Tools of the Trade: Machining
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 OD, 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 adjustable 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.
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 running 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.
Although there is a natural assumption to think something along the lines of “Machines/Metal,” Curless points out that electronics developments—both in terms of software for parts programming and optimization, as well as vector drives and high-speed servos—are having a huge effect on the nature of machine tools and their capabilities. Speaking of the former, Curless notes that there is greater modularity of the equipment, which leads to the sourcing of components from a variety of sources (e.g., components for a machine, say way systems, might come from any number of countries, ranging from Japan to Switzerland). And speaking of contributions of things like the drives, servos and controls, he points out that the traverse rates of machines have been marching forward at a considerable rate during the past several years, going up to around 80 m/min today, with an acceleration of at least 0.5 G being almost an expectation.
One of the characteristics that is keenly sought by both OEMs and suppliers alike in terms of machining capability is flexibility, the former’s interest deriving from the heavy investment in major machine lines, and the latter being concerned with the consequences of losing programs. While this has been a discernable trend for the last few years, Szuba says the extent to which this is occurring is somewhat surprising, as in even performing applications like gundrilling crankshaft oil channels on flexible CNC machines rather than on dedicated pieces of equipment.
A DIFFERENT GRIND
Those who have a need to (1) perform cylindrical grinding, both internal and external, and (2) find themselves doing so on various parts should be interested in the capabilities of the Studer S151cnc, which has a swing diameter of 350 mm and a between-centers grinding length of 350 mm. There are two independently programmed grinding spindles on the turret head so that there is the ability to rough and finish grind in a single setup. Because changing from one part to another means a whole lot more than adjusting workholding, the machine has a Fanuc 16i digital control loaded with Studer Pictogramming, which is a step-by-step approach for operator programming. The machine is available from United Grinding Technologies (Miamisburg, OH).
Need to mill some heavy metal—as in steel, stainless steel, or even heat-resistant super alloys? Check out the CoroMill 390 long-edge milling cutter from Sandvik Coromant (Fair Lawn, NJ), which features a hardened-steel cutter body (in diameters from 40 to 200 mm) and handles 18-mm long inserts. The cutter can mill depths up to 3.9-in. and can provide 90° corners.
BIG BUT FAST
Although the a81 horizontal machining center is big—it has a 630-mm square pallet, a standard 50-taper spindle (capable of 10,000 rpm), a payload capacity of 1,500 kg, and X-, Y-, Z-axis travels of 900 x 800 x 900 mm—it is a quick machine, as well. That is, it provides a rapid traverse rate of 60 m/min, as well as the same speed for the feedrate. There’s a 40-tool magazine that works in conjunction with an automatic toolchanger that handles tools with a 1.7-sec. tool-to-tool time. Yet the a81 from Makino (Mason, OH) has a comparatively compact footprint: 3,460 x 5,370 mm.
Optimal working space is a fundamental characteristic of the TWIN 42 turning machine from Gildemeister Group (DMG America; Schaumburg, IL), as it has, as its name implies, twin spindles. In addition, the machine has 12-station turrets for handling a good variety of tools, all of which can be driven. The machine has a turning diameter of 42 mm and can handle 580 mm between centers. Four-axis machining can be performed on either of the spindles or there can be simultaneous two-axis machining on both spindles. In addition, there is the capability of automatically transferring a workpiece from one spindle to the other, thereby providing the means to do full processing without manual intervention.
For those of you who have a small lathe from Haas Automation (Oxnard, CA)—such as the SL-10 turning center—and are looking to up your production, check out the new Barr-100, pneumatic, automatic bar feeder that the company has developed for its small machines. It can handle bars up to 1-in. diameter. When used in the pneumatic mode, 6-ft. long bars can be automatically loaded. This additional productivity is cost-effective: the Bar-100 has a retail price of $2,995.
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