Laser Modules for Cutting/Engraving (CNC)

0. The ability of a small diode laser to cut or engrave depends on many factors but the basic principle is that the laser must transfer enough power to the target to reach the burning temperature. Important factors are:

   • Surface adsorption by target (matt black is best).

   • Thermal conductivity of the target - if the target conducts too well e.g. metal, the heat is dispersed rapidly. For a material to be engraved or cut he target must adsorb laser energy more rapidly than it loses it in order to heat up.

   • The amount of laser energy per unit area of the target (the laser needs to be focused to a small point on the target rather than a big spot).

   • The power of the laser.

   Commercial Laser Engravers

   Most ‘small’ commercial laser cutters and engravers use a CO2 laser, typically with a power of 20-40W (20,000- 40,000mW). A 20W CO2 laser can typically cut 3mm plywood and 8mm acrylic easily at full power and will run at ~5-10% power (1-2W) to engrave wood, cut paper etc.

   CO2 lasers are commonly used simply because they are the cheapest way to generate laser light at these power levels.

   The power output of common semi-conductor lasers (laser diodes) is much lower and the cost of laser diodes increases above a couple of watts to the point where they are no longer economic to use compared to a CO2 laser.

   It is however possible to use laser diodes to engrave wood, cut thin paper, balsa wood and pattern resist layers for PCB etching. Reducing the cutting/ engraving speed is often required.

1. Laser Diode Performance

   Laser diodes are produced commercially to have lifetimes of thousands of hours at their rated power. Often experimenters will run these diodes at higher powers (e.g. +50%) and still get lifetimes of at least tens and sometimes hundreds of hours. The exact results vary from diode to diode and depend on a stable driver and adequate cooling.

    

2. Blue Laser Diodes

   The most powerful low-cost diodes are 445-450nm Blue (1.6W - 4.5W), these are often run at +20-30% of the rated power in engraving/cutting applications.

3. Our laser modules are all built with laser diodes running at the manufacturers rated maximum current, we do not overdrive the diodes to increase the output.

4.  

5. 2W 445nm (Blue) Laser Diode Performance

6. Multiple slow passes are needed for thicker materials.

   1-2mm white acrylic                 Cuts acceptably at 120mm/minute with 2-3 passes. / Engraves well.

   1-2mm tinted acrylic                Cuts acceptably at 120mm/minute with 2-3 passes. / Engraves well.

   0.125mm Mylar sheet              Cut/engrave

   Paper, white, brown                 Cut/engrave

   0.4mm hard card                     Cut at 100-150mm/minute /Engraves well.

   3mm corrugated card              Cut/engrave

   Balsa wood:                            Engraves well.

7. 1/32″ Balsa:  Cuts well at 250-300mm/minute with one pass.  Two passes recommended for cleanest cut.
8. 1/16″ Balsa:  Cuts well at 200mm/minute with two passes.
9. 1/8″ Balsa:    Cuts acceptably at 150mm/minute with three passes.                 

10. 2mm light plywood                  Cuts acceptably at 100-150mm/minute with three-four passes. / Engraves well.

    0.5mm standard plywood        Cuts acceptably at 100-150mm/minute with three-four passes. / Engraves well.

    2mm leather                            Cuts acceptably at 100-150mm/minute with three-four passes. / Engraves well.

    5mm Foam board                   Cuts well at 150mm/minute with two passes.

    Anodised aluminium               Engrave anodised finish only.

11. Bare metal (brass, copper, aluminium)  – no engraving or cutting possible.

12. Glass – no engraving or cutting possible.

          Typical Modules:

OFL419 2W 450nm Blue TTL Laser Module with Adjustable Focus 12V

OFL365 2W 450nm Blue Focusing Laser Module (12V) TTL Driver

OFL365-2 2W 450nm Blue Focusing Laser Module (12V) Analogue Driver

0. 3.5W and 4/5W 445nm (Blue) Laser Diode Performance

1. The tests we have done with a 3.5W diode allow faster cutting / less passes but do not give a significant increase in the thickness of materials that can be processed.

2. Materials that require 2 passes with a 2W laser typically require 1 pass with a 3.5W or 4W laser. The higher cutting rate of the most powerful diodes normally gives a cleaner cut.

3. Typical Modules:

OFL419-2  3.5W 450nm Blue TTL Laser Module, Adjustable Focus 12V (CNC Engraving)

OFL365-1 4W 450nm Blue TTL Laser Module, Adjustable Focus 12V (CNC Engraving)

0.  

1. Red Laser Diodes

   These are the cheapest laser diodes for powers of 200-300mW, a 700mW diode is available but is nearing the cost of the more powerful blue diodes.

   200- 300mW red lasers are less well adsorbed than blue diodes so often paper and plastic need masking with a black marker or thin black paper to cut. They may also need several passes to cut materials.

   250mW Red Laser Diode

   Paper black                             Cut

   Chocolate                                Cut/engrave

   Paper white                             Cut with masking/engrave

   Coloured fabric: silk, cotton     Cut

   Hard Cardboard                       Engrave

   Balsa, Plywood                        Engrave

    

   Bluray (405nm) Laser Diodes

   These diodes are available as in 100mW, 200mW and ~600mW. OEM versions of these diodes are normally extracted from high speed Bluray writers as these are much cheaper than catalogue components.

   The 405nm laser light is adsorbed better than red laser light by many materials so black masking is not required. They are particularly useful for exposing photoresist.

   200mW 405nm Laser Diode

   Paper black                             Cut

   Chocolate                                Cut/engrave

   Paper white                             Cut /engrave

   Coloured fabric: silk, cotton     Cut

   Hard Cardboard                       Engrave

   Balsa, Plywood                        Engrave

   0.5mm balsa                            Cut/Engrave

   600mW 405nm Laser Diode

   Paper black                             Cut

   Chocolate                                Cut/engrave

   Paper white                             Cut /engrave

   Coloured fabric: silk, cotton     Cut/engrave

   Hard Cardboard                       Cut/Engrave

   Balsa, Plywood                        Engrave

   1.0mm balsa                            Cut

2. Laser Beam Profiles

3. The beam profile of the higher power blue (445-450nm) diodes is asymmetric due to the diode emitter shape and the difference in divergence between the fast and slow axis. 
   With the beam collimated (“parallel”) the ‘aspect ratio’ is typically around 1:4 depending on distance, when expanded it will increase but focused it will similarly decrease which allows it to be used for effective engraving when focused to the smallest size at short distances.
   For light show applications where a collimated beam is needed a pair of anamorphic prisms can be used to reshape the beam by compressing the fast axis and expanding the slow axis. This works for light show projectors but is not practical for engraving and in practice does not improve the result over focusing.
   The single mode lower power diodes like the 120mW blue Osram and the 405nm diodes have near-circular beams but the maximum power of these diodes is around 600mW (405nm).
   In high power commercial engravers,  CO2 gas lasers or fiber lasers are used which have a near symmetric beam - the gas lasers naturally have this profile and the fibre optic used in the solid state lasers acts as a beam homogeniser.
4.  

5. Building Laser Modules

   To build a laser module 4 main items are needed:

• Laser Diode (this is normally chosen by wavelength (colour) and power output)
• Housing (this should be chosen to match the diode size, normally 3.8mm, 5.6mm or 9.0mm and the expected heat dissipation requirements, most diodes can run at up to 60 degrees C)
• Lens (this should be chosen to match the wavelength of the laser diode)
• Driver (this should be chosen to match the current and voltage requirements of the diode, some drivers also have optional TTL switching for fast pulse operation)

0. Building a module will require the laser driver current to be set to match the diode, this is normally done using a dummy load such as:

   OFL70 Component Bundle for 3A /5W Laser Diode Test Load (supplied with instructions)

1. Driver (this should be chosen to match the current and voltage requirements of the diode, some drivers also have optional TTL switching for fast pulse operation)

Analogue vs TTL Drivers

The difference between analogue and TTL drivers is as follows:

With a "TTL”  driver a TTL level signal (nominally 5V but normally anything between 2.5v and 5V will work) will switch the laser on or off.
The TTL circuit avoids the soft start function of the driver and allows rapid switching so a pulse width modulated (PWM) signal can be used to control the average power.
The switching is between off and full power, the power variation is from the pulse duration, e.g. a 50% pulse cycle will keep the laser on for 50% of the time so the average power will be 50%.
TTL drivers accept very rapid switching (thousands of times per second), if the switching rate is greater than ~150Hz (times per second) the beam appears continuous to the eye but lower intensity (depending on the pulse width).

With an “analogue" driver the switching is the same except the laser output also depends on the voltage of the signal.
If a 5V signal is used the driver will act like a “TTL” module switching between 0 and 100% power with the pulse signal.
If the signal is less than 5V, e.g. 2.5V the laser will switch between off and 50% output.
Analogue drivers allow the true power to be varied by voltage and the the average power by pulse width.