Page 25 - MetalForming September 2017

making sure that the axle is cen- tered in the press during the bearing-assembly operation. This new approach required an upgrade to the PLC and the incorporation of a new digital elec- tro-hydraulic motion controller.
Mittler Seeks New Motion Controller
At the recommendation of Mit- tler’slocalhydraulicdistributor,John Henry Foster Co., St. Louis, MO, the Mittler Brothers team selected the RMC150, an eight-axis controller with special capabilities for precise closed- loop control of hydraulic systems (Fig. 2), from Delta Computer Systems, Inc., Battle Ground, WA. Fig. 3 shows the RMC151 in the electrical panel to the left of the 16-in. bore cylinder in the wheel press.
With the new motion controller in place, the two-phase manufacturing process has been successfully auto- mated. In the first phase of the opera-
tion, when the wheels are attached to the axle, the RMC receives inputs from position transducers mounted in the wheel-press cylinders, pressing the wheels, one at a time, onto the axle journals until precise target positions are reached. During these operations, the motion controller monitors the force exerted by computing the differ- ential pressure between pressure sen- sors mounted in each wheel-press cylinder on either side of the piston. The pressures are logged and the data
Fig. 2—The RMC151 motion con- troller installed in a redesigned assembly press can control and synchronize as many as eight axes simultaneously, and contains a built-in Ethernet interface.
are retained in an information log kept for each axle.
“Per the AAR spec, we need to position the wheels to within a tol- erance of 0.090 in.,” says Jim Hein-
rich, Mittler Brothers engineer.
“And this tolerance must be achieved while exerting as much as 200 tons of force in attaching the
wheels.”
The second phase of the assembly
process involves attaching bearings to the axle, one on each end, outboard of the wheels. It is critical for the axle not to shift while the bearings are pressed onto it from each end. Sensors were added, enabling the RMC to mon- itor the axle’s position, press velocities and forces exerted, while comparing them against setpoint values. The RMC refers to this information as it performs
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