Experimental investigation on electro-discharge surface modification phenomenon of P20+Ni die steel using green P/M composite electrode

In the present work, attempts have been made to optimize the EDM process with an aspect of surface modification of AISI P20+Ni die steel using powder metallurgy (P/M) electrode. Experiments have been performed according to central composite rotatable (CCD) design using response surface methodology (RSM). Effects of compaction pressure (Cp), peak current (Ip), pulse-on time (Ton), and duty cycle (τ) were correlated with surface roughness (SR) and microhardness (MH). Adequacy of mathematical model has been checked by performing ANOVA. Composite desirability approach was used to obtain optimal set of parameters for minimum SR and maximum MH. The errors between the predicted and experimental value of responses at the optimal set of parameters for SR and MH maintain within 5.26% and -3.64% respectively. Scanning electron microscope and energy dispersive spectroscopy analysis confirmed the transfer of P/M electrode material on the work surface. The result indicates three times improvement in microhardness of EDMed surface.

Effect of Electron Beam Welding Parameters on Temperature and Stress Field of AISI P20 Tool Steel in Vacuum Roll-cladding Process

Vacuum roll-cladding (VRC) is an effective method to produce high quality ultra-heavy AISI P20 plate steel. In the process of VRC, reasonable welding process of electron beam welding (EBW) can significantly avoid welding cracks and reduce the cost. In this paper, the electron beam welding process of AISI P20 tool steel was simulated by using a combined heat source model based on finite element method, and the temperature field and stress field under different welding parameters were studied respectively . The results showed that welding parameters have a greater effect on weld penetration than that of weld width, which making the aspect ratio increases with the increase of welding current, and decrease with the increase of welding speed. The weld morphologies were consistent with those of the modeling and the measured thermal heat curves were good agreement with those of simulated, which was verified the feasibility and effectiveness of temperature fields. The results of stress fields under different welding parameters indicat ed that lower welding speed and higher welding current resulting in lower residual stress at welded joint, which means lower risk of cracking after EBW. The results of this study have been successfully applied to industrial production.

Optimization of Surface Roughness of AISI P20 on Electrical Discharge Machining Sinking Process using Taguchi Method

This research aims to obtain optimal value for the surface roughness of the material AISI P20 on the Electrical Discharge Machining (EDM) Sinking process. In the present research, the Taguchi method is used to investigate the significant influence of process variables on the machining performance and determine the combination of process variables on the EDM process. Orthogonal array L18 (21 × 33) based on the Taguchi method is chosen for the design of experiment. The experiment is replicated twice to finding out the influence of four process variables such as type of electrode, voltage gap, on-time, and off-time on the response performance. Machining performance is evaluated by surface roughness as a response variable that had quality characteristics, smaller is better. These experimental data were analyzed using the Signal-to-noise ratio and Analysis of Variance. The analysis results show that the surface roughness is influenced by the type of electrode and on time. Combination of process variables to obtain optimal surface roughness are using graphite electrodes, and setting values of gap voltage 40 volt, on-time 250 μs, and off-time 20 μs. This combination of process variables can be applied to the manufacturing process using EDM sinking in order to produce a good quality product that determined based on the surface roughness value.

Effects of Laser Energy Density On Carbide Dissolution, Element Distribution and Microstructure Evolution of AISI P20 Steel During Laser Surface Quenching

Laser surface quenching (LSQ) was performed on AISI P20 mould and hot-working die steel with an objective to improve surface characteristics. The steel was treated under three different process parameter conditions. The microstructure, element distribution and residual stresses were investigated through SEM, EDS and XRD analyses. The effect of laser energy density on carbide dissolution/ablation, microstructure evolution were thoroughly investigated. The dissolution/ablation of carbides significantly affected the formation of martensite and retained austenite, and the distribution of elements and phase in the microstructure. The results of the study and analyses of treated surface revealed that the LSQ treatment significantly improved the microstructure, eliminated the pores or other defects. Furthermore, the degree of carbide dissolution/ablation was closely related to the laser energy density. Comparing to Cr7C3, Cr3C2 was more difficult to dissolve at lower laser energy density. Thus, those incompletely dissolved Cr3C2 would hinder the growth of austenite and reduce the carbon content in austenite and lead to the formation of low-carbon martensite. The highest laser energy density (150 J/mm2), was able to produce finer microstructure and significantly reduced the inhomogeneity in distribution of Cr between the poor and the rich Cr areas.