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Estimation

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									               Engineering Design
                          GE121
Design for X




                 Design for ‘X’

                      Lecture 11A

                    GE 121 Engineering Design--2012   1
                                 Design for ‘X’
               Design for X is a key element of successful
                design
               Design for:
                 Manufacturing and Assembly
Design for X




                 Affordability (engineering economics)
                 Reliability
                 Maintainability
                 Sustainability (i.e., environmental issues)
                 Testability
               All these issues are tied together in terms
                of design for quality (quality function
                deployment or house of quality)
                                  GE 121 Engineering Design--2012   2
               Design for Manufacturing / Assembly:
                     Can This Design be Made?
               Design for manufacturing and assembly
                is an important issue
Design for X




               Most companies are very concerned with
                how to get high quality products to
                market quickly




                            GE 121 Engineering Design--2012   3
                   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
Design for X




                experts in manufacturing, marketing, and
                engineering




                              GE 121 Engineering Design--2012   4
                 Design for Manufacturing (DFM) (cont)
               One basic methodology consists of six steps:
                1. Estimate the manufacturing costs for a given
                   design alternative
                2. Reduce the cost and number of the
Design for X




                   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


                                GE 121 Engineering Design--2012   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
Design for X




                     essential to the working of the finished product
                  2. Using standard fasteners and integrating fasteners
                     into the product itself (e.g., plastic clips)
                  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
                                   GE 121 Engineering Design--2012      6
                         Bill of Materials (BOM)
               A listing of all parts required to manufacture
                an object or system
               Used in concert with both assembly and
Design for X




                with the ordering and inventorying of parts
               Also has a great use in studying the
                economics of a product




                               GE 121 Engineering Design--2012   7
                     Design for Affordability:
                 How Much Does This Design Cost?
               Design for Affordability (Engineering
                Economics)
               Important in almost any project
Design for X




               Money almost always has an effect on
                design choices, and so should be
                understood in the proper context




                            GE 121 Engineering Design--2012   8
                            Time Value of Money
               Money owed tomorrow is worth less than the
                same amount paid today
               Money owed in the future is subject to opportunity
                costs and risks
                 1. Opportunity cost – Money could have been used for
Design for X




                    something else (or 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

                                   GE 121 Engineering Design--2012         9
                         Time Value of Money:
                          Affects Design Choices
               Time value of money affects design choices
                in many ways
Design for X




               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
                              GE 121 Engineering Design--2012   10
                               Estimating Costs
               A key skill in understanding the life cycle costs of
                a design
               In the simplest terms, costs include:
                  1. Labour costs
Design for X




                    • 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




                                  GE 121 Engineering Design--2012     11
                       Estimating Costs (continued)
               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
Design for X




                   discounts
               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
                 • In many companies, overhead can constitute as
                   much as 50-100% of the direct labour expenditure


                                 GE 121 Engineering Design--2012       12
                         Estimating Costs (continued)
                 4. Profit (or Return on Investment) for stakeholders
                   • Most companies want to make money on their
                     products
               When estimating costs, designers generally get
Design for X




                higher levels of detail and accuracy in the later
                stages of designs.




                                  GE 121 Engineering Design--2012        13
                           Costing and Pricing
               Costing and pricing are often confused by
                students and inexperienced engineers
               With the exception of large public works,
Design for X




                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
                enter (or remain) in a market
               For pricing, however, they will use market
                information
                              GE 121 Engineering Design--2012   14
                     Designing for Reliability:
                  How Long Will This Design Last?
               Design for reliability is important for most
                products
Design for X




               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, reliability and maintainability
                              GE 121 Engineering Design--2012   15
                                       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.).” (p282)
Design for X




               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

                                    GE 121 Engineering Design--2012         16
                               Reliability (continued)
               In practice, we think in terms of probability of
                failure (continued):
                  3. Series systems are like chains - when the weakest link
                     fails, the system goes down
Design for X




                  4. Parallel systems are like multi-strand cables - all the
                     parts in parallel must fail before the system will no
                     longer work
                  5. Economics and safety 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)




                                   GE 121 Engineering Design--2012      17
                             Maintainability
               Maintainability is “the probability that a
                failed component or system will be
                restored or repaired to a specific
Design for X




                condition within a period of time when
                maintenance is performed within
                prescribed procedures.” (p285)
               Closely related to the choices made in
                DFM and DFA.


                              GE 121 Engineering Design--2012   18
                      Design for Sustainability:
                     What About the Environment?
               Engineers have an ethical obligation to
                consider the environmental consequences
Design for X




                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




                              GE 121 Engineering Design--2012   19
                 Environmental Issues and Design
               One way to characterize environmental
                impacts of designed systems or artifacts
                is in terms of:
Design for X




                 Air quality
                 Water quality and consumption
                 Energy demands
                 Waste streams




                             GE 121 Engineering Design--2012   20
               Environmental Life Cycle Assessment
               Environmental life cycle assessment has
                three essential steps:
                 1. Inventory analysis — list all the inputs and
Design for X




                    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

                              GE 121 Engineering Design--2012   21
                              Testability
               Not in the text
               Many products require testing after
                manufacture to ensure proper operation
Design for X




                 • May be operation via user interface
                 • May be “burn-in” tests to eliminate early
                   failures (related to Reliability)
                 • May be at final stage of manufacture to tune
                   some function for optimum performance
               Testing may also be used to ensure
                consistency in the manufacturing process
                              GE 121 Engineering Design--2012   22
                         Testability (continued)
               Some products are expected to be maintained
                / repaired (e.g. automobiles)
                 • Status lights used to indicate normal / abnormal
Design for X




                   operation (e.g., power on / over-temperature)
                 • Built-in test circuits or software
                    • Auto-tests common on start-up
                    • May generate error codes for diagnostics
                 • Test points made available to connect equipment
                    • Internal to the product
                 • Test jumpers
                    • Removed to isolate modules / blocks
                    • Inserted to create test condition
                                GE 121 Engineering Design--2012       23
                          Testability (continued)
               Some products are expected to be maintained
                / repaired (e.g. automobiles) (continued)
                 • Test sockets for externally connected test
Design for X




                   equipment (e.g., automotive diagnostic computer)
                 • Physical layout
                    • Also related to Maintainability
                    • Facilitates inclusion of and access to test points
                      and jumpers




                                 GE 121 Engineering Design--2012           24
                            Design for Quality:
                               Building a House
               Quality is the concept which unites all the
                previous ideas
               Quality can be defined as “fitness for use”
Design for X




               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



                                  GE 121 Engineering Design--2012     25
               Abstract version – House of Quality
Design for X




                                                            Fig. 11.4 p290


                          GE 121 Engineering Design--2012                26
               House of Quality – Office Laptop
Design for X




                                                          Part of Fig. 11.5 p291
                        GE 121 Engineering Design--2012                            27
               Other Design for ‘X’ Considerations
               Disassembly
               Serviceability (related to Maintainability)
               Safety
Design for X




               Simplicity
               Standard Parts (overall inventory control)
               Accessibility (handicapped)



                             GE 121 Engineering Design--2012   28

								
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