Multi-spindle machines on rise

Machine tool builder Matsuura Machinery began U.S. distribution of its twin-spindle vertical machining centers in 1981. Production volumes were typically higher back then. Therefore, the long setup times associated with these machines weren’t as much of a concern as they are in today’s low-quantity, quick-turnaround world.

Still, two spindles meant twice as many tools to set and maintain. There were expensive two-sided fixtures to build and twice as many first article parts to inspect. When you loaded an endmill in one spindle, the length of its partner on the other side needed to match exactly—a challenge without a presetter. Heavy cuts could be a problem. The two spindles tended to resonate off one another, generating weird harmonics that led to chatter. And the operators of these machines complained that they had to do twice as much work as their single-spindle co-workers.

The STAMA System 8 TWIN is particularly beneficial for manufacturers of automotive components such as turbine housings. Image courtesy of STAMA

Each of these costs and obstacles was easily justified, however, by the greater output of these machines, making them a favorite of any shop with limited floor space and long-running repeat jobs. It was a sad day for many when Matsuura ceased production of its DC series twin-spindle VMCs.

Stop the Tears

If you’re one of those who wept on that day, cheer up. A number of machine tool builders have begun addressing this admittedly niche market. Doosan Machine Tools America Corp., Pine Brook, New Jersey, for example, recently began building and marketing a twin-spindle VMC at the request of several large automotive customers.

“Twin-spindles were once very popular with the aerospace industry, but we’re now seeing a resurgence in the automotive market,” said Andy McNamara, Doosan’s director of sales. “In response, we developed the DMP 500/2SP, a dual-spindle, 500mm, Y-axis vertical machining center that’s ideal for high-production environments.”

Like most such machines, it’s also ideal where floor space is at a premium. The DMP 500/2SP is actually 8″ narrower than Doosan’s comparably sized DNM 500 II single-spindle VMC. Thanks to a W-axis, which allows the operator to independently adjust the right-hand spindle’s Z-axis height by up to 0.800″, complaints about finicky tool lengths are history.

If floor space is at a premium, Doosan Machine Tools America’s DMP 500/2SP twin-spindle VMC is actually a bit smaller than comparably sized single-spindle VMCs. Image courtesy of Doosan Machine Tools America

So too are concerns about rigidity, because Doosan and the other builders interviewed for this article have redesigned their products with this critical attribute in mind. “We overbuilt the machine for that very reason and have had no complaints from our customers over chatter or metal-removal capabilities,” McNamara said. “There are several hundred of these in service now, machining cast iron, alloy steel and die-cast aluminum around the clock. Our customers set them up with high-quality fixturing, load a program and go to town, producing two parts for every cycle.”

2×5

Alex Vojinovich, COO at Racer Machinery International Inc., Cambridge, Ontario, has a similar story to tell. The machine tool builder expanded its Phantom Machine Technology line of CNC machine tools to include twin-spindle vertical and horizontal machining centers, also primarily for the automotive market. According to Vojinovich, a patented manufacturing process allows the company to build a twin-spindle machine that prevents the vibration from one spindle to affect the performance of the other, even at spindle speeds over 25,000 rpm.

Racer also sees interest from the aerospace and medical industries. However, ideal buyers for twin-spindle machines are manufacturers that need to make lots of parts in the shortest time possible and do so with a conservative eye toward available floor space and quick part-model changeovers.

“They want to keep footprints as small as possible and have the ability to machine greater part volumes efficiently,” Vojinovich said. “Many opt for a pallet changer or robotic part loading, but quite a few are still loading parts by hand. We’re also seeing great interest in 4- and 5-axis machining, a need we address with our TSHX series horizontals and TSVX series verticals.”

For those concerned about the crash potential of producing two parts via simultaneous 5-axis machining, Vojinovich said there’s nothing to worry about. Each spindle, whether horizontal or vertical, can be equipped with its own independent rotary or trunnion-style table. Programming and operating one of these machines—or any twin-spindle machine, for that matter—is virtually identical to its single-spindle counterpart.