Examine the processes in Example 13.2 One of the processes that was rejected in the second round of decision making has great potential for making the integral bladed hub for the fan from an aluminum alloy. This process selection would have required a creative design for the die that might have required considerable development time and cost. Identify the process, and briefly describe what technical issues prevented its selection.
Another approach is to abandon the concept that the hub and blades should be made as an integral piece. Instead, think about making the part as separate pieces to be assembled. What manufacturing processes does this open up for consideration?
Example 132
The selection of materials for an automobile fan, Example 113, was done with the assumption that the manufacturing costs for each material would be approximately equal since they were either casting or molding processes. The top-ranked materials were
(1) an aluminum casting alloy,
(2) a magnesium casting alloy, and
(3) nylon 6/6 with 30 percent chopped glass fiber to increase the fracture toughness of the material. Casting or molding were given high consideration since we expect to be able to manufacture the component with the fan blades integrally attached to the fan hub.
Now we need to think more broadly about possible processes for making 500,000 parts per year. Figure 13.9 and Table 13.5 are used to perform a preliminary screening for potential processes before making a final decision based on costs calculated from Eq. (13.9). Table 13.7 shows the processes suggested in Fig. 13.9 for an aluminum alloy, a magnesium alloy, and the thermoplastic nylon 6/6.
Eq. (13.9).

In interpreting Table 13.7, the first consideration was whether Fig. 13.9 indicated that the process was suitable for one of the materials. The matrix of possible processes versus materials shows the greatest number of potential processes for an aluminum alloy, and the fewest for nylon 6/6. The first round of screening is made on the basis of the predominant shapes produced by each process. Thus, blow molding was eliminated because it produces thin, hollow shapes, extrusion and drawing because they produce straight shapes with high length-to-diameter ratios and because the blades must have a slight degree of twist. Sheet metal processes were eliminated because they create only 2-D shapes. Machining was declared too costly by management edict The preliminary screening left the following processes for further consideration:

It is clear that injection molding is the only feasible process for the thermoplastic nylon 616. The available processes for aluminum or magnesium alloy come down to several casting processes and closed die forging. These remaining processes are compared using the selection criteria given in Table 13.5 and enumerated at the beginning of Sec13.3.7. Investment casting is added as an additional process because it is known to make high-quality castings. Data for shell molding is not listed in Table 13.5, but its entry in Table 13.8 was constructed from data given in Process Selection. The gravity die casting process is most commonly found under the name of permanent mold casting, and the data for permanent mold casting from Table 13.5 was used in Table 13.8. The rating for each criterion is totaled for each process, as seen in Table 13.8.
The results of this process ranking are not very discriminating. All casting processes rank 13 or 14. except investment casting. The ranking for hot forging is slightly lower at 12 Moreover, designing a forging die to produce a part with 12 blades integrally attached to the fan hub is more difficult than designing a casting mold for the same shape. For this application there appears to be no advantage of forging over casting, and since the company does not have in-house forging capability, the forged fan component would have to be provided by an outside supplier.
The next step in deciding on the manufacturing process is to compare the estimated cost to manufacture a part using Eq. (13.9). The following processes will be compared: injection molding for nylon 6/6, and low-pressure permanent mold casting, investment casting, and squeeze casting for metal alloys. Squeeze casting is included because it has the potential to produce low-porosity, fine detail castings when compared to shell molding and pressure die casting.

Example 113
Selection of Materials for Automobile Coding Fans
Problem Statement/ Selection of Design Space
The radiator cooling fan in automobiles has typically been driven by a belt from the main drive shaft of the engine. Sudden acceleration of the engine causes high bending moments and centrifugal forces on the fan blades. On several occasions blades have broken, causing serious injury to mechanics working on the engine. Find a better material than the sheet steel used in the blades.
Boundaries of the Problem
The redesign will be limited to the selection of a cost-effective material that has more resistance to the propagation of small cracks than the current material.
Available Information Published Ashby charts and the database of material properties available in the CES software will be used.
Physical Laws/Assumptions
Basic mechanics of materials relationships will be used. It is assumed that the radius of the fan is determined by the needed flow rate of air, so the size of the fan hub and blade remain the same for all design options. It also is assumed that all fan blades will be damaged by impact of road debris, so that some blades will contain small cracks or other defects. Thttufore, the bask material property controlling service performance is fracture toughness, Kk: see Sec. 122

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mC C, AC (139) Nylon 6/6 Aluminum alloy Shell molding Gravity die casting Pressure die casting Squeeze casting Closed die forging Magneslum alloy Gravity die casting Pressure die casting Closed die forging Squccze casting Injection molding Table 13.5 Rating of Characteristics of Common Manufacturing Processes Tooling Time Flexibility Utilization Quality Costs Handbook Shape molding (RIM) Forging, open die 3-D solid 2 3-D solid 3-D hollow 4 3-D solid 2 Table 13.5 continued) Tooling Handbook Shape Time exibility Utilization Quality Csts 3-D AHB, vol 16, p. 421 AHB, vol 16, p. 557 3-D 4 AHB, vol. 6, p. 175 AHB, vol. 6, p. 328, Fusion welding All 349 Adhesive bonding All 3-D EMH, vol 3 Shot peening Surface hardening CVDVPVD All All All 5 4 AHB, vol. 5, p. 126 AHB, vol. 5, p. 257 AHB, vol 5, p. 510 Rating scheme: I, poorest; 5, best.From ASM Handbool, Val. 20, p. 299, ASM InternationalL Used with permission. TABLE 13.6 Rating Scale for Ranking Manufacturing Processes Rating Cycle time Flexibility Utilization Tooling Costs 1 >15 min Changeover very waste >100% of Poor quality Average quality Tooling and machines Average to High machine and tool. difficult Slow changeover Avg, changeover finished part ing costs 5 to 15 min waste 5010 100% ito 5 min waste 10 to 50% and setup time Fast changeover Tooling and machines relatively inexpensive Tooling costs low good quality 20s to Waste <10% Good to finished part exellent 20s No setup tme No appreciable Excellent Equip. and tool very low Rating scale I-poorest;5-best TABLE 13.7 Inltlal Screening of Candidate Processes Aluminum Alloy Magesum Alloy Yes or Nylon 6/6 Reason for Elimination Yes or Yes or Possible Process 1.2 Shell molding 1.3 Gravity die casting Y 1.4 Pressure die casting Y 1.9 Squecze casting 2.1 Injection molding N 2.6 Blow molding 2.9 Plastic extrusion 3.1 Closed dic forging Y 3.2 Rolling No? Reject? No?Reject? No? Reject? Used for 3-D hollow Neod to twist thc blades 2-D process for making Makes shapes with 3.3 Drawing high LID Used for hollow 3-D 3.4 Cold forming 3.5 Cold heading 3.8 Sheet shearing 3.12 Mctal extrusion 4A Automatic shapes Used for making bolts A 2-D forming process Need to twist the blades Machining is ruled out by edict machining Table 13.8 Second Screening of Possible Manufacturing Processes Cycle Process Material Time Flexibility Utilization Quality Tooling Costs Total Equipment & Shell molding Low pressure permanent 14 Pressure die casting Squeeze casting Investment casti Hot closed die forging4 13 13 14 17 12 TABLE 13.9 Comparison of Characterlstics of Each Process with Requirements of the Fan Permanent InvestmentInjection Squeeze Process Requirements Design Mold Casting Casting Molding Casting range, max 3.9 mass (kg) (Fig. 13.7) max (mm) (Fig. 13.8) min (mm)...(Fig. 138) Section thickness, 13 120 Section thickness, 0.6 0.5 0.1 Tolerance (+mm) Surface roughness (Am) R Economic batch 1.6 5 x 10 103 105 size, units (Fig. 13.5) AVERAGE BLADE SECTION A FIGURE 11.11 Sketch of the fan blades and hub.