Innovative Manufacturing used to spend ten minutes per part machining cast iron differential housings for golf carts, but now total machining time is down to three minutes, 45 seconds. According to Innovative owner and president Rob Sander, the productivity leap came when the company consolidated turning, milling, drilling and reaming into a single machine tool. Mr. Sander's search for a high-efficiency turning center led him to consider a variety of single and multispindle CNC lathes, then led him to IMTS, where he saw his first demonstration of the Nighthawk multi-purpose CNC turning center (MPC) (GBI Cincinnati, Cincinnati, Ohio).
Innovative has two Nighthawk MPCs purchased, says Mr. Sander, for two particular features of the machine: a 12-station tool turret including both fixed and "live" tools, both parallel and perpendicular to the spindle; plus, a two-position automatic workchanger (AWC) incorporating two chucks or fixtures. One chuck is safely loaded and unloaded from a vertical position outside the machining chamber, while the second chuck--inside the chamber--is engaged in a horizontal machining process.
Because of the latter feature, Mr. Sander notes, the 62 percent cut time reduction actually understates Innovative's productivity gain.
"We had a three-setup operation before the Nighthawks," he says. "There were two setups on a lathe and one on a pivoting fixture on a machining center, all three of which required the spindle to be idle until the part was ready. Now, the Nighthawks not only reduce the number of setups to two, they also allow us to stage the next part entirely while the current part is in-work. As a result, our productivity gain is actually far greater than what the cycle time reduction would suggest."
Except for maintenance and tool replacement, machining is now continuous. In most cases, says Mr. Sander, the only delay between consecutive cycles consists of six seconds necessary for the workchanger to switch the two chucks.
Mr. Sander keeps the Nighhawk MPCs running round-the-clock, servicing them with a shared robot that allows a single operator to oversee both machines simultaneously. In less than the time required for either of the two differential housing machining cycles, the robot unloads the previous part from the idle chuck, and either inverts it for the next step in the process, or loads a new partusing a locator hole in the flange to position it in the powered chuck's grip.
The dividing line for the part's two machining cycles is a flange 5-5/16" in diameter. In the first cycle, the Nighthawk turns the flange, as well as the part's central bore, then stops the headstock spindle while powering up the live tool spindle. Like a small horizontal machining center, the Nighthawk then face mills surfaces for four holes, and drills the holes themselves.
In the second cycle, the machine turns the other sides of the flange and bore, then drills and reams a single cross hole using powered tools oriented perpendicular to the chuck centerline.
Mr. Sander says it was the combination of single-part productivity and part-to-part flexibility that convinced him to choose the Nighthawk.
"The differential housings were uppermost in my mind, because I needed to get my cycle time for these as low as possible," he says. "Still, I have other customers, too, many of whom place their orders on a JIT basis. Therefore, I needed a machine that would provide not just rapid machining, but also rapid changeover. The Nighthawk met both requirements." Roger Stebelton concurs. A long-time Innovative machinist who is responsible for almost all of the Nighthawk's programming, Mr. Stebelton reports that he can completely change over a Nighthawk to a new job in just under three hours. This is the same amount of time necessary to change over one of Innovative's conventional CNC lathes, but to Mr. Stebelton, this represents a significant savings.
He explains: "Unlike the CNC lathe, the Nighthawk MPC usually performs all of the machining needed for a part. The lathe, on the other hand, is generally only one step in the total machining processmeaning I would have not just the lathe to changeover, but probably a machining center, too, adding hours to the total process."
The Nighthawk's 10.82 inch by 10.00 inch diameter workzone accommodates most of the parts Innovative typically machines. Between batches of differential housings, the Nighthawks have been used on about 20 other parts--including an aluminum motor housing, which Innovative machines in batches of about 1000 per month.
According to Mr. Sander, not only does machining the motor housing employ all 12 of the Nighthawk's tool positions, it also takes advantage of the machine's accuracy, holding the part's critical bore to a total tolerance of 0.0005 inch.
"This is a new part for us, one we never could have produced competitively without the Nighthawks," he says. "By turning, then end milling and drilling in both the X and Z directions, all on one machine, we were able to bring total cycle time down to less than five minutes." MMS