Choosing the correct f-theta lens for a fiber laser marking and engraving machine

Most workstation format fiber laser marking machines have the functionality of using interchangeable lenses the extent of which will be determined by the maximum travel distance of the Z-axis. If the Z-axis is longer then the variety of focal length lenses that can be used with the laser engraving machine is greater.

It’s very important to understand how the different characteristics between lenses influence the performance of the laser marking machine and the results it produces. We cover in detail the characteristics of f-theta lenses in a separate article. Here we outline why certain lenses should be used instead of others.

The majority of laser engraving machine operators will only ever use a single focal length (f/l) lens for all of their work.

Most commonly this will be 163mm f/l, which provides for a marking area of approximately 110mm. For most applications this is a good all-round lens.

The next most popular would be a lens with 254mm f/l delivering a work area of 175mm and the third most popular would be a lens with 100mm f/l providing for a work area of 70mm

Other commonly used but less popular lenses would be 330mm f/l providing for a work area 220mm and 420mm f/l providing for a work area of 300mm. These very long f/l lenses are generally only effective when used with lasers >30w.

As the focal length increases, aside from the scan (work) area increasing so too does the size of the focal point and the depth of focus

When choosing which lens to use there are five main fundamentals to consider:

  1. Resolution, energy density and marking speed.

A lens with a shorter focal length will provide for a smaller focal point (laser spot), which in turn can achieve a higher resolution and a higher degree of energy density. This is useful for marking very high levels of detail and/or where the power of the laser source is low and the application requires maximum material ablation

Conversely, some applications do not require high resolution so can benefit from a longer focal length and a larger focal point because the marking process can be much faster with a wider spaced hatch fill

Using a lens with a longer focal length also requires shorter mirror movement, which again can make the marking process much faster

  1. Clearance between the lens and the material being marked.

Some components require marking inside them. For example, to the bottom of a bowl and here it’s important that there is sufficient clearance between the lens and the highest point of the part that is being marked to avoid any collision.

  1. Depth of focus

This means the effective distance from the perfectly focused focal point to the point where the laser is not marking desirably (because it is too far out of focus).

This is only an issue for parts being marked that are not flat; for example, the surface of a pen. In this example it is sometimes better to use a 254mm f/l lens rather than a 163mm f/l lens because with the longer focal length lens the height of the mark can be larger

  1. Mark area

A lens with a longer focal length provides for a larger effective marking area. This is especially useful where a single mark is very large or where a single part must be marked in numerous locations

  1. Contamination

Some applications can generate corrosive fumes that can contaminate and deteriorate the lens. A longer focal length will place the lens further away from the surface of the material making it unlikely to become contaminated

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.


Software for controlling a laser marking and engraving machine

When customers ask about the various performance features of a laser marking machine it’s typical for them to be concentrating on important factors such as the make/model /power of the laser source, whether or not the scan head is digital or analogue and at what speed it can operate up to, etc.

One aspect of a laser marker that is often not considered with enough scrutiny is the software that controls and acts as an interface between the user and the laser engraving machine

The differences between laser engraving software packages can be very significant but not so easy to identify by an inexperienced person.

The ideal software for a laser engraving machine should operate fast and reliably, be easy to use and intuitive to learn. Unfortunately, many software packages supplied as standard by some vendors are far from these ideals. In some cases the software offers no more than very basic levels of functionality. Typically such software will be found operating a laser coding machine, for example, laser marking food packaging where all that’s required is to produce simple date/time/batch codes. This type of software can be quite useless, for example, in a job shop type business where there are other functionalities required such as laser marking logos’, laser marking photos or variable text. In this scenario a workstation format of laser marking machine is a far better choice

Workstation format laser engraving machines should by their very definition be very featured enriched in all aspects including software, however, some manufacturers lock-out the user from software functionalities that many deem essential for day-to-day operations. Such vendors then offer to ‘unlock’ extra functionality by selling upgrade packages.  In stark contrast other vendors provide full software functionality even with their entry level models at no extra cost.

Software for controlling a laser marking machine

Therefore, one of the first things to look for before you purchase a laser marking machine are offers of ‘software upgrades’ at extra cost because without these, the system could be seriously limited in application excluding the user for taking on work that could be potentially very profitable..

Most laser engraving software will be loaded to a Windows PC in a way similar to how Office type applications will be installed. This can be problematic for some customers because the level of PC user rights can cause performance and/or reliability issues with the software.

A lower risk and far more accessible solution is simply to run the control software as an executable (.exe) program. This design allows for the control software to be operated from almost any location without the software being actually installed to the local PC. Such software can even run from a USB memory stick or a remote server location, which provides for extremely fast corrections if, for example, technical support or disaster recovery is required because with a single mouse click any lost/corrupted program files can be overwritten with an error free,  previously saved version.

With a modern laser marking system the capability to mark all True Type fonts, bitmap images, vector drawings and any common form of barcode are essential requirements. More frequently these days it’s important to be able to quickly and easily import and automatically position/configure variable text such as, for example, the marking of names or externally generated serial numbers.

To provide capacity to grow with potential future demands the software should allow the user the ability to connect and drive external devices such as, for example, a rotary device, conveyor feed or any other kind of handling device

At Lotus Laser Systems we believe that all laser marking systems should ship with a full suite of software with full functionality so that the customer has the ability to take full advantage of any situation they may encounter and so maximise the return on their investment.

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.

Optical configuration for a CO2 galvo laser marking and engraving machine

The most commonly known technology for a CO2 laser engraving machine is the flying optic plotter format. This type of machine exists in almost every high street used by general engravers, trophy shops and sign makers. For laser engraving applications such machines are limited with regard to throughput; how many parts can be laser engraved per hour

An alternative to the plotter format of beam delivery is the galvo laser. If the application allows, using a CO2 galvo laser marking machine is by far the fastest way to laser engrave where often the difference in throughput can be many times more, even by as much as x80 to x90 times faster than the plotter alternative

While both formats can contain an identical laser source the optical configuration varies considerably and is specific to each format.

The plotter format of laser engraving machine will use a very short focal length lens, which provides for a very small focal point. By contrast, with the beam delivered through a fixed lens of a massively longer focal length the galvo laser delivers a far larger focal point. From a negative perspective this can not only reduce the rate of ablation (material removal) at a given laser power but it can also reduce the achieveable marking resolution.

One way to counteract this is by carefully optimising the optical configuration of the galvo laser to deliver the smallest possible focal point so as to achieve near to the final effect that a plotter can produce but still at many, many times faster.

Starting from the laser, to achieve a smaller focal point the beam should be expanded by as much as possible because the larger the beam diameter is the smaller the focal point will be after the lens

It is not uncommon to expand some lasers by a factor of x12.

Within the scan head, to allow for the significantly expanded beam diameter the aperture (the hole where the beam enters the scan head) must be several millimetres larger than the beam diameter exiting the expander. For example, if the beam exitts the laser at 2.2mm and is expanded x12 the resulting diameter will be approx 26.4mm. A suitable scan head would therefore have an aperture of 30mm.

After the aperture the deflection mirrors must also be large enough to receive the wide diameter beam. This necessitates the need to us larger, heaveier mirrors, which in turn must be mounted to larger galvanometer motors (galvos). The increased size of the mirrors/motors does mean that they are more expensive to purchase and slower than a smaller alternative, however, on the upside should the mirrors contaminate any resulting power loss is less noticeable with a beam that’s expanded larger.

After the mirrors, to achieve the highest resolution an F-theta lens with the shortest possible focal length should be used. While this increases quality (resolution) and the rate of ablation it does have a limiting factor with regard to the work area because shorter focal length lenses have smaller working areas. Sitting closer to the material a shorter focal length will likely suffer increased frequency of contamination and the marking speed is also slower.

Converesly, using a longer focal length lens will deliver a higher speed of mark and in some cases can reduce contamination to near zero because the surface being ablated is much further away from the lens.

For some applications a larger focal point is actually desireable: for example, marking single stroke fonts to packaging for coding applications or where marking is required with a minimal rate of ablation.   

The ultimate solution is to incorporate a beam expander that can be varied in magnitude and also to utilise a variety of focal length lenses that are interchangeable according to the demands of the application

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your applicatio

Why You Must Use a Digital Scan Head in a Laser Marking Machine

In a basic laser marking or laser engraving machine the scan head, otherwise known as the beam deflection unit or the galvo head, is a key component with regard to the performance and reliability of the system.

There are many manufacturers of these types of device with significantly variable performance characteristics but one major differential to consider is whether or not the unit is digital or analogue.

Lower cost laser marking machines tend to use analogue technology because the component cost is significantly lower. The downside to using an analogue scan head is that it is more prone to drift out of accuracy especially if the unit is worked hard and builds-up a significant degree of retained heat (thermal drift).

Over time, especially after suffering significant wear and tear the galvanometers (motors) within an analogue scan head can become permanently misaligned. The only way to fix this is to recalibrate the scan head, which is a laborious task that can only be performed by a skilled professional with reasonably sophisticated equipment.

In the case where a galvanometer totally fails an analogue scan head needs to be return to the factory for repair.

Analogue scan heads are in general slower and less accurate too.

While visually there is little to differentiate the two, in all other aspects the digital alternative is a far superior product. Not only can it work faster and more accurately (sometimes up to twice the speed of an analogue alternative), it will not suffer from misalignment in the same way that an analogue scan head can.

A well designed laser marking machine incorporating the latest digital scan head technology will benefit from a self calibration process on start-up. This test process occurs during the first 30 seconds or so after powering-up the unit. Self calibration not only corrects minor misalignments but is particularly useful if, for example, one of the galvanometers fails and requires replacement because rather than having to send the whole unit back to the factory for repair the galvanometer can be changed in the field, saving significant time and costs for the repair.

Digital scan heads are faster to response to control signals, which significantly contributes to overall performance speeds. This is not only beneficial to increase throughput but also is useful in terms of system set-up too: an analogue unit can take hours to perfectly calibrate conversely a digital alternative can be set-up in a matter of minutes.

Lastly, the more efficient electronics of the digital unit contributes to lowering the overall operating temperature of the scan head, which in turns enhances performance and extends the working life of the component.

In recent times the premium to be paid for a digital scan head has reduced to near zero, so there is no longer any reason to use analogue scan heads in a laser marking machine. Therefore, should the vendor offer such a head take care to inspect the machine very carefully as it is likely other design/performance comprises have been made to the disadvantage of the customer.

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.


Focusing a 1µm Galvo Fiber Laser Marking Machine

Accurate focusing of any laser marking machine is fundamental to achieving a successful laser mark.

When the laser marker is precisely focused, the resulting optimally sized focal point will deliver maximum resolution, higher energy density, higher productivity and a consistent mark with a desirable aesthetic.

A laser marker that is incorrectly focused will not only produce an undesirable result but it will potentially work at a far slower rate too, having a significant adverse impact on productivity.

For this reason, with every laser engraving machine that we manufacture we incorporate an electronic Z axis to which the beam deflection unit (scan head) is mounted, which is controlled by our software so that the user can precisely focus the laser.

Systems that incorporate a manual method of focusing (not controlled by software) are much more prone to operator error.

Even worse, with poorly designed machines where the worktable is moved to focus the laser rather than the scan head, significant errors are almost guaranteed. This is especially common where machines use a ‘lab jack’ type table that is often never perfectly level and/or can move during the laser marking process, especially when heavier items are loaded to the machine.

The problem of inaccurate focusing of the laser is compounded where the laser source is lower in power because any loss of energy density will be a significantly larger portion of the overall laser power. Therefore, it’s somewhat true that lasers of a higher power are more forgiving if they are used out of focus compared to the same machine fitted with a lower power laser source.

For some applications it can be desirable to deliberately defocus the laser. For example, when laser marking stainless steel with a near to black annealed effect, defocusing a machine by several millimetres can actually enhance the effect.

Marking with an intentionally defocused laser can also prevent unwanted material ablation that would otherwise occur with a perfectly focused laser. For example, when laser marking food packaging (coding), such as the foils used to wrap ice-creams, a perfectly focused laser can pierce the foil and deliver a very narrow mark that is harder to read where a defocused laser is less likely to pierce the foil and the larger focal point will provide for a wider character that is easier to read.

Also, when some products require marking at exceptionally high speed and high resolution is not a priority, using a defocused laser with a larger focal point size can allow for a lower hatch density, providing for a much faster mark. This technique can be used, for example, for marking of cattle tags.

In summary, precise control of focusing the laser is often critical to achieving the best overall result.

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.


A simple Explanation of Laser Safety Classifications within a Laser Marking or Laser Cutting Machine

Almost all manufacturing equipment has inherent safety risks. For most types of machinery these risks are obvious, easily identifiable through visual or audible inspection.

The laser source within a laser marking or laser cutting machine cannot be monitored by the user visually or audibly without the use of special equipment. Therefore, there are specific safety classifications given to laser devices so that the degree of hazard can be understood and the risks mitigated to avoid accidents.

All laser devices must be labelled to identify the level of laser safety hazard, called the laser safety class.

There are 4 laser safety classes according to the degree of risk with Class 1 being the lowest risk and Class 4 being the highest risk. Within some of these classes are a number of sub-classes specific to the system configuration, in particular the laser wavelength and/or its AEL (Accessible Emission Limit) i.e. the degree of power emitted from the laser and the exposure time before it becomes hazardous.

By far the greatest hazard to the user is the risk of damage to eyesight. This can be permanent or temporary depending on the power and wavelength of the laser as well as the AEL.

Other risks relate to damage to materials biological, for example damage to skin, or non-biological as well as the risk to cause fire and/or explosion when coming in to contact with flammable or combustible materials such as petroleum, flammable gases, etc.

Within a laser marking, laser engraving, or laser cutting machine the laser source at any wavelength is always Class 4. The Class 4 laser hazard can be reduced by the addition of extra safety measures and devices built around the laser source.

Class 1 defines the laser marking machine or laser cutting machine as being of the lowest risk. A Class 1 laser machine can be operated in almost any environment suitable for an electronic device and emits no harmful laser radiation whatsoever.

To meet the requirements of Class 1 the laser hazard must be contained within a ‘light tight’ enclosure with all access panels being used for general operation interlocked and all service panels being secured with screws, or similar semi permanent fixings, so that opening of the service panels requires the use of a tool.

When an interlocked access panel is open an indicator must show that the system has moved from Class 1 to Class 4 and power to the laser must be removed so as to prevent accidental operation.

Class 2 is essentially the same as Class 1, however, this type of machine incorporates a visible guiding laser at 1mW. Typically this will be a red guiding laser at the 655nm wavelength.

Class 3 is not typically applicable for a laser marking or laser cutting machine and is more commonly found assigned to equipment incorporating a very strong, visible guiding laser typically at 5mW.

Class 4 is the most dangerous of all the laser safety classes. A Class 4 laser marking machine exposes the user to potentially immediate and harmful laser radiation as well as adds risk for damage to materials that can combust and/or explode. Use of a Class 4 laser must be restricted to a specifically designated and appropriately signed area, segregated from the general work area. Operators of Class 4 lasers should be specially trained and advised of the risks as well as wear specifically configured PPE while working in the designated Class 4 area.

In a perfect world only Class 1 or Class 2 laser marking or laser cutting machines would exist but in some circumstances the safety enclosure becomes an obstacle to the process. In such case Class 4 lasers are required, however, a Class 4 laser should never be operated without the owner and user being fully aware of the safety risks and having in place safety measures to prevent unnecessary accidents.

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.


Why to Use the 9.3µm Wave length for Laser Marking and Laser Cutting

The vast majority of gas lasers in use today are CO2 lasers operating at the 10.6µm wavelength where there are literally hundreds of thousands of lasers working every day for laser marking, laser engraving and laser cutting applications.

Glass Laser Marking MachineIn recent years some of the main laser technology manufacturers have introduced a more specialised version of their 10.6µm lasers modified to operate specifically at the 9.3µm wavelength.

Some materials, such as Polyethylene terephthalate (PET) for example, can be laser marked at the 10.6µm wavelength but will react better at the slightly shorter 9.3µm wavelength.

PET is a thermoplastic best known as a material to manufacture synthetic fabrics for clothing (commonly known as polyester) and it is also used to manufacture bottles containing drinking water, carbonated pops, fruit juices and other beverages.

In the case of a beverage bottle the vessel must be marked with coding such as date of manufacture, date of expiration (use by date) as well as other variables such as product type and batch numbers. Laser marking is a great technology for this process as a laser engraved code can be applied directly to the PET vessel so that it is wear resistant, fast, cheap, difficult to alter/counterfeit and eco-friendly to produce as there are no inks involved.

Using a 10.6µm laser marking machine to mark PET directly creates a clean, glossy mark with some material ablation. When filled with liquids that are highly transparent, such as water for example, the 10.6µm laser engraved code can be low in contrast and therefore hard to read.

When the bottle is filled with a carbonated beverage the engraved (ablated) area can cause a weak spot that in some cases can cause the vessel to fail and the liquid escape, wasting the product completely. This is an increasing problem as bottling plants move towards thinner walled vessels to aid in lowering material use and product cost/weight.

Using the same laser marking machine but at the 9.3µm wavelength creates a different material reaction where the laser marking is frosted in appearance without any ablation taking place, thereby increasing the contrast and readability of the mark no matter what the contents are and reducing the risk for failures of the vessel near to zero.

PET is also used in some specialist applications. For example, it can be combined with PVC to make a film used for the hologram on a credit card. Here, a specifically configured laser cutting machine at the 9.3µm wavelength can kiss-cut the surface film without piercing its backing film with a far cleaner edge and less adverse heat reaction than a similar machine would produce with a 10.6µm laser. Therefore, using the 9.3µm laser for this laser cutting process increases output quality while simultaneously reducing waste through rejected parts.

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.


Why Laser Marking is Fast Replacing Printing

For many years Continuous Ink Jet printing (CIJ) has dominated the industrial sector for coding applications such as, for example, applying time/date/batch codes to food and beverage packaging.

During recent years, laser marking technology has seen a significant improvement in both performance and reliability simultaneous to a lowering of prices. These advancements now make laser marking a viable alternative to CIJ.

In terms of the code itself, laser marking offers many advantages over CIJ.

The CIJ process utilises ink, which as a consumable is costly to purchase over time and the printing heads of CIJ must be constantly cleaned and/or replaced too. A laser marker has no consumables, so running costs are far lower, as is the requirement for maintenance.

The low requirement for maintenance of a laser marking machine can mean that it’s a far more reliable method compared to CIJ and the fact that the laser uses no ink makes the laser marking process more environmentally responsible too.

In cases where the mark requires the application of logos as well as simple coding, here the laser is often a much better solution. CIJ is very limited as to what type of mark it can produce and over what area but a laser marking machine can deliver a wide variety of graphic formats from logos to barcodes to simple text and over a much bigger area too than a CIJ can apply.

For the mark itself, a laser mark is permanent and difficult to counterfeit. CIJ is quite the opposite; for example, when coding milk cartons by CIJ it is common for the mark to rub off as the carton is exposed to temperature changes, condensation and wear. A laser mark is resilient to such things.

A laser marker can also be easier/better to integrate to production lines. With CIJ the head is commonly positioned close to the surface to which it is printing. With a laser marking machine it is possible to place the beam deflection unit (sometimes known as the scan head) several hundred millimetres away from the product being marked.

A laser mark can add significantly to the perceived value of the item itself. For example, for a recent project we configured a fiber laser marking machine to brand stainless steel razor blades. Historically the blades were marked by CIJ. The aesthetic of the laser mark was significantly better, raising the perceived value of the item itself and addressing the counterfeiting issue our customer was having with their product marked by CIJ.

CIJ is a single process solution; i.e. it is simply a surface print. In some cases it’s possible for the laser to code and produce other processes at the same time such as, for example, perforation of packaging or cutting of thin films

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.


When to Use a DC or RF Laser for Laser Cutting

At the heart of every 10.6µm laser cutting machine is the laser source. For low power (<100w) laser cutters there are two different types of laser source most commonly available.Both are essentially gas lasers emitting a laser at the 10.6µm wavelength but here the similarity ends. We cover the specification and manufacture differences between these technologies in other articles.

The oldest, most stable and reliable, highest performing laser is the RF variety. A high quality RF excited laser can produce excellent beam quality with a very short (fast) rise/fall time. This makes the RF laser ideal for laser cutters where the process needs to be delivered at high speed.

RF lasers are also much better for applications that require a high degree of detail to be cut. This is because when the motion system slows down to turn an acute angle or change in direction, to avoid burning-out the material where the motion system turns/dwells the laser power must be ramped down proportionally. DC lasers are difficult to control when ramping, often producing unreliable results.

The high-speed pulse of the RF laser is also much better suited for laser cutting materials that react adversely to overheating where the RF laser will minimise this undesirable reaction. For example, laser cutting wood with an RF laser can produce a cleaner edge than when using a DC laser. Another example would be the laser cutting of thin materials, such as laser cutting veneers where too much heat can cause the material to warp. Using an RF laser will again minimise this adverse effect.

Another preferred application for using an RF laser is where the cutting control needs to be very precise: for example, the laser kiss-cutting of labels where the laser cuts the surface material but not the backing paper. This application can require the use of very low laser power, even just a few watts. All gas lasers do not work well when the duty cycle falls near to or below 10%. For DC lasers at 60w we find they do not perform well below 30% (18w), which is often too much power for kiss-cutting.

A DC laser is best applied to laser cutting materials that work well with heat and where the duty cycle is almost always 100%. For example, laser cutting acrylic, especially at thickness >3mm (1/8”) where the slower pulse and greater heat of the DC laser can be an advantage. In this example a DC laser will often laser cut acrylic with a far smoother edge than its RF alternative.

Of course, DC lasers being a fraction of the price of the RF alternative means the user can afford to use a far higher DC laser power than the nearest cost RF alternative closest in price. This means that using a higher power DC you can cut thicker materials much faster. For example, one of our 30w RF machines actually costs more money than the same machine fitted with a 100w DC laser. In this example, the DC version would cut thicker materials near to three times faster.

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.


Laser Marking Stainless Steel With a Black Annealed Effect

Stainless steel is an excellent material for laser engraving at the 1µm wavelength where a range of different effects can be produced such as ablation (engraving), the laser marking of various degrees of shading from light to dark and even a limited range of colours can be produced too.

IMeta-C CO2One of the most visually appealing of laser marked effects is dark annealed stainless steel where the near jet-black effect of the laser mark contrasts beautifully with the clean and crisp surface of the stainless steel finish.

This type of mark is high in contrast and is often used to increase the perceived value of products that are marked in this way.

The colour change occurs by using the laser to heat the metal and create within it an oxide layer. Colours and shading will vary according to the amount of heat generated during the laser marking process.

A laser marking machine with a higher laser power can produce these types of mark at a much faster rate than a lower power laser marking machine.

For a laser engraver with a lower power, the feed rate (speed of beam delivery) will need to be lowered in order to expose the material to the laser for longer and generate enough heat. Even more heat can be added by closing the distance between the hatch lines in the graphic thereby multiplying the degree of overlapping of the focal point from hatch line to hatch line. Even more heat can be generated by delivering the hatch in a localised way; hatching small connected areas at a time.

The smoothest, most uniform results are achieved by deliberately marking the material out of focus (defoucused). This provides for a much larger, softer focal point to add even more heat. The required degree of defocus will vary depending on the configuration of the machine. How far to defocus in order to achieve the best result is initially a trial and error process but once the ‘sweet spot’ is found the process is easily repeatable.

If using a lens with 163mm f/l (110mm work area) the sweet spot is usually found between 3-5mm defocus. When using a lens with 254mm f/l (180mm work area) the sweet spot is usually found between 7-9mm defocus.

The oxidised layer of annealed material will only be approx 20-30µm in depth. Therefore, this is not a particularly hard-wearing form of laser mark. To produce a harder wearing mark it is possible to fist ablate (engrave) the steel then to anneal the material to further darken it. While this type of mark is certainly more resilient to wear and tear it is however not a visually smooth and lustrous as a mark annealed without ablation. Using a machine with a Z-axis that is controllable by software is essential for this process.

Even further enhancement can be achieved by first lightening the surface of the material with the laser delivered at an alternative angle, such as 45 degrees for example, then annealing over it with further passes. This procedure can produce a near to black on white effect for maximum contrast.

The laser annealing process can raise the stainless steel to nearly 600c, so this is not a suitable process to apply over large areas and/or to thin material as to do so can cause the material to deform. Materials that do not have a flat surface are not suitable for this process.

At Lotus Laser Systems we manufacture a wide range laser marking and engraving solutions ideally configured for laser cutting, laser marking and laser engraving all types of materials. Our experts would be happy to recommend which configuration best suits your application.