Although some machine tool companies seem hell bent for election when it comes to the application of linear motors on the machines they are designing and building, this is not the case at Lamb Technicon. Sure, there's a test stand in a development shop where Phillip S. Szuba, manager of Research & Development, and his staff are looking at the motors' performance characteristics. And Mark C. Tomlinson, vice president of Engineering, says that machines being developed as a replacement for machines that will be introduced in 1998 are being designed to use linear motors.
A-ha! Doesn't this simply mean that Lamb Technicon is lagging in this speed race, which the machines-after-next are supposed to rectify? No, Tomlinson, replies. They are simply determining the viability of the motors (as in the test stands) and will use them if there are two changes in the attributes of the motors in the months to come: the motors will become more reliable, and the cost to buy them will go down. Otherwise, it's a no-go. Until then, they are satisfied with servos and ballscrews.
Actually, satisfied may be too neutral a word. So far as they have been able to determine by running computer models of machining operations, using data from competitive machine tool makers as well as their own, the gains that can be attained in using linear motors may not be quite as substantial as some people have been led to believe. In fact, they point out that one of the biggest time losses during machining operations is in toolchange time, which is a problem that they have addressed with a machine that became available on the market in the first quarter of 1997, the Mach I machine.
The Mach I machine is equipped with two spindles. As a result, one of the spindles can be in the cut while the other is having a toolchange. Consequently, the machining keeps on going without any downtime for toolchange. And although it uses ballscrews, they are still fast: the acceleration rate is 33 ft/sec—or 1 g—in all axes; the rapid traverse rate is 148 ft/min.
According to Tomlinson, more than 50 Mach I's have been sold since the introduction. In two instances, the machines are integral to production operations. In one application, the machines will be used in a transmission manufacturing operation that will combine the flexible machines at the front end of the process and dedicated finishing machines at the end. In the other application the machines will be used to machine aluminum cylinder heads for diesel engines.
Wouldn't it be better, still, to have two spindles and linear motors? Well, Tomlinson says that it might be nice in theory, but in the physical, tangible world of cast iron, aluminum and budgets, the price for such a machine would be "way out of the spectrum" of equipment prices. He adds, "It is certainly out of the price range of our served market."
In terms of spindle speeds, Lamb Technicon analysis shows them that there really is no great advantage to be realized in going beyond 16,000 rpm. There are a couple of points to be considered here. One is that they say that grease-pack spindles can be used for speeds up to 16,000 rpm, which helps maintain reliability. Their second point is that there is quite a bit of control complexity required for spindles that operate at higher speeds, and one of their points of focus is to simplify, not complicate things.
For example, Tomlinson points out that one of the reasons that some Japanese manufacturers have had success in their implementation of CNC equipment for higher-volume manufacturing operations is because they concentrate on implementing just the amount of technology that's actually needed, not more.
Simpler solutions can be better.
Tomlinson says that there are various things that must be considered with regard to the type of machining process to be employed, not only technical issues, like the part, fixtures, material handling, coolant and machinery, but also organizational ones, like whether there are trade union represented workers (and if so, what are the rules with regard to working on/with the equipment), when part inspection is performed (in process or at the end of the line), and whether there's dedicated or central maintenance. These things can play a big role with regard to what sort of equipment should be implemented.
The cutting tool issue, so far as Lamb Technicon engineers are concerned, is one that needs more analysis, especially as it pertains to tool life. Szuba observes, "Tooling is not well understood from a science base." One area of concern that they have is the correlation between spindle speeds and tool life: what will be the effect on tool life, say, by going from 10,000 rpm to 20,000 rpm? They suggest that there is no reliable information that can allow a prediction of the effect of speed on tool life. And as tool life is key in achieving productivity, they think that this is essential information for reliable manufacturing operations.
Transfer lines are still part of the high-volume mix so far as Tomlinson is concerned. For those operations that are producing 400,000 components per year it is the way to go, he suggests. But he points out that the so-called "dedicated transfer line" of today isn't what it was a few years ago. Among the terms that he uses to describe it are "leaner, faster, and more reconfigurable."
Get the Speed You Really Need
High-speed machining in the sense of machines with linear motors may not be the only means by which improved throughput can be most effectively obtained. So suggests John S. Klimach, president and CEO, and Jack Pulliam, vice president of Sales, Ex-Cell-O Machine Tools (Sterling Heights, MI). Note well that Ex-Cell-O is one of the pioneering companies offering a high-speed machining center. The company's XHC-240 was recently updated as the XHC-241 and launched at the EMO exposition in Hannover this past September.
Recommending that people take their time in examining actual needs, they suggest that people consider the process requirements and the alternative methods that can be employed in order to fulfill them. As Klimach says, "It's a matter of what people need, can afford, and are able to maintain." Which can be interpreted as (1) they really may not need as much technology as they think; (2) many of the high-speed machines are rather expensive; (3) maintaining sophisticated technology may not be as simple as maintaining less advanced equipment.
A recommended way of thinking about what's really needed is found in this example:
Say there's a line where there is a feature that requires 10 holes. So use a drillhead with 10 spindles.
Somewhere else on the line there is a programmable, three-axis module (or two) that's being used to pick up the machining of an occasional feature. Klimach recommends that this equipment be run at a rate lower than capacity—perhaps at 50% capacity. This provides a margin of safety, or a reserve capacity.
Two of the 10 holes move. What then?
Klimack answers that the solution might be simply to:
- Remove two of the drills from the head
- Place an order for a new drill head
- Pick up the new hole location with the CNC module(s) (this is why the less-than-full capacity scheduling is used)
- Receive the new drillhead
- Install it over a weekend (or whenever there's downtime)
- Resume the now-modified status quo.
Klimach says that using the drillhead is a whole lot faster way to make multiple holes than even a machine with the quickest linear motors on its axes. He notes that not only does this get the job done, but it is something that is familiar, maintainable, and affordable.
Tapping has tended to be a comparatively slow metalcutting operation... but the people at Emuge Corp. (Northborough, MA) maintain that their new tap design can offer as much as a 6X improvement in tapping speeds.
That is, whereas a conventional tap can machine iron at 65 sfpm, the Full-Speed tap can run at 262 sfpm. If a conventional tap runs at 65 sfpm in steel, a Full-Speed tap can be used at 328 sfpm. And the same sort of relationships exist for stainless, aluminum and copper.
The taps are produced with cobalt-enriched tool steel and coated with TiN or TiCN. Coolant holes for through-tool-cooling are featured. The taps come in standard sizes of UNC-2B and UNF-2B from #10 through 1 in.; metric coarse and fine from M5 through M24.
According to the people at GE Fanuc Automation (Charlottesville, VA), conventional machine tool drive systems have 17 or more parts, several of which move.
Linear motors, on the other hand, have two parts: a coil section and a magnet plate.
The coil section is a steel laminate core wrapped with coils. This is potted in epoxy and coated with a polyurethane that is fluid-resistant. The magnet plate is a steel plate covered with magnets that are embedded in epoxy and covered with the same polyurethane (these plates are available from GE Fanuc in 4 lengths—240, 420, 600, and 960 mm—that can be assembled to the required length).
There are zero moving parts.
What's more, there's no need to lubricate things like ballscrews. There are none. There are no belts to adjust or couplings to tighten. All of which means reduced maintenance.
Since these are digital devices, tuning is done electronically, not manually.
Consider the specs:
•0 to 15,000 rpm in 1.8 sec.
•2,362 ipm rapid traverse in all axes (all axes are 20.1 in.)
•0.45-sec tool-to-tool change
•2.8-sec chip-to-chip time
These are some of the features of the FF-510 horizontal machining center from Mazak (Florence, KY) for both aluminum and cast iron machining. Fast machining, that is.