Bending, projection, shearing, staking

Bending is a process by which metal can be deformed by plastically deforming the material and changing its shape. The material is stressed beyond the yield strength but below the ultimate tensile strength. The surface area of the material does not change much. Bending usually refers to deformation about one axis.

Bending is a flexible process by which many different shapes can be produced. Standard die sets are used to produce a wide variety of shapes. The material is placed on the die, and positioned in place with stops or gages. It is held in place with hold-downs. The upper part of the press, the ram with the appropriately shaped punch descends and forms the v-shaped bend.

Bending is done using Press Brakes. Large and small presses are used for specialized applications. Programmable back gages, and multiple die sets available currently can make for a very economical process.

Air Bending is done with the punch touching the work piece and the work piece, not bottoming in the lower cavity. This is called air bending. As the punch is released, the work piece ends up with less bend than that on the punch (greater included angle). This is called spring-back. The amount of spring back depends on the material, thickness, grain and temper. The spring back usually ranges from 5 to 10 degrees. Usually the same angle is used in both the punch and the die to minimize setup time. The inner radius of the bend is the same as the radius on the punch.

Bottoming or coining is the bending process where the punch and the work piece bottom on the die. This makes for a controlled angle with very little spring back. The tonnage required on this type of press is more than in air bending. The inner radius of the work piece should be a minimum of 1 material thickness in the case of bottoming; and up to 0.75 material thickness, in the case of coining.

Projection welding is a variation of spot welding. Projections are designed in one part. These act as current concentrators for the welding process. When the two parts are mated together, these projections are the high points that first make contact. As the power is cycled, the projections simultaneously carry the current and are welded. This process is known as Resistance Projection Welding, RPW.

Due to the efficiency of power transfer, thicker materials can be successfully welded. Materials as thick as 3 mm (0.125 in) can be successfully welded. For thin stock, the traditional spot welding is a preferred method.

Low carbon steels, low alloy steels, stainless steels, as well as aluminum can be welded using this process.

Projections are usually semi-spherical or blunt conical type.

Projection welding requires that the height of projections be controlled to within a range of 0.075 mm (0.003 in).

Shearing is a process for cutting sheet metal to size out of a larger stock such as roll stock. Shears are used as the preliminary step in preparing stock for stamping processes.

Material thickness ranges from 0.125 mm to 6.35 mm.

The shearing process produces a shear edge burr, which can be minimized to less than 10% of the material thickness. The burr is a function of clearance between the punch and the die (which is nominally designed to be the material thickness), and the sharpness of the punch and the die.

Staking is a method of fastening (usually sheet metal) by squeezing protrusion formed in one part inside a hole in the second part, and then deforming the protrusion. The act of deformation causes radial expansion of the inner part and locks it in the hole.

Exercises

1. Learn the following words and word combinations:

bending -згинання

projection -рельєф

shearing -зрізування

staking -закарбування

yield strength -зворотня сила

tensile strength -сила напруги

die -матриця, прес-форма

ram -прес-штемпель

brakes -гальма

punch -перфоратор

resistance projection welding -рельєфне зварювання

blunt conical type -тип тупого конусу

stock -заготівка

preliminary -попередній, завчасний

burr -задир

Дата добавления: 2015-11-16