Logansport Matsumoto Co., (LMC) in Logansport, Indiana, manufactures and repairs hydraulic and pneumatic cylinders, international-style high speed chucks, Neidlein face drivers and rotary tables for the machine tool industry.
The company was recently approached by Hitachi Seiki, USA (now Mori Seiki HITECH) to manufacture draw tubes for use in chuck and cylinder packages provided by LMC. LMC initially assigned the draw tube production to an outside vendor who utilized traditional chucking to manufacture the tubes. The chucking method involved inserting half of the draw tube into the machine while turning the other half. The tube was then extracted from the machine, turned around and reinserted to finish the other half. The moment the draw tubes were taken out of the machine, the accuracy of the parts were compromised. The results were far from the less than 2.5 gram-inch balance requirement given by Hitachi.
"We were determined to produce a better, more balanced part for the customer, without raising our price," said LMC General Manager, Brian Lane. "In order to accomplish this goal, we decided it was essential to start with better quality material and then machine the OD in one operation."
LMC solved the first part of the problem by changing their material spec. Originally, the vendor made the draw tubes from 1026 carbon steel tubing. Although any imperfections on the OD of the tubes could be corrected during the machining, the irregularities of the ID were impossible to machine. These imperfections were detrimental to the balance and overall quality of the part. LMC decided to utilize higher quality 1026 honed tubing which has a truer ID and improved the balance of the finished draw tubes.
The second, and perhaps largest, part of the solution was changing the overall method of production. The previous method necessitated removing the part in order to machine the other half of the tube. Even assuming each of the two halves had concentric OD's and ID's, which was often not the case, this two-step process increased the chance that the two halves might not run on the same centerline.
LMC realized the key to a truly balanced part was finding the center of the ID and using it as the point of reference while machining the OD in one operation. The OD and the ID would then be concentric to one another, running along the same centerline down the entire length of the tube. LMC engineers decided to implement a Neidlein face driver in order to accomplish the machining of the OD in one application.
Before implementing the driver, the center of the ID had to be located. This was accomplished through the use of an indicator and steady rest. After the center point was found, the inside of both ends of the draw tube were chamfered at 45 degrees. Chamfering the ends insured that the same center point would be located by the Neidlein face driver, which would play a major role in LMC's new production method.
The pipe-style Neidlein face driver was implemented in the production of the draw tubes for two reasons. Its design enables the driver to "grab" from the inside of the tube, giving it a natural, self-centering capability. In addition, the face driver's ability to hold the inside of the tube allows the entire OD to be machined in one operation, reducing inaccuracies and improving balance. On the tailstock end, a special live center with changeable heads was designed to accommodate different sizes of draw tubes. LMC machines draw tubes from 1-inch to 3-inch diameter. This particular draw tube has M60 threads on each end. The OD of the tube is 2.358 inches (±0.003 inch) and the ID of the tube is 2.065 inches (±0.003 inch).
The results speak for themselves. When manufactured by the outside vendor, the tubes were out to the G630 on the ISO 1940 balance quality grade. LMC's new, single turn operation provides a G 6.3 balance quality grade. In order to guarantee this quality grade, each part is individually tested prior to shipment.
But the new method improved on more than just balance. By turning the draw tube complete in one set-up, cycle time was improved from one tube per hour to one tube per 45 minutes, an improvement in productivity of 25 percent.
"We're extremely pleased with this new method of production," said Dave Mussche, LMC Manager of Manufacturing Engineering. "The Neidlein face driver is a well-made, rigid, high precision instrument that has allowed us to manufacture quality parts on a consistent basis."