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Plate Rolling Process and Plate Bending Process

Metal sheet and plate rolling play an essential part in metal fabrication.

Plate Rolling

plate rolling machine
Plate Rolling Machine

Metal sheet and plate rolling is typically the 2nd step in the tank or ductwork fabrication process after the flat sheet or plate is typically cut to size on a CNC laser or plasma cutting table, the metal plate rolling process is used for steel and aluminum plates into full cylinders, cylinder segments, full cones, and cone segments for future fabrication at your facility. Plate rolling can help form tanks, metal ductwork, pipe, cones, and more.

Plate rolling machines typically use a series of hardened precision rolls utilizing either hydraulic or mechanical power.

Plate rolling machines work with a wide range of materials in sheet metal and heavy plate rolling services. Plate rolling machines can roll plates in most metal materials and grades. For sheet metal, a plate roller can roll aluminum, stainless steel, galvanized steel, mild steel, painted, and polished materials.

Plate rolling process

In the plate rolling process, a flat plate of metal is formed into a specific curve or radius. The plate is placed between rollers, which turn in opposite directions, and which have a gap smaller than the thickness of the metal plate. As the plate moves between the rollers it is compressed or made thinner. As the work is performed, the plate is eventually molded into a full cylinder, cylinder segment, full cone, and cone segment that can then be used as part of a fabrication project.

Plate Rolling Capacities

The narrower the width of the plate entering the machine, the thicker the one plate that can be rolled. For example, the plate bending machine can roll a 2″ thick, 12′ wide steel plate, or it can roll a 12″ thick, 3′ wide steel plate. The bending rolls can also roll thick material to very tight diameters—for example, 2″ thick, 10″ wide material can be rolled to a 19″ diameter.

The type and grade of the material determine both the largest dimensions that can be rolled and the minimum radii that can be rolled. For harder materials, maximum heavy plate rolling dimensions become smaller and minimum radii become larger.

Applications for Heavy Steel Plate Rolling

While there are countless applications for rolled plate and rolled sheet metal, encounter certain applications more than others. The heavy plate rolling services are most often used to create components for metal duct work, circular tank walls, machine housings, piping, stacks, molds, and bridges.

The Math Behind Plate Rolling

The plate rolling process entails two groups of important variables. The first group hinges on the machine, such as the number of rolls, their diameter, position, and how they move. All these depend on the machine being used. The second variable group deals with the workpiece involved, such as the maximum plate width (W), maximum plate thickness (Th), and minimum workpiece diameter (Ø), as well as the type of metal and its yield strength (YS). These variables can be plugged into an equation: W x Th2 x YS/g = K, where K is the constant and g is a parameter that takes into account the workpiece diameter and the machine geometry.

Applying such equations requires detailed application information, of course, but the important takeaway here is the factor Th2. Note that the sheet thickness value is squared, implying that a small change in thickness can have a dramatic effect on roll parameters.

PER-BENDING PROCESS

The per-bending process involves pinching the plate material firmly between two of the rolls and then using the side or lateral roll to force the material into an initial bend before rolling commences. This process must be repeated on each end of the plate being rolled to avoid large flattened sections at the mating ends of the cylinder.

Pre-Bend capacity is always less than that of the rated bending capacity so it is important to ensure the rolling system you are looking at can properly pre-bend the material you are working with.

4 REASONS PRE-BENDING IS CRUCIAL IN THE PLATE ROLLING PROCESS

  1. Eliminates Waste: The pre-bending process helps minimize waste by creating an optimum geometrical formation so that both ends of the material can get in touch after rolling as perfectly as possible. Practicing the pre-bending process while having experience and being a skilled plate rolling machine operator plays a very critical role in eliminating waste.
  2. Eliminates the Need for Extra Trimming: The resources used on extra material trimming in plate rolling are nothing to be ignored for any efficiently and effectively functioning fabrication shops or operations. The need for extra trimming can easily be avoided through pre-bending by forming an optimum alignment of both ends of plate metal after rolling the material.
  3. Saves Time: Especially for high-volume production shops, wasting a minute out of the production time means wasting money and it can add up really fast over time. Since pre-bending helps an operator to form the desired shapes faster, the operating time per plate metal on a plate bending machine diminishes, which means rolling more parts with less time.
  4. Smooth Bending Surface and Uniform Curvature / Thickness: The pre-bending process is one of the most important practices in plate rolling when it comes to being able to get the results that were initially intended to get, which is simply rolling the material correctly. Properly rolled material will inevitably result in smooth material surface and uniformity in material curvature and thickness.

MINIMUM BENDING RADIUS

The minimum diameter is the smallest diameter you desire to roll your material into because it is a great driving factor for the size of the machine that will be appropriate for your workshop’s certain needs.

There’s a rule of thumb to determine a steel’s minimum bend radius: Divide 50 by the material’s tensile reduction percentage as specified by your supplier. This value will vary by grade.

If the steel has a tensile reduction value of 10 percent, divide 50 by that value: 50/10 = 5. Next, subtract 1 from that answer: 5 – 1 = 4. Now, multiply that answer by the plate thickness. If the material is 0.5 in. thick: 4 × 0.5 = 2. So in this case, the minimum inside bend radius is 2 times the material thickness.

Plate Bending

Steel plate bending is used to create U shapes, V shapes, or channel shapes along a level axis in ductile materials such as sheet metal. Common equipment used within this manufacturing process includes brake presses, box, and pan brakes, and other specialized machine presses.

Plate Bending Process

In the press brake forming process, a workpiece is placed over the die block which presses the sheet to create the desired shape. When bending is complete the material will attempt to spring back towards its initial position; therefore the workpiece must be over-bent in order to achieve the desired angle. The amount of spring back is totally reliant on the workpiece material and the type of bending.

Air Bending

This process works by pressing a punch onto the workpiece and forcing it down into a bottom V-shaped die. This die is mounted onto the press. The punch creates the bend so that the space between the side wall of the V and the punch is larger than the thickness of the workpiece. As this process requires less bend force, it tends to use smaller tools than other techniques. Air bending is extremely flexible, allowing a number of different materials and thicknesses to be bent at variable angles. This process also requires fewer tool changes than other methods, meaning higher productivity.

Bottoming

In the bottoming technique, sheet metal is forced against the V opening within the bottom tool. A set amount of space is left between the bottom of the V opening and the workpiece. This method offers more precision and less spring back, but a different tool set will be required for every different material, bend angle, and thickness.

Coining

In the coining process, the top tool forces the material down into the bottom die with 5-30 times the amount of power of air bending. This causes perpetual deformation through the workpiece and there is very little spring back if any at all. This method offers high levels of accuracy.

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