Whether it is a 6.6-liter turbocharged diesel for a GMC Savana van (above) or a 550-hp V8 for the 2011 Ford Shelby GT500, the number of holes needed is remarkable, which is why Dr. Jun Ni calls holemaking the “primary process” in automotive metalcutting. He also suggests that even minor improvements in holemaking productivity can have a big effect on overall throughput.
Jun Ni of the University of Michigan is professor, Department of Mechanical Engineering (me.engin.umich.edu); director, S.M. Wu Manufacturing Research Center; co-director, Multi-Campus National Science Foundation Center for Intelligent Maintenance Systems; deputy director, NSF-Engineering Research Center for Reconfigurable Manufacturing Systems; collegiate professor, SM Wu Manufacturing Science; and Shien-Ming (Sam) Wu collegiate professor of Manufacturing. After that, it should go without saying that Dr. Ni knows a lot about manufacturing, including metalcutting.
In point of fact, Ni says, "I've personally worked with the auto industry for over 20 years in machining." (And then he adds that he's also been working on body-in-white processing, factory-level production control, maintenance, scheduling, and throughput improvement.)
So, given what he knows, what does he think is one of the biggest challenges in metalcutting?
Holemaking. Particularly in powertrain operations. In fact, he says that in automotive, "Drilling is the primary process." And by way of substantiation, he suggests the consideration of all of the holes that are in an engine alone.
Holemaking is challenging for a few reasons. He cites the change in manu-facturing equipment in powertrain plants from transfer lines to CNC machines. Whereas before there tended to be drillheads at transfer line stations that were able to make multiple holes in a single slide actuation, nowadays with single spindles, this means that to make drilling less of a bottleneck operation "you have to poke holes 20 to 30 times faster than you did before."
There are changes in materials. He cites a crankshaft line where the workpiece had increased levels of manganese as the alloying material—good for the crankshaft, not so good for the gundrilling operations, where tool life became a big problem.
Then there are tricky part designs, like an ABS valve body, an aluminum part with multiple holes—some connecting—that are on the order of 2 to 3 mm in diameter and 70- to 80-mm deep. "Break the drill, scrap the part," he says.
Compared to other cutting operations—say milling—holemaking is much more demanding, he says. He points out that the tool is submerged in the workpiece. This means that there is no place for the heat to go. Depending on the size of the hole, there can be serious chip evacuation problems. Chips can be welded to the inside of the hole, which then causes the drill to break, and then . . .
What's more, he suggests that often-times the actual cost of holemaking is over-looked. "The cost of the drill is not so big. The cost of making holes is huge," he says. And making matters even a bit trickier: "Holemaking is still a black art." To be sure there is a lot of science associated with that art—Ni says that they've granted more than 20 doctorates related to research on holemaking.
But a problem that exists, he points out, is that due to the reduction in the engineering ranks within auto com-panies and an increasing dependence on outsourcing, the inherent know-ledge that existed about holemaking is gone. Perhaps because he is an academic he is not particularly keen on a reliance of vendors—either of tools or equipment—for advice on setups on holemaking because he thinks that it is in their best interest not to optimize the operation.
Here's the point: Ni says that hole-making is generally the slowest station in a powertrain production line. It is possible to improve throughput by 20% without the addition of capital equipment. "If management was to look at the number of engine products they have and the number of holes, if they could improve productivity by just a few percent, that would more than pay for the engineers."
“Metalcutting has the most black art of any manufacturing operations I’ve ever seen,” says Kerry Marusich, founder and president of Third Wave Systems (thirdwavesys.com), a company that specializes in computer-aided engineering software for improving machining operations. He says that while there is a whole lot of experiential understanding of what works and what doesn’t, more, better information can provide improved operations. And as he says they’re seeing increases in production quantities as the auto industry recovers as well as demands for machining materials including magnesium and titanium (“A few years ago, the only requests we got about machining titanium was from motorsports.”), getting more output is key. Especially given the observation, “a lot of existing spindles are under-utilized.”
That is, they’re running, but they may not be running in a way such that there is balanced loading in the machining operation. Marusich explains that by having feeds and speeds correctly modeled (which means taking into account parameters including workpiece materials, tool geometries, etc.), it is possible to achieve a consistent load on the cutting tool, which results not only in longer tool life but more consistency in the product. And more productive spindles.