Accordingly, all arc welding, gas welding, resistance welding and intense energy beam welding processes fall within the envelop of fusion welding. In arc welding, an electric arc is constituted between a pointed electrode and the conductive base metals. This arc is the prime source of heat for melting faying surfaces and filler metals. There exist quite a few such processes—all of them follow the same basic principle but substantially vary with respect to procedure, benefits, limitations and feasible areas of application. Shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) are three such arc welding processes—each of them offers certain advantages over others. Differences between SMAW, GMAW and GTAW welding processes are discussed below.

Consumable and non-consumable electrode: Electrode is integral to every arc welding process for establishing and maintaining electric arc. Such electrodes can be two types—consumable and non-consumable. A consumable electrode melts down during welding due to arc heating and subsequently deposits on weld bead that finally becomes an integral part of the joint. Contrary to this, a non-consumable electrode does not melt down during welding and remains intact. A particular arc welding process utilize only one type. With respect to consumable and non-consumable nature of electrode, comparison among SMAW, GMAW and GTAW welding processes is enlisted below.

• SMAW—Consumable electrode.
• GMAW—Consumable electrode.
• GTAW—Non-consumable electrode.

Application of filler metal: Filler metal is required to supply for filling up the root gap. When root gap is substantially larger (>2mm) and/or edge is prepared then filler should be applied. With consumable electrode, the electrode itself melts down and deposits on weld bead. Thus no additional filler is required to supply. Such electrode behaves as filler and feeding rate of electrode can be controlled to manipulate filler deposition rate. On the contrary, non-consumable electrode supplies no filler on weld bead. Thus if filler is required then it must be supplied separately.

• SMAW—No additional filler is required. Electrode acts as filler.
• GMAW—No additional filler is required. Electrode acts as filler.
• GTAW—Electrode is non-consumable. So additional filler in the form of small diameter rod is supplied, only when it is required, by constantly feeding it below the arc column.

Continuous nature of electrode/filler: The filler material, either in the form of electrode or a separate one, continuously melts down and deposits on weld bead. Thus its length gradually shortens with welding time. If this filler length is short then it has to be replaced frequently by a new one. This reduces rate of production and interrupts the process. On the other hand, a long filler can be continuously fed to the welding zone for longer duration without any interruption. Such method is productive but requires bulk storage of costly filler.

• SMAW—Filler-cum-electrode is in the form of small diameter straight rod of length 2 – 3ft. Thus it requires frequent changing and interruption of process.
• GMAW—Filler-cum-electrode is in the form of small diameter wire that is wound on a wire pool. Quite long wire electrode is stored in that pool and thus welding can be carried out continuously for longer duration without intermediate stoppage for electrode changing. This electrode is continuously fed by means of mechanized arrangements.
• GTAW—Electrode is non-consumable. Additional filler usually comes in the form of short, small diameter rod and thus requires frequent stoppage for changing the filler. However, welding can be carried out continuously if no filler is utilized.

Preferable welding mode: Arc welding can be performed in three different modes. As mentioned earlier, filler is not necessary to supply when root gap is very small or base materials are thin. When welding is carried out without applying any filler, it is termed as autogenous mode. However, if filler is applied and metallurgical composition of filler is similar to that of parent component, then it is termed as homogenous mode. If metallurgical composition of filler substantially differs from that of parent component, it is termed as heterogeneous mode. Different welding processes are suitable for different modes.

• SMAW—Filler is inherent to this process because of consumable electrode. So autogenous mode is not possible. It is suitable for mainly homogenous welding.
• GMAW—Similar to SMAW, filler is inherent to this process because of consumable electrode. So autogenous mode is not possible. It is suitable for homogenous and heterogeneous welding.
• GTAW—Electrode is non-consumable. So autogenous mode is feasible; in fact, TIG welding is suitable for this mode only. However, it can also be applied for homogenous and heterogeneous welding by utilizing optimum set of process parameters.

Electrode material: Electrode material of every arc welding process must possesses few basic characteristics like good electrically conductive, good electron emissivity, desired melting point, etc. It is worth mentioning that filler metal must be compatible with parent metal otherwise they will not mix up properly leading defective welding. Thus with consumable electrode, electrode material should be chosen based on compatibility with base metal. With non-consumable electrode, filler material should be chosen based on compatibility with base metal, whereas electrode should be made of such material with high melting.

• SMAW—Electrode is mostly made of ferrous materials. It has only few variety in terms of electrode material. Thus it is suitable for homogeneous joining of ferrous components only.
• GMAW—Wide variety of electrode materials are available in market. Although most electrodes are ferrous, their metallurgical composition can be varied to harness desired result.
• GTAW—This electrode is made of tungsten only. This is irrespective of base metal or filler metal as electrode is non-consumable. Tungsten has highest melting point (3422°C). Other desired properties can also be manipulated by adding alloying elements in small proportions. For example thorium, lanthanum oxide, cerium oxide, zirconia, etc. are added with tungsten for improving various welding characteristics like electron emissivity, electrode erosion, etc.

Coated or bare electrode: Electrode can be coated to protect it from oxidation or atmospheric contamination. Apart from protection against oxidation, coating also provides other advantages such as supplying shielding gas, reducing spatter, stabilizing arc, inducing chemical elements into weld bead, etc. However, a coated electrode is costly and prone to damage with time. Different processes utilize different types of coating, each having desired function.

• SMAW—Utilizes thick flux coated electrode. Apart from protecting the electrode, this flux supplies shielding gas.
• GMAW—No flux coating is available on electrode. However, a thin coating of stable material is applied to protect electrode material from oxidation.
• GTAW—Utilizes bare tungsten electrode. No coating is applied on electrode.

Shielding gas supply: Shielding gas is supplied in arc welding to dispense the oxygen from welding zone and create an envelope of inert gases surrounding the weld bead. Its primary function is to protect hot weld bead from oxidation. Such shielding gas can be supplied directly from a gas cylinder or indirectly by disintegrating other chemical elements during welding.

• SMAW—Flux coating of electrode disintegrates during welding and produces shielding gas. No separate shielding gas is applied separately.
• GMAW—Shielding gas (inert or active) is supplies from gas cylinder.
• GTAW—Inert shielding gas is supplied from gas cylinder.

Spatter problem: Spatter is small droplets of molten filer metal that is produced due to scattering of arc and comes out from the welding zone. This spatter causes loss of filler metal and thus non-uniform filler deposition rate that sometime leads to various welding defects including negative reinforcement and dimensional inaccuracy. It also hampers appearance and requires grinding after welding for its removal.

• SMAW—Produces excessive spatter even with optimum set of process parameters.
• GMAW—It also produces spatter; however, can be reduced by utilizing optimum set of process parameters.
• GTAW—It is mostly free from spatter.

Manual and automation: Shielded metal arc welding is carried out manually and thus it is also called manual metal arc welding (MMAW). Gas metal arc welding can be automated easily where electrode wire is continuously fed rom the spool using mechanised arrangement and at the same time torch is moved by another automatic vehicle. Gas tungsten arc welding is commonly performed manually; however, can be automated also, especially the movement of torch. An automated process is fast and more productive; but manual process is more flexible and virtually possess no restriction of location for its application.

Productivity and quality issues: SMAW does not offer good quality joint. Thus it is carried out mostly for household and general industrial requirements. Frequent changing of electrodes causes interruption in process and thus it is not suitable for longer welding requirement. GMAW is highly productive and can be carried out continuously for long duration. It can be automated easily. Its volume deposition rate is also very high. Thus it is suitable where wide root gap exists, edges are prepared in U or V shapes, longer joining requirements or even for cladding. Although it is less prone to defects, its joint quality is not very good. Spatter also hampers weld bead appearance. In terms of quality, GTAW is best among the three. It provides superior joint with splendid appearance. It is less prone to defects, but deposition rate or welding rate is comparatively low.

Scientific comparison among shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

• Gas Metal Arc Welding Handbook by W. H. Minnick (2007, Goodheart Willcox).
• Basic TIG & MIG Welding (GTAW & GMAW) by I. H. Griffin, E. M. Roden and C. W. Briggs (3^rd edition, Delmar Cengage Learning).
• Shielded Metal Arc Welding by W. L. Ballis (2011, Xulon Press).

The post Difference Between SMAW, GMAW and GTAW Welding Processes appeared first on Difference Box.

Once again, arc welding encompasses a large group of welding processes, each having varying capability in terms of joint quality, workable material, feasible position, welding time and productivity. Notable examples include manual metal arc welding, gas metal arc welding, gas tungsten arc welding, flux core arc welding, submerged arc welding, etc. In every arc welding process an electric arc is constituted between the electrode and conductive parent components under the presence of sufficient potential difference. This arc is the prime source of heat for fusing faying surfaces of components. SMAW and TIG both are arc welding processes and follow the same basic principle; however, each has different capability and applications.

Shielded metal arc welding (SMAW), also called manual metal arc welding (MMAW), is one arc welding process in which arc is established between a consumable electrode and base metals. It is mostly carried out manually. The consumable electrode supplies filler to fill root gap, thus no additional filler is required. Electrode is coated with suitable flux for protection against corrosion. This flux also disintegrates during welding to produce shielding gas. Tungsten inert gas (TIG) welding, formally known as gas tungsten arc welding (GTAW), is also one arc welding process where arc is established between a non-consumable electrode and base metals. Thus filler, if required, can be supplied additionally by feeding a filler rod at welding zone. Inert shielding gas is also supplied from additional source to protect weld bead. While SMAW is more flexible and has diverse applications, TIG can fetch sound, reliable, defect-free and apparently good joints. Various differences between SMAW and TIG welding processes are given below in table format.

Table: Differences between SMAW and TIG welding processes

Consumable and non-consumable electrode and filler metal: A consumable electrode is one that melts down during arc welding and supply necessary filler metal to fill root gap between parent components. Thus no additional filler metal is required to supply. Contrary to this, a non-consumable electrode does not melt down during welding and thus filler is required to supply additionally if required. Filler may not require if root gap is too small or base plates are thin. Shielded metal arc welding utilizes a consumable electrode and thus the electrode supplies filler. Tungsten inert gas welding is carried out with non-consumable electrode and therefore filler is supplied by feeding additional filler rod at the welding zone whenever required.

Electrode material: Every arc welding electrode must be electrically conductive so as to establish arc by the avalanche of flow of electrons between electrode tip and base plate surface. SMAW electrode comes in the form of small diameter rod of length 2 – 3ft. Composition of this electrode metal is more or less similar to that for parent metals. Therefore SMAW electrode comes in different materials and the compatible one can be selected primarily based on parent material. Contrary to this, TIG welding electrode is independent of work material as it does not fuse and deposit on weld bead. TIG electrode is made of titanium (highest melting point), with some alloying elements like thorium, lanthanum oxide, cerium oxide, and zirconia in order to improve various welding characteristics such as electron emissivity, electrode erosion, etc.

Three modes of welding: As mentioned earlier, filler material is not necessarily required during welding, especially when root gap is very small or base plates are thin. However, if filler is applied, its metallurgical composition must be compatible to that of base materials. Arc welding can be carried out in three different modes—autogenous, homogenous and heterogeneous modes. When joining is carried out without filler, it is termed as autogenous mode. When filler is applied and filler composition is almost similar to base metal composition then it is termed as homogenous mode. If filler composition substantially differs from base metal composition then it is termed as heterogeneous mode. Since filler is inherent to SMAW process (consumable electrode), so it cannot be carried out in autogenous mode. It is particularly suitable for homogenous mode; while, TIG is particularly suitable for autogenous mode. However, TIG can also be satisfactorily applied for other two modes; however, compatible filler is to be supplied additionally at a constant rate (process will be complicated).

Electrode coating and shielding gas: Arc welding electrodes can be either coated or bare. Coating is usually provided to protect electrode from corrosion. Flux coated electrode offers another benefit. During welding, this flux disintegrates to produce enough inert gas which can displace oxygen from welding zone and subsequently protects hot weld bead from oxidation or other contamination. Such shielding is indispensably necessary to obtain defect-free welding. If electrode is bare then shielding gas is required to supply from external source (such as gas cylinder) with the help of suitable accessories. SMAW utilizes a flux-coated electrode and thus flux supplies shielding gas during welding. Contrary to this, TIG welding employs a bare tungsten electrode and thus shielding gas is required to supply externally.

Welding spatter: In context of arc welding, spatter is the tiny droplets of molten filler metal that come out of the welding zone mostly due to scattering of electric arc. This spatter causes loss of costly filler metal as well as reduces filler deposition rate. It also tend to make the arc unstable causing difficulty in maintaining it. Unwanted deposition of metal droplets surrounding the weld bead also hampers appearance and sometimes requires additional post-processing like grinding. Certain arc welding processes are inherent to spatter formation, even with optimum set of parameters. Shielded metal arc welding is one such method that is always associated with spatter. However, spatter level can be minimized using optimum process parameters, properly cleaning parent metal surface and controlling environment in a desirable way. TIG welding is usually free from spatter and spatter related defects.

Manual and automatic operation and joint quality: Shielded metal arc welding is carried out manually and thus it is also called manual metal arc welding. Therefore maintaining constant arc length, weld direction, feed rate etc. are quite difficult; but such parameters influence on quality and strength of joint. Accordingly weld quality depends on experience and capability of welder. However, initiation and maintaining the arc is quite easy. No filler is also required to supply additionally. Thus the process is comparatively easier. Tungsten inert gas welding can be carried out manually else an automated system can be employed. Feeding filler metal at a constant rate is a bit difficult; but maintaining the arc is more complicated. Although process is quite difficult and requires experienced welder, TIG welding can easily produce sound, reliable and defect-free joint.

Scientific comparison among SMAW and TIG welding processes is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

• Tungsten inert gas (TIG or GTA) welding by TWI-Global.com.
• Gas Metal Arc Welding Handbook by W. H. Minnick (2007, Goodheart Willcox).
• SMAW, GMAW, and TIG Welding Comparison by weldingschool.com.

The post Difference Between SMAW and TIG Welding Processes appeared first on Difference Box.

In order to stabilize the arc and also to protect the hot molten metal pool beneath this arc from oxidation and other contamination, proper shielding gas is used to shield or cover entire welding zone surrounding this arc. This shielding gas can be chemically inert one or can contribute in many relevant properties by actively participating in the welding process. Accordingly GMAW can be classified into two groups—Metal active gas (MAG) and Metal inert gas (MIG) welding. So MIG and MAG both are basically variants of GMAW process; only difference lies on the shielding gas used in those processes.

As the name suggest, Metal Inert Gas (MIG) welding process utilizes suitable inert gas for shielding purpose during welding. Such gas is mainly argon or helium, or a mixture of these two in different proportions. Since these gases are chemically inert thus they remain stable even at extreme arc heat. Therefore they do not contribute in altering any weld characteristics apart from protecting the weld bead and electric arc from any external influence.

On the other hand, Metal Active Gas (MAG) welding utilizes an active gas mixture as shielding gas. For example, a suitable mixture of carbon di-oxide (CO₂) and oxygen (O₂) along with other comparatively stable gases like argon, helium, nitrogen, etc. Besides fulfilling basic requirement of shielding gas, such active gases can break down due to arc heating and subsequently induce various chemical elements on weld bead that can enhance joint properties. It also contributes in stabilizing arc, reducing spatter level, etc. Various differences between MIG welding and MAG welding are given below in table format.

Table: Differences between MIG welding and MAG welding

Characteristics of shielding gas: As the name suggests, metal inert gas (MIG) welding utilizes only inert gas like argon or helium. Such gases remain stable even at extreme arc temperature. Metal active gas (MAG) welding utilizes a mixture of inert gas and active gases as shielding gas. Such active gas mainly includes oxygen and carbon di-oxide. The mixing proportion between inert and active gases can significantly vary based on many parameters like base metal and its thickness, filler metal, root gap, welding polarity, intended properties of weld bead, etc. Sometimes environmental condition also governs this proportion.

Capability of altering properties of weld bead: Inert shielding gases remain stable during welding and thus do not induce any chemical elements on weld bead. However, active gases can break down under extreme arc temperature and can subsequently induce relevant chemical elements on weld bead. This leads to change in chemical and mechanical properties of joint. For example, while joining low carbon steel (like mild steel) using carbon di-oxide rich shielding gas, carbon inclusion may occur and this can enhance surface hardness of joint. Therefore, MIG welding cannot alter weld bead properties; while, MAG can do the same.

Cost of shielding gas and application area: In GMAW, shielding gas flow rate in the order of 10 – 20L/min is utilized. Cylinders, filled with industrially pure shielding gas, is comparatively costlier and thus MIG welding is one costlier process. It is primarily used for welding non-ferrous materials like aluminum. Oxygen based active gas is not favored when parent materials are non-ferrous because of high chances of oxidation. In this sense, MAG is economical and preferred for welding of ferrous metals, especially stainless steel.

Scientific comparison among metal active gas (MAG) and metal inert gas (MIG) welding is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

• Metal Inert Gas (MIG) / Metal Active Gas (MAG) Welding by linde-gas.com.
• What is the difference between MIG and MAG by twi-global.com.

The post Difference Between Metal Inert Gas and Metal Active Gas Welding appeared first on Difference Box.

Gas metal arc welding (GMAW) is one economic joining process in which coalescence is formed by melting faying surfaces and filler metal by means of electric arc constituted between consumable electrode and conductive parent metal. Since electrode is a consumable one so it is continuously fed at a constant rate by means of a mechanized wire feeder. So it cannot be performed in autogenous mode as consumable electrode is one integral part of the process. Suitable shielding gas (inert or active) can be used for protecting the weld bed from contamination. However, filler metal can be deposited on the weld bead at a faster rate and thus this process is productive and economic. If performed properly using optimum set of parameters, it can produce a sound and reliable joint.

Gas tungsten arc welding (GTAW), popularly known as tungsten inert gas (TIG) welding, is one sophisticated fusion welding process where joining is realized by coalescence formation due to fusion of faying surfaces. Here electric arc is constituted between conductive base material and non-consumable tungsten electrode. Since electrode is non-consumable one, filler material is required to apply separately when sufficient root gap exists. It is also favorable for autogenous mode of welding where no filler is applied. Shielding gas, preferably inert gas like argon, is also applied for protecting the hot metal pool during welding from atmospheric oxygen. Although is the process is comparatively slower, its capability of joining diverse metals and producing strong and reliable joints makes it one favorable process in many applications. Splendid weld bead appearance and defect-free joint are also two important advantages. GMAW differs from GTAW in many aspects and their differences are given below in table form.

Table: Differences between GMAW and GTAW welding processes

Consumable and non-consumable electrode: During arc welding, the electric arc is established between an electrode and conductive work materials. High heat density of this arc melts down faying surfaces of the parent components as well as filler metal if applied. When an electrode fuses and consequently deposits on weld bead during welding, it is termed as consumable electrode. In other word, when electrode is consumed for providing filler, it is called consumable electrode. In gas metal arc welding (GMAW), the electrode is consumable type as it melts down due to arc heating and subsequently deposits on weld bead. Contrary to this, in gas tungsten arc welding process (GTAW) process, electrode remains intact under intense arc heating. Since it does not melts down to deposit necessary filler metal, so it is non-consumable type. Consequently, life of GTAW electrode is higher than that for GMAW electrode.

Composition of electrode material: In GMAW, metallurgical composition of electrode (or filler) is more or less same with that of parent components, which are to be joined. GTAW always utilizes a pointed tungsten electrode, irrespective of the composition of parent material. However, few alloying elements (for example thorium, lanthanum oxide, cerium oxide, zirconia, etc.) are also added with tungsten for improving various welding characteristics like electron emissivity, electrode erosion, etc.

Possibility to perform in autogenous mode: An autogenous mode of welding is performed without applying any filler metal. Here root gap is maintained minimum, usually zero. During welding, only faying surfaces are fused by heating via electric arc and are allowed to cool down. The fused material of the two surfaces gets mixed and upon cooling it creates the weld bead. GMAW process inherently deposits filler metal on weld bead as it utilizes a consumable electrode. So it cannot be performed in autogenous mode. Since TIG welding utilizes a non-consumable electrode, so it can be advantageously performed in autogenous mode. In fact, it is one preferred welding process for joining in autogenous mode.

Application of filler metal externally: No filler metal is required to apply from external source in GMAW process as the electrode itself acts as filler metal. In TIG welding, however, filler can be applied separately if desired. Although TIG is preferred for autogenous mode joining, it can also be performed in homogeneous mode or heterogeneous mode. Filler in the form of small diameter rod can be fed to the weld zone beneath the electric arc at a constant pre-determined rate. This filler rod melts down due to arc heating and deposits necessary filler. Composition of this filler rod can be similar to that of work material or can be different; however, it must be compatible with parent metal otherwise defective joint will be produced.

Inert and active shielding gas: Shielding gas is used to protect hot weld bead from atmospheric oxygen by creating a protecting layer surrounding the entire weld zone. It also, directly or indirectly, help reducing spatter level, stabilizing arc and improving weld bead properties. This shielding gas can be inert or an active gas also. An active shielding gas can show better capability in certain situations. Such gases can also induce chemical elements on weld bead to improve various mechanical properties of the joint. GMAW process can utilize both types of shielding gas; and accordingly it can be classified into two groups—metal inert gas (MIG) and metal active gas (MAG). MIG utilizes only inert gas like argon, helium, etc. MAG utilizes active gas like carbon di-oxide, oxygen, etc., usually mixed with inert gas in different proportions. On the other hand, GTAW or TIG welding process uses inert gas only, predominantly argon.

GMAW is faster process compared to TIG: In GMAW process, electrode in the form of small diameter wire and wound in a pool is continuously fed by a proper mechanized arrangement. So filler can be deposited at a faster rate and consequently this welding process is highly productive as compared to TIG welding.

Spatter level and appearance: Spatter is small droplets of molten filer metal that is produced due to scattering of arc and come out from the welding zone. This spatter causes loss of filler metal and thus non-uniform filler deposition rate that sometime leads to various welding defects including negative reinforcement and dimensional inaccuracy. It also hampers appearance and requires grinding after welding for its removal. Many arc welding processes produce spatter including GMAW. It cannot be performed in spatter-free way even if optimum set of process parameters are used and proper welding technique is employed. TIG welding usually does not produce spatter unless the work material surface is not clean. Weld bead produced by TIG welding is smooth and superficially attractive.

Proficiency of welder: GMAW is quite easier to perform as most motions are automated. Even the movement of torch can be automated using suitable arrangement. Establishing arc is also easier. Compared to this, TIG welding is one sophisticated process and thus it requires experienced welder to carry out welding smoothly without arc blow or undesired arc termination. Establishing arc is quite crucial as tungsten electrode may stick to the work surface leading to tungsten inclusion defect.

Scientific comparison among Gas metal arc welding (GMAW) and Gas tungsten arc welding (GTAW) is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

• Tungsten inert gas (TIG or GTA) welding by TWI-Global.com.
• Gas Metal Arc Welding Handbook by W. H. Minnick (2007, Goodheart Willcox).
• Basic TIG & MIG Welding (GTAW & GMAW) by I. H. Griffin, E. M. Roden and C. W. Briggs (3^rd edition, Delmar Cengage Learning).

The post Difference Between GMAW and GTAW Welding Processes appeared first on Difference Box.

In arc welding, an electric arc is established in between parent metal and electrode. This arc is prime source of heat to melt down faying surfaces of base metal to form coalescence. Since base metals are required to fuse to achieve joining, so all arc welding processes are basically fusion welding. There are several arc welding processes such as manual metal arc welding (MMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), submerged arc welding (SAW), flux core arc welding (FCAW), electro slag welding (ESW), etc. All of them are based on same principle in terms of joining technique, but their capability and process are different. Each of them offers certain advantages over others.

Gas metal arc welding (GMAW) is one highly productive fusion welding process where consumable electrode is continuously fed to the welding zone from a wire spool using an automated system. Arc, constituted between electrode and base metals under the presence of sufficient potential difference, fuses electrode at a faster rate and subsequently deposits on root gap to perpetuate the process. Proper shielding gas is also supplied to protect high temperature arc and surrounding areas from oxidation. Based on shielding gas property, GMAW can be of two types—metal active gas and metal inert gas. In metal inert gas (MIG) welding, a chemically inert gas (like argon, helium, etc.) is used for shielding purpose; while in metal active gas welding, a chemically active gas (like carbon di-oxide or oxygen) is mixed with inert gas to use for shielding purpose.

Gas tungsten arc welding (GTAW), popularly known as tungsten inert gas (TIG) welding, is a versatile and reliable fusion welding process that utilizes a non-consumable tungsten electrode to constitute the electric arc. Filler metal, if needed, can also be supplied externally by feeding a filer rod into welding zone. Unlike MIG welding, TIG welding is not suitable for high filler deposition rate; however, the quality of joint and appearance of weld bead is much better. Therefore both MIG and TIG welding are fusion welding processes where heat is supplied by an electric arc and both of them utilize inert gas as shielding gas. However, they are different in certain ways including the process and capability. Various differences between MIG welding and TIG welding are provided below in table format.

Table: Differences between MIG welding and TIG welding

Consumable and non-consumable electrode: A conductive electrode is mandatory in every arc welding process to constitute the arc. Sometimes this electrode itself deposits molten metal in root gap between base plates. A consumable electrode is one which can melt down by arc heat to deposit filler during welding. On the contrary, a non-consumable electrode is not expected melt down during welding and thus filler metal is required to supply externally whenever intended. In MIG welding, the consumable electrode melts down by arc heat and subsequently supplies filler metal. Thus electrode is continuously fed into welding zone at a pre-defined rate. TIG welding is performed using a non-consumable electrode and thus it does not melt down to supply filler. In case filler is desired, the same is supplied additionally by feeding a small diameter filler rod beneath the arc.

Electrode material: Filler material should be compatible with parent material, otherwise defective welding will be produced. With MIG welding, filler metal (same as electrode metal) can be chosen according to base metal. So electrode can be made of wide variety of metals, each one is usually suitable for a small group of base metals. In TIG welding, electrode is always made of tungsten because of its strength, high melting temperature and good shape retention capability. Sometimes few alloying elements are also added to (for example thorium, lanthanum oxide, cerium oxide, zirconia, etc.) with tungsten for improving various welding characteristics like electron emissivity, electrode erosion, etc.

Filler deposition rate and productivity: In MIG welding process, electrode in the form of small diameter wire that is wound in a pool is continuously fed by a proper mechanized arrangement. So filler can be deposited at a faster rate and consequently this welding process is highly productive as compared to TIG welding. Thus MIG welding is suitable when edge is prepared in V or U shaped or root gap is more.

Spatter level and appearance: Spatter is small droplets of molten filer metal that is produced due to scattering of arc and subsequently emerge out from the welding zone. This spatter causes loss of filler metal that leads to non-uniform filler deposition rate. It also destabilize the arc. Abruptly deposited molten metal droplets also hamper appearance and sometimes require grinding for its removal. Many arc welding processes produce spatter including GMAW (both MIG and MAG). Although MIG tends to produce low level spatter, it cannot be performed in spatter-free way even if optimum set of process parameters and proper welding technique are employed. TIG welding usually does not produce spatter unless the work material surface is not clean. Weld bead produced by TIG welding is clean, smooth and attractive.

Autogenous, homogenous and heterogeneous modes: On the basis of filler metal application and its composition, welding can be classified as autogenous, homogenous and heterogeneous modes. An autogenous mode of welding is performed without applying any filler metal. When root gap is virtually zero or very small then filler does not require. In homogeneous mode of welding, filler is applied and composition of filler is more or less same with that for parent metal. Filler is also applied in heterogeneous welding mode but composition of filler differs substantially from that of parent metal. Since consumable electrode is inherent to MIG welding, so it cannot be performed in autogenous mode. Contrary to this, TIG is suitable and preferred for such purpose. TIG can be also applied advantageously for homogenous and heterogeneous modes with optimum set of parameters.

Possibility for overhead joining: Welding position includes down-hand, inclined, overhead, etc. Overhead joining position is very difficult to execute as filler is required to deposit against to gravity. Molten metal pool always has a tendency to fall down and it can even injure welder. Thus gravitational force alone is not suitable for proper filler deposition; in fact, it imposes restriction. Lorentz force helps in such situation. TIG welding with optimum set of parameters can be employed for overhead welding. However, it requires experienced welder to achieve good penetration and welding quality.

Scientific comparison among metal inert gas (MIG) welding and tungsten inert gas (TIG) welding is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

1. Gas Metal Arc Welding Handbook by W. H. Minnick (2007, Goodheart Willcox).
2. Basic TIG & MIG Welding (GTAW & GMAW) by I. H. Griffin, E. M. Roden and C. W. Briggs (3^rd edition, Delmar Cengage Learning).

The post Difference Between MIG Welding and TIG Welding appeared first on Difference Box.

Fusion welding processes are those where faying surfaces of base metal are fused by applying heat to form coalescence for realization of joining; whereas, no such melting talks place in solid state welding processes. All arc welding, gas welding, resistance welding, and intense energy welding processes are basically fusion processes. In arc welding, an electric arc is constituted in between parent components and electrode by supplying sufficient potential difference in between them. This arc is the prime source of heat (thermal energy) to melt down base plates and filler. Once again there are various arc welding processes; for example, MMAW or SMAW, GMAW (MIG and MAG), GTAW or TIG, SAW, FCAW, ESW, etc. Each of them offer certain benefits over others.

Manual metal arc welding (MMAW), also called shielded metal arc welding (SMAW), is one fusion welding process where electric arc is constituted between a electrode and base plates. This welding is mostly carried out manually and thus the name. The consumable electrode is covered with suitable flux that disintegrates during welding to produce shielding gas and slag layer, which help protecting the arc and molten metal pool from oxidation or contamination. Thus it does not require application of shielding gas separately. Gas metal arc welding (GMAW) is also one fusion welding process where the arc is constituted between consumable electrode and parent components. The electrode, in the form of wire, is continuously fed to the welding zone from a wire spool using a mechanized system and at the same time appropriate shielding gas is supplied from external source to protect the arc and surrounding regions. GMAW is very fast process with high filler deposition rate. Various differences between manual metal arc welding (MMAW) and gas metal arc welding (GMAW) processes are given below in table format.

Table: Differences between MMAW and GMAW welding processes

Intermittent and continuous process: A small diameter (0.5 – 2.0mm) rod of length 30 – 50cm and coated with suitable flux is used as electrode in manual metal arc welding. Since this electrode is consumable so its length shortens with welding time because of its deposition on weld bead. Thus after certain interval (when flux coated part ended), electrode is required to be replaced by a new one to carry out welding. Thus MMAW requires frequent stoppage and is one intermittent process. On the contrary, a consumable electrode (in the form of wire) is supplied continuously from a wire pool in gas metal arc welding. This wire pool can store sufficient length of wire (it is usually measured by its weight). Thus GMAW can be carried out for longer duration without any pause for electrode changing.

Sources of shielding gas: Shielding gas is indispensably necessary in arc welding processes to protect the arc and molten metal pool from oxidation or other contamination. During arc welding, a thick layer of shielding gas encloses the entire welding zone and restricts atmospheric air to come in contact with weld bead and surrounding hot areas. In MMAW process, the electrode is coated with a flux which disintegrates by the welding heat and produces enough shielding gas to cover up heated areas. So no shielding gas is required to supply additionally. But in GMAW, no such flux coating exists on the electrode. Thus shielding gas is supplied from additional sources (like gas cylinder) using proper delivery pipeline and nozzle.

Slag deposition and its removal: MMAW utilizes a flux coated electrode and this flux actually produces intended shielding gas during welding. Flux also produces slag that deposits at the top surface of weld bead and protects it from contamination. But this slag layer is required to remove after welding is over in order to improve appearance. Usually grinding is adopted for such removal. However, if slag remains trapped within the weld bead and fail to float out at surface then defects like slag inclusion are observed. Such defects can reduce load carrying capacity, joint strength and make it vulnerable under corrosion—all of these ultimately reduce service life. GMAW is free from slag as no flux coated electrode is used. Thus it eliminates defects related to slag and also requirement of post-processing for slag removal.

Productivity: MMAW is not highly productive. In multi-pass welding, slag deposited on weld bead is required to remove completely after every pass so as to avoid slag inclusion defect. Moreover, electrode is required to change frequently. So it is not suitable if high volume of molten metal is required to deposit on weld bead. Thus it is not productive for multi-pass welding. GMAW is free from slag and also no electrode changing is desired. So it can deposit large volume of filler at short period of time. Thus it is perfect choice when root gap is more, edge is prepared in U or V shaped and/or plate thickness is more. Moreover, GMAW electrode diameter is smaller than that for MMAW, which increases arc current density and thus filler deposition rate.

Flexibility of welding: Flexibility indicates ability of a welding process to accommodate various shapes to join in diverse ways in different conditions. Indirectly it refers capability and feasibility to apply a particular process under certain conditions. GMAW requires shielding gas cylinder and pipelines and accessories for its controlled delivery. So it is not suitable for outdoor small scale applications. MMAW can be applied virtually for every location in all positions within the reach of electrode; however, its performance may not be at same level in all scenarios. Even though MMAW is not productive, it is highly flexible and has diverse applications.

Welding quality and dependency on welder: As the name suggests, manual metal arc welding is mostly carried out by human operators. So welding quality relies on the skill and experience of welder. It is also susceptible to human error including random and chance errors. Contrary to this, GMAW can be automated and requires little intervention of welder. So it can provide better quality joints if appropriate parameters are employed.

Scientific comparison among manual metal arc welding (MMAW) and gas metal arc welding (GMAW) processes is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

1. Arc welding processes by magmaweld.com.
2. Shielded Metal Arc Welding by W. L. Ballis (2011, Xulon Press).
3. Gas Metal Arc Welding Handbook by W. H. Minnick (2007, Goodheart Willcox).

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As a consequence of extensive development throughout the last few decades, TIG welding has emerged as one promising and reliable welding technique for permanently joining two or more metallic components. It can be performed in autogenous mode; however, filler material can also be applied as and when intended (both homogenous and heterogeneous modes are possible). Sumptuous appearance of weld bead, higher arc efficiency, lesser chance of defect and minimum spatter level made this process a favorable fabrication technique in a wide range of industrial applications including construction, automobile and aerospace arenas.

In TIG welding, electric arc is stuck between the non-consumable electrode (made of tungsten with small alloying elements) and the conductive workpiece. This arc heat melts down the faying surfaces of the parent components, which ultimately produces coalescence. Filler metal, if applied, also deposits on the root gap in molten state due to arc heating. Edge preparation can also be carried out if plate thickness is more than 4 – 5mm. In spite of many advantages, TIG welding is limited by the achievable penetration, which is around 3 – 3.5mm based on many relevant parameters. Achieving depth of penetration more than 3.5mm in a single pass is practically difficult with TIG welding, if not impossible.

This limitation triggers palpable research interest and as a consequence many variants have emerged that provide unique advantages over conventional TIG welding process. Activated and flux-bound TIG welding are two notable variants. In Activated Tungsten Inert Gas (A-TIG) welding a thin layer of activating flux is applied on the faying surfaces and surrounding region of the parent components prior to welding. This shows a promising result by enhancing depth of penetration by 3 times or even more as compared to conventional TIG welding with similar process parameters. So achieving penetration of 7 – 11mm is feasible with A-TIG welding, which ultimately results in remarkable improvement of productivity in entire manufacturing. Various differences between Tungsten Inert Gas (TIG) welding and Activated Tungsten Inert Gas (A-TIG) welding are given below in table format. It is worth mentioning that both processes are performed in same set up and in same way except the application of flux in A-TIG welding.

Table: Differences between TIG welding and A-TIG welding

Usage of activating flux: This is the prime difference between TIG welding and A-TIG welding as activating flux is used only in the later one. Such activating flux include a large number of oxides and halides of metal such as titanium oxide (TiO₂), silica (SiO₂), chromium oxide (Cr₂O₃), magnesium carbonate (MgCO₃), magnesium oxide (MgO), manganese dioxide (MnO₂), calcium oxide (CaO), aluminum oxide (Al₂O₃), zirconium dioxide (ZrO₂), etc. A homogeneous mixture of such fluxes in different proportions are also used. Such flux is first mixed with suitable solvent to prepare a semi-solid paste and the same is applied on the faying surfaces and surrounding regions of the parent component. It has to be applied prior to welding and must be allowed to dry before establishing the arc. Flux can be applied manually or with the assistance of mechanized system; however, thickness of this flux layer has to uniform in order to achieve defect-free joint. Usually this thickness varies from 30 – 75µm based on a number of relevant parameters.

Penetration depth, weld bead width and HAZ: Various researches have clearly shown that a depth of 7 – 11mm is achievable in single pass without any edge preparation but with the usage of suitable flux; as compared to common TIG welding that can provide maximum 3.5mm penetration under similar conditions. Such remarkable improvement in penetration is attributed to the reversal of Marangoni Effect when flux is applied. Use of activating flux also leads to arc constriction, which subsequently increases heat density of electric arc. A constricted arc results in narrower weld bead and also narrower heat affected zone (HAZ) as lower rate of heat input is desired in a particular area.

Establishing arc between electrodes: Every arc welding process requires an electric arc to be established in between the electrode and conductive work materials. In fact, this arc is the prime source of heat for melting faying surfaces of parent material. In TIG welding, constituting arc between pointed tungsten electrode and conductive parent metal is not problematic. However, with A-TIG welding, because of presence insulating layer on work metal surfaces, flow of electrons is restricted and thus establishing arc is a bit difficult. Often additional flux-free supporting plate is used at the entry of joint to facilitate this purpose. It also requires a little larger closed circuit voltage for maintaining the arc throughout the process.

Thin sheet and tick sheet joining: A-TIG welding inherently provides deeper penetration and thus it is not economical to use it for joining thin sheets or plates having thickness below 4mm. Even if it is used for such cases, then excess penetration, dimensional inaccuracy and high deformation will be observed. However, for joining thicker components, A-TIG is preferred as it can give penetration of 7 – 11mm in a single pass and that too without any edge preparation. On the contrary, TIG welding can be advantageously used for both thin and thick component joining following necessary technique.

Edge preparation, multiple passes and productivity: Joining thick plates (thickness>3.5mm) by TIG welding requires proper edge preparation and multiple passes to properly fill entire root gap. Multiple pass welding also increases level of heat input in a particular area and thus HAZ width, deformation, etc. also increases, which are usually undesirable. This requires large volume of costly filler metal as well as considerable amount of time. In fact, TIG welding is not suitable when large volume of filler metal is required to deposit; gas metal arc welding (GMAW) is preferred choice in such scenario. However, A-TIG welding can also be advantageously used for such purposes without requiring edge preparation or multiple pass welding.

Scientific comparison among TIG welding and A-TIG welding is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

• Babu et al. (2016); Development of flux bounded tungsten inert gas welding process to join aluminum alloys; American Journal of Mechanical and Industrial Engineering; Vol. 1 (3); pp. 58-63.
• Saha et al. (2018); Investigation on the effect of activating flux on tungsten inert gas welding of austenitic stainless steel using ac polarity; Indian Welding Journal; Vol. 51 (2).

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Variants of tungsten inert gas (TIG) welding

Limited penetration sparks research interest on this topic and the result is emergence of few variants of TIG welding that shows remarkable improvement in achievable penetration depth. Activated tungsten inert gas (A-TIG) welding and Flux bound tungsten inert gas (FB-TIG) welding are two such variants that utilize suitable activating flux to improve upon various characteristics of conventional TIG welding. These processes are also called flux assisted TIG welding as they mandatorily require a layer of activating flux on the components to be joined.

Activating flux and its application on metal surface

In both the cases a thin layer (thickness usually below 50µm) of activating flux is applied on the surface of parent material prior to welding. Such activating flux include a large number of oxides and halides of metal such as titanium oxide (TiO₂), silica (SiO₂), chromium oxide (Cr₂O₃), magnesium carbonate (MgCO₃), magnesium oxide (MgO), manganese dioxide (MnO₂), calcium oxide (CaO), aluminum oxide (Al₂O₃), zirconium dioxide (ZrO₂), etc. A homogeneous mixture of such fluxes in different proportions are also used.

Such flux is first mixed with acetone to form a paste like solution and then applied on the surface of parent metal either manually using soft brush or automatically using a mechanized system. Mixing ratio is not important as acetone is highly volatile and thus this ratio will not remain constant even during application of flux layer on metal. However, maintaining uniformity in flux coating thickness is crucial factor in obtaining defect-free welding. After applying flux coating, welding is carried out exactly in same way as in case of conventional TIG welding. All process parameters remain same, except that the closed circuit voltage increase slightly in some cases (usually this change is negligible).

Activated tungsten inert gas (A-TIG) welding

Although A-TIG and FB-TIG follow same aforementioned principle, they differ on the position of application of activating flux on parent metals. In activated tungsten inert gas (A-TIG) welding, flux is applied at the faying surface of the parent metal and surrounding it. Usually flus is applied up to a width of about 4mm from faying surface across the root gap in each side. So here flux lies just below the arc during welding. A typical layer of flux on parent metal for A-TIG welding is schematically shown here.

Flux bound tungsten inert gas (FB-TIG) welding

In flux bound tungsten inert gas (FB-TIG) welding, no flux is applied on faying surface and surrounding it; instead, it is applied on the top surface of parent metal maintaining small space after root gap. So here flux does not lie just below electric arc during welding. Activating flux, method of its application on metal surface and the welding procedure remain exactly same with A-TIG welding. The only difference lies on the position where flux is applied. However both exhibit palpable improvement in achievable depth of penetration. A typical layer of flux on parent metal for FB-TIG is schematically shown here.

Advantages offered by A-TIG and FB-TIG over conventional TIG

Various investigations have revealed that use of such flux can fetch numerous advantages as compared to conventional TIG welding. Both A-TIG and FB-TIG provides similar results and thus their advantages are also same when compared with conventional one. Their advantages are enlisted below.

1. Enhanced depth of penetration: Use of activating flux leads to constricted arc that increases heat density of the arc. Many proponents claimed that reversal of Marangoni Effect causes such increase in penetration. Flux assisted TIG welding usually gives penetration in the range of 6 – 9mm; however, with use of optimum parameters as deep as 11mm penetration can also be achieved in a single pass. This indicates about 3 times increase in penetration as compared to conventional TIG welding process.
2. Narrow weld bead: Constricted arc also results in narrow weld bead. This has certain indirect advantages like lower deformation, less heat affected zone (HAZ), etc. HAZ is considered as weak point in weld joint as its metallurgical properties are severely affected by arc heating and narrower HAZ is always desirable.

Scientific comparison among activated tungsten inert gas (A-TIG) welding and flux bound tungsten inert gas (FB-TIG) welding is provided in this article. The author also suggests you to go through the following references for better understanding of the topic.

• Babu et al. (2016); Development of flux bounded tungsten inert gas welding process to join aluminum alloys; American Journal of Mechanical and Industrial Engineering; Vol. 1 (3); pp. 58-63.
• Saha et al. (2018); Investigation on the effect of activating flux on tungsten inert gas welding of austenitic stainless steel using ac polarity; Indian Welding Journal; Vol. 51 (2).

The post Difference Between A-TIG Welding and FB-TIG Welding appeared first on Difference Box.

In all those welding processes where sufficient heat is applied from external source for fusion or melting of faying surfaces of the base components in order to form weld bead are termed as fusion welding processes. No pressure is usually desired in such processes. All arc welding, gas welding and resistance welding processes come under fusion welding. It is also worth mentioning that melting of faying surfaces of base plate occurs due to direct application of heat and not as a consequence of pressure, friction, etc.

On the other hand, in solid state welding processes, no heat is applied directly; instead sufficient pressure is applied in most cases. As a consequence of pressure, heat may generate at contact zone; however, usually this temperature remains well below the melting point of base components. Diffusion welding, forge welding, explosion welding, pressure welding, friction welding, etc. are examples of this category. Important differences between fusion welding and solid state welding are given below in table form.

Table: Differences between fusion welding and solid state welding

Melting of faying surfaces: As the name suggests, in fusion welding, faying surfaces of the parent component are allowed to fuse in order to create weld bead or coalescence. Filler metal, if applied, also melts down and mixes with molten parent metal. Contrary to this, no fusion or melting takes place in solid state welding and thus joining takes place while the components are in solid state. Although due to simultaneous application of pressure and friction, temperature of parent components may increase; however, it always remains below the melting point of base metal and thus no fusion occurs. In fact, this is the main difference between two types of welding.

Application of heat and pressure: It is obvious that heat must be applied from external source in fusion welding. This heat source can be of different types like electric arc in case of arc welding, burning of oxy-fuel gas in case of gas welding, electric resistance heating in case of resistance welding and even an intense energy beam like plasma, laser or electron beam in case of PAW, LBW or EBW. On the other hand, solid state welding processes usually require application of pressure. No direct application of heat is desired; however, heat may produce as a consequence of pressure, friction, etc.

Application of filler material: Filler material is desired to fill the root gap that exists in between parent components. Based on application of filler and its composition, welding can be classified into three categories—autogenous, homogeneous and heterogeneous. When root gap is very small then filler is not required and such process is termed as autogenous. Solid state welding are usually performed in autogenous mode. On the other hand when filler is applied and metallurgical composition of filler is similar to that of parent metal, it is termed as homogeneous welding; while if metallurgical composition of filler is different from that of parent metal, it is called heterogeneous welding. Fusion welding can be advantageously performed in all three modes; however, extra precautions and optimum parameters must be utilized for joining in heterogeneous mode.

Presence of HAZ: Heat Affected Zone (HAZ) is the narrow layer in the welded components surrounding weld bead where material has not been melted but various physical and mechanical properties have been affected due to heating and subsequent cooling. This HAZ is considered as weak region as it is highly susceptible to mechanical and chemical failure. Due to extreme heating at a temperature above melting point of concerned material, broader HAZ exists surrounding the weld bead when components are joined by fusion welding processes; whereas a narrow (sometime negligible) HAZ can be observed when components are joined by solid state welding processes as lesser heat generates during welding.

Changes in mechanical and metallurgical properties: Various metallurgical properties like grain orientation, grain structure, atomic defects, etc. are usually affected during welding. Many mechanical properties like strength, hardness, toughness, etc. are also affected as a consequence of metallurgical changes. Usually such changes are associated with level of heating and subsequent cooling of components. In fusion welding processes high heat is applied and materials are melted, so such processes can alter various properties to an extreme level. Contrary to this, such changes are meagre and mostly within acceptable limit when joining is performed using solid state welding processes.

Capability of dissimilar metal joining: One of the biggest advantage of welding among all joining processes is leak-proof and sound joining of dissimilar materials. However, every welding process is not suitable for this purpose. Since dissimilar metal joining is basically heterogeneous welding, so only few fusion welding processes can fulfill this requirement. However, it requires extreme care and optimum process parameters to obtain sound joint. Solid state welding is not suitable at all for dissimilar metal joining.

Level of distortion in welded structures: Due to uneven expansion and contraction during heating and cooling in welding, the assembled structures distorts to a different plane leading to welding defect. Such distortion in joined structures causes dimensional inaccuracy and rejected parts. Distortion tendency in welded structures increases with the increase in heat input. So if proper fixture is not employed or proper distortion minimization technique (like skip welding, pre-setting the parts in opposite direction, etc.) is not adopted, then fusion welded parts show higher distortion than the other one as heat input is higher in former case.

Examples of the processes: All arc welding processes (MMAW, GMAW, TIG, SAW, FCAW, ESW, etc.), gas welding processes (OAW, OHW, AAW, PGW, etc.), resistance welding processes (RSW, RSEW, PW, PEW, FW, etc.) and intense energy beam welding processes (PAW, LBM and EBW) are examples for fusion welding. Diffusion welding (DFW), pressure welding (PW), roll welding (ROW), cold welding (CW), friction welding (FRW), forge welding (FOW), etc. are examples of solid state welding.

Scientific comparison among fusion welding and solid state welding is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

1. Difference between fusion welding and solid state welding by difference.minaprem.com.
2. Welding Defects by M. Preto (1^st edition, Aracne).
3. Physical Chemistry of Fusion Welding by G. F. Deyev and D. G. Deyev (1^st edition, DGD Press).

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