April 2012 / Volume 64 / Issue 4|
Changing tools to achieve tolerances
By CTE Staff
Richardson Manufacturing Co. provides machining services to heavy equipment, mining and oil field customers and operates 24/7 at its 125,000-sq.-ft. facility in Springfield, Ill. RMC, which employs more than 220 workers, has more than 40 CNC machine tools, including vertical and horizontal lathes with live tooling, vertical and horizontal machining centers, and gear shaping and hobbing machines.
One part that RMC makes is a wheel-hub adapter for a mining truck. “At about 40 pieces per month, the volume is low to medium by our standards,” said Brad Albrecht, manufacturing engineering manager. Because the hub adapter only requires drilling, machining it on a HMC using through-coolant at 40 psi is relatively simple compared to other parts RMC makes, according to Albrecht. “Most of our parts require multiple turning and milling operations in a combination of vertical or horizontal lathes and machining centers,” he said.
However, the part, which is made of modified 4140 steel, requires a considerable amount of holemaking. It has 57 1.362 "-dia., 2½ "-deep through-holes and 54 1.438 "-dia., 4½ "-deep through-holes.
RMC was applying three cutting tools to complete each of the 57 holes: a drill, a twin boring bar and a chamfer mill. The challenge was consistently achieving the tolerance while maintaining the production rate, Albrecht noted. “The ±0.002 " tolerance was too tight for the twin boring bar setup we were using, and we were having trouble holding size,” he said. “We thought about going to single-point boring or reaming, but didn’t want to increase cycle time.”
(The 54-hole pattern in the hub adapter is drilled with an indexable-insert drill, which is able to achieve its 0.020 "/ -0.010 " tolerance without a problem.)
Courtesy of Richardson Manufacturing
Courtesy of Allied Machine
RMC uses GEN3SYS drills from Allied Machine & Engineering Corp., Dover, Ohio, throughout the shop for making holes that are later tapped. “We hold size within ±0.002 " of the upper limit on the minor diameter,” Albrecht said. “So we thought it might be possible to hold that tolerance on the 57 holes in the hub adapter.”
RMC tested a standard GEN3SYS XT drill for making holes up to 3 diameters deep and successfully held the tolerance. The shop then decided to have a special made to both drill the hole and cut the 0.150 "×45° chamfer. Still tooled with the GEN3SYS XT insert, the tool body was customized to have a built-in chamfer. Not only did this shorten the cycle time, it also reduced inventory by eliminating the boring bar and chamfer mill.
RMC runs two parts before replacing an insert. Each tip is reground at least once to further reduce costs. “We see virtually identical performance on the reground inserts,” Albrecht said.
By switching to the GEN3SYS XT drill, RMC went from a 1,600-rpm spindle speed, 524-sfm cutting speed, 8.0-ipm feed rate and 1-minute cycle time per hole, to 865 rpm, 308 sfm, 12.11 ipm and 14.12 seconds per hole.
“The speed has to be much slower because the insert was designed to run at midlevel spindle speeds and higher feeds,” said Mark Stevens, field sales engineer for Allied Machine. “This setup is commonly referred to as a high-penetration drill or tipped drill, which achieves tighter tolerances.”
RMC was happy with the results and liked having more control over the process. “By far, the greatest productivity gain came from being able to consistently make the hole the first time without having to constantly adjust the boring head and run the boring bar multiple times,” Albrecht said.
CUTTING TOOL ENGINEERING Magazine is protected under U.S. and international copyright laws. Before reproducing anything from this Web site, call the Copyright Clearance Center Inc. |
at (978) 750-8400.