Placing a well planned part in the right operation with proper casting parameters cuts costs.

Denise Kape, Senior Editor

(Click here to see the story as it appears in March/April 2014's Metal Casting Design & Purchasing.)

The factors that enter into cast component pricing extend beyond the design of the casting. While part engineering often has the greatest impact on price, production costs can vary greatly from one metalcasting facility to another. Knowing about the processes involved in casting production as well as how a metalcaster’s operations are managed before placing a job can help ensure the best performance at the right price. 

Casting Choices

For every job, there is a “sweet spot” where all of the production factors fall into place so the casting can be produced most efficiently at the right level of quality. It will be different from one shop to the next, and even within each casting facility, opportunities exist to decide between variables such as the level of automation used, finishing requirements, etc. At the 2014 Metal Casting Supply Chain Summit, hosted by the American Foundry Society in Chicago this February, two metalcasting executives—from a ferrous and a nonferrous facility—lent their views on casting cost considerations.

“Choices a foundry has made over decades define who they are and what their cost structure is,” said Jean Bye, president and CEO, Dotson Iron Castings, Mankato, Minn. Dotson is a green sand, nonautomotive jobbing shop pouring 1 to 50-lb. ductile iron castings. “Our typical casting-only job is done in about four hours. We work on timing, lean and flow. Our key metrics are on-time delivery, PPM [parts per million, a measure of quality] and a 12 calendar day lead time.”

Bye offered the following points to evaluate when choosing the right casting supplier for a particular job:

Strategy: Does the metalcaster focus on short-run or long-run jobs, short lead times, value-added services or automation? 

Bottlenecks: Are there potential shortcomings in metal or sand, in employees or employee training, in engineering or in capital? 

Quantity: How many castings will it take to achieve a cost reduction? Equipment: Costs vary based on the level of automation from the beginning of the casting production process through grinding and finishing. For a short-run job, manual molding might offer a cost savings in comparison to running it through an automated line. The opposite situation arises when you have a high number of castings or when there are numerous cores going into the mold. 

“[In Dotson’s] cost breakdown (see Fig. 1), our biggest single item is labor at 34% followed by metals and alloys at 22%. Contract purchases at 14% is the payments we make to people who do value-added service on castings, such as austempering or painting,” said Bye. “It would not be a safe assumption that this will be similar in other companies, because it can vary widely. Comparing apples to apples rarely works in the metalcasting industry. The real trick is to find the foundry that has a structure that works best for the job you’re trying to place.” 

Design Cost Drivers 

While an ideal casting would have specifications such as zero porosity, perfect proportions and a flawless finish, compromises are made when costs outweigh application requirements. Casting designers and suppliers work together to ensure those requirements are met in the most cost-effective manner.

“I would argue that what is in the file or on the blueprint has a bigger impact on cost than anything that can be done in the foundry to improve productivity,” said David Weiss, vice president of engineering/R&D for Eck Industries Inc., Manitowoc, Wis. Eck is an aluminum specialist running a variety of casting processes as well as value-added services.

“Our average order sizes are somewhere between 100 and 500 pieces,” he said. “We do structural aluminum castings—if the part fails, it’s a load-bearing casting, so someone could be hurt.”

One interesting example Weiss offered was the effect welding has on strength: “A half-weld is a typical sort of defect that has better fatigue results than something that is not welded.”  Welding adds cost to the job, but in some cases, it is not considered a problem but an improvement. “We have a customer that asks us to weld strips onto a casting to improve its fatigue strength,” he said (see Fig. 2). “With certain castings, it makes more sense to do a repair than to make a new casting. You have to consider complexity along with what you’re trying to do with the casting, and whether it’s worth it.”

With aluminum, filtering often is required to meet high specification standards, and additions such as cores and metal inserts make casting a part a more complex process, adding to the cost. Design considerations such as wall thickness determine the number of chills and risers required to achieve the necessary mechanical properties, also affecting cost. 

“People like to reduce wall thickness for lightweighting or add thickness for structural stability,” said Weiss. “The optimal range is between 4mm and 6mm for aluminum castings. When you’re above or below that, the cost factor goes up because of misruns on thin sections and chills or risers on heavy sections.”

The choice of aluminum alloy most often does not have as great an impact on cost as the engineering choices and quality requirements beyond visual inspection (see Fig. 3).

“When you are specifying very high mechanical properties or those higher than what is normally accepted in the industry or specifications such as ASTM or ASM, you can expect to pay more for that casting,” said Weiss, “especially with aluminum.” 

Bye’s example of an iron casting that was specified to be 100% porosity free took 50 simulation trials to achieve and was found to result in a 38% yield. By contrast, for an application that did not need as stringent a porosity requirement, accepting some porosity resulted in an 82% yield and a 15% cost savings. Reducing iron casting weight can shave a little off the cost. Running castings through a trim press rather than manual grinding also can reduce costs, if it is a job of high enough volume.

Time Is Money

Scheduling happens when a job order is accepted, but there are many steps in the process of completing the work that can impact on-time delivery. 

“A lot of time the only setup people think of is at the mold machine, but it takes place at each step in the process,” Bye noted. “Starting with the person at order entry, the time can vary based on the complexity. If we’re going to make 1,000 castings, 10 orders of 100 each, setup takes less time than if it’s 100 orders of 10 each.”

Setup varies at the core machine, where some products require an additive and some don’t. 

“The pattern for the track pad (see p. 19) takes date tags to show when it was made, so you’ve got to put those tags on and take them off again,” said Bye. “It isn’t a big deal on this job, with two impressions in the mold, but if you have a pattern that has 30 impressions and the customer is ordering 50 pieces, you’re now taking date tags on and off 30 impressions to run two molds. They order that every other month, and think about what the costs are associated with getting that pattern ready to run.”

Manual finishing doesn’t require much setup, but automated finishing equipment’s setup time offsets its faster, more accurate throughput. "The more automation you have, the more setup [cost] you might have to spread across the quantity,” said Bye. 

Shipping is the last step where scheduling impacts cost. As in Bye’s order entry example, shipping costs vary based on whether there are 10 or 100 orders being processed to ship those 1,000 castings. 

“We’re all rushing to get castings qualified on the front end, but sometimes that gives us insufficient time to build and develop the casting,” Weiss added. “And sometimes when you don’t have the time to do it right to begin with, you pay for it again and again and again. In the engineering process, lead time is important to have. We often add cost to the product to give you sound castings based on unsound design principles,” said Weiss. “So it is very much a cost driver.”

His greatest recommendation for driving down non-value-added cost issues is solidification modeling software, which facilitates communication and understanding between casting designers and metalcasters.

“It would lead to a lot more intelligent engineering dialogue,” he said.

Vertical Integration

Increasingly, metalcasters are taking on all of the steps involved in producing a part, from casting through assembly and shipping. It is challenging logistically, but the benefits extend to both the supplier and the buyer.

“Single-source responsibility definitely is a plus,” said Bye. “There’s no blame game—if something’s wrong, the supplier has to find out what’s changed, whether it’s the metal or the fixturing, the cutting tool or whatever. It’s one person’s responsibility without argument or the customer having to get involved in it.”

Scheduling is more accurate when the myriad tasks involved in completing a job are all performed in-house. And with fewer suppliers, a part might be managed from start to finish by the same engineers. 

“One of the most fun things we’ve had since we got into machining in-house,” Bye offered, “was finding we could remove cores and add machining to achieve the same part at a lower cost. [Vertical integration] means agility,” she said. “You can get parts quicker,  change your mind, and you won’t have parts sitting in inventory for months. With single sourcing you’ve got that communication to speed it up. The value of it is hard to say, but we have some customers that say it’s a 50% savings because they get just what they want, how they want it.”

Communication between casting designers, buyers and suppliers can reveal hidden costs and opportunities for improvement as well as savings. The more involved the metalcaster is in the planning stages, the better the end result.   ■