Capacitor Discharge Spot Welding of Aluminum, Part 1: Weldability Assessments

A key aspect of integrating automotive sheet into automotive production are the costs associated with joining. While the majority of sheet steel assembly is done with resistance spot welding, that has not readily translated to aluminum. Resistance spot welding of aluminum sheet is challenged by high current demand as well as reduced electrode life. In the latter case, direct current (DC) power supplied by state-of-the-art systems has exacerbated the problem. Recently, technology employing capacitor discharge (CD) welding in conjunction with polarity switching has been developed. This work is a first effort in examining the response of resistance spot welding on aluminum sheet to polarity-switching CD power. In this paper, the current range response between medium-frequency DC (MFDC) and polarity-switching CD was investigated. It was found that polarity-switching CD welding offered improved current ranges over MFDC. In addition, replicate mechanical testing cross-tension results were similar, but tensile shear strengths improved nominally 20–25%. Finally, some limited tests were done to assess the suitability of CD resistance spot welding in the presence of an adhesive. Current range tests with and without a prepulse were done, and both showed excellent weldability.

CONTACT INTERACTION OF DISCRETE-CONTINUALLY STRENGTHENED PARTS OF INTERNAL COMBUSTION ENGINES

Studies of the stress-strain state of discrete-continuously strengthening parts of internal combustion engines are described in the paper. A parametric model of a microcell containing a two-part cell has been developed. The first part simulates a fragment of an aluminum part with a surface corundum layer. The second part is a fragment of a cast iron part with a zone of discrete strengthening of steel. Vary: modulus of elasticity of the corundum layer material and the shape of the discrete hardening zone. The dependences of the strength and stiffness characteristics of the studied system on the varied parameters are established. They are the basis for substantiation of rational modes of technology of discrete-continuous strengthening of parts of internal combustion engines. In the course of research, it was found that previously determined for discrete strengthening, the effects of a favourable redistribution of contact interaction between parts are preserved for discrete-continuous strengthening. The characteristic dependences of the features of the stress-strain state of the elements of discrete-continuously strengthening parts on the varied properties of the surface layers of the continuously strengthened part, on the one hand, and the shape of the discrete strengthening zone, on the other, are determined. This makes it possible to determine the sensitivity of the characteristics to purposeful or random variation of these factors. It is also expedient to set and solve optimization problems to determine such modes of technological operation of discrete-continuous strengthening, which increase the characteristics of strength, durability, efficiency of internal combustion engines and other machines, units and assemblies containing such strengthened parts. The developed approach, models and research methods will be further applied to studies of the stress-strain state of contacting discrete-continuously strengthened parts of structures to improve the technical and tactical and technical characteristics of products of machine-building enterprises.

Real-Time Laser Tracker Compensation of Robotic Drilling and Machining

Due to their flexibility, low cost and large working volume, 6-axis articulated industrial robots are increasingly being used for drilling, trimming and machining operations, especially in aerospace manufacturing. However, producing high quality components has demonstrated to be difficult, as a result of the inherent problems of robots, including low structural stiffness and low positional accuracy. These limit robotic machining to non-critical components and parts with low accuracy and surface finish requirements. Studies have been carried out to improve robotic machine capability, specifically positioning accuracy and vibration reduction. This study includes the description of the hardware, software and methodologies developed to compensate robot path errors in real time using a single three-degrees-of-freedom (DOF) laser tracker, as well as the experimental results with and without compensation. Performance tests conducted include ballbar dynamic path accuracy test, a series of drilling case studies and a machining test. The results demonstrate major improvements in path accuracy, hole position accuracy and hole quality, as well as increases in accuracy of a machined aluminum part.

Effective power of the reverse polarity welding arc when surfacing aluminum with a consumable electrode

The paper analyzes the information about the effective power of a reverse polarity arc on an aluminum part and the influence of the arc cathode region on it. The study differentiated the effective power of the direct polarity arc into its main components. The authors carried out the experiments to measure the effective power of the reverse polarity arc for aluminum welding. To determine the effective power, the calorimetry was used when hardfacing a wire of 1.2 mm diameter on the Al-Mn alloy plate and the deposited metal then was weighed. Based on the experiment results, the authors calculated an average algebraic deviation of αН∙I hardfacing performance and effective power. As a result, the authors proposed the procedure to determine the electrode wire fusion coefficient at zero stick-out α0 according to its dependence on the arc current, which increases at electrode diameter decreasing. This coefficient is about 25 % less than that of steel. By assuming a weak dependence of anode power on the arc current, this fact proves the obtained data on the high heat content of electrode metal droplets of an aluminum wire in comparison with a steel wire. At the droplet transfer of electrode metal, the cathode region power of the arc makes the prevailing contribution to the total effective power of the reverse polarity arc. At the current density equal to 175 А/mm2, the specific effective power of the cathode region action is qSC=9.0 W/А, the power of the electrode metal is qE=4.6 W/А, and the plasma flow power is qP=5.2 W/А.

Junction Characterization in a Functionally Graded Aluminum Part

Aluminum alloys are widely used to produce automotive components, thanks to their great mechanical properties–to–density ratio. Engine components such as pistons are conventionally produced by casting of Al–Si eutectic alloys (Silumin alloys) such as EN AC 48000. Due to the harsh working conditions and the lower ductility if compared to aluminum–silicon alloys with lower silicon content, pistons made of this alloy are prone to fatigue failures in the skirt region. In order to overcome such limits, the use of a Functionally Graded Material (FGM) in the production of a piston is proposed. The adoption of a functionally graded architecture can maximize the properties of the component in specific areas. A higher level of thermal resistance in the crown of the piston can be achieved with EN AC 48000 (AlSi12CuNiMg), while higher elongation at rupture in the skirt region would be conferred by an EN AC 42100 (AlSi9Mg0.3). The FGM properties are strictly related to the metallurgical bonding between the alloys as well as to the presence of intermetallic phases in the alloys junction. In the present article, the characterization of gravity casted FGM samples based on Al–Si alloys with respect to microstructure and mechanical testing is presented, with a specific focus on the characterization by impact testing of the joint between the two alloys.

To the Technology of Laser Welding of Aluminum with Titanium

The results of experimental study of laser welding alloys based on aluminum and titanium an intermediate composite Al+Ti insert obtained by explosion, using nanopowder additives and plastic deformation of the aluminum seam are presented. Morphologically high-quality welds have been obtained both in the welding of the aluminum plate and of the titanium one with the corresponding parts of the insert. It was found out that breakdown of the joint in the tensile test occurred along the aluminum part of the insert, which had a lower tensile strength than the titanium. The use of the nanomodifier without plastic deformation increases the strength of the weld joint by about 10% compared to the unmodified compound. The use of nanomodifying and strain hardening can significantly increase the tensile strength, the value of which is more than 97% of the strength of alloy (AA1135). The carried out experiments on laser butt welding of plates made of aluminum alloy 1424 systems Al-Mg-Li-Zr-Sc with their subsequent plastic deformation have confirmed the effectiveness of strain hardening of weld joints of aluminum alloys.