Engineering Design GE121 Design for ‘X’

1. Engineering DesignGE121Design for ‘X’ Lecture 12B

2. Design for ‘X’ • Design for X is a key element of successful design • Design for: • Manufacturing and Assembly • Affordability (engineering economics) • Reliability and Maintainability • Sustainability (i.e., environmental issues) • All these issues are tied together in terms of design for quality, quality function deployment, and the house of quality

3. Design for Manufacturing / Assembly: Can This Design be Made? • Design for manufacturing and assembly is an important issue • Most companies are very concerned with how to get high quality products to market quickly

4. Design for Manufacturing (DFM) • Based on minimizing costs of production and/or time to market for a product, while maintaining an appropriate level of quality • Requires that the design team include experts in manufacturing, marketing, and engineering • One basic methodology consists of six steps: • 1. Estimate the manufacturing costs for a given design alternative • 2. Reduce the cost of the components where possible • 3. Reduce the cost of assembly • 4. Reduce the cost of supporting production • 5. Consider the effects of DFM on other objectives • 6. If the results are not acceptable, revise the design and try again

5. Design for Assembly (DFA) • Related to DFM, but focuses specifically on the aspect of manufacturing in which the artifact/system is put together • A number of design choices can impact assembly such as: • 1. Limiting number of components to the fewest that are essential to the working of the finished product • 2. Using standard fasteners and integrating fasteners into the product itself • 3. Designing the product to have a base component on which other components can be located • 4. Designing the product to have components that facilitate retrieval and assembly • 5. Designing the product and its component parts to maximize accessibility, both for manufacture and during repairs

6. Bill of Materials (BOM) • A listing of all parts required to manufacture an object or system • Used in concert with both assembly and with the ordering and inventorying of parts • Also has a great use in studying the economics of a product

7. Design for Affordability:How Much Does This Design Cost? • Design for Affordability(Engineering Economics) • Important in almost any project • Money almost always has an effect on design choices, and so should be understood in the proper context

8. Time Value of Money • Money owed tomorrow is worth less than the same amount actually paid today • Money owed in the future is subject to opportunity costs and risks • 1. Opportunity cost – Money could have been used for something else (or at least put in a bank to earn interest) • 2. Risk - Money paid in the future may be less useful, due to inflation or other factors, or may not be paid at all (bankruptcy) • 3. To address these concerns, economists have developed the notion of discounting. Formula is given in the text on p278 • 4. We want to consider the full set of life cycle costs for a design, not merely the initial costs

9. Time Value of Money:Affects Design Choices • Time value of money affects design choices in many ways • We are often comparing designs that are not identical in their time frames • We need a way to get them into comparable terms • Many engineers use Equivalent Uniform Annual Cost (EUAC) to do this • Text has more details

10. Estimating Costs • A key skill in understanding the life cycle costs of a design • In the simplest terms, costs include: • 1. Labour costs • Include not only wages directly paid to workers who produce a product • Also various indirect costs, such as unemployment insurance, other insurance,pensions, etc. • Most inexperienced designers tend to underestimate labour costs by at least one half • 2. Material costs • Include costs of all parts in the Bill of Materials, and any inventory that is lost in the production process • whether component parts are ordered in large lots or not usually affects unit price through volume discounts

11. Estimating Costs (continued) • 3. Overhead costs • Account for costs shared by all the various products a company makes, such as executive salaries, warehouse or factory costs, administrative services, etc. • In many companies, overhead can constitute as much as 50-100% of the direct labour expenditure • 4. Profit for various stakeholders • Most companies want to make money on their products • When estimating costs, designers generally get higher levels of detail and accuracy in the later stages of designs. During conceptual design, rules of thumb that can be used

12. Costing and Pricing • Costing and pricing are often confused by students and inexperienced engineers • With the exception of large public works, most products are priced on basis of what consumers will pay rather than costs • Firms tend to use cost to establish a floor to help them decide whether or not to remain in a market • For pricing, however, they will use market information

13. Designing for Reliability:How Long Will This Design Last? • Design for reliability is important for most products • Few people knowingly select unreliable goods or services • In some cases, reliability can be the difference between life and death, as in the case of airplanes • Engineers often consider two related concepts,reliabilityandmaintainability

14. Reliability • Defined as “the probability that an item will perform its function under stated conditions of use and maintenance for a stated measure of the variate (time, distance, etc.).” • In practice, we think in terms of probability of failure • 1. Types of failures: in-service failure, incidental failure, and catastrophic failure. Designers are often concerned with the Mean Time Between Failures (MTBF) • 2. To reduce the consequences of failure, engineers often introduce redundancy into systems, using parallel parts • 3. Series systems are like chains - when the weakest link fails, the system goes down • 4. Parallel systems are like multi-strand cables - all the parts in parallel must fail before the system will no longer work • 5. Economics often drives the choice. Engineers determine the probability and costs of failures and design parallel systems when failure is costly (in dollar or life terms)

15. Maintainability • Maintainability is “the probability that a failed component or system will be restored or repaired to a specific condition within a period of time when maintenance is performed within prescribed procedures.” • Closely related to the choices made in DFM and DFA.

16. Design for Sustainability:What About the Environment? • Engineers have an ethical obligation to consider the environmental consequences of the things they design • Often done by first determining the types of impacts, and then estimating the overall size and scope of the impacts

17. Environmental Issues and Design • One way to characterize environmental impacts of designed systems or artifacts is in terms of: • Air quality • Water quality and consumption • Energy demands • Waste streams

18. Environmental Life Cycle Assessment • Environmental life cycle assessment has three essential steps: • 1) Inventory analysis — list all the inputs and outputs as well as any intermediate products associated with the design • 2) Impact analysis — determine all the effects on the environment and measure or estimate the magnitude of the effects • 3) Improvement analysis — determine the needs and opportunities to address adverse effects found in the first two steps

19. Design for Quality:Building a House • Quality is the concept which unites all the previous ideas • Quality can be defined as “fitness for use” • Quality Function Deployment (QFD) is sometimes referred to as the “house of quality” • Refers to a graphical way of organizing all the major relationships among stakeholder interests, desired design attributes, measures and metrics, targets, and current products or designs

20. Abstract version – House of Quality Fig. 11.4 p290

21. House of Quality – Office Laptop Fig. 11.5 p291

22. Other Design for ‘X’ Considerations • Disassembly • Testing • Serviceability • Safety • Simplicity • Standard Parts • Accessibility (handicapped) • …