October 2007 Edition

WORKHOLDING

Accurate Holding Speeds UK Shop's Production

Introduction of a workholding system decreased setup time for small part runs

Spindle speeds, rapid traverses, cutting feedrates, and tool changes are getting faster and faster. Productivity, however, is often restricted because components aren't presented to the cutting spindle quickly enough after the previous batch has been completed. With trends toward smaller lot sizes, the inability to setup quickly for the next part run seriously impacts profitability.

Production output increased from eight vertical machining centers on the shop floor of Adaero Precision Components Ltd., Crediton, UK, as a direct result of retrofitting each machine with the Visher & Bolli DockLock Zero-Point system distributed in North America by Kurt Manufacturing Co.

"At Adaero, we shorten spindle downtime between part runs using the DockLock workholding system," Andy Dickinson, managing director, said.

"On average, we cut 25 to 30 percent of our setup time on eight 4-axis Chiron and Fanuc machining centers using the DockLock. The savings have been huge because some of our runs call for only 10 to 20 parts with three to four part changeovers a day. We save about a half hour for each setup."

Founded in 1988, Adaero Precision serves customers in the medical, optical, laser, and aerospace industries. It doubled its volume in the last five years and expanded its Crediton facilities twice to handle the increased volume.

Facing Eastern European Competition

However, increasing competition from Eastern European countries and India threatened to restrict its growth. In 2005 Adaero investigated Lean manufacturing methods, including the DockLock system, for developing a lean initiative.

"On average, we cut 25 to 30 percent of our setup time on eight 4-axis Chiron and Fanuc machining centers using the DockLock."

"Our original idea was to install one DockLock system on one machining center and spend some time evaluating it," Gary Raymont, works manager, said.

"In the process of installing the first system, it became clear that the benefits were going to be so profound, there was no point delaying the installation of DockLock systems on most of our other machining centers.

"New initiatives such as this can meet employee resistance, but that wasn't the case with the workholding system. Everyone, particularly the machine operators, championed the systems from the start."

Another benefit Adaero Precision experienced with DockLock was the reduction in skilled setup time. Using DockLock for most setups, tedious and time-consuming setups were eliminated with a corresponding reduction in required skill level.

Raymont also cited improvement in certain small lots that previously required two-hour setups, but only a 25 minute run.

"By implementing the DockLock, setup time for these jobs was reduced to one hour with the removal and replacement of the fixture requiring less than a minute. The overall 50 percent savings in setup time impacts enormously the profitability on these jobs," Raymont reported.

"In addition, the larger the part, the more difficult the setup process," Raymont said. "Special fixtures for large parts are difficult to lock accurately into position, which takes time and adds to machine downtime. This is true with angle plates, trunion fixtures, indexing heads, vises, and air chucks, all of which are changed frequently. DockLock solves large part setup problems with these different holding devices."

Keep It Simple

Adaero Precision's machine operators like the DockLock because of its simplicity and ease of use. Top-down design eases the fixture-handling process. With the DockLock, fixtures and workholding devices are fitted with centering plugs on their undersides.

This positions the devices precisely and repeatedly to within a few microns in the DockLock receiving plate's collet locks, which are mounted on the machining center bed.

If the component to be machined is especially large, a centering plug can be fixed directly into the part itself for five-sided machining. Each fixture or component is located every time to ±0.0002", so the machining cycle can start quickly with the first-off component usually within tolerance. There are few scrapped parts, according to Adaero Precision.

Another advantage of the DockLock system for Adaero Precision is jobs can be interchanged between the Fanuc and Chiron machining centers without additional setup requirements. There is no loss of production time if a machine goes down or a job needs to be moved to another machine. Similarly, if an incoming rush order requires intervening in a part run, only a small productivity loss results to fulfill the rush job.

Lock 'em Up

The system operates by integrating a receiving plate onto the machining center bed. A series of locking cylinders are arranged in a grid pattern over the plate, according to customer requirements, which in the case of Adaero Precision, involve primarily plates with 4 locking cylinders – some 2-, 6-, and 8-cylinder plates are also used in various combinations.

Each cylinder is located at 250mm center and generates 1.5 tons of holding pressure. Systems with three tons of holding pressure are also available for heavy duty applications.

Adaero Precision employs a variety of fixturing devices in its machining setups, including Kurt precision vises, angle plates, and indexing heads. Each is fitted with centering plugs that locate in the locking cylinders with ±0.0002" positioning accuracy. Hydraulic pressure locks and releases the fixturing devices in the exact position with the flip of a switch.

"We're pleased with the DockLock system and what it's done for our productivity," Dickinson said. "It is only by adopting Lean manufacturing techniques made possible by innovations that UK companies can compete with low-wage manufacturing economies.

"We calculate that our DockLock systems will pay for themselves in less than two years. As we get better using them, changeover times continue to decrease."
Kurt Manufacturing Co.

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