Precision Machine Shop Profits From New Six-Axis Swiss-turn CNC Lathes

Devon Precision Industries (Wolcott, Connecticut) makes precision parts for medical, automotive, telecommunications and aerospace customers. Five years ago, Devon began preparations for the future of precision machining. Several trends were evident. Many more runs were short, ranging from 10,000 to 25,000 pieces. Furthermore, complex jobs requiring more than eight operations—the limit of a conventional machine—became more common. Increasingly, Devon's customers demanded quick turnaround and on-the-fly design. Additionally, more parts were made of exotic materials such as Inconel and titanium.

Yvon Desaulniers, Devon president, decided to take several steps to prepare for the future. These included evaluating CNC Swiss turning machines, recruiting qualified machinists, obtaining ISO 9002 registration and upgrading cam-driven machines. About three years ago, Devon began trying to streamline short-run production of precision parts. The company decided to have trials with four CNC Swiss machines.

Devon asked each potential vendor to perform a trial run on the same part. The part was made from 0.236inch diameter A2 tool steel. Eight operations were required to produce the part, including face and turn, milling the part in half, inserting a skive slot, milling two chamfers, combination spot/drill, tapping (356), cutoff and transfer to subspindle, and air blast to eject the part. Transfer to the subspindle was tricky because it required a special collet shape and precise synchronization to insert the nonsymmetrical part.

Devon sent drawings and bar stock to the four machine manufacturers. After receiving the finished trial parts, a team from Devon visited the vendors to verify their production data.

Based on these results, Devon decided to order its first machine from Hardinge (Elmira, New York)—a Conquest ST220 six-axis Swiss-turn CNC lathe. Hardinge was included on Devon's initial short list because it already supplied collets for Devon's conventional Swiss machines. Another reason, according to Mr. Desaulniers, is that Hardinge is the only U. S. manufacturer of this type of machine. "We had negative downtime experiences in the past because we had to wait for parts," he says. "So we made spares availability part of our vendor evaluation."

In machining the test part, the Hardinge Conquest machine performed best, completing the necessary operations in shorter cycles per part while holding closer tolerances than competitive CNC Swiss machines. "The Hardinge CNC Swiss machine is faster and easier to program, and it provides readier access to tools. These features add up to more productivity per usable hour of machine time, and more usable hours overall, compared to other CNC Swiss machines," says Mr. Desaulniers.

The machine's heavy Harcrete base provides better damping characteristics than cast iron, thus yielding 30 percent longer tool life and better surface finish. Regarding overall part quality, Mr. Desaulniers says, "The machine base is paramount."

Devon's team also compared each vendor's support capabilities. Tom Hintz of Hardinge remembers one spot quiz: "Mr. Desaulniers brought a parts manual for the ST220 machine he was interested in buying into our parts department. He opened the book and named ten parts he had selected beforehand. He wanted to know if he could expect immediate delivery of these parts or what the target delivery date would be for parts not immediately available." According to Mr. Desaulniers, in this regard as well, Hardinge's support organization influenced his decision. Eight of the ten parts selected were instock items, and only one week was required to deliver the other two.

The precision machining capabilities of the Hardinge CNC lathes are illustrated by two other parts recently fabricated by Devon. These include a plunger guide for a mechanical device and small piston for a fiberoptics assembly. The Conquest machine easily executes the plunger guide's complex form. Its indexing headstock spindle mills the two flats, as well as the elongated window that requires a 10-Rms microfinish and very close tolerance of ±0.0003 inch. The small piston presents even more demanding requirements: more difficult material (52100 bearing steel); a closer tolerance of ±0.0002 inch; and an 8 Rms microfinish.

Mr. Desaulniers says the real benefits to his business began to appear over time when he compared the productivity and profitability of his shop's CNC Swiss machines to its conventional Swiss machines. For example, a typical job on the camdriven machines takes about two days, or 18 hours, for setup. With the Hardinge CNC units, setup typically takes two to four hours, allowing Devon to gain 12 hours or more on every job.

One highmargin job involves 200 units of each of three parts, all three on the same program and from the same bar. Once the part program is written, it is stored in the CNC control unit. Mr. Desaulniers reports that younger programmers have been able to gradually capture the knowhow of the seasoned machinists by observation. As more manual setups are analyzed, CNC setup times are further reduced.

Devon has standardized toolholders in its three Hardinge CNC Swiss machines. This also reduces setup time because some setups only require minor adjustment. In addition, programming for all three units is performed by the same engineer.

The setup adaptability of CNC Swiss units often eliminates secondary operations needed with conventional Swiss machining. This reduces time and labor needed for fixture making and other preparations. The key to higher profits is the CNC machine's ability to exceed the technical capacities of a conventional Swiss automatic machine.

For example, a typical shortrun job involves more than 16 operations. The conventional machine is limited to eight tools and requires two or more setups to complete the part. Furthermore, any given operation must be performed within a 360-degree turn, limited by one revolution of the cam. By comparison, the Hardinge CNC Swiss machine permits up to 19 operations on one part from a single setup, thus providing much greater flexibility. When working with exotic materials, the CNC unit automatically deburrs the workpiece. But deburring with a camdriven Swiss machine is more difficult, requiring a dedicated operation.

Additional capability provided by the new CNC Swiss machines also enabled Devon to secure new and profitable business from industries that require precision manufacturing. Some examples are medical equipment parts, valves and solenoids for industrial process machinery, telecommunications components and aerospace parts.