Faster machining

When Winfried Benz, managing director, LiCON[MT] (Laupheim, Germany; Ann Arbor, MI; www.licon.com), relates the types of systems and machines that the company has provided to companies (Volkswagen is a big customer) for a variety of parts, ferrous and nonferrous alike, it becomes clear that there is a focus on high uptime, especially as he's talking about equipment that typically runs in the range of 100,000 to two million parts per year. When you get to those kinds of volumes, then whatever time the spindles aren't removing metal is time wasted. So they have developed a machining module called the "Linear Tool Changer" (LTC) that reduces toolchange time to less than one second. That's right: less than one second.

This isn't predicated just on a mechanism but, rather on a rethinking of what is actually occurring in conventional high(er) volume applications. That is, LiCON[MT] engineers have calculated that in the typical production machining operation, the cutting cycle time for a given tool is on the order of three seconds. What's more, they've determined that overall, there are fewer than 20 tools used to machine a given part. So instead of the approach that is often used by machine builders, which is to provide a means where tools can be swapped in and out of the spindle in, say, three seconds, what they've done is essentially eliminate the automatic tool change--which is, perhaps, more astonishing than the one-second time. In this case, "toolchange" means using another tool. And the other tool is fitted to the spindle head that is part of the LTC.

Essentially, each head, which has four to six CNC spindles, is powered all the time by a 15-kW motor (standard). Spindle speeds (standard) of up to 10,000 rpm can be achieved on the four-spindle version; 15,000 rpm on the six-spindle. Distances between each of the spindle centers is 160 mm. Maximum tool diameter is 125 mm. The axis travels are 400 X 400 X 630 mm for the four-spindle version; 600 X 600 X 800 for the six-spindle style; the positioning accuracy and repeatability are 0.01 mm and 0.005 mm, respectively. Rapid traverse can be performed at 60 m/min. The approach is to have a series of LTCs (four- and six-spindle configurations are available) setup in a line. Each of the machines is tooled to perform a limited number of operations, unlike the typical case in a machining center-based line (parallel processing), wherein a single machine typically performs all of the operations required to finish a part. So what happens in an LTC system is that the part, which is fixtured to a pallet (which provides the opportunity for five-axis machining through part positioning), undergoes metal removal in a series of machines that can provide "toolchange" in 0.8 seconds, which means positioning another of tooled spindles to the work, not changing discrete tools from toolchanger to spindle. This is a serial processing approach.

Benz admits that in addition to being quick, this approach is somewhat more expensive if there is a simple comparison made of, say, machining center to LTC. But he notes, "Price isn't everything," and goes on to point out that what needs to be taken into account is "the total cost of ownership."

In other words, if it is possible to produce parts much more quickly--in one time study on an aluminum steering knuckle, the job required 143 seconds with machining centers and could be done in 45 seconds with three LTC six-spindle machines integrated with a rotary part transfer device--then the investment may be well spent, Benz adds, "Our machines are used where labor costs are high." Which means that they're used in places where the machinery and equipment need to be exceedingly productive.