purchasing points P Why Don’t Metalcasters Analyze Cost
on a Price Per Pound Basis? Bob Mueller Jr., Joy Global Surface Mining, Milwaukee
“Why don’t metalcasters do cost analysis on a price per pound basis?” Metal castings are not commodi-
D
ties. Many factors go into pricing a cast part. Rarely are two castings identical. Families of parts may be of the same cast material and perform the same function, but come in several size and weight ranges. As we explore part costs, we can begin to realize the diff erences that make up the pricing we as metal casting customers face. Several key factors go into the cost of a metal casting. First, let’s look at the weight of the part. An associ- ate of mine from a sister division was quoting two clevis fastener cast- ings. T e parts were the same except for their weights. One part was 280 lbs. and the other was 1,000 lbs., with identical geometry. Quotations from several domestic metalcast- ers caused confusion, as one of the parts was priced nearly $1 per lb. more than the other. When look- ing into the cost diff erences of these identical parts, the lighter of the two parts fi t onto a molding line that was designed for that weight range, while the heavier of the two had to be produced on a diff erent line that supported the heavier weight and larger mold size. Two factors directly impacted the price: 1. T e burden and overhead that each of the two molding lines car- ried was vastly diff erent.
2. T e amount of molding sand each of the two molds required to fi ll their mold boxes diff ered. T ese two considerations alone
were enough to drive the price per pound of the larger part well beyond
uring my time in metalcasting and on the purchasing side of the fence, I have been asked the question,
that of the smaller identical part. In another case, the purchasing
agent was quoting two parts poured of the same cast material at nearly the same weight, but they were completely diff erent designs (a solid bearing cap vs. a lightened cross member). T is time, the sourcing agent received quotes that refl ected a nearly $3 per lb. diff erence. T e diff erences in the two parts
were beyond the material and weight. T e solid bearing block part was cast using no cores and a single
“
risers, feed pads, chills and properly designed and placed gating systems. When a metalcaster is quoting a part, it takes the soundness require- ment into direct consideration. When quoting the same part at two different soundness levels, the costs may vary significantly due to the increased amount of feeding aids (risers, feed pads and chills). Another quality factor with a
Coring is a signifi cant cost driver in metal castings.”
riser that allowed effi cient feeding to meet the customer’s soundness requirements. T e cross member part was produced using two cores that were glued together and fi ve risers to feed the part to the same soundness requirements. T e big cost drivers in this case: 1. The number of risers required to meet identical soundness requirements.
2. T e use of cores in one part but not the other. Coring of metal castings is one of
the true separations between forged parts and cast parts. Coring allows metal castings to take on the net shape of the fi nal product without machining. However, coring is a cost driver in metal castings and one the metal casting purchasing community needs to be aware of. Quality requirements vary from
part to part and from customer to customer. These requirements will directly impact the cost of your metal castings. Soundness levels in established metal castings are met through the application of
direct impact on pricing is testing requirements. Let’s use the same example above of two identical parts. One part requires 100% magnetic particle inspec- tion per the print, while the other needs only to meet a commercial grade quality standard that can be controlled by the pro- cess. These two “identical
parts” will have a significant cost difference because of the 100% test- ing requirement on one of the parts. This assures one part will take on an additional process with added lead time. The metalcaster will make assumptions that a higher percent- age of parts will require some level of rework and higher scrap rates to meet these more stringent require- ments. This, in itself, will result in higher part costs. Understand your quality require- ments and how they impact your cast products. I have given you real-world examples of how pricing on even identical products can result in price diff erentials. Metal castings are not candidates for vanilla dollar- per-pound pricing, as plate and bar stock are. Too many factors, coupled with customer requirements, exist in the production of metal castings to classify them as anything other than highly engineered components.
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.
May/Jun 2013 | METAL CASTING DESIGN & PURCHASING | 47
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