Stokes Vacuum, Inc., (Philadelphia, Pennsylvania) is a manufacturer and worldwide marketer of vacuum systems including pumps, condensers, spray dryers and vacuum accessories. Like any manufacturer in a competitive market, Stokes constantly is seeking ways to reduce costs and increase machining efficiency. To pursue these goals, Stokes employs high-tech ideas such as state-of-the-art machine tools and advanced ceramic milling inserts, as well as simple and effective concepts such as a chip scoop that resembles a garden hoe.
Production flow at Stokes combines characteristics of both high volume and job shop operations. Many lots are low in volume but are run repeatedly and frequently. This magnifies the benefits gained by fine-tuning operations to reduce cycle time per workpiece. After programs are initially generated on a computer, they often are edited manually at the machine tool to optimize cutting time.
"We try to keep the machines running," says second shift foreman Bill Gerstadt. "Theoretically we want the spindle turning eight hours in an eight hour shift. We don't accomplish that, but we're approaching it." Mr. Gerstadt analyzes operations "to find what's taking the time . . . where I can attack to save the most time," he says. "We've got pretty good teamwork here; our first shift foreman Tom Marple usually gets the original program going and gathers tooling, while I can get into the cost reductions on second shift."
In some cases a simple idea can produce big savings. One CNC program for rough machining a pump body included four cycle stops to clear chips from the bores. Because operators usually tend more than one machine, as well as other factors, each cycle stop was costing as much as ten minutes in machine downtime. To solve the problem, Mr. Gerstadt devised a "chip scoop" that looks like a garden hoe attached to a standard Vflange holder. The hollow shaft that holds the blade also carries coolant to flush away chips. The scoop is stored in the machining center's tool chain and is programmed to move in and sweep the bores clean at appropriate times during machining. The process takes about 30 seconds, and no cycle stop is required.
Many of the other timesaving solutions are more hightech. In a significant commitment to increased productivity, Stokes recently added three 40 hp Makino A77 high speed machining centers. "We were running Makino MC65 machining centers, and we jumped from those seven horsepower machines to these A77s with 40 horsepower," Mr. Gerstadt says. "We've been using highfeed machining techniques that take advantage of the high spindle rpm and horsepower of the A77 machines. When we acquired the new machines, we went looking for tooling. We invited the major tooling suppliers, and they've been very cooperative with us."
A change in tooling to match the capability of the A77 machines generated a big productivity boost in rough milling a cast-iron pump housing. Previously, Stokes had used a 4inch milling cutter tooled with 14 coated carbide inserts to make the cut at 550 sfm and a feed rate of 81 ipm. Total cutting time was 20.68 minutes, and Stokes wanted this to decrease with the new machines. Kennametal Inc. metalworking systems engineer Rick Doerr analyzed the operation and suggested Stokes try a 4inch cutter tooled with 14 silicon nitride ceramic grade Kyon 3500 inserts from Kennametal Inc. (Latrobe, Pennsylvania). With the new tooling, Stokes was able to mill the housing at 3,000 sfm and a feed rate of 230 ipm. Cutting time dropped to 12.74 minutes, a savings of nearly 40 percent.
As Stokes Vacuum looked at every aspect of the machining process for ways to save time, it was clear that tool change and setup could consume as much or more machine time as actual cutting. The A77 machines include Makino's tool management system and the Makino PRO 3 control. The tool management system includes an automatic tool life monitor and spare tool pickup. All tools are registered in the tool table along with tool gage length. Each tool is assigned a tool life value in linear inches of cut. When a tool uses up its assigned life, the control automatically brings in a replacement tool if one is assigned. Mr. Marple points out one of the tool management system's key benefits. "Our insert breakage has been reduced to just about zero for those tools that have a tool life assigned to them," he says.
Mr. Gerstadt notes additional advantages of Stokes' machine tool setup. "The A77s have 132tool magazines that enable us to dedicate each machine to a family of parts using common tools. This reduces setup time and thus cycle time from job to job, but in no way diminishes our options to run parts that are not in the common tool family if the need arises," he says. "We intend to prudently expand the family of parts programmed for each machine with minimal tool displacement."
To maintain competitiveness and enhance its ability to respond to the needs of its customers, Stokes Vacuum plans to continue to evaluate its machining processes and find ways to make them more efficient.