VMCs Cut Cycle Time

Precision is critical in this job shop, because it machines laser, medical, microscope, projector, presentation equipment and eye examination components out of aluminum, brass and stainless steel. Read how these new VMCs fit their plans and kept them on track.

Case Study From: 5/15/1999 Modern Machine Shop

Kronenberger Mfg. Corporation (East Rochester, New York), is a job shop in which precision is critical because it machines laser, medical, microscope, projector, presentation equipment and eye examination components out of aluminum, brass and stainless steel.

The company has purchased ten Fadal (Chatsworth, California) 4020 model VMCs with box ways since 1989. The VMCs feature 10,000 rpm, high torque spindles and wye/delta with a mechanical Hi/Lo spindle system. One of the VMCs features a Fadal automatic twin pallet changer. Four of the Fadal VMCs have new Cool Power that uses a refrigerant system to circulate coolant through the center of the ballscrews and around the headstock, maintaining a constant temperature and ensuring accurate positioning and repeatability.

"We are able to use roughing tools to cut three times the depth of its diameter," says Eric Kronenberger, vice president and programmer at Kronenberger Mfg. "With the high-torque spindle, we can maintain a high rate of machining without stalling the tool. Since we manufacture a large percentage of our parts out of billets, quick material removal is an important issue for us. The Fadals allow us to run at either high or low rpm without stalling."

The Fadal's 10,000-rpm mechanical two-speed, gearless spindle system with the wye/delta Vector spindle drive doubles the horsepower at high rpm for better performance with high-speed tools. The gearless spindle system eliminates broken gears if a crash occurs, as well as noise, heat, vibration and power loss associated with a gearbox.

"Some of our components require cutting multiple cams that use thousands of data points," says Mr. Kronenberger. "These cams require a high degree of machining expertise, and the Fadal VMCs provide vital tools for this operation, including extended memory and true simultaneous 4th axis."

The Fadal 88HS Fanuc-compatible control features parallel processing, which utilizes up to nine microprocessors that work simultaneously to achieve fast and precise control. Parallel processing assigns a dedicated microprocessor to each axis, which contributes to the control's fast program execution speed of 3,000 blocks per second. The high-speed control virtually eliminates data starvation.

Auto tool setting allows tool offsets to be set automatically by loading the tools for the operator. The operator utilizes the jog handle or keyboard to touch off the tool. "Tolerances can be affected by the speed of the control," says Mr. Kronenberger, "We don't have a problem with the Fadal VMCs. When we cut cams, the processor speed is critical in order to hold a tight tolerance and to maintain a good finish. A slow processor would not allow the tool to move smoothly across the thousands

of data points required to mill a cam."
According to Mr. Kronenberger, productivity has increased where coolant through the spindle is justified. The Coolant-Thru Spindle feature provides high pressure coolant (250 psi) at the cutting edge of the tool that flushes out chips that would otherwise require a peck drilling cycle and extends tool life.

Fadal's automatic pallet changer delivers higher productivity on jobs that involve multi-part fixturing and time consuming part changeover. Parts are machined on one pallet, while the operator unloads and loads the off-line pallet. Downtime from loading and unloading pallets is virtually eliminated. The Fadal VMC lets the operator set multiple zero points, so many parts will fit on the table and can be machined without extra programming.

Rigid tapping can save a lot of cycle time when utilized properly. Fadal VMCs allow rigid tapping speeds from 150 to 3,000 rpm. "Some [shallow, blind] holes are drilled not much further than you need to tap them," says Mr. Kronenberger. "We have some larger diameter holes that are quite deep where rigid tapping comes in very handy because you tap without the stress that you do with conventional tapping heads. We can program the depth of a hole within 0.005 inch and get excellent repeatability. Odd-sized shanks are held in rigid tap holders, but the smaller sized taps are held with standard drill holders.

The Fadal 4020 model VMCs feature solid cast iron construction and box ways for rigidity that delivers 0.0002 inch accuracy. The box ways feature a large surface contact area that resists side thrust and provides damping, stiffness and stability. The box ways utilize nonmetallic way liners, which reduce friction, stick slip and pick-up as well as increase machine life. Box way systems provide a combination of low friction, high stiffness, high-load carrying capacity and vibration damping characteristics for longer life and more accurate parts.

"We hold tolerances very easily within the 0.0005 inch range which most of our parts require," says Mr. Kronenberger. "Combined with our own fixturing methods, we calculate that the Fadals reduce setup time by 30 percent, and we've reduced cycle times by 50 percent."

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