purchasing points P A Purchaser’s Sand Casting


Pattern Primer Bob Mueller Jr., Joy Global Surface Mining, Milwaukee


I


want to provide you with some insight to a vastly unknown area casting sourc- ing professionals face with all their cast components:


pattern equipment. Pattern equipment consists of the


tools, dies or masters used to pro- duce the molds for your components. For sand casting, most often they consist of a cope (top) and a drag (bottom) pattern and potentially a number of core boxes. Each pattern half is mounted on a solid wood board, insert panel or matchplate. In the case of large castings, they can be fi tted loosely together. Equipment can be fi tted with one or multiple cavities depending on size and the annual sales volume of a given part. A number of considerations factor


into the choice of pattern material, pattern construction and, more impor- tantly, pattern cost. Patterns 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. Each has its advantages and disadvantages. Pattern material has the highest


direct impact on the price of tooling, and the annual volume of compo- nents typically will dictate the mate- rial required. Repairing patterns throughout


the life of the tool incurs another cost. Your casting supplier typically is responsible for daily maintenance including the repairs of nicks and dings, new paint jobs and any dam- age they themselves might cause. It becomes your cost to bear when the pattern reaches the wear cycle and the dimensional stability of the tool is lost. In these cases, a refurbish- ment or complete replacement may be required. When having new pattern equip- ment quoted, it is advisable to procure quotations from multiple shops either


Pattern Material Longevity


T e following is a basic guide


for determining how each pattern material relates to your needs, based on the life expectancy of patterns in various materials before a formal wear review would be required.


Styrofoam


Single mold “one and done” is least expensive


Soft Woods (pine) 100 molds, less expensive, susceptible to damage, re- quires more maintenance


Hard Woods (mahogany, poplar, maple)


500 molds, mid-range price, more resistant to damage, less maintenance


Epoxy-Based Plastics


750 molds, mid-range price, durable but diffi cult to repair


Ren-Board Plastics


1,000 molds, upper price range, durable and easier to repair


Aluminum


2,000 molds, much higher price, durable but can be diffi cult to repair


Iron


5,000 molds, highest price, durable and costly to repair.


through your casting supplier or on your own. When choosing to quote tooling on your own, be aware that this conversation will require vast knowl- edge about the methods and processes the casting supplier intends to use to manufacture your parts. When sourcing patterns on your


own, most metalcasting plants will not take responsibility for dimen- sional 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. In review of your pattern quotes,


you might fi nd a striking diff erence in costs. Why? Consider both the amount of


work a pattern shop is produc- ing and its manufacturing process. Since pattern equipment was fi rst made, highly skilled craftsmen have constructed it by hand. Today, the same craftsmen utilize solid model and CNC machining technology to produce pattern equipment. T is jump in technology has helped to signifi cantly reduce dimensional inconsistencies and dramatically reduce pattern lead times. Pattern shops using the handmade manufac- turing processes most likely will bear higher costs, while CNC produced patterns can be less expensive due to the shorter overall lead time. Quality pattern shops build solid,


reinforced tools that are screwed and glued together. Do your homework and take some time to visit the pat- tern shops your casting supplier is using. They most likely have already weeded out the lower quality shops. Spending a few extra dollars up front for a quality pattern will save you significant money and head- aches 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.


Mar/Apr 2013 | METAL CASTING DESIGN & PURCHASING | 49


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