Fabrication

Below is an introduction to the topic Fabrication. You can also search for your specific topic using the Search box at the top of the page or click on any of the following keywords and phrases: Cutting and burning; Drilling; Welding; Assembly.

Introduction

Fabrication, when used as an industrial term, applies to the building of structures, by cutting, shaping and assembling components made from steel. Steel fabrication shops generally concentrate on the preparation, welding and assembly aspect with a much greater use of the multi functioning machines many aspects of the labour intensive work is now automated.

Fabrication (cutting and drilling features) of structural steel elements has always been performed using manually operated techniques, and these remain today as fabrication methods. The emergence of CNC (computer numerical control) technology brought automation and greater accuracy to these techniques, resulting in families of special purpose machines dedicated to performing individual fabrication tasks

Cutting and burning

The steel plates or sections have to be cut to size. This is done with a variety of tools. The most common way to cut steel is by Shearing, this is a metalworking process which cuts without the formation of chips or the use of burning or melting. Strictly speaking, if the cutting blades are straight the process is called shearing. The most commonly sheared materials are in the form of sheet metal or plates.

Special band saws designed for cutting metal have hardened blades and a feed mechanism for even cutting. A band saw uses a blade consisting of a continuous band of metal with teeth along one edge. The band rides on two wheels rotating in the same plane. Band sawing produces uniform cutting action as a result of an evenly distributed tooth load.
Abrasive cut-off saws, also known as chop saws, are similar to miter saws but with a steel cutting abrasive disk.

Cutting torches can cut very large sections of steel with little effort. In oxy-fuel cutting, a cutting torch is used to heat metal to kindling temperature. A stream of oxygen then trained on the metal combines with the metal which then flows out of the cut (kerf) as an oxide slag.
Burning machines are CNC cutting torches, usually fuel gas powered, plasma or laser cutting. Steel is loaded on a machine bed and the parts are cut out as programmed. The support bed is made of a grid of bars that can be replaced. Some burning machines also include CNC punch capability, with a carousel of different punches and stamps. The preparation of structural steel by plasma and laser cutting introduces robots to move the cutting head in three dimensions around the material to be cut. Preparation of dimensional (non-flat) sections has historically been performed by sequential operations involving sawing, drilling and high temperature flame cutting to remove material. Each of these operations is performed on special purpose machinery; hence the time involved in loading and unloading and transporting the structural steel elements between machines can add considerable time to the total fabrication process.
In recent years, developments in plasma cutting and laser cutting of metals have been combined with computer motion control to accomplish the sequential operations on a single machine. This has the advantage of minimizing the non-productive loading and unloading transport time, and can also improve dimensional accuracy of the fabricated element, due to the use of position sensors and highly accurate servo motor drives to position the cutting head or "torch" of the machine.

Drilling

A drill line has long been considered an indispensible way to drill holes and mill slots into beams, channels and sections. CNC drill lines are typically equipped with feed conveyors and position sensors to move the element into position for drilling, plus probing capability to determine the precise location where the hole or slot is to be cut.

Welding

Welding is a major focus of steel fabrication. The formed and machined parts will be assembled and tack welded into place then re-checked for accuracy. The welder then completes welding following the weld specification to match the requirements of the general arrangement.

Special precautions may be needed to prevent warping of the steel due to heat. These may include; re-designing the weld to use less weld, welding in a staggered fashion, using a strong back to keep the shape required, and straightening operations after welding.

Final assembly

After the steel has been cut, drilled and welded and has cooled it is generally shot blasted, primed and painted. Any additional manufacturing specified by the customer is then completed. The finished product is then inspected and made ready for transportation to site.