Page 27 - Metalforming Magazine April 2022

Fabrication: Cutting Methods
CNC oxyfuel machines, simple to use and affordable, offer a Plasma cutting results in a small heat-affected zone and deliv- relatively low cutting speed that requires a high use of gas. ers a weldable edge with no hanging slag.
in mind that the slope of the cut can affect bottom-surface dimensions.
• Edge quality and metallurgical properties. Each metal-cutting process differs in effects on metal machinability and forming properties as well as weld- ability.
• Maintenance needs. To reduce the long-term cost, consider the mainte- nance needs of machines for the vari- ous metal-cutting processes, as well as ease of maintenance.
Now, let’s explore these considera- tions for systems that employ flame cutting, fine plasma cutting, 3-kW fiber laser cutting and waterjet cutting. To standardize, we will compare the cost considerations and cutting character- istics for complete systems that include a 5 by 10-ft. cutting area, an industrial CNC setup (neither entry level nor maximum configuration) and CAD/ CAM software. As far as purchase price, flame-cutting machines represent the lowest initial cost, followed by plasma, waterjet and fiber laser cutting machines.
Flame Cutting
The oxyfuel cutting process repre- sents the simplest of all cutting meth- ods discussed here. This process involves preheating ferrous material, primarily mild and low-alloy steel, with a gas combustible to reach the "ignition temperature" (approximately 1800 F), then injecting pure oxygen to cause an
exothermic reaction with the hot steel, which rapidly erodes the steel.
The flame typically can cut material in thicknesses from 0.25 to 6 in. Mul- tiple flame-torch installations on a machine, simple to do and affordable, greatly boost machine capacity.
CNC oxyfuel machines offer a rela- tively low cutting speed that requires a high use of gas. Cutting cost becomes more favorable on thicker plate.
To achieve the fastest cutting speed with the highest-quality cut, flame CNC cutting machines should be operated by highly skilled operators, though advances in the machinery enable use by less-skilled operators in some cases. Even so, due to long preheating times and slow cutting speeds, oxyfuel cutting typically lacks in productivity com- pared to other processes. And, flame cutting results in a large heat-affected area with rough edges and hanging slag.
Flame-cutting bed maintenance, a simple affair, is performed easily by the user.
Plasma Cutting
Plasma proves an ideal technology for cutting carbon steel in thicknesses to 2 in., and stainless steel or aluminum in thicknesses to 6.25 in. Achieve cost- effective cutting on carbon steel in thicknesses starting at 0.25 in.
A relatively simple process to learn and use, plasma cutting becomes more
effective through the use of the most recent control and process software. In most cases, nesting software includes process parameters to ease use by inexperienced operators. Over- all, plasma cutting delivers greater effi- ciency and speed than other processes, but laser machines cut more quickly for workpiece thicknesses greater than 0.25 in. At thicknesses below 2 in., plas- ma cuts more quickly than flame. Expect tolerances of ±0.015 in. on car- bon steel.
Plasma cutting results in a small heat-affected zone and delivers a weld- able edge with no hanging slag. Similar to oxyfuel cutting machines, plasma cutting machines offer simple main- tenance.
Fiber Laser Cutting
Fiber laser cutting employs the latest laser technology, with solid-state laser generators operating more efficiently than their CO2-laser counterparts. Addi- tionally, the wavelength of a fiber laser can be used for conduction in thin, flex- ible fibers—simpler and more flexible than operation of a CO2 laser, which only conducts via mirror reflection.
In operation, a high-energy laser beam melts the work material at cut- ting edges, with an auxiliary gas, usually oxygen, which is used for cutting car- bon steel, blowing out the molten metal.
A 3-kW fiber laser compares in
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