Cashing in on complexity

Oct. 10, 2005
Production shops survive off-shore competition running complicated parts on multispindle machines.

For a demanding valve-cartridge-body job, Model Screw pumps out over five million pieces yearly on an Index MS32P CNC multispindle machine.

High-accuracy, CNC multispindle machines complete complex parts in single setups and give today's production shops an effective weapon against off-shore competition.

Index's special compact spindle drum with six independent, air-cool spindles is the heart of the company's CNC multispindle machines.

Losing work to overseas suppliers has spelled disaster for many U.S. production shops, but it has also spawned survival strategies for others. Successful shops realize that most of the lost work is highvolume simple-to-machine parts. So they, in turn, pursue complex jobs involving complicated processes done on single parts because those are less likely to go off-shore. In most cases, the strategy is profitable if shops complete such parts in one operation or setup using CNC multispindle machines.

Model Screw Products in Clearwater, Fla., is one shop cashing in on complexity. The hydraulic-components supplier relies on multispindle machines to remain competitive on such complex jobs as multi-part, hydraulic hex-valve bodies.

The parts Model Screw makes go into cartridge-valve-body assemblies that are shipped worldwide. They include an insert (machined to 0.0002-in. tolerances) that slips into body I.D.s and a sleeve with intricate internal details.

Using a Multiline MS32P multispindle CNC machine from Index Corp, Noblesville, Ind., the shop machines valve-body sleeves in 11 seconds, holding ±0.0005-in. tolerances and 32-micro surface finishes. For hex valve-bodies made of 1141 steel, the MS32P reduces cycle times from 85 to 25 seconds.

According to Tony Farrell, general manager at Model Screw, the MS32P's numerous available axes let the shop accomplish more in single operations. "Having CNC on each of its six drives and 12 tool slides, the machine cuts parts more efficiently in single setups than is possible in multiple operations on traditional screw machines," says Farrell. The MS32P turns, mills, drills and broaches, and any of its slides accommodate either I.D. or O.D. tools, even driven ones, all of which lets Model Screw choose the mix of operations that best suits a particular job and where those operations occur on the machine.

This ability, adds Olaf Tessarzyk, chairman and CEO of Index, differentiates the MS32P from other similar machines, such as cam types with CNC slides. "Finishing high-accuracy, complex parts in one setup is the driving concept behind Index machines."

To accomplish done-in-one machining, the MS32P, which is a front-open machine with four live backworking tools, packs 17 tool carriers and as many as two tools on most of them. It's second opposing-headstock housing accommodates as many as seven additional compound slides identical to those on the main-spindle headstock and two counterspindles that pick up workpieces during cutoff for backworking. The live backworking tools on the MS32P let shops such as Model Screw machine offcenter holes and also tap on cutoff sides.

Index's special spindle drum is at the heart of the MS32P. A three-piece Hirth coupling precisely positions the compact drum's six independent air-cool spindles with stepless-motor speed ranges, high torque, compact design and AC synchronous drive technology.

For thread milling, polygon turning and synchronized or counterspindle pick-up, the machine's drives couple electronically to its spindle drives. Each main and counterspindle stops and positions independently for machining with live tools, and its C-axis-controlled spindle maintains position even when the spindle drum indexes, allowing the distribution of accurately positioned machining operations over several spindle places. With options such as C-axis interpolation, Y axis and gear hobbing, the MS32P expands into a full turn-mill center.

Previously, complex parts required four or five operations to complete because stations on Model Screw's old machines were lower value ones as compared with the Index machine. Part handling, scheduling and wait time increased costs and cycle times and increased quality-control challenges because of the need for multiple setups.

However, purchasing multispindle CNC equipment is only half a shop's commitment in gaining full advantage of the technology. "The problem with 90 percent of manufacturing companies is not with capital availability to purchase equipment, it is committing to training and maintenance," says Farrell.

Model Screw learned the Index machine's software and mechanical functions in three months and spent another three to six months going beyond the manufacturer's training and programming examples. As a result of this commitment, the shop slashed the 32-second cycle time Index quoted for a high-end hydraulic-valve sleeve with milled slots, internal recesses and cross holes to 18 seconds.

A Siemens 840D CNC controls spindle and axis movements, monitors tool wear and engages various safety options on the MS32P. According to Farrell, the Siemens CNC lets the shop store multiple programs because of its software capabilities and communicate with the quality department on statistical-process-control data, as well as with its customers for real-time production scheduling. In addition, data programs store on a hard drive for long term, while current programs reside and run out of a RAM chip for fast access.

As part of its complex-part strategy, Model Screw also uses a Traub CNC TNL Series single-spindle turning machine from Index that works on four quadrants of a part simultaneously. In addition, the sliding-headstock turning machine's programmable guide bushing provides rigidity necessary for heavy machining of unground barstock.

Typically, shops such as Model Screw use sliding-headstock machines for cutting small parts, mainly because these shops do not want to work with conventional Swiss guide bushings. Those machines often require more-precise barstock, increased set-up times and leave users with long bar remnants.

According to Model Screw, the overallflexibility offered by a machine with two turrets that have a common X axis and the ability to clamp stock with the guide bushing justify investing in a machine such as a TNL. The number of live tools a shop can have in the cut is another advantage.

"The TNL lets us crank out more completed parts in the middle-quantity range, without having to use special tooling," comments Farrell. "In addition, we quickly deliver preproduction samples of new highvolume jobs while building special tooling for the larger quantities."

Such jobs demand part quality, and negotiating deviations from customer specifications is no longer an option. "Parts meet prints, and that's it," says Farrell. "The TNL lets us meet those specs and do it faster than the competition."

For example, Model Screw shaves six seconds off the cycle time of a 36-second part using the TNL, which runs 24 hours a day unattended for further time savings.

The shop purchased the TNL to machine parts from two customers that wanted Model Screw to furnish them complete. The customers were running the parts in-house on conventional multispindle screw machines. However, Model Screw determined that method would involve difficult secondary operations, so it conducted a time study and discovered that the TNL would do the parts in less time than the secondaries alone would require.