This technical information has been contributed by
Devon Precision Industries, Inc.

Size, Precision Reign Supreme at Swiss Screw Machining Specialist

Screw Machining

Acquiring a technological edge has enabled one of the nation's largest screw machine shops to hold close tolerances on almost any screw machining challenge.

The New England region of the U.S. is notable for having a large number of job shops and also many screw machine shops. Moreover, the screw machine industry in America is reported to be a hefty $2 billion dollar marketplace. One New England job shop that specializes in screw machining is a big player in this arena. Out of about 6,600 screw machine job shops in the country, Devon Precision Industries, located in Wolcott, Connecticut, is one of the industry's leaders.

"With over 550 production machines, we're one of the largest screw machine shops in the country," says Denis Desaulniers, the Vice President of Sales and Marketing at Devon Precision. "And we have plans to add $1 million to $3 million worth of new equipment every year. The average contract shop has about 20 or 30 machines, so we have a decided technological edge over most shops, and we're now ISO 9002 certified, which attests to our high level of quality. And we use the Japanese cell production system extensively, which gives us added efficiencies."

Devon Precision operates more than 200 primary screw machines and approximately 350 secondary pieces of equipment for a variety of different operations. The company machines most of its work with cold rolled and stainless steels, some copper, brass and aluminum, and a little bit of titanium. Desaulniers says that most contract shops turn out blanks on their screw machines and then farm out the multitude of secondary operations. Devon, however, performs primary and secondary operations in its plant. Heat treating, anodizing, and plating are the only processes that the company vends to others.

"We do all of our machining in-house instead of sending out work to several different shops, like many job shops have to do," Desaulniers insists. "We even do jobs for shops that have their own screw machines, but are having problems holding tolerances or dealing with other quality issues. We can hold +/- 0.0002 inch on all of the screw machines, so we feel confident that we can handle most any screw machining challenge. And, we're now able to watch 100% of our parts with PLCs (programmable logic controllers) that we attach to our machines. With the PLCs, we are alerted to any problems that might occur during production."

Parts for Many Industries

Devon provides parts for a large marketplace, turning out small, medium, and large production runs. Most of the parts that the firm provides are for Fortune 500 companies-including GE, Dana Corp, HP, GM, Ford, Chrysler, 3M, and IBM-for plants in 48 states and seven countries. Although the company manufactures parts for many industries, its primary markets are automotive, medical, consumer appliances, telecommunications, and military defense. Many of the products are miniature drive shafts, rods, firing pins, pump assembly parts, valves, pins, pinions, and gears.

In the automotive market, the firm supplies about 200 different parts to most of the auto manufacturers currently doing business. The parts are used in air bag systems, brakes, cruise controls, wiper motor shafts, and instrument panels. For the medical field, the company makes precision gears, router bits for angioplasty surgery, and many pieces of hardware for medical instruments and surgical tools. Devon has been making small firing pins and arming devices for bombs for the military for many years. For the cluster bomb alone, the company has supplied over 65 million sub-assemblies with zero defects.

"We make windshield wiper shafts for almost every car in the world," Desaulniers asserts proudly. "Many years ago Honda was having their shafts made by another vendor that was charging them a lot for the parts. After analyzing the situation, we found that we could do the shafts more economically. After producing the parts for a while, we were able to save them 25% to 35% of the cost they were spending with the other vendor. So, over the past several years, we've saved them millions of dollars for the part."

Devon Precision was established in 1967 in Waterbury, Connecticut only a few miles from its present location. Company President Yvon Desaulniers started the fledgling company with only three screw machines set up in a converted garage. After several years, the company moved to larger facilities and added extra equipment, before settling at its present location in Wolcott in 1974. The company doubled the size of its plant in 1982, and now operates in a large, modern 50,000-sq-ft building with 235 full-time employees working on two shifts. In 1997, the family-owned company achieved its ISO 9002 certification.

CNC Swiss Machines Enhance Precision

Devon Precision's vast inventory of machining equipment is truly impressive. In the screw machine department, the firm has some 200 machines, including many Bechler single-spindle, automatic Swiss screw machines that handle a maximum workpiece diameter of 3/4 inch and a maximum length of 22 inches. The company makes use of several Escomatic automatic screw machines that handle workpieces up to 5/32 inch. Also in the department are many Gildemeister multi-spindle (six-spindle) automatic screw machines with a maximum diameter of 3/4 inch. Rounding out the technology complement are three CNC Hardinge Swiss screw machines with a 3/4-inch diameter capacity, several rotary transfer machines with eight stations each, and a Macor CNC cam cutting machine for the company's cam-operated machinery.

The company's recent claim to fame are three high-tech, Hardinge, CNC Swiss screw machines. The sophisticated machine tools offer the perfect array of features to ride the trend toward low-volume, high precision, quick turnaround parts. And, the CNC machines are ideal for the global marketplace, where operators with more computer skills are more prevalent than those with machinist know-how.

"Our CNC Swiss machines each have 19 tools, which allow us to drop parts very quickly and accurately without any secondary operations at all," Desaulniers explains. "We can even do milling, drilling, slotting, and broaching on the CNCs. And we make our own broaching tools with a dedicated, million-dollar Swedish machine," he added. "We can't really run jobs economically that are a few hundred pieces, but we offer batch runs of 5,000 to 10,000 pieces that are competitively priced. Our charges for machine time are higher for our CNCs and multi-spindles, but production runs are reasonable in medium volumes."

Devon's multi-spindle machines are Gildemeisters, a German machine that is assembled in Italy. They are also automatic and have six spindles that allow them to make five parts imultaneously. Tooling costs for the multi-spindle machines are quite high (between $10,000 and $50,000 per machine), while tooling can be produced for about $500 per machine for the single-spindles. Both machines have only five tools per spindle, but eight tools can be actuated with specialized attachments. However, cycle times are quicker for the multi-spindles, at approximately 20 seconds per part, compared to two minutes per part for the single-spindles.

The diverse screw-machine company also has an Escomatic, a specialized screw machine that has two tools and runs on coils of wire stock. The diameter of the wire ranges from 0.030 inch to 0.157 inch, and tolerances near 0.001 inch are all that these machines are required to hold.

"We use the Escomatics for the simple, less demanding work, since they are not as precision as our other machines for roundness and concentricity," Desaulniers points out. "They're fine for making things like dowel pins, but not too good for precision shafts."

Capabilities for Large and Small Runs

Devon's cam-operated machines are best suited for handling long runs, from 20,000 to 50,000 parts and higher. This is especially true of the single-spindle machines, ten of which can be run by one operator. Routinely, when a customer needs more than 500,000 or a million parts, the company will acquire cold-headed, cold-formed, or even powdered metals, since these metals are more economical for large runs. All of Devon's screw machines have bar loaders that automatically feed in bar stock for continuous, non-stop running.

Machine setup times differ greatly between cam and CNC machines. Less setup time is necessary, usually only a couple of hours with preprogrammed CNC machines, so they are perfect for repeat jobs and short and medium runs. A cam machine, on the other hand, usually takes about 16 to 24 hours to set up because of time-consuming cam installation. Even single-spindle machines can have anywhere from three to twelve cams on one machine. Many job shops send out cams for machining, but Devon Precision does it in-house with a Macor cam cutting machine, reportedly the only one in the United States. When in operation, a cam contour pushes carbide insert tools down to the workpiece, with the workpiece spinning anywhere from 1200 to 2000 rpm.

"When we are setting up a cam-operated machine for a new job, we have to install all of the cams first and then produce one or two parts to check that everything is set up OK," Desaulniers affirmed. "We then pull off the cams to harden the steel because there will be excess wear on them during the production run. This is why tooling, which includes cam grinding, is very expensive for the multi-spindle machines."

Besides its giant, diverse platoon of screw machines, Devon has an even larger cluster of secondary equipment that allows the firm to do any particular operation many different ways. The equipment handles secondary operations such as gear hobbing, burnishing, thread rolling, knurling, worming, splining, broaching, centerless grinding, and deburring, as well as additional tapping and drilling. Included in the mix are twelve cylindrical die machines in different sizes for thread rolling, knurling, and worming. Devon finds it to be quicker and more economical, in many cases, to do this work as a secondary operation, since the die machines can produce 1000 pieces per hour. The smart machines load parts automatically, and will reject parts that are too long, too short, or have burrs.

Devon's rotary transfer machines have eight stations, six to carry out the work, and two to load and unload parts. The machines handle drilling, slotting, deburring, milling, and tapping very precisely. "The quality is very good on the rotary transfer machines," says Desaulniers. "Quite often, if I'm running 2000 pieces, I will blank off the parts on the screw machines and then send them off to heat treating. In the meantime, we will set up the rotary transfer machines to do all of the secondary operations. The drawback to rotary transfer," he continues, "is that the tooling is expensive and takes a long time to make, and the machine takes a long time to set up. However, the uniformity, repeatability, and quality is excellent, and the machine can perform many operations very quickly during production."

Whether it's excellent quality, innovative engineering, employee training, or stringent quality control, Devon Precision Industries' motto says it all: "Exceeding your expectations is our business."

This technical information has been contributed by
Devon Precision Industries, Inc.

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