January 2007 Edition

Turning Centers

From Bar to Box in Half the Time

Turning centers cut diesel part production time in half

Mitchel & Scott Machine Co., Indianapolis, was touching parts too many times and, in some cases, not getting the results it wanted. The company specializes in difficult-to-machine metal components for Cummins Engine Co., Allison Transmission, John Deere & Co, Caterpillar, and Eaton.

One secret of Mitchel & Scott’s success is to do as many machining operations on as few machines as possible. The firm went from using three different machines for producing some pieces to a number of Index and Traub ABC Speedline machines that could do the multiple operations on one unit.

Diesel engine parts produced by Mitchel & Scott were turned on multispindle machines, followed by a grinding operation, and then a chucker for boring and threading. The three-step process for 11,000 parts took about two weeks.

Now, the plant completes the same number of parts in one week on Index single-spindle turning machines and Traub CNC turning centers from Index Corp., Noblesville, IN., resulting in improved surface finishes and accuracy, and more consistency.

“We were producing a family of products that required a multitasking turning machine,” Jim Lee, facility manager, said.

Three years ago when Mitchel & Scott purchased the Index ABC Speedline turning machines, the company found it could use them for multi-process work, allowing them to produce parts in a single chucking, and dropping them completed at the end of a compressed machining cycle.

“Achieving a one-machine operation process is a big part of staying competitive,” Lee said.

“One of the things we have tried to focus on in the company is to give the people on the floor ownership of the machines they oversee,” Jim Lee, Mitchel & Scott Machine facility manager, said. “They know they have something to gain from successful runs.”

The company also services the diesel engine, transmission, agricultural, automotive, medical, hydraulic, motion control, consumer products, and marine and power industries. The company makes 30 different parts during two shifts, using the six Index ABC Speedlines – running 100 hours a week. The diesel engine component is machined from 1144 steel.

The company also has seven Traub precision CNC turning centers with and without sliding headstocks.

Learning the ABCs

Lee said the ABC Speedlines eliminated a grinding operation as well as performing internal threading within the complete machining cycle. With synchronized pick-off spindles, the machines work parts within one machining cycle and drops them into the box.

The Index single-spindle automatics produce turned and complex parts automatically from bar stock. The ABC Speedlines also machine simple screw machine parts to medium complexity parts.

The flexibility of CNC technology, combined with the high speed of automatics, is ideal for competitive production of small to medium lot sizes, Lee said.

“We get extremely short cycle times due to simultaneous machining with up to three tools, plus we have the productivity of driven tools for complete machining of parts and backworking with up to five tools,” Lee said.

Lee’s company found that an extensive range of attachments, including a polygon turning attachment, let it perform complete machining.

With the ability to complete a part in one step, there was a reduction of in-process inventory. Previously, parts would queue in batches in front of the grinders.

From Bar to Box

Multiple operations on one machine replaced three machines and halved machining time for Mitchel & Scott

“Now each machine takes the part from bar to box,” Lee said.

Besides the automatic lathes, Mitchel & Scott invested in an Index CNC multispindle MS32. The unit produces turned and threaded steel hydraulic parts.

Prior to purchasing the machine, Mitchel & Scott could not process the parts. The most difficult machining operation for those parts was an internal thread very close to the parts’ flat bottom – something not easy to accomplish with a tap. With a thread milling cycle on the MS32, the company has been able to meet specs.

“We’ve seen that milling the thread provides longer tool life and reduces tooling cost compared to taps,” Lee said.

On Mitchel & Scott’s previous multispindle machines, changeovers took up to 15 hours when switching cams and tooling to produce different parts. Parts now produced on the Index machines could not be done on the cam-style machines. It now takes six hours or less for a complete changeover for the family of eight parts on an Index machine.

“One of the things we have tried to focus on in the company is to give the people on the floor ownership of the machines they oversee,” Jim said. “They know they have something to gain from successful runs.” Index Corp.

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