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Shop Solutions: Magnetic Chucks Boost Milling Productivity

Synventive Molding Solutions (Peabody, MA) provides hot-runner systems and related components for plastic injection molding. One of the world's largest and most innovative suppliers of such equipment, the company holds 39 patents and has 79 patent applications pending worldwide. The company's new XP line of hot runners, for example, combine proprietary heat pipe and MultiZone technologies, and must be manufactured to precise specifications supplied by moldmakers.       

Synventive's four magnetic chucks are used with an integrated variable controller that facilitates machine setup and load/unload.  

Synventive uses a 50-hp (37.3-kW) Mazak VMC with a 50 X 80" (1.3 X 2-m) table to machine large hot-runner manifolds from various work materials, including 4140 steel, P20 mold steel, and type 420 stainless. Originally, milling setup required manually locating multiple mechanical clamps to hold the various parts to the machining table. Milling required two separate NC programs, one to machine the part around the clamps, and a second to continue the machining process after the clamps were manually removed and reattached.

"It could take up to 16 hr to completely machine the largest components," recalls CNC process engineer/lead programmer Jerry Tremblay. Production of multiple parts or components with varying dimensions increased setup time exponentially, he says.

And setup time wasn't the only issue. Part quality sometimes suffered as a result of multiple fixturings. "Any time the machining process was interrupted, there was a chance we'd get a mark or line in the part," explains Tremblay. "We needed to get a better finish on every part and eliminate the need for bench work."

Researching alternatives to traditional clamping and fixturing methods, Tremblay became convinced that new magnetic workholding technology had the potential to reduce lead times and improve finish quality. Magnetic chucks are easier and faster to set up than mechanical clamps, and provide uniform support and holding over the entire workpiece surface. The solid construction of the magnet also damps machining vibrations, allowing use of faster feeds and speeds without chatter.

Synventive eventually purchased four Turbo-Mill magnetic chucks from Walker Magnetics Group (Worcester, MA). The 16 X 40" (0.4 X 1 m) chucks were installed on the VMC with an integrated variable controller.

The chucks use electronically activated permanent-magnet holding, meaning they maintain holding power even when disconnected from their power supply. The feature makes the chucks portable and suitable for use in off-machine pallet loading applications.

With mechanical clamps no longer a consideration in the machining process, Tremblay was able to implement a single NC program. And, in combination with tooling improvements, the chucks significantly reduced machining time.

According to Tremblay, the process that previously required two working shifts now takes just four hours. "We're able to accomplish in one operation what previously took several, and the magnetic chuck withstands the forces generated by the milling machine, holding and repeating the required tolerances time and again in the process," he says.

Increased milling productivity contributes to Synventive's short lead times. The industry average for delivery of a hot-runner system is eight weeks. Synventive can deliver its XP product line in half that, and is said to be the only supplier in the industry that promises a four-week turnaround.


Traceability Key for Ceramic Parts 

A supplier of components for aerospace, medical, and other critical systems uses a new indent marking system to provide the 100% traceability required for its patented products.

Carleton Life Support Systems Inc. (Davenport, IA) manufactures injection-molded ceramic parts for gas separation and cryogenic applications. The components are used in on-board aircraft oxygen generation systems, breathing regulators, and oxygen concentrators; inert-gas generating systems, which increase the survivability of a low-flying aircraft; cryogenic coolers for use in infrared night vision equipment; and residential-based oxygen generators for emphysema sufferers, among other applications. Carleton supports a complete quality control program, including part marking for traceability.       

For marking, Carleton uses an Indent-a-Mark ProPoint 2331 system from Matthews International Corp. (Pittsburgh). The system permanently marks each ceramic part with a date code plus a three-character ascending sequential part number on one line. Custom marking software allows Carleton to transmit ASCII tracking data.

Manufacturing engineer Brad Bagby, who surveyed marking technology suppliers before settling on the indenting system, says marking helps Carleton track a variety of process parameters as well as production trends and operator efficiency. "We basically keep track of every parameter used to make every part we make, which gives us 100% traceability."

Production at the plant begins with preparation of the injection molding feedstock--a mixture of ceramic powders, plastics, and waxes. The complex shapes are marked after molding, then sintered to densify them and burn off the binder materials. The dense, marked ceramic parts, which shrink up to 50% volumetrically during sintering, are later coated with special materials which permit electrical charging of the part, then heated in an oven.       

"Ceramic injection molding gives our parts good dimensional accuracy and consistency, and enables production without additional operations such as machining, reaming, honing, polishing, or straightening," Bagby explains. Dimensional precision of ±0.5% is standard, but Carleton can hold ±0.05% if needed, he adds.

The marking equipment, which replaced a manual marking system, operates using a touch-screen control unit incorporating the Microsoft Windows CE operating system. The stylus indent marking system allows variable message marking, has a trigger/emergency stop switch, and requires no inks for marking.

According to Bagby, the manual marking technique was inconsistent, had poor legibility, and couldn't meet Carleton's evolving quality requirements, which adhere to US Federal Aviation Administration guidelines, among others.

"Our manufacturing techniques focus on producing complex ceramic components at relatively low cost and with high precision," Bagby says. "Efficient marking is only one of several tools we use to maintain our reputation for high quality, but it's an integral part of our success."                 



Inserts Break Chips, Boost Tool Life

A sign on the desk of Paul Bruggeman, director of manufacturing at Stihl Inc. (Virginia Beach, VA) reads simply: "I refuse to participate in the recession."       

"We are constantly looking for ways to improve our processes and cut costs," Bruggeman says. "It's a part of our everyday job."

Based in Germany, parent company Stihl Group opened the Virginia Beach plant in 1974. Today, the nearly 700,000 ft2 (65,000 m2) facility employs approximately 1300 people and produces more than two million powerheads for chainsaws, leaf blowers, and other yard equipment annually.

The company was experiencing chip-control and tool life problems on three turning machines used to produce shaft-type components for professional-model chain saws. The work material was 4140 steel pre-hardened to RC 40. Seven cutting-tool suppliers had come in with inserts to address the problem, but none had met with much success. Poor chip control was also causing problems on the chip conveyers, and stringy chips meant bins had to be emptied once a shift. Tool life ranged from 200 to 350 pieces per index.

Enter yet another cutting tool supplier, Walter (Waukesha, WI). Over a period of about six weeks, the Walter representative worked with Stihl to improve chip control and increase tool life.       

"The first insert broke chips very well, but tool life was still an issue," Bruggeman recalls. "Then we switched to the Tiger-tec WAK10 insert, and began running at 2800 rpm with a feed of 0.007 ipr [0.18 mm/rev]. That's when we saw dramatic improvement."

The first test produced 850 pieces, and held size and finish while continuing to control chips. "Things just kept getting better from there," Bruggeman says. "At an index of 1000 pieces, we ran consistently. We found that we were able to achieve optimum tool life at a depth of cut of 0.157" [3.98 mm], feed of 0.012 ipr [0.3 mm/rev], and speed of 310 fpm [94 m/min]. Up time has increased by 34%, and tool life by 50%."

Today, Stihl is operating a fourth shaft turning machine, and all four run the Walter WAK10 inserts. Scrap rates are lower than they were with three machines using competitive inserts, and production rates are above the company's projections. One operator runs all four machines for a complete shift, and calculated downtime per machine is less than two minutes per shift.

Chip conveyors are being emptied once a day as opposed to once a shift. Stihl is using only about 40 inserts per month, as opposed to 100 pieces from another cutting tool supplier. As a result of the positive experience, Stihl is now testing Walter milling cutters and drills in other operations.


Laser Inspection Speeds Automaker Approval   

By replacing a template system for inspecting Chrysler PT Cruiser seats with laser scanning, Johnson Controls Inc.'s (JCI) Toluca, Mexico facility saved $60,000 in template costs and reduced pre-production validation time from almost four months to three weeks.

"The main benefit of using the ModelMaker laser scanner [made by NVision Inc., Southlake, TX] was the time savings since we had to delay production until the testing was completed," says quality manager Rosa Leyva. "But the scanner also gives more accurate information, which we are using to establish manufacturing tolerances."

The inspections were part of the production part approval process (PPAP) for JCI's seat manufacturing processes. In the past, they would have been performed by comparing the seats to contoured plastic templates. For DaimlerChryslers' PT Cruiser, seats would have to follow the template contours within ±12 mm. At a cost of $2500 per set, templates for inspecting the PT seats would have cost $60,000. Producing the templates would have taken about three months, and inspecting the 360 seats required for PPAP would have taken another three weeks.

Plant management investigated a number of other inspection technologies and eventually settled on the NVision system, which consists of a 3-D laser sensor, an arm or position-sensing device to which the sensor is attached, a PC, and software to extract, display, and manipulate the scan data. The unit's laser stripe sensor works by projecting a line of laser light onto the object while a CCD camera views the line as it appears on the surface. The PC translates the video image into 3-D coordinates at a maximum data capture rate of 10,000 points/sec. The resulting cloud of 3-D data accurately describes the surface of the object.

After two weeks of training with the system, the technician began inspecting seats. The process required only a week, allowing JCI to get the seats into production about three and a half months faster than if templates had been used.

In addition to speeding validation for these seats, the new inspection process is also used for process control. The quality department identified 25 critical points on each seat configuration. Coordinates for these points were entered into a spreadsheet, where an average was obtained from the 30 seats tested. These values were then used to set manufacturing tolerances, creating a master model against which production seats are measured.

Yet another ongoing use of the laser system is validating engineering changes. "Any time there is an engineering change that affects a seat, we have to test it," says Leyva. "In the past, that would have meant modifying the template or building a new one. Now, we can handle engineering changes more quickly because new seats can be scanned immediately."


This article was first published in the November 2004 edition of Manufacturing Engineering magazine. 

Published Date : 11/1/2004

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