Parts produced on an MC-300 FI CNC PowerBox Kine-Roller are awaiting inspecAs the nuclear power industry has returned to importance as a key factor in creating green energy, the metalforming industry, and in particular companies involved in producing large high strength threads, have encountered unique, new processing problems and opportunities.
As the nuclear power industry has returned to importance as a key factor in creating green energy, the metalforming industry, and in particular companies involved in producing large high strength threads, have encountered unique, new processing problems and opportunities. Until recently, most high strength rolled threads were generally rolled at hardnesses around Rc 28 - 32 and were mostly 3″ in diameter and below. However, the capability to contain large volumes of very high pressure steam, in nuclear reactors, resulted in the need for a new family of giant threaded studs.
These tensile members generally have threads in the 4″ to 6″ diameter range and must be rolled hard to achieve the physical characteristics and fatigue resistance required. In addition, these cover mounting studs join thick flange elements and are frequently between 5ft and 7ft long. To address this new thread rolling requirement, the need was for the development of a much more powerful family of rolling machines that are able to provided rolling forces up to 660,000 lb and are capable of holding thread tolerances generally found on much smaller diameter precision threads.
As Kinefac engineers began to define the required specifications for such a machine, the basic assumption was made that the Kinefac PowerBox design structure could be scaled-up with CNC control of the individual die rotation together with penetration and special tolerances on the spindles, dies, and the die actuation system. The scaled-up machine would be approximately twice the size of the field proven MC-150 PowerBox Kine-Roller and it would have the radial die load capacity of the hydro-mechanical MC-300.
Proceeding on that basis, engineers designed, built, and delivered the MC-300 FI CNC PowerBox Kine-Roller to Guizhou Aerospace Xinli Casting and Forging Co. Ltd., Guizhou, China, where it is initially being used to infeed thread roll large 155mm diameter threads up to 10” long (250mm) on Rc 42 forged shafts.
The MC-300 FI CNC two cylindrical die Kine-Roller uses the PowerBox structure to provide the radial, axial, and torsional stiffness necessary to roll large, low-lead, high-precision, high-strength threads on studs such as those that secure the cover units on a nuclear reactor pressure vessel. In addition, it may be used to roll other reactor parts, as well as large diameter gas compressor piston rods, wind turbine blade mounting bolts and tower anchor bolts, and similar energy-related tensile members.
This MC-300 Kine-Roller is the second infeed cylindrical die thread rolling machine built that offers more than 300 tons rolling load capability. Based on this experience, the engineers found it necessary to provide a high level of CNC control to all the die motions – radial and rotational. It is the first such thread rolling machine of this size to be equipped with such an integrated CNC rolling process control system. The Kine-Trol system incorporates an automatic rotary die matching system for variable-controlled die penetration rates. To do this, all the process variables for each individual part are recorded and maintained for quick resetup and traceability. Since the MC-300 FI PowerBox Kine-Roller machine will be used primarily to roll threads on high value parts, it must be capable of rolling the first piece to print in order to minimize test blank requirements.
Because of the potential hardness variability, and other rolling blank dimensional variables, the Kinefac Kine-Trol system includes the Automatic Die Compensation (ADC) system, which is designed to eliminate the effect of unexpected blank or other setup variations on spindle system deflection. The ADC system was originally developed by Kinefac more than two decades ago for applications where the root diameter of the form being rolled had to be maintained very precisely in spite of large blank diameter and material variations.
Other CNC cylindrical die rolling machines generally sense the relative position of the two-die spindle system structures with respect to one another. This approach works well when the rolling force required for the application is around 300,000 lb or below. However, as the required rolling force exceeds that level, the resulting deflection of the spindle, spindle bearings, dies, and other elements of the spindle system – which occur beyond the point of typical die position sensor contact – have a significant variable effect on the final die position produced by conventional CNC control.
To counteract the effects of the spindle system deflection variability under high load, the system locates the die position sensor probes to contact the dies on a high precision hub at the back of each die. This is done in an area which is precisely concentric to, and at a known radial distance from, the pitch diameter of the actual die. This allows the Kine-Trol system to perform all of its functions based on a continuously monitored die position, which is independent of virtually all other process variables.
MC-300 FI CNCPowerBox Kine-RollerThe Kine-Trol system then activates the dies based on the actual die pitch diameter position, with minimal need for any additional compensation due to variable stiffness of the spindle system elements. It does, however, require compensation for Hertzian deflection of the die and the part and other small structural discontinuities that occur during the rolling operation. Once the rolling program for the part, including that compensation, is established, the Kine-Trol system implements this improved level of process diametrial control. This CNC die position control, combined with the electronic servo drive of the spindles, allows the operator to precisely repeat the proven setup for the part.
In addition, automatic match capability of the Kine-Trol system enables the setup person to establish the rotational match of the two thread rolling dies with respect to one another. During the die match procedure, the die actuation system automatically closes to the correct diameter to create a shallow die match contact on the blank diameter, and then rotates the part approximately 190° in order to ascertain the level of mismatch in the setup. The operator then measures that axial mismatch of the thread forms and enters that measured value into the Kine-Trol system.
The system then calculates the amount of differential die rotation necessary to bring the matching die thread form into the correct phased relationship, with respect to the thread form on the base die. Next, it adjusts the rolling program to retain that match correction value and automatically inserts that value into the CNC production rolling program. Thereafter, provided the dies are mounted on the spindles in the same relative position, the user can resume production without any re-matching of the dies.
All of the rolling forces, of the basic MC-300 PowerBox CNC Kine-Roller, are constrained within the rectangular high stiffness PowerBox which maintains the spindle systems with their centerlines to a preset parallel or required skew relationship. Within that relationship, the die actuation cylinder at the right end of the PowerBox actuates the right, moving spindle toward the left spindle, which is fixed with respect to the PowerBox. To maintain the rolling centerline in a fixed horizontal position, while the right spindle unit moves toward the rolling centerline, a die centralizing system mounted on the Kine-Roller base moves the left spindle, including the PowerBox, toward the rolling centerline at the same rate as the right cylinder is moving toward it. As a result, it is possible, with the PowerBox system, to mount all work support fixtures on the horizontally-fixed centerline, regardless of the work or die diameters.
For small parts, mounting the part on centers or on a roller support blade and outboard steady rest, provides adequate rolling support. However, when rolling large parts, it requires a precision work support and handling system since the parts must be held at a precisely-controlled position below center.
On the MC-300, the work support system is built into the basic rolling machine structure to provide the required stiffness and precise location of the rolling axis. This Kine-Mat feed unit includes a center system for parts which have sufficient stiffness to support the part against the controlled downward rolling force. It is also equipped with a series of adjustable rollers so it is capable of handling a multi-diameter part up to 6ft long. In addition, this automatic feeder is servo-controlled by the Kine-Trol system to locate the part in the correct axial location with respect to the dies.
The integration of the CNC part position, along with other part position and safety sensors, provides a level of operator convenience and safety which are vital when handling large parts while applying a 300 ton rolling load to them. The work support system also serves as a convenient support for making in-process measurements with open side gages or micrometers.
With respect to the axial position of the dies, it is generally recommended that the centerline of the rolling load be as close as convenient to the centerline of the hydraulic actuation cylinder. If this is done, it is generally practical to roll the threads to the maximum capacity of the MC-300, without requiring any taper adjustment.
The MC-300 FI CNC PowerBox Kine-Roller is the largest two cylindrical die rolling machine in the Kinefac PowerBox family. It is currently being used for rolling threads for aerospace fasteners, electric power turbines, automotive steering shafts, appliance shafts, gas compressor piston rods, wind turbine studs, railway engine bolts, transmission tower foundation bolts, and truck drive train elements.
http://www.onlinetes.com/tes-0510-rolling-large-thread-diameters.aspx
May 30th, 2010 by 
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