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. 326