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RPM Pioneer is One-Stop Source for Complete, Machined Castings

A.L. Johnson's RPM process and new CNC machinery translate into fast turnaround and shorter lead times for prototypes and low--volume production--all from the same tooling.

By Rebecca Carnes
Design-2-Part Magazine

Those who have worked with the design-engineering and production teams at A.L. Johnson Company know that they don't shy away from complicated parts; in fact, they embrace them. Since pioneering the rubber plaster mold (RPM) process in the 1950s, the company has become quite proficient at delivering low-volume, precision aluminum and zinc castings, and has recently invested in expanding its CNC machining capabilities to meet increasing demand.

The company (www.aljcast.com) services a wide variety of leading technology industries, including biomedical, defense, aerospace, telecommunications, computer peripherals, guidance, and navigation. With a focus on quick turnaround, the company's services include complete machining and finishing operations, as well as low-cost tooling and no-draft castings with thin walls and smooth surfaces.

Based in Camarillo, Calif., where it employs 80 people at its 45,000-square-foot facility, A.L. Johnson is geared toward low-volume, long-term production. Company owners say they've thrown away the old rule book on castings, giving engineers more freedom to design while eliminating hard-and-fast requirements for draft and uniform wall thickness. Rubber plaster mold patterns are machined from stock, and tooling can be fabricated without draft--an advantage over dies that are machined from tool steel or iron, always with draft. Tooling cost is also lower because, unlike other processes, RPM doesn't require the lightening of cavities to maintain uniform section thickness.

"Undercuts are a welcome feature in our process. If you take a trip on our shop floor, there are lots of parts with complicated geometry," said Barton Riggs, national sales manager. "So adding cast features can be very cost effective in our process."

During the past few years, A.L. Johnson has focused on expanding its CNC machining capabilities to produce complete-to-print parts. The company recently added a tenth CNC machine to its equipment list, which also includes a newly acquired CNC lathe, a multi-pallet CNC workstation, a test bar pulling machine, and a plaster mixer. Aiming for an AS9100 Rev C certification in November, the company also offers in-house heat treating, design services, and an in-house metallurgical lab.

In-house heat treating and test bar pulling provide a number of advantages, according to Riggs. "We don't have to ship them out, so our lead time for outsource test bars is one to two weeks," he noted. "If we sent it outside for heat treating, we could be looking at four to twelve weeks. Having that in-house reduces the lead time and it also notifies us very rapidly if there is an error somewhere in the system. We can pull a test bar the day after parts were heat-treated and find out they didn't meet spec. Then we can re-heat treat them; whereas, using the alternate route, we'd be two weeks out before we knew we had to heat treat them again."

The company's ability to provide in-house services has caught the eye of customers who are looking to save time and money. "Basically, customers want to get a part back that's finished," Riggs said. "A lot of our customers are not interested in receiving a raw casting, bringing it in, inspecting it, sending it out to another machine shop, bringing it back in, inspecting it, then sending it out to a plating shop and bringing it back in. We see the demand from our customers for the one-stop shop. It takes a lot of risk out of their supply chain, it reduces lead times, and it reduces their cost burden and their risk associated with producing a product. By having those services in-house, we can control them tightly and we can do them very quickly."

Five years ago, A.L. Johnson was working at lower capacity, using only three or four machines to machine about 20 percent of the castings that came through its foundry. Since then, the company has made great strides in boosting its machining capacity, adding several new CNC machines while bringing in higher-skilled employees to operate them. A.L. Johnson is now machining about 80 percent of the castings that it manufactures, having gone from a single shift to two shifts running anywhere between 16 and 20 hours a day, up to six days a week. One of the latest additions is a Haas CNC Lathe ST-30.

"That machine has live tooling, so I can do milling operations and tooling operations in the same machine," said A.L. Johnson General Manager Rick Klein. "It's pretty unique and not a lot of shops have that. That's what we're trying to expand," he said, adding that the company also recently purchased a Haas EC-400, which has enabled multiple jobs to be set up at any given time.

The Pioneered RPM Process Takes Shape

The machining can accomplish a typical flatness of plus or minus 0.005 inch and 0.015 inch over a larger area. Wall thicknesses of 0.075, plus or minus 0.015 can be obtained. Corners and fillets are 0.12R maximum, and draft is one degree maximum. Cast surfaces come in at 125 micro inch.

In 1954, as a pottery industry worker, company founder Albert Lloyd Johnson developed the RPM process while making molds for slip casting used in pottery production. Interested in casting aerospace nut plate drills instead of machining them, Johnson was contacted by a Winslow Manufacturing employee to see what he could come up with. The RPM process was born when Johnson developed an aerating plaster that could be used as a mold material. The use of this material in metal casting applications would not require vacuum assistance and would offer customers near net-shape castings that could be produced in less than two weeks. Griffith & Carlson International, located in Camarillo, co-purchased the casting firm in 1975. In 1991, A.L. Johnson moved to its present facility, where it brought together an RPM tooling line, casting line, and CNC machining capabilities.

A big advantage of the RPM process is a fine finish of 125 RMS or better with very high density and good dimensional accuracy.

"Complicated parts are really something we excel at in this process," said Riggs. "That goes back to low-cost tooling. We like undercuts of any shape and are very driven towards difficult geometry and complicated parts, which are expensive and difficult to procure. By having the casting and the machine shop in-house, we can offer a very cost-effective advantage making complicated parts."

Overall, the time and cost savings associated with the company's RPM process are said to be significant. Unit costs can be lower than other methods when considering the combined casting price and finished machining cost. The combination of lower unit cost and tooling amortization make it feasible to cast as few as seven to 10 units with the RPM method, according to the company.

With most tooling, the first article will be delivered in two to three weeks, which is considered quite fast in the casting industry. "Typically, it takes two to three weeks, but we have the ability to tool in as little as a week," said Terry Carlson, vice president of sales. "We're not trying to compete just on time, we're also trying to compete on a part that fits the [customer's] needs, and then being able to provide them with beautiful work within a reasonable time period, which is really what it's all about. The real thing we're trying to strive for is getting good parts to our customer on time."

A.L. Johnson's precision aluminum and zinc castings, manufactured to exacting quality standards in small quantities, are a natural fit for the medical and defense industries. Makers of non-disposable medical equipment, for example, often need long-term, low-volume production of products with high quality and cosmetic appeal.

"We have very fine surface finish on our parts," Riggs said. "They get a nice, strong, high-density piece. Some of these manufacturers see making parts out of metal as showing more value in their part than plastic. They want the heavy, robust feel of a big piece of equipment. Someone who's going to pay a million dollars for a machine to go into their operating room wants it to feel like a million bucks," Riggs said.

Unlike processes that use potting agents and coarse grain media, the RPM technique ensures that surface finishes are compatible with painting and oxidizing without additional surface finishing. The use of very fine grain plaster in the RPM process is said to allow for the accurate reproduction of minute detail, such as cast part numbers, nomenclature, and customer's logotypes.

Riggs explained that the operating room is not a fickle environment for medical equipment. If the doctors like a particular machine, then it's likely to stay there for many years. Strong and durable metal components, such as aluminum castings, are valued in medical equipment applications because healthcare providers don't want to invest in a product that can be easily dented, cracked, or otherwise damaged. They're also sought by makers of medical and telecommunications equipment for their ability to provide EMI/RFI shielding. Demand for the components is also high in the defense industry, which has similar needs for high-quality parts in relatively low volumes, according to Riggs.

"We're talking about high-dollar, low-volume pieces of equipment, whether it's a defense-related telecommunications unit or a turret for an armored personnel carrier," he said. Again, they're never going to make hundreds and hundreds of thousands of them. They're going to make maybe 10,000 over ten years. And that fits in very well with what we do."

In 2005, A.L. Johnson won the Casting of the Year Honorable Mention Award from Modern Casting. And in 2010, the company was awarded the California OSHA Golden Gate Award for promoting workplace safety and health by motivating employers and employees to be actively involved in preventing hazards that lead to injuries and illnesses on the job. The company has become more aware, Klein said, by forming safety committees, department safety heads, and requiring employee participation. Regular safety meetings are held and employees are invited to bring up any concerns or suggestions.

"We have a very open-door policy with that kind of communication and work very closely with free OSHA consulting in which they've helped us to identify what we should be looking for," Carlson said. "We try to be as proactive as we can."