Bending stabilizing bars used to be a process that required heat. In some particular cases and for certain types of material, this process is still used owadays. After having been shaped, the material undergoes to a thermal treatment. This process was the only one known that was able to grant an homogeneous bending and the lack of cracks induced by warping shock.

Metamorphosis of the geometric shape
Several years ago, the shape of the stabilizing bar was quite a simple one: straight in the middle part, and bended at the two ends. This shape allowed to perform the thermal treatment after bending (800°-900° Celsius) with acceptable warping.

With the new technologies as well as new demands and needs, the middle part had to be adapted to narrow and winding lines.
Furthermore, by using the warping reaction of the bar in particular conditions of the vehicles when driven in curves, during a brake, when accelerating etc it was possible to apply to the bar the few sensor that control the safety of the working vehicle – such as ABS and stability.

These two factors changed completely the classic shape of the bar by imposing an increasingly complex geometry. In order to have these requisites, a normal stabilizing bar is made up of at least about ten curves up to 20-25 curves for the most complex applications.

Weight metamorphosis
Another change was imposed because of the constant need of decreasing the weight of the vehicle; also the bar had to be decreased in weight as well. Because of this need, the stabilizing bar made in pipe was projected; also this bar has to follow the strict geometric shapes discussed previously.

Hot bending process
The bar, coming from an oven (with an internal heat of about 900° degrees) is placed in a machine that can perform heat bending, and shaped. Afterwards, it is placed in a bath of oil to undergo the thermal treatment. The working cycle for shaping the bar takes about fifteen seconds – time can vary according to the bending cycle. During this lapse of time, two processes occur:
• Bar oxidation due to the contact with the atmosphere
• Partial cooling of all the bended parts that are placed within the bending tools the result of this irregular cooling generates a variable roughness (after thermal treatment) in various parts of the bar.
During the cooling of the bar in the oil bath there is another important negative factor taking place: the geometric warping. When this warping exceeds the tolerance range, a recalibration process has to be performed.

Cold bending process employing a double head machine ’Montorfano’ standard system
Montorfano S.a.s, a company in Cantù, has a long experience with cold bending processes. It was founded in 1965, and it produces double head bending machines to cold bend metallic wire, bars, sections and pipe. Since the beginning, it’s imposed itself on the market with its ‘balanced’ bending process, which consists in bending both ends of the piece at the same time.
The piece is locked in the middle and bended at its ends with the two heads. The two heads, rolling on the piece axis, move to another position for the next bending; this is performed until the end of the cycle.
The following years have been full of innovations and patents concerning the double head bending system. The first innovation that granted the space bending of the double head was a hydraulic controller that could provide 3D bending and would allow to execute two bends at the same time. This happened about thirty years ago.

In 1979 the first electronic controlled machines were produced with a series of patents that characterized the most interesting solutions and with an incredible range of new possibilities due to the use of electronic technologies.
The new CNC models were produced thanks to these new technologies; these machines can satisfy the need for flexibility maintaining the ease of use in particular in the bending tools. Having a bending tool that is easy to use and simple allows to work the piece, even in the narrow spaces in which tools cannot operate well.
Flexibility, due to the simplicity of the bending machines, has allowed Montorfano to get in the stabilizing bars field by producing a specific equipment that was supplied to an important German company, world leader in this field. This allowed to Montorfano to increase the search for new solutions, and to produce rolled steel that grant the lack of internal cracks during cold bending. After the bending, thermal treatment would take place. This led to the following advantages:
• Cold bar manipulation
• Easy and compact bending equipment
• Lack of superficial oxidation
• mConstant roughness after tempering
• Possibility to perform additional works

Cold bending of pre-tempered bar
The advantages granted by cold bending would face the warping problem during thermal treatment, just like it would happen with the hot bending process.
The continuous research on steels led to obtain the pre-tempered bar that can be bended with a cold process with the absence of internal cracks and/or breaks. Parallel to this research, the bending process was modified and it started to be adjusted to the increasingly complex shapes of the bars. Furthermore, automation was added to the process and this simplified it even more.
Bending capability was enhanced due to the high endurance of the pre-tempered materials, both bars and pipes. These results and the success could be achieved thanks to the ‘elastic’ structure of the machine together with the rigidity and power of the two bending mandrills as well as their sophisticated electronic control.
The new simplified bending process takes place with the following steps:
• The bar or pipe are placed within the bending tools of the machine. The loading operation can be manual or automatic, or even robot controlled.
• Cold bending that can realize 3D bends with fixed and/or variable radius.
• Automatic unload of the bended piece
• Stretching treatment at about 160° degrees

Robot controlled shaping isle
The steps described in the previous paragraphs have allowed Montorfano to acquire the necessary know-how to build up a totally automated isle to perform cold bending of the pre-tempered stabilizing bar. The standard isle is made up of:
• Universal bending machine patent mod. 2030M-DS
• ABB loading robot
• Bar loader
• Piece shaping station (if desired)
• Shaped piece unloading station
The shaping sequence, managed by the control unit of the bending machine, is totally automatic, and it takes place with the following steps:
• The bar or pipe are placed by the robot in the bending machine, and the shaping operation starts automatically (if the bar or pipe have already shaped ends, the bending machine orients them and starts the bending cycle).
• During the bending cycle the robot unloads the piece that was previously bended and (if required) places it in the machine to outline the two ends. Afterwards it takes a new bar from the bar stock, and places it in front of the bending machine, ready to be loaded.
• At the end of the bending cycle, the machine unloads the piece on the waiting prop, and the robot loads the new piece and starts the new bending cycle.

‘Zero Arm’ bending
New Montorfano’s patent deposited in January 2008
The increasingly complex geometry of the bar led to make bends closer and closer to each other, thus eliminating the straight part inbetween bends. The straight line is very important to perform the bending process, and therefore when it is missing it becomes harder to bend the piece.
The biggest problem lies in the bending equipment that has to be built by outlining the matrix to accommodate the part that was previously bended. If the following bend has the same problem, the matrix has to be outlined again, but, since it already has the previous outline, it cannot contain any more.
On the pipe bending machines this problem is solved by building more than just one bending matrixes one on top of the other. This solution is complex and expensive, and it has a big downfall: if the distances between one bend and the other are modified even by a few millimeters, or if the orientation is modified or the width of the bends, all the equipment has to be modified or redone.
Another problem is given by the encumbrance of the matrixes, because it can preclude the fast and easy placing of the matrix in the bending spot.

Montorfano’s new patent, applied to double head bending machines, solved all these problems in bending both pipes and bars. The bending cycle is fully performed with only one matrix and one bending roller that are placed on any reversible bending unit of the machine.

The geometric disposition of the matrix related to the bending roller are the center of the machine. This solution allows to have a simple equipment with a reduced encumbrance. As a result, this equipment grants an exceptional flexibility that makes it easy to bend even the most complex shapes, which are commonly requested by the automotive sector.
The new patent also allowed to maintain the same features such as:
• Variation of the bending radius on the pipe, obtained with the same equipment and during the same cycle (patented by Montorfano in 1993)
• Variation of the 3D plans between bends (patented by Montorfano in 1984) and now can be performed also with the absence of the straight part without modifying the matrix
• Automation of the bending program, starting with polar or Cartesian coordinates, and simulation of the bending cycle

Bending precision, shape repeatability, short performing time of the cycle
The piece that has to be bended is placed manually or automatically within the bending tools of the machine, and the shaping cycle can begin. The first task performed by the machine is locking the piece that is locked throughout the whole cycle. Immediately after locking, the piece is bended according to the sequence and shape programmed.
This feature grants two essential requisites that are normally always demanded, especially for important pieces such as stabilizing bars:
• Precision bending, respecting strictly the measures requested (distances, angles, third dimension)
• Repeatability of the shape

All these operations are strictly pertinent to the worked piece: there are no matrix changes (see the previous paragraph), or piece movements during bending. Furthermore, the double head (that can perform two bends at the same time) reduces considerably the machine working cycle. This feature has as a result a more brilliant production, which increases the possibility to produce pieces with more precision and repeatability.

Automatic planning MONCAM
The attention to planning and the frequent updates of the control software allowed to maintain a simplicity in programming the machine; this allows the operator to elaborate the working sequence in an intuitive and fast way. In one single line of code there is the information regarding two bends such as:
• The position of the bend
• The bending radius
• Width
• The bending verse (clockwise, counter-clockwise)
• Distance
• Third dimension
• Axis speed
• Sixth axis intervention
• Advance or postponement of the operations
• Combined bending
• Elasticity correction
• Other units intervention (radius correction, deflector, cut, lock etc.)

To increase the speed in programming more complex pieces which have a high number of bends, Montorfano implemented a software – MONCAM – that can realize the machine program automatically, considering all the information regarding the operations listed above.
To activate the software, only the Cartesian or polar coordinates are necessary. Other than writing the machine program, it can also display the graphic of the piece, the bending simulation, the development of the bends, the end to end quota, and the timeframe of the cycle.

MONCAM can be installed on the server that, through LAN, can transfer and/or call the program to and from the machine. Furthermore, the LAN connection allows to verify the status of the machine, the production time, the already bended pieces and those that are yet to be worked, the weight of the material etc.

By Renzo Montorfano