Millions of components machined to millionths - Street Smarts - machine tool tolerances

"Inch worm, inch worm. Measuring the marigolds. Seems to me you'd stop and see how beautiful they are."

Let me tell you something about inch worms. We couldn't live without them.

In 1958 a U.S. Air Force contract was let to MIT and Giddings & Lewis Machine Tool to retrofit a standard boring mill for completely automatic operation. The result was the first numerically controlled machine tool, at least in North America. Kearney & Trecker came up with the automatic tool changer and it was off to the races. The advent of PLCs and microprocessors accelerated the manufacturing revolution.

I used to argue with my father that this was clearly the greatest advance in manufacturing in the second half of the 1900s. As he was chief of metrology for the U.S. Army Signal Corps in the early 1970s, his perspective was a little different. He insisted the coordinate measuring machine (CMM) and laser alignment were more important because they provided the foundation for accuracy and interchangeability on a repeatable basis. It really made plants interchangeable as well as parts.

A story told to me many years ago said that it was Henry Ford who brought back the first set of Johansson gauge blocks from Europe to the U.S. to put a sound metrology backbone into his flourishing enterprise. Jo blocks became standard throughout industry but they had limitations. They were ground to an accuracy of 1/100,000th of an inch. The accuracy of anything aligned with Jo blocks would thus be somewhat less than that. And the farther away you got from the master blocks, the looser the assured accuracy would be.

All this came to mind recently as I was visiting the Indianapolis diesel engine plant of International Truck and Engine and later the Sharonville transmission plant of Ford Motor Co. These are the respective homes of the new 6.0 L Power Stroke Diesel and the new R5 TorqShift automatic transmission. The Sharonville plant has recently received the highest score for quality among all Ford powertrain plants.

It is remarkable that both the engines and the transmissions have parts that are machined to the micron level, one millionth of an inch. That means that such parts are actually 10 times more accurate than yesterday's Jo blocks. Just think about that.

The superior shifting characteristics and durability of the new R5 are grounded in the ability to machine to the micron level. The new Siemens G-2 fuel injectors could not approach the level of performance required without micron level accuracy.

It's one thing to achieve micron level accuracy with a couple of parts, but now we're doing it with millions of parts and while it isn't exactly SOP at this point, it is not unusual either. When necessary, it is an advanced weapon available in today's arsenal of mass production manufacturing technology.

Not so long ago, injector parts were often sorted into undersize and oversize classes after machining was complete and then selectively assembled with other components that were broken down the same way Well, that just doesn't cut it anymore. And tell me that isn't an extremely expensive proposition.

Imagine producing over 8000 injectors per day in Carolina and getting them to Indianapolis JIT for tomorrow's 6.0 L production. You sure want to keep selective assembly to a minimum. High precision machining does have an economic payoff. Can you image the havoc that could be wrought by a bad batch of injectors?

There is an extreme need for consistency in order to meet performance and emission standards now and even more so in the future. When we are getting into pilot injection and rate shaping, playing with post injection, when we are peeling a second like an onion, when we need a very precise amount of fuel delivered with an exact atomization pattern, our dependence on micron level accuracy in parts production will only become greater.

It is only with the more accurate metrology base that we have been able to field the new generation of powertrain components and systems. And this is the base on which future progress depends. In short, only the inch worms can help us build a better marigold.