How accurate is plasma and what kind of cut and edge quality can I expect?

By Jim Colt, Hypertherm
Posted on 29/03/2019 in SPARK the blog, Plasma cutting

This question is not a simple one. As a general rule, accuracy will vary based on the capabilities of the plasma system and how it is set-up. For instance, the accuracy of a hand-held plasma system will be different than the accuracy of a plasma mounted on a CNC cutting table, and within the broad range of automated CNC plasma systems, high definition plasma will always be more accurate than light-industrial and entry-level plasma systems. Expectations about cut quality need to be realistic and relate specifically to the plasma system being used and the application.  

 

Hand plasma  

 

Hand-cutting is only as accurate as the operator’s comfort with the plasma torch. Torch motion, cut speed, and torch-to-work distance are all variables that affect accuracy. When cutting by hand - either using a guide or following a soapstone line - experienced operators can cut within 1/16 inch (1.6 mm) tolerance. There are highly skilled people out there with amazing physical control, though the human hand will not be more accurate than a plasma torch guided by a digitally controlled CNC machine and torch height control.  

 

Automated plasma 

 

Entry level CNC plasma systems are ideal for the serious hobbyist or small business owner. The accuracy of these systems will be impacted by the quality of the plasma system, the CNC, and the drives. Slight variations in cut angles are normal and you can expect a plus or minus .030 inch (.77 mm) tolerance. 

Entry level systems have x – y motion, but do not typically come with automatic torch height control (the z axis). Torch height control is significant because it automatically adjusts to the proper torch-to-work distance as the consumables wear and that keeps cut’s square. In the absence of automatic torch height control, the likelihood of negative or positive cut angles increases and can add costs when grinding and cleanup are required. Torch height control should be installed on every CNC plasma system. It is necessary for good cut quality. 

Light industrial systems come with torch height control, yet their accuracy can be about the same as an entry level system. The advantages are reaped over the life of the light industrial system. They are sturdier and built for low-level to moderate production, maintenance is minimal by comparison, the CNC and drive systems are better, and they just last longer. With the addition of a full feature torch height control, edge tolerances can get within the .015" to .025" range (.38 to .64 mm). Your cut edges are relatively square, hole quality is good, and most rework is eliminated.  

In high production shops, heavy Industrial machines can run for multiple shifts a day. These system are the most complex, but are the easiest to operate. That is due to the advanced software and controls used to drive them. These plasma systems can cut square edges on steel plate from gauge to 2" (50 mm) thick, create nearly perfect holes, and hold tolerances from .010" to .020" (.25 to .51 mm) depending on material and thickness. Most of the time, parts do not require rework and are ready to use.   

So as you can see, plasma accuracy will relate specifically to the plasma system and how it is set up. When making your decision about which plasma system to purchase the accuracy is important, but also consider the importance of system reliability, consumable life, operating costs, and manufacturer support. You will find that you truly get what you pay for.  

Quick Tips

Check the accuracy of a plasma system before you make a purchase:

Hand Plasma

  • Ask to demo the plasma system and cut with it
  • Compare system specs

Automated plasma

  • Site visit, either go to the OEM showroom and/or ask the OEM to take you to companies already using the system that you are looking to purchase
  • Ask for a cut sample and/or see if the OEM will cut a part from one of your own files on the system you’re considering
  • Ask the OEM for references and speak to people who are already using the equipment

In both hand and automated options, be sure to speak to industry experts. Representatives from the plasma manufacturers are a good source for information. Share your needs regarding the thickness and types of materials you want to cut, your productivity and accuracy requirements, and even your budget. That information will help them determine which technology is best suited for you.

Posted in SPARK the blog, Plasma cutting
Tagged with Cut quality

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