Flexibility in Screw Machining
Computer control of multiple axes allows programming CNC machines in a fraction of the time and gives them the ability to perform a wider range of operations. "Although cam machines still have great value on jobs of 1 million or more pieces, they are restricted to 360°, a full revolution, which limits the operations that they can do," notes Yvon Desaulniers, President, Devon Precision Industries Inc. (Wolcott, CT). "They don't have room for cross-tapping, for instance. They also don't have the advantages of maintaining constant surface speeds and tool nose radius compensation."
This is why Devon, one of the largest privately owned machine shops in the US, has added three Hardinge CNC Swiss-style machines. Desaulniers sees them as complementing the 200 Swiss-style cam-operated automatics that constitute roughly 48% of the company's $30 million investment in capital machinery. For a job shop tooled up to average 1.2 million parts a week, orders of 15,000 pieces for medical jobs and 150,000 pieces for smart weapons can seem small. But such orders and smaller are the trend today and the kind that Devon puts on the new CNCs.
Among those are guidance-system components for Tomahawk cruise missiles. "If these components are not right, the missile will miss its target and will waste the $1.5 million spent to build it," says Desaulniers, founder of the 300-employee shop. The challenge for machining this component is the square corners at several shoulders and ID diameters. Tolerances are usually 0.0003 in. and a 16 pin. finish on the square surfaces.
The flexibility necessary to profit from such work begins before the work hits the floor. From the moment Devon receives a request for a quote, a team of mechanical engineers and experienced machinists evaluate the job. "We model the parts in three dimensions on a computer, choose the tools for making them, and check for interference," says Desaulniers. "So that when the machine stops making parts and it's time to change it over, any questions are answered ahead of time."
Moreover, the drawings and tools for the setup are waiting for the tool setter. "For flexibility, we use carbide inserts because they are very quick to change," Desaulniers continues. "On the CNCs, the toolposts stay on the machine, and we just replace the insert. There could be a difference of 0.020 in., but we make the offset right on the CNC. So the changes are very minimal at the machine."
Also part of Devon's strategy for flexibility are pushing work through the spindles' standard collars and not being fussy about raw material. "Although we keep a variety of standard raw materials on hand, we sometimes use the material already loaded on the machine, turning it down to the customer's specifications," says Desaulniers. "This way we don't have to change the collar or order raw material. A two to three-day wait for material is too long in today's market. If a customer just wants 500 pieces, we put in new inserts, program the machine, and start producing parts within a couple of hours."
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