How To Avoid Beveling When Using A Plasma Cutter

Industrial & Manufacturing Articles

When cutting plate steel, the goal of most metal fabrication professionals is creating clean edges that lie exactly perpendicular to the plane of the plate's surface. A failure to achieve a 90 degree relationship between cut and material is known as beveling. Bevels are simply more than a cosmetic concern when cutting steel; they can result in edge surfaces being poorly mated during joining. As a result, end products with imperfectly-joined edges can fail, sometimes catastrophically, due to the weakness of the joint.

Being a relatively recent technological advance in mainstream welding, not all fabricators are as familiar or comfortable with the operation of plasma cutters as they should be. In addition, the ease with which plasma cutters can be used, even by novices, can actually be detrimental to learning proper technique and following best practices. Below are several considerations that can help metal fabricators produce clean, bevel-free cuts:

Keep cutter in appropriate position relative to work piece

Keeping the plasma cutter head in its proper orientation as related to the cutting surface is essential to avoiding beveling. If the head is tilted to either the right or left, the angle of plasma flow will create a correspondingly inclined bevel. However, depth also effects beveling; plasma does not flow in a completely cylindrical fashion. Instead it is tapered at the top and bottom with a wider portion in the middle. As a result, pushing the nozzle too close to the surface will create an inward-facing bevel, while holding it too far away will be the source of an outward-facing bevel.

To understand how far to keep your plasma nozzle away from the work piece, you will need to conduct informal tests on various pieces of metal. Practice is the best way to determine the optimum location for holding the cutter. In addition, once you have arrived at a suitable location, the use of an adjustable shield added to the tip of the cutter can help maintain consistent cutting quality.

Understand the consequences of cut directionality

Inside the plasma flow, a clockwise vortex is induced by airflow through holes in the swirl ring, a piece that lies just above the nozzle. This swirling effect allows the cutter to operate more efficiently and permits a cleaner cut as long as the user utilizes this advantage.

In mechanical devices that use rotating cutting heads, the cutting implement usually engages the metal so the cutting action is away from the material, thus creating a conventional cut. The opposite cut, termed as climbing, is where the implement cuts toward the material.

With devices that can bind, such as mechanical cutting tools, a conventional cut is less likely to backlash and break the tool or damage the work piece. However, the resulting cut is not as clean and beveling is a possible consequence of using this method. For climbing cuts, the action of the implement creates a cleaner cut, and since a plasma cutter has no mechanical parts to bind, becomes the preferred directionality.

In cutting situations, always position the plasma cutter so the right side moves into the material. For example, when cutting an inside arc, the cutter will move counter-clockwise circle. Conversely, if you are cutting an outside arc, move the cutter clockwise. Even though the movements are different, both are examples of climbing cuts.

Utilize proper cornering technique

Keeping a consistent speed while moving the plasma cutter is important to maintaining a consistent, unbeveled edge. However, this becomes tricky in certain situations, especially when changing direction to cut corners. Slowing the cutter may cause beveling at the edges near the corners.

To reduce occurrences where beveling occurs at corners, you need to keep the plasma flow moving. Instead of slowing to change direction, continue moving the cutter on beyond the corner and sweep it around in a 270 degree arc. This will enable you to approach the corner from a new direction and maintain a constant speed as you continue across the work piece.

Monitor equipment and replace worn consumables

Plasma cutters are robust, but they do possess parts that wear by design. Plasma nozzles, electrodes and swirl rings both become gradually less-capable of providing consistent performance. A nozzle that is deformed may cause plasma to eject at a skewed angle across the piece, causing beveling. Nozzles that are clogged or broken swirl rings prevent the proper vortex from forming, and this can interfere with a clean cutting action.

To understand when these consumables need replacing, frequently inspect them for these signs:

• The opening in the nozzle increases in diameter above original specifications
• The nozzle opening is distorted or partially clogged
• The swirl ring develops cracks due to constant heating and cooling
• The electrode becomes deeply-pitted or burns away

27 May 2015