CNC Metal Bending

Boval Engineering has extensive experience in CNC metal bending. Metal bending is a highly specialised bending process that can produce tight radius bends on sheet metal with no wrinkles or deformation.

Commonly used equipment includes box and pan brakes, brake presses, and other specialised machine presses. Boval Engineering manufactures typical products using bending techniques, such as electrical enclosures and cabinets. Types of CNC Metal

Bending:

Air Bending

Air bending is the most common type of bending used in sheet metal manufacturing. In the air-bending process, the sheet metal 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 more profound than the angle sought in the workpiece. This allows overbending to compensate for the spring back of the sheet metal. The sheet metal may also be overbent depending on material properties to pay 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 cargo is required to bend compared to Bottom Bending and Coining. This gives Air Bending a significant advantage in 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 forces the sheet metal against the V opening in the bottom tool. When bottom turning, the die angle should match the intended angle of the workpiece, adjusting a few degrees for spring back, hence the existence of 88 ° punch tooling to achieve 90-degree angles. The sheet metal is first bottomed against the die, and then the radius of the punch is forced into the workpiece, which reaches the punch's angle. It is then released, and the workpiece springs back to meet the die again. U-shaped openings cannot be used.

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

Coining

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

The term Coining comes from the idea that when it comes to money, each metal coin is made precisely 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 is that there is little, if any, spring back. 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 folding angle of the beam, tool geometry, and material properties influence the resulting bend angle. This process can handle large sheets, 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. An upper shoe drives the flange, and the lower shoe supports the die. 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 stroke of the wiping punch controls the Bend Angle. The punch must have the proper offset for the thickness of the material to prevent shearing. Wiping does not allow for overbending 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 type of punch die combination that 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 sheet metal 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 several benefits over traditional punch die combinations. This bending process can produce angles greater than 90° in a single hit on standard press brakes or flat presses, compensating for spring back. The rotary bending method is typically considered a “non-marking” forming process suitable to pre-painted or quickly 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 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 strengthens the edge and makes it safe for handling. The curls created through roll bending come in two primary forms: off-centre and on-centre rolls. Off-centre rolls have the roll's centre above the sheet metal's original plane. On the centre, rolls will have the centre 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 replacing the bottom V-die with a flat pad of urethane or rubber. As the punch forms the part, the urethane deflects and allows the material to create around the punch.

The elastomer bending method has several advantages. The elastomer bending method is typically considered a “non-marking” forming process suitable to pre-painted or quickly marred surfaces as the urethane wraps the material around the punch, and the end bend radius will be very close to the actual radius on the punch. A special punch called a radius ruler with relieved areas on the urethane U-bends greater than 180° can be achieved in one hit, which is impossible 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 five workpiece thicknesses. Often, the offset will be one workpiece thickness to allow a smooth lap joint on the ‘show-face’.