equivalent to the cost of manufacture by 3-D printed sand. T is can be ex- pressed in the number of parts. Figure 5 shows the cross-over point for the thermal command center. Similarly, as shown in Table 1, it is possible to de- termine the lead time for both routes of manufacture. T e conventional way to manu-
facture a small number of prototype castings would be to make urethane soft tools by CNC machining blocks of urethane board. In this project the conventional tooling was designed in detail, ready for manufacture, but be- cause of the success of the 3D printed route, it was never made. For the thermal command center,
where just two parts were required in a compressed timescale, there were clear advantages from both a cost and tim- ing standpoint to using 3-D printed sand to manufacture the molds. T e only downside of using 3-D print- ing was that the surface fi nish was approximately 400 microinches RMS while with soft tooling the surface fi nish would be approximately 200 microinches. T e increase in surface roughness was not an issue for the function of the component. T e graph in Figure 5 shows that
the cross-over point when soft tooling would become more cost-eff ective for the thermal command center is 22 parts. At that point, the unit casting price with soft tooling is approxi- mately half of the cost of the 3-D printed casting. For all cast parts there is an equivalent graph, and the cross-over point moves to the left or the right depending on the overall size of the casting (large castings are expensive in 3D printed sand) and the number of cores (tooling and piece price increase).
In another example, a complex pump housing has a cross-over point in excess of 150 castings (Figure 6). T is example shows the potential for 3-D printed cores to enter serial production in relatively low volume applications. Volumes of fewer than 500 units a year are common in high performance vehicles and aerospace applications.
Fig. 5. The cost comparison graph for the thermal command center shows that tooling becomes more cost-effective when 22 castings or more are produced.
Table 1. Lead Time Comparison for Thermal Command Center Time to First Part (Days)
3-D Printed Sand Soft Tooling
Time to First Part (Days) 15
35
Fig. 6. This small but complex pump housing is an example of a cross-over candidate for 3-D printed sand vs. conventional tooling.
Sept/Oct 2016 | METAL CASTING DESIGN & PURCHASING | 39
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60