There are so many methods when it comes to machining sheet metal. Depending on the geometries you’re looking for, you might wind up just scribing it by hand and using a circular saw.
When you start looking at the price per piece when you have to use all of these man-hours, you could start getting discouraged.
It’s already hard enough to make money on a project with how narrow the margins are, now if one of the machinists makes a mistake cutting a hole, it could wind up losing you money.
That’s where you need automation, and a CNC plasma cutter should be your go-to.
What is a CNC Plasma Cutter?
A CNC plasma cutter is a computer-operated machine that uses electrical arcs to cut through sheet metal.
They are extremely useful when it comes to sheet metal because they cut through like butter. Usually when you hear the phrase “CNC” your heart drops thinking of how high the price tag is – but CNC plasma cutters are a little different.
There are a lot of very cost-conscious tables that you can get just to do a proof-of-concept to see how much you can save.
You purchase a CNC plasma cutter that has a certain table dimension. This table dimension will indicate how big of a sheet you can load.
For example, a 5’ x 5’ CNC plasma cutter can cut into a 5’ x 5’ sheet of metal. Tables can come as small as 2’ x 2’ to minimize area and lower the cost of the unit.
How does a CNC Plasma Cutter Work?
The way a CNC plasma cutter works is there is a plasma tip affixed to a 3-axis gantry. There is motion on the x-axis, y-axis, and z-axis. In most tables, a few small and accurate servo motors power the gantries to optimize accuracy.
The plasma tip is hooked up electrically and connected to the drivers. The tip is rated at a certain amperage, and it cuts by heating up the tip, creating an arc, then blowing the arc with compressed air through the sheet below it.
These units can cut through a variety of metals, of different varying thicknesses. Certain tables can even cut titanium.
Other tables will advertise that it can cut hot rolled steel of up to 1.25 inches thick. This makes the table a very versatile tool if you’re working in a general machine shop.
The other key point about operating one of these units is the only manpower required is to load a sheet of metal onto the table and press “Go”. The CNC plasma cutter will receive input of a 2D CAD drawing in the form of a .dxf file.
The engineer will load the drawing into whatever CAM software they prefer, and layout the pieces on whatever sheet size you’re cutting on. The program will automatically nest the pieces to optimize the space on the sheet.
The file is then saved, uploaded into the computer connected to the CNC plasma cutter, then the operator loads the material and presses “Go”.
Ease of Use
A feature to highlight here is how easy it is to cut multiple pieces out of one sheet. Say I need 20 brackets made for a customer.
I will draw the flat model of the bracket, then after uploading it onto my CAM software, the computer will automatically layout all 20 pieces to minimize scrap material.
Who Can Operate a CNC Plasma Cutter?
The operator of the plasma cutter doesn’t need to be mechanically savvy or have any knowledge of machining processes.
This means you don’t need to pay for a machinist, you can hire an intern to run the machine, saving you money.
The machine also works very fast. The feed rate is dependent on the type and thickness of the material. Some tables can go up to 200 inches per minute, and even faster. Seeing one of these tools in action is pretty insane.
They zip through metal like it’s nothing and instantly index to the next part. To do a batch job with one of these guys is a breeze.
Within minutes you can cut tens of parts out of a sheet. Additionally, you don’t even need to be there when it’s running!
Scrap Associated With the Machine
Next, let’s look at the scrap associated with the tool. In the CAM software, you can either let the computer nest the pieces or you can manually place them. Either way, you can place each part so that you can minimize scrap.
It’s like you’re playing Tetris. Then consider that each cut is strictly the outline of the part. That’s right. There are no rough-cutting pieces out and wasting all of the additional material.
Beyond that, the kerf of the plasma tip is so much smaller than your bandsaw – so that’s even less material wasted each run.
Optimizing the placement of parts on a sheet could yield double the amount from a single sheet.
Appeal of a CNC Plasma Cutter
Picture one of these machines in a giant machine shop that gets tons of batch orders a week, perhaps repeat customers with repeat parts. Once you create a program to cut a certain part out of a sheet, it is saved forever on your computer.
That means that when customer X wants a repeat order of quantity Y of part Z, you go to the computer, click the program, load the sheet, and then start it up.
It isn’t hard to see the impact of using even one of these machines in a machine shop.
After loading the job, a few minutes pass and all of the parts are done and ready. Remove the parts and the scrap material from the table, and then load the next job. A nearly automated process, except the manual loading and unloading of material.
So we know this machine is fast and automatic, but surely that means the accuracy suffers? No way. Compare it to scribing and manually cutting the geometries.
There is so much human error there, this machine doesn’t even come close to that. A robotic plasma cutter will run through the job and complete the project with accuracy a human couldn’t dream of.
There are tips to increase your accuracy even further beyond what you get out of the box when you buy a CNC plasma cutter.
Once the table is set up, the only maintenance you’ll have to do is change over the liquid under the cutting head when you change materials you’re cutting.
The liquid acts to mitigate sparks and smoke, reduce heat, and prevent emissions. It also keeps the head cooler and cools the parts after a cut.
From time to time you’ll have to lube the linear rails but other than that it’s a pretty low-maintenance machine.
Potential Cost Savings
Finally, you have to consider the cost compared to how much money you’ll save over time. These machines range from a few thousand to a hundred thousand dollars.
Obviously, this spectrum covers a huge range of sizes, accuracies, and material cutting capabilities. But the way you calculate your potential savings is mostly in man hours.
If you buy a $20,000 CNC plasma cutter, and you typically pay your machinists $20 an hour, it will take 1,000 man hours to recoup your costs.
Now you have to determine how much time per project you’re saving. You save in rough cutting, measuring and indicating, scribing, any mistakes that result in scrapping the piece, and final cuts.
Say it takes 2 hours to make one bracket. Then multiply that by how many pieces you can make in one go. Maybe you can make 25 brackets on one sheet of metal.
That means every time you run an order of 25 brackets, you’re saving 50 man hours and subsequently $1,000. You still have to do final polishing/deburring, painting, and any bending required, but you save time on every previous operation.
Keeping this math in mind, you can quickly see just how much money you will save over time, and you can calculate how long before the machine pays for itself.
So let’s recap; why is a CNC plasma cutter better than a manual machining operation? To get the same part, it excels in every aspect.
The plasma cutting table is much faster, it wastes less material, it eliminates most of the labor time associated with jobs, it can almost completely automate a job, it’s more accurate, has exponentially less human error, can cut a variety of material types and thicknesses, and requires little to no maintenance.
It checks every box, and as a result, it’s definitely the go-to machining tool in 2020 to maximize production and lower operating costs.