Precision Machining Grows Larger

Busch Precision (Milwaukee, Wisconsin) management wanted to leverage its first 90 years of responding to individual precision machining needs—especially those for machine tools and other heavy equipment—to include the larger, more complex components needed for construction equipment, farm machinery, valves, power generation and today's growing number of other large products.

There were challenges in doing this, including replacing the company's long-held belief that machine tool CNC was too complex, too expensive and too inflexible for the company's small-quantity runs with recognition that new-generation CNC can involve easier programming and simplified operation; and finding machine tools able to process large workpieces with the same precision accuracies it had for precision custom machining of smaller sized parts.

Busch Precision thought it would be able to address these problems. "In our years of evaluating equipment for customers, we obviously have many opportunities to `get inside' all types of machine tools built by companies all over the world," says George Grove, president. As a result, he adds, his people know how much strength and rigidity is built into the different machines originally, and which machines can absorb heavy chip loads without losing accuracy on large, complex parts.

So as Busch Precision developed its new strategy for larger-scale automated machining operations, it focused on two needs: CNC machines simple to program and operate, yet providing the versatility needed by a contract machining services center; and machine tools with the rigidity and strength to produce large parts with uniform, precise accuracy under the continuous cutting forces experienced with automatic operation.

To do this, the company decided to add a VTL with an 84-inch diameter table, 96-inch maximum swing, 84-inch maximum height under the rail, 75-hp table drive motor and 125-ton table load capacity at maximum 200 rpm from Giddings & Lewis (Fond du Lac, Wisconsin). Also added was a G & L G50-T table-type horizontal production center, which has a 6-foot by 14-foot table, 168-inch X axis, 115-inch Y axis, 72-inch W axis and 36 inches of spindle travel in the Z axis. Soon to be installed is an even larger VTL with a 138-inch table diameter, 180-inch maximum swing and 96-inch maximum height under the rail and 73.5-hp table drive motor. Table load capacity of this VTL is 250 tons at maximum 126 rpm. All three machines operate automatically with a G & L NumeriPath 8000 computer numerical control.

"These combinations of machine size, strength and automatic operation are helping us earn new business that we couldn't even consider in the past," says Busch Precision customer services manager Mike Mallwitz. "In other cases, the new technologies allow us to deliver large precision-machined parts to our customers much faster than ever before."

Typical of the latter is the giant pump impeller. Total turning time to remove more than 400 pounds of chips from this cast steel workpiece has been reduced more than 30 percent. Roughing operations are performed at a constant 475 sfm, to a tolerance of ±0.002 inch.

When the company wanted to find machine tools able to expand its precision machining capabilities up to large workpieces, it looked for a machine with the structural rigidity it knew would be needed.

Citing VTLs as an example, Mr. Mallwitz says, "From our years of experience making machine tool parts, plus repairing and rebuilding machine tools, we don't feel a VTL fabricated from separate machine members can provide the rigidity we need." He explains that total structural integrity is especially critical for maintaining precise accuracies under the heavier chip loads and at the higher production rates of CNC machining on large parts.

The depth of machine strength and rigidity that Mr. Grove and Mr. Mallwitz identify as their first fundamental is embodied in the structure of both new VTLs. A Meehanite casting forms the one-piece column base with integral circular bowl. In addition, radial ribbing forms an A-frame configuration that provides a strong foundation for the table bearing assembly; table drive transmission and double triangular vertical columns.

Amply supported by the double columns, a massive crossrail and rail head allow full ram travel left and right of center. Adjustment of crossrail height is infinitely variable, using power elevation and clamping to column ways with 80,000 pounds of force. Crossrail position on Busch Precision's 180-inch VTL also is programmable and includes automatic rail leveling.

To maximize use of the rigidity and torsion-resistance of this machine structure, the 96-inch VTL has a forged steel rail head ram almost 8 inches square that travels up to 4 ½ feet. The 180-inch VTL has a ram larger than 10 ½ inches square with almost 6 feet of maximum ram travel.

Both of Busch Precision's VTLs also include a rail-mounted automatic toolchanger, 12-matrix for the 96-inch VTL and 20-matrix for the 180-inch VTL. The high chip volumes these CNC machines continuously remove from large workpieces are handled with a combination of flood coolant system, double-door chip shield plus automatic chip conveyor and elevator positioned in a trench under the machine.

With the NumeriPath 8000 CNC designed specifically for machine tool applications, Busch Precision uses the Type II commands for subroutines, probing and other programming. Each of its NumeriPath operator stations also has a personal computer integrated into it. "Because the NumeriPath CNC is more sophisticated, some people think it's a more complex control," notes production manager Peter Gies. "Actually, once you understand how NumeriPath works, and what the Giddings & Lewis software can do, you realize it is really simple and user friendly throughout. Essentially, it's the way NumeriPath CNC understands the program information you put into it."

In conjunction with its advanced CNC and programming capabilities, Busch Precision uses tool tip probing that automatically verifies tool length and radius, and allows tool offsets to be reset automatically. All three of the company's machines also use the Giddings & Lewis NumeriProbe in-process part gaging system to automatically inspect workpiece location and adjust tool length offsets based on a probed part dimension. As a result, the time previously required for "cut-and-try" steps has been eliminated.

In addition, Busch Precision's 180-inch VTL and its horizontal production center each include a tool life monitoring system that uses Giddings & Lewis software to automatically monitor the time pre-programmed for each tool's effective use. When preset tool life has expired, the tool may be replaced automatically by another tool of the same type, or another action can be taken.