Investigation and Optimization of Plasma Arc Cutting Process

Abstract

High strength materials are most widely used in producing the parts of military, automobile, marine and mining industries. Special abrasion resistance material is used for above industries because of their superior mechanical properties like good weld capacity, good bendability, higher toughness and better workability. These alloy materials are classified as “Hard-to-cut” type materials and very difficult to cut the work piece. Cutting of high abrasion resistance alloy material with better dimensional accuracy in faster cutting speed within economic cost is still a challenging task for manufacturing industries. Generally fabrication units employed plasma arc cutting machine to cut the high strength material due to its advantages over the other cutting processes. The correct selection of machining parameter and plasma gas is very important for smooth cutting with high precision. The optimization of input parameters reveals the proper machining condition for cutting process. In addition to that, it was also noticed that the selection of appropriate plasma gas could enhanced the cutting process. Therefore, in the first stage of the research work, Investigation and optimization of plasma arc cutting process using different optimization techniques of some high strength and high abrasion resistance alloy material which was not sufficiently addressed so far were carried out. A CNC plasma arc cutting machine of MESSER industry named (BURNY 1250) was used to conduct the experiment of sailhard steel, abrex 400 steel and hardox 400 steel. These alloy materials have superior mechanical properties for manufacturing the parts of mining, automobile, petrochemical, oil and natural gas industries. On the other hand, a portable laboratorial plasma arc cutting machine was employed to investigate and optimize the cutting operation of 304L stainless steel. This alloy material has mostly employed for household and commercial application because of its superior corrosion resistance in nature. The cutting parameters were selected as cutting current, gas supply pressure, cutting speed, stand-off-distance and feed rate were selected as cutting parameter. Surface roughness, material removal rate, kerf, chamfer and dross were considered as output responses. Taguchi’s orthogonal array was taken to design the run of experiment during cutting process. Additionally, three different multi criteria decision making techniques viz. Desirability approach, Technique for order of preference by similar to ideal solution (TOPSIS) and Vlsekriterijumska optimizacija KOm-promisno Resenje (VIKOR) were suggested to attain optimal cutting condition in order to minimize the production cost and maximize the productivity without compromising the quality. Also, a prediction model was developed to estimate the responses using multiple regression analysis (MRA). A comparison between experimental and predicted result shows the accuracy of the model. An ANOVA test was established to evaluate the significance of process parameter. Finally, a confirmation test was obtained to show the degree of effectiveness of proposed method. The optimum setting of process parameters will offer a very good cutting condition in order to achieve the preciseness.

In the second stage, an experimental analysis was carried out to observe the effect of different plasma gas on the work piece material during plasma arc cutting process. The influence of flow rate of plasma gas on the plasma arc cutting process was investigated. Four different plasma gases were selected for this experiment viz. air, argon, oxygen and nitrogen. The thermo physical properties of plasma gases, properties of generated arc, cutting performance and energy balance was explained for different plasma gases. This research work was also clarified the potential of cutting process by varying the flow rate and chemical composition of the plasma gas.

Finally, a temperature analysis was developed over the surface of work piece during plasma arc cutting process. The moving heat source was taken into consideration for calculation the heat created by plasma arc. The heat of fusion was also considered for estimation due to molten layer separates the plasma and solid layer. Different thickness of molten layer were taken for calculation viz. zero thickness, 10% and 20%. The estimated results are shown in non-dimensional form. So, the method can be applied for any other types of material.