How To Get The Best Laser Cut Quality Possible PT.1 – Laser Cutting Factors

fiber laser cutting metal
fiber laser cutting metal

Hello and welcome to the first part of this series called: how to get the best laser cut quality possible. My name is William from Senfeng laser and in this series my mission is to help you figure out how to get the best quality cut with your fiber laser when cutting metal. We all know it can get pretty complicated figuring out what parameters to choose with your laser cutting machine or what is causing the problem that’s making your laser cut get that burr or any other defect. So hopefully with this series, I can clear up many questions in your head when it comes to cutting with laser and help you better understand how to get the right cut. This series is for everyone: beginner or expert. So, if you’re ready, let’s dive in!

In this first part of the series, I will talk about all the major factors you should know that can affect the quality of your laser cut. Knowing all the factors that affect your laser cut a first step to optimizing your laser cut quality. Let’s get to it!

Laser Power

The laser power is the most common factor people hear about when it comes to laser cutting. That’s because what you can cut is limited by the amount of power your laser machine has. For example, reflective metals like aluminum require more power that say stainless steel to cut. Without enough power, you won’t be able to cut aluminum.

So, having more laser power means you can cut a larger range of material and a larger range of thickness for each material.

A 1kW fiber laser can cut stainless steel up to 5mm. But a 3kW can cut the same stainless steel up to 12mm.

If you can’t cut through a certain material, then you probably need more power to do so. Don’t be so quick to blame power though. Make sure to check out stuff like cutting speed, focal point and distance, and gas pressure before determining if power is the reason something can cut (unless you obviously know the material is way thick and hard to cut).

Higher power on your laser machine also gives you the ability to cut metal faster than laser machines with less power.

One very good thing of having a high-power laser machine is that figuring out laser parameters can become easier to configure. You don’t have to be so precise when trying to set laser parameters. You see, laser parameters like power, cutting speed, gas pressure, and so on are interconnected. And almost all parameters are set based on how much power your laser machine has. IF you have limited amount of power, you have to make sure the rest of the parameters are precise so you can get the right cut. IF you have a lot of power, then you don’t need to worry about getting the other parameters to be precise because high amounts of power can pretty much cut through everything regardless.

Type of Gas and Pressure

Gas assist or auxiliary gas in laser cutting has a few roles. One major one is to blow out molten material (metal that’s melted) from laser cutting process. Another major one is to protect the laser lenses from getting any molten metal or other stuff splash into it.

The type of gas, the quality of the gas, and how much gas pressure you output can have huge impact in your cut quality.

The types of gasses used in laser cutting are usually oxygen, nitrogen, argon, and compressed air (mix of nitrogen and some oxygen that is captured from the environment).   

Gas purity also plays a role in laser cutting quality. Laser technology requires gas to be really pure. Meaning there shouldn’t be any stuff in the gas like dust or other stuff. Laser gas usually should be 95.5% pure (and for some types of jobs even more). So, if you have laser quality cutting problems, then checking gas purity should be on your checklist.

Gas pressure is usually neglected when figuring out how to get the perfect laser cut. Gas pressure is used to melt and blow away molten metal (metal that is melted and in a semi liquid state). If this molten metal is not blow away fast enough, it can leave stuff like dross. If there is a lot of residue on the metal that seems to not go away, checking the gas pressure should be on your checklist.

Nozzle Type, Size, and Centering

The nozzle type and nozzle size that’s used in a laser head has an impact in how your laser will cut. Generally, there are two types of nozzle type. There is a single layer and a double layer.  The single layer nozzles are used with nitrogen as an auxiliary gas, and it is usually used to cut stainless steel, aluminum alloy, brass, etc.; Double-layer nozzles are generally used with oxygen as an auxiliary gas and it is usually used for cutting carbon steel. Make sure you check with the laser cutting machine manufacturer to see which nozzle type you need to use for your cutting situation.

Some laser manufacturers provide specific type of nozzles for specific kind of cutting jobs. For example, cutting small holes on thick metal plates with laser is hard. So, to be able to do that you will need a specific kind of nozzle. Make sure to talk to your laser machine company manufacturer to see what kind of nozzles they have and what they can be good for.

The nozzle size, which is measured through its diameter, has an effect in cutting quality. You will also hear it sometimes referred to as “size of orifice”.

Usually the thicker the metal, the bigger the nozzle size should be.

Another thing you must do to get proper laser cuts is center the nozzle. If the nozzle is not centered, you will get bad cuts. Sometimes you’ll get cuts that don’t make sense. For example, you’ll see your laser machine cutting good in one direction, but in the other direction it does not cut very well. This is probably a sign that the nozzle is not centered. Centering the nozzle is one of the first things you should do before cutting anything. In an upcoming post, I will explain how to do this.

Focal Lens

Having dirty focal lens can ruin your laser cut quality if it’s not cleaned. EVEN worse, a very dirty laser lens can ruin internal parts of your laser machine if not cleaned. So part getting the right cut quality is to clean your laser lenses.

Focal Point, Position, and Length

When a laser machine cuts metal plates, the laser forms kind of a hourglass shape. See the image below.

focal_point_lengt_2
focal_point_lengt_2

As you can see, the middle section of this hourglass laser cut is where all the cutting action is happening. This middle section is called the depth of focus. The exact middle is called the focal point or spot. Note, that the depth of focus is more like a bar or vertical line than a dot or point.

Having the focal point in the right position is crucial when trying to get high quality cuts with no burr other defects. Having the wrong focal position can result in really bad quality cuts.

The position of the focus point will depend on the material you’re trying to cut and the thickness of it. In an upcoming post, I will talk about how to get the right focus position based on a few guidelines. So stay tuned for that.

Cutting Speed

Having cutting speeds that are too slow or too fast can cause problems in your laser cutting quality. Having the right balance between cutting speed and other parameters like power and gas pressure is crucial.

Slow cutting speeds usually leave stuff behind like too much melted metal and burn marks (think about what happens when you burn something for too long). If the cutting speed is too fast, you will not be able to cut through metals. You have to think of laser like a stream of water (like a waterjet cutter). You need enough pressure (power and gas pressure) and time (cutting speed) to pierce and cut through something.

Continuous Wave and Pulsed Processing

When the laser machine is shooting out laser, it can do it in two ways: 1. continuous wave mode and 2. Pulse wave.

In continuous wave mode, the laser machine shoots out laser continuously (the name gives it, doesn’t it?). So, you can think of it like a stream of water.

In pulse wave mode, instead of shooting out laser persistently, you shoot out laser in great quantities at once. It is like a shot gun. Instead of shooting many bullets over time (continuous wave mode), it can shoot multiple bullets at once.

Continuous wave mode is good for when cutting straight lines and sharp corners. Pulse wave mode is good for cutting small holes.

Material Consideration

The type of material you’re gonna cut and it’s properties are also a factor when figuring out how to set cutting parameters. So, it’s good to check out the characteristics of the material you’re gonna cut and how it interacts with laser and heat.

For example, some metals absorb heat more easily, while other are more reflective in nature and don’t absorb light very well.

Usually metals with low silicon, phosphorous and carbon contents will be easier to cut with laser. High amount of carbon (like carbon steel) or high alloy content are harder to cut with laser.

Metal that are highly reflective in nature, also knows as non-ferrous metals, require a lot more power than other metals to cut. The reason they’re called reflective metals is because they reflect more light (think of how some metals look shinny under the sun) whi89ch makes it harder for laser to penetrate and cut. Highly reflective metals are stuff like aluminum, brass, and copper. Usually, you require about 30% more power to cut these kinds of reflected metals or else you can’t do your cutting job or worse, damage your laser machine (reflective metals can reflect light back to the laser head and into the laser lens and then damaging it).

Also, note that spray finishes, painting, and coatings (like plastic coatings) on the materials affect how cutting will happen on the material.

The Simplicity or Complexity Of Your Cutting Design

The shape of your design is something you need to consider when trying to achieve a good laser cut.

Simple design are ones where your mostly have straight lines and sharp corners. Complicated designs are designs that have a lot of curves and small holes in it. Complicated designs require different parameters and even equipment (like maybe a different nozzle type) to be able to cut. Figuring out the right parameters for complicated designs can become a little bit tricky. For example, in design with curves you need to lower the cutting speed and acceleration so your laser machine accurately cuts your design.

Conclusion

Thank you for reading the first part of this series: how to get the best laser cut quality possible. In the next post we will talk about a process you can go through to achieve high quality laser cut for any situation possible. So stay tuned. Also note that this post will be updated continually, so make sure to come back to see if you can learn more. Thank you very much, this is William from Senfeng and hope you’re having a great day!

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