Tool of the trade: machining

Automotive Design & Production, Feb, 2003 by Gary S. Vasilash

Here are some things to know if you're in the metal removal arena-they'll help you get it done faster, better, and probably less expensively.

TURN, TURN, TURN

The amount of things that you can do with turning may be surprising. At least that's the sense one gets from spending time talking to the people at Fuji Machine America Corp. (Vernon Hills, IL). If there is any question of the company's bona fides in relation to the work that it is doing in the auto industry, this should dispel it: According to company information, 64% of the lathes used by Toyota in Japan are from Fuji (the parent company is based in Chiryu City, Japan), and apparently there is a good working relationship between engineers from both companies such that there are mutually beneficial developments, developments that eventually make their way into commercial availability.

Consider, for example, a camshaft cell that is available, one that meets "automation level C" within the Toyota Production System ranking of automation (ranging from A, fully automatic to D, which is essentially a standard CNC machine). In the "C" configuration, there is manual part load/unload and then fully automatic within-machine part handling. The camshaft cell makes use of a CE-30 mill and centering machine and a GN-30TTS four-axis turning machine. The CE-30 has double turrets for workpiece facing and centering; it can handle parts from 300 to 550 mm long. Then it is passed on to the GN-30TTS, which has two slides above the centerline of the bed. Through the use of CNC tailstocks, the machine is capable of handling various shaft lengths. A hybrid chuck grips the ends of the shaft wherever appropriate for the specific turning operations performed (e.g., edge- or mid-section turning).

Whereas a traditional crankshaft line is typically configured with op. 10: centering; op. 20: turning; Op. 30: turning; Op. 40: pin broach/mill; Op. 50: gauging, Fuji has a flexible alternative. Instead of dedicated equipment, there is the ability to change to other crank configurations in a reasonable amount of time. For op. 10, the centering machine is replaced with a machining center (model YM-40) that performs facing on both ends and center drilling. op. 20 is performed with a two-turret lathe (model GN-51TTS); the steps here including machining the front shaft OD and counterweight ODs, and facing the journals. The part orientation is reversed for op. 30 (a double-hand gantry loader is used to transfer parts between machines); at op. 30 there's machining the rear shaft 00, threading, and journal finishing. Op. 40 is where there is some awfully clever turning performed (in fact, there is a patent pending). Here a GN-51TWS lathe is employed: it is capable of turning the eccentrics because the machine has ad justable offsets in the eccentric chucks that mean that off-center turning can be performed. Compared with the traditional dedicated broach/mill with special ring cutter, this alternative employs less expensive tooling and an overall lower investment cost. As for Op. 50, Fuji offers a variety of gauging alternatives, from a C-gage to laser.

CONSIDER THESE BENEFITS:

* Cycle time: improved 10%

* Machine cost: reduced 25%

* Total manufacturing cost: reduced 60%

* Machine space requirement: reduced 30%

* Power consumption: reduced 50% In addition to which, environmental concerns are greatly reduced.

Those are the sorts of benefits that can be achieved by utilizing hard turning in place of grinding for a variety of workpieces, ranging from gear blanks to wheel hubs. One of the big issues that can be overcome through the use of a turning machine in place of a grinder is the fact that the form tools ordinarily required for tapers, radii and chamfers aren't necessary for hard turning equipment. Rather, because these machines can be programmed, tools can be rapidly oriented where required.

About that environmental issue: the folks at Fuji point out that this process can be performed without coolant, so the grinding sludge that's characteristic of the alternative operation isn't generated. Turning can have big benefits.

MAINLY MILLING

It wasn't all that long ago that it seemed as though high-speed machining (as in milling) was all the rage--or at least something that consumed a lot of rhetoric. People were fascinated by the possibility of spinning spindles at high rates, rates in excess of 25,000 rpm at minimum, in order to remove metal more rapidly. And there were discussions of how this would lead to manifold benefits. The technology was pioneered in the aerospace industry, where the workpiece material tends to be aluminum. As the auto industry began its transition to aluminum blocks, heads, transmission housings, etc., it seemed like a natural transition to make: If the aero guys were running quite quickly on aluminum, then why not do it in powertrain plants?

Well, there were some issues encountered, notes Richard A. Curless, director of Research & Development, Unova Manufacturing Technologies (UMT), a division of Unova, Inc. (Fundamentally, UMT combines the capabilities and products of Lamb Technicon and Cincinnati Machine.) For example, consider the nature of machining in the aerospace industry. There are large workpieces (e.g., wing spars) that are milled and contoured. These operations are long, as plenty of material is removed from the billets (as Dr. Phil Szuba, director of R&D for Lamb products at UMT, points out, they're removing about 90% from a billet to end up with a spar), so working with a high spindle speed can be exceedingly helpful. But Curless notes that in auto, "There's a lot of starting and stopping." As in: Drill. Stop. Tap. Stop. One of the burgeoning characteristics of more and more automotive parts is that they are being cast to a near-net shape, which requires comparatively less metal removal. It is one thing to keep a high-speed spindle r unning for a long time, generating lots of chips, a la aero. It is entirely another to put them through the sort of duty cycle that goes on in auto. Which can lead to the need to change spindles more frequently than would be liked, for, as Curless notes, one of the key issues in automotive machining is uptime, with particular attention being paid to mean time to repair (MTTR). So, according to Szuba, a spindle speed in auto of 16,000 rpm is fairly common (achieved through the use of grease-pack bearings that provide reliability), as compared with the 30,000 to 40,000 rpm that might be run in aero. What's more, given the faster pace of car making as a whole compared with the number of aircraft built, the fundamental focus is not merely on the speed of the spindle, but on the entire cycle time. Which includes the time required to load and unload parts.