Ultimate Precision, Inc. (Madison Heights, Michigan) provides precision machining services for customers in the automotive and other industries, primarily in response to emergency or production off-load machining requirements. The company uses both CNC machining centers and dedicated equipment to machine mainly cast-iron and steel components ranging in size from connecting rod caps to engine blocks.
Because quick response to customer needs is important, Ultimate Precision relies on agile production equipment, including CNC machining centers and flexible tooling. In producing 10-inch by 8-inch parts from raw castings for a builder of special machine tools, two ID bores and one OD surface, ranging from 3.3 inches to 5 inches in diameter, had to be finish-machined to exacting tolerances and fine surface finishes. Each of these cuts, and several other finishing operations, was performed on a 40 hp Niigata SPN-63 CNC horizontal machining center (HMC).
Standard dedicated tooling could not be used for either the 3.3-inch diameter finish-boring cut, which required an 8-inch tool overhang, or the 5-inch diameter OD cut, which had to be performed using a finish-boring tool that required a special setup. Custom-made special tooling was ruled out for these cuts because of the fast turnaround required for producing the parts.
Ultimate Precision decided to solve these problems by creating the special tooling it needed from components available in the Graflex modular tooling system from EPB SA (France) and marketed in North America by Carboloy Inc. (Detroit, Michigan).
The Graflex modular tooling system consists of a wide array of standard interchangeable tooling components that can be quickly and easily assembled for boring, milling, drilling, tapping or turning applications.
"The Graflex tools allow me to be interchangeable," says Ultimate Precision process engineer Nelson Gibson, who is responsible for tooling. "In one job, I may need an 8-inch reach with a small boring head. But I can also use the same boring head to do a hole that's only 1 inch deep. It has adjustable boring heads that allow you to catch `in-between' diameters."
Another feature of the Graflex system Mr. Gibson likes is the ease of applying available adjustable finish-boring heads and setting them up. The finish-boring heads take less than a minute to adjust.
In finish machining the 3.2635-inch diameter bore (±0.0005 inch tolerance) in the hydraulic pump housings that accept the bearing diameter for the pump drive shaft, an 8-inch tool extension was needed to reach the face of the bore, which was finished to a bore length of 1.05 inches. To achieve the required reach, two 2.95-inch long tool extensions were coupled with a radial-type balanceable single-point finish boring head, with an adjustable diameter of 2.52 to 3.39 inches.
"We used the balanceable-type adjustable head to help reduce cutting forces on the toolholder/spindle coupling," Mr. Gibson says. "Obviously, that was important, given the length of the tool overhang." Balancing of the head is done in seconds, he adds, simply by setting two graduated rings for the diameter to be bored.
Overall concentricity of the extended-reach tool assembly is maintained by the Graflex connection system, which ensures tool rigidity in three ways. First, any two components in the assembly are tightly connected by two ballscrews placed 120 degrees apart. A guiding tenon, or key, prevents misalignment. Second, face contact pressure obtained by screw tightening provides absolute rigidity throughout the system. And third, cutting forces during machining further tighten the connection between pairs of components. With this three-way connection system, the assembled tool maintains precise concentricity in use, holding a flex-free 0.005-inch true-position tolerance even at a long extended reach.
In finish-machining the main-shaft bearing diameter bore of the pump housings, requirements were consistently met for the ±0.0005 inch dimensional tolerance and a surface finish of 63 microns, despite the 8-inch tool overhang. Average machining time for the cut, taken at a surface speed of 342 sfpm and a feed of 2.5 ipm, was 15 seconds.
Capabilities of the Graflex system for creative tool assembly were used in setting up the OD finishing operation on the 5-inch diameter, roughly half-inch long surface used to pilot a mating component of the pump housing that holds the drive assembly.
To tool the operation using the Graflex system, a small-diameter radial-adjustable single-point boring head (1.181- to 1.575-inch diameter capacity) was combined with six tooling components. These included a 1.57-inch tool extension, an adapter to connect the boring head and extension to a spindle base plate, the spindle base plate, a second adapter to connect the spindle base plate to the spindle, and two counterweights to balance the tool rotation. In addition, to perform the OD operation with what was essentially a boring tool assembly, the fine-adjustable boring head had to be inverted to take an OD cut, and the spindle motion reversed.
Despite the unusual tool configuration and machining technique used for this operation, requirements were consistently met for an OD size tolerance of 4.9980 to 4.9999 inch, with a fine surface finish of 63 microns. Average machining time for the operation, run at a surface speed of 1212 sfpm, a feed of 4.0 ipm and a 0.020 inch depth of cut, was 8 seconds.
The Graflex tooling system offers Ultimate Precision the important benefit of instant solutions to special tooling requirements. "You can get delivery of any new tooling you need in as little as an hour, or no more than a day, " Mr. Gibson says. "Most of our projects are like this. They're emergency or production off-load jobs requiring on the spot responses to immediate customer requirements. When standard tooling can't do the job, the modular tooling lets us instantly create the special tooling we need."blog comments powered by Disqus