The influence of the tilt angle on the quality of Friction Stir welds made on polycarbonate sheets is investigated, experimentally. Welding tests were conducted by varying the tilt angle and the ...welding speed to determine possible interactions between these process parameters. Temperature distribution, material flow, and processing loads were analyzed. The quality of the welds was assessed by means of mechanical characterization and morphological analysis. The results indicated that the processing loads and temperature increased when higher tilt angles were adopted. Under low welding speed (20 mm/s), this enabled to improve the mechanical behavior of the welds. On the other hand, high tilting involved different issues. The tensile strength of the welds was severely compromised as high tilting produced severe thinning of the weld seam. In addition, tilt angles higher than 2° involved great amount of material ejection. This material formed a coherent side flash, which required subsequent machining, and worsened the surface appearance of the welds.
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The influence of welding and tool rotation speeds on processing loads and temperature distribution developing is Friction Stir Welding of polycarbonate is investigated, ...experimentally. The development of critical conditions leading to macroscopic defects were correlated to the features of loads and temperature trends. Two macroscopic defects were identified on FSW welds. Under low welding speeds, the welds were characterized by circular rifts. These developed due to unsteady conditions and low contact pressure. High welding speeds involved heavier loads and temperature within the weld seam. This came with the formation of built-up edge (BUE) under the tool shoulder. The BUE induced a “milling action” on the weld path leading to significant thinning of the weld seam. The acquired signals (loads and temperature measurements) revealed the features of the surface morphology. This suggests the possibility to use such measurements to predict (and possibly to avoid) the onset of the aforementioned defects.
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•CFRP was joined successfully to Polycarbonate by Laser Assisted Direct Joining.•During the Joining process the covering epoxy layer was expelled from the weld seam.•Then, the heated ...and softened PC penetrates through the carbon fibers.•The effective strength of optimized joints reached 8.4MPa.
Laser-Assisted Direct Joining (LADJ) has been employed for a wide variety of materials including metals, thermoplastics and reinforced thermoplastics. The feasibility of Laser-Assisted Direct Joining (LADJ) of Carbon Fibre Reinforced Polymer (CFRP) with thermosetting matrix to polycarbonate sheets is investigated in this work. The process was performed by means of a high-power diode laser with a maximum power of 200W. Experimental tests were carried out by varying the main process conditions including the laser power and scanning speed. Morphological analysis using Optical and Scanning Electron Microscopy (SEM) as well as mechanical characterization of the welds were performed to understand the influence of the processing conditions on the weld quality, defects, and strength. Preliminary results have been encouraging: the process consists in removing the exterior epoxy layer from the CFRP and the adhesion of the carbon fibres to the PC. According to the achieved findings, the mechanical strength of the welds was highly affected by the Linear Energy Density (LE): low values of LE resulted in poor adhesion of the polycarbonate through the carbon fibres, which led to poor mechanical fastening and adhesion. On the other hand, processing conditions leading to excessive values of LE resulted in considerable damage of the composite matrix (the epoxy resin underlying the exposed carbon-fibre layer) and formation of bubbles on the PC substrate, which produced a dramatic reduction of the mechanical behaviour of the welds. The apparent shear strength, calculated as the ultimate shear force by the effective adhesion area was 8.4MPa.
The present investigation analyses the force and torque developing during friction stir spot welding (FSSW) of thermoplastic sheets varying the main process parameters. In addition, measurements of ...the tool temperature and those of the material close to the welding region were carried out to better understand the variation of the forces during FSSW and quality of the joints. Experimental tests involving an instrumented drilling machine were performed on polycarbonate sheets. The study involved the variation of dwell time, tool plunge rate and rotational speed. Mechanical characterization and dimensional analysis of the joints were performed in order to assess the influence of the process parameters on the joint quality under considered processing conditions. According to the achieved results, using low values of the plunging speed has beneficial effects on both the process (reduction in the force and torque) and the mechanical behaviour of the joints. Increasing the tool rotational speed results in reduced processing forces and higher material mixing and temperature. The dwell time has a negligible effect on developing forces while it highly influences the material temperature, dimension of the welded region and consequently the mechanical behaviour of the joint.
The joinability of aluminium alloy sheets with reduced ductility produced by mechanical clinching is analyzed. A modified tool set geometry was developed to reduce the localization and magnitude of ...plastic strain. Sheets preheating was adopted to increase the material formability. Optical microscopy and scanning electron microscopy were utilized to observe possible presence of cracks in clinched connections and to perform dimensional analysis. Mechanical characterization tests comprising micro-hardness test and single lap shear tests were conducted to evaluate the influence of the processing conditions on joints strength.
The variation of forces, torque, absorbed energy, and temperature distribution during friction stir welding process is investigated. Friction stir welding experiments were performed on an aluminum ...Al-Si-Mg alloy varying the tool rotation speed and the welding speed. An instrumented milling machine equipped with 3-axis load cell was adopted to measure the forces during the process. Temperature measurements were performed by means of an IR camera. A significant increase in temperature was observed during the process due to a “process preheating effect.” This resulted in the variation of the main forces. Phenomenological models were developed to describe these trends. The results indicated that processing conditions involving higher energy produced higher variation of temperature during the process, up to 2.3 °C mm
−1
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The present investigation is aimed at analyzing the influence of the processing speeds and processing times on mechanical behaviour of friction stir spot welding (FSSW) joints produced on ...polycarbonate sheets. The analysis involved the variation of rotational speed, tool plunge rate, pre-heating time, dwell time and waiting time. Mechanical characterization of joints was carried out by means of single lap shear test. Experimental tests were conducted according to two full factorial designs. First, an exploratory 2
5
full factorial plan was carried out to determine the most influencing factors determining the mechanical behaviour of FSSW joints. Then, a 3
3
optimization plan was performed by varying the most relevant process parameters among three levels. Therefore, analytical models were developed to predict the mechanical behaviour of welds (maximum shear strength, stiffness and absorbed energy) produced under different processing conditions. In addition, an artificial neural network (ANN) model was developed to improve the matching between experimental measurements and model predictions. On the basis of the achieved results, a framework for improving the mechanical performances of thermoplastic joints was established. According to the achieved results, tool plunge rate, dwell time and waiting time are the most influencing parameters for the joint strength and weld extension. On the other hand, pre-heating time and tool rotational speed have lower influence on the mechanical behaviour of FSSW joints.
The work aims to identify the key factors (KFs) influencing the product quality in the Friction Assisted Joining process and how these depend on the process parameters. Experimental tests were ...performed under low and high-speed conditions. The tests were conducted on hybrid joints made of aluminum alloy AA7075 alloy and semicrystalline Polyamide PA66. Friction Assisted Joining experiments were conducted using an instrumented CNC machine equipped with load and position sensors. The temperature variation and distribution were measured through an Infrared Camera. The influence of plunging load, tool rotation speed, plunging rate and dwell time on the quality of the joints was investigated. Single lap shear tests were conducted to determine the mechanical behavior of the joints. The results indicated that the quality of the joints is mainly determined by the processing temperature reached during the joining process. The processability window along with the onset of main adverse phenomena affecting the mechanical behavior of the joints was determined.
The influence of the welding and tool rotation speed on morphology and mechanical behavior of friction spot stir welds made on polycarbonate is investigated. The welds were performed in butt ...configuration. The mechanical behavior of the welds was assessed by means of tensile tests. Digital image correlation (DIC) analysis was performed to determine the strain distribution (over the cross section) during the tests. This enabled to determine the precise position of crack onset and simplified the determination of the welds’ failure. These data were crossed with observation of the welds morphology to better understand the mutual relation among process conditions-morphology and mechanical behavior. The results indicated that the welds produced under low welding speed were characterized by adhesive failure between the stirred region and the substrate. The welds produced under higher speed were affected by excessive thinning. This led to failure in the stirred region or in some cases within the base material due to localized thinning. The mechanical characteristics of the welds were highly correlated to the temperature of the stirred region. This suggests the possibility to use IR thermography for online control and qualitative assessment of the mechanical behavior of the FSW welds made on amorphous thermoplastics.
This study investigates the influence of the plunging force in friction spot stir welding of polycarbonate sheets on the mechanical behavior of the welds. Experimental tests were carried out by ...varying the tool geometry and the applied plunging force. Mechanical tests based on single-lap shear tests were carried out for mechanical characterization of the welds. Thus, the morphology of the welds was analyzed to clarify the influence of the plunging force on geometry and defects of the welds. According to the achieved results, the control of the plunging force allows improving the mechanical behavior of the welds up to 37 % without requiring for additional energy during the welding process or affecting the process production time. The increase of the weld strength is due to the reduction of porosities developing at the interface between the stirred zone and the surrounding material. However, excessive plunging force results in weaker welds due to excessive thinning of the punch-sided sheet. Under optimal conditions, the shear strength of the welds was 34.5 MPa that yields that of the base material.
