7 Types of Reflective Materials for Laser Cutting
Learn more about these types of materials and their applications.
Laser cutting reflective materials can be challenging because the surface of the material can cause the laser to reflect coherent, high-energy beams in unexpected directions. This can damage the laser optic head, but more importantly, it creates a user hazard. It is important to take appropriate safety measures when laser cutting reflective materials, such as wearing appropriate protective gear and ensuring that the laser cutting area is properly ventilated. With high-value workpieces (silver, gold, platinum, etc.), using a precious-metals specialist cutting service can reduce costly mistakes. Some general suggestions for laser cutting reflective materials are: use a high-power fiber laser, use laser pulses to reduce bulk heating, use high feed rates to reduce localized heating, and use argon or nitrogen assist to clear the cut. Listed below are the seven types of reflective materials for laser cutting:
Gold is particularly reflective in the frequencies of common laser types used for cutting. A few work methods can help in producing good quality cuts, including:
- Where possible, use an Nd:YAG (green) laser.
- Use pulsed laser bursts to allow some cooling time. Also, use aggressive air (or even better, argon or nitrogen) assist to encourage cooling and remove the molten material fast.
- Use a specialist precious metals optics head to improve cut quality.
- Clamping the workpiece is a good idea—though inconvenient for load/unloading. The cost of the material moving during the cut can also be quite high.
Silver requires much the same precautions as gold. Although, you can be a little more aggressive with heat because silver isn’t quite such a good conductor as gold. Pure silver is hard to cut in its cold state, and the laser energy required increases by almost 100%. The reflection is reduced quickly by the onset of melting, but the cut is very difficult to start. Molten material absorbs IR better, so the cut can proceed once started. It is useful to use a very slow feed at the start, after which it can increase slightly. Trial below 90% of full speed. Reduce the amount of “cold” material that the laser has to handle by setting the focus at the top of the target material. This increases energy levels, and the wider kerf below cuts more easily as the material impacted by the laser is liquid. The use of oxygen at high pressure can assist in cutting considerably. The oxidation of the surface layer will not be enough to spoil the material.
Pure copper is particularly hard to cut. In its cold state, it reflects 99% of the incident IR energy in the beam for both CO2 and fiber lasers. Nd:YAG is considerably better absorbed by the cold metal. The reflected percentage drops off quickly once the metal melts, so the difficulty is in initiating the cut. Once melt has occurred, the laser is better absorbed (in the molten metal), carrying heat outwards and allowing the cut to advance. It is important to reduce feed speeds to give the beam time to initiate the cut. Dropping the feed to 10–15% below the maximum is likely a good starting point. Focus the beam on the upper surface of the material. Increased energy concentration will give the fastest cut initiation and a partially melted cut area will absorb IR much more strongly. The use of high-pressure oxygen can greatly assist the cutting process. The oxidation of the surface layer will not be enough to spoil the material, but copper oxide absorbs IR much better than clean metal. For more information, see our guide on Copper.
Brass shares most of the cut difficulties of copper. But it absorbs slightly more strongly in the fiber laser output frequency range, making cut initiation and rate slightly better. Brass laser cutting benefits a lot from air assistance, to clear molten material from the cut zone.
Bronze is also a difficult material to cut because of the IR reflectivity of the solid material. The same strategies used for copper are required for bronze, although the IR reflectance of the copper is lowered a little by the tin alloying element.
Titanium is very similar in laser cut behavior to stainless steel. It is recommended to use a high power setting for titanium cutting, a slightly reduced feed speed (compared with similar thickness stainless steel) and argon assist to improve cut speed/quality. Argon is beneficial as it will reduce the yellow or bronze staining of oxidation at the cut, compared with air or even nitrogen assist.
Aluminum is widely acknowledged as more difficult to cut than stainless steel due to its high reflectivity. A fiber laser's main wavelength (1.06 µm) is fairly well absorbed, however. A surface coating can be effective with aluminum, so long as it doesn’t burn away before melting has started. The highest available power, combined with a high feed rate will generally give the best results in cutting aluminum. It should be noted that the higher the alloying content there is, the easier it is to cut aluminum. Meanwhile, pure, soft, ductile aluminum is the hardest to get good results from. For more information, see our guide on Anodized Aluminum.
Many reflective materials pose only “learning” challenges in cutting. If the machine is appropriate for the task—i.e., has a good gas-assist option, a fiber laser or Nd:YAG (for copper and precious metals), and the settings have been trialed thoroughly—even the most reflective of materials can be cut. But it is not easy, and common home laser cutters, with limited gas assist and CO2 lasers, will not give good results.
Yes, reflective materials can be laser cut, provided that the recommended parameters are followed and considerable experience and application knowledge are present. With enough power and with a fiber laser, preferably with a cutting head developed specifically for precious metals (to withstand the high reflected energy), most materials that are highly IR reflective can be cut.
The best laser cutting technique to use on reflective materials is to use a fiber laser. These lasers have enough power to melt the surface more quickly, altering the target material’s albedo. It is recommended to use a gas assist, such as nitrogen or argon, to reduce the reflection of the laser by disrupting the liquified surface. A cutting head that is designed to handle reflective materials also works better for reflective materials. A coating or tape should be applied to the surface of the material to reduce its reflectivity during the initial beam contact. The reflectivity is likely to change once liquefaction has started. Trial adjustments to the feed rate and laser power are also advised to optimize for the cutting you are making.
It is possible to get satisfactory results with high-power CO2 laser equipment, but initiation of the cut requires a surface coating that improves the instant absorption spectrum to initiate melting. Once melt has occurred, the cut can proceed, but each start point will require the same issue to be addressed. For more information, see our guide on the Types of Laser Cutting.
Laser cutting reflective materials works by first applying just enough power to melt a spot. With a dot melted, the cut can drill down. If the focal point is at the upper surface, energy concentration is highest at the cut initiation. The absorption of IR increases greatly and the laser can drill down once the surface has melted. Feed speeds are varied. For example, precious metals need pulsed laser energy and low feed rates, whereas aluminum benefits from higher feed rates. Use gas assist when laser cutting. Air assist can be used to blow away sticky molten metal and expose the deeper cut. It can reduce the heat-affected zone that can mar precious metal cutting. Nitrogen assist, on the other hand, can be used for clearance of cut debris and to suppress oxidation, which can otherwise stain some materials in cutting. Argon assist serves the same purpose as nitrogen but gives more protection against oxidation. Oxygen assist is better used on some metals, to encourage oxidation staining which improves IR absorption.
The reflective material laser cutting settings are:
- High laser power (higher-power fiber laser machines give the best results, CO2 machines are not suitable without surface coating for absorption, which is not always possible or suitable).
- Use pulsed power to reduce the heat-affected zone.
- The material surface focus of the optics is necessary.
- Low feed rates allow cutting to commence—at 85–90% of full speed.
- Feed rates can be raised slightly once cutting is commenced. Each restart requires low speed.
- Air/inert gas/oxygen assist should be selected according to recommendations from the machine supplier.
For more information, see our guide on Laser Cutter Settings for Different Materials.
No, low-power cutting of reflective materials is generally not possible. If the material is very thin (foil rather than sheet) and a wide heat-affected zone can be accepted, lower-power machines are possible. In general, small, low-power machines—particularly those with CO2 lasers, are poorly suited to cutting reflective materials.
Yes, a machine setup that can cut reflective materials can also engrave them. The control setting that delivers engraving is easier to achieve, given the well-understood difficulties of cutting these materials. Settings that can barely initiate the cut can be adjusted to deliver partial cutting with a fairly wide margin of error.
This article presented reflective materials for laser cutting, explained what they are, and discussed their various applications. To learn more about laser cutting materials, contact a Xometry representative.
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