Company Offers Single-source Solutions for Aluminum Castings, Machining

Aluminum Castings

Focusing on quality, a St. Charles, Mo., contract manufacturer provides OEMs the services they need to be competitive in their markets.

No longer can contract manufacturers compete without high-tech software and production equipment, strategic value-added services, and a technical edge that is constantly being upgraded. One company with the capabilities to take on the competition squarely is Corbitt Manufacturing of St. Charles, Missouri, near St. Louis. A contract manufacturer with almost 60 years of experience in its core competency, Corbitt Manufacturing is a single-source supplier for companies that need finished aluminum alloy castings that have been machined to net shape specifications. The firm is part of a large, public corporation, American Railcar Industries (ARI) — a company that has been in existence in one form or another since the late 1800s. And because of its relationship with ARI, Corbitt has the financial and logistical backing that many smaller companies can only dream about.

"Our work is basic manufacturing," says Allan Hopkins, Corbitt's sales and marketing manager. "What sets us apart is the fact that we do it very well and we're very dependable. What we try to do is maximize service and quality, and minimize cost, which will give our clients maximum value."

Machining Complex Parts to Rigid Specifications

In one particular instance, Corbitt obtained a contract for the machining of a steel forging for Terex, a large manufacturer of construction equipment. At one time, the OEM had machining capability in its own facility. But its equipment was becoming old and outdated, and the company had to decide if it wanted to reinvest in new, more modern machining equipment or start to outsource the work. The company was also afraid that it would be hard to find a machine shop that could do its complex parts.

The part was 24 inches long by 10 inches square and used for the operating mechanism of a hammer drill. According to Hopkins, it had a machined bore down the middle of it, with about five bushing lands inside of it. Each of these lands had to be concentric to within +/- 0.0005-inch.

"They told us we could machine all of their parts—several dozen—if we could do this very difficult part," Hopkins recalls. "They tried four or five other potential suppliers prior to giving us a try, but we were the only one that was able to do it."

Hopkins says the part took a bit of trial and error from the beginning, but they were eventually able to do the part to Terex's rigid specifications. Corbitt now makes about 50 or 60 different parts for the large OEM. "We told them initially that we would pass on any cost savings to them once we perfected the process," Hopkins continued. "We succeeded; so we were able to pass on the savings to them after doing about 50 parts, a savings to them of about 10%. But mainly, it saved them about $7 million because they didn't have to revamp their existing machine shop."

A Diverse Contract Manufacturing Environment

The ISO 9001:2000-certified parts manufacturer has 150 full-time employees working out of a 130,000-square-foot facility, where they mainly produce permanent-mold aluminum alloy castings, often with precision machining requirements. Corbitt also machines steel castings or other metal components brought in house from outside sources, and performs progressive stamping, welding, fixture building, and light assembly on site as secondary processes. The company also uses a progressive stamping process to make a product for ARI, its parent company. Markets served by Corbitt include rail transportation, recreation vehicles (motorcycles and ATVs), construction and mining equipment, and food service equipment.

In the construction field, the company has made parts—including aluminum oil pans, after-cooler covers, and brake housings—for Caterpillar, John Deere, and Terex, all large OEMs. The parts for the hammer drills are steel castings and forgings that are sourced to them for the machining processes. In addition, Corbitt makes machined castings that go into ATVs for Kawasaki, and several machined aluminum castings for Salvajor, a manufacturer of commercial food waste disposal equipment. The company also performed work for John Deere farm equipment, until losing the work to a parts supplier near the OEM's plant in Europe. In addition to being a tier-two vendor for Caterpillar, the large manufacturer of earthmoving equipment, Corbitt continues to mold and machine several castings for its parent company.

Corbitt started business in 1948, mostly doing work for American Railcar Industries. About 20 years ago, the firm was acquired by ARI, a company that manufactures mostly tank cars and covered hopper cars.

"For many years, most of our work was for American Railcar, where we've made valve outlets, hatch covers, delivery piping, and other aluminum components for tank cars and covered hopper cars," Hopkins explains. "During the past decade, we've branched out into other markets."

Just-in-Time Plays Key Role in Customers' Value Chains

The company performs Just-in-Time deliveries and could be considered a single-source supplier for many of their finished parts. "Typically, when an OEM gives us repeat business, they will give us a long-range forecast of their parts needs for six months to a year," says Hopkins. "As the time frame gets smaller, maybe two to three months out, they'll start to solidify their requirements. Then around two to three weeks out, they tell us what has to be delivered on which days. The OEM can then take the parts off the delivery truck and stage them right into their assembly line. As a supplier becomes more credible in terms of quality, they can bypass having their parts inspected when they get to the OEM. We've reached this level with several of our clients."

Just-in-Time delivery ties perfectly into the manufacturing concept of supply chain, or value chain, management. Supply chain management starts with ordering materials and supplies that will be needed in the manufacturing process, and goes all the way to the selling of the finished products. Ideally, everyone in the chain would sit down with the OEM and offer input about what needs to be accomplished to get a finished product out on time and to eliminate any unnecessary activity or waste.

"Value chain management takes a certain amount of extra time and effort, but it's time that has a positive payback if it's handled correctly," says Hopkins.

From Design to Production

To enhance its workflow, Corbitt has six engineers on staff to assist customers with their designs and to handle production planning. The company has two engineers that mainly review customer requirements and respond to requests for a quote, while the other four engineers work out the manufacturing plan for the part. The engineers don't design any parts, but they can help an OEM make its designs more manufacturable. They primarily take a customer's specifications for a part, including geometry, materials, and quality specifications, and make it as manufacturable and cost-effective as possible.

"More and more OEMs are looking to their suppliers to be experts in their field, so they are very open to us making suggestions as to the best way to design and run the part," according to Hopkins. "It could be changing to another aluminum alloy or reducing a tolerance on a machined feature. Years ago, we would get exact specifications for a part, but now they just give us the size specifications for the final part, and we figure out all of the elements of the casting and machining processes."

Corbitt uses a standard tilt/pour gravity process to get the molten metal into the mold. A machine operator first gets a ladle of molten metal out of the furnace and pours it into the pour cups of the mold. The operator then initiates the molding by pushing a button that tilts the machine into the vertical position so that the metal runs into the mold. After molding, the operator manually takes the part out of the machine and stacks it individually before they are taken to an area where the gates and runners are sawed off.

In another operation, the cores are cleaned out or heated so that they disintegrate. Heat treating hardens the castings at the surface of the part. Aging is like a heat treating process, only the heating lasts longer and tends to harden molecules in the whole part. Most of Corbitt's production volumes are anywhere from 1,000 to 50,000 pieces per year, since it's hard to justify the expense of tooling if customers have less than 1,000 units per year. An iron mold for a permanent-mold casting can cost anywhere from $25,000 to $100,000.

In contrast, molds made of hardened steel for much higher production volumes can cost in the high hundreds of thousands. A steel mold can be used anywhere from 20,000 to 50,000 cycles before it has to be repaired or remade. Moldmaking takes anywhere from one month to six months at Corbitt, depending on the complexity of the part and the work schedule of the moldmaking company where they are outsourced. Part-holding fixtures, however, are made in the company's own tooling department. Throughput time for a machined casting that Corbitt has produced previously is about two weeks.

"One of the parts we're making for a customer right now takes about 17 steps to complete," Hopkins maintains. "The part is molded with interior sand cores and then heat treated. Next, it's de-gated and ground smooth, several machining processes are added, and then it's polished and tested. We do all of the heat treating and aging and make our own sand cores in-house, which is fairly unique for a casting company."

Corbitt can also make castings with hardware inserts. If a casting has to be bolted to something, the firm can insert a hardened-steel, threaded insert for the bolt. Another example would be for the heating elements in an aluminum cooking grill, which need to be inserted into the grill. The firm also offers secondary processes, including TIG and MIG welding, light fabrication, and light assembly processes. Corbitt can also handle bead blasting of parts to achieve surface finishes. It often holds tolerances to +/- 0.0001 for machining, +/- 0.0015 with casting processes.

Most of the company's casting work is actuated with aluminum alloys, most often with 356 and 319. These alloys are easy to heat treat, very ductile, and easy to machine. Parts that can be molded in-house vary in size from the size of a fist to about 50 inches long by 18 inches wide by 15 inches deep, and about 75 pounds in weight. Quite often, the casting company will get a steel forging that only needs machining.

"We buy one large forging from a vendor that weighs about 550 pounds," say Hopkins. "We heat treat it and then machine it in a horizontal machining center for about 25 hours, and then heat treat it a second time. We finish it with a grinding operation."

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