Influence of material degradation on weld seam quality in hot gas butt welding of polyamides

The joining of plastics is required because component geometries are severely restricted in conventional manufacturing processes such as injection molding or extrusion. In addition to established processes such as hot plate welding, infrared welding, or vibration welding, hot gas butt welding is becoming more and more important industrially due to its advantages. The main benefits are the contactless heating process, the suitability for glass fiber reinforced, and high-temperature plastics as well as complex component geometries. However, various degradation phenomena can occur during the heating process used for economic reasons, due to the presence of oxygen in the air and to the high gas temperatures. In addition, the current patent situation suggests that welding with an oxidizing gas is not permissible depending on the material. On the other hand, however, there is experience from extrusion welding, with which long-term resistant weld seams can be produced using air. Investigations have shown that the same weld seam properties can be achieved with polypropylene using either air or nitrogen as the process gas. Experimental investigations have now been carried out on the suitability of different gases with regard to the weld seam quality when welding polyamides, which are generally regarded as more prone to oxidation. The results show that weld strengths are higher when nitrogen is used as process gas. However, equal weld strengths can be achieved with air and nitrogen when the material contains heat stabilizers.

Homogenization of 7075 and 7049 Aluminium Alloys Intended for Extrusion Welding

During the extrusion of aluminum alloys profiles using porthole dies, the temperature of the material in the welding chamber is one of crucial parameters determining the quality of longitudinal welds. In order to extend the permissible temperature range, the billets intended for this process should be characterized by the maximum attainable solidus temperature. Within the present work, the homogenization of AlZnMgCu alloys DC-cast (Direct Chill-cast) billets was investigated, with the aim of solidus temperature maximization. Conditions of soaking and cooling stages were analyzed. The materials were homogenized in laboratory conditions, and the microstructural effects were evaluated on the basis of DSC (Differential Scanning Calorimetry) tests and SEM/EDS (Scanning Electron Microscopy/Energy-Dispersive Spectroscopy) investigations. For all examined alloys, the unequilibrium low-melting microstructure components were dissolved during soaking, which led to the significant solidus temperature increase, in comparison to the as-cast state. The values within the range of 525–548 °C were obtained. In the case of alloy with highest Cu concentration, the application of two-step soaking was necessary. In order to take advantage of the high solidus temperature obtained after soaking, the cooling rate from homogenization must be controlled, and the effective cooling manner is strongly dependent on alloy composition. For high-Cu alloy, the solidus decreased, despite the fast cooling and the careful billets preheating being necessary.

Effect of shoulder features during friction spot extrusion welding of 2024-T3 to 6061-T6 aluminium alloys

Friction spot extrusion welding process is successfully performed on dissimilar aluminum alloys of AA2024-T3 and AA6061-T6 under the influence of shoulder features. The joints were analysed by microstructural features and mechanical properties using conventional and advanced tools of visual inspection, optical microscopy, scanning electron microscopy, transmission electron microscopy, electron back scattered diffractions, tensile testing and hardness testing. The results revealed that the joining was obtained by combination of mechanical locking from extruded material of top surface to predrilled bottom surface and diffusion in solid state. The stir zone and plastically deformed metal flow zone were influenced by scroll shoulder and smooth shoulder features. The tensile specimen of scroll shoulder was resulted to higher fracture load of 6381 N whereas the same was 4916 N in case of smooth shoulder. The interface of between plastically deformed metal flow zone and base material of AA6061-T6 can be considered as critical/weakest zone in case of friction spot extrusion. The variations of hardness were observed in stir zone, plastically deformed metal flow zone and thermo-mechanically affected zone in case of friction spot extrusion welding process.

Steel-Reinforced Polyethylene Pipe: Extrusion Welding, Investigation, and Mechanical Testing

This work presents extrusion welding with a square butt joint of V-shaped steel-reinforced polyethylene (SRPE) corrugated pipe. The SRPE pipe was welded in a single pass on the inside of the pipe. The welding temperature was controlled at 190°–200°C. The welding extruder was modified for controlling the travel speed and preheating conditions for welding. A high-density polyethylene (HDPE) rod was used as the welding filler metal, which was inserted into the extruder with a speed of 2.20 m/min. Welding progressed downhill from the overhead position with a travel speed of 3.0 cm/min. The effects of welding methods, with and without preheat conditions, on the weld quality were investigated by visual and radiographic inspections. From the results, the preheated welding condition showed complete fusion of the weld without any defects, while that of the nonpreheat exhibited a great number of voids inside the weld. The crystal structures of the preheated and nonpreheated welds were analyzed with an x-ray diffractometer and compared with the HDPE base material. From mechanical testing, the weld from the preheat condition showed a good ability to endure the tension force of 46 MPa and compressive stress of up to 0.41 MPa at 5%deflection. In addition, it was found the welded SRPE could tolerate hydrostatic pressure of up to 0.18 MPa without any water leakage when being used as a water-containing tank.