Technically, metal bending is rather involved due to the physical change that occurs within the material during the bending operation and also because the numerous types of alloys available each react differently when formed.

Rather than discuss these technical problems, the purpose of this booklet is to illustrate and describe the multitude of bending operations that can easily be accomplished without special engineering knowledge provided a few elementary principles are observed.

PRODUCT DESIGN – Design of the formed parts in a product generally determines whether or not they can be efficiently and economically produced.  Give careful consideration to these suggestions.

Selection of material is of first importance as it must be sufficiently ductile to produce a satisfactory bend of the smallest radius required and still be strong enough to provide the rigidity which the product demands.

It is usually desirable to designate the largest practical radius as this gives wider latitude in choice of material and often assures a better bend in both strength and appearance.

By using the same size material and designating identical radii for each bend whenever possible, the tooling of the bending machine can be simplified and the highest possible production obtained as a number of successive bends can then be progressively made in a part, thereby completing it before it is removed from the machine.

Compound bends or adjacent bends in different planes should be avoided if possible because of confliction that may occur between the bends which might necessitate special tooling.  This is especially true in tubing but also holds for solid materials.

Generally the smallest recommended radius for tubing, measured to the exact center of the tube is 1-1/2 times the outside diameter of the tube provided an inside mandrel is used when bending.  This minimum centerline radius should be increased to at least 2-1/2 times the outside diameter of the tube if the bend is to be made without an inside mandrel.

In making a bend near the end of a tube, a straight length equal to at least the diameter of the tube should extend beyond the bend.  If a bend is required to the very end of the tube, a straight length should be allowed and trimmed after forming.

SELECTION OF MATERIAL – From the numerous types of material available in tubing, extrusions, moldings, channel and solid bars, the most suitable material for production of a part can usually be chosen.

In making this selection the ductility of the material should be given prime consideration and before a decision is made a sample should be formed to the smallest required radius or assurance obtained from the supplier that the bend can be satisfactorily made.

Elasticity of the material, which causes it to spring back after it has been bent, must also be considered as it may be impossible to form a closed eye or a complete circle in some alloys.

If tubing is to be bent without an inside mandrel the heaviest practical wall should be used.  As a rule, in non-ferrous metals, on quarter to half hard tubing provides best results.  When bending channels, angles, moldings, and extrusions the centerline radius of the bend should usually be at least three times the width of the flange to be formed edgewise.

CHOICE OF BENDING MACHINE – A number of bending machines are offered on the market today and your choice of the most suitable bender can largely be determined by the range of your bending requirements.

These machines are available in both small and large manually operated models as well as power driven units some designed for one specific applications and others capable of performing a wide variety of operations.

Should your work consist only of one specialized operation such as the bending of thin wall tubing on a high speed basis, obviously a completely automatic bender is the answer.  If, on the other hand, your jobs are so varied that you are called on to form a variety of materials such as tubing, angle, channel, extrusions, moldings, and bus bars in addition to solid materials, a universal all-purpose bender will best serve your needs.

Oftentimes small parts can be formed faster and cheaper with manually operated benders provided production quantities do not warrant completely automatic equipment.

Careful study of specifications, capacities and working range of the various benders under consideration will enable you to choose the most logical unit for your own operations.

TOOLING THE BENDER – All bending machines merely provide a means of applying power either manually or mechanically to perform the bending operation and supply mountings for the bending tools. 

These tools consist of a form, or radius collar, having the same shape as the desired bend, a clamping block or locking pin that securely grips the material during the bending operation and a forming roller, or follow block, which moves around the bending form.

When bending materials of open cross section such as tubing, channel, angle and extrusions, the bending form should exactly fit the contour of the material to provide support during the forming operation.  This is also true of the clamping block and forming roller, as only by completely confining the material can a perfect bend be obtained.

Since all metals are somewhat elastic, they will spring back more or less after they are formed and for that reason he bending form must usually have a smaller radius than the required bend.  The amount of spring back is dependent upon the type of material, its size and hardness, as well as the radius of the bend and it is usually necessary to experiment somewhat to determine the exact size of the bending form. 

Bending is no different than any machining operation in that the results obtained will be direct proportion to the care taken in properly tooling the bender for the job to be done.