Features of optical systems of CNC laser machines

Contents:

Laser cutting and engraving is one of the newest types of machining workpieces. In comparison with contact mechanical cutting (widely used today), the optics of the laser machine has a number of significant advantages, and the main ones are:

• high quality of the processed seam;
• unsurpassed thinness of the cut (approximately a fraction of a millimeter);
• high processing speed.
• the ability to process a wide range of materials (including leather, paper, polymer film, rubber, i.e. those materials whose contact machining on machine tools is extremely difficult);
• high quality laser treatment regardless of the type of workpiece surface (its purity, roughness, the presence of protective coatings, etc.);
• no noise and vibration during processing;
• complete absence of chips and dust;
• no tool wear (the “eternal” laser sits for it) and less wear of the machine equipment during operation.

The only drawback of laser processing is the impossibility (for most “budget” machines) of full-fledged work with metal workpieces. It should also be noted that laser equipment is not intended to completely replace contact processing machines (CNC milling or CNC turning), but is intended for effective use in its personal niche.

Laser processing equipment

Compact, inexpensive and easy-to-operate CNC laser engraving machines are used for laser processing. They are designed for shaping, cutting and engraving workpieces of any configuration (suitable in size to the working area of a particular machine) and obtain high-quality products. Most models of laser engraving machines have a mechanism for loading / pulling through the working area of rolled blanks that eliminates the need for pre-cutting of the material and simplifies the process.

Thanks to the numerical control system (CNC), laser machines are easily programmed and reconfigured to produce a particular type of product. Moreover, such a readjusting is carried out within a few minutes — you just need to load the necessary files into the memory of the CNC system. Any graphic sketch with the trajectory of the laser emitter built on its base can be used as a program for processing. This principle of creating programs makes it possible to prepare different models for processing, and the ability of the laser emitter head to move over the workpiece in three independent planes will allow the material to embody the most daring ideas of the designer. At the same time, precise mechanics and a high-resolution optical system make it possible to produce very high — quality products on a laser machine regardless of their complexity (whether it is an ordinary snowflake made of paper or a three-dimensional artistic bas-relief!).

Device of optical system of the CNC laser machine 

As you know, to create laser radiation you need:

• an active medium that emits photons of the desired frequency (visible spectrum);
• pumping energy (external power, to be simple);
• optical resonator (lens and mirror system).

Most models of CNC laser machines use the so-called “CO2 laser”, which has a high radiation stability and low specific energy consumption during operation. The active gas medium (a mixture of carbon dioxide, nitrogen and helium) is sealed in an oblong glass tube (0.8 to 1.8 m long). The tube is equipped with an optical resonator and a cooling system. A separate transformer with a primary “ignition” device is used for power supply (providing pumping energy).

The laser tube is installed horizontally in the back of the machine body (behind the main compartment, the working area, for placing workpieces). A high-energy beam emitted from one end of the laser tube passes through a system of prisms and hits the mirror of the laser head, which deflects it down. A special focusing lens “collects” the beam in a narrow beam (about a fraction of a millimeter) directly on the surface of the workpiece.

Triangular prisms are mounted on a movable tool portal and can freely change the distance relative to each other, so that the head of the laser emitter makes a complex movement over the workpiece, implementing the processing route laid down in the program. However, the prisms always remain parallel to each other, so that the laser beam only changes the “dyne” between them, but does not go beyond the boundary of the optical axis.

Bearings with a reduced coefficient of friction provide prisms sliding, and their movement through the belt drive set the executive elements of the CNC system – stepper motors. The length of the control pulses and, accordingly, the distance to which the prisms move (and as a consequence, the head of the laser emitter) is formed by the microprocessor of the CNC system – based on the codes of the control program file.

Various options for optical systems of CNC machines

In the basic configuration, CNC laser machines are usually equipped with tubes with a power of 40-80 watts. This is enough for confident cutting of blanks from various materials (acrylic plate up to 20 mm thick is cut through). By varying the power of the radiation and the speed of the laser head, you can achieve the desired quality of processing workpieces from different materials (at partial power, the laser leaves a clear qualitative trace of engraving on the surface of the workpiece).

However, when processing high-density workpieces (for example, wood, glass, stone) may require more power. Accordingly, each model of the CNC laser machine allows the installation of high-power laser tubes (optional-up to 200 W). In principle, such a replacement can be made independently. You only need to carefully handle the fragile laser tube and replace it with an “ignition” device (their power must match).

To increase productivity, a number of models of CNC laser machines have two emitters and are respectively equipped with two laser tubes. Their mutual work is automatically coordinated by the CNC system of the machine, which allows parallel processing of two workpieces at once having a double increase in the intensity of output.

Optical systems of some machines have a built-in digital camera for automatic pattern recognition on the workpiece. This allows processing on top of existing images or with any binding (indent, offset, etc.). Such models of CNC laser machines are in demand for the manufacturing of products included in the general technological chain and involving further processing (for example, tags, labels, barcodes, etc.).

Finally, where higher processing quality is required, models of laser machines with a movable tube mounted directly on the tool portal are used. This scheme minimizes the path of the laser beam from the source to the emitter head. Accordingly, the losses are reduced due to the absence of multiple refractions/reflections of the beam in the “intermediate” prisms and mirrors. The only drawback of such a scheme is the complication of the laser machine maintenance (first of all, the replacement of the tube) and restrictions on the processing speed (the tool portal, weighted by the tube, cannot develop too large accelerations).