Achieving top-notch cut quality with plasma cutting involves understanding the main factors that impact the results. In this blog guide, we’ll explore these crucial elements to help you get the best possible cut every time.

The 7 Key Factors: 

1. Amperage (Cutting Current)
2. Gases Used for Plasma Cutting 
3. Arc Voltage
4. Torch Height
5. Cutting Speed
6. Kerf Width

1. Amperage: The Power Player   

Amperage measures the flow of electrons in an electrical circuit. Higher current levels can reduce dross (the unwanted material that forms on the edge of a cut) for a given material thickness. For instance: 

I_c = 260 Amp; Thickness 1 inch, mild steel, cutting speed 66 inches/min

A lower current level usually results in better edge quality and squareness for a given thickness, but maximum dross formation.

I_c = 260 Amp; Thickness 1 inch, mild steel, cutting speed 66 inches/min

Bonus tip: Lower current consumables generally last longer, especially when cutting with oxygen.

To ensure optimal amperage performance, it’s also essential to maintain a clean and dry air supply system, with regular checks on air quality, gas quality, and CFM (cubic feet per minute) flow rate.

2. Choosing the Right Gases

The purity of gases used in plasma cutting is critical for maintaining cut quality and consumable life. Here’s a quick guide:

Oxygen (O2) and Nitrogen (N2): O2 at 99.5% purity, N2 at 99.99%.

Argon-Hydrogen (H35) and Nitrogen-Hydrogen (N5): H35 at 99.995% purity (65% Argon, 35% Hydrogen), N5 at 99.98% purity.

Air: Should be clean, dry, and oil-free.

Methane: 93% pure.

Typically used plasma gases include Compressed Air, Oxygen, Nitrogen, and Argon-Hydrogen. Shielding gases help in arc constriction and cooling, enhancing the cut quality by reducing oxidation at the cut edge. The choice of gases depends on the material you’re cutting and the desired cut quality. Always refer to the manufacturer’s instructions for the best results.

3. Arc Voltage: The Balancing Act 

Arc voltage is crucial for controlling the torch height and, consequently, the quality of your cut. Higher arc voltage means a taller torch height, which affects the bevel angle and overall cut quality.

Keep an eye on the cutting speed—it directly influences arc voltage. As speed increases, voltage drops, and vice versa. This relationship is vital for maintaining quality cuts, especially around corners and intricate contours.

Relation between the arc voltage and cutting speed.
(Note: Graph is dependent on system and metal thickness)

THC (torch height control) reacts like this: The torch will lower as speed decreases, or rise as speed increases. THC must be turned off or “AVC Disabled” when speed decreases.

4. Torch Height: The Perfect Distance 

Getting the torch height right is key, especially during piercing and cutting.

Piercing Height: Set at 1.5-2 times the ideal stand-off distance.

Cutting Height: Maintained during the cut for optimal results.

How does it work? The torch height control system (THC) adjusts the torch based on the surface, ensuring consistent cut quality. Remember, the THC is “blind” before cutting starts, so it must first touch the material to detect the initial position.

5. Cutting Speed: The Sweet Spot

Speed is everything when it comes to plasma cutting. The correct cutting speed minimizes dross and ensures a clean cut. Follow the cutting charts provided by your equipment manufacturer to find the optimal settings for amperage, arc voltage, and torch-to-work distance. Proper handling and storage of consumables is also crucial to prevent damage and contamination.

Example of plasma arc formation
From left to right: Low cutting speed, Correct cutting speed, Fast cutting speed

6. Kerf Width: Precision Matters

Kerf width, the void created by the cutting process, is crucial for the dimensional accuracy of your parts. A wider kerf is often the result of slower speeds or higher power settings. Typically, kerf width is about 1.5-2.0 times the nozzle’s orifice diameter. Regular torch maintenance and proper mounting on the gantry arm ensure accurate kerf width control.

7. Coolant Condition

Regularly replace the coolant (every 6 months or quarterly for heavy use) and completely flush the system to prevent performance issues and torch failure.

By considering these critical factors, you’ll be well on your way to achieving top-notch plasma cutting quality and optimizing your workflow. Remember, attention to detail is key to producing precise, high-quality cuts.

Text:               Thermacut®
Photo:            Archive of Thermacut, k.s.