Shielded Metal Arc Welding Design for Construction Joint

Shielded Metal Arc Welding Design for Construction Joint - Construction in the machine design is a static part of the most important in building a machine that is strong, stable and aesthetics. Machine construction isn’t only formed by a solid component, but strung together by two or more components that are becoming an integral component assembly machine. Machine construction powerful should be supported by a strong joint between components as well. Many types of construction joint are used in the assembly process of the machine construction such welding joint, folding joint, rivet joint, bolt joint etc.

In this article only focuses on welding joint used in the assembly process. Welding joint is one type of the fixed joint that is a connection that can’t be released again except by destroying it. Many types of welding but in this post I will explain the arc welding process, more specifically about how to design a construction joint by shielded metal arc welding.

Prior to the main topic, we must first know what it is the shielded metal arc welding. Shielded metal arc welding (SMAW) is a manual arc welding process in which welding heat generated by the electric arc formed between the electrodes shielded flux with the workpiece. Shielded metal arc welding has been chosen by the designer in the design process of construction machinery as it has many advantages such as (1) the initial investment cost is low, (2) a reliable and simple operation, (3) the filler material (electrode) cost is low, (4) filler material can vary, (5) can use the same equipment for all types of material, (6) can be done to part with a variety of thicknesses and (7) can be done for all position welding.

When you will design the machine construction with welded joints strong, to note that the value must be greater welding strength of the welding stress occurs, otherwise it will lead to plastic deformation, cracks or broken. Welding strength is affected by the electrode material and the material properties of the main metal while welding stress is affected by the welding dimension and load.

Welding Electrode for Shielded Metal Arc Welding 

Electrode used for shielded metal arc welding is a type of metal electrode wire wrapped in flux. Electrode metal removal process occurs when the tip of the electrode melts and forms the items carried by the arc electric current.

Selection of electrode is determined by the type of wire and flux are used with reference to the code electrode according to the classification AWS (American Welding Society). According to the classification AWS (American Welding Society), the electrode of mild steel and low alloy steel for electric arc welding expressed by the code:

Note:
1. E    = Electrode of arc welding
2. XX = Tensile strength (thousands Psi)
3. X    = Welding position
4. X    = Type of flux and current suitable for welding

Example:

E 6013, which means arc welding electrodes with a minimum tensile strength of 60,000 psi or 42.2 kg / mm2, can be used for all position welding, flux type is the high potassium titanium and electric current with AC or DC+ or DC.

The table below is a list of electrode classification code of mild steel according to AWS A.5.1-64T.

Code	Type Flux	Welding Position	Electric Current
E60 Group = Minimum tensile strength after welded is 60.000 Psi or 42,2 kg/mm2
E6010	High Cellulose Sodium	F, V, OH, H	DCR
E6011	High Cellulose Potassium	F, V, OH, H	DCR - AC
E6012	High Titanium Sodium	F, V, OH, H	DCS - AC
E6013	High Titanium Potassium	F, V, OH, H	DCR - DCS - AC
E6020	High Iron Oxide	F, H	DCR - DCS - AC
E6027	Iron Powder, Iron Oxide	F, H	DCR - DCS - AC
E70 Group = Minimum tensile strength after welded is 70.000 Psi or 49,2 kg/mm2
E7014	Iron Powder, Titanium	F, V, OH, H	DCR - DCS - AC
E7015	Low Hydrogen Sodium	F, V, OH, H	DCR
E7016	Low Hydrogen Potassium	F, V, OH, H	DCR - AC
E7018	Iron Powder, Low Hydrogen	F, V, OH, H	DCR - AC
E7024	Iron Powder, Titanium	F, H	DCR - DCS - AC
E7028	Iron Powder, Low Hydrogen	F, H	DCR - AC
Note:      Welding Position                 F = Flat                 V = Vertical                 OH = Overhead                 H = Horizontal		Note :     Electric Current                 DC = Direct Current                 AC = Alternating Current                 DCR = DC Reverse Polarity                 DCS = DC Straight Polarity

Based on the table above, the minimum tensile strength after welding related to the weld traction properties associated with tensile testing. In the weld joint, capable of tensile properties strongly influenced by the primary metal properties, HAZ regions, weld metal (electrode core wire) and the dynamic properties of the welding joint.

Welding Stress

What is meant by welding stress herein include tensile stress, bending stress and welding efficiency. How welding strength designed for a connection in machine construction design, the following I will explain one by one according to welding stress that occurs in the welding joint.

(1) Tensile Stress 

Welding joint will experience tensile stresses if there is tensile load or force acting on the cross section of the weld results. Tensile stress of welding joint is affected by welding load and cross-sectional area with the following formula.

Note:
s_t = Tensile Stress (kg/mm2)
F = Force or Welding Load (kg)
A = Cross-sectional area (mm2)

Force or welding load in construction joint can be caused by cutting force, part weight that is supported by construction, tightening force of bolt etc.

Cross-sectional area of the welding joint has a different value depending on thickness and length of the weld seam. Weld seam has a different shape according to the type of welding joint as blunt joint, T-joint, cross joint, edge joint, joint angle and overlap joint (read more in the Type of Welding). Type of seam welding is i-seam, v-seam, v-tapered seam, u-seam, double V-seam, k-seam etc.
Therefore, the tensile stress in welding joint for each type of seam welding would have a different formula. (Formulas related to the tensile stress on each type of seam welding you can see on the post Seam Welding Design).

(2) Bending Stress

Welding Joint will experience a bending stress if there is bending load acting on the cross section of the weld results. Bending loads occur due to the force that causes the bending moment on the cross section of the weld results. As well as tensile stress, bending stress formula also depends on the type of welding joint and seam welding. But in general the bending stress that occurs in the welding joint can be formulated as follows:

Note:

s_b = Bending Stress (kg/mm2)

M   = Bending Moment (kgmm)

h = Seam Thickness (mm)

l = Seam Length (mm)

(3) Welding efficiency

Welding efficiency is defined as a decrease factor of the allowable stress of main metal which is formulated as follows:

Note:

h   = Welding efficiency

σ_w  = Allowable Stress of Welding Joint (kg/mm2)

σ    = Allowable Stress of Main Metal (kg/mm2)

The value of the welding efficiency is determined by the welding material, welding method, inspection method and conditions of use connection.

That is a description about Shielded Metal Arc Welding Design for Construction Joint. If you find misconceptions in the arc welding formula, please provide the correction in the comment box.