Robotic Laser Welding Research Articles

Robotic laser welding: how to increase quality while reducing process times*

A robotic laser welding cell for stainless steel components, which includes a Cartesian robot, is described. The solution allows a drastic reduction in production times along with increased final quality compared to traditional welding technology, thus representing a particularly significant example of the advantages of the flexibility of a robot and the quality of the laser.

Robotic laser welding for the fabrication of stainless steel components

Robotic laser welding is emerging as the leading joining technology for the fabrication of stainless steel components, but this does not mean it should always be applied indiscriminately. The present work examines the laser welding technology in terms of the process, joint preparation and the necessary automation, with particular reference to stainless steel components. Analysis shows the crucial points associated with the necessary design and/or fabrication variations for components to be welded essential for achieving the qualitative and financial advantages of the laser process. Certain applications are then described, focussing on two families of stainless steel products. The first family is significant as an example of welding of components with axial symmetry, such as valves or pumps for fluids. These are European applications operating in Italy, some of which recently installed, the others have been operational for several years. On the other hand, the other family is an example of parallelepiped-shaped components, such as boxes and cases for isolators or containers for hazardous materials, where weld quality is fundamental. These are installations in Europe and Asia, where they have recently seen extensive development. The apparent advantages in weld quality, cycle times, automation and safety are described in full detail. From comparison of the preliminary analyses and examples presented, the reader is presented with a limited ‘guide’ in order to assess the convenience of the use of this recently developed robotic joining technology.

Total Energy Estimation Model for Remote Laser Welding Process

The issues in the energy-efficiency process have much interest in the automotive industry. The energy criteria are also important in machine selection as well as productivity when new equipment is introduced on a shop floor. Remote laser welding having benefits for productivity and for energy saving is receiving attention in automotive assembly lines, but introducing this innovative equipment is a significant decision because of high initial cost in spite of the advantages. This paper specifically provides an estimation model of the total energy which is consumed by a robot arm, laser source, and cooling system. It considers the energy determined by robot operation parameters, arm path, and welding parts instead of the one for the laser melting phenomenon. Operational parameters and kinematic models are adjusted by comparison with experimental data of a car door assembly process. By developing an estimation model the major factors and devices determining consumed energy were found. This model will contribute to finding the effective process which will be improved by applying remote laser welding robot to legacy welding processes.

Height control of laser metal-wire deposition based on iterative learning control and 3D scanning

Laser Metal-wire Deposition is an additive manufacturing technique for solid freeform fabrication of fully dense metal structures. The technique is based on robotized laser welding and wire filler material, and the structures are built up layer by layer. The deposition process is, however, sensitive to disturbances and thus requires continuous monitoring and adjustments. In this work a 3D scanning system is developed and integrated with the robot control system for automatic in-process control of the deposition. The goal is to ensure stable deposition, by means of choosing a correct offset of the robot in the vertical direction, and obtaining a flat surface, for each deposited layer. The deviations in the layer height are compensated by controlling the wire feed rate on next deposition layer, based on the 3D scanned data, by means of iterative learning control. The system is tested through deposition of bosses, which is expected to be a typical application for this technique in the manufacture of jet engine components. The results show that iterative learning control including 3D scanning is a suitable method for automatic deposition of such structures. This paper presents the equipment, the control strategy and demonstrates the proposed approach with practical experiments.

Image Detection of Seam Line for Laser Welding Robot

Automating robot laser welding requires that laser irradiation direction and laser focus positioning influencing welding strength be controlled precisely along the seam line. Since the edge of the welded object can be transformed in processing by such as cutting, bending and grinding, direct measurement is necessary to detect the seam line. A robust image detection method of seam lines is proposed for hand-eye laser welding system equipped with an optical microscope, a CMOS camera and two slit lasers for measurement. The seam line is detected indirectly to utilize the difference between local and global distribution of image of measurement lasers. Results of experiments demonstrated the effectiveness of our proposal.

Predictive seam tracking with iteratively learned feedforward compensation for high-precision robotic laser welding

In this paper, a novel architecture for robotic seam tracking using an industrial robot and off-the-shelf sensors is proposed to compensate the residual errors that are commonly observed in high-precision robotic laser welding due to the nonlinearity of a seam and the fast path drifts along a robot path. Our experiments demonstrate that the robot system can track both linear and nonlinear long seams at a high speed of 100 mm/s with TCP offset-error within ±0.1 mm using the proposed method.

Image Measurement on Curvature Around Seam Line for Motion Control of Laser Welding Robot

Automating robot laser welding requires that the laser irradiation direction and laser focus positioning influencing welding strength are controlled precisely. Since the edge of the welded object can be transformed on processing by such as cutting, bending and grinding, the direct measurement is necessary to control the laser irradiation. Especially, the information of the curvature around the seam line is important because the precision influences the molten direction. The image measurement for curvatures around the seam line derives a three-dimensional approximation of the welded object’s curved surface from core-lines of images of the laser for measurement. By results of experiments the effectiveness and the limitations of our proposal are demonstrated.

Laser lap welding of zinc coated steel sheet with laser-dimple technology

Laser beam welding technology has been widely used to weld automobile components, especially for tailored blank welding. In order to provide best corrosion resistance to the welded sheet metal parts, zinc coated steel sheets are normally used. The zinc coating poses no issues to the butt joining of the sheet metals. However, when laser welding technology is applied to lap joint of these sheets, the welding process is not straightforward. Special techniques must be employed to allow the venting of the zinc vapor that is generated at the interface between the paired sheets. Many efforts have been attempted around the world trying to develop a practical technique for laser lap welding of zinc coated steel sheets. Most of the developed technologies has some success but with limitations—extra cost for equipment and process or limited convenience of implementation. In this paper, a new concept of laser lap welding with laser dimpling technology is described. This lap welding technique was implemented successfully in a robotic laser welding system in the laboratory environment and is capable of incorporation into manufacturing processes.

Real-time seam tracking for robotic laser welding using trajectory-based control

In this paper a real-time seam tracking algorithm is proposed that can cope with the accuracy demands of robotic laser welding. A trajectory-based control architecture is presented, which had to be developed for this seam tracking algorithm. Cartesian locations (position and orientation) are added to the robot trajectory during the robot motion. In this way, sensor information obtained during the robot motion is used to generate the robot trajectory while moving. Experiments have been performed to prove the tracking capabilities of the seam tracking algorithm.

Profile measurement sensor for robotic laser welding

A profile measurement sensor is developed and applied to robotic laser welding. The sensor consists of a PC based camera and a stripe-type laser diode. The surface profile of welding objects and other useful features are available with the sensor. Especially, the working distance of the sensor can be changed according to the application. Design of the sensor and implementation of necessary image processing are highlighted in this paper. A simple and efficient control scheme of the whole system is also presented. The profile measurement and seam tracking experiments were performed to evaluate operations of the system.

Microassembly of Artificial Crystals by Inter-Particle Laser Welding and Optical Characterization

To fabricate artificial crystals with any structure from monosized spherical particles, we have so far manufactured a three-dimensionally particle assembling system with a combination of pick-and-place robotic manipulation and inter-particle laser welding. In the present study, we aimed to assemble large-scale artificial crystals of polyethylene (PE) particles by mean of the new system. In this method, an optimization of the laser welding conditions was indispensable for the strong bonding with maintaining the shape of particles. Thus, the two-particle welding tests were preliminarily conducted. On the basis of this result, we successfully assembled the large-scale artificial crystals with diamond structure from the PE -ceramic or -carbon composite particles. In order to discuss applicability of the obtained crystals to terahertz (THz) wave photonic crystals, the transmittance spectrum of the crystals was evaluated by a THz wave time domain spectroscopy. The PE-ceramic particle crystal presented an ideal photonic band gap which perfectly agreed with the theoretical one.

자동차 부품의 원격 레이저 용접기술

The laser welding of the car body and components has been spread in the automotive industry. The Nd:YAG laser welding system could be used in 3D welding with robot. However, this system cannot efficiently reduce the welding cycle time according to various welding sequences because the robot's moving time is same that of the resistant spot welding system. But the remote welding system with high power <TEX>$CO_2$</TEX> laser and scanner makes it possible welding cycle time much faster than the robot laser welding system. In the <TEX>$CO_2$</TEX> laser remote welding system, laser beam can be rapidly transferred to a workpiece by moving mirrors of scanner system. So, it makes reducing the cycle time of welding process and shaping various welding patterns easily. Therefore, in this paper, the characteristic of weld strength according to patterns of weld bead on <TEX>$CO_2$</TEX> laser welding was investigated. Also, the relationship between shape of weld bead and value of tensile load was studied. Finally, the optimum remote welding condition for car bumper was investigated.

Robot Based Laser Welding Technology

In order to obtain a good result in the laser welding process, the laser welding technology for manufacturing an automobile body is studied in this research. The monitoring of the welding quality and the seam tracking are studied to improve the productivity. The robot, the seam tracking system and CW Nd:YAG laser are used for the robot laser welding system. The laser system is 4kW Nd:YAG laser_(HL4006D) of Trumpf and the robot system is IRB6400R of ABB. The robot laser welding system is equipped with the seam tracker and plasma sensor. The seam tracking system is composed of SMART-20LS and RAPAL of Servo-Robot and MVS-5 sensor of MVS. The precise positioning of the laser beam on the joint to be assembled is obtained by seam tracker. The welding joints of steel plate are butt and lap joint. The three dimensional welding for non-linear tailored blank is performed after the fundamental experiments of bead-on-plate. Finally, the welding process for non-linear tailored blank and front side member is studied. The monitoring method of welding quality and seam tracking along the butt-joint are studied. The artificial defects in joint are well observed by the plasma intensity signal from the plasma sensor of UV and IR. The robot based laser welding system is developed for the precision seam tracking and the real-time monitoring of welding quality.

Sensor Guided Laser Welding Robot System

In order to obtain a good result in the laser welding process, the laser welding technology for manufacturing an automobile body is studied in this research. The robot, the seam tracking system, and CW Nd:YAG laser are used for the laser welding robot system. Especially, the development of the laser-stripe sensor is highlighted. The laser-stripe sensor can measure the profile of the welding object and obtain the gap and seam line. Moreover, the working distance of the sensor can be varied. The control scheme of the whole system is also presented. The profile and gap measurement and the seam tracking experiments were carried out to validate the operation of the system.

Robotic laser welding: seam sensor and laser focal frame registration

Robotic laser welding places extreme demands on the spatial accuracy with which the robot must position the focal point of the laser with respect to the joint to be welded. The required level of accuracy is difficult to achieve in a production environment without the use of end-point sensor based control of the robot. This requires that the end-point sensor frame and welding laser frame be accurately calibrated with respect to each other, as well as with respect to the robot wrist frame. This calibration can be difficult to perform since the sensor and laser frames are virtual in the sense that these are located in space with respect to the physical hardware, and the wrist frame of the robot is often not physically accessible. This paper presents the design of a calibration system with which these frames may be precisely defined with respect to each other.