purchasing points P Pattern Primer: Consider Equipment,
Manufacturing Methods and Costs Bob Mueller Jr., Joy Global Surface Mining, Milwaukee
I
n this month’s column I want to provide some insight to a vastly unknown area that casting sourcing professionals face with all their cast components: pat-
tern equipment. Pattern equipment is the tools, dies or masters used to produce the molds for your components. Most often they consist of a cope (top) and a drag (bot- tom) pattern and potentially a number of core boxes. Each pattern half is mounted on either a solid wood board, insert panel, matchplate or, in the case of large castings, they remain loose altogether. Equipment can be fi tt ed with either one or multiple cavities depending on a given part’s size and annual sales volumes. So what is it that dictates pattern mate- rial, pattern con- struction and, most importantly, pattern costs? As far as materials go, what are the
Ren-board plastics, 1,000 molds:
Upper price range, very durable and relatively easier to repair. Aluminum, 2,000 molds: Much
higher priced, very durable but can be diffi cult to repair. Iron, 5,000 molds: Most expensive
and durable but very costly to repair. Pattern material, which has the highest impact on pricing of your tooling, will typically be dictated by the annual volume of your compo- nents. Repairing patterns throughout the life of the tool is another cost
“
advantages and disadvantages? Pat- terns come in a wide range of materials, from Styrofoam to cast iron and just about everything in between, including a variety of woods, plastics and metals. So how does each material relate to my needs? Below is a basic guide to the life expectancy of various materials along with a few advantages and drawbacks. Styrofoam, single mold: “One and
done” but the least expensive material. Soft woods (pine), 100 molds:
Minimizes expense, but susceptible to damage and requires more maintenance. Hard woods (mahogany, pop-
lar, maple), 500 molds: Mid-range priced, more resistant to damage, less maintenance. Epoxy based plastics, 750 molds:
Mid-range priced, very durable but dif- fi cult to repair.
responsibility for dimensional errors related to the pattern. T is burden falls back on you and your pattern source. Sourcing the equipment through your metalcaster alleviates you from this responsibility. When reviewing pattern quotes,
As with most things, you get what you pay for. Be aware of shops that take short cuts in construction.”
you will face. Casting suppliers are typically responsible for daily main- tenance, including repairs of nicks and dings, new paint jobs and any damage they themselves may cause. It becomes your cost to bear when the pattern reaches the end of its wear cycle and the dimensional stability of the tool is lost. In these cases, a re- furbishment or complete replacement may be required. When having new pattern equip- ment quoted, procure quotes from multiple shops either through your casting supplier or on your own. When choosing to quote tooling on your own, be aware that this conver- sation will require vast knowledge about the methods and processes that will be used to manufacture your parts. I suggest you leave this to the casting supplier. One note on sourcing patterns on your own: Most metalcasting facilities will not take
48 | METAL CASTING DESIGN & PURCHASING | Jul/Aug 2015
you may fi nd a striking diff erence in costs. Why? Well, my fi rst guess would be the amount of work a particular pattern shop may have. T e more work, the higher the potential cost. T e second reason may be the pattern manufacturing process. Pat- terns have always been constructed by highly skilled craftsmen. Today, these craftsmen can utilize solid model and CNC machining tech- nology to produce pat- tern equipment, which has helped to reduce dimensional inconsis- tencies and lead times. Pattern shops using the
handmade manufacturing processes will most likely lead to higher costs, while CNC-produced patterns can be less expensive. Another element to be aware of in costs is the construction method used by individual shops. As with most things, you get what you pay for. Be aware of shops that take short cuts in construction. T is will lead you down a road of endless repairs, dimensional issues and eventually back to purchas- ing a new pattern. Quality pattern shops build solid, reinforced tools that are screwed and glued together. Do your homework and take some time to visit the pattern shops your casting supplier is utilizing. Spending a few extra dollars up front will save you signifi cant money and headaches down the road. ■
Bob Mueller Jr. is senior supplier quality engineer, cast product and casting supplier development, for Joy Global Surface Mining, Milwaukee. He has more than 30 years of casting experience.
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