Mylar® and Stencil Laser Engraving and Cutting (Extruded and Cast)

Mylar® is a trade name owned by Dupont that refers to a specific grade of PET (polyethylene terephthalate) film. It is typically manufactured via extrusion and is formed into thin sheets of varying thicknesses. Mylar is a laser-safe material that can be used in both engraving and cutting applications. The typical settings for cutting Mylar stencils on a 4 mil (0.1 mm) sheet are a speed of 150 mm/s and a laser power of 6 W. Mylar should be cut relatively quickly to prevent the edges from melting. This article will describe Mylar laser cutting and engraving to create high-quality stencils. A typical Mylar stencil is illustrated in Figure 1 below:

How To Laser Cut Stencils With Mylar

The general step-by-step process for laser-cutting stencils out of Mylar is described below:

1. Convert the design image to vector format. The conversion to vector format can be done with free software such as Inkscape. If possible, use designs that already come in vector format, i.e. with an SVG file extension. This file extension makes it easy to convert the edges of the design into paths for the laser cutter to follow.
2. Select the correct Mylar sheet thickness based on the required characteristics of the stencil design and the power of the available laser cutter. Thicker sheets may demand a more powerful laser. In general, thin Mylar sheets (with a thickness of between 4 (0.1 mm) and 10 (0.25 mm) mils) are all that is required for an effective stencil. Such sheets can be easily cut on a Glowforge laser cutter.
3. Secure the Mylar sheet to the base of the machine's cutting bed. Make sure the sheet is completely flat, as any raised areas can result in a poor-quality edge. Once cutting is complete, the stencil can be removed and is ready for use. 

What Are Custom Laser-Cut Stencils?

A stencil is a template for reproducing multiple exact replicas of a shape or pattern onto a target surface. Stencils are usually made of flexible materials, such as cardboard, plastic sheet, or thin metals. The cut-out parts of a stencil are the design, while the remaining material acts as a mask. The ink or paint applied to the stencil creates the desired image on the target surface. Stencils are often created using a laser cutter, because a laser cutter produces the cleanest possible design edges, resulting in the best possible quality stencil and, ultimately, the final artwork.

How To Laser Cut or Engrave Mylar Stencils for Use With Solder Paste

Soldering SMD (surface mount device) components onto a circuit board is extremely difficult, if not impossible, to achieve with a standard soldering iron. A popular alternative is to make use of a transparent mask in conjunction with solder paste as described below:

1. The planned positions and shapes of all the components on a circuit board are extracted to a CAD file format like .dxf that can be read by the software used to generate the stencil laser-cutting instructions. The shapes of the components must account for the width of the laser’s cutting path.
2. The CAD file is converted into a set of instructions that the laser cutter can  follow. These instructions are referred to as G-code.
3. Each position where the connections of each specific component to the board are situated is cut from a sheet of transparent Mylar. Alternatively, the areas can be vaporized by engraving at suitably high power. 
4. Once the cut is complete, the Mylar sheet is aligned with the circuit board. Using  transparent Mylar sheets makes it possible to visually align the stencil on the board so that the underlying component connection locations can be easily seen.
5. Once aligned, the stencil is held in place and solder paste is applied over the Mylar sheet. The solder paste then fills in the areas that correspond to the SMD pad locations on the board. The SMD parts can then be placed onto the board and soldered into place. 

What are the Differences Between "General" and "Presentation" Laser-Cut Mylar Parts?

“General” Mylar stencils do not need high-quality cosmetic finishes and can be made at increased manufacturing speeds and lower cost which is especially useful for one-off applications. Whether for stencils or for other applications, Mylar can also be used to create cosmetic-quality parts. These require clean-cut, precise edges. These parts are called “presentation” parts.

What is the Best Cutting Speed for Presentation-Quality Mylar Parts?

The best speed for Mylar with presentation parts depends on the thickness of the part. Presentation parts need clean and sharp cut edges. This is especially important if the material is relatively thick, i.e. from 8 mils (0.203) to 14 mils (0.36 mm), as any poor edges are more visible in the stenciled artwork. To get good results with thicker material, a slow cutting speed and a high laser power are required. A 30 mm/s cut speed with a power rating of 10 W is typically used.

What is the Best Laser Cutting Power Level for General-Quality Mylar Parts?

The best power rating for Mylar with general parts is 6 W with a cut speed of 150 mm/s. For general-quality parts, such as Mylar stencils, a thickness of 4 mils (0.1 mm) is typically used. Cosmetic finishes are not important for general parts. However, a crisp edge is still beneficial for a clean transfer. For that reason, the cutting speed must be increased to prevent the laser from melting the thin sheet away from the cut path. 

How Does Mylar Sheet Thickness Affect Required Laser Cutter Power?

As the thickness of a Mylar sheet to be cut increases, the laser power required to cut it also increases. Reduced cutting speed may also be necessary. Cutting at too low a power on thick sheets can result in incomplete separation of the plastic while cutting at too high a power level on thin sheets will produce a ragged edge when the increased energy input melts the cut path instead of vaporizing the Mylar.

What Are the Best Settings for Laser Cutting With Mylar?

The best settings depend on the available machine as well as the thickness of the Mylar sheet to be cut. The list of typical settings below is for a 4-mil thick Mylar sheet being cut on a Glowforge Pro laser cutter:

1. Power: A laser power of 25 watts can be used to successfully cut 4 mils (0.1 mm) Mylar. 
2. Speed: A machine speed of 250 mm/s ensures that the laser does not spend too much time at one point, thus causing the edges of the cut material to melt. 
3. Passes: For thin sheets, a single pass is all that is required.
4. Focus Height: While the focus height can be manually set, the Glowforge autofocusing feature should be used for optimal results.

It is important to note that these settings are only a guideline. Trial runs must be performed before cutting the final part. 

What Are the Common Mistakes Made When Laser Cutting Mylar?

Despite the ease with which Mylar can be cut, there is still some room for error. Listed below are some common mistakes:

1. Using the Incorrect Settings: Getting the settings correct is critical for successfully laser cutting Mylar. The speed, power, and focus height all need to be precisely set for the specific material thickness to prevent the edges from melting or to prevent incomplete cutting.
2. Using the Wrong Mylar Sheet: Not all Mylar sheets are ideal for laser cutting. Generally, thinner sheets of between 4 and 10 mils are best suited for making stencils.

What Are the Best Beginner Tips for Laser Engraving Mylar  Stencils?

While laser cutting a stencil on Mylar is relatively easy, sometimes it is better to create the stencil features using the engraving function of the laser cutter. Listed below are some tips to help the beginner make great stencils right from the start:

1. Secure the Sheet: Make sure the Mylar sheet is properly secured to the laser bed. If the bed is steel, then magnets can be used for this purpose. Alternatively, tape can be applied to the edges of the sheet to keep it in place. This is even more important if the machine has
2. Optimize Your Laser Settings for Engraving: When cutting very fine features on thin Mylar sheets, it may be easier to simply vaporize the material rather than cutting it. This can be done by making use of raster engraving, which essentially colors in the areas to be removed with the laser. The power must be set high enough to ensure vaporization, This is only effective for sheets of between 4 and 7.5 mils. 
3. Work Safely: Make sure there is sufficient ventilation when laser cutting mylar as the plastic fumes generated during cutting should not be inhaled. In addition, make sure that proper laser-safe eye protection is used and when cutting a new material, make sure that the first cut is observed to ensure it does not burn.

Which Laser Cutter Is Best for Mylar?

In general, the CO2 laser is the type best suited to laser cutting Mylar. Listed below are some of the best laser cutters for making stencils with Mylar:

1. Glowforge Pro: This 40 W CO2 laser cutter is one of the most popular machines on the market due to its high build quality, large user base, and excellent cutting quality. 
2. OM Tech: The OM Tech is a low-cost CO2 laser cutter that is available in a range of different laser powers. For stencil cutting, the 40 W version is recommended. 
3. Flux Beamo: This CO2 laser has a maximum power of 30 W. It is a good mid-range laser cutter that can produce excellent quality stencils. 

What Are Some Examples of Mylar Projects for Laser Cutting?

Mylar sheets are easy to cut and can be purchased in a variety of thicknesses, making them ideal for a wide range of applications, some of which are listed below:

1. Solder stencils
2. Etching stencils
3. Airbrushing and painting
4. Artwork for scrapbooking
5. Card-making
6. Quilt-making stencil/guide
7. Custom product labels and tags
8. Architectural model making
9. Lamp shades
10. Sewing stencils

What Plastics Are the Best for Use With Laser Cutting?

Listed below are some popular plastics which work well with laser cutting:

1. Acrylic: Acrylic is a rigid plastic that is available as a clear, transparent material, or in a wide range of colors. It is often used for engraved awards or signs.
2. Mylar: Mylar is frequently used for applications where thin, flexible sheets are required. It is available as transparent material or in a wide range of colors. Mylar is often used for stencils.
3. Polypropylene: Polycarbonate is a rigid plastic that has excellent toughness and is resistant to a wide range of chemicals. It can also be welded after laser cutting to create complex geometries. 

What Are the Alternatives to Mylar for Laser Cutting Stencils?

Listed below are some alternatives to Mylar for making laser-cut stencils:

1. Acrylic: Transparent acrylic can be used to create a stencil. However, acrylic is rigid.  Because of that, an acrylic stencil can only be used on a flat surface.
2. Metal: A very thin metal sheet is often used to make more durable, long-lasting stencils. However, most entry-level laser cutters do not have sufficient power to cut metal.
3. Paper / Cardboard: For cheap, limited-use stencils, paper or cardboard is an excellent choice, as it is flexible, cheap, and easy to cut.

Is It Hard to Create a Stencil for Laser Cutting?

No, laser cutting a stencil is not difficult. This is because stencils are cut from thin plastic sheets which can be handled by the vast majority of low-power entry-level laser cutters.

What Materials Are Used in Laser Cut Stencils?

The most commonly used materials for making laser-cut stencils are Mylar and thin sheet metal. Stencils need to be made from durable, flexible materials. If a single-use stencil is required then a cheaper material like paper or cardboard can also be used.

What Is the Difference Between Laser Cutting Stencils vs. Other Applications?

Laser cutting is not performed with a stencil. Rather, laser cutters are used to cut stencils that are then used to transfer the design to other surfaces using paint or some other marking material. Laser cutting stencils are a relatively niche application for laser cutting but follow all the same basic laser cutting principles. Laser cutting is used for a wide range of applications and materials for artistic projects using paper, polystyrene for architectural models, steel for industrial products, and fabrics for automotive and apparel applications. 

Summary

This article presented Mylar and stencil laser engraving, explained what it is, and discussed how the different stencil laser engraving applications with Mylar. To learn more about Mylar and stencil laser engraving, contact a Xometry representative.

Xometry provides a wide range of manufacturing capabilities, including sheet cutting and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.

Copyright and Trademark Notice

1. Mylar® is a trademark of DuPont Teijin Films™

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