Torch Stand-off Distance Research Articles

Self-Adaptive Control System for Additive Manufacturing Using Double Electrode Micro Plasma Arc Welding

Wire arc additive manufacturing (WAAM) has been investigated to deposit large-scale metal parts due to its high deposition efficiency and low material cost. However, in the process of automatically manufacturing the high-quality metal parts by WAAM, several problems about the heat build-up, the deposit-path optimization, and the stability of the process parameters need to be well addressed. To overcome these issues, a new WAAM method based on the double electrode micro plasma arc welding (DE-MPAW) was designed. The circuit principles of different metal-transfer models in the DE-MPAW deposition process were analyzed theoretically. The effects between the parameters, wire feed rate and torch stand-off distance, in the process of WAAM were investigated experimentally. In addition, a real-time DE-MPAW control system was developed to optimize and stabilize the deposition process by self-adaptively changing the wire feed rate and torch stand-off distance. Finally, a series of tests were performed to evaluate the control system’s performance. The results show that the capability against interferences in the process of WAAM has been enhanced by this self-adaptive adjustment system. Further, the deposition paths about the metal part’s layer heights in WAAM are simplified. Finally, the appearance of the WAAM-deposited metal layers is also improved with the use of the control system.

Combustion Flame Spray of CoNiCrAlY & YSZ coatings

The properties of CoNiCrAlY and ∼7–8%YSZ layers, used as thermal barrier coatings (TBC) to protect hot gas paths of power generation and aerospace gas turbines, that have been deposited through the Combustion Flame Spray (CFS) process, are assessed and compared to coatings of the same materials deposited through Atmospheric Plasma Spray (APS). Fuel-to-oxygen equivalence ratio, combustion and carrier gases flows, torch standoff distance and powder feed rate values have been varied during the CFS tests in order to assess their effect on microstructural characteristics, i.e. thickness, total porosity, oxide level and microhardness. Results show that, in CFS-deposited coatings, although a higher content of oxide strings and porosity is observed compared to APS, also comparable phase transformations and a higher thermal cyclic lifetime can be achieved with an appropriate tuning of the deposition parameters. Thus, the study demonstrates the excellent capability of the CFS process in depositing thermal barrier coating systems, providing a viable alternative deposition technology for this class of materials at significant hardware simplicity. As the CFS setup has a simple design, this research stimulates a miniaturization concept of the combustion flame spray torch for allowing its deployment into highly restricted workspaces.

Plasma Arc Cutting Dimensional Accuracy Optimization employing the Parameter Design approach

Plasma Arc Cutting (PAC) is a thermal manufacturing process used for metal plates cutting. This work experimentally investigates the influence of process parameters onto the dimensional accuracy performance of the plasma arc cutting process. The cutting parameters studied were cutting speed (mm/min), torch standoff distance (mm), and arc voltage (volts). Linear dimensions of a rectangular workpiece were measured after PAC cutting following the full factorial design experimental approach. For each one of the three process parameters, three parameter levels were used. Analysis of means (ANOM) and analysis of variances (ANOVA) were performed in order for the effect of each parameter on the leaner dimensional accuracy to be assessed.

Investigations on the Influence of Surfacing Process Parameters Over Bead Properties During Stainless Steel Cladding

The bead parameters play a vital role in determining and understanding the properties of the weld cladding in fusion welding process. This investigation aims at minimizing weld dilution and predicting the behavior of the bead parameters during weld cladding of AISI 316 L (UNS 316 03) metal powder over carbon steel (ASTM A105/ IS: 2062), by plasma transferred arc (PTA) surfacing through response surface method. The data for modeling were collected from experiments conducted using a five level factorial technique. The predictions reveal that the travel speed has a phenomenal effect in increasing the penetration of the weld bead at lower level. The torch stand-off distance has a predominant effect in deciding the penetration and dilution of the weld bead during lower level while increasing welding current. The reinforcement of the weld bead reduced the dilution level with increase in the oscillation frequency and the powder feed rate.

A parameter design of CNC plasma-arc cutting of carbon steel plates using robust design

An optimisation of the cutting parameters during CNC plasma-arc cutting of St37 mild steel plates is attempted using robust design. The process parameters tested were plate thickness, cutting speed, arc ampere, arc voltage, air pressure, pierce height, and torch standoff distance. An orthogonal matrix experiment [L18 (21 × 37) ] was conducted and the right bevel angle was measured and optimised according to the process parameters using an analysis of means and an analysis of variances. The results show that the arc ampere has an effect mainly on the bevel angle (50.89%), while the plate thickness and torch standoff distance also have an influence of 6.22 and 15.9% respectively. The other parameters have an F factor smaller than one, and thus their variations do not significantly affect the bevel angle in the experimental region. Finally, an additive model was applied on the experimental results to predict the optimum combination and was compared with actual values.

Modeling of a substrate thermomechanical behavior during plasma spraying

Abstract Plasma coating performances and lifetimes may be ruined during service conditions because of uncontrolled residual stress development within the coating. This study presents the results of a CAST3M® thermomechanical numerical model which purpose is to simulate the different residual stresses development within the duplex coating–substrate during the coating built-up and its comparison with the experimental results. To achieve the thermal spray process understanding all the thermal fluxes transferred to a metallic beam and surrounding temperatures were measured so as to provide the CAST3M® model with precise boundary conditions, corresponding to a specific geometry. The residual stresses were experimentally determined by the in situ curvature measurement and, afterwards, by the hole drilling method. The plasma torch stand-off distance, the relative torch/substrate velocity and the substrate material were considered as the parameters of this study. The main results concern the substrate temperature and deflection during the preheating stage, the thermal energy transferred by the molten splats to the substrate together with the quenching stress and the development of thermal stress during the final cooling.

Influence of Process Variables in Flux Cored Arc Welding of Hardfacing Deposits

A lack of knowledge and objective data on the effects of welding process variables in the application and performance of weld deposited hardfacings has led to many past failures and a subsequent mistrust of the technology. This paper sets out, first, to review both the influence of welding process variables in hardfacing and the important characteristics and properties which determine the effective performance of a hardfacing deposit. Second, the results are presented of a full factorial experiment, which was performed in an effort to evaluate and interpret the effects of arc current, voltage, and polarity, as well as of travel speed, torch stand-off distance, and preheat, on the nature and properties of a commercial flux cored arc welded hardfacing deposit. In this programme, the effects of the welding parameters were evaluated with the aid of a number of computer analyses, with arc current, voltage, and polarity being shown to have the greatest effect: a high arc current (360 A) gives the most satisfactory deposit in terms of weld metal dilution, hardness, and porosity, as well as of both deposition rate and efficiency, provided that electrode negative arc polarity is used, together with a low (24 V) arc voltage. In attempting to achieve more cost effective use of hardfacings in abrasive wear resistant applications, both the potential of this approach and the value of the results obtained are clearly demonstrated.