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Precision Hydraulics
Integrated axis control valves improve tolerances, reduce machine size
Al Presher, Contributing Editor -- Design News, April 28, 2008
As diesel engines are increasingly required to have greater output at smaller sizes, engine parts manufacturers are seeking new ways to efficiently meet these criteria in their production environments. Crankshaft manufacturers, for example, are constantly 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 produces special equipment used in automotive crankshaft manufacturing, including crankshaft deep fillet rolling machines which induce compressive residual stress at and below the surface of the crankshaft being rolled. In the past, the rolling machines used separate control cards for each of the 13 axes of motion, but Ingersoll wanted its next generation of crankshaft rolling machines to be more compact.
Selecting Bosch Rexroth's IAC-R proportional valves with integrated motion control on the hydraulic axes and combining them with the company's MTX controller, helped achieve a design that's 25 percent more compact.
Deep fillet rolling is the name given to the process of rolling under high loads. As the name would imply, the crankshaft deep fillet rolling machine rolls or “cold works” the fillets or undercuts located at each end of a crankshaft's bearing surfaces. The term is used because of the depth to which the material is strengthened — up to .125 inches.
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. 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 if it is found to have an unacceptable amount of distortion after rolling.
In this application, a higher load force is selectively applied. One proportional hydraulic valve is assigned to each rolling axis of motion on the machine and, in the past, the control of each hydraulic drive axis has required a separate axis motion controller. The new design provides a programmable, fieldbus-compatible, 32-bit digital motion controller for the hydraulic axis, all packaged on-board a high-performance servo solenoid valve. Axis feedback devices including position, pressure and force plug directly into the valve's on-board electronics.
“The use of the IAC-R valve reduced field wiring by 25 percent and eliminated one of the four previously required electrical panels, saving us approximately 15 percent in machine control costs,” says Gary Munger, Ingersoll controls engineering manager. Other benefits of the system include PLC communication with the motion axes over PROFIBUS.
According to Munger, control package requirements for the crankshaft deep fillet rolling machine were primarily that the system supply incremental, precise pressure variations for a resulting force up to 30 kN within a ±1 percent tolerance band. Programmed force changes had to be achieved in ¹/10 of a sec for the hydraulic actuator.
“Essentially, logic execution and synchronization are much faster. We're able to achieve a PLC scan time of less than two milliseconds, which is more than 10 times faster than the other controls we have used recently,” says Munger.
The overall machine is controlled using an MTX CNC controller. The MTX uses SERCOS with fiber-optic cable to control all servo and spindle motion, and PROFIBUS DP to permit fast control of distributed I/O and hydraulic axis control via the IAC-R valve. Machine-to-machine digital communications between all control elements is a key benefit of the new system.
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