CNC (Computer Numeric Control) plasma cutting is becoming steadily more accepted and the preferred process of metal cutting for the industry, small fab shops, and hobbyists. Due to the initial low startup cost, quality of cut, and ease of use, CNC plasma cutting is stealing the spotlight from other CNC cutting machines such as the waterjet and fiber laser. In this article, you will learn the basics of what CNC is and how to utilize this technology. This will give you a head start on fully understanding the world of CNC plasma cutting.
What is CNC?
CNC stands for Computer Numeric Control. Many industrial CNC machines that are used today were not always CNC machines but rather just machines that an operator controlled through their physical input. CNC removes the need for a physical input and replaces it with a computer and a program that can interpret a part file and execute a command generated by the program. The command generated by the software is in the form of G-code which the computer can understand and use to machine the part per the part file. G-code can be programmed by hand because its language is in the form of cartesian coordinates. This is your X, Y, and Z. Most of the time, your part will be positioned at the zero marks. This is where the origin of the part sits at the zero position of the X coordinate and the Y coordinate. From there by typing in the corresponding axis and a number it will move the part or tool given the machine and which axis is being told to move. There are many other commands that can be used in G-code and depending on your software will designate which does what. For example, you can program a stop command or adjust the feed rate and much more. If your machine has 3 degrees of freedom this makes the machine a 3-axis machine. However, not all machines are 3 axis machines. Once you get to 4, 5, and 6 axis machines, things get difficult. Additionally, programming by hand becomes virtually impossible. The 4, 5, and 6 axes are the rotation about your X, Y, and Z; also known as roll, yaw, and pitch. The most common are 3, 4, and 5 axis CNC machines. Having the sixth axis is not as common due to the added cost and because only a few benefits are added. Therefore, this addition is typically not a worth-while investment for the manufacturer. The more degree of freedom a machine has makes programming it that much more difficult. Thus, if you could not program it by hand without a software, an operator could not run it just by a part’s drawing print. This is the reason CNC is so important.
CNC is the future.
Now that you understand what CNC is, it is important to know why CNC is so popular. Humans are not perfect, we make mistakes and get tired. A computer does not. A computer will perform the same task repeatedly with perfect consistency. Try to draw a circle on paper 5 times, chances are each circle will be slightly different. A CNC cutting machine will make every circle the exact same. In industry, consistency and time are two major factors that all shops live by. A CNC machine can achieve this. When looking at time and consistency, a CNC machine will almost always outperform a hand operated machine in every way. A computer will never need a break, never make a mistake, and always do as it is told. The biggest part of this is removing the human side of machining and cutting. Thus, removing the inherent problems that come with the restrictions of being human. CNC machines do not just pertain to machines that make a part, but to all aspects of the manufacturing process. The purpose is to even further remove restrictions of the operator. For example, CNC machines were so efficient at their job that the operator could not keep up with the supply of material for it to run continuously. Developers then went a step further and created machines that loaded in raw material and unloaded the finished product. This was with the use of CNC. Thus, making the production of a part almost fully programmable. The less time in an operator’s hand, the more streamline production becomes and less chance of human error.
How to use CNC to Create a part?
Making a part is not as easy as turning over the on button and letting the CNC machine spit out a perfect part that a customer requested. CNC does need human input, but rather in the form of programming. A computer can only do what it is told to do. As explained above, the process to make a part by means of CNC is to have a computer and a program that can interpret a part file and execute a command generated by the program. This is tricky to fully understand, and I will explain through an example. Say you want to plasma cut a certain part out. You must first have some type of drawing made by a CAD (Computer Aided Drafting) program. There are many CAD programs that you can use to create a drawing. Some are free and some you need to pay for. The most widely used CAD program is AutoCAD. Once you have a drawing of the part you need, you then import that drawing into a CAM (Computer Aided Manufacturing) program. CAM programs accept different file formats; however, the most widely accepted format is the DXF (Drawing Exchange File). Once the drawing is imported into the CAM program you are ready to program the part. There are many different CAM programs and depending on the machine you buy and from what company, they will differ. Even though they will be different they both will achieve the final goal of creating a program for the computer to read. Many CAM programs that come with the CNC machine package have a lot of resources to help you learn their program and begin programming. So, do not be nervous about having to learn this step. Once the program is complete your machine is now ready to make your desired part per your original drafted print.
CNC machines can feel like a big jump in technology or a big investment to take on. However, the more they are understood, the less scary it seems to implement that machine in your manufacturing process. It now should be understood what CNC is, why they are so popular, and how this technology can work for you in your business, shop, or garage.
Author Nicholas Kinney,
Nicholas is employed at Diamond Manufacturing Company as a mechanical engineer. His responsibilities/experience include the CNC programming of their turrets and fiber laser. Outside of work, he enjoys machining, plasma cutting and working on his invention of an electromechanical anti-jackknifing system for tractor trailers.