MRO Today - Drilling through the bottleneck

Drilling through the bottleneck

A Ford Motor Co. plant “de-bottlenecks” crankshaft drilling operations with replaceable-point drills

Few things stall a high volume CNC operation like premature drill failure. Even when the probe catches a broken drill right away, the unscheduled shutdown hurts throughput, requires extra labor and runs up your tooling expenditures. Worse yet, when the failure is just chipping of the edge, which the probe misses yet still causes bad parts, you risk running up scrap and rework rates as well.

In their 220,000-per-year crankshaft machining operation, process engineers at Ford Motor Company’s Essex Engine Plant in Windsor, Ontario, figured that the premature failure rates with solid carbide drills were plain unacceptable. Most drills didn’t even make it to reconditioning time.

The plant makes the 5.4 liter Triton engine that goes into Ford SUVs, F-Series trucks and other large vehicles. Drilling originally represented just three of 15 CNC operations on the crankshafts but accounted for most of the stoppages. The solution Ford found eliminated premature breakages, dramatically increased throughput and ultimately realized annual savings in the mid six figures.

Balancing inherently unstable holes
The most severe problem was in drilling balancing holes, due largely to an unavoidably unstable workholding setup. The crankshafts are suspended only between centers, so they can be spun, much as in wheel balancing. In crankshaft balancing, though, lightening holes are drilled into the heavy side rather than weights being added to the light side.

Ford runs two identical balancing machines. First, each machine rough-drills one to four balancing holes depending on the out-of-balance condition. Next, it follows with shallower finishing passes at the same feed rate.

Ford’s engineers determined that the inherent instability of the unsupported setup let vibration creep in, which can be deadly to brittle solid-carbide drills.

“Tool breakage was out of control,” said one engineer. “We couldn’t keep drills in the machine. A drill snapped at least once every shift. None of the solid-carbide drills lasted long enough to be sent out for reconditioning.”

The resulting downtime for tool changes reduced throughput to unacceptable levels. So Ford tried a few indexable type drills, assuming that their tougher alloy steel bodies could better handle the vibration.

Ford was right — to a point. Tool life improved with the switch to one type of indexable drill, but only incrementally. So their engineers kept searching.

Improvement “like flipping a switch”
Their search led to a dialog with Ingersoll’s Glen Margerison, who, after reviewing the problem with Ford engineers, recommended Ingersoll’s then-new Qwik-Twist replaceable-point drill as a drop-in replacement.

The impact was immediate: drill life improved from 1,000 to 7,000 hits per tip for rough balancing and from 6,000 to 15,000 for finish balancing.

“It was like flipping a switch,” commented one Ford engineer. On that basis, Ford standardized on the Qwik-Twist drill. The move saved substantially in both tool costs and downtime. Over both balancing machines, the reduction in downtime translated to an additional 415 crankshafts a year.

Edges on the Qwik-Twist drill didn’t chip under the conditions that caused solid-carbide drills and other indexables to fail. Edge security was much better; Ford could depend on the tool to last through to its entire scheduled service interval. Unscheduled shutdowns due to drill failure simply went away. With one tool, operators were able change out points in just 20 seconds, often right in the spindle. And, since the points lock in place with plus-or-minus 0.002 of an inch axial-length repeatability, the need for touching off or re-zeroing after each tip change was eliminated.

Leveraging the success
Based on success in the rebalancing operation, Ford engineers and Margerison teamed up to improve another drilling operation earlier in the crankshaft production cycle. That process involves 13 drilling, boring and tapping operations in all. The parts are done two-up on three identical Grob BZ 600 single spindle CNC machines. Together they convert 300 steel forgings into finished crankshafts every shift.

The bottleneck drilling operation in this sequence was to open a post end hole in three steps:

1. Drill a 14.75 mm diameter by 22 mm counterbore and
pilot for the tap hole

2. Drill a 60-degree chamfer

3. Drill a 10.50 mm diameter by 27mm deep tap hole

All three operations suffered from premature failure of the solid carbide drills, though not as severely as in the balancing operation. None of the holes was especially deep, and the setup was much more stable than for balancing. Nevertheless, the solid carbide drills lasted only 500 hits for the pilot holes and just 1,000 for the tap holes.

Even though these applications were milder than balancing-hole drilling, the new drill produced a much larger dollar saving. Tip life improved from 500 to 2,500 hits for the larger hole and from 500 to 2,000 hits for the smaller. A substantial contributor to the labor savings was the elimination of deburring, a consequence of the edge chipping that plagued the original process.

Customized bit eliminates entire operation
After running the step drill for about a year, Ford engineers and Margerison considered adding the 60-degree chamfer to impart a feature to the hole that required an additional operation and extra tool. Ingersoll created the custom tool, resulting in an 11-second cycle time saving per two cranks (which are done 2-up) and removing one tool from the operation. The additional chamfer not only eliminated the separate operation — it also outlasted the original chamfering tool by five to one.

“These savings don’t include eliminating the ‘reconditioning merry-go-round’ that inevitably accompanies solid carbide drills in high-volume operations,” Margerison says. “Given the typical 4- to 15-week turnaround time for reconditioning solid carbide tools, a plant will need to inventory three to six drills for every one in active service. And with the premature and unpredictable failures at Ford, that number would have to be much higher. With a replaceable-point drill, by contrast, you need just a couple of alloy steel shanks and a supply of replaceable points.”

Indexables: Safe haven as carbide prices rise
Looking more broadly, indexable tools also provide a safe haven against escalating tungsten carbide costs. An indexable tool puts the carbide only where it’s needed — at the cutting edge. The other 85 per cent of the tool can be constructed of much less expensive alloy steel. Since carbide prices have risen more than five-fold since 2004, this is no small consideration. As the Ford case shows, the savings a company can realize by exploring indexable round tools can be dramatic.

This article was provided by Ingersoll Cutting Tools. For more information, phone 815-387-6600; e-mail info@ingersoll-imc.com; Web site: www.ingersoll-imc.com.

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