Job Shop Boosts Productivity, Precision with Bar Loader
At Instrument Development Corporation (IDC), Mukwonago, Wisconsin, pushing the limits of conventional machining technology is the norm.
Instrument Development Corp. is a 50-person job shop that specializes in the production of close-tolerance automotive parts and aerospace components. The firm takes on jobs such as guidance and navigation system components with extremely complex geometries and precision control valvesthat many other shops would think twice about trying.
Over the past decade, IDC has built a reputation among original equipment manufacturers for providing not only technical expertise, but also the investment in equipment necessary to meet production and quality goals. Today, the company operates a range of sophisticated turning machines and auxiliary equipment. It also specializes in handling a variety of materials, including exotic stainless steels, titanium, precious metals, tungsten, and aluminum.
"Our operation is unique in that we're set up to produce large runs of highly complex parts, from difficult-to-machine materials to very close tolerances, usually tenths all over," said Kevin Sinnett, IDC owner and CEO. "It's not something a lot of shops do," he asserted.
Getting the Most from Production Lathes
Maintaining high accuracy and repeatability in production parts requires precision workholding systems as well as precision machine tools. Recently, the company installed magazine short bar load systems to complement production lathes for the machining of a particularly complex, high-volume part.
The aluminum part, one inch in diameter, is a variable-frequency solenoid (VFS) body that is used to regulate pressure in an automobile transmission. The nozzle, as it is called, has a 1/4-inch bore that requires a 0.0003-inch tolerance to accommodate a high-speed spool. It also requires 12 drilled holes and a multi-faceted outside diameter with O-ring grooves. Maintaining tight tolerances during production is critical because the timing of the solenoid body is controlled by the positions of the holes.
Part production is continuous. The lathes are in operation 24 hours per day, six days per week, producing 6,000 pieces per day.
"Generally, we'd use a standard 12-foot aluminum bar for this type of production operation, but because of the close tolerances we had to use a shorter bar length," Mr. Sinnett said. "When you try to run a 12-foot bar at 6,000 to 7,000 rpm, the vibration makes it difficult to hold tight tolerances, plus, over time, it can destroy a machine tool."
To overcome the bar vibration problem, the company installed five Multifeed Magazine Short Bar Loaders from Lexair, Inc., Lexington, Kentucky. The compact, fully automatic bar loaders have a much smaller footprint than conventional bar feeders; they can also handle bar diameters from 1/8 inch to 31/8 inch and lengths up to 60 inches.
The company cuts aluminum bars one inch in diameter and 12 feet long into four, 36-inch lengths and loads them into the magazine, which has a capacity of 36 one-inch-diameter bars. Straightness of the bar is not critical to system operation, and no end machining of the bar is required prior to loading the magazine, only deburring.
The Lexair Multifeed system has a remote hand-held pendant control that permits setup in as little as two to three minutes. A swing-out mechanism allows the bar feed to be moved out of the way for lathe maintenance without losing the alignment to the lathe. The push rod partially retracts from the bar as the collet closes, reducing the possibility of vibration during the turning operation. The system has no rpm limit.
Rapid Cycle Time Augments Throughput
During operation, the insert pusher inserts the stock into the lathe. As the pusher retracts, the cross slide on the bar loader changes position in approximately two seconds, so that the push rod is in line with the lathe and pushes the bar through the collet.
During the turning process, the next bar in the magazine is simultaneously loaded into the insertion channel. When "end of bar" is reached, the lathe stops and the bar end is ejected. The push rod retracts at high speed, the cross slide moves over, and the next bar in the channel is inserted into the lathe.
When stock has been depleted from the magazine, the main pusher retracts after ejecting the last end. The cross slide moves out, and the controller forces a safe condition and signals that the magazine is empty.
"We also found that in addition to eliminating the vibration problem, the Multifeed system has a very fast next bar insert and start time of about 10 seconds," Mr. Sinnett said. "That helps us keep the part cycle time at 107 to 108 seconds, which is important in meeting our throughput goals," he explained.
The Multifeed system is designed to interface easily with most CNC lathes. At IDC, the systems work in conjunction with Hardinge Conquest GT and Wasino LG-6 CNC flat-slide gang tool lathes.
"The one-inch-diameter bar is the same as the draw tube on the collet," Mr. Sinnett said, "so we are able to operate the bar feeders without a liner."
The Lexair Master Spindle Reduction Liner is said to prevent whip while running a short bar at maximum rpm. The master liner, combined with a set of customer-supplied bushings, handles most bar sizes without the need for separate spindle reduction liners for each bar size used.
Since being installed by Instrument Development Corp. about two years ago, the Multifeed bar loaders have been in continuous operation. "Running short bar lengths has been a simple and cost-effective solution to the challenge we faced of maintaining quality production for a high-volume job," Mr. Sinnett concluded.
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