Simulation: not just for the big guys: small metalcasters might forego the frills, but they can still bank on the benefits of casting simulation basics.

A metalcasting facility promised delivery on a part in a few weeks, but the scrap rate on the sting has kept production erratic. If the troublesome defect isn't fixed soon, they'll lose the job and the customer, but the metalcaster's engineers are at a loss for what is going awry.

Adi Sholapurwalla, engineering manager for simulation company ESI North America, Bloomfield Hills, Mich., is familiar with the scenario. He said it's the primary reason metalcasters look into casting process modeling.

Utilized for the most part by large metalcasting facilities, casting process modeling tools at their core give casting engineers a visual depiction of what goes on in a mold when a casting is poured, aiding in gating and riser design and the elimination of defects. Although the tools have been available for two decades and have increased in sophistication to include stress analysis, microstructure simulations, and thermal analysis, they have been slow to catch on in casting facilities with fewer than 100 employees and revenues of $10 million a year or less. Modeling tools require an investment that can be hard to justify for small casting shops. Often, it isn't until a crisis occurs that casting process modeling is viewed as a necessary purchase.

But modeling tools can be used just as effectively to avoid problems and optimize production on a daily basis, according to Rafael Nariman, who has worked in the metalcasting industry on simulation as a user and now is president of RNariman MetalCasting Consulting, Orwigsburg, Pa. "By looking at a visual aid, you find a lot of surprises in a process that you thought you knew," he said. "You may have a set idea about risers and see that you were wrong. It's a great learning tool. You will improve a single casting but also improve your entire capability."

Out of Pocket

Casting process modeling tools come in a range of cost and sophistication. Large, high production facilities or plants familiar with simulation software may opt for modeling tools with added features, such as mesh generation, microstructure analysis and stress analysis. But more affordable options are available in tools offering the barebones modeling metal solidification and fluid flow.

Modeling software can be leased on an annual basis or purchased outright. Typically, one-year leases range between $12,000-$13,000 for an entry level tool and $50,000 for the most sophisticated module. In general, the purchase price for modeling software is two and a half times that of a one-year lease, ranging from $30,000 to $125,000. The software company may then charge an annual maintenance fee, usually around 10% of the purchase price.

Some simulation software companies allow users to lease for the first year with the option of purchasing. Most major providers have payment plan options or offer a short trial period.

"If you expect to use the software for more than three or four years, it makes sense to go ahead and purchase it rather than pay to lease each year," Sholapurwalla said.

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Highly sophisticated modeling tools may give metalcasters an edge in optimizing production, but the entry-level tools will meet most of the immediate needs of small sand casting firms.

"The only thing a sand metalcaster really needs is to be able to put the model in a sand mold and perform solidification and flow modeling," Nariman said. According to him, modeling elements beyond metal solidification and fluid flow likely will not provide enough cost savings at the outset to a sand caster's operation to justify the purchase price.

Along with the software, metalcasters new to simulation software can expect to pay $2,500 on a computer with a satisfactory amount of memory and processing speed (at least 2 GB, 2 GHz).

Why Buy

Small metalcasting firms producing simple parts with a low scrap rate will be hard-pressed to find a quick and obvious cost benefit to purchasing or leasing simulation software, according to Nariman, but for those who are making difficult-to-cast parts--or want to start making them--the money is well-spent.

"For people who make a lot of castings out of one pattern, simulation software is a no-brainer because casting trial and error is expensive at that stage," Nariman said, "For people making lower volumes, the casting must be complex to get your money's worth [from simulation software]. A simple casting can be designed by a casting engineer."

Along with answering a crisis, Sholapurwalla said the second reason casting facilities began looking at casting process modeling is because they want to bring in new business or retain business by designing a new component that stretches the firm's engineering capabilities. Rather than running numerous casting trials, simulations can be run on the computer. While early simulation techniques took days to complete, modern modeling tools can spit out results from several design iterations in hours. When an optimal design is found, the simulation can be shown to the customer to instill confidence in a metalcaster's ability to successfully cast the part.

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"Over and over, metalcasters tell us stories of how a casting designer agreed to a change in the part design after he was shown simulation results proving that the change would make the casting better, stronger and/or less expensive," said Christof Heisser, president of Magma Foundry Technologies, Schaumburg, Ill.

But to rely on simulation modeling as a mere marketing tool will do your operations a disservice, according to Nariman, who has seen metalcasters purchase simulation software for its prestige and fail to utilize it to improve their processes.

"Having a simulation is like having an airplane; you have to know how to fly it," he said. "A lot of metalcasters will have the program but no one who can use it, or the person who can use it is too busy."

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Payback 

The most obvious simulation software return on investment comes through the reduction of scrap through a better casting design derived from solidification and fluid flow modeling, which helps predict porosity and inclusions.

"Let's work with a fictional metalcasting facilty with 50 employees and $5 million of revenue a year, and assume they have a scrap rate of 5%, or $250,000," Heiser said. "Nobody would argue that a reduction from 5% to 4% is realistic with casting simulation. This would result in an annual savings of $50,000. There is not a single simulation tool on the market that costs more than $50,000 a year."

Heisser said that simulation modeling can improve yield, as well, since it can be used to optimize gating systems to use smaller or fewer risers.

Casting process modeling also reduces the number of trial runs performed to find the lowest possible scrap rate and best yield.

"A lot of metalcasters don't factor in the cost of trials, but if one considers the time spent on designing gating systems, making patterns, interrupting production, special handling of the special castings, and time spent on cutting them apart and evaluating them, it is a conservative number to assume it costs $1,500 per casting trial," Heisser said. "How many trials does it take to come up with a perfect rigging system? Simulation provides a window into the mold, thereby showing the entire history of a defect and making finding a cure easier and faster."

Sholapurwalla said metalcasters considering simulation software should take into account the following factors: annual volume, casting weight, yield, alloy cost, production rate, and pre- and post-casting operations. Metalcasters can use these parameters to predict the monetary value of a range of scrap rates to determine what could be saved through scrap reduction.

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Pitfalls

Both Sholapurwalla and Heisser claim that a "simulation specialist" is not required to run casting process modeling software, but at the very least, someone is needed who can read and build a CAD model.

"You can build a solid model yourself from a drawing or transfer the model from the customer," Nariman said. "But you will still have to manipulate the drawing to change the part model into a casting model, adjusting it for risers and gates, where the hot spots are or where shrinkage will occur."

Most major simulation software providers will train personnel to use the program and follow up in a few months to check how well it is being implemented. One of the most common ways to waste simulation modeling is leaving it unused because either the original person who was trained on the program has left the company or the trained person only uses it during down times.

"The biggest problem is when the person in charge of the simulation tool is asked to do other things that leave little time to run the program," Sholapurwalla said. "Simulation needs to be made a priority by management."

The more casting process modeling is used, the more savings a metalcaster will incur through reduced scrap and greater productivity.

"How do other countries with higher labor, energy and environmental costs have firms competing successfully with U.S. metalcasters?" Heisser asked. "Productivity, productivity, productivity, through investment into technology, not cutting personnel."

According to Heisser, many college students are being trained to use simulation tools, and they could be hired as interns to run the program. But Nariman suggested also involving someone with metalcasting experience who can determine whether an output from a simulation would logically fit within the firm's operations.

Know the Competition

Metalcasting facilities that aren't using simulation software should be prepared to compete for jobs against facilities that are. "Believe it or not, there are already small metalcasting facilities with less than 35 employees out there using high end simulation," Heisser said. "They don't want their customers to know because they like to blow them away in sales presentations."

Casting process modeling should be viewed in the same light as any other process equipment, such as a molding machine or furnace, Heisser said. "Metalcasters just don't have a reference for simulation tools. A metalcaster new to simulation needs to see how the tool can work for them and make an educated and financially justifiable decision. It pays for itself, just like a molding line."

For More Information

"Rounding Up Casting Process Modeling," MODERN CASTING Staff, MODERN CASTING, September 2007, p. 31.

Shannon Wetzel, Senior Editor