Using the laser to process plastics has become firmly established in recent years and this technique repeatedly poses new challenges for the experts. This is due to the wide variety of the plastics and their tremendous range of properties – and new versions are appearing regularly. Matching the laser system to the material and identifying the perfect parameters are the keys to successful and profitable manufacture. To do this, TRUMPF operates one of the world’s most comprehensive and modern laser applications centers, not far from Stuttgart. “We can quickly try out a project on many different machines, regardless of whether the customer wants to use the laser to mark, cut or weld plastics,” says Martin Sauter, TRUMPF’s manager for the non-ferrous machining industry.
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Compact diode lasers for welding work
- The diode lasers create an interesting beam profile: virtually rectangular and with a flat plateau, reminiscent of a top hat. Thus the lasers apply uniform intensity across the entire width of the seam.
- The diode lasers engineered by TRUMPF deliver beams with wavelengths of between 930 and 1,030 nanometers and excellent beam quality of < 8 mm x mrad. This high beam quality makes it possible to employ long focal lengths. In turn, the galvano scanner can work large areas.
- An external beam management box makes it possible to connect two output points. This permits time sharing, in which two optical arrays work alternately, each with full laser power. Here, for instance, two systems will alternate, welding one part while chucking the next. The box also enables power sharing, in which two optical arrays work simultaneously, each with the half of the output power.
Compact CO2 lasers for cutting and drilling work
- High-frequency control using transistors is energy-efficient, requires no maintenance, and emits very stable pulses with a highly uniform shape and repetition rate. This is important in micro-perforation, for instance.
- A wavelength of 9.3 microns is used instead of 10.6 microns. This improves the focusing properties as well as the absorption and thus raises the processing speed. With many plastic compounds, and at identical laser power, this may be as much as ten percent higher. In many applications, this new wavelength brings about considerable advantages. One example is high-speed drilling of holes in the printed circuit boards used by the electronics industry.
Consequently, the smallest CO2 laser unit built by TRUMPF can also be used to cut and weld metals. Where a plastic item is finished with a metallic surface, this can be cut in a single pass.
More about welding special materials
Lasers for marking plastics
Marking plastic components with lasers has already made its debut in many sectors. One important reason behind this is the demand for product traceability. This need can be satisfied permanently in the form of numbers, a barcode, or a QR code. Individualizing consumer products also helps to boost demand. Manufacturers of vehicles, yachts, private jets, and even consumer goods like smartphones and advertising items are enhancing their products with special patterns, logos or lettering on the surface or for interior fittings.
Solid-state infrared lasers can be used to apply lettering to most of the plastics used in industrial settings. Most thermoplastics can also be marked in this way. TRUMPF recently added the compact and economical TruMark 1110 for such purposes. Inquiries from the automotive industry arrive at the Laser Applications Center almost daily. They often involve using PBT GF30 or glass fiber reinforced PA6 GF30 polyamide for housing components.
Using an ultraviolet laser beam is often required to mark electronic housings that incorporate flame retardants. Available for over a year now is the new TruMark 6350. It aligns exactly with the trend toward using UV lasers to work carbon fiber reinforced plastics (CFRP). This laser is used not only for marking, but for drilling, too.
Welding plastics with lasers
Welding plastic parts with the laser beam is becoming ever more prevalent. Two experts – Dr. Birgit Faisst, manager for marking and micro-laser applications, and applications engineer Daniel Kaiser – count off the advantages. Ms. Faisst begins: “When compared with ultrasound joining, laser welding is easier on the part, is very flexible, can be programmed to cut every conceivable curve, preserves the qualities of the surfaces, is fast and reproducible, is environment-friendly, and does without any toxic bonding agents. The seams can withstand heavy mechanical loading and a minimal amount of thermal energy is injected into the workpiece.”
There is one proviso: “It is very important for the user to know which materials are needed for the product,” Daniel Kaiser emphasizes. If the laser is to join two parts with an overlapped seam, then the upper component must be transparent to the usual wavelengths of diode lasers, i.e. between 800 and 1,100 nm. The backing component will, however, have to be doped with color pigments or carbon black so that the energy of the laser beam can be absorbed, causing the material to soften. The heat is then transferred to the upper part, melting its surface, too, so that the two parts can be joined. This is why the melting temperatures of the plastics being joined have to be similar. Otherwise, one plastic might have already broken down, while the other had not yet reached its softening point.
Diode lasers are especially suitable for joining plastics. Welding by means of the galvano scanner is referred to as quasi-simultaneous machining. “The plastic component can be heated evenly in this process and both parts are pressed together uniformly, across the entire surface area, so that no stress is created,” Kaiser explains. The beam darts along typically at a speed of 1 to 5 meters per second, passing over the welding seam three to five times. Thus two squares, each measuring about 150 millimeters × 150 millimeters × 3 millimeters, can be joined in one to two seconds.
Cutting plastics with lasers
In contrast to marking and welding, plastics need not be doped with additives in preparation for cutting. Thus polyethylene, polyamide, fiber-reinforced plastics, and expanded products like PU foam are perfect for cutting by the CO2 laser. This offers users many benefits when compared with mechanical techniques. Laser cutting offers top quality and separates even fiber-containing materials smoothly and without any fraying. The machine is flexible, fast, clean and dry. There is no wear on parts and there are no hazardous solid or liquid wastes, which are difficult to dispose of.
When choosing between a beam-deflection scanner or Cartesian cutting, both the material’s thickness and the size of the parts play a role – along with the desired production speed. Cutting using the galvano scanner is extremely fast – five to ten meters per second are possible. This technique is used especially for thin materials such as packing films, since the high-speed production equipment calls for high traversing speeds. When the material is more than about 1.5 millimeters thick, cuts at the edge of the processing range start to show a visible slope at the edge, due to the angle of the laser beam, as industry manager Martin Sauter explains. “During the Cartesian process with standard X and Y axes, by contrast, the cutting line is always at right angles to the surface. The downside is that travel speed is not as high. The two processes can be combined with good results, however.”
TRUMPF’s experts recommend using the CO2 laser to cut plastics. The CO2 laser couples the laser beam’s energy into the surface instantly and, as a consequence, leaves a cut surface that is very clean.
By selecting the new TRUMPF CO2 lasers, the user demonstrates awareness of quality, energy efficiency, and flexibility. This applies regardless of whether automotive headlamps, decorative facings, or floor coverings are being cut. The same holds true for plastic-coated panels that are being trimmed to size for the furniture or construction industry, or whether it is a question of making holes in hybrid films for the packaging materials industry. The user will be sure to find the expertise needed for plastics processing at the Applications Center in Ditzingen. Every field is covered: marking, joining and cutting.