In general, laser material processing is carried out using CO2 and YAG systems. This work typically covers welding, cladding and cutting to produce such unlikely products as juice cans and razor blades. Excimer lasers are fast becoming the next most popular processing machine. They are especially suited for the removal of thermally sensitive materials with minimal heat damage and production of micron sized features. Beginning with what can be achieved in various materials this paper will step through the main requirements in developing a fully operational excimer laser process. This should reflect an efficient beam delivery design, high quality aperture masks and specialized part handling equipment. This paper will also address aspects of motion control, vibration isolation and specialized vision systems.
Waveguide excimer lasers in combination with high-resolution imaging and precision motion control systems are capable of direct-write shaping of diamond and diamond-like materials. 3D structures can be produced by scanning the worksurface under the focused beam and varying the energy delivered to the worksurface through use of various exposure algorithms. Using this technique, we have produced microstructures in diamond that demonstrated high spatial resolution and good surface finish.
Results are reported for the use of a 266 nm frequency quadrupled Nd:YAG ultraviolet laser in the areas of wire stripping of small coaxial type transmission lines and for micro-machining of various materials including copper, glass, polyimide and DuPont TEFLONTM. This new laser is typically run with a 2 KHz repetition rate, 40 ns FWHM pulse and a fluence of about 50 joules/cm2 which makes it possible to micro-machine metals, polymers, glasses and ceramics. The high fluence of this laser allows shielding structures such as Al-MylarTM, Al-KaptonTM or the plated copper used in small coaxial cables to be precisely cut. Cut rates are reported for the above materials as well as results and photos of wire stripping and micro- machining.
The copper vapor laser (CVL) is an efficient, high average power, high pulse rate visible laser, emitting in the green and the yellow. Previous applications of CVLs have been limited to those requiring a high power visible laser source but with no specific need for high output beam quality. Recently we have made substantial progress in understanding the factors that influence CVL beam quality. As a result we are now able to achieve efficient non-linear frequency conversion to produce a number of ultraviolet wavelengths with near- diffraction limited beam quality. The high repetition rate and low divergence uv output of the frequency-doubled CVL makes it an attractive alternative to the excimer laser for a number of applications, including high-speed precision hole-drilling, cutting and scoring in polymers and for deep-uv photolithography. We report here recent developments that have led to efficient generation of uv wavelengths from copper vapor lasers and we demonstrate its potential as a laser source for high-speed precision ultraviolet micromachining.
Optical characteristics of the output coupler in a high-power CO2 laser can be measured while the optic is in the laser and functioning normally. This is done by using a beam propagation analyzer to measure the rate at which the beam waist location changes with increasing beam power. The characteristics that can be measured with this technique include the fraction of beam power absorbed by the optic and its radius of curvature.
The temporal beam power fluctuations of a high-power CO2 laser are analyzed according to their frequency spectrum and its time dependent variation. Simultaneously to the laser beam diagnostic, signals obtained from the light emission during the cutting and welding process have been detected. By comparison of corresponding spectra the interaction between beam oscillations and process dynamics is studied. The influence on the surface structure of the processed material is discussed especially in the case of laser beam cutting. For this the spatial surface morphology is also analyzed by means of local fast Fourier transformation. The overall result is that the spectra are not constant, but show time-dependent behavior. Thus a more detailed correlation analysis is necessary for full description of dynamical beam--process-interactions.
The focusing characteristics of divergent laser beams change with the distance between laser source and processing head. To keep the energy distribution on the workpiece surface on the same level while working with a flying lens, the use of deformable mirror systems has proven to be a suitable solution. In this case, a newly-developed system is brought into the beam guidance system to keep the focal spot diameter constant.
Hollow sapphire fibers have been used to deliver up to 1500 W of CO2 laser power for industrial laser applications. These hollow waveguides incorporate a water jacket to prevent overheating. The fibers are about 110 cm in length and they have been bent to 90 degree(s). The bending loss for the large 1070-micrometers bore fiber is less than 15% of the straight loss.
Programmable hole sizes and shapes may be cut by trepanning a beam focus on the workpiece. In order to minimize the number of optical elements, a device which relies on offsetting the focusing lens axis from the beam axis was used. Since the beam focus always moves with the lens, holes may be cut by moving the lens axis around a stationary beam. Optical analysis on the effects of an off axis beam on its focus spot aberration, size and position were performed. Their effects on cut quality will also be presented. This study also provides an insight into how accurately a laser beam needs to be aligned with the lens center in order to obtain good quality cutting.
SCOUT a seam tracker system designed for precise machining with the capability to position the axes of an industrial robot or gantry in space (three dimensions). This system was developed to meet the positioning accuracy of +/- 0.05 mm (+/- 0.0127 inch) and path speed above 20 m/min (800 IPM) for laser welding as well as e.g. sealing or gluing. With SCOUT system it is not necessary to define a welding path with the very time consuming teach-in process.
The working quality in laser material processing is influenced by a number of parameters as to laser source, beam guiding system and material. Although the reliability of the lasers and the stability of the system components have been improved there are still some weak points. In the following a closed-loop control system is presented which will help to meet the requirements.
3D laser machining requires a considerable investment, handling devices of high precision and a great expense for the planning of an application and for program generation. With new applications, one has to consider the specific properties, requirements and the advantages of laser systems to achieve economical results. The time consuming methods that are used today--e.g. program generation by teach-in--lead to a low productivity and low machine utilization, especially with small batches. The two examples given here are focusing on 3D laser processing, e.g. of deep drawn workpieces, and high process flexibility. They are intended to show, how new methods for program generation, simulation and sensor assistance in laser processing can be used to save time in the planning phase and to significantly reduce the expense that is caused by tolerances in shape and position of the parts to process.
Iomega decided that be developing our own Floptical media production equipment, we could enhance the basic Floptical technology with our servowriting experience and capabilities acquired from our own patented BernoulliTM Box magnetic storage technology. This technology synthesis has led to our proprietary laser ablation servowriting equipment for magnetic media. This system has been dubbed LightSaberTM.
Laser cutting of ceramics is a promising alternative to conventional machining methods. In this paper, processing results using several lasers and beam guidance optics to cut different oxide and non-oxide ceramics are presented. Adapted process parameters in pulsed mode operation provide high quality cut surfaces at acceptable feed rates. Especially Nd:YAG lasers can be used for cutting extremely brittle ceramics. The use of fiber optics for beam guidance, however, is limited to certain ceramics with high fracture toughness, due to a loss in beam quality. In laser cutting of ceramics, thermally-induced crack damage is one of the main problems preventing a wider use of this method in industry. Several methods were investigated in order to reduce crack formation. Adapted pulse parameters, calculated by a theoretical model, and also a newly-developed process control system lead to a remarkable reduction of crack damage. Crack-free cutting can be obtained by preheating the workpiece above a temperature of 1.100 degree(s)C. Based on these investigations, requirements on laser systems for ceramics cutting are worked out.
The power output capability of the CW Nd:YAG laser has made rapid increases recently. This laser format allows the power to be easily scaled. The beam quality of this laser format also allows for beam delivery by fiber optic cable. The welding performance of this laser type is useful and productive for industrial applications. The welding capability of a CW Nd:YAG laser will be examined in the power levels above 2 KW on low carbon and stainless steel. This will allow comparison to the efficiency and capability of the lasers available to industry for welding.
In this paper, laser cladding of CuSnP alloy on HT2040 cast iron was investigated. By adding a proper ratio of Si or H3BO3 to improve the self-melting property of the CuSnP alloy and optimizing the processing parameters, a large area, homogeneous CuSnP clad was achieved. The metallographic structure of the laser clad is (alpha) -Cu + (beta) -Cu5Sn with hardness of Hv150.
Results of experiments on gas-laser cutting of composition glasses three ply using emission of an electric discharge close circuit subsonic CO laser are presented. The parameters of the experimental arrangement are given. It is shown that satisfactory results for division of three ply glass with thickness about 7 mm are obtained when the rate of stretching is 2 m/min and output power is 400 W. Cw supersonic e-beam sustained CO laser (SS CO EIL) was shown to be the most effective and compact among all high power lasers. Experimental testing proved that we have in possession the technical solution enabling to construct technological supersonic e-beam sustained cw closed-cycle CO laser with the power of several hundred kilowatts and wall plug efficiency being more than 20% (power supply from AC-net and water cooling).
In this paper we present the development of laser fibers and connectors in four steps. First is the development of a new coupling method of the laser and fiber. This includes the specially designed connectors which suppress temperature rise of the fibers. Second, we discuss the difference in the power transmission between a step index fiber and a graded index fiber. Third, we discuss the development of a new material for fiber coating which drastically eliminates the chance of heat break of the fiber. Finally we discuss the development of a special high power connector. The connector which has a mechanical fiber clamping structure can withstand 2 kw energy transmission and allows for easy connection of fibers and long distance laser beam transmission using a 200 m-long fiber.
Solid State lasers using diode array excitation continue to make significant progress in laboratory development. Though used in certain industrial applications in semiconductor manufacture, this type of solid state laser has not yet seen broader use. This article summarizes the status of this technology and projects the conditions of cost and market volume needed for greater use of such lasers. Large volume, high power industrial applications must play a substantive role in the adaptation of this technology since the high power industrial laser market is one of the few markets with volumes large enough to drive the cost of the diode component sufficiently low for mass usage to be affordable.