Bending

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Boval Engineering have extensive experience in CNC metal bending. Metal bending is a highly specialised bending process which gives the ability to produce tight radius bends on sheetmetal with no wrinkles or deformation.

 

Commonly used equipment include box and pan brakes, brake presses, and other specialised machine presses. Typical products that Boval Engineering manufacture using bending techniques are boxes such as electrical enclosures and cabinets.

 

Types of CNC Metal Bending:

Air Bending

Air bending is the most common type bending used in sheetmetal manufacturing. In the air bending process the sheetmetal comes in contact with the outside edges of the die, as well as the punch tip. The punch is then forced past the top of the die into the v-opening without coming into contact with the bottom of the v. The v opening is typically deeper than the angle which is sought in the work piece. This allows for over bending to compensate for the spring back of the sheetmetal. Depending on material properties, the sheetmetal may also be overbent to compensate for springback.

 

There are many advantages of air bending when compared to other bending processes. The flexibility and relatively low tonnage required by air bending are helping to make it a popular choice, the punch tip does not need to be forced past the surface of the metal much less tonnage is required to bend compared to Bottom Bending and Coining. This gives Air Bending a significant advantage in terms of tooling, both in geometry and longevity. Air bending also means that non specific tooling can be used, within reason, the inside radius is determined by the die  width, not the  punch  tip.

 

Bottoming

Bottoming bending is the process of forcing the sheetmetal against the V opening in the bottom tool. When bottom bending  the die angle should match the intended angle of the work piece, adjusting a few degrees for  spring back, hence the  existence  of 88 ° punch tooling to achieve 90 degree angles. The sheetmetal is first bottomed against the die, then the radius of the punch is forced into the work piece which achieves the angle of the punch, it is then released and the workpiece springs back to meet the die again. U-shaped openings cannot be used.

 

Advantages of bottoming include greater accuracy and less spring back. A disadvantage is that a different tool set is needed for each bend angle, sheet thickness, and material.

Coining

Coining fabrication is a basic type of bending in which the sheetmetal is stamped between the punch and die. The top tool forces the material into the bottom die with 5 to 30 times the force of air bending, causing permanent deformation through the sheet. Both the punch tip and the punch actually penetrate into the metal past the  neutral  axis under a high amount of pressure.

 

The term Coining comes from the idea that when it comes to money each metal coin is made exactly the same as the last despite being mass produced.  From this idea the name Coining was applied to the bending method which creates accurate bends consistently.

 

The advantage of coining are that there is little, if any, spring back and coining can attain a high level of repeatability, precision, and the  ability  to reduce the inside radius to as small as desired.

Folding

In folding, clamping beams hold the longer side of the sheet. The beam rises and folds the sheet around a bend profile. The bend beam can move the sheet up or down, permitting the fabricating of parts with positive and negative bend angles. The resulting bend angle is influenced by the folding angle of the beam, tool geometry, and material properties. Large sheets can be handled in this process, making the operation easily automated.

 

The main advantage of folding is that there is little risk of surface damage to the sheet.

Wiping

Wiping bending is performed by holding the sheet between a pad and die then sliding the wiping flange across the face pushing and bending the sheet metal which protrudes from the pad and die. The flange is driven by an upper shoe and the die is supported by a lower shoe.  A spring between the pad and upper shoe grabs the metal before the flange hits it and holds the workpiece down during the bending process.  The Bend Angle is controlled by the stroke of the wiping punch.  It is necessary that the punch has the proper offset for the thickness of the material to prevent shearing.  Wiping does not allow for over bending past 90 ° because of the tooling geometry.

 

The advantages of wiping bending are high levels of repeatability and precision.

Rotary Bending

Rotary Bending is a special type of punch die combination which bends the sheet metal using a rotating cylinder with a v opening cut into the side of the cylinder.   The cylinder is seated into a saddle making up the punch section of the die.   The sheetmetal lays on an anvil and the rotary die is pushed down on top of it.   As the die engages the sheet it begins to rotate and bends the metal around the tip of the anvil. Sometimes a backing plate (not shown) called a heel keeps the saddle steady as the machine is closed and the bend completed.

 

Rotary dies provide a number of benefits over traditional punch die combination. This bending process can produce angles greater than 90° in a single hit on standard press brakes or flat presses, which compensates for spring back.  The rotary bending method is typically considered a “non-marking” forming process suitable to pre-painted or easily marred surfaces.

Roll Bending

The roll bending process induces a curve into bar or plate workpieces. Rollers are used to form a metal bar into a circular arc. The rollers freely rotate about three parallel axes, which are arranged with uniform horizontal spacing. Two outer rollers, usually immobile, cradle the bottom of the material while the inner roller, whose position is adjustable, presses on the topside of the material.

 

The rolled / curled edge provides strength to the edge and makes it safe for handling.  The curls created through roll bending come in two basic forms, off center and on center rolls.  Off center rolls have the center of the roll above the original plane of the sheet metal. On center rolls will have the center of the roll in line with the plane of the sheet metal.

 

Roll bending may be done to both sheet metal and bars of metal.

Elastomer Bending

Elastomer bending involves the bottom V-die being replaced by a flat pad of urethane or rubber. As the punch forms the part, the urethane deflects and allows the material to form around the punch.

 

Elastomer bending method has a number of advantages. The elastomer bending method is typically considered a “non-marking” forming process suitable to pre-painted or easily marred surfaces as the urethane will wrap the material around the punch and the end bend radius will be very close to the actual radius on the punch. Using a special punch called a radius ruler with relieved areas on the urethane U-bends greater than 180° can be achieved in one hit, something that is not possible with conventional press tooling.

Joggling

Joggling (joggle bending) is an offset bending process in which the two opposite bends are each less than 90° and are separated by a neutral web so that the offset is less than 5 workpiece thicknesses. Often the offset will be one workpiece thickness, in order to allow a lap joint which is smooth on the ‘show-face’.

Air Bending

Bottoming

Coining

Folding

Wiping

Rotary Bending

Roll Bending

Elastomer Bending

Joggling

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