Bending Process Basics: 6 Types of Edge Bending Process

edge bending process

Edge bending

One of the most common methods used, but not always the most effective, is simple wipe bending. Unfortunately, this method does not allow for much overbending other than the very slight acute angle that can be achieved by wiping the side extremely tight. Even though wipe bending effectively creates a bend, controlling the bend angle is very difficult. This method is not well-suited to bending high-strength metals or for parts requiring precision bend angle tolerances. Wipe bending can be improved by capturing the outside profile of the radius with the forming die section.

Edge bending (wipe bending) is another very common sheet metal process and is performed with a wiping die, they are different from plate roll bending. Edge bending gives a good mechanical advantage when forming a bend. However, angles greater than 90 degrees will require more complex equipment, capable of some horizontal force delivery. Also, the wiping die employed in edge bending must have a pressure pad. The action of the pressure pad may be controlled separately from that of the punch. Basically, the pressure pad holds a section of the work in place on the die, the area for the bend is located on the edge of the die and the rest of the work is held over space like a cantilever beam. The punch then applies force to the cantilever beam section, causing the work to bend over the edge of the die.

edge bending process
edge bending process

Sheet metal of different sizes can be bent in an innumerable amounts of ways, at different locations, to achieve desired part geometries. One of the most important considerations in sheet metal manufacture is the condition of the sheet metal’s edges, particularly with regard to the part after manufacture. Edge bending operations are commonly used in industrial sheet metal processing and involve bending a section of the metal that is small relative to the part. These sections are located at the edges. Edge bending is used to eliminate sharp edges, to provide geometric surfaces for purposes such as joining, protecting the part, increasing stiffness, and for cosmetic appearance.

Flanging Bending

Flanging is bonding and forming technology used in sheet-metal forming. By bending over the edge of metal sheets using a flanging machine, the process reinforces the bent edge or creates a connection consisting of multiple components, usually to a 90 degree angle.

Sometimes the sheet metal’s material is purposely subjected to tensions or compressions, in the processes of stretch flanging and shrink flanging respectively. In addition to bending the edge, these operations also give it a curve.

The flanging process requires tools made from materials that have low friction properties and are capable of withstanding high mechanical loads.

High mechanical loads, the surface quality of the tools, dimensional accuracy, and wear resistance are the challenges presented by this application.

Beading

Beading is common in the edge treatment of sheet metal parts and can also be used to form the working structure of parts, such as hinges. Beading forms a curl over a part’s edge. This bead can be formed over a straight or curved axis. There are many different techniques for forming a bead. Some methods form the bead progressively, with multiple stages, using several different die arrangements. Other sheet metal beading processes produce a bead with a single die. In a process called wiring, the metal’s edge is bent over a wire. How the bead is formed will depend on the specific requirements of the manufacturing process and sheet metal part.

A Bead Roller is a machine tool that makes rigid lines in the sheet metal to make surfaces more rugged and durable. The line bead rollers add to sheet metal prevent warping and disfigurement by adding structural integrity to the metal.

Hemming

Hemming is a metalworking process that involves rolling the edge of sheet metal over and onto itself, essentially creating an area of two layers, in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part, and reinforce part edges.

Application

In car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming, and flanging operations to join two sheet metal parts (outer and inner) together. Typical parts for this type of assembly are hoods, doors, trunk lids, and fenders.

Accuracy

The accuracy of the hemming operation is very important since it affects the appearance of the surface and surface quality. Material deformations, which occur during the hemming process, can lead to dimensional variations and other defects in parts. Typical hemming defects are splits or wrinkles in the flange, material overlaps in the corner areas, or material roll-in. This is why it is important to use simulation tools in order to, on the one hand, better understand the hemming process and, on the other hand, significantly reduce the number of “trial and error” loops during tryout and production.

There are various types of hemming operations:

  • Conventional die hemming
  • Roll hemming
  • Conventional die hemming
  • In conventional die hemming, the flange is folded over the entire length with a hemming tool.

Conventional die hemming

Conventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool. Normally the actual hemming is a result of a farming operation in which the flange is formed with a hemming tool after the drawing and trimming operations have been completed. The formed flange is then hemmed in several process steps. These steps include, for example, the pre-hemming and final hemming depending on the respective opening angle of the flange. Production plants for conventional die hemming are very expensive, but the cycle times are very low.

Roll hemming

In roll hemming, the hemming roller is guided by an industrial robot to form the flange.

Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operation can also be divided into several pre-hemming and final hemming process steps. Roll hemming is very flexible to use and tool costs are significantly lower as compared to those of conventional die hemming. However, the cycle times are much higher since the hemming is realized using a hemming roller that follows a defined path.

Seaming

Seaming plays an important role in the processing and preparation of various metal constructions. Seaming, also referred to as hemming, is the bending and closing of metal sheets, it is a sheet metal joining process that uses a similar process of rolling sheet metal over and onto itself, except it uses a seam to join the two layers.
Seaming involves bending the edges of two parts over each other. The strength of the metal resists breaking the joint because the material is plastically deformed into position. As the bends are locked together, each bend helps resist the deformation of the other bend, providing a well-fortified joint structure. Double seaming has been employed to create watertight or airtight joints between sheet metal parts.
With hemming, the edge of sheet metal is folded so that it becomes flush with the area onto which it’s rolled. With seaming, the edge of sheet metal is folded but it doesn’t sit flush. Rather, the two layers of the folded sheet metal are joined using a seam.

Seaming is different from the ordinary bending in that the metal sheet is bent and pushed closed at up to 180 degrees, and this metalworking technology is primarily used for postprocessing of metal components for different security reasons – to improve security (for example, by protecting from getting injured by sharp, rough edges), to strengthen the structure itself, as well as to improve its overall visual appearance.

You’ll often find seams on metal roofs. The edges of metal roofs are folded and then joined using a seam. Other applications for seaming involve canned foods, automotive components, and storage sheds.

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