Precision Machining Opens New Markets

Manufacturing Engineering, Mar 2007

Continental NH3 Products Co. Inc. (Dallas, TX) has been in the manufacturing business for more than 50 years. Founded in 1955, the company specializes in manufacturing equipment for the agriculture industry, and is well known for meters, valves, fittings, adapters, couplings, and manifolds for handling anhydrous ammonia.

In the past few years, Continental's president, Judd Stretcher, has pursued a policy of sound growth. In 2005, Stretcher formed Continental Manufacturing to help the company expand into non-agriculture-related precision-turned products. Continental Manufacturing occupies a 28,000 ft^sup 2^ (2601 m^sup 2^) facility, which features high-volume multispindle automatics, CNC turning and milling machines, multiaxis lathes with live tools, Y-axis with subspindle and CNC Swiss machines.

Its production capabilities include production work handled on multispindle automatics, as well as CNC turning and milling, multiaxis lathe machining with live tooling, and Swiss turning. secondary operations are supplied by drill presses, turret lathes, and manual mills and lathes. The facility also includes an onsite tool-grinding shop where it fabricates form tools and sharpens drills.

One of the first contracts awarded to Continental Manufacturing was to produce take-down pins for the M-16 rifle. Over the past eighteen months, Continental manufacturing has reengineered the traditional process from the ground up and eliminated secondary operations to achieve what many thought impossible, a complete take-down pin in less than sixty seconds. The manufacturing process for the key defense component resulted in a 56% reduction in cycle time and improved part quality.

Machined from 86L20 stainless, these 1.01'' (25.6-mm) long parts had been a headache to manufacture. Operations required to complete the part included facing, turning, drilling, hole chamfering, and slot milling. Drilled and chamfered holes on one side of the part added another level of complexity by making it difficult to produce the part in one chucking.

A number of manufacturing process sequences were attempted with varying degrees of success. "We began using multispindle automatics to blank the part before taking them to a milling machine, placing them one by one in a custom-built fixture for milling and drilling operations," Stretcher explains. While the cycle time was acceptable, multiple setups made staying within the 0.0005'' (0.013-mm) tolerance challenging. "It is extremely challenging to maintain a 0.0005'' [0.013-mm] tolerance once you re-chuck."

Recognizing the need to machine the part complete from bar stock, Stretcher consolidated the two operations on one gang-tooled lathe with live milling tools. This approach had the desired effect, yielding a slightly faster cycle time, and producing parts within tolerance. With pneumatic milling attachments, the lathe began to struggle with the extensive cross milling of an 0.0725'' (1.84-mm) slot. The machine's poor thermal compensation characteristics caused parts to grow throughout the day.

"We found that our parts at the beginning of the third shift were within tolerance and by the next morning a substantial number had exceeded tolerance," Stretcher says. The need to run untended and consistently produce parts within tolerance led him to seek a more permanent solution using the company's recently installed Tsugami BS26C Swiss-turn from Rem Sales Inc. (East Granby, CT).

Feasibility of manufacturing the part on the BS26C Swiss-turn was assigned to operator Rodney Grabatin, who was familiar with the Fanuc control. Grabatin immediately set to work programming the BS26C, which is a rigid machine with Swiss capabilities, including subspindle and 5000-rpm cross rotary tools, for the part. The result was that the Tsugami BS26C Swiss-turn was soon cutting the parts to print in 1 min 26 sec. Subsequent tweaking, including adjustments to tool positioning, reduced the final cycle time to 1 min 2 sec.

The transition from multispindle automatics to the more flexible Swiss platform virtually eliminated downtime. "Changing a tool on a Swiss machine usually involves throwing an insert away and replacing it with another. To do the same thing on an automatic requires removing the tool, regrinding it, reinstalling, and retouching it." With a better understanding of exactly how the company could benefit from Swiss-turns, Continental soon sold one of its standard lathes, using the proceeds to purchase a new Tsugami BE19.

Awarded the take-down pin contract for a second time, Stretcher decided to make two additional changes to further reduce the cycle time. The first change was to machine the part on the new Tsugami BEl9. Featuring 8000-rpm cross rotary tools, the Tsugami BEl 9 proved to be a significant improvement over the Tsugami BS26C for this job. Continental handed over the reins of the BEl 9 to their latest employee, Kody Dill, who came to Continental with previous Swiss machining experience. "This time around we were able to reduce the slot-milling operation by around 75%."