Movement
to higher speeds in machining automotive engines and transmissions, according to Gary
Mobarack, Automotive Market Manager, Valenite (Madison Heights, MI), is really a joint
venture: between the auto companies, the tooling vendors, and machine tool and spindle
manufacturers (somewhere there's probably an academic connection, too--if not here, then
certainly in Europe). All working together to drive production efficiencies forward.
"We have to keep in constant touch," Mobarack says, "with the car makers
to see what their needs are likely to be, near and far term, so we can develop the tools
to meet those needs. It's not unusual for us to be working three, four, five years out in
tool development."
Agile Lines. The auto companies, not surprisingly, are pushing the speed
envelopdemanding tools and machines that run ever faster--but they're also looking at the
ways they approach how they make product--meaning examining process. Mobarack refers to
"agile" machining lines. These are "lines" of machining centers, and
the reason they're considered "agile" is because of the flexibility of machining
center technology as opposed to fixed, less-than-flexible transfer lines. The idea here is
that you can change from one engine block to another and back again basically involving
little more than a change of tools and program.
At issue here, however, is more than mere machine flexibility. Things like the price of
floor space have become real drivers. And that of the capital equipment that goes into
that floor space. Mobarack refers to a recent project involving an agile line of 84
machining centers. Which seems like a lot--and is. But if you run the numbers the
investment makes sense.
For the purpose of argument, let's say that buying that many machining centers brings
them in at about $150,000 apiece, for a total of $12.6-million. However, to do the volume
the agile line will do would require two transfer lines, costing as much if not more, that
would occupy some 1,000 ft. by 1,000 ft. The agile line occupies only about 1/4 of that
floor space.
And if you want to increase the speed of an agile line, you just replace slower
spindles with faster ones. And if you have a problem with one machine in an agile line,
you just take it out and replace it with another. You don't have to shut down the entire
operation because a station or two is down.
Mobarack: "You used to need a couple of transfer lines to do half a million engine
blocks or transmissions a year. Today, on an agile line, you can produce the same numbers
for about half the cost. You get twice the parts per hour, per shift, per day, per
year--however you want to calculate it--out of less floor space, at a smaller investment.
And the line is entirely flexible, modular."
Materials, Tools, Chips. As the aluminum content of engine blocks and
transmissions increases, cutting tool manufacturers have had to make adjustments in tool
materials--both for the aluminum and the higher speed. "We run a lot of
PCD--polycrystalline diamond--tools," Mobarack says, "when it comes to aluminum.
Because of the silicon content."
He notes that transmission cases are a grade 390 aluminum, which has about 18% silicon.
Engine blocks are a grade 356, with about 12% silicon. The significance of the silicon
content is that it makes for tougher machining; the aluminum becomes more abrasive.
"Automotive metallurgists will tell you," Mobarack says, "it's there for
tensile strength. Regardless, we're seeing tool life as high as 150,000 bores in engine
work with the PCD--which is considerably better than carbide tools perform."
The role of coolant, too, has changed as machining speeds have increased: Generally,
it's not unusual to see through-the-tool pressures of 800 psi, as opposed to yesterday's
conventional systems and lower speeds requiring, say, 50 psi. Surprisingly, it's not
higher-speed-related heat driving the higher pressures. "On the contrary,"
Mobarack says. "You're simply moving across the surface too fast to dramatically
impact part or tool temperatures. What you do need to do is flush the chips outand
quickly. Which means higher psi."
He also notes that the HSK-design tool holders, a technology of which Valenite has been
a leading proponent, has had an impact on the move to higher speeds. "The faster you
run," Mobarack says, "the harder it locks in. Thus, the faster you machine, the
more rigid the connection becomes--plus it's a short taper, and the shorter the tool, the
better. You have less overhang, better control, more rigidity, higher attainable speeds.
Limits & Limitations. Trying to define high-speed (or what its upper limits
might be) is a bit risky. However, today there's nothing unusual about 10,000 sfpm in
practice, and Mobarack says they're doing lab tests at 20,000 sfpm. Also, instead of 10
ipm of feed, 400 ipm at a depth of cut of 0.001 in. is not uncommon. But the limiting
factors, right now at least, seem to be in the area of spindles and feed drives--machine
issues. But everything levels out: "We all reach a certain plateau," Mobarack
says, "and then one player--the car makers, the machine builders, tool vendors--will
push the envelop further, and then everyone else rises up to that level."
And so on, one can bet, ever faster. |
