Laser Cutting Sheet Metal With Protective Film: 4 Key Points!

Bubbles may form under the film if cutting gas escapes between the sheet and the film during cutting. The risks are as follows:

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• a large bubble catching on the laser head and dragging the sheet away, resulting in uncontrolled movements and consequently significant damage.
• damage to the head and lens.

In 90% of cases, bubbling occurs during the drilling phase.

The risk of bubbling is amplified when the cuts are very close together. For example, small holes that are very close together. The gas pressure is concentrated on a very small surface and bubbles appear. There is also a strong risk of bubbling when the holes are less than 5mm apart. In this case, vaporisation must be carried out to avoid bubbling, i.e., burning the film before the cutting and, more specifically, the drilling phase. ‘Pre-drilling’ is available on most machines and can be done in the same operation as drilling, without significantly impacting productivity.

When the distance between the holes is greater, the holes are made in an area where the film is intact. There is therefore less risk of bubbles.
 

Protective film on sheet metal impacts the production process. Yet, suppliers standardise films, at the cost of optimising the cutting process. However, when the volumes are high enough, or if the film is applied in-house, then the manufacturer can choose a more suitable film.

When choosing the film, it’s important to find a balance between high adhesion to limit bubbles and low adhesion to make the film easier to remove.

A) With this in mind, there are several aspects to consider when choosing a film :

? the cutting technology: fibre laser source or CO2 laser
A fibre laser’s wavelength is ten times shorter than that of a CO2 laser and is not absorbed by the plastic. Thus, using a film designed for CO2 laser would create a very uneven cut if used with a fibre laser source. In fact, films specifically for fibre laser cutting have built-in absorbers.

? the material: stainless steel, aluminium, pre-lacquered,  etc.

Stainless steel/aluminium: Some materials are highly thermally conductive, e.g., aluminium, copper, etc. In this case, the heat spreads when cutting and can melt the film. The sheet protection for these materials therefore must be adapted, with a higher level of thermal resistance than a film for stainless steel, for example.

Pre-lacquered steel: Cutting pre-lacquered steel can be problematic if the lacquer used is not designed for good laser wave absorption. Even if there are specific films, the lacquer must be adapted, in particular with specific additives.

Double-sided: Double-sided protection can cause a small amount of burring during cutting, because the film on the table side retains the material. It is therefore recommended to use thin films, which reduce, or even eliminate, quality problems.

? Thickness of the sheet metal used
Depending on the thickness, the pressure of the cutting gas is different and therefore does not require the same level of adhesion. As a result, a film designed for thin sheet metal will result in a lot of bubbling if used on thick sheet metal.

? Material finishes: brushed, glossy, scotch-brite, etc.
Adhesion depends on the surface and the film products are adapted to each surface. It is therefore important to take the finish of the material into account when choosing a film.

B) Quality control: how to ensure that the film is suitable and properly applied?

? Specific colour codes and markings enable the operator to identify the type of film for visual inspection. Brice Lequette – Novacel explains: "The protective film for a CO2 laser is black on the glue side and white on the outside, whereas for a fibre laser it is black on the glue side and grey on the outside.”

? It is important to properly apply the film, especially by limiting its elongation. This is because plastic is a shape memory material that will return to its original size if elongated. Elongation reduces adhesion and the film will therefore be less resistant to gas pressure, leading to an increased risk of bubbling.

A quick test can be carried out to check that the film has been properly applied:

• peel off a strip of film from the sheet,
• wait a minute,
• compare the length of the removed film to the area where it was stuck. The difference should not be more than 1%.

A few visual clues can also alert to any issues, such as small application defects like bubbles, etc.

? The sheet metal should not be cut for 48 hours after applying the film.
 

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EDIT TO ADD:
Per the SDS provided by the manufacturer, Sabic/Plaskolite Lexan XL appears to be safe for use in a laser cutter. (If you can get a good cut is still TBD.)
Link to SDS, also posted below

SECOND ADDITION:
See below for a photo of what appears to be the best appearance you can get from cutting polycarbonate–smooth cuts, but brown edges.

For a part I want to make, I need something tougher than acrylic. Lexan/polycarbonate and PET-G are used for these kinds of products when you buy them. Since Home Depot carries Lexan, I picked up a sheet of 11"x14"x.093".

Upon further reading I have seen claims that some polycarbonate formulations contain chlorine. I wanted to start a thread to identify safe products and discuss cut settings. I know polycarbonate is not supposed to be the best material for laser cutters, but I have seen many claims that it can be cut successfully, so I want to try if it’s safe for the machine.

Here’s the label on the Home Depot 11"x14" Lexan:

I believe this is Sabic/Plaskolite part number 1PCA. I also see this product referred to generically as XL10 Lexan, which is listed on Sabic’s page of UV-coated Lexan products.

https://www.sabic.com/en/products/specialties/lexan-solid-sheet/uv-protected-sheet

Sadly, no documents are available from Sabic! I used their contact form to ask for the SDS. In the meantime, does anyone have laser-safe polycarbonate sources or cutting tips to share?

For more protective tape for aluminiuminformation, please contact us. We will provide professional answers.