 inches in diameter, weighs 1,000 pounds, is made of 4330 steel, and spins at 3,000 rpm. We have been hired to design and fabricate a solution to accomplish the rapid stopping of the shaft.

Problem formulation (not to solve but to understand):

- Obtain details of existing shaft geometry and operating conditions in the factory, including available power.

- Clarify the type of performance that would satisfy the customer (e.g. How quickly should the shaft stop?, Would the customer be fully satisfied with 5 seconds and unsatisfied if longer than 20 seconds?)

- Do some mathematical calculations, using simple relations from physics, to better understand the overall mechanical forces and/or torques of the system.

Concept Design:i. Generate alternatives (working

principles/concepts and their abstract embodiment):3 alternative concepts:

a. Air friction as the working principle and fan blades as the embodiment.

b. Opposing magnetic fields as the working principle and an electric generator as the embodiment

c. Surface friction as the working principle and a disk-and-caliper brake as the embodiment.

ii. After evaluation, select one for further development.

Configuration design (let say concept c. is chosen for further development) :

i. Generate alternative configurations:- Alternative shaft locations- Geometries for the disk and caliper, etc

ii. Analyze each alternative configurations.

iii. Evaluate and select the best configuration.

Note: Analysing is the process of predicting the performance or behaviour of a design candidate. The candidate designs that fail to satisfy the constraints are reiterated.Evaluating is the process of comparing the predicted performance of each feasible design candidate to determine the ‘best’ design alternative.

Parametric design : i. Specify design variables: Determine specific values:

- Rotor diameter (outer)- Rotor thickness- Brake pad width

Select: - Pad material type- Operating pressure of the hydraulic

piston- Rotor manufacturing processes

ii. Analyze performance- Conventional machine design formulas- Computer programs- Physical experiments

iii. Check the analysis results to assure that all constraints are satisfied and optimal performance is obtained. Iterate/ redesign if otherwise.

Detail Design: Determine remaining product specifications:

- Surface finish- Pad bonding resin- Assembly process procedures

Fabricate and test a number of critical parts. Prepare a complete package of

manufacturing specifications:- Detail and assembly drawings- Bill of materials- Manufacturing process recommendations,- Prototype performance tests results

Product specifications:- Height- Width - Depth- Weight- Expected performance

9-step Model of Engineering Design Process1. Recognizing the need. 2. Defining the problem. 3. Planning the project.4. Gathering information.5. Conceptualizing alternative approaches. 6. Evaluating alternatives.7. Selecting the preferred alternatives.8. Communicating the design.9. Implementing the preferred design.

Step 1: Recognizing the Need

– to establish the ultimate purpose of the project via a general statement of the client’s dissatisfaction with the current situation.

Sandra: “Jane, we need you to design a stronger bumper for our new passenger car.”

Jane: “Why do we need a stronger bumper?”

Sandra: “Well, our current bumper gets easily damaged in low-speed collisions, such as those that occur in parking lots.”

Jane: “Well, a stronger bumper may be the way to go, but there may be better approaches. For example, what about a more flexible bumper that absorbs the impact but then returns

to its original shape?”

Sandra: “I never thought of that. I guess I was jumping to conclusions. Let’s restate the need as “there is too much damage to bumpers in low-speed collisions.” That should give you

more flexibility in exploring alternative design approaches.”

Step 2: Defining the Problem

- Expressed through a problem statement.- A problem statement has generally 3

components:i. Goal

ii. Objectives

iii. Constraints

Step 3: Planning the Project

- To identify what tasks to do and in what order it is to be done. - Example of planning tools: Gantt Chart, Critical Path Method.

Step 4: Gathering Information

For well developed design areas/ existing ideas information are easily available.

For novel/new design ideas lack information. Therefore need to do theoretical research, experiments/ models, etc.

Step 5: Conceptualizing Alternative Approaches

- To generate a wide range of design options.

- Design options/ alternatives need to satisfy the need/ problem statement.

- Requires an engineer to be creative and imaginative.

Step 6: Evaluating Design Alternatives Using engineering sciences, economics

i.e. objective approaches.

Step 7: Selecting the Best Alternatives Comparison of performance criteria. Subjective decision. Should reflect the client’s values, preferences, priorities. Can be decided using systematic ways/ techniques. E.g. of performance criteria: cost, recylability, damage control.

Step 8: Communicating the Design

To inform parties involved of the project progress and status. As a record for the design engineer to reconstruct/ justify design. 2 types of formal communication: written records and oral

presentation.

Step 9: Implementing the Preferred Design

To translate the design concepts into actions.

Implementation construction and testing.

Product Realization Process

Engineering design is just one part of the product realization process, that involves many departments and employees during the life of a product.

It is the means by which a customer need is transformed into a realized product. Involves physical and decision-making activities : sales, marketing, industrial design,

engineering design, production design, manufacturing, distribution, service and disposal.

Product development: The collection of activities leading up to, but not including, production.

The origin of customer needs: Service department. Distribution of shipments to retail outlets inadequate product packaging. Sales or marketing group - where most of the new/ revised product ideas originate.

Industrial design activities: Focus on how the new/ revised product idea is compatible with the customer’s anatomical

limitations and/ or aesthetic trends in the market place. Artistic rendering/ a physical model that illustrates basic product form, color, texture and

intended functionality. Engineering design activities:

Recommended manufacturing specifications that satisfy customer’s functional performance requirements and manufacturing constraints.

Production design activities: Involves the design, fabrication, and installation of production equipment (e.g. jigs, fixtures,

machine tools, quality control instrumentation, material-handling equipment) Can also be the construction of a new factory. Also manual and automated assembly equipment. Making changes to reduce material waste and rework.

Manufacturing activities: Fabrication, assembly and testing.

Distribution activities: Shipping the product in wholesale sized lots to distribution centres located around the

country/ world. Railcar full shipments, containerized freight trailers, personal-computer mail ordering, etc.

Service activities: Repairs/ replacement at the factory. Repair persons for home service. Equipment installation, routine maintenance at the customer’s site.

Disposal activities: removal, elimination, and/ or recycling of hazardous chemicals or scarce materials such as

in nuclear power plant fuel rods, automotive oil, printer cartridge recycling. Indirect activities:

administrative activities – accounting, finance, personnel, strategic planning, legal, management.

Indirect expenses.

The 4 Stages in the Life of a Product A simplified model of

the product realization process having four main stages.

Economic Life Cycle of a Product Product life cycle: the ‘birth’ and ultimate ‘death’ of a

product. As the current product declines, a new product is

introduced and thereby keeps the company financially happy.

The Manufacturing Enterprise