Bending and forming

Bending of sheet, plate

Most shops that process heavy-gage materials use press brakes. Light-gage metal typically forms through bending machines, described as leaf, pan, or box brakes, wing folders, and as swivel benders. Bending equipment groups into these categories:

* Mechanical press brakes with motor-driven flywheel for power, 3- to 4-in. stroke length.

* Hydraulic press brakes have a stretched C-frame. Hydraulic cylinders supply force, usually downwards, with a stroke length usually exceeding 6 in.

* Hydraulic-mechanical press brakes combine forces to push the ram toward the bed.

* Pneumatic press brakes provide low-tonnage bending.

* Automated folding equipment for light-gage, short-run, precision bending.

* Custom-built benders and panel formers designed for specific applications.

PRESS BRAKES

In press-brake bending, a workpiece placed between upper and lower dies forms through the force and pressure exerted by lowering the ram. It is a specialized type of press consisting of a long, narrow ram and bed. Manufacturers offer press brakes in a variety of sizes and capabilities, ranging from hand-operated units to machines with a capacity of 3,000 t. or more.

Mechanical press brakes operate with eccentrics forcing the ram down for bending. They offer speed and accuracy, but little flexibility compared to hydraulic brakes. With a hydraulic brake, the operator can program changes to bend angle and gage repositioning in a sequence, making a complete part per material-handling cycle.

Mating a hydraulic power source to a mechanical linkage, the hydromechanical press brake combines the benefits of hydraulics- flexibility and programmable CNC-with the accuracy and repeatability of mechanical devices.

Conventional press brakes operate in a down-acting mode-the upper ram and its punch travel downward toward lower tooling attached to a stationary bed. Conversely, up-acting machines stroke upward with the top beam stationary.

PRESS BRAKE DIES

Bending dies comprise the bulk of press-brake tooling; other tooling performs punching, countersinking, dimpling, and embossing operations.

V-type dies are the most extensive family of punches and dies for bending. The lower dies, with different die openings, for air bending have included angles of up to 85 degrees, while dies for bottom bending normally have a 90-degree angle. V-type tooling can be ordered with various material capacities and with acute-angle dies that permit forming angles as small as 30 degrees.

Rotary bending tooling eliminates the need for any type of hold- down pad or device. It provides its own inherent holding action at the same time the bending operation proceeds.

Segmented tooling allows the creation of any specific length of tool within 0.020-in. increments.

Laser-hardened tooling offers increased durability and eliminates tool distortion associated with other types of tool-hardening processes.

Plastic tooling includes urethanes and other materials used for tooling that embodies reformable dies. A key characteristic is the inherent property of changing shape while retaining a constant volume.

Material requirements determine choice of die sets and procedures. High-- tensile low-yield steels are almost as formable as mild steels. They can be formed on the same die sets.

GAGING EQUIPMENT

Successful bending depends on accurate workpiece positioning, through precise gaging, and a predictable tool stroke. How deep the punch penetrates the V die, in air bending, and how far the material is inserted into the dies determine the bend angle and location. Automatic gaging permits economical manufacturing of multiple-- bend, multiple-stroke, air-formed piece parts in one handling.

Fixed gages-mount two permanent gage blocks on the lower die. Setup depends on upper and lower die alignment to hold gage dimensions.

Nc gaging (front or back)-gage positions depend on proper calibration. Nc gages allow use of repeat setups by recalling a previous program.

Manual gages-The most flexible manual gage is the general-purpose bracket. L-shaped brackets mount in the front- or rear-dovetail slots of most press-- brake beds.

Scribed lines-an operator uses a soapstick to scribe the bend line on heavy materials. He then jogs the upper die down onto the line, locking the part in place between the dies, then completes the bend.

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