Two of the main factors when developing a new vehicle are higher efficiency and greater passenger safety. They both depend to a great extent on the body of the car or truck. Obtaining an efficient vehicle requires controlling its weight in order to reduce fuel consumption. And safety requires a very strong structure against collision, vibration or fatigue which could be achieved by increasing its weight.
This apparent contradiction is resolved by using steel of high elastic limit that provides great resistance with a small section and with a more intelligent design using more complex shapes to obtain the perfect configuration against shocks with a minimum amount of material. Designing complex body parts, manufactured with ultra-resistant steel creates new problems. The most important one being that the parts that could be manufactured in the past using stamping processes have become very complicated and very costly to manufacture. Another problem is the complexity of controlling the spring-back effect of these new steels that cause the part to lose the tolerances used when stamping it.
Variable profiling -also called flexible profiling- has been developed precisely as the right answer to these challenges because it makes it possible to manufacture complex parts inexpensively and may be applied in the design of automotive bodywork.
Experience has proven that for manufacturing some of this type of complex parts that use very resistant materials, the profiling process is more reliable than the stamping process. However, usually there is a limitation due to the fact that forming rollers are fixed and, consequently, the resulting part should be straight which strongly limits the use of profiling in cars.
Fagor Arrasate knows the profiling technology very well since the beginning of their activity in 1957 with hundreds of installations running nowadays; they are one of the leading manufacturers of stamping systems in the world and provides to the main manufacturers of the automotive sector. Therefore, they know rollforming and stamping technologies as well as the engineering demands for designing bodywork.
Fagor Arrasate, in cooperation with Fagor Automation, one of the main CNC manufacturers worldwide, with ample experience in the machine-tool sector, has considered a project to respond to the modern demands of variable profiling. In particular, they have designed a new profiling machine especially aimed at the automotive sector that helps develop and optimize new systems.
The new machine has been designed to meticulously analyze the feasibility of the parts using flexible profiling as well as design prototypes and experimental parts to study the possible limitations and to model the profiling process of a particular shape in a reliable and safe way.
To achieve this, they have thought of a machine with 6 double spindles with 4 degrees of flexibility on each one so as to ensure very high flexibility.
Synchronizing these movements with the position of the sheet metal requires certain special algorithms already developed for Fagor Automation’s 8070 CNC.
Surprisingly, the new concept of variable profiling provides a “rebirth” to a mature technology. Among the advantages of flexible profiling we could mention:
- It makes the most of the material resulting in lower costs. This is particularly important because highly expensive steels with high elastic limit are used (boron steel, Trip, IF, etc.). It is estimated that the profiling process makes the most of 95% (5% waste) of the material that enters the facilities whereas the stamping process with a lot of cut-offs and scrap usually reaches a bare 60% (40% waste).
- For many types of parts, it is a more profitable process than stamping because the cost of the dies increases exponentially when the shapes are very complex. They calculate that in many cases, the cost of the tools may be twice that of the rollers.
- The time for preparing and adapting to new models is much shorter because it consists in manufacturing (or adjusting) simple sets of rollers instead of complicated tools.
- It is possible to make cuts and holes in hard-to-access positions that would be very difficult and expensive to make with dies. This is so because, in many cases, those holes may be made before profiling the material.
- The resulting tolerances are better than those obtained with stamping.
- In many cases, the processing speed is higher.
- Noise is reduced considerably and the ergonomics of the process is much higher.
- PC-based forming programs are more developed and more accurate for profiling processes than for stamping, which allows a more detailed engineering analysis and fewer setup errors. This, obviously, results in shorter market launch time.
- The cost of production facilities is lower using profiling machines than presses that require steels of high elastic limit, capacity of thousands of tons and huge tables in order to use transfer machines.
- It starts out with a coil whereas on a press, it is more common to start out from a format. This means that the start-out material is less expensive also because it does not require the cutting and flattening steps.
The resulting parts are widely used as carrying elements of vehicle bodies especially on the heavy ones like trucks or buses. They are elements that, for example, may build the lower beams that support the floor. Fagor Arrasate, for example, has supplied in the past presses with a capacity of 4000 tons and a table 12 meter long to manufacture this type of parts to truck manufacturers. Now, with the new technology of variable profiling, that would no longer necessary and the overall manufacturing costs would be lower.
The machine has been designed and manufactured with 6 independent spindles on each side in order to ensure great flexibility and adjustability to be able to handle as many parts as possible. Each spindle has four independent movements and a motor to rotate each roller. In other words, each set of rollers (stand) may be actuated in a particular and precise way as required. This is a distinguishing factor when compared to conventional profiling machines where several rollers are handled with a single motor.
The whole motor system is handled by Fagor Automation servo drives that communicate digitally with the 8070 CNC in order to optimize the efficiency and precision of the roller system.
Control algorithms and electrical configuration
On a machine of this kind, control is especially important because of the many flexible axes that may be adjusted and the necessary synchronism between each spindle and the sheet metal mentioned earlier. The Fagor 8070 CNC meets these requirements and offers a solution adapted to the machine.
The machine must be totally flexible and must adapt to the paths of the parts it makes. In order for this adjustment to be easily programmed and operated, the machine has been developed based on a program that reads the part code and automatically generates the paths and positioning of each degree of freedom.
The part position is known at all times thanks to a number of Fagor encoders located along the machine and connected directly to the 8070 CNC.
It is up to the 8070 CNC to generate the velocity commands for the movement, synchronize the rollers, calculate the path, etc. That’s why they’ve counted on Fagor Automation’s R&D department to develop control algorithms and specific controls adapted to the requirements of the machine. Presenting the 8070 CNC, that allows customizing its work interface, has made it possible to adapt the CNC to the machine to make the operator’s job easier.