The most important factor influencing the speed of earning money by a laser is efficiency, and efficiency is the number of elements produced per unit time. It should be remembered that in order to calculate the actual laser efficiency, we cannot take into account only the cutting time, because it often turns out that the preparatory activities significantly limit the actual cutting efficiency because any changes or implementation of a new part to production cause downtime in the laser, in which this is the time the laser does not make money.
Few are aware that the differences between the performance of different lasers can be multiple. Often, entrepreneurs change machines or technologies to improve efficiency by 20-30%, and the choice of laser alone can decide whether we will make 1000 or 5000 specific parts within an hour. There are many factors that make a big difference.
Optical fiber or CO2?
In the last few years, the dynamic development of fiber lasers has significantly upset the balance on the laser market. During the 30 years of presence on the market of CO2 technology, little has changed in the capabilities of these lasers because the companies producing them have already reached the physical limits of increasing efficiency, which does not exceed a few percent. That is why a CO2 laser with an output power of 4kW may need as much as 80kW of power. Fiber lasers have incomparably greater efficiency, currently reaching 35%, which means that the 4kW fiber laser source consumes only 12kW.
The differences between CO2 lasers and fiber lasers also apply to the wavelength of light. CO2 lasers generate light with a wavelength of about 10um, and fiber lasers about 1um. According to the laws of physics, the size of the spot of focused light depends on the wavelength, so the light of a fiber laser can be focused to a much smaller diameter than from a CO2 laser. The laser power affects the ability to melt a specific volume of material per unit time, and therefore the speed of cutting. If we are able to cut a gap several times narrower with a fiber laser, using the same power we can cut proportionally faster. Absorption is also important. Metals reflect light, and the amount of light reflected depends on the wavelength. Part of the light falling on the material is reflected, therefore only a certain percentage of the power generated by the laser is involved in the cutting process. The light generated by fiber lasers is much better absorbed by metals, which in turn also leads to an increase in cutting speed.
Due to the above factors, fiber lasers with the same power can cut material even several times faster. This applies in particular to thin materials because when cutting them you can use a very high concentration of the beam. Along with increasing the thickness of the cut, it is necessary to increase the diameter of the focused beam, because if we cut too narrow a slit in a thick material, then before the gas has time to blow out the melted material from the slit, it will have time to solidify again, causing the material to "weld". It is precisely because of the necessity to increase the diameter of the focused beam when increasing the thickness of the cut material, the disproportions between the efficiency of these lasers are reduced. However, it should be remembered that despite the reduction of differences in performance, the cost of an hour of fiber laser operation still remains up to 4 times lower than in the case of CO2 lasers. It follows that even if we obtain the same cutting speed with very thick sheets, the cost of cutting parts on the fiber laser remains up to 4 times lower.
It turns out, however, that among popular brands, there is no point in looking for fiber lasers that would be significantly faster than previous models with a CO2 source, often after switching to fiber lasers the efficiency increases only by 10-20%. This is because companies often do not design machines for the new technology from the very beginning, but only install a fiber optic source on existing structures made of CO2 lasers. Unfortunately, they are thus wasting the potential of the new technology. Why, if the linear cutting speed of fiber lasers can be several times higher, most lasers cut only up to 20% more efficiently? It turns out that the main reason is CNC control systems, which were designed for use in cutting machines, and were adapted to control lasers. Lasers cut many times faster than milling machines and some parameters of the control system are insufficient for lasers. One of them is the frequency of the position regulator, it is a parameter that determines how many times per second the machine corrects its coordinates. In the available control systems, this parameter reaches the value of 2000 Hz, i.e. the position is corrected 2000 times per second. Is that a lot? In cutting machines, the working feeds are so low that correcting the position with such a frequency is sufficient. However, in the case of lasers with a fiber-type source, cutting speeds can reach 1 m / s, which means that the position will be corrected only every half a millimeter - this is much too little to maintain the correct geometry. In particular, this problem concerns complex shapes, holes, corners that would be deformed under such conditions. The only thing that remains for producers using such control systems is to limit the cutting speed when passing shapes. It is true that the distances between position corrections get denser so that the shape may be correct, but we are wasting time, and a lot of time! It turns out that most lasers slow down many times more when cornering than would be required by the laws of physics due to the moving masses.
For 20 years, the Kimla company has been producing and developing very high-performance control systems, which, when fiber lasers appeared, made it possible to fully use their potential. Due to the fact that the frequency of the position regulators of the Kimla control system is 20kHz, it is possible to correct the coordinates ten times more often, which means that the head can move around complicated shapes several times faster without deteriorating the geometry. The differences are so visible that one Kimla laser can replace up to several laser cutters from other companies.
Commonly used control systems have one more ailment. The whole concept of their operation comes from the 1950s, when fledgling processors had low performance, and programs were stored on perforated tape. It was then that the first CNC machines were created that used programs stored on this paper carrier, and due to the fact that many commands in the format of the program describing the geometry to be machined began with the letter G, this entry was called G-code. Despite the rapid development of computer techniques, manufacturers of CNC control systems have not introduced new standards to this day, and their development over the years resembles an evolution rather than a revolution. Initially, programs were created by hand, but it took a long time. It was only in the 1980s that the first programs for automatic generation of the toolpath began to appear, which automatically created G-code based on the loaded geometry. This was a great help as the programming time for the machine was reduced from days to hours, but it was still not profitable to run such a machine to make individual parts. Entering the new century, manual programming of CNC machines was practically no longer encountered, and CAM programs continued to develop and allowed for more convenient and faster program generation. Only one problem remained - 2 people were needed to perform any treatment. Machine operator and technologist with a CAM program that generated machining programs for the operator. The operator himself usually could not do much on the machine himself. In addition, the process of implementing a new detail often requires many corrections and adaptation of technology, which means that before starting production, the process of generating the tool path must be repeated many times.
Kimla lasers use a control system that integrates all the functions necessary to prepare, correct and cut out details. In addition, this system includes a module for optimal nesting, production management and allows for cooperation with ERP systems to support the company. There is no need for a technologist to cut the required details anymore because the operator can easily perform all the necessary activities directly on the laser control system. However, if the need arises for the technologist to prepare projects for the laser, the driver software can be installed on an external computer and work in the classic way.
Laser drives
Various types of drives are used in CNC machines, but they are almost always drives in which the rotational movement of the motor is converted into a linear movement by means of a ball screw or a toothed bar. In the case of lasers, a gear drive has been the basic solution for many years, because it allows for driving relatively long axes at high speed. However, this solution has significant drawbacks that limit the capabilities of the machine. Like all driveline components working in contact with each other, they are subject to wear. This is especially important at high speeds and dynamic loads, which are not lacking in lasers. This problem is particularly evident in lasers with a fiber optic source because the possibility of cutting at high speeds makes it tempting to exceed the technical capabilities of this type of drives, which leads to their rapid wear and costly repairs. An alternative to rotary actuators are magnetic linear drives which do not have any rotary elements because they use the magnetic field directly to move the head. The linear drive consists of a magnetic path made of permanent magnets and a forger with a core and coils that moves over the magnetic path. This drive is non-contact and has no wearing parts. The position measurement is also non-contact, which is performed with a ruler with precisely applied stripes resembling a bar code. The optical head moving above the ruler reads the position of the head and on this basis corrects its position. Such scales have a very high resolution, reaching 1 nm, and the accuracy of the position measuring system is 0.005 mm / m. Thanks to the use of measuring rulers, the reading of the position is made directly, which allows to avoid errors introduced by systems with rack and pinion drive.
The Kimla company has developed special linear drives dedicated to forest cutters
The Kimla company has developed special linear drives dedicated to laser cutters. They are characterized by a high power density, because in applications as dynamic as laser cutting, the power-to-weight ratio of the drive is crucial. Thanks to this innovation, the self-limiting performance barrier, which is caused by the large mass of commercially available linear motors, has been surpassed. A significant increase in the drive power without lifting its weight allowed the barrier to be surpassed so far.
Most laser manufacturers do not have their own control systems and are based on solutions purchased from third parties, which limits service competences, often repairs take a disproportionately long time to the problem, and the costs generated by replacing components "in the dark" escape out of control. The practice of not repairing damaged modules has also become common, instead, in the event of a failure, only the possibility of replacing it is proposed, often at a price disproportionately greater than the actual cost of the damaged components. Large companies with extensive distribution structures willingly use this practice due to the need to compensate for their high maintenance costs. Often, the elements of control systems are designed in such a way that their repair is not possible, and the only way to start the machine is to replace them completely.
