The technique of plasma cutting it is best known for its simplicity and ability to cut through virtually any metal. These qualities, added to the productivity it offers, have transformed plasma cutting into a universally accepted resource that enjoys a large number of applications.
Although the plasma cutting process has been used commercially for half a century, it should be noted that the greatest engineering achievements that have contributed to improving its performance have occurred in the last 10-15 years, a trend that continues today. .
In previous articles of Of Machines and Tools We provide details about the fundamentals and basic equipment of plasma cutting, we present the types of machines most used in this technique and we include a video of the operation of these machines. In this article we are going to delve into the advances in mechanized plasma cutting.
Plasma cutting technologies
The flexible nature of the plasma cutting process lends itself to many applications and capabilities. Generally, plasma cutting systems can be classified into three different categories which we mention below.
air plasma: Designed for hand torch cutting, these systems are available in 12 amp power level outputs, with a maximum cut thickness of 1/8 inch and a hand torch, up to 120 amps. Most air plasma cutting equipment employs inverter technology, making it portable. Many can be purchased with a machine torch and have electrical interfaces that allow them to be used in mechanized cutting applications.
Conventional mechanized plasma: Typically, these systems are provided only with torches installed on a motion device (a CNC cutting table, a robot, or a cutting turtle running on a rail) and have more complex interfaces to provide better performance when used. used in applications with cnc cutting machines. Power levels for these systems range from 130 amps to as high as 1000 amps.
Designed for high productivity with mid-level tolerances for cutting non-ferrous materials (stainless steel and aluminum) up to 4 inches thick, these systems are widely used in steel, shipbuilding and heavy machinery industries. Although some manufacturers of these conventional mechanized plasma systems have introduced improvements, such as technology designed to extend the life of oxygen consumables and sophisticated interface systems that can communicate with the common PC-based CNC used in most of the current cutting machines, these systems still maintain great similarity with the industrial cutting machines conventional used during the last 20 years.
For the most part, this class of machine requires an experienced operator capable of addressing the multiple setup parameters required to achieve consistent cut quality. These systems require continuous monitoring of arc voltage, gas flow, and pressure, as well as many other parameters that must be set correctly to produce the best cut quality, such as power level, material thickness, and consumable parts. .
High Definition Mechanized Plasma: High-production plate and sheet cutting is the category that is receiving the most attention in terms of process research and development. As a result, high definition plasma cutting systems have made great strides in quality, speed, power level, operating costs, and more recently, ease of use.
In high-definition mechanized plasma cutting, developed some 20 years ago, the plasma arc is forced through a smaller orifice in the nozzle, taking full advantage of the laws of high-temperature physics. This produces cleaner, squarer edges while keeping torch consumable life at acceptable levels.
Early systems were limited in amperage and thickness capacity (70 amps for a maximum thickness of 3/8-inch steel) and required a skilled operator to monitor and adjust various parameters that affect cut quality. However, even in its early stages, high definition plasma technology stood out as one of the first three or four developments in the history of plasma cutting.
Today’s high definition mechanized plasma systems are available in amperages from 130-800 with a capacity to cut thicknesses from 3 inches in mild steel and up to 4 inches in steel and aluminum. Consumable life and cut quality and consistency have improved substantially in recent years, making these systems a primary choice for metal cutting among sheet metal fabricators. Low operating cost, high cutting speeds and improved quality are the results of applied high-level engineering and have greatly increased demand.
In the video that follows we will see some applications of high definition mechanized plasma cutting.
Although research and development continues today, many of the recent advances in cut quality, consumable life, productivity, and ease of use are based on what used to be thought of as “external systems” in the laser cutting process. mechanized plasma.
While it has always been known that machine motion (accuracy, acceleration, and smoothness), torch height control (pierce height, cut height, collision avoidance, and cycle times), and CAM software (post-processing for width of cut, entry and exit point settings, and nesting) serve important functions that affect mechanized cutting operations in terms of cutting accuracy, operating cost, and performance, the parameters associated with each of these external systems have always been controlled by the programmer and the machine operator. A cutting operation with a skilled programmer and experienced operator could produce higher quality than an operation with less attentive or less experienced staff.
Knowing that greater control of critical operating parameters that affect all levels of performance in a high-definition plasma system could further improve cutting processes on a production floor, systems engineers got to work. The manufacturers of these systems joined forces with the suppliers of the CNC machines, torch height controls, and CAD software (commonly called nesting software). After a few years of development work, today’s high-definition plasma cutting machines employ the full suite of CNC cutting machine components to fully automate and coordinate functions that affect cut quality.
Today, these plasma systems can accept the same AutoCAD-format drawing file inputs used by older machines, plus incorporate new CAM software to analyze part drawing features such as holes, external features, etc. shape, type of material and thickness. This analysis is then used to nest the parts, insert the best entry and exit points, cut speed, amperage and gases, and set all the cutting parameters that were previously controlled by the machine operator.
The result is high-quality parts obtained through plasma cutting, with the following characteristics:
- Perfectly round and taper-free holes, as we see, for example, in the following comparative video:
- Consistent and repeatable quality of cut.
- Less downtime due to plate collision avoidance technology.
- Less cutting waste due to less or no setup errors by the operator or programmer.
- Faster cycle times between cut and cut.
- Very appropriate operating cost (in thicknesses between 3 and 38 mm it is less than oxyfuel and laser).
- Great versatility, since the same equipment can cut various thicknesses.
- Possibility of making complex shapes with a high level of repetition.
- Dispensing with the use of guillotines, presses and other mechanical elements.
Advances in CNC technology employ Windows-based touch screen operator controls that are easy to use, reducing the learning curve for a novice operator.
In the next article we will present a comparison between the technologies available for thermal cutting of sheets, highlighting the main characteristics of each one and their relationship between quality, productivity and operating cost.