From what material is the component to be machined?
11.3 DFV—Design For Value
325 11.2.4 The Cost of Injection-Molded Components Probably the most popular manufacturing method for high-volume products is plastic injection molding. This method allows for great flexibility in the shape of the components and, for manufacturing volumes over 10,000, is usually cost effec- tive. On a coarse level, all the factors that affect the cost of machined components also affect the cost of injection-molded components. The only differences are that there is only one type of machine, an injection-molding machine, and the questions concerning geometry are modified. Besides the major dimensions of the compo- nent, it is important to know the wall thickness and component complexity in order to determine the size of the molding machine needed, the time it will take the com- ponents to cool sufficiently for ejection from the machine, the number of cavities in the mold the number of components molded at one time, and the cost of the mold. To demonstrate the effect of the factors, we show the cost for a clip, shown in Fig. 11.8. 2 The significant factors affecting cost are 1. The overall dimensions are 9.46 cm 3.72 in. by 4.52 cm 1.77 in. in the mold plane and 4.13 cm 1.6 in. deep.2. The wall thickness is 3.2 mm 0.125 in..
3. The number of components to be manufactured is 1 million.
4. The labor hourly rate is 35.
5. The tolerance level is intermediate. 6. The surface finish is not critical. The cost of manufacturing the component in Fig. 11.8 is shown in Fig. 11.9 for varying production volumes. The capital cost of making a mold is high enough to dominate the cost of the component at low volumes. This is why making just 1000 injection-molded plastic parts would be very expensive. A rule of thumb is that if the manufacturing volume is less than 10,000, plastic injection molding may be cost prohibited. The manufacturing cost can be affected by the wall thickness. In the drawing, the thickness is 3.2 mm. If this is lowered to 2.5 mm, the part cost will drop about 18. This is primarily because the time needed in the mold for cooling drops from 18 sec to 13 sec, saving cycle time. 11.3 DFV—DESIGN FOR VALUE The concept of value engineering also called value analysis was developed by General Electric in the 1940s and evolved into the 1980s. Value engineering is a customer-oriented approach to the entire design process. It changes the focus from the cost of a component to its value to the customer. The key point of value 2 The cost estimates in this section were made by entering values for these factors on a spreadsheet available as a template that can be used to estimate the cost of any machined part. 9.46 cm 3.72 in. 9.17 cm 3.61 in. 7.62 cm 3.0 in. 6.48 cm 2.55 in. 4.13 cm 1.6 in. 2.54 cm 1.0 in. 3.49 cm 1.4 in. 3.95 cm 1.55 in. 0.16 cm 0.0625 in. 0.30 cm 0.12 in. 0.57 cm 0.22 in. R 0.64 cm 0.25 in. 2.97 cm 1.17 in. 1.84 cm 0.72 in. R127 cm 0.5 in. R127 cm 0.5 in. 0.32 cm 0.125 in. Brad Tittle Oregon State Univ. December 28, 1990 CLIP Tol: +– 0.01 cm Approved: Figure 11.8 Component for cost estimation. 18 16 14 12 10 8 6 4 2 1000 10,000 100,000 1M 10M 16.88 2.12 0.19 Manufactured volume Manufacturing cost per unit 0.65 0.27 Figure 11.9 The effect of volume on the cost of a plastic part. 326Parts
» Mechanical engineering design process
» Introduction Measuring the Design Process with Product
» The History of the Design Process The Life of a Product
» The Many Solutions for Design The Basic Actions of Problem Solving
» Summary Mechanical Design Languages
» Different Types of Mechanical Constraints, Goals, and
» Product Decomposition Summary Introduction
» The Individual Designer: A Model of Human Mental Processes That Occur
» Characteristics of Creators The Structure of Design Teams
» Building Design Team Performance Overview of the Design Process
» Designing Quality into Products Product Discovery
» Choosing a Project Summary Sources Exercises On the Web
» Product, Project, and Decision Risk
» In engineering design, the designer uses three types of knowledge: knowl-
» A design process that results in a quality product can be learned, provided
» Improved material on project planning.
» Insist on rights of humanity and nature to coexist
» Recognize interdependence. On the Web
» Accept responsibility for the consequences of design
» Create safe objects of long-term value.
» Eliminate the concept of waste.
» Rely on natural energy flows.
» Understand the limitations of design.
» Seek constant improvement by the sharing of knowledge.
» Respect relationships between spirit and matter.
» Engineering Changes Patent Applications Design for End of Life Sources Placing a piece in a puzzle
» Decompose a simple system such as a home appliance, bicycle, or toy into its assemblies,
» For the device decomposed, list all the important features of one component.
» Select a fastener from a catalog that meets these requirements:
» Sketch at least five ways to configure two passengers in a new four-wheeled commuter
» You are a designer of diving boards. A simple model of your product is a cantilever beam.
» Find five examples of mature designs. Also, find one mature design that has been recently
» Teams develop decisions by consensus rather than by authority. This leads to
» Beneficial team behaviors. Well-defined decision process.
» Use of sound generationevaluation approach.
» Standardizes, organizes, and controls operations.
» Provides for consistent dissemination of information.
» Encourages improvement. Team nam
» Generate alternatives Team nam
» Identify criteria importance Team nam
» Based on the evaluation results, decide what to do next. This decision will
» “What I want for myself out of this.” Refine criteria.
» Refine evaluation—work to gain consensus and reduce uncertainty.
» Choose an alternative—you’ve made a decision, document it and address
» Develop a list of original design problems that you would like to do at least 3. Choose
» Make a list of features you don’t like about products you use. One way to develop this
» Executive summary: Team Members:
» Gantt chart: All diagrams, figures, and tables should be accurately and clearly labeled
» References: Appendices: All diagrams, figures, and tables should be accurately and clearly labeled
» For the features of the redesign problem Exercise 4.2 develop a plan as in Exercise 5.1.
» Develop a plan for making a breakfast consisting of toast, coffee, a fried egg, and juice. Be
» Developing the specifications or goals for the product
» Finding out how the specifications measure the customers’ desires
» Determining how well the competition meets the goals
» Developing numerical targets to work toward
» The QFD method can be applied to the entire problem and any subprob-
» Both competitors have good lifting position when transferring the passenger
» Both products have poor stability. Clearly, this is a market opportunity.
» The Colub is easy to move and Delton is not, need to determine why and do
» For most of adjustment requirements, neither of the competitors score above 3,
» Each specification should measure at least one customers’ requirement at
» Each specification should be measurable. Every specification should be writ-
» The first specification “seat width relative to frame width” is not clear. What
» Two points about specifications that are in terms of “number of steps”:
» For a design problem Exercise 4.1, develop a house of quality and supporting informa-
» The interface to the jam plate. Energy flows between the trigger and the jam
» Articulate the conflicting positions or functions. Identify the needs forcing the two positions.
» Articulate the conflicting positions
» Identify the issue, the objective of the needs
» Articulate injections that can relieve the conflict while meeting the objective.
» Many of the problems that engineers face contain elements that have already
» There are predictable patterns of technological change that can be applied to
» Increase degree of an object’s segmentation
» Arrange objects so they can go into action without time loss
» Stating the overall function.
» Decomposing the overall function into subfunctions. If assumptions are needed to
» Identifying all the objects nouns used and defending their inclusion in the functional
» For the redesign problem Exercise 4.2, apply items a–c from Exercise 7.1 and also study
» Which subfunctions must remain unchanged during redesign?
» Which subfunctions if any must be changed to meet new requirements?
» Which subfunctions may cease to exist?
» For the functional decomposition developed in Exercise 7.1,
» A perpetual motion machine. In recent times the patent office has refused to consider
» Use brainstorming to develop at least 25 ideas for
» A way to fasten together loose sheets of paper.
» A device to keep water off a mountain-bike rider.
» A way to convert human energy to power a boat.
» A method to teach the design process.
» Use brainwriting to develop at least 25 ideas for
» A device to leap tall buildings in a single bound.
» Are the critical parameters identified?
» Are the safe operating latitude and sensitivity of the parameters known?
» Have the failure modes been identified?
» Does hardware exist that demonstrates positive answers to the preceding four
» Is the technology controllable throughout the product’s life cycle?
» The source of the component.
» Wheel and chain must clear frame for all deflections. Wheel should move straight up and down.
» Your body while holding a 5-kg weight straight out in front of you with your
» Maximum acceleration on a standard street
» Maximum acceleration on a 5-cm standard pothole
» Identify the critical parameters and interfaces for evaluation.
» Develop a P-diagram for each.
» Choose whether to build physical models for testing or run an analytical experiment
» Perform the experiments or analysis and develop the most robust product.
» For the redesign problem Exercise 4.2, repeat the steps in Exercise 10.1.
» You have just designed a tennis-ball serving machine. You take it out to the court, turn it
» Does your machine have an accuracy or a variation problem?
» Itemize some of the potential causes of each type of error. Consider the types of
» A new, spring-powered can opener
» A diving board for your new swimming pool
» An art nouveau shelf bracket
» From what material is the component to be machined?
» The overall dimensions are 9.46 cm 3.72 in. by 4.52 cm 77 in. in the
» The wall thickness is 3.2 mm 0.125 in..
» The number of components to be manufactured is 1 million.
» The labor hourly rate is 35.
» Find the Theoretical Minimum Number of Components. Examine each
» hr R Mechanical engineering design process
» For the product developed in response to the design problem begun in Exercise 4.1,
» For the redesign problem begun in Exercise 4.2, estimate the changes in selling price
» Estimate the manufacturing cost for a plastic injection-molded component:
» Compare the costs for manufacturing volumes of 100, 1000, 10,000, and 100,000.
» Compare the cost for a change in tolerance.
» Why does changing the material have virtually no effect on cost at low plastic
» Perform a design-for-assembly evaluation for one of these devices. Based on the results
» A simple toy fewer than 10 parts
» Read as many similar instruction manuals as you can. Many companies post
» Organize instructions into sections to make it easy to find answers. Do not
» Recruit members of the user community not familiar with the product to test
» Know your goals and your vendor’s goals. Building a strong vendor relation-
» Involve vendors early. When dealing with vendors, you cannot afford delays
» Establish relationships. It is important to have vendor partners who under-
» Communicate. Put everything in writing—responsibilities, expected sales
» Stay professional. Things go wrong in life. When they go wrong in a relation-
Show more