“
[Engineers] don’t understand idiosyncrasies like shrink or where to put draft. We have people here who can fix it from a foundry perspective, but it takes time.” —ROB PEASLEE, MANITOWOC GREY IRON
mold to produce the part represented in the model. Often this will require design change requests from the sup- plier to make casting the part feasible, more cost effective or just plain easier. For customers, most casting knowl-
edge will come from experience, which is hard to gain. Close collaboration with suppliers during the design phase, when they are determining how to feed the molten metal into the mold or releasing the pattern from the mold, will build that knowledge. It may not reduce lead time for that part, but it
could lead to fewer design changes for the next part.
pattern for the mold. Add a core, and tooling to make that core must be made. Add additional cores, ad- ditional tooling must be designed, built and tested. “You do have to do the engineer-
5
ing. Even if you have a model, you have to modify it for draft. You have
Complexity of the part. A part that does not
require a core needs only the set of tools to make the
to build models for the cores. It can be a lengthy process,” Boyd Sr. said. “Lead time for a part with no core might be four to six weeks compared to 16 weeks for a multi-cored part.”
6
Part volume. Te more a casting sup-
plier knows about future orders, the better it can
schedule the deliveries and plan for optimal tooling for the job upfront. If your metalcaster knows you will need a regular delivery of castings through- out a year, it can slot the job in when it makes the most sense from a pro- duction standpoint. Sometimes the supplier will build up an inventory of parts for you so it can ship instantly when the order is placed. “If I have a customer who I make
100 castings a week for, he will have quick lead times because I can see his orders and maybe I can accumulate some inventory,” Boyd Jr. said. “Te buyer who gets into trouble is the one who orders two weeks out. If I have no future orders for him, he moves to the back of the schedule.” Knowing the future production
schedule will also impact tooling design. “We look at the least expensive
tooling for the amount of castings needed,” Peaslee said. “Tere is a big difference between 500 and 5,000.” Your casting supplier may consider
7 40 | METAL CASTING DESIGN & PURCHASING | Mar/Apr 2015
using multicavity tooling—where multiple parts are cast in a single mold—if the volume is high enough. More castings made at once reduces time of manufacture and cost.
Amount of testing required. More tests means more
time. “The level of PPAP (production part approval
process) required will affect how long it will take in the system,” Pea- slee said. “If the customer is asking for a lot beyond X-rays, it extends the timeframe more and more.” The number of tests and how
many parts need to be tested affects lead time by more than just the time to do each individual test. When too many parts don’t fail inspection, they have to be remade to fill the order, so there is a risk factor that may
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