Improving Transmission Shaft Machining
The Halewood Transmission Plant in Halewood, Liverpool, UK, is a 50:50 joint venture operation between Ford and Getrag. There are two transmissions produced in the plant, both manuals. There is the MT82, which is fitted into the Transit, and the B6 six-speed (a.k.a., the Durashift) which goes into the B-MAX, C-MAX, Focus, and Mondeo. Given the application of the B6, it is easy to understand that it accounts for about 65% of the production at the 1,247,548-ft2 plant.
The transmission went into production there about two years ago. Given a keen interest in continuous improvement, engineers from Sandvik Coromant Co. (sandvik.coromant.com) were called in, and began to work on a project related to the machining—face milling and chamfering—of a 60-mm forged, low-alloy steel output shaft.
In the then-existing setup, there were two operations, the face milling and the chamfering.
The engineers deployed a proprietary software tool, called the “Productivity Analyzer,” and determined that there were inefficiencies in the operation. For example, the chamfering tool was overextended, which led to chatter and potential productivity and quality problems.
So they developed a single tool that could handle both operations. A chamfering insert was incorporated on the underside ring of the 100-mm diameter face mill, which solved the vibration problem. Ten additional inserts were added to the face mill, thereby permitting an increase in feedrate.
The shaft machining is performed on a purpose-built mach-ining center. First, there are two cuts taken on the forged blank. The operation is performed at 280 m/min with a 0.2 mm/rev feed. The cuts are made to approximately 3.5 mm. Then, there is a return to center line, and a short index in the Z-axis permits turning the chamfer.
The double-sided inserts (eight cutting edges) are Sandvik 345R-1305M in grade GC4240. The inserts have an 0.8-mm radius and a 19° rake angle; it is capable of cuts up to 6 mm deep. The insert features a tough coated-carbide substrate to handle steel milling.
The chamfering insert is a Sandvik TCMT in GC4225. Based on the combination of geometry and material, it can achieve depths of cut of as much as 4.8 mm.
So what was achieved at Getrag Ford?
The total cycle time is now 8 seconds. It had been 21 seconds. This is because of the elimination of a toolchange (remember: it is being done with a single tool, not two) and because the cutter’s feedrate is increased from 1,656 mm/min to 1,826 mm/min (due to the increased number of inserts used).
On an annual basis, they are saving 1,431 hours. And from a financial standpoint, the annual savings are on the order of £75,000 (which is in the vicinity of $128,000).
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