A study of machining characteristics of AISI 4340 alloy steel by wire electrical discharge machining process

Abstract

However, over the past fifty years the rapid growth in the development of harder, tougher and stronger work piece materials. The 4340 steel is a medium carbon, low alloy steel (Heat-treatable). It has excellent toughness, superior strength in the heat treated condition, good fatigue resistance, admirable hardness and wear resistance. The 4340 steel is widely used in different applications as: Automotive system, Aircraft landing gears, transmission, Gas & oil sectors, forged hydraulic and structural areas. A WEDM is a non-contact erosion cutting process. It has a capability of machining parts with varying hardness, intricate shapes, contours and complex shapes. The WEDM is a competitive and economical machining option fulfilling the demanding machining requirements. In WEDM the electric sparks is generated between the tool and workpiece and it used to cut the various types of electrical conductive as well as non-conductive materials. The machining process is controlled by various process parameters such as pulse on time, pulse off time and servo voltage. It was found that servo-voltage and pulse on time are the significant factors affecting the SR. While increases the pulse off time and pulse duration affects the MRR, as the reason of pulse off time limits the spark energy and interrupting the discharge energies. From the experimental result, increases the pulse duration, wire speed, open circuit voltage causes the increases in material removal rate. The wire speed and wire tension play the dominant role in the machining of 4340 steel. Machining with zinc coated brass is found to be the best alternative to the 4340 alloy steel.

Introduction

The WEDM (Wire electrical discharge machining) process is a specialized machining process and used to manufacture components with intricate shapes and complex structures. It has proficient to generate the 2D and 3D components with great flexibility and excellent accuracy. A WEDM offers the tolerance as ± 0.0001 mm and they can cut the plate thickness up to 300 mm. In WEDM the thin wire of about 0.2 mm Diameter. The WEDM is based on the concept of electro-thermal mechanism [1]. The WEDM Technology is based on the conventional EDM sparking process. The material is eroded ahead of the wire and there is no contact between the tool and workpiece during machining. The WEDM Process is able to machine exotic, high strength, super alloys and temperature resistant materials. The WEDM process is able to cut the various materials as: Aluminum, bronze, copper, Tungsten, Titanium, molybdenum, Nickel, stainless steel and composites. The WEDM discharges the electrified current by means of thin wire. The WEDM process experiences a very high temperature of around 8000–12,000˚C [2]. It resulted the localized melting and vaporization of working material, hence extreme spark is produced. In WEDM the metal erosion by means of rapid consequent spark discharges between the tool electrode and workpiece [3]. The wire is kept under tension using mechanical tension devices, reducing the tendency of inaccurate parts. The discharge of sparks repeats rapidly up to 250,000 times per second and there is no contact between the wire electrode and material. In WEDM the discharge sparks are maintained the gap around the workpiece and wire from (0.025 to 0.05 mm) [4]. The WEDM uses a de-ionized water as a dielectric fluid, they act as a non conductive barrier, avoids the formation of electrically conductive channel in the machining area. The wire breakage and wire vibration cause the undesirable machining characteristics greatly affecting the machining accuracy and quality of performance. The breakage of wire leads to unfavorable to thermal load and high temperature of the electrode. The WEDM is the best alternative of making micro-scale parts with dimensional accuracy and surface finish quality. The most common applications of WEDM follows as: Fixtures, Die & mold, extrusion dies, stamping dies, prototype, stripper plates, aircraft components, missile devices and medical parts. The features of WEDM include as: lesser cutting force, no tooling, higher utilization, good surface finish, repeatable length without deformation and machining complex profiles. The WEDM is used for various applications: Aerospace, Automobile, bio-medical, missile, chemical, Robotics and tool industries. WEDM is used for the manufacturing of special gears, bearing cage, splines and hand tools. Hence the WEDM Technique is an accurate and efficient machining process without compromising the machining performance.

The Wire electrical discharge machining is an electro-thermal production process, They are used for machining the electrically conductive materials, brittle materials and ductile materials irrespective of hardness and toughness. Owing to inherent properties of WEDM, it can conveniently machining the complex parts and precision components. The pulse off time, pulse on time and wire speed are the significant parameters of machining Tungsten steel [5].They studied the effect of different process parameters of: Pulse on time, Pulse off time, Wire tension, Taper angle and Dielectric flow rate in WEDM of WC-Co composite (5.3% Co), it presents the reduction of the taper angle leads to higher MRR. The reason of easy removal of debris from the machining zone [6]. They investigated the machining behavior of Al-Gr-B4c (MMCs) by WEDM. It shows the influences of process parameters shows the discrepancy in reinforcement particle and increasing of reinforcement owing to increase the hardness, ultimate stress and wear resistance [7].They described the effects of the WEDM process on titanium alloy by using coated wire electrode under different parametric combinations. They noted the conventional brass wire electrode shows the maximum MRR and Lower SR. The zinc diffused coated wire exhibits the lower surface roughness [8]. They explored the WEDM of MRR on different workpiece material, it enumerates the influencing of process parameters, produces better performance [9]. They reported the WEDM machining of Inconel 625 super-alloy, the output factors such as: MRR, SR, Surface crack density, White layer thickness, Circularity, Hole taper and radial overcut [10]. They explored the hybrid machining method of combining the WEDM and fixed abrasive diamond wire saw process. The hybrid machining process shows the lower surface roughness, kerf width and eliminates the recast layer and HAZ, when compared to WEDM process [11]. They explained the effect of different machining parameters of WEDM in Inconel 625, using of molybdenum wire is attaining the larger MRR and lower SR [12]. They studied the machinability characteristics of Inconel-625 alloy by cryogenically treated wire and explores the effects of machining parameters. It flaunts the MRR is increased in Cryogenically treated wire, it causes low wear rate, increases the spark by raising the pulse on time [13]. They researched the multi-criteria decision analysis and desirability function to identify the input parameters of Inconel alloy in WEDM [14]. They identified the crystallographic plane accuracy by means of specific crystallographic plane cutting of silicon in WEDM. The results shows the mechanical polishing and chemical etching barely affects the surface quality and process exhibits the minimal effects on surface contour [15]. They explored the machining of AISI 4140 steel by WEDM process, it reveals the open circuit voltage and pulse duration are the most important parameters of MRR and SR [16]. They investigated the multiresponse optimization of process parameters in NFQML assisted turning of Titanium alloy by WEDM. The application of TOPSIS method is used to recognize the ideal machining parameters and resulted lower tool wear, less cutting force and minimum surface roughness [17]. They investigated the optimization of responses as Surface roughness and Dimensional deviation, they displays the increases the pulse on time and servo voltage causes the lower cutting rate, minimum surface roughness and lower dimensional deviation [18]. They experimented with the concurrent optimization of process parameters in WEDM of aluminium 5083, it shows the poor machinability and intricate shapes with dimensions [19]. The reported the tool wear mechanism of WEDM of P-20, EN-31 and Stavax tool material, it shows for all the materials 80–90% predicted values are within the 95% confidence level [20].