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END USER: Richardson Manufacturing Co., (217) 546-2249, www.rmc-bigcnc.com. CHALLENGE: Achieve a tight tolerance without increasing cycle time. SOLUTION: A combination drill that eliminated an unreliable boring operation. SOLUTION PROVIDER: Allied Machine & Engineering Corp., (800) 321-5537, www.alliedmachine.com
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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
RMC produced this stack of wheel-hub adapters, each with 57 1.362 "-dia. through-holes and 54 1.438 "-dia. through-holes.
Courtesy of Allied Machine
Allied Machine designed this combination tool for drilling and chamfering.
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.
Related Glossary Terms
- boring
boring
Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.
- boring bar
boring bar
Essentially a cantilever beam that holds one or more cutting tools in position during a boring operation. Can be held stationary and moved axially while the workpiece revolves around it, or revolved and moved axially while the workpiece is held stationary, or a combination of these actions. Installed on milling, drilling and boring machines, as well as lathes and machining centers.
- boring head
boring head
Single- or multiple-point precision tool used to bring an existing hole within dimensional tolerance. The head attaches to a standard toolholder and a mechanism permits fine adjustments to be made to the head within a diameter range.
- centers
centers
Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.
- chamfering
chamfering
Machining a bevel on a workpiece or tool; improves a tool’s entrance into the cut.
- computer numerical control ( CNC)
computer numerical control ( CNC)
Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.
- cutting speed
cutting speed
Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).
- feed
feed
Rate of change of position of the tool as a whole, relative to the workpiece while cutting.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- inches per minute ( ipm)
inches per minute ( ipm)
Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.
- milling
milling
Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.
- milling machine ( mill)
milling machine ( mill)
Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.
- shaping
shaping
Using a shaper primarily to produce flat surfaces in horizontal, vertical or angular planes. It can also include the machining of curved surfaces, helixes, serrations and special work involving odd and irregular shapes. Often used for prototype or short-run manufacturing to eliminate the need for expensive special tooling or processes.
- tolerance
tolerance
Minimum and maximum amount a workpiece dimension is allowed to vary from a set standard and still be acceptable.
- turning
turning
Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.
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