Welding Design: How to Choose the Appropriate Type of Welding

Welding Design: How to Choose the Appropriate Type of Welding - In the design of construction, welding plays an important role in connecting two or more construction materials that can be formed construction components as needed. The material used in the construction design is usually derived from the steel plate, steel profile (angle, UNP, IWF, H-Beam), strip, plate, square hollow, steel pipe etc. Most of the manufacturing process from material derived construction is done through the connection process and certainly in this post will only be explained about the welding joint.

Welding is one of the types of construction joints. According to the definition of Deutsche Industrie Normen (DIN), welding is a metallurgical bond at the metal or metal alloy joint which is carried out in a molten or liquid state. In other words, welding is a local joint of several pieces of metal by using thermal energy.

There are so many types of welding that can be used in the connection process. Harsono and Toshi in the handbook of welding engineering welding classify based on the principle of work into gas welding, arc welding, electric welding slag, electric welding gas, thermite welding, electron beam welding and plasma arc welding. However, the most commonly used in the construction industry and manufacturing are gas welding and arc welding. In this post, gas welding is limited in oxyacetylene welding, arc welding is limited in Shielded Metal Arc Welding (SMAW), and a combination of both gas welding and arc welding is limited to Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW). How to select or specify the type of welding that, in this post will be explained in more detail based on the form of the base material, type of filler, weld strength, thermal energy source and welding cost.

Before choosing the type of welding that according to the construction design, we must first understand the characteristics of each type of welding. Here will be explained one by one characteristic of some types of welding used in the construction design.

(1) Oxy-Acetylene Welding

Oxy-acetylene welding is one type of welding that uses a heat source coming from the gas. The gas obtained from the combustion of fuel gas mixed with oxygen (O2). The combustion process produces flame with high temperature (3000 Celsius degree), which can melt the base metal and filler metal. The type of fuel gas used is acetylene, propane or hydrogen, so this welding method is often called oxy-acetylene welding. This welding can also be done directly or by using a filler metal depending on the connection type and thickness of the metal base.

Oxy-acetylene welding principle is not very complicated, that only by setting the acetylene gas and oxygen, then the tip is brought near to the fire will arise the flame. But the amount of acetylene gas and oxygen must be arranged by turning the pressure regulator slowly. If acetylene gas is turned on it will issue ordinary flames with soot, whereas if the acetylene gas is too little then there would be no flame.

Oxy-acetylene welding advantages include:

• The equipment is relatively inexpensive and requires low maintenance
• How to use a very simple does not require a high welding technique so easy to learn
• The welding equipment is small and simple, so easy to carry and can be used in the field, factory or workshop.
• Almost all types of metals can be welded, through proper welding technique
• Welding can be used for the process of cutting and splicing

(2) Shielded Metal Arc Welding (SMAW)

Shielded Metal Arc Welding (SMAW) is one type of welding that uses a heat source that comes from an electric arc. Electric arc occurs when the electrode has been electrified positive contact with the base metal wing negative electric current. The heat from the electric arc formed between the base metal and the electrode is capable of causing the base metal and electrode tip melts and then freezes simultaneously.

Shielded Metal Arc Welding (SMAW) is also quite simple principle that only by raising or lowering the electrical current (ampere) we can adjust the size of the generated electric arc. The larger the electric arc occurs, the faster the process of melting the base metal and the electrode.

The advantages of Shielded Metal Arc Welding (SMAW):

• Welding equipment price is lower, so the initial cost of investment is low
• Operationally reliable and simple
• Cost of filler material (electrode) is quite low
• Can use various types of filler material (electrode)
• Can use the same equipment for different types of base metal
• Can be done at any thickness
• Can be done in all welding positions

Further explanation of the Shielded Metal Arc Welding and how to design it, you can see the post about Shielded Metal Arc Welding Design.

(3) Gas Tungsten Arc Welding (GTAW)

Gas Tungsten Arc Welding (GTAW) or better known as Tungsten Inert Gas (TIG) welding is the kind of gas arc welding with electrodes are not fed means electrode does not function as a filler material. Welding uses tungsten rods as electrodes that can generate an electric arc but the electrodes remain intact (not melted). As fillers used welding wire which is included separately with the electrode. TIG welding is using noble gas as a protective gas which generally uses pure argon gas.

The use of TIG welding has the advantage of;

• Filler metal feeding speed can be set themselves without being affected by electrical current so that the penetration of filler metal into the base metal can be set directly as required (easy setup for thin or thick plate).
• Better quality in the welding area.

(4) Gas Metal Arc Welding (GMAW)

Gas Metal Arc Welding (GMAW) or better known as Metal Inert Gas (MIG) Welding is the kind of gas arc welding with electrodes fed directly. MIG welding using a wire electrode welding as well as filler wire. MIG welding using noble gases as a shielding gas generally use gas Ar and CO2.

The use of MIG welding has the advantage of;

• The welding operation is easy because of the high concentration of the arc with a little splash
• The efficiency is excellent because it can use the high current at high speed
• Weld metal formed quite a lot
• The nature of toughness, elasticity, airtight and insensitivity to the slag is very good.

Considerations in choosing Type of Welding

Once we know the type of welding used in the manufacture of construction, we can then choose the appropriate type of welding we need to consider several things, among others:

1. Metal base, what type of material to be welded and how the thickness of the material. This information is very important because there are some types of welding are not suitable for the particular material or very difficult process to a certain thickness.
2. Filler, we must determine in accordance with the type of filler metal base material. Filler can be selected based on the material and type. Examples of filler materials such as carbon steel, stainless steel, aluminum, brass etc. Examples of types of filler such as filler rods, filler wire, electrodes encased etc. After the material and the type of filler selected, we can determine the appropriate type of welding.
3. Welding strength, is related to the cross-sectional thickness of the weld. To obtain the appropriate thickness of the weld cross section, we must determine the type of connection and seam welding are used.
4. Thermal energy source, an energy source that we have in accordance with the type of welding.
5. Welding cost, this consideration is crucial in business. Welding costs including the initial investment, the cost of equipment, operating costs, the cost of the filler rod or electrode and man cost.

Having in mind some of the considerations above, then we can determine the type of welding that is appropriate to the characteristics and advantages of each type of welding.

That is a description of Welding Design with the topic about How to Choose the Appropriate Type of Welding. If you find misconceptions in the welding design, please provide the correction in the comment box.

read more

Seam Welding Design for Butt Joint

Seam Welding Design for Butt Joint - Seam welding having an important role in the welding construction joint. In a post titled Shielded Metal Arc Welding Design has been described on how to design welding construction with welded joint strong and how the role of seam welding in overcoming the tensile loads and bending loads acting on the welds. Welding stress that occurs in the welding joint will be different for each type of seam welding. Therefore, in this post we will explain about how to design of seam welding for construction joint base on the seam type and welding strength.

To facilitate the design process more applicable, seam welding design will be described in more detail for each type of welding joint. Welding joint in question include butt joint, tee joint, corner joint, edge joint and a lap joint. But in this post is only limited to the topic of the Seam Welding Design for Butt Joint, whereas for the other welding joint will be explained in the next post.

Butt Joint is the most efficient type of connection. This connection is further divided into two namely, full penetration and penetration joint portion. Full penetration connections is divided further into connection with the auxiliary plate is subdivided into plates maid who also became part of the construction and auxiliary plate just as a helper at the welding process alone.

Butt Joint able to use some kind of seam welding such as seam square, vee seam, bevel seam, u-seam, double vee seam, double bevel seam and double u-seam. Selection of seam types and welding symbols can be seen in the table below. (More detailed for discussion about the seam type and welding symbols can be seen on the post Basic Welding Design)

Type of seam welding in the butt joint greatly affects the working efficiency, the efficiency of the connection and the power connection, so the selection of the proper seam shape is very important. The shape and size for butt joint welding seam is already widely standardized in AWS, BS, DIN, GOST, JSCC and others.

Each type of seam welding in butt joint has a different welding strength. Welding strength is meant here is the ability to withstand weld tensile stress, bending stress and shear stress. How welding stress that occurs for every type of welding seam on the butt joint, let us refer to the following description.

Single seam design for butt joint welding

Single seam welding is only made on one surface of the joint welding course. Which belong to the single seam welding are square seam, vee seam, bevel seam and u-seam. If the welds are given the force parallel to the attached plate as in the picture below, there will be tension in the cross section of the weld.

Tensile stress will make a deformation in the form of an extension of seam welding. (1) Seam welding will return to its original shape if the tensile stress is still below the limit of elasticity of welding material. (2) Seam welding will experience a permanent extension (plastic deformation) if the tensile stress is above the limit of elasticity of welding material. (3) Seam welding would break up if the tensile stress exceeds the maximum tensile strength of welding material. Tensile stress of butt joint with single seam welding can be calculated by the formula:

Note:

s_t = Tensile Stress (kg/mm2)

F = Force or Welding Load (kg)

h = Seam Width (mm)

l = Seam Length (mm)

If the butt joint is given two forces in opposite directions perpendicular to the plates which are connected as shown below, there will be shear stress at the weld cross section.

Both forces on the welding seam consist of the action and reaction force, so it has the same value and meet force equilibrium system. Seam welding will have cracks when the shear stress exceeds the capability of welding material (shear strength). Shear strength is calculated 40% of the maximum tensile strength of welding material. Shear stress of butt joint with single seam welding can be calculated by the formula:

Note:

t = Shear Stress (kg/mm2)

F = Force or Welding Load (kg)

h = Seam Width (mm)

l = Seam Length (mm)

If the force is perpendicular to the plate in the butt joint has a certain distance to a cross-seam welding, it will happen the bending moment like in the picture below. This condition causes the bending stress at the weld cross section.

Bending stress will cause a deflection on the seam welding of butt joint. (Calculation of deflection you can see in the post about the shaft design in the calculation of shaft deflection). Bending stress of butt joint with single seam welding can be calculated by the formula:

Note:

σ_b = Bending Stress (kg/mm2)

M = Bending Moment (kgmm)

h = Seam Width (mm)

l = Seam Length (mm)

Double seam design for butt joint welding

Double seam welding is made on the second surface of the welding seam joint with the same size or different. Which belong to the double seam welding are double vee seam, double-bevel seam and double u-seam. As well as the single seem welding some types of forces acting on the double seam welding will cause a tensile stress, shear stress and bending stress with different formulas.

The forces that cause tensile stress on the double seam welding for butt joint can be seen in the image below.

Tensile stress of butt joint with double seam welding can be calculated by formula:

Note:

s_t = Tensile Stress (kg/mm2)

F = Force or Welding Load (kg)

h₁  = Upper Seam Width (mm)

h₂  = Lower Seam Width (mm)

l = Seam Length (mm)

The forces that cause the shear stress on the double seam welding for a butt joint can be seen in the image below.

Shear stress of butt joint with double seam welding can be calculated by formula:

Note:

t = Shear Stress (kg/mm2)

F = Force or Welding Load (kg)

h₁  = Upper Seam Width (mm)

h₂  = Lower Seam Width (mm)

l = Seam Length (mm)

The forces that cause the bending stress on the double seam welding for a butt joint can be seen in the image below.

Bending stress of butt joint with double seam welding calculated by formula:

With,

h = h₁ + h₂

Note:

σ_b = Bending Stress (kg/mm2)

M = Bending Moment (kgmm)

T = Plate Thickness (mm)

h₁  = Upper Seam Width (mm)

h₂  = Lower Seam Width (mm)

l = Seam Length (mm)

That is a description about Seam Welding Design for Butt Joint. If you find misconceptions in the seam welding formula, please provide the correction in the comment box.

read more