This article presents a look at current seamless ring-rolling technology and how it has advanced at Muraro Presse in Italy. This technology has substituted hydraulic power with a system of specially designed electric motors and power screws to provide the forging capacity of the machine. Advanced software and control systems are integrated into the machinery.
Ring rolling is one of the most complicated and fascinating processes in the realm of hot-metal forging. Early ring-rolling systems were manually controlled by an operator who had to skillfully negotiate the proper working of the rolling cycle and execute a quality rolled ring using command levers and lots of experience.
As the years passed, the advent of modern hydraulics and computerized control enabled the design of more sophisticated and automated rolling plants. Today, it is possible to easily program a radial-axial rolling cycle and fully automate the ring-rolling process from start to finish.
In developing new ring-rolling systems to advance the modern process, our team had to answer the following questions:
- What and where are the weak points of the machines currently on market, and how can we develop a new machine that satisfies the increasingly stringent requirements of customers?
- What are the possibilities for technological development in this field?
- How can we work with customers who use our hydraulic and mechanical presses to prepare simple forging blanks to roll while still being able to accommodate those who produce very complex rings using difficult-to-roll materials?
Improving Ring-Rolling Equipment
As it turned out, customers that manufactured rolled blanks wanted many of the same considerations that customers rolling complex rings did. The 10 items listed below summarize their common requirements.
- Increase productivity
- Reduce maintenance costs
- Increase the speed and facility of workpiece loading and unloading
- Improve the precision of the machinery and the speed of each cycle
- Improve the filling of the cavities of shaped tools, increasing the movement of the material (axially to the ring) during the cycle
- Increase the true roundness of the workpiece and calculate its working cycle
- Reduce machining requirements and expenses
- Equip the machine with its own intelligence; the machine must be able to program most of the process parameters on its own.
- Increase energy efficiency
- Equip finite element analysis (FEA) process simulation software with the same piloting technology installed in the CNC of the machinery. This ensures that the simulated ring-rolling plant behaves and reacts as the real system, increasing the value and credibility of the numerically simulated results.
At the outset, our engineers realized that to achieve all of these 10 items simultaneously would be a nearly impossible task. In fact, some items initially seemed mutually exclusive of each other and incompatible with a full-system design overhaul. It quickly became clear that meeting the targeted criteria would require an exhaustive rethinking of the equipment and component technologies in order to achieve the necessary improvements.
It would require many more pages to describe in detail all the innovative points that characterize our new ring-rolling system. That being the case, we will keep things succinct and examine a few fundamental design changes in the machinery.
The first element of change that our machine has brought to the field of axial-radial ring rolling is that the rolling plane, as well as the lower cone, can be commanded and driven vertically during the cycle. Two controlled axes have been added to the machine so that it is possible to move the lower cone and the upper cone in a symmetrical or asymmetrical way during the cycle. This capability is critical to the production of certain more-complex ring shapes because there is more control over workpiece deformation, and it enhances the redistribution of material to desired areas during the rolling cycle. Additionally, this new technology has enabled the creation of a new working cycle of the machine that adapts to particular rolled parts, such as bevel gears used in the automotive market or flanges for the oil-and-gas market.
Welding neck flanges in stainless/Inconel steels are especially difficult to produce because the thin edge of the neck can become very hot during rolling. However, the new design utilizes both active mobile cones of the new ring-rolling machine, and the problem of overheating the thin neck is finally solved. Also, the blanks that can be used for this process become much easier and less costly to produce.
Contrast with Hydraulic Systems
If we had used a traditional hydraulic-system design, it would have been impossible to achieve the increased productivity, speed, precision, efficiency and maintainability of the new system. Through the coordinated joint design efforts of Muraro’s big plants and motor divisions, a new drive system that involves the integration of a series of specially designed electric motors and power screws was created.
This system is able to act exactly like a hydraulic design but with higher precision in both position and force applied. In fact, it can switch from control of one variable to another as a function of the data detected by CNC and related sensors
Engineers have developed a drive system capable of performing controlled movements in increments of 0.0004 inch (0.01 mm) with a feedback reaction time of 0.001 seconds and an efficiency exceeding 90%. These differences are huge relative to a hydraulic system, with the new design offering two orders of magnitude in greater precision and responsiveness.
Maintenance requirements are also greatly reduced. Events such as clogged valves, temperature-based changes in oil performance and oil changes are things of the past. Energy savings are significant. Also, the machine’s high precision and speed achievable by the feedback and control loop allows the system to better control the process and increase product quality and uniformity.
When considering the dimensional quality of a rolled ring, the problems of residual ovality after the rolling function and cycle time must be considered. Variables such as these are not easily understood, and setting the machine parameters to yield desired results is also a difficult process. However, Muraro engineers have worked hard to integrate advanced production software into the system. Called M-ROLLING, the package includes information required to program the system quickly and safely. This advanced software offers the machine operator “experience” in skillfully setting process parameters by means of a simple mouse click. For example, if there was a need to roll a ring with a rectangular or shaped section, the operator can set this up directly in M-ROLLING, which would then self-calculate the machine parameters necessary to obtain the desired result.
The software can estimate the actual cycle time of rolling and will offer the capability of analyzing the various forces withstood by the machine as a function of the materials and the temperatures in use. The operator has the ability to achieve the right balance between the cycle time and residual ovality of the rolled piece. It is also possible to create the growth curve of the ring as a function of its diameter as well as the curve that defines the variation of the ring thickness and height during the cycle. When considering different ring shapes and profiles, the software can calculate the dimensions of the ideal forging blank with a single click of the mouse.
M-ROLLING can also be easily installed in the office computer and used to program the machine remotely.
Muraro’s ring-rolling machinery design is the result of many years of forging experience. We pride ourselves in being not just a supplier of machinery but a partner to our customers by assisting them in process design, from digital process simulations to the final production of forged and rolled products.