UNDERSTANDING PART PRICING
H
What’s driving the cost of your casting design? DAVID M. CHARBAUSKI, PROCESS CONTROL ENGINEER, CATERPILLAR INC.
ere is a comment that comes up often when talking to new casting buyers: “I have a casting design and I’ve received quotes back from several casting suppliers on the part. T e cost of the part seems high to me. How should I go about securing a lower price on this part?” T e reaction some buyers have is to quote the work at
additional metalcasters to see if they can fi nd a lower cost. T is might not be the best approach. If the quotes you have are from metalcasters you have experience with and all are uniformly high, the reason may be related to the casting
design itself. Ask these questions as you determine what could be driving excess cost into the casting and whether you are working with the correct source.
Does the part fi t the metalcaster? T ere are several key factors in play here: metal type, casting weight and size, and
annual volume. T e casting sourcing team must make sure the metalcaster being con- sidered produces castings, on a daily basis, that are within these three parameters. Metal type: Is the cast material an industry standard grade or one unique to your
organization? If it is unique or rarely produced, this could be a major cost driver. Con- sider changing the material to a commonly cast grade to reduce the cost. Another factor to consider is if the material type is correct for the application and if there are alternate material selections available. For example, let’s say a steel fabrication is being redesigned as a casting. T e designer specifi es steel because that was the material used in the origi- nal fabrication. However, the part could possibly function just as well in ductile or gray iron, and it is likely an iron casting will cost less than a steel casting. T e engineering team should be enlisted to help determine if a material change is warranted. Casting weight and size: Does the casting fi t within the weight and size range
commonly poured by the facility? If the casting is on the high or low end of the range, the part may not be a good fi t for that particular metalcaster. Being on one end of the weight/size spectrum may require special handling processes and increase costs. For example, small parts may need to be handled diff erently through shakeout to prevent the castings from becoming damaged. Large and heavier parts may require extended cooling times in the mold that add delays when the plant is producing the casting in an automated process. Either of these situations can add signifi cant cost to a casting. Annual volume: T e annual volume of parts you plan to buy must fi t the chosen
metalcaster’s lot size range. For instance, if your part has a small volume, it would be wise to choose a company that specializes in low volume/small lot size casting production. Sourcing a low volume part at a high volume facility will in increase costs, because the metalcaster’s entire manufacturing process is designed around handling larger lot sizes and the low volume work just won’t fi t well. Keep in mind that casting suppliers charac- terize low, medium and high volume diff erently, so communication is vital on this point.
26 | METAL CASTING DESIGN & PURCHASING | Sept/Oct 2014
The casting fi ts the metalcaster. What’s next?
After you have examined these three
categories and determined your casting is a good fi t for the chosen supplier, the next step is to collaborate with its engineering team to determine if there are any requirements in your design that could be identifi ed as cost drivers. It is important to identify cost drivers as early in the design stage as possible so they can be minimized or eliminat- ed. In this context, a cost driver is any requirement or combination of require- ments with a large infl uence on total cost of the part, and these can be either design or process related. Following are some of the more common cost drivers that should be considered.
1
The Basics Don’t overlook these. Most cast-
ings have a few basic requirements that need to be addressed correctly dur- ing the design phase. In this discussion, two of these would be draft angles and fi nish stock allowances. If these are cho- sen correctly, there will not be a problem with the resulting casting, however, if the wrong parameters are applied there can be increased cost driven into the casting. Draft is added to vertical surfaces of
the casting (surfaces that are at a right angle to the parting plane) to facilitate easy removal of the pattern from the mold. Most metalcasters would like to see between 1 to 2 degrees of draft added to these surfaces, but that is dependant on the height of the surface from the parting plane. A good rule of thumb to follow: T e shorter the feature, the more
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