Integrated axes crank up cold working

By Marc St. Pierre, Ingersoll CM Systems

As engines are required to have greater output in smaller sizes, engine parts manufacturers seek new ways to efficiently meet these criteria in their production environments. Crankshaft manufacturers, for example, constantly are driven to improve product strength, reliability, and quality. One way they achieve this is by applying external forces to the crankshaft’s surface to reduce fatigue.

Ingersoll CM Systems, Midland, Mich., is a leading developer of crankshaft manufacturing systems and machinery. The company produces special equipment used in crankshaft manufacturing, including its crankshaft deep fillet rolling machines. The machine induces compressive residual stress at and below the surface of the crankshaft being rolled or “cold worked.” The automotive, truck, and off-road industries have used this method for many years, and it’s proven to be a reliable and cost-effective method to improve the fatigue strength of crankshafts.

Multiple Axes, Multiple Forces
“Depending on the crankshaft requirements, specifically if the crankshaft is for a four or six-cylinder engine, the rolling machine includes from nine to 13 arms of independent rolling axes per machine,” says Gary Munger, Ingersoll’s controls engineering manager. “Each arm applies a different force at a different point along the length of the crankshaft to condense and strengthen the crankshaft.” In some cases, the rolling machine is used to restore a crankshaft that’s found to have an unacceptable amount of distortion after rolling. In this case, a higher load force is applied selectively. One proportional hydraulic valve is assigned to each rolling axis of motion on the machine. The overall machine is controlled by the motion controller, which tightly integrates the multi-tasking PLC with the CNC, and is capable of controlling up to 64 axes of motion (See Figure 1 below).

	FIGURE 1: OVERALL CONTROL
	The rolling machine includes nine to 13 arms of independent rolling axes, each arm applying a different force at a different point along the length of the crankshaft. The overall machine is controlled by the motion controller, which tightly integrates the multi-tasking PLC with the CNC and is capable of controlling up to 64 axes of motion.

“Previously, Ingersoll’s rolling machines used separate control cards for each of the up to 13 axes of hydraulic motion,” says Munger. “This meant a larger processing area on the machine, expansive cabinet space for individual controllers, and excessive wiring for components and I/O. The previous version of the valve controller used an analog interface, which added a great deal of field wiring and panel space, along with the normal challenges of signal noise. But as crankshafts have become more compact, Ingersoll wanted its next generation of crankshaft rolling machines to be more compact.”

Munger says Ingersoll’s primary control package requirements for the machine were that the system supply incremental, precise pressure variations for a resulting force up to 30 kN with a ±1% tolerance band. In addition, the hydraulic actuator had to execute programmed force changes in 0.1 sec.

Ingersoll CM Systems has a relationship with a number of automation suppliers and, in this case, called on the hydraulics and electric drives and controls groups of Bosch Rexroth to provide a control solution that would help them satisfy industry demands for greater crankshaft strength and precision as well as faster crankshaft production.

Ingersoll now uses Rexroth’s IAC-R axis controller proportional valves with integrated motion control on the hydraulic axes and combined them with a Rexroth IndraMotion MTX controller.

“We actually use other controllers as well, but the IAC-R hydraulic valve remains a constant in our designs because we’re not aware of another device with the same functional capability for on-board axis control and a digital interface,” says Munger.

Proportional valves with electronics directly on the valve have been widely used for some time. However, the control of the hydraulic drive axis has normally required a separate axis motion controller. The Rexroth valve provides a programmable, fieldbus-compatible, 32-bit digital motion controller for the hydraulic axis—all packaged on a servo solenoid valve. The axis feedback devices, including position, pressure and force, plug directly into the valve’s onboard electronics. The result is a completely integrated assembly for electro-hydraulic motion control that significantly cuts panel space and wiring requirements. These advantages become available with the use of distributed digital intelligent devices such as the IAC-R hydraulic valve, fieldbus I/O, and electrical drives.

Faster, Smaller Achieved
“The use of the IAC-R valve reduced field wiring by 25% and eliminated a 24x48-in. electrical panel used for analog I/O and wiring (See Figure 2 below), saving us approximately 10% in machine control costs,” says Munger.

FIGURE 2: ANALOG ELIMINATION
The use of the IAC-R valve reduced field wiring by 25% and eliminated this 24x48-in. electrical panel that housed analog I/O and wiring.

The solution includes PLC communication with the motion axes over a Profibus network. This, coupled with distributed intelligence in the valves, removes limitations in control performance commonly associated with continuous, closed-loop control concepts over a fieldbus.