All About Copper Laser Cutting

Laser cutting is an efficient way to produce elaborate parts and designs for both industrial and hobbyist applications. From organic materials like leather, wood, and paper to non-organic materials like metals and plastics, lasers can be used to cut, engrave, and etch a variety of materials. 

The reflectivity and melting and vaporization temperatures of a particular material have an enormous impact on the final quality of a laser cut. Reflectivity affects the ability of the material to absorb energy from the laser beam. In contrast, a material’s melting and vaporization temperatures impact the required power and energy density needed to complete a cut. Copper and its alloys are materials that are notorious for being difficult to laser cut due to their tendency to reflect infrared light; however, with the right type of laser and the right settings, it can be done. This article will review the most important factors in laser cutting copper.

What Is the Definition of Copper Laser Cutting?

Copper laser cutting is the act of through-cutting a copper workpiece with a laser cutting machine. Fiber lasers are the best type for cutting copper. Copper readily absorbs the blue, violet, and ultraviolet wavelengths from fiber lasers. It is also possible to laser-cut copper using a CO2 laser. However, copper is not a natural candidate for cutting with CO2 lasers because it tends to reflect the red and infrared wavelengths generated by CO2 lasers. To compensate for the lower laser energy absorption, the copper workpiece must first be coated with a metal marking spray or paste that is able to absorb the CO2 laser energy. The process is less efficient than cutting copper with a fiber laser. Because of this, CO2 lasers are generally best for cutting copper in the context of hobbyist and small business applications. The fiber laser is more appropriate for industrial settings due to its efficiency and superior cut quality. Figure 1 is an example of a laser-cut copper:

What Is Copper Laser Engraving?

Copper laser engraving is the process of making shallow cuts into a copper workpiece to make elaborate patterns and designs. Copper is widely used for laser engraving because it is a low-cost, readily available material. When engraved using a CO2 laser, copper workpieces must first be coated with a metal marking spray or paste to prevent reflection and to force the workpiece to absorb the energy from the laser. Using a fiber laser avoids the need for such a coating. 

What Issues Most Frequently Arise When Copper Is Laser Cut?

The issues that most frequently arise during copper laser cutting are listed below:

1. Copper exhibits low absorption and high reflectivity of infrared wavelengths, leading to inefficient laser cutting.
2. Copper’s high reflectivity can damage laser optics equipment.
3. Copper reflects over 95% of infrared radiation when in its solid state. This makes the cutting process unstable and difficult to control. It absorbs more energy from infrared wavelengths as it warms up and becomes molten — making laser cutting easier and more efficient.

To counter the difficulty surrounding copper laser cutting, users have two options. Firstly, users can opt to use a fiber laser that emits shorter wavelengths than infrared to laser cut copper. While fiber lasers are preferred for laser cutting copper, they are much more costly than CO2 lasers and may not be an economical choice for some users. The second option is to coat copper workpieces with a metal marking spray or paste to reduce the reflectivity of the copper and force the workpiece to absorb energy from the laser. 

Which Type of Laser Cutting Is Employed When Cutting Copper?

There are three main types of laser cutting materials: flame cutting, fusion cutting, and sublimation cutting (also known as vaporization cutting). The best type of laser cutting method to use depends on the workpiece material. The three types are described in more detail below.

1. Flame Cutting: Oxygen is used to assist the laser cutting process. It creates an exothermic reaction to assist in heating the workpiece and forms oxides that reduce material reflectivity. Oxygen also increases the amount of energy available to the workpiece.
2. Fusion Cutting: An inert gas, like nitrogen, is used to force molten material from the kerf. This helps produce clean, smooth cuts.
3. Sublimation Cutting (Vaporization Cutting): The material is heated so rapidly that minimal melting occurs, and instead, the material is directly vaporized. Shield gas is used with this cutting process to prevent the workpiece edges from oxidizing.

Flame cutting is the best technique for copper laser cutting because it heats the workpiece and causes oxidation on the surfaces of the part near the cut. The presence of copper oxide makes the workpiece less reflective and allows it to absorb energy from the laser more efficiently. Post-processing is typically required to achieve desired dimensions and appearance because flame cutting tends to leave burrs on the part

What Are the Elements in Laser Cutting Copper Successfully?

The biggest challenge in laser cutting copper is getting it to absorb enough laser energy, because of its high reflectivity. This requires careful optimization of the laser-cutting process settings. Listed below are some of the parameters that must be set correctly to laser cut copper successfully: 

• Laser Power: Users should set the maximum allowed power on their particular laser system for both the initial piercing and for subsequent cutting of a copper workpiece. Higher power reduces the amount of time that copper is most reflective and consequently makes copper laser cutting more efficient and effective. Table 1 below can serve as a guide to the required laser power for a range of material thicknesses:

• Cut Speed: Use a cut speed of around 85-90% of the maximum allowed speed. This will ensure that the copper workpiece remains heated and is not highly reflective so that cutting can continue without interruption. Consider using a slower cut speed if cuts are initially unsuccessful.
• Point of Focus: The laser's focal point should be on the surface of the workpiece or as close as allowed. The focal point is adjusted by different optical lenses and by modifying the distance between the lens and the worktable. This maximizes the energy density of the laser at the workpiece surface, which results in faster melting.
• High-Pressure Oxygen Gas: Use pressurized oxygen gas at between 100 and 300 psi depending on the workpiece thickness. High-pressure oxygen helps improve the efficiency of the copper laser cutting process because it leads to the creation of copper oxide, which in turn lowers the reflectivity of the workpiece.

Does Oxygen Assist Gas in Making Copper Cut Faster?

Yes, oxygen gas makes copper laser cutting faster. While copper laser cutting can be accomplished without oxygen-assists gas if using a fiber laser, the presence of oxygen creates an exothermic reaction that helps make the laser cutting process more efficient. This is more applicable to CO2 laser cutting than fiber laser cutting. The exothermic reaction between the copper and the oxygen creates heat and copper oxide at the material surface. The copper oxide then reduces the workpiece's reflectivity, which assists in increasing the absorption of the laser energy. Using oxygen during cutting makes the process easier. However, it also leads to the formation of burrs along the length of the cut. This results in additional post-processing of the part to achieve the desired surface finish.

Does Using a Fiber Laser Make Cutting Copper Easier?

Yes, using a fiber laser makes copper laser cutting substantially easier. Fiber lasers emit much shorter wavelengths (around 1.07 μm) than CO2 lasers (around 10.6 μm). Because copper is highly reflective of infrared light when in its solid state, CO2 laser cutting is difficult. By using a fiber laser, a copper or brass workpiece can readily absorb the energy of the laser without the aid of oxygen gas — making laser cutting copper much easier with a fiber laser. 

Does Employing Faster Cut Speeds Cut Copper Well?

No, using faster cutting speeds is not an effective way to laser-cut copper. Because of copper’s high reflectivity, faster cutting speeds prevent the laser from effectively heating the surface of the workpiece. This can cause reflection back into the optics and potential damage to the laser system. It is best to start with slower cutting speeds, coupled with a high-powered laser that is focused on the surface of the workpiece. This will maximize both the heat generation rate in the copper and the amount of energy absorbed.

Summary

This article presented copper laser cutting, explained what it is, and discussed its different types and elements. To learn more about copper laser cutting, contact a Xometry representative.

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