Background: Structural Steel Components
Structural steel is typically thought of as the “skeleton” of multi-story construction, in that it gives the framework upon which floor, wall and exterior cladding systems are affixed. Individual pieces of structural steel (interchangeably named elements, sections or members) are created in steel mills or foundries, conforming to chemical composition and geometric/dimensional specifications established by regulatory agencies and business associations, such as the American Institute of Steel Building.
The most common structural steel elements are beams (also known as I-beams, H-beams or girders), channels, HSS (for hollow structural shapes), angles, columns and plate. These components are cut to essential lengths and joined together, either by welding or mechanical fastening (bolting) in the manner prescribed to accomplish the objectives for supporting each static and dynamic loads.
Traditional Fabrication Strategies
Fabrication (cutting and drilling features) of structural steel elements has often been performed utilizing “metal against metal” techniques, and these stay the most widespread fabrication strategies nowadays. The emergence of CNC (personal computer numerical manage) technology brought automation and greater accuracy to these techniques, resulting in families of unique objective machines dedicated to performing individual fabrication tasks.
Non-CNC Metal Cutting Bandsaw – Horizontal Kind
Maybe the most common such machine is the bandsaw. A bandsaw employs a continuously rotating band of toothed metal to saw via the structural steel and is normally utilised to reduce via the complete cross section of the element to attain the prescribed length.
A beam drill line (drill line) has lengthy been regarded as an indispensable way to drill holes and mill slots into beams, channels and HSS components. CNC beam drill lines are normally equipped with feed conveyors and position sensors to move the element into position for drilling, plus probing capability to establish the precise place where the hole or slot is to be reduce.
For cutting irregular openings or non-uniform ends on dimensional (non-plate) elements, a cutting torch is usually utilized. Oxy-fuel torches are the most common technology and range from easy hand-held torches to automated CNC ‘coping machines’ that move the torch head around the structural element in accordance with cutting guidelines programmed into the machine.
Fabricating flat plate is performed on a plate processing center where the plate is laid flat on a stationary ‘table’ and different cutting heads traverse the plate from a gantry-style arm or “bridge.” The cutting heads can include a punch, drill or torch.
Plasma and Laser Technologies Applied To Industrial Metal Cutting
Plasma Cutting – a technologies that grew out of plasma welding in the 1960s – emerged as a quite productive way to reduce sheet metal and plate in the 1980s. It had the advantages over standard “metal against metal” cutting of generating no metal chips and providing accurate cuts, and made a cleaner edge than oxy-fuel cutting. Early plasma cutters were massive, somewhat slow and costly and, consequently, tended to be committed to repeating cutting patterns in a “mass production” mode.
Industrial Laser Cutting of Steel with Cutting Directions Programmed Through the CNC Interface
As with other machine tools, CNC (pc numerical manage) technologies was applied to plasma cutting machines in the late 1980s into the 1990’s, giving plasma cutting machines higher flexibility to cut diverse shapes “on demand” based on a set of instructions that were programmed into the machine’s numerical control. These CNC plasma cutting machines were, however, usually restricted to cutting patterns and parts in flat sheets of steel, using only two axes of motion (referred to as X Y cutting).
Industrial laser technologies followed a commercialization path for industrial use equivalent to that of plasma, but roughly a decade later. Industrial laser cutting technology for metals has the positive aspects over plasma cutting of being far more precise and utilizing much less power when cutting sheet metal, however, most industrial lasers can’t cut via the greater metal thickness that plasma can. Newer lasers machines operating at greater power (6000 watts, as contrasted with early laser cutting machines’ 1500 watt ratings) are approaching plasma machines in their potential to cut by means of thick components, but the capital expense of such machines is a lot higher than that of plasma cutting machines capable of cutting thick components like steel plate.
The majority of industrial laser cutting machines are also employed to reduce flat supplies, employing two axes of motion for the cutting head.
Multi-Axis Plasma and Laser Cutting of Structural Sections
Beginning in the late 1990s, programmable industrial robots had been integrated with plasma and laser cutting to allow these metal cutting technologies to be applied to a lot more generalized cutting of non-flat shapes. These “3D Systems” use the industrial robot to move the laser or plasma cutting head around the element to be reduce, so that the cutting path could encompass the complete outer surface of the element. Numerous systems also grip the element to be reduce in a “chuck” so that the element itself can be rotated or indexed forward or backward in concert with the movement of the cutting head. This serves to reduce general cutting time and improve accuracy by optimizing the motion of the element with the motion of the cutting head.
Robotic 3D laser cutting systems regularly make use of this strategy of moving the element to be reduce, due to the fact laser systems function effectively with smaller thin-wall components such as tubes. As OD and wall thickness of the pipe/tube increases, 3D laser cutting becomes significantly less appealing due to the improved cutting time and higher capital expense of laser cutting technologies.
Robotic plasma cutting is far more extensively employed for 3D cutting of pipe, including HSS, utilized as structural steel components. Vernon Tool Firm was an early innovator in creating 3D plasma cutting machinery for oil/gas field and structural tube/pipe. Similar systems introduced by QuickPen, Watts Specialties and Bickle Manufacturing are capable of cutting pipe diameters up to 32 inches and producing straight, angled and saddle cuts, like beveled-edge cuts needed for joining collectively distinct pipes.
The task of robotic plasma cutting of more diverse shapes, such as beams and channels, has proven to be much more challenging. The large sizes and assortment of shapes involved make the approach of gripping the structural steel element in a chuck impractical. This locations the entire burden of cutting motion back on the robot. In order to have the cuts and attributes placed exactly where they are intended on the element, the robot must be given some instruction as to the place, size and shape of the element.
Robotic plasma cutting of a structural steel beam
Burlington Automation developed software capable of reading CAD drawings of the structural element, and combining this info with motion manage and sensor feedback to arrive at a 3D plasma cutting method that in impact “sees” the structural steel element it is to reduce. There are no vision systems involved, rather the robotic arm that carries the plasma torch head gently touches (probes) the element to be cut in numerous places and combines this information along with the CAD drawing information to determine the exact contours of the element in 3 dimensions. With this info, the robotic plasma cutting system, which goes by the trade name PythonX is capable to reduce a range of functions (bolt holes, copes, notches) or marks into precise locations along the structural elements. This extends the automated 3D plasma cutting capability pioneered by Vernon Tool and other individuals to the complete variety of structural steel components, hence permitting the PythonX system to replace beam drill lines, coping machines, bandsaws and plate burning centers.
If the previous is prologue, it may possibly be anticipated that robotic 3D laser cutting technologies will quickly be commonly applied to the fabrication of structural steel elements, as has already been done with plasma cutting. The steel thickness limitation of laser cutting has been overcome by the evolution of more potent laser systems. Even so, as a general rule, tolerances on structural steel elements are less exacting than for other manufactured steel goods (such as auto components), for that reason the additional precision that laser cutting provides is generally not required for structural steel. Places of exception might be structural components for ships and massive, highly customized fabrications for power plants. For the time becoming, the reduce capital cost and greater cutting speeds of robotic 3D plasma cutting make it the technologies of option for generalized fabrication of structural steel elements.
^ How Structural Steel Is Produced by Bradford McKee, Contemporary Steel Construction, August 2007.
^ The Life and Times of Plasma Cutting – How The Technologies Got Where It Is These days by Thierry Renault and Nakhleh.
^ Making Plasma Cutting Easier – Using CNC Automation Technology by Brad Thompson and Kris Hanchette, The Fabricator, August 2003.
^ Science Nonfiction by Kevin Cole, The Fabricator, August 2002.
^ Tube, Profile Cutting With Lightning Speed – Laser Cutting Tube With A Rotary Axis by Dr. A. Pieter Schwarzenbach, The Fabricator, October 2005.
^ Focusing On Tube Cutting Lasers by Eric Lundin, Tube & Pipe Journal, November 2002.
^ Generating Hands-Totally free Straight, Saddle and Miter Cuts by Eric Lundin, Tube & Pipe Journal, June 2003.
^ Burlington Automation – Breaking The Robot Barrier Case Study from ABB Robotics.
How stuff functions – Plasma cutters
How stuff performs – Laser
Background: Structural Steel Components