Machined Tooling or 3-D Printing?
Certain conditions in which short leadtimes and a small production order is
required for a complex part can make a case for the use of 3-D printed molds. OLIV ER JOHNSON, TOOLING AND EQUIPMENT INTERNATIONAL CORP., LIVONIA, MICHIGAN; TOM MUELLER, VOXELJET USA, CANTON, MICHIGAN; AND MIKE LINDBERG, ILMOR ENGINEERING, PLYMOUTH, MICHIGAN.
T
he 3-D printing of cores and complete molds, with- out any requirement for
tooling, is revolutionizing the industry of fast prototype casting manufactur- ing but it also off ers distinct advan- tages for certain production castings. A recent case study of a complex
thermal command center casting for a high performance marine powertrain illustrates the calculation metalcast- ers and end-users may take in deter- mining the cost factors that would promote the use of 3-D printed molds over conventional soft tooling. T e thermal command center,
which combines a water pump, thermostat housing, and a series of bypass valves into one single casting was required for early mechanical development testing (Fig. 1). T e part’s overall dimensions were 29 x 13 x 6 in. (736 mm x 330 mm x 152 mm), and it weighed 14 lbs. (6.35 kg). Two castings were needed on an accelerated timeline. T e fi rst cast and
38 | MODERN CASTING August 2016
machined part was needed in four weeks. More parts would be required after development testing, and it was likely the design would be modifi ed based on the results of dynamometer testing. T e casting was to be made in A356 alloy and heat treated to a T6 condition prior to CNC machining. T e designer communicated informa-
tion to the metalcasting facility strictly through 3-D data in order to accelerate the manufacturing process by eliminat- ing two-dimensional drawings. 3-D printing the entire sand mold holds many advantages: • Backdraft and zero draft present no obstacles and considerably reduce time for the product designer.
• The ability to make a casting, quickly evaluate the casting size and alter the shrink factor for the second casting is possible with 3-D printing, but not with tooling where remanufacturing the tools at great expense is necessary.
• Complex in-gate and riser geom- etries can be created more easily with 3-D printing than tooling.
• Design features can be quickly revised without any cost of tooling updates.
Fig. 2. This 3-D printed oil gallery core is currently expensive as a large amount of activated sand has to be wasted during its manufacture.
• Internal core positions are accurate as cores can be grouped together or printed directly into the cope and drag, eliminating core clearances and the resulting core shift in the casting.
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