Advancing Metalcutting

Work at Mori Seiki, a leading machine tool builder, is not just on developing better machine structures and spindles. While there is that, they're also focusing on improvements in gaging, workholding, and tooling.

Although the tagline that Mori Seiki U.S.A. (www.moriseiki.com; Rolling Meadows, IL) uses to describe itself is "The Machine Tool Company," what's interesting is that as Gregory A. Hyatt, its vp and Chief Technical Officer, talks about research that they're doing in the company's Machining Technology Laboratory, research that is being transformed into commercial product, he's not talking about improvements to the machine tool, but, rather, to things like tooling and gaging. That's right: Things that improve the performance of machine tools. He acknowledges that the work they are doing is predicated on the capabilities of the company's lineup of machining centers and turning centers, that the Adaptive Balancer, the Spinning Tool, and the Hydrogage are all developments that are specifically designed for use on the company's machine tools. It's like the old line that no one wants a drill; they want holes. No one wants a machine tool; they want finished parts that have been made accurately and economically. Which is arguably what Hyatt and his colleagues are providing. Just as you need the drill for the hole, you need the machine tools to achieve better metalcutting results.

 

Leveraging Liquid.

As its name implies, the Hydrogage is based on water-well, at least liquid. Hyatt explains that while air gages have long been used for ID and OD measurements, there are a number of limitations to that approach, particularly when submicron measures are to be made. For one thing, there can be issues with swarf remaining on the workpiece after machining, which could lead to erroneous results being obtained via the air gaging. In addition to which, the air gaging is a post-process operation, which can mean that the machine tool could sit idle while the measurements are being made.

The Hydrogage is based on calculating the dimensions of a part with two-micron repeatability via the measurement of back pressure that is generated as coolant passes between the gage and the workpiece while the workpiece is still in the machine. Hyatt points out that there are a couple of aspects of this that should be noted. First of all, because coolant is being used, the swarf that could throw off air gaging results is being washed away by the coolant. Because there can be variations in the fluid due to changes in temperature and viscosity, the system measures those parameters and makes the necessary changes to the calibration. Second, this is occurring within the machine tool itself, so it is possible that the information obtained from the measurement routine can be used to generate tool offsets so that the part can be machined to the required tolerance. The gage has a robust design (essentially, steel tooling is used for applying the coolant to the part) for long life; all of the associated electronics are well out of the machining zone, in the machine tool's electrical cabinet. The Hydrogage is retrofittable to an array of Mori machines, machining centers and lathes alike.

But no one necessarily wants the gage; they want the quality parts. Which brings us to the various benefits of the system. For one thing, if the parts being produced lead to short tool life (e.g., titanium valves), the wait for dimensional information means that the machine tool is not making chips during that period. By having the gaging done right in the machine, the delay is greatly diminished. If there is a family of parts being produced, the costs associated with having automated external gages can be high; the Hydrogage is said to be significantly more cost effective. As the Hydrogage system is programmed through the machine's CNC and operates like another operation within the cycle, it facilitates unattended machining operations while assuring that parts are being produced to spec.

 

Back in Balance.

What do parts like water pumps and crankshafts have in common? For one thing, Hyatt says, given that these parts are not symmetrical during machining operations, and because the balance changes during machining (e.g., casting risers are cut off during machining, so there is a shift in the imbalance), the machining is typically done at suboptimal speeds in order to control the shake and vibration that could otherwise occur. What's more, in cases like pump housings, where there can be the same overall shape but differences in terms of size and balance, there can be significant setup work required when establishing the best balance conditions from workpiece type to workpiece type.

Hyatt says that if you consider the blades of a turboprop aircraft engine, there is an analogous situation as the speed of and the load on the blades change during operation. So to accommodate these changes, the blades are automatically adjusted. This led to the development of a system that is capable of accommodating changes in the balance of parts during machining operations. The Adaptive Balancer is attached directly to the chuck of a machine tool and rotates with the workpiece. Essentially, there are two rings in the balancer, each of which has an embedded weight. If the weights are located directly across from each other (e.g., one at 12 and one at 6 on a clock face), then they cancel each other out; the balance is neutral. Add an unbalanced workpiece into the mix. Through a stepper motor that is part of the system, adjustment is automatically made to the locations of the weights in the rings so as to compensate for unbalance condition. This is particularly useful in machining on mill-turn machines, where part balance tends to shift as different operations are performed on the part.

What's more, some parts-like wheels or flywheels-are often machined, measured, then refixtured in a machine in order to be brought into balance. With the Adaptive Balancer, the removal of the part from the machine for checking and subsequent machining can be eliminated and the processes performed within the cycle of the machine.

According to Hyatt, this balance capability allows machining at higher speeds. He cites, for example, machining on cast iron pump housings, where the maximum spindle speed went from 800 rpm without the balancer to 2,300 rpm with it and the cycle time for parts was approximately 40% shorter than had been the case, while tool life was improved by five times.

Adaptive Balancers have been developed for several Mori machines, mill-turn and lathes among them.

 

Turning the Tool, Too.

Speaking of the subjects of vibration and tool life, there is a tooling development that Hyatt cites, this one a joint development between Mori Seiki and cutting tool manufacturer Kennametal (www.kennametal.com). It's called the "Spinning Tool." Typically, either a tool or the part is rotated during a machining operation. But Hyatt points out that there are benefits if both are rotated, which led to the Spinning Tool, which is essentially a button insert on the end of a tool holder. Consider a part that has to be turned. Typically, the workpiece rotates and the single-point tool is static. With the rotation of both elements, there are a variety of benefits, not the least of which is significant increases in tool life (measured at up to 2,000%, according to Mori Seiki) due in large part to the fact that cutting temperatures are reduced via the dual rotation. Because of the reduced heat, dry machining is facilitated. Another benefit is found on materials where it is difficult to generate chips; the tool rotation facilitates chip generation. What's more, Hyatt notes that when the tool is rotated in relation to the main spindle it is possible to turn elliptical surfaces. The Spinning Tool is available for use on NT and NL Y-axis turning centers from Mori.

Looking out about a year into the future, Hyatt says that there is another spinning tool on the horizon. Initially this would be for turning, then milling. Picture, simply, a carbide or a ceramic rod. That's the tool. Then within the machine there would be a built-in tool grinder, one, Hyatt explains, that would be analogous to a dresser within a grinding machine. As needed, the rod would be indexed to the grinder and its end redressed. "This could result in unmanned operations lasting a month," he suggests.