Shop Solutions: Trunnion Table Provides Economical Multiaxis Capability
Mechanical seals can be found in oil pipelines, automobile water pumps, air conditioning compressors, and beverage processing systems, among many other places. Simply put, a mechanical seal is a containment device that prevents leakage over a rotating shaft. Depending on its application, a seal may have a number of components, and each one needs to be made to exacting tolerances.
The demand for mechanical seals continues to grow as manufacturing, processing, and pipeline operations are constructed all over the world. To keep up with orders from Central and South America, managers at the Mexico City plant of John Crane Mexico--there are nine other Crane facilities in the country--realized that they needed additional CNC equipment.
"We were looking for a reliable machine with five-axis capability," recalls Production Manager Ricardo Almazan. "We did some investigating, and got recommendations from other John Crane facilities in Illinois and Rhode Island."
Based on those recommendations, the plant purchased and installed a VF-5 vertical machining center from Haas Automation Inc. (Oxnard, CA). Equipped with a Haas TR 210 dual-axis trunnion table, the VMC quickly went into daily operation. It was followed by purchase of another Haas VMC, a VF-4, six months later.
John Crane purchased the machine with five-axis capabilities to improve accuracy on difficult parts. "On one part, we were having problems with a thread," says Almazan. "Threading was the last operation, so we would have to scrap the entire part if it was bad. But with the five-axis machine, the number of rejects has dropped dramatically."
The mechanical seal components produced in the Mexico City plant are made of type 316 stainless steel, and must meet tight tolerances to work properly in high-stress environments such as oil pipelines and food processing plants. "We have to hold tolerances of 0.0005 to 0.0001" [0.013 - 0.0025 mm], Almazan says. "We've had no problems with the Haas machines holding tolerances."
Parts for the mechanical seals are first turned on lathes, then moved to the Haas VMCs for drilling and tapping. At one time, parts went to three different machining centers, but now the five-axis Haas handles all the work. "One way we save time is by doing multiple operations," Almazan says. "We've combined work from three machines into one. As a result, we've reduced cycle times on some parts from five hours to two-and-a-half hours."
With the reduction in cycle times, of course, came a reduction in delivery time. "We have been able to fill orders faster," relates Almazan. "We went from taking 19 days on orders to 12 days, and recently, we were filling orders in five days." Lot sizes range from a single piece to 15 or 20 pieces, he adds.
The company also is taking advantage of editing features in the machine's Haas CNC. "We program right on the control, using the background edit feature," says Almazan. "This saves us a lot of time, because we have so many different parts that we make. The programs are already loaded, and then we just have to make small changes to each program using the background edit."
Insert Switch Boosts Productivity, Quality
Founded more than 50 years ago, JP Carlton Co. Inc. (Spartanburg, SC) manufactures high-quality stump cutters and grinders. Products range from a 9-hp (7-kW) handlebar model to large, tracked machines with attached hydraulic blades that can cut 72" (1.8 m) high and 25" (0.6 m) below grade.
Carlton manufacturing personnel recently faced a production problem in rough turning of some of the company's 4150 alloy steel shaft-type components. Long setups and low feeds and speeds were limiting turning productivity. Another issue was flexing of the relatively long parts, which engineers wanted to hold using a face driver, during machining. Engineers needed a tool that would require minimal setup time, would have a longer tool life than the inserts they were using, and would reduce cutting forces to minimize part runout.
Specifically, Carlton engineers wanted to cut down the number of setups required per part while keeping concentricity over the length of the shaft to <0.0005" (0.013 mm) TIR. Among the cutting tool suppliers they contacted was Iscar Metals Inc. (Arlington, TX).
After analyzing how JP Carlton wanted to hold the parts--with a Rohm face driver--the Iscar representative suggested the company's SLANR 16-15 Tang turning tool. The insert would decrease cutting pressure on the long shaft while increasing tool life, enable higher feeds that would result in better chip control, and cut down on the amount of material left for finish turning.
The insert is part of the HeliTurn family of tools, which have helical-shaped cutting edges that enable users to take large depths of cut at higher than normal feed rates. Tangential clamping and double-sided helical design also support increased speeds/feeds, and mounting of the upper rake face of the insert at the same level as the holder body improves chip flow, protects the tool holder, and allows more efficient cutting.
After testing the inserts, JP Carlton engineers concluded that the tool allowed them to achieve superior results over conventional turning tools. Roughing time was reduced by 18 minutes at surface speed of 600 fpm (180 m/min) and feed of 0.018 ipr (mm/rev) depth of cut. Tool life was eight parts per insert, and total processing time for roughing was reduced to 12 minutes.
Implementing the Rohm face driver system with the Iscar inserts reduced setups from three to one. Concentricity decreased from 0.0015" (0.38 mm) to less than 0.0005".
Laser Shines at Aluminum Cutting
Production Manufacturing Inc. (PMI; Hamilton, OH) processes a lot of aluminum sheet--about 750,000 lb (337,500 kg) a year, in fact.
"We started looking at laser cutting back in the early '90s," recalls president Jim Napier, "but the reflectivity of aluminum was a problem. We also wanted to avoid the costs of using nitrogen as the assist gas."
When a laser supplier showed that it could resolve both issues, Napier was sold. PMI now cuts sheet aluminum at high speed using a CL-707 laser cutting center supplied by Cincinnati Inc. (Cincinnati). Installed in 2002, the system features linear motor drives. But speed is only part of the story--PMI also saves on assist gases by using specially conditioned shop air.
In fact, that savings was key to the company's cost justification for the machine. "If we couldn't have done it with air, we wouldn't have bought the machine," Napier says. He estimates that PMI realizes 65 - 70% cost savings by using shop air instead of bottled gas.
According to Napier, PMI is a high-production sheetmetal shop. "We run some steel, stainless and galvanized, but 90% of our production is aluminum, mostly in the 0.020 to 0.125" [0.5 - 3.2-mm] thickness range," he says. The high-speed laser delivered faster throughput on volume jobs--as much as twice the processing speed of the company's turret presses, with edge quality that requires no deburring or post-processing.
The laser typically cuts aluminum at 800 ipm (20 m/min). "We can run at 1100 and 1200 ipm [28 and 30.5 m/min], but then the machine may actually outrun the operator," Napier says. "We adjust the machine speed so it works comfortably for the operator and provides time for loading and part transfer."
Napier also credits the laser with opening the door to new work and part improvement opportunities. "Our customers want very tiny openings that our turret presses can't do," he explains. "And, the laser makes it quicker and simpler to do prototyping and custom work. I don't have to blank everything and cut each part independently. Usually, we can cut everything from one sheet and have all the parts ready for fit-up and check-out."
PMI has worked with customers on redesigning parts to take advantage of the laser's capabilities. For example, one customer approved a change to a part made from rectangular tubing, requiring multiple cutouts and processing steps. Instead, PMI forms the 3-D piece from a flat laser-cut blank, at considerable savings.
"We fight cost all the time -- finding ways to produce parts for customers at lower costs by modifying the design and simplifying the processing," Napier says. "We're constantly looking for ways to do it better."
Thin parts are cut almost totally using shop air as the assist gas. The laser is located in its own cell, and is served by a dedicated, two-head reciprocal compressor. Typically, one head runs while the other rests.
Air lines are stainless steel, and the system has its own filters and refrigerated dryer. "The cleaner your system is, the more precise your cutting will be," Napier says. Air pressures and usage vary with work material, from 60 psi (415 kPa) on 20-gage steel to 115 - 165 psi (790 - 1140 kPa) on aluminum, he notes.
The laser features a diffusion-cooled resonator that provides consistent edge quality and allow production of small, tight-tolerance part features. Diffusion cooling allows the beam to be focused into a small spot, resulting in faster, cleaner cutting with narrower kerf, superior edge quality, and small heat-affected zone (HAZ).
Minimizing heat input to the aluminum also avoids other undesirable thermal effects. "Flatness is a big issue with our customers," explains Napier. "Aluminum is difficult, because it holds the heat and is especially reactive."
"Frankenstein" Lathe Turns Ship Shafts
A supplier of large ship shafts to the US government needed a finishing lathe to meet a tight timetable-and a tight budget.
The company turned to Machine Tool Research Inc. (MTR; Rochester, NY) for help, and wound up with a novel solution: an extra-long lathe cobbled together in Frankenstein fashion using components from several old machines.
MTR took World War II-vintage Niles lathes and combined bed sections to create a nearly 100' (30-m) long bed. While two beds had decent hard ways, the third had badly worn ways that required matching and replacement. Guide surfaces for all three beds were machined to match on a CNC planer mill.
The headstock and tailstock came from a scrapped Farrel lathe. These elements had been abused in a steel plant, so MTR rebuilt them and fitted them to the new bed. Spindle runout is critical on ship shafts, and was held to 0.0002" (0.05 mm) on the headstock. The tailstock needed new bearings to achieve this runout.
The carriage also required full remanufacturing, including a new cross slide with tool slides to suit the workpiece. To provide the needed precision, MTR designed a new twin-pinion drive for the carriage (Z axis) and a preloaded ballscrew for the cross slide (X axis) of the machine.
The long ship shafts require steadyrests for support, so MTR designed and built three roller-type rests. A 1990s vintage Allen-Bradley 9-series CNC from a scrapped lathe carcass and software to handle the new twin-pinion drives, plus a new operator platform with a CNC pendant and an overhead powertrack, completed the package.
The machine was run off at MTR's plant, and is scheduled for turnkey installation just in time for the recent workload bubble of ship shafts.
This article was first published in the January 2005 edition of Manufacturing Engineering magazine.