Types of Laser Engraving: Ablation, Concave, Convex

Laser engraving is a subtractive manufacturing process that uses a laser to vaporize the material, producing a permanent mark on the surface in desired shape or pattern.

Although all the engravings look alike, there are significant differences in their process and applications.

Depending upon the material removal pattern and depth, laser engravings can be classified into different categories.

This article discusses the different types of laser engraving along with the types of lasers used and the materials that can be processed under a laser.

Types of Laser Engraving

Laser engraving can be differentiated into three main types: laser ablation, concave laser engraving, and convex laser engraving. Each of these laser engravings differentiates from each other in terms of their mode of operation, depth of engraving, and the type of contours they create.

Apart from these, some special types of laser engraving include deep laser engraving, laser marking, and laser etching.

Generally, as the depth of engraving increases, the requirement for higher laser power also increases, thereby increasing the cost of laser engraver required for the job.

However, these engravers are powerful tools that can be used for performing various operations, and learning about various factors associated with laser engraving provides you the ability to explore the full potential of your laser engraver.

Laser Ablation

Laser ablation is a process by which layers of material are removed by irradiating a laser beam on the surface and vaporizing it.

This can be achieved by using either a continuous or pulsed laser beam.

Pulsed laser beam, as the name suggests, operates in short pulses of high-energy laser, and the amount of material removal depends upon the duration of the pulse.

Short-pulsed laser beams can precisely laser engrave or cut materials with a minimum heat-affected zone, such that the surrounding area of the material is not affected by the heat.

Every material has an ablation threshold. Once that threshold is exceeded, the irradiated area vaporizes into fumes.

Certain materials like aluminum reach the ablation threshold more quickly if they are pre-heated. This way they can be laser engraved faster and deeper.

Pre-heating can be done by using heating plates on the work area of the laser machine.

Laser ablation has many applications in different branches of medicine like ophthalmology, general surgery, ENT, dentistry, etc.

Concave Laser Engraving

Concave engraving is a process in which the laser beam follows the path of the required pattern, thereby producing the design in the form of voids.

As a result, the engraving achieves a concave shape with the material around the pattern left intact.

Constant laser energy is maintained throughout the process to engrave simple shapes like texts and numbers by concave engraving method.

On the other hand, laser energy is varied when engraving detailed projects with dark and light contrast areas.

Concave engraving generally uses raster designs to remove material in the desired shape, making it ideal for producing intricate designs with a high level of detail.

Convex Laser Engraving

Opposite to concave engraving, this process works on the part around the pattern. 

Convex engraving removes the material around the pattern, thereby producing an elevated design.

This type of engraving is generally used for letter carving, graphic outlines, and other minimal patterns that do not require a high level of detail.

Here the laser energy is the same at all points on the pattern. 

You should be careful about the laser power settings and the material thickness. Since you are engraving out your design, the edge burns may be more prominent.

Although convex engraving cannot produce detailed engravings, it is ideal for producing intricate patterns while ensuring the structural integrity of the workpiece.

Special Laser Techniques to Produce a Permanent Mark

Deep Laser Engraving

Deep laser engraving differs from generic laser engraving in terms of depth and is generally used for performing 3D laser engravings.

The major drawback of laser engraving, when compared to CNC engraving, is the ability to engrave at depth. This drawback can be overcome by using a powerful laser.

A high-powered pulsed fiber laser, usually 100W or above, is used for deep laser engraving on metals, whereas a CO₂ laser with a power rating of above 100W is ideal for deep engraving on wood.

Generic laser engravings have a maximum depth of about 0.02” while deep laser engravings can have a depth of around 0.02"-0.125”.

This provides the ability to engrave at varying depths to create 3D forms on the surface of the workpiece.

Apart from laser power, the focusing lens also plays an important role in producing deep laser engravings.

The focusing lens with a tight spot will be able to focus the laser and attain the energy intensity needed for deep engraving.

A higher-powered laser can work faster, but it also poses the risk of burning or discoloring the surface.

So you should choose the power level such that you can laser engrave at the maximum speed without burning the material.

Deep engraving stainless steel removes the top protective layer and compromises its anti-corrosive properties.

Therefore, it is recommended to paint or chrome plate the engraved surface to make it rustproof again.

Deep laser engraving is used to create logos, stamping plates, artwork, mold inserts, drawings, texts, serial numbers, and barcodes on the surface of different materials. 

Laser Marking

Laser marking requires a comparatively low-powered laser machine. The laser heat oxidizes the surface of the material and produces a black mark.

This produces a high-contrast permanent mark on the surface of the workpiece without removing the material.

It must be noted that laser marking is sometimes also referred to as "laser dark marking" or "laser coloration".

UV lasers are most commonly to mark on materials as they have a comparatively lower operating temperature, which prevents them from overheating the material and vaporizing it.

Laser Etching

Laser etching is similar to laser engraving. Their main difference lies in the depth at which the laser affects the material.

Laser etching either melts and solidifies the material or vaporizes the area to create the engravings.

It generally affects the material at a maximum depth of around 1/1000".

Laser etching does not cause significant alteration to the surface, but it changes the surface finish of the metal and creates a high-contrast mark.

It can be performed on anodized, plated, or bare metal surfaces.

 

Materials Compatible With Laser Engraving

With the appropriate type of laser and optimal laser power, laser engraving can be used on various materials to produce a permanent mark.

Material	Link to Guide
Acrylic	Laser Cutting and Engraving Acrylic
Glass	Laser Cutting Glass without Chipping
Wood	Laser Cutting Wood
Plastics	Laser Cutting and Engraving Plastic
Brass	Laser Engraving Brass
Leather	Laser Cutting and Engraving Leather
Fabric	Laser Cutting Fabric without Fraying
Aluminum	Laser Cutting and Engraving Aluminum

Laser engraving and cutting chart

Laser engraving requires a balance between the speed and power parameters of the laser. To achieve this, you need to learn the basics of laser engraving.

In the tables below, I have listed out laser power settings for engraving and cutting different materials.

Material	60W CO2 Laser (speed in ipm, % power)	5.6W Diode Laser (speed in ipm, % power)	30W Fiber Laser (speed in ipm, % power)
Acrylic	236, 22	39, 100
Glass (Raster)	590, 70	30, 70
Wood	236, 22	40, 100
Anodized aluminum	700, 35	40, 100	470, 100
Leather	460, 20	40, 100
Ceramic	700, 65	39, 100

It must be noted that laser engraving material that contains PVC or vinyl content can produce harmful fumes that can damage the machine and harm the operator.

Therefore, it is important to check the contents of the material before engraving it under a laser.

Different Laser Types

Depending upon their source and wavelength, there are different types of lasers that can be used for engraving variety of materials.

Ultraviolet (UV) lasers

UV laser is also called Blue Laser or Cold Laser because it works at a comparatively lower temperature than fiber and CO₂ lasers.

Its property of creating high contrast markings at relatively low temperatures allows it to work on plastics like Polyethylene (PE), Polyvinyl Chloride (PVC) that are prone to melting when processed under a laser.

UV lasers can also engrave on wood, glass, fabric, and paper. But it can’t be used for deep laser engraving. 

Due to their low heat-affected zone, UV lasers are commonly used to engrave medical and pharmaceutical devices.  

Fiber Lasers

Fiber lasers are solid-state lasers that operate at an infrared wavelength range of 780nm to 2200nm.

Compared to CO₂ lasers, their lower wavelength allows them to have a smaller spot size and are readily absorbed by metals.

Fiber lasers are best suited for marking, etching, and engraving metals, and are therefore generally used in metal laser engravers and cutters.

When used in combination with an amplifier (MOPA), fiber lasers can also be used for color engraving. 

They also offer a significant edge over other lasers in terms of long lifetime and low maintenance. 

CO₂ lasers

CO₂ lasers operate at a wavelength of 10,600 nm (10.6 µm). Due to its high wavelength, the spot size is larger compared to fiber and UV lasers.

Its longer wavelength makes CO₂ lasers suitable for engraving on almost all non-metals like wood, glass, fabrics, leather, and stone. 

These lasers have a high laser power output and are best suited for deep engraving.

CO₂ lasers have a lower lifetime and higher maintenance compared to fiber lasers. 

Diode lasers

Diode lasers are solid-state lasers. They generally have a low power output. 

Diode lasers can engrave on plywood, acrylic, ceramic, stainless steel, aluminum, leather, and cardboard. They are generally not used in deep laser engraving. 

These lasers operate in the visible light spectrum and have a wavelength of 550nm-950nm. 

At this wavelength, it can engrave on most metals and non-metals. 

Applications of laser engraving

Some of the major applications of laser engraving are marking on awards, trophies, barcode/QR on machine parts, electronic devices, medical devices, signs, and badges. 

Depending on the laser type and wattage of the laser machine, materials of various densities can be processed using laser engravers.

Final thoughts

Laser engraving has numerous applications due to its precision and versatility. From hobbyists to businesses, laser engraving has become an important part of modern-day manufacturing. 

While laser engraving is ideal for engraving lines and curves, similar to a cutting process, concave laser engraving is recommended for applications that require variable contrast, such as engraving a photograph.

On the other hand, convex engravings are ideal for applications where minimalistic designs are to be engraved.

The most commonly used lasers for engraving applications are CO₂ lasers, UV lasers, diode lasers, and fiber lasers. 

While CO₂ lasers are ideal for engraving non-metals, fiber lasers perform better on metals. Both these lasers are available in high-power outputs, making them ideal for deep laser engraving.

Diode lasers and UV lasers, on the other hand, can engrave both metals and non-metals, but their low power output limits them from performing deep laser engravings.

Frequently asked questions

Can Fiber lasers be used to engrave glass and wood?

No, you can't use fiber lasers to engrave glass and wood because they have a very short wavelength (780nm to 2200nm).  Hence they get partially absorbed in wood and create heat spots. These heat spots can cause the wood to ignite. However, you can engrave glass by placing a stainless steel plate below the glass. The fiber laser will pass through the glass and engrave on the steel plate which leaves a clear impression on the back of the glass.

Is it safe to laser engrave and cut PVC? 

No, it is not safe to engrave or cut PVC (Polyvinyl Chloride) because when PVC is vaporized, it releases chlorine gas which is hazardous to humans. If you are to work on PVC, make sure you have a very well-ventilated room with a strong air assist system to extract the fumes coming from the material. 

What are some of the affordable laser engraving machines?

Some of the affordable laser engraving machines are ATOMSTACK A5, ATOMSTACK X7, OMTech K40, FLUX beamo Laser, and Glowforge Plus.