Description
CHAPTER ONE
1.0 INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Welding is a manufacturing process of creating a permanent joint obtained by the fusion of the surface of the parts to be joined together, with or without the application of pressure and a filler material. The materials to be joined may be similar or dissimilar to each other. The heat required for the fusion of the material may be obtained by burning of gas or by an electric arc. The latter method is more extensively used because of greater welding speed.
Welding technology has obtained access virtually to every branch of manufacturing; to name a few, ships, rail road equipment, building construction, boilers, launch vehicles, pipelines, nuclear power plants, aircrafts, automobiles, pipelines. Welding technology needs constant upgrading and with the widespread applications of welding (Khanna et al., 2016). To consistently produce high quality of welds, arc welding requires experienced welding personnel. One reason for this is the need to properly select welding parameters for a given task to provide a good weld quality which identified by its micro-structure and the amount of spatter, and relied on the correct bead geometry size.
Mild steel is the most common form of steel because its price is relatively low while it provides material properties that are acceptable for many applications.
Metal Inert Gas (MIG) welding is an arc welding process that uses a continuous solid wire electrode heated and fed into the weld pool from a welding gun. The two base materials are melted together forming a join. The gun feeds a shielding gas alongside the electrode helping protect the weld pool from airborne contaminants. Temperature distribution depends upon current, voltage, welding speed, Material to be welded, composition of material to be welded. In welding heat flows from welding source to work piece and after this heat flow into the work piece by conduction. Heat loss is also occurred due to convention and radiation. Since this heat which flow into the body of work piece is responsible for changes in mechanical properties and microstructure it is important to know the amount heat produce at certain critical points. In this paper, varying the welding speed on temperature distribution was simulated using finite element (FE) techniques to analyze the effect. For this simulation ANSYS software package program was used (Parmar, 2010). The main objective of the present work is to simulate the general behavior of the butt Joint weld under different parameters process parameters.
1.2 PROBLEM STATEMENT
Welding is one of the processes that have versatile application mostly used in industries, such as, welding is extensively used in fabrication as an alternative method for casting or forging and as a replacement for bolted and riveted joints. It is also used as a repair medium e.g. to reunite a metal at a crack or to build up a small part that has broken off such as a gear tooth or to repair a worn surface such as a bearing surface. To consistently produce high quality of welds, arc welding requires experienced welding personnel. One reason for this is the need to properly select welding parameters for a given task to provide a good weld quality which identified by its micro-structure and the amount of spatter, and relied on the correct bead geometry size. Therefore, the use of the control system in MIG welding can eliminate much of the “guess work” often employed by welders to specify welding parameters for a given task (Kim et al., 2015). Investigation into the relationship between the welding process parameters and bead geometry began in the mid 1900s and regression analysis was applied to welding geometry research by Lee and Raveendra (Lee et al., 2010). Many efforts have been carried out for the development of various algorithms in the modeling of Metal Inert Gas (MIG) welding process. In the early days, arc welding was carried out manually so that the weld quality can be totally controlled by the welder ability.
McGlone and Chadwick (2018) have reported a mathematical analysis correlating process variables and bead geometry for the submerged Metal Inert Gas (MIG) welding of square edge close butts. Similar mathematical relationship between welding variables and fillet weld geometry for Metal Inert Gas (MIG) welding using flux cored wires have also been reported (Doherty et al, 2018). Chandel (2018) first applied this technique to the Metal Inert Gas (MIG) welding process and investigated relationship between process variables and bead geometry. These results showed that arc current has the greatest influence on bead geometry, and that mathematical models derived from experimental results can be used to predict bead geometry accurately. Nearly 90% of welding in world is carried out by one or the other arc welding process; therefore it is imperative to discuss the effects of welding parameters on the weldability of the materials during the arc welding.
This study was carried out to study the effect of those parameters on welding process.
1.3 AIM AND OBJECTIVES OF THE STUDY
The main aim of this work is to carry out a study on the effect of welding parameters on welding temperature of a mild steel welded plate using MIG. The objectives are:
- To determine the effect of welding parameters on the weld ability of mild steel.
- To investigate the depth of penetration and Heat input which are considered as output parameters of
- To determine the weld ability and property of a mild steel
- To optimize MIG welding of some economically important similar materials or dissimilar materials in industry.
- To simulate the effect of welding parameters of submerged arc welding on temperature distribution so as to determine the cooling rates in different directions with respect to weld axis
1.4 SIGNIFICANCE OF THE STUDY
This study shall serve as a means of knowing the heat flow and effect of heat input in welding and to know about important process parameters which are required to be considered in any welding such heat source, welding speed, heat input, temperature dependent material properties etc.
Finally, the study will explore the reader on how temperature distribution is effected by the process parameters like welding speed current.
1.5 SCOPE / LIMITATION OF THE STUDY
The scope of this work covers the investigation of the effect of welding parameters on the weld ability of mild steel specimen, which is welded by Metal MIG welding and butt joint. In this work, current and voltage are considered as welding parameters. The effect of welding parameters is investigated on depth of penetration and Heat input which are considered as output parameters of welding.
1.6 DEFINITION AND APPLICATION OF WELDING
Welding process remains an important process for the fabrication of ships, rail road equipment, boilers, vehicle, air craft industries, and pipelines. welding is a fabrication process that joins two materials usually metals or thermoplastics by melting the workpices and adding filler material to the molten pool of materials ,that on cooling becomes a strong joint, with pressure sometimes used in conjunction with heat or by itself, to produce the weld.
1.7 MIG WELDING VARIABLE
The variables affecting weld quality in arc welding are classified into the following groups:
- Welding current
Welding current is the most influential variable in arc welding process which controls the electrode burn off rate, the depth of fusion and geometry of the welded materials.
- Welding voltage
This is the electrical potential difference between the tip of the welding wire and the surface of the molten weld pool. It determines the shape of the fusion zone and weld reinforcement. High welding voltage produces wider, flatter and less deeply penetrating welds than low welding voltages. Depth of penetration is maximum at optimum arc voltage.
- Welding speed
Speed of welding is defined as the rate of travel of the electrode along the seam or the rate of the travel of the work under the electrode along the seam. Some general statements can be made regarding speed of travel.
Increasing the speed of travel and maintaining constant arc voltage and current will reduce the width of bead and also increase penetration until an optimum speed is reached at which penetration will be maximum. Increasing the speed beyond this optimum will result in decreasing penetration (Ibrahim, 2017).
In the MIG welding process increase in welding speed causes:
¨ Decrease in the heat input per unit length of the weld.
¨ Decrease in the electrode burn off rate.
¨ Decrease in the weld reinforcement.
If the welding speed decreases beyond a certain point, the penetration also will decrease due to the pressure of the large amount of weld pool beneath the electrode, which will cushion the arc penetrating force (Welding handbook, 4th edition, section 2).
