This basic introduction provides information on laser processing that is relevant for every materials processing situation.
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Since its inception in 1966, Coherent has been at the forefront of Materials Processing applications. Beginning with its first product, the CO2 laser, Coherent has served a wide variety of applications with the broadest product portfolio in the market – power levels ranging from a few mWs up to multiple kWs, pulse widths from femtosecond to continuous wave (CW), and laser wavelengths from 193 nm to 10.6 µm.
In the Materials Processing market, Coherent focuses on laser cutting and converting, laser welding, marking & engraving, surface treatment and rapid prototyping applications.
Laser cutting is a mature industrial process with high flexibility, non-contact and stress free processes that produce finished parts right from the tool. Laser cutting is very precise, with excellent dimensional stability, very small heat affected zone, and narrow cut kerfs. Various technologies are used depending on the type of material to be cut. In our descriptions below, we differentiate between metal cutting and non-metal cutting. Typical metals include stainless steels, mild (carbon) steels, aluminum, brass and copper. Non-metals include plastics, ceramics, fiber reinforced materials, and organics such as leather, fabric, paper, wood and others.
Laser welding is one of many techniques for joining materials. The main benefit resulting from using a laser for this technique is high processing speeds with no tool wear due to a contact free process. The process leaves low heat affected zones and low part distortion resulting in small welding seams with very little need for post processing. A high degree of automation including process monitoring, control and documentation enable excellent product quality and repeatability. Process speed is dependent on the laser type used, its power, the material type and the weld geometry. A large variety of materials with different thicknesses can be welded with various methods. Typically all metals, which can be welded by conventional technology, can be welded by laser. These are steel and aluminum parts but also copper used in the electronics industry. Laser welding of metal can be differentiated between keyhole welding and heat conduction welding. A selection of plastics can be successfully welded by using a diode laser.
Many materials like fabrics, plastic foils, and papers are processed on the fly using a reel to reel process. Applications may be found in the medical and food industry in the manufacturing of pouches for soups, coffee or beverages, but also in digital printing lines or production lines for grinding paper. Lasers are an established tool in these converting lines. Typical applications are cutting (incl. kiss cutting), scoring and drilling. In one example, the material is processed in the direction of travel or in a down web application. In this case, the laser beam is focused on the web by a fixed optic, while the material is moved underneath by web, allowing the material to be slit to width. In another example, the material is processed perpendicular to the material (web) flow direction. This is referred to as a cross web application. A galvanometric scanner steers the laser beam across the material while compensating for the material flow speed by using a velocity sensor. In most cases, a CO2 laser is used emitting a wavelength of 10.6 µm or 10.2 µm (ideal for PP processing), as mainly organic materials and plastics are processed. This wavelength is absorbed with most of the materials very well. In some special instances such as in the medical segment, UV lasers are used. Coherent is addressing this market segment with its DIAMOND C- and E-series CO2 and AVIA UV lasers.
|Typical examples for laser processes in converting are:|
Lasers are commonly used for marking and engraving of materials. There are a wide range of applications in automotive, electronics/semiconductor, aerospace, medical, consumer product and food/beverage industry. Benefits of laser marking and engraving in comparison to other traditional marking technologies are multifold. The processes are non-tactile and do not induce mechanical stress. It is a very flexible, basically maintenance free process, and the results are very precise and sustainable marks on a large variety of materials. It is also low in consumable cost.
Laser marking uses the laser beam from a CO2 laser like the DIAMOND C-Series, or from a DPSS laser like the Matrix Series is steered with a galvanometric scanner head. The mark is typically created by a vector based procedure which allows for the highest mark speeds. Flat field lenses focus the laser beam and make sure that the focal position is always in the same focal plane throughout the whole laser marking area. The focal length of the lens defines the size of the marking field.
In laser engraving, the laser beam is steered through a flying optic system. The focusing optic is moved in X- and Y- directions in a raster pattern across the engraving area. A large variety of materials can be marked or engraved using a laser. Different laser types are used depending on the material.
Surface treatment is used in a variety of Industries to improve the surface material properties of a component. Laser cladding is a process where material is added to the melt pool on the surface of a part in the form of powder or wire to create a surface layer with different properties. This process can be either used in manufacturing or repair of large or complex geometries. In laser heat treatment, large or complex components are rapidly heated and cooled to increase surface hardness.
Rapid prototyping is used in applications where design prototypes or a low volume of complex parts are required to be fabricated quickly. The process enables manufacturing of complex parts out of either an epoxy polymer or powder without the need of complex tooling. The process is differentiated between Stereolithography (SLA) and Selective Laser Sintering (SLM). In both the SLA and SLM processes, a 3-D CAD model is sliced into many layers like a stack of cards then transferred to the SLA or SLM tool. The laser beam is steered by a galvanometric scanner head and builds up the part layer by layer. After each layer is processed, a layer of polymer or powder is deposited on top of the part and the next laser processing step begins.
Laser Processing of Carbon or Glass Reinforced Plastic
Carbon Fiber Reinforced Plastics (CFRP) and Glass Fiber Reinforced Plastics (GFPR) are widely used in a large variety of industries. These composite materials are used in Sports and Aerospace industries, as well as various other industrial applications like Wind Energy and Automotive. In the past, manufacturing processes were based on lower production volumes of composite materials. A desire for energy efficient vehicles and aircraft now drive the demand for lightweight materials leading to increased production volumes of these materials. The aerospace industry as an example is increasing the share of CFRP in their aircraft to greater than 50%. The automotive industry is looking to use CFRP to reduce fuel consumption and therefore meet new directives for carbon emissions. Additional advantages of using Carbon Fiber include improved vehicle performance, larger wind mill designs due to the use of lightweight materials, and an increasing amount of offshore installation demands for new mounting and service concepts.
When processing composite material, the proper choice of the laser wavelength is critical. Most resins are transparent by commonly used 1 µm wavelength. Absorption on carbon fibers is very high. Thus this wavelength leaves a heat affected zone that is not acceptable in most applications. A CO2 laser wavelength (10.6 µm) is well absorbed by most resins and fibers. Unfortunately it inputs a lot of heat into the composite material and leaves a burnt surface or edge. The ideal wavelength for most composite processing applications is in the UV range as it is absorbed by the resin and the fiber, and offers a cold process with a low heat affected zone.