Shop Solutions: Cutting Tool Partnership Boosts Productivity
Choice Precision Machine (Whitehall, PA) is a mid-sized CNC job shop that manufactures precision components for customers in a variety of industries. Workpiece materials include alloy steels, stainless steels, titanium alloys, and Inconel alloys.
According to tooling engineer Rick Hujcs, working with such a variety of materials places a premium on development of a solid working relationship with cutting tool manufacturers. For tapping, Hujcs’ supplier of choice was Emuge Corp. (Northborough, MA). But he soon found that the company’s expertise also extended to other machining operations.
Case in point: a hardened 4140 steel workpiece that required production of a series of ¼-18 NPT threads. A counterbore geometry above the thread complicated tapping, and the first tap Emuge and Choice tried was re-cutting chips and breaking taps. A coolant-through tool and change in tapholder helped, but tool life was still questionable. Taps from other manufacturers also failed.
| Emuge threading and milling tools boosted productivity in a variety of workpiece materials at Choice Precision Machine.
After a review of the machine and fixturing, Hujcs and Emuge engineer Tom Kowalski decided to try thread milling. The resulting chips were extremely small, and coolant through the tool eliminated re-cutting of chips and made the threading process very smooth and reliable. Milling also provided quality threads and substantially longer tool life--the thread mill averages 600 threads, while a tap never produced more than 20. The thread mill can also be resharpened and recoated.
Another job involved milling of a 1" (25-mm) thick type 304 stainless steel workpiece. Choice was doing the job in multiple passes. Two roughing cuts were made using a 1" diam square-shoulder mill with two helical inserts at speed/feed of 300 fpm/11.5 ipm (90 m/min and 292 mm/min, respectively). Finishing required a 5/8" (16-mm) diam, four-flute solid carbide mill running at 150 fpm and 7.3 ipm (45 m/min and 185 mm/min). Hujcs wanted to increase speed and feed and do the job with a single tool.
Emuge recommended a milling cutter with an extremely high helix angle and high flute count. The tool completed both roughing and finishing at speed of 350 fpm (107 m/min), at feed rate of 30 and 60 ipm (760 and 1520 mm/min), respectively.
“The cutter cut so smoothly it was hard to determine whether or not it was actually working,” Hujcs recalls. The result was an 83% decrease in cycle time and elimination of separate tools for roughing and finishing.
Yet another milling operation-a high-volume job in 9" (228-mm) diam 4140 heat-treated steel bar-ran loud and slow using a square-shoulder insert cutter on a CAT50 VMC. Chatter and vibration limited speed and feed to 400 fpm and 12.2 ipm (122 m/min and 310 mm/min, respectively), with roughing cycle time of 226 sec.
After reviewing the process, Emuge recommended its Time-S-Cut milling cutters. Experiments comparing water-soluble coolant and cold air demonstrated that insert life increased substantially using cold air. Improvements were also made to workholding fixtures.
Using a 52-mm diam Time-S-Cut milling cutter with four TiAlN-coated, 12.5-mm inserts, the new process parameters were surface speed of 700 fpm (213 m/min) and feed of 261 ipm (6.6 m/min). Cycle time decreased to 53 sec-a time saving of nearly 3 minutes off the primary roughing cycle. The new cutter also reduced spindle load as well as noise and vibration.
A secondary roughing pass using a solid carbide Emuge tool eliminated the radius and shoulder material, and added 40 sec to total roughing cycle time. Final time savings were 130 sec/part, a 58% cycle-time reduction that translated into total savings of $1.78/part. The initial investment in the cutter and arbor was paid for after approximately 400 parts, and the job runs more smoothly and quietly with less stress on the machine.
The Time-S-Cut system was also applied to a similar job that runs on a CAT40 machining center. Cycle-time reduction alone saved $1.79/part, and the number of tools needed for finish milling was cut from six to four. Tool life was good enough that 1000 pieces could be completed with only one change of the 8-mm inserts.
Reliable Machines Key to Shop’s
Since 1998, when Vector wanted to increase productivity by moving into more high-speed hard milling and improve machining accuracy, adhering to this philosophy has meant using machine tools from Mori Seiki (Irving, TX). “The Mori machines not only helped in the areas we expected them too, they gave us the ability to redesign a lot of our processes,” says operations manager Bruce Eagleburger. “We don’t do things the way we did six years ago.”
Launched in 1995 as an in-house supplier of plastic injection molds for its parent company, large vehicular lighting manufacturer Petersen Mfg., Vector Tool & Engineering (Grandview, MO) now serves an array of customers and has experienced steady growth throughout its history. When Vector began completing the in-house mold work with time to spare, managers decided to expand their customer base. “It just didn’t make financial sense to operate at less than full capacity,” recalls plant manager Dale Sass.
Today, the company has grown to the point that jobs for Petersen make up only 30-40% of the shop’s total workload. Sales and profits have increased every year, even in the face of a poor economy and increasing global competition.
“We never focus on being the cheapest, we focus on being the best,” explains Sass. “We concentrate on four things to accomplish this. First of all, quality. Second, turnaround time. Third, always being honest with our customers. Fourth, taking care of any problem that comes up, regardless of who’s responsible for it.”
| Experienced operators and reliable machines are two ingredients of Vector’s success. Bottom photo shows a food mold being machined.
In the past, a large quantity of Vector’s work required electrical discharge machining (EDM). Electrodes were machined either from copper or graphite, then used to burn the workpiece. The company now uses several Mori Seiki machining centers, including an SV-500B, SVD-403 mold/die, and two NV5000s, to machine jobs that used to be EDM’ed. The quantity of high-precision work going through the shop has continued to grow, but EDM use has dropped 30-40%.
“I was most impressed with our machines on an injection mold for an automotive lighting fixture,” recalls Eagleburger. “We were doing the core half on one Mori and the cavity on another, and there were literally no straight lines or flat spots on either half. With that kind of job, we need to hold tolerances of less than 0.001" [0.025 mm]. Both halves of the mold came off the two machines pretty much perfect.”
Vector also improved productivity on parts it was already milling by minimizing hand polishing. A tool for an injection-molded food product, for example, came off Vector’s Mori NV5000 HMCs with the required surface finish, saving approximately 15% of total production time.
The Mori machines also support untended operation, substantially increasing shop productivity. Automating time-consuming jobs to run during nights and weekends helps offset rising costs of doing business, allowing Vector to minimize price mark-ups and stay a step ahead of overseas competition.
Machine Tests Cut Retooling Costs
With tighter tolerances demanded by a new part, engineers at DaimlerChrysler (DCX; Auburn Hills, MI) found that machining cells targeted for retool might need major rebuilding before they could meet the new requirements.
The line, which included nine automated and palletized HMCs and two vertical turning centers, was producing 150,000 gray cast iron housings annually for a four-speed automatic, rear-wheel-drive transmission. The new housing weighed 12 lb (5.4 kg), compared to 7 lb (3.2 kg) for the old part, and was 2" (51 mm) larger in diameter. The part also required tighter machined tolerances. Some critical ID areas, for example, had tightened from ±0.002" (0.05 mm) to ±0.0005" (0.013 mm). Housings had about 200 machined features, and processing included turning, boring, drilling, milling, tapping, and reaming.
Project engineer Steve Skinner knew achieving process capability (Cpk) of 1.67 on the new process would require reprogramming, new cutting tools, new workholding fixtures for the HMCs, and new chucks for the turning centers. He also wanted to be sure the machines had the capability to hold the needed tolerances.
DCX worked with the original machine tool builders to develop a plan to rebuild each machine. The company also bid work out to U.S. Equipment Company (Detroit), which proposed testing to assess the machines’ capabilities relative to the process and statistical run-off requirements. This would allow rebuilding only to the extent necessary to meet requirements.
Tests included static, dynamic, and load (circle, diamond, square) tests for each machine to establish baseline condition. The company also inspected lubrication, coolant, and filtration systems, and performed visual checks for the condition of hydraulic hoses, electrical cabling, power tracks, push-button panels and overall cleanliness.
The HMCs were determined to be in very good condition overall. U.S. Equipment technicians replaced a spindle that had crashed, realigned another, and repaired broken ancillary items such as push-buttons. Dryers were installed and spindles recharged to deal with a contaminated air supply at the plant, and Renishaw probes were installed on six of the nine machines. All work on the machining centers was done at the DCX plant.
The vertical turning machines had fared less well. Both were out of square and no longer met OEM specs. They were completely rebuilt at U.S. Equipment’s Detroit shop.
Other equipment in the cell was in varying degrees of condition. Three AGVs that served the HMCs were rebuilt at U.S. Equipment. A parts washer was repaired and configured for the new part, and a CMM integrated into the line was recalibrated and reprogrammed at DCX. Six work-set stations were so worn that pallets from the AGVs wouldn’t seat properly. Inaccurate pallet positioning would cause system faults, so the workstations were redesigned and rebuilt at U.S. Equipment. The company also revamped workholding, developed new programs, supplied three sets of toolholders and perishable tooling, and helped with run-off and debugging.
Selective rebuilding saved DCX $1.5 million and considerable time by performing only the necessary corrective actions versus a complete rebuild of all machines. Skinner reports there have been no warranty calls since production on the retooled line began at the end of 2002.
Electroformed Parts Go to Extremes
Two critical parts for a new timepiece that will travel to the ends of the Earth were produced using a specialized electroplating process.
Part supplier Tecan (Rancho Santa Margarita, CA) says it used photo electroforming (PEF) to fabricate a multilevel backplate for the watch face and a multi-aperture grid overlay. The timepiece will have to withstand temperatures of -50°F when it is carried to the South Pole by modern-day polar explorer Jorgen Amundsen this fall. Amundsen is a direct descendant of Roald Amundsen, the first man ever to set foot on the South Pole on December 14, 1911.
Manufactured in a single PEF process, the nickel backplate includes mounting apertures, date display aperture, peripheral concentric enamelling recess, stepped rim location lugs, and a mock “engine-turned” central region. The second part, also in nickel, is a web-like grid which locates accurately over the back-plate and represents the longitude lines emanating from the poles.
In PEF, complex components are produced using a predominantly 2-D electroplating process. Shapes are grown atom by atom, and fine process control allows very accurate tolerances with good repeatability, according to Tecan.
Parts are generally produced on a flat metal mandrel, which is coated with a light-sensitive photo-resist material. The mandrel is then exposed to ultraviolet light, and the photo-resist on the unexposed area is developed away to produce a matrix before the mandrel is immersed in the electroforming solution. Carefully controlled electrolysis migrates metal atoms to the mandrel to achieve the desired thickness. Once the mandrel is removed from the solution and rinsed, the component can be separated from it.
The most frequently used metal for PEF is nickel, the company says. Nickel can be deposited at high speeds, is strong and fairly resistant to corrosion and wear, and the physical properties of the deposit can be closely controlled. The company says its can routinely handle tolerances of microns, while sub-micron tolerances can be achieved. PEF produces parts using a specialized electroplating process to grow shapes atom by atom with fine process control.
Jorgen Amundsen’s company, Amundsen Oslo, has produced 500 of the sub-zero “Polar Timepiece” wrist watches. The explorer plans to conquer both the North Pole and the South Pole within a year, taking 250 of the timepieces to each Pole. He completed the first half of the adventure in April when he and his Arctic team successfully skied to the North Pole. Amundsen expects to complete the second leg of the two-Pole trip in December.
This article was first published in the October 2004 edition of Manufacturing Engineering magazine.