This urethane pattern was CNC ma- chined from a CAD fi le.
With so many options available,
choosing the best one for your applica- tion can seem daunting. But Poweleit said engineers shouldn’t put too much pressure on themselves to pick the cor- rect rapid prototyping method. “T e reality is you don’t want the method to be the deciding factor,” Poweleit said. “More importantly, you want to fi nd a foundry that goes fast, and whatever that particular foundry fi nds works best for them to go fast, go with that method.”
When to Consider Rapid Prototyping
Don’t assume your metal casting supplier will inform you when a rapid manufacturing method is the most economical, according to Gary Burrow, president of HA Burrow Pattern Works, Joliet, Mont. “Some casting suppliers
Only three pieces were required for this defense in- dustry replacement part made with an SLA pattern.
will just provide normal quoting unless you ask for rapid prototyping.” According to Burrow, rapid proto-
typing might be right for your part if: 1. you only need one or two pieces; 2. you are not sure of the part’s fi nal design;
3. production tooling is expensive when amortizing against required or limited production quantities;
4. the design requires intricate and complex cores that need consid- erable assembly.
For instance, HA Burrow was
contracted to provide a 54-lb. (24.5- kg) 17-4 stainless steel investment casting for Honeywell. “We had to do some modifi cations to the original design to make the part castable, and we were able to proof those modifi ca- tions out using stereolithograpy (SLA) rather than producing an $80,000 tool
ARRAY OF OPTIONS The most established rapid prototyping methods,
such as stereolithography (SLA) and selective laser sin- tering, often are matched up with the investment casting process. While some small tweaks to the process may be required, many companies fi nd it simple to incorporate the patterns. “Investment casters have done a good job of adopting
SLA patterns, and it’s a good way to go from a piece of plastic to a piece of metal,” said David Poweleit, application engineer for the American Metalcasting Consortium. Although additive manufactured patterns can be
pieced together to produce larger parts, typically it is most cost-effective with smaller pieces. Other methods have been developed that are better equipped for larger parts, such as robotically machining sand molds or printing sand molds layer by layer, without fi rst creating a pattern. Sand molds produced via 3-D printing can be a good
42 | METAL CASTING DESIGN & PURCHASING | Nov/Dec 2011
that would have required extensive modifi cations to produce an acceptable casting,” Burrow said. Power transmission part-maker Baldor-Maska, Quebec, Canada, had a client that needed a three-week delivery on a nonstandard part, and it didn’t have an existing pattern. In a typical order, Baldor quotes for a pattern price, places a pattern order and waits two or three weeks to receive the pattern. After the pattern is delivered, Baldor sends it to the casting supplier to cast the com- ponent. For this part, the OEM utilized a sand machining process in which a robot CNC machines the mold used to pour a part, skipping the time consum- ing patternmaking steps. “I know that some foundries or
patternmakers use polystyrene when they need a pattern and sample in a short delay,” said Jean Philippe Lefeb- vre, patternshop supervisor at Baldor. “But I didn’t have any relationships with a foundry that used that technol- ogy, and I didn’t have time to fi nd and contact one.” Instead, Baldor worked with exist- ing supplier Fonderie Saguenay, which employed its version of robotic sand machining to provide the part on time. According to Lefebvre, since Baldor
needed only one large part and it did not have an existing pattern, using a
match for small runs of larger parts or for producing mul- tiple small parts at a time. It is not uncommon for sand printing machines to handle quantities up to 200 parts, if they are small enough. While machining sand molds wouldn’t make economic
sense for a long production run, the process can be used to prove out the design before investing in permanent tooling. According to Reg Gustafson, project manager for
Clinkenbeard & Associates, Rockford, Ill., tooling-less pro- cesses eliminate the need to store tooling and provide the opportunity to start up new part numbers faster and run parts in multiple locations, making spare parts on demand and onsite. “Tooling-less methods, such as machining molds and
cores, provide a faster and less expensive way to make prototype sand castings with less capital investment in tool- ing,” he said.
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