Papers by Keyword: Process Stability

Abstract: Wire arc additive manufacturing (WAAM) has been established to be an efficient and cost-effective additive manufacturing technique for fabricating functional metallic parts from scratch. However, there is need to determine optimal processing condition for each material system to produce high-quality parts. In this work, a parametric study of WAAM of AISI 308LSi was performed to determine the processing condition(s) at which single tracks of high dimensional accuracy, excellent geometry, no visible crack and pore, and high hardness required for high-quality multi-track deposition can be achieved. The track geometries were investigated using a combination of optical microscopy and image processing software. The microstructure and hardness of the deposited single tracks were examined using optical microscopy and Vickers hardness tester respectively. A process map predicting the process stability of WAAM of AISI 308LSi was developed within a process window. Continuous single tracks of high dimensional accuracy were produced from a stable deposition process. The process becomes unstable whenever the wire deposition volume per unit length of track is in excess of the available heat energy per unit length of track. The wire feed rate and traverse speed significantly influence the stability and geometry of the single tracks. The processing conditions at which single tracks of low wetting angle (<90◦), high aspect ratio (>1.5), high surface quality, and high hardness (close to the as-received material) can be deposited were determined. These processing conditions were considered suitable for the fabrication, surface modification and repair of functional engineering parts made of 308LSi stainless steel.

Abstract: Magnesium (Mg)-based wires are in the focus of interest for numerous applications like micro-forming technologies or medical engineering. Manufacturing thin Mg-based wires is widely realized by applying a conventional multiple pass cold wire drawing process. This requires a complex manufacturing schedule of multiple passes with intermediate heat treatments to overcome work hardening, because of the cold forming process. Especially Mg and its alloys are known for their rather low formability at room temperature associated with the hexagonal close-packed lattice structure. The dieless drawing process uses local heating to initialize a localized plastic zone under an external tensile load to achieve higher reductions in diameter in a single wire drawing pass. It can therefore present a solution for a more efficient warm manufacturing process of Mg-based wires. In this study, the stability of the steady state material flow during a dieless wire drawing process and its reproducibility was investigated. For this purpose, a variation of process parameters was selected and wire manufacturing was carried out using magnesium alloy AZ31. A single and double dieless drawing process was applied. Additionally, a conventional cold wire drawing process including a die with the same forming schedule was executed as a benchmark experiment. The results of this study show, that the dieless drawing process is not only a stable process after reaching the steady state, but it is also a reproducible and accurately adjustable process. Moreover, the dieless drawing process maintains the property profile of the starting material to a large extend.

Abstract: Additive manufacturing (AM) is currently one of the most promising and advanced tools to make high-end components. For industrial acceptance of these components, there is a demand for the delivery of high quality parts, certified under recognized standards. Pre-requisites for such certified parts are the certification of the powder feed-stock and the use of qualified facilities. Such a certification and qualification project encompasses different challenges regarding both powder testing and print process stability. Today there are insufficient quantitative acceptance criteria for AM metal powders in the standards. The main challenge is determining which properties to test and how to define some key indicators that can guarantee consistent quality of the end product. To face this challenge several relevant powder properties were tested in order to link powder performance to the properties of the printed material. To guarantee process stability and repeatability, a good knowledge and control of the different process parameters and their influence on the material quality is needed. Hence, an extensive study on the homogeneity of properties over the 3D printer platform was performed. A qualification testing platform was designed to guarantee and periodically check the quality of the printed AM316L material. The proper procedures and parameter settings were determined and fixed. This methodology finally lead to the qualification of the ENGIE Laborelec Powder Lab and the ENGIE Fabricom AM printing facility and the certification of AM 316L material through a recognized external qualification body. This initiative paves the way to ensure industrial acceptance of the selective laser melting process for high quality applications.

Abstract: Compared to conventional mesophilic anaerobic digestion, thermophilic anaerobic digestion may offer attractive advantages such as higher volatile solid destruction efficiency, higher biogas generation, and higher disinfection effect and better dewater ability. In this study, two experiments of waste activated sludge were conducted to evaluate the influence of total solid and inoculums ratio on the biogas production and thermophilic (55±1°C) anaerobic process stability. In first experiment, the biogas production of 4 reactors with solid concentration of 6%, 8%, 10% and 12% respectively was observed. The biogas productions in 4 reactors were 4444 mL, 4891 mL, 5573 mL and 6327 mL respectively, the biogas productions per unit VS digested of each group were all above 360 mL/g and the methane content in biogas of each reactor was kept about 70%. During the operation, pH value in the reactor was kept between 6.5 and 8.4. In second experiment, the biogas production of 4 reactors with inoculums ratio of 20%, 30%, 40% and 50% respectively was observed. The biogas productions in 4 reactors were 4730 mL, 6630 mL, 6820 mL and 7175 mL respectively, the biogas productions per unit VS digested of each group were all above 340 mL/g and the methane content in biogas of each reactor was kept about 70%. During the operation, pH value in the reactor was kept between 6.4 and 8.6. Putting into consideration, the shortening of anaerobic digestion cycle, costs saving, and increasing economic benefits; choosing TS within the scope of 8-10%and inoculums ratio within the scope of 30-40% are more recommended. And the results showed that thermophilic anaerobic digestion process for waste activated sludge could be operated steadily.

Abstract: Micro forming processes are very well suited for manufacturing of small metal parts in large quantities and micro deep drawing provides a great application potential for the manufacturing of parts with complex shapes. But size effects like changed tribology and material properties usually result in smaller process windows for micro forming operations. Process caused wear as well as large inaccuracy in manufacturing of micro forming tools is responsible for geometrical deviation of the tools from nominal size. Both influences can have essential impact on the process window size and process stability. A better understanding of the influence of tool geometry on process stability can help to improve and optimize process control in micro forming. In addition, a quantitative judgment of the impact of wear and manufacturing inaccuracy will be possible. Therefore, in this study, the impact of different tool geometries on the punch force in micro deep drawing was investigated. Significantly varied tool geometries were punch diameter, drawing gap, punch and drawing die radius and shape of the die edge. FEM simulations as well as experiments were used to determine tool geometry influence on the punch force of a micro deep drawing process. Hereby, it was possible to classify each geometry variation regarding its impact on the punch force and therefore on one important parameter of the process stability. Results show that the greatest impact on the punch force was caused by modifications of the punch diameter and variation of the drawing gap. Changes in punch or drawing die radii proved to be of minor importance.

Abstract: During milling of thin-walled components, chatter vibrations give rise to process issues. These include dimensional inaccuracy, damaged and scrap parts, and damaged cutting tools. This, in turn, leads to loss of production time with increasing cost as a consequence. This paper identifies the force profile during a single cut milling process. It focuses on the exit and post-exit behavior of the cut and discusses the process dynamics. The force profiles of various tool-to-workpiece positions are analyzed as regards the exit and post exit phases. A standard on-the-market cutter and a specially designed zero rake cutter are used in the investigation. Finally, a time-domain simulation of the force is performed and compared to the experimental results. The study concludes that a small change in exit angle may result in a considerable improvement in cutting behavior. In addition, the tool position should be chosen so that the cutter exits in the least flexible direction possible for the workpiece.

Abstract: This paper details the correlation between the input parameters with the tool material on the machining response in comparison of two different combinations of toolworkpiece material, namely copper-H13 and graphite-H13. The considered machining input parameters included pulse current and pulse on-time, and the investigated characteristics of the machining response were the material removal rate, tool wear, and surface roughness of the workpiece. Furthermore, differences in pulse shapes and process stability between the copper-H13 and graphite-H13 combinations were investigated.

Abstract: The parameters obtained in the study of single layer of laser cladding forming are not suitable for the forming of actual structures. The cooling condition varies with the height of clad layers, which result in instability and then failure of cladding. Therefore, the stability of laser cladding forming is of significance. In this paper, melt pool depth is used as a criteria for stability. And the effect of processing parameters such as laser power and laser velocity on melt pool depth, are investigated by numerical simulation method. The results unveil that there is a transition zone from the beginning to stable stage during laser cladding forming. In the transition zone, laser power should be decreased or laser velocity should be increased to maintain the constant melt pool depth and to ensure the former clad layer would not be remelt. The optimized processing parameters are obtained for stable processing for a thin flat wall and a cylindrical wall, which successfully guide the manufacturing of the real structures.