Low-cost machining accessories make big bottom line numbers: short run lathe and machining center runs make short setup times critical; quick-changeover chucks make it possible and productive
Machining lot sizes from 25 to 100 pieces of cast iron and stainless steel pump components, MP Pumps, Inc. (Fraser, MI), a unit of Tecumseh Products Company, works 3 shifts, 6 days a week.
In order to minimize on-the-shelf inventory cost, major goals in its cost reduction efforts have focused on ways to facilitate fast changeover by slashing setup time any way possible.
“On turning operations, back when we were using conventional chucks, we either setup two lathes for first- and second-end operations, or we endured chuck changeover times of 20 minutes or so in order to machine both ends on one lathe. Eventually, our investigations into quick-changeover chucks led us to purchase three SMW Ultimate CNC chucks,” explains Jim McMain, MP manufacturing engineer.
“We typically make 2 changeovers per shift, or six per day. These chucks allow us to make hard to soft jaw changes in one minute which permits us to use one lathe, and to eliminate close to two hours of chuck changeover downtime per day.”
The major part of the savings in this case comes from the chuck’s ability to eliminate the need to rebore remounted soft jaws for second-end operations. “With our old chucks, when we remounted soft jaws we’d have to take a skim cut to true them up in order to maintain first-end, second-end concentricity. The jaw tolerances and accuracy of the jaw mounting and actuating system on the SMW chuck allow us to remount previously bored soft jaws with runout of less than 0.0005″ TIR. We simply bore a set of soft jaws for each second-end gripping diameter and store them for use over and over again,” notes McMain.
The chucks also offer other advantages. Two levels of jaw clamping pressure can be applied in one machining cycle without having to stop the machine, unclamp, and reclamp the workpiece. This allows roughing cuts to be made at high clamping force, then the spindle is stopped and the lower clamp pressure is automatically applied to reduce distortion for light finishing cuts.
Another advantage that fits well with today’s high speed lathes and cutting tool materials is the chuck’s ability to eliminate clamp-force dropoff due to centrifugal force at high spindle speeds. This eliminates the need to “overclamp”, which can cause workpiece distortion, in order to produce sufficient clamp force to resist cutting forces at high speed.
Another accessory that increased output and lowered piece-cost on vertical machining center operations, is explained by McMain: “We’re always looking for ways to reduce setup downtime. One of the approaches we use is to apply the use of a cradle fixture with an outboard support. This allows us to machine up to four sides of a component in one setup. This not only eliminates three setups,” adds McMain “but improves bore concentricities and face-to-face accuracies, because it avoids having to unclamp and relocate the workpiece several times in order to expose each side to the machine spindle.”
The key to MP’s ability to process in this manner and still maintain high metal removal rates is the SMW ET-series indexer. It is not a wormgear driven table that relies on a power brake to resist offset cutting load forces. The table uses a precision face-gear coupling to position and lock the indexer spindle. This indexing and clamping method not only provides solid rigidity to resist offset loads, but it offers exceptional indexing positioning accuracy. Our units are guaranteed to repeat within 0.0002′ on an 8″ dia.
“Until these tables came along we had given up on using this multi-side machining processing method. Our previous indexers would deflect under the heavy offset loads, causing significant loss of accuracy,” says McMain.
In these times of intense competition and close to non-existent capital spending budgets, many companies are turning to accessories to boost productivity with low-level investments. The current focus on setup downtime reduction has also drawn attention to other accessories such as low-cost manual pallet changers that can frequently double machine output on both short and long run work. These units have caused shops to realize that performing setups and loading parts on the machine table is a major source of downtime. When these tasks are performed on the machine table the spindle sits idle. When they are performed on an offline pallet the machine is not down, it’s cutting parts on the pallet clamped on the machine table.
Another accessory that is gaining popularity is the application of relatively low-cost automatic loaded, short-bar barfeeds to CNC lathes.
Today’s barfeed designs overcome the objections to traditional barfeeds. They do not use a messy re-circulating pressurized oil system to suspend the barstock to allow higher spindle speeds — the new units run dry. The short, typically 5′ length bar is supported in a spindle liner tube so that bar, tube and spindle are in direct contact and rotate at the same high speed without vibration.
Further, these barfeeds only require about 8′ of space behind the machine, compared to 25′ or more with traditional 12′ bar length systems. The big payoff, however, comes from the ability to produce the complete workpiece in one automatic cycle. This eliminates the need for a second-end lathe setup, and the automatic magazine-fed feature can allow machines to run up to 24-hours unattended. SMW Systems, Inc.
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