Choosing the right material for your pattern tooling
What’s the best material to use for your pattern tooling? That depends on numerous factors, including estimated annual usage (EAU), the geometry of the part and the durability required.
Helping customers work through the trade-offs of material, cost and lead times is something that State Line Foundries’ sales manager and estimator Dave Murphy does intuitively well, based on many years of experience. He gives us an inside look at the art and science of pattern tooling material selection.
Few customers realize how much experience and expertise is leveraged in material selection. The number of options at State Line Foundries’ disposal would likely surprise them as well. Those materials – and, specifically, the durability and flexibility they offer – can have a significant impact on both project cost and lead time.
Many of Murphy’s suggestions are driven by estimated annual usage (EAU). The more times the pattern will be used, the harder the material that’s required.
Geometry is another driver in the selection process. “If the tool will have thin walls or ribs, we use a stronger material such as redboard, aluminum or urethane,” he explains.
Here are some of the material options Murphy weighs when generating patterns.
Materials for prototypes
Prototypes are essentially one-off creations – they are as “low volume” as you can get. That means durability isn’t as much of an issue as it is with other mold tooling applications.
3D sand printing
An increasingly common process is the use of 3D sand printing for developing prototypes. This technique eliminates the need to use a conventional material like redboard or aluminum to create a pattern. Instead, the 3D printer produces a mold directly from a computer model using a polymer substance that binds sand particles into the desired shape.
“There is no pattern whatsoever,” Murphy declares. “You don’t have to make a pattern and put in the sand and make a mold. You have a printed sand mold right from the start.”
That means prototype molds can be created very quickly. It’s also easy to tweak or adjust them as needed. State Line’s in-house engineers model the mold and cores, as well as the gating for the customers casting design.
“If the OEM designer missed a boss, or something doesn’t work quite right, they can make changes without developing a new pattern,” Murphy clarifies. “If they want to beef it up or reduce it all they have to do is adjust the CAD drawing and print a new mold.”
3D sand molding tends to more expensive than some other options, such as foam – but comparable in price or even less expensive if multiple adjustments to the tool design are needed.
Foam is another option when making a pattern for a prototype part. “It’s an inexpensive material that cuts easily,” Murphy says.
The foam comes in big sheets and is cut and glued to create the pattern. “You can CNC a piece of foam to the desired shape,” he explains.
The problem? “It’s only good for one casting,” Murphy reveals. That means revisions are problematic. “If we run into shrinkage or a bad casting, then we have to make another pattern.”
It’s a slower process than 3D sand printing because a pattern is required.
But there is a place for foam. “It can work for a one-shot deal – for example, some of the service parts that OEMs order once every 20 years,” Murphy clarifies.
Materials for lower-volume production
Sometimes a pattern is needed more than once – but not very often. Those situations require a more durable pattern material with an eye toward ease of use.
Pine is easy to work with and performs well in limited use. It’s inexpensive, too. But, again, “limited use” is key. In addition, when pine or other woods are used, the direction of the grain must be taken into account.
“Mahogany is a commonly used material for us,” Murphy reveals. “It is considerably harder than pine, so it can produce higher volumes.” Mahogany is durable enough that Murphy describes it as “in-between” a low-volume and a high-volume material.
State Line sometimes combines pine and mahogany to create a pattern. “If we have a big part, we’ll make it mostly out of pine,” Murphy explains. “Then we’ll make the surfaces and edges out of mahogany because it’s a strong wood and it holds up better. That gives us the best of both worlds: it improves durability and keeps costs down.”
This urethane-based composite checks many boxes. “It’s easy to work with, it’s stable and it’s cost-effective,” Murphy details. “You don’t have to worry about the direction of the grain like you do with wood.”
It can be purchased in a variety of thicknesses to make preparation even more convenient – and it’s suitable for detailed designs. “Lettering and logos can be cut into it, for example,” Murphy reveals.
Brownboard can be repaired, too. But it simply doesn’t have the durability required for higher-volume casting.
Materials for higher-volume production
When a pattern will be used frequently, State Line recommends a long-lasting material, such as these:
Redboard, like brownboard, is a composite. “Redboard holds up well for wear,” Murphy explains. “It’s more expensive than brownboard, which is stable but tends to wear and chip faster.”
Redboard also holds its shape well. “You don’t have to glue it up in segments and you don’t have to worry about the grain of the wood,” Murphy points out.
It has high tolerance, good durability and costs less than metal.
Redboard and aluminum are similar in terms of wear resistance. “For the sand wear and the number of molds you can get, the two are very comparable,” Murphy says. Yet the higher the volume, the more likely Murphy is to specify aluminum. “The redboard will chip and break, where the aluminum won’t,” he explains.
The reality in the foundry world is that patterns tend to get banged around during their lifetime. Aluminum is better able to withstand rough handling.
While aluminum lasts longer, it also costs more and requires longer lead times. “It takes more time to develop a pattern from aluminum than from redboard,” Murphy acknowledges.
Trust the experts
How does a customer know which material to select for a pattern?
“We use our experience to make the best material suggestion for the customer’s project,” Murphy assures. Some customers specify the pattern material to quote but most rely on the foundry’s discretion.
“We know about the latest technology, such as 3D sand printing, and when and where it can be used,” Murphy states. “We also have years of experience working with all types of materials. The right choice is usually pretty obvious to us.”
“That expertise is something that you get when you work with State Line. It’s part of the package,” Murphy points out.
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