On the Innovation Tour, we demonstrate bending precision with a Dyna-Press Pro electric press brake featuring our Easy-Form® Laser adaptive bending technology. The bending method used is air bending.
When it comes to achieving the perfect bend angle, the bending method makes a critical difference. Are you bending thick material? Material with a high tensile strength? Need to bend a small inside radius or a large radius? Are you using an older press brake?
Here’s what you should know when selecting a bending method:
Air Bending: offers flexibility
The most commonly used method of bending metal is air bending. When air bending, the position of the punch is controlled. The thickness of the sheet and the behavior of the material determine the angle that can be achieved by the position of the punch.
In air bending, the sheet metal only comes in contact with the radius of the punch and the shoulder radius of the die and is pressed to a known ram position. The V opening of the die is typically deeper than the intended bend angle. The larger the V opening, the larger the radius created.
Air bending is highly flexible as well as cost efficient because with a single die and punch all angles larger than the angle of the punch and/or die can be formed. You can use the same tooling for multiple material thicknesses because the angle is being formed by the positioning of the ram. It’s best to use precision ground tooling for air bending. While precision ground tooling carries a higher price tag, better tool steel and overall load capacity allow you to apply this tooling to a much wider range of material thicknesses and use the tools over a longer life span.
While air bending is popular for these reasons, this bending method also has the most variables to consider. Springback, bend allowance, and angle correction are just a few of the factors that must be accurately calculated.
Bottoming: delivers high accuracy
When bottoming, the sheet metal is pressed against the sides of the die allowing some space between the sheet metal and bottom of the die. In bottom bending, the bending force is the determining factor. The die angle should match that of the desired bend angle with a minor degree difference to account for springback. The depth of the punch determines the bend angle. The required force is less than what’s need for coining yet greater than what’s needed for air bending.
Bottom bending produces higher precision compared to standard air bending but has much less flexibility. This process also has limitations in that only one type of bending profile can be achieved. To obtain a radius with very large or very small radii, bottoming tools are required.
Another disadvantage is the thickness of material that can be bottom bent. Commonly, material no thicker than 1/8” can be bent using bottoming. Each material thickness and hardness require a different tooling set. As a result, bottoming is ideal for processing thin materials with little variations in material properties and thickness as well as narrow Z-bends and special profiles.
In a production environment, bottom bending will produce better part consistency than air bending and is not impacted by minor variations in sheet thickness and material properties. In thin sheets
(< 1 mm) bottoming is virtually the only method used, certainly for angles of 90 degrees and provides an angle accuracy of ± 0.25 degree, while air bending only delivers an accuracy of ± 0.5 degree. Common parts in the industry for bottom bending normally are channels, simple one-bend brackets along with parts requiring the exact radius of the punch being used.
Coining: requires high tonnage
The coining method involves using a great amount of tonnage to conform the sheet metal to the exact angle of the punch and V-die being used. During this process, the sheet metal is pressed into the bottom die causing a thinning of the material. Similar to bottoming, coining requires the tooling to match specific to the desired angle. The high amount of pressure on the sheet metal relieves internal stress of the material which eliminates springback issues. Coining is not affected by minor variations in sheet thickness or material properties; it is only impacted by applied pressure. Coining is ideal when producing a very sharp bend, for bending specific parts with very large or very small radii, or for forming narrow Z-bends or other profiles.
A distinct advantage of the coining method is that it does not require sophisticated CNC press brakes. It does, however, require very large tonnages compared to all other bending methods, up to 10 times more tonnage per foot than air bending. Other advantages of coining can be found in its high repeatability and capability to produce a very small inside radius. Disadvantages of coining fall to the wear of the machine, tooling limitations, wear of the tooling, and high tonnage requirements. Because of these restrictions, coining is mainly used in very specific applications consisting of thin material which require small inside radius such as electronics. While most any radius can be coined it is more commonly found using radius under 1mm.
Real-time Angle Measurement: measures bend angle in-process
Adaptive bending is a type of air bending. In this method, the bend angle itself is controlled. The same tool set-up is used as in air bending except that the punch position is not pre-set to a particular value. The position of the punch is controlled through the in-process angle measurement system. In contrast to air bending, the resulting bend angle is no longer influenced by the sheet thickness or the strain hardening of the material. The angle measurement system feeds data back to the control during the bend process. The control then calculates any needed adjustment in real-time and sends the new values to the machine. As a result, adaptive bending has a high accuracy.
Adaptive bending offers several advantages: manual test bending and correcting is eliminated as is the need to check parts within a batch run, scrap is reduced, set-up time is reduced and so is operator involvement.
Most press brake manufacturers offer some form of angle measurement technology, though there is variability between these systems. Beware of any system that significantly increases cycle time. A true “real-time” angle measurement system provides feedback to the machine control for positioning of the ram to produce an accurate bend without secondary compensation. Systems that do not operate in real time take a measurement of the angle at a ram position above what is required to create the bend. From the measurement taken, the system then calculates the final position to create the accurate bend angle. This all takes time, which significantly slows the cycle. For bending applications with little to no angle tolerances or materials with varying grain direction, material hardness attributes, high known elasticity and spring back make adaptive bending the best overall solution to lessen scrap and to produce perfect parts.
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