Laser-assisted Forming Research Articles

Multi-scale finite element analysis of laser-assisted forming of CF/PEEK composite corner structures

Laser-assisted forming can significantly increase the forming efficiency of thermoplastic composites. However, when forming CF/PEEK curved corner structures using laser-assisted forming, bending spring-back generated by the prepreg tape constrains the shape accuracy of the component. The bending deformation of unidirectional resin matrix composite materials is highly nonlinear. In this study, a multi-scale finite element method is used to obtain the bending properties of CF/PEEK composites for bending spring-back phenomenon of thermoplastic composite samples and predict the spring-back angle of CF/PEEK corner structures fabricated via laser-assisted forming. The average material properties were first calculated using RVE. Following this, a mesoscale model was developed to analyze kink deformation of the composite. Finally, the macroscopic prepreg bending spring-back was calculated. It was determined that the main mechanism of corner forming corresponds to the occurrence of a fiber kinking phenomenon on the interior of the corner. Furthermore, spring-back deformation is caused by residual stresses resulting from insufficient fiber kinking. The accuracy of the simulation results is verified via corner forming experiments. This study contributes to a deeper understanding of the spring-back mechanisms of laser-assisted forming of corner structures and provides a theoretical guidance for precision forming of multilayer thermoplastic composite bent structures.

Experimental investigation on process parameters of laser-assisted robotic roller bending of a thin-walled structure

Laser-assisted robotic roller forming (LRRF) combines the process capabilities of robot-based manufacturing and laser-assisted forming. In this work, the LRRF process was applied to bending DP1180 steel sheets to thin-walled structures designed for seat trails. Comprehensive experimental investigations were conducted to explore the influences of laser power, forming passes and scanning speed on the forming forces, springback and bending radii of final parts. Experimental results show that the effects of process parameters on the springback and bending radii are similar to those on the forming forces, while forming passes make an insignificant difference to the springback. The optimized process window was subsequently determined out of the balance between geometrical accuracy and experimental efficiency. By applying the optimized process parameters (laser power of 750 W, 6 forming passes, scanning speed of 5 mm/s), the peak force during LRRF was reduced to ∼2.1kN. Meanwhile, a thin-walled profile with higher precision was achieved. Specifically, the springback angle was reduced to ∼4.1° and a compact profile with a radius-to-thickness ratio of ∼1.0 was obtained.

Analysis of spring-back deformation of CF/PEEK thin angled laminates by laser-assisted forming

Laser-assisted forming is an advanced manufacturing method for thermoplastic composites, which has attracted much attention in recent years. Angled structure is the basic element of complex components. In this paper, the influence of forming characteristics and process parameters of laser-assisted forming on the angle deviation of angled thermoplastic laminates is studied. The results show that thin angled laminates with no more than 7 layers of thermoplastic tapes manufactured by laser-assisted forming have angles larger than that of the mold, that is, the spring-back deformation. Laser power, consolidation force and the number of layers have significant effects on the spring-back deformation. The local heating and pressing, and the fast cooling rate during laser-assisted forming cause large residual stress in the samples, which is the main reason for the spring-back deformation. In addition, the effect of repass treatment on spring-back deformation is studied. It turns out that the repass treatment can significantly reduce the spring-back deformation. This is due to the prolonged time of samples at high temperature, which could relax the molecular chain and reduces the residual stress.

CF/PEEK interleaved laminates with PEEK film interleaving manufactured by laser-assisted forming: Microstructure and interlaminar shear strength

In this work, adding PEEK film interleaving between layers is proposed to reduce the interlaminar voids and improve the interlaminar shear strength. CF/PEEK interleaved laminates are manufactured with PEEK film interleaving and repass treatment. The porosity and microscopic features of voids are measured and characterized through the water displacement method and optical microscope. It turns out that the interleaving in interleaved laminates with repass treatment has a significant effect on reducing porosity. The crystallinity of laminates, analyzed and calculated by differential scanning calorimeter, is observed to decrease slightly with the increase of interleaving thickness. This is possibly caused by less fibers in the interleaving areas, which act as nuclei of PEEK crystallization. Interlaminar shear strength of interleaved laminates with repass treatment is higher than those without interleaving. This could be attributed to the reduction of porosity, uniform distribution of fiber/resin and the long diffusion time of chains across the interface.

Effect of voids and crystallinity on the interlaminar shear strength of in-situ manufactured CF/PEEK laminates using repass treatment

Voids and crystallinity, both affected by the temperature history, have an effect on the interlaminar shear strength of thermoplastic composites. In this paper, CF/PEEK laminates with varied porosity and crystallinity are manufactured by repass treatment (based on the laser-assisted forming) under different interlaminar temperature and times of treatment. The porosity and microscopic features of voids are characterized via the water displacement method and optical microscope, respectively. And further squeeze flow of fiber-resin composite and percolation flow of resin occur during repass treatment, which account for the inhabitation of voids. Crystallinity is analyzed through differential scanning calorimetry, which is affected by both cooling rate and recrystallization of the amorphous phase during repass treatment. The interlaminar shear strength of laminates with varied voids and crystallinity is tested, and the failure modes are studied by optical microscope and scanning electron microscope. As a result, the interlaminar shear strength of laminates, with less voids and higher degree of crystallinity, is improved 32.87% than that of the laminates without repass treatment.

Effect of consolidation force on interlaminar shear strength of CF/PEEK laminates manufactured by laser-assisted forming

Interlaminar shear strength (ILSS) is an important quality indicator to evaluate laminates, which requires further studies to produce high-quality laminates by automated placement. In this work, CF/PEEK laminates at different consolidation forces were manufactured by laser-assisted forming. Micro-observation shows that voids, which are confirmed not rebounded ones through analyzing void morphology and temperature history, are formed in the inter-laminar fiber-rich regions. The formation of voids is investigated through the state of tapes with or without laser radiation and roller contact. Void content decreases and average value of ILSS increases with consolidation force. The average value of ILSS at a consolidation force of 109 N is 49.95 MPa, increased by 9.08% compared with 48 N. Cross-sections of fracture samples indicate that layer-by-layer fracture mode is easy to form at 48 N, while multi-layer fracture mode at 109 N indicates that voids are the weak spots.

工艺参数对激光辅助预应力成形效率的影响

工艺参数对激光辅助预应力成形效率的影响

Laser and forming technology—an idea and the way of implementation

This paper will give a survey of some of the actual research activities at the Chair of Manufacturing Technology in Erlangen concerning laser and forming technology. In detail the paper will deal with two main focuses of development: laser forming of aluminum alloys and laser-assisted forming of high strength steels. Laser forming is a technology often used for small series productions and for adjustment of small electronic components. In contrast to laser forming, which is a forming technology that is common for over 20 years, laser-assisted forming is an example of a new production technology that is able to enhance the forming limits of high strength steels.

Laser processing of materials

Light amplification by stimulated emission of radiation (laser) is a coherent and monochromatic beam of electromagnetic radiation that can propagate in a straight line with negligible divergence and occur in a wide range of wave-length, energy/power and beam-modes/configurations. As a result, lasers find wide applications in the mundane to the most sophisticated devices, in commercial to purely scientific purposes, and in life-saving as well as life-threatening causes. In the present contribution, we provide an overview of the application of lasers for material processing. The processes covered are broadly divided into four major categories; namely, laser-assisted forming, joining, machining and surface engineering. Apart from briefly introducing the fundamentals of these operations, we present an updated review of the relevant literature to highlight the recent advances and open questions. We begin our discussion with the general applications of lasers, fundamentals of laser-matter interaction and classification of laser material processing. A major part of the discussion focuses on laser surface engineering that has attracted a good deal of attention from the scientific community for its technological significance and scientific challenges. In this regard, a special mention is made about laser surface vitrification or amorphization that remains a very attractive but unaccomplished proposition.

Process planning for laser-assisted forming

Laser forming has emerged as a viable means of assisting conventional forming processes with geometrical accuracy-related problems. By combining the incremental nature of laser forming with conventional processes such as brakeforming which forms material by a single continuous movement of the tooling, the exact specified bend angle and radius of curvature of the bent component may be approached. This may be achieved by sequential or simultaneous application of the conventional tooling and the laser beam. The laser beam may be applied once to the forming zone or multiple laser beam scans may be used. The combined process allows the forming of highly accurate sheet metal products in a cost effective way, through the possibility to make corrections to the bend angle in a controlled way. Furthermore, the combined process makes it possible to form intricate products that cannot be bent on a press brake due to collision problems or problems emanating from spring-back. Consequently there are new implications for process planning in brakeforming when a laser beam is used in combination. These implications are discussed for some primitive applications.