Welding is the process of joining two members of metal using filler metal and some joints. Based on the joints, welds are classified into various kinds. However, the main feature of every welding process is for a welder to ensure that the weld is the integrity of a good product that has no demerits. Every industry or manufacturer has the ideal goal to follow and meet the quality standards of the certification ISO 3834. Since welding is considered to be one of the most economical ways for building objects made out of metals and joining them together, it is done with the utmost care and is done efficiently.
Watch Video: Good Weld vs Bad Weld (Expert Opinion)
A good weld is one which has a finished error-free product and that need not be worried about its lifetime (or) performance in the future. The weld and the base metal must be free from dust, dirt, grease, moisture, Sulphur and phosphorous.
In order to identify the quality and performance ratio of a weld, we need to do some quality tests based on its functionality:
Distribution: The filler metal and weld bead that is applied between the two metal members is evenly spread and applied in equal quantities.
Contaminants: We need to make sure that the weld and base metal is free from dust, dirt, moisture, Sulphur, phosphorous and other harmful contaminants as these cause deformation and crack on its surface.
Permeable: It is an essential aspect of a welded metal to check for its level of porosity as porosity is the definition of a poor weld and it means that the weld done is defective. Tiny holes as these, cause slow deterioration to the metal over time. It generally indicates that the shielding gas supplied was not sufficient enough for the weld.
Strength: The project that we are currently doing will definitely have a minimum filler metal requirement. So. if the filler metal supplied is higher than that required an electrode rating is pretty high, then we can say that the particular weld is ‘strong’.
Joint efficiency: Gaps in any instrument or model is an important drawback for that project and hence adequate amount of filler metal used is essential. This verifies the tightness of the joints. [Joint efficiency = Strength of weld joint / Strength of the base material used]. A butt-joint generally avoids stresses on its joint and hence has a joint efficiency of 100% or higher.
Leaks: Make sure that the metal does not leak any gas or liquid at any cost.
Power Source: Make sure you are getting the correct required power for your welding process. For a 120-voltage machine, the amp breaker must be of 20 amps.
Thickness of Metal: The electrode must match with the thickness of base metal used. Large machines of 220-volt input or higher are considered to be more effective for thicker metals as other thin metals get penetrated and damaged easily producing holes in them.
Regular Maintenance: The welding lead must be checked frequently for any kind of damages or breakage. Contact tips must be regularly changed after a weld is done to fit correct size for the welding wire and moreover to avoid the presence of contaminants, dirt, moisture etc.
Adjust your machine: Based on the given chart, adjust your voltage settings and wire speed. Try to make several practice welds to get the perfect weld conditions for your final weld. If you get an issue where the end tip of your wire forms a blob like structure, you will need to turn-down your voltage supplied to the machine.
The presence of pores, lack of uniformity, insufficient shielding gas supply, cracks and deformation on the body of the base metal are some of the signs of a ‘Bad Weld’.
Most basic poor weld cases include:
The final product does not match the design dimensions given earlier.
The product does not offer required functionality as quoted.
Bead meandering also causes a major deterioration to the quality of a welded product.
Incomplete Penetration: It generally defines the phase where thejoint has not properly joined the filler and base metal together. Causes for this include:
High travel rate.
Welding voltage supplied is either too large or less.
Electrode polarity is incorrect.
Undercut: When the toe end of the weld has no base metal, it is known as an ‘Undercut’. Its causes include high current supply, long arc gap and impossibility to fill the crater with the filler metal.
Slag: Generally, slag formation is due to the metal oxides or other electrode coating formed over metal Slag formation leads to pores and cracks that leads to deformation and damage to the final product overtime. It can be prevented by:
Removing existing slag and other surface contaminants.
Preparation of the groove weld beforehand.
Slag must rise to the weld pool.
Do not leave behind any contours or residual contaminants on the metal surface.
The presence of tiny holes and pockets on the surface of the welded metal is known as ‘Pores’. They contain gases in these pockets unlike slag. It can be prevented by:
Overlap: When excessive molten weld flows over the base metal and cooling down without proper fusion of base metal is known as an ‘Overlap’.
Arc Strike:This defect is one that is caused due to excessive of the arc on the base metal regularly which might lead to the cracking of the surface of the base metal.
Inadequate Shielding Gas:
Solid Carbon Steel Wire: Solid carbon steel wire must be used with CO2 shielding gaswhich is best used indoors with no wind for automotive manufacturing and fabrication applications.
Aluminum Wire: Argon shielding gas must be used with aluminum wire, which is highly essential for stronger welding processes.
Stainless Steel Wire: Stainless steel wire works well with a combination of helium, argon and CO2.
TIG welding concerns:
Proper gas flow is a must that is at a rate of 15-20 cubic meters per hour. Similarly, excessive gas flow also causes certain kinds of swift currents of air pulling in contaminants.
Analyzing the correct polarity. Aluminum TIG welding always uses an Alternating Current (AC) polarity.
There must be minimal filler metal problems that can be visually inspected as grans on the filler metal surfaces.
A T-joint must be check twice for the perfect amount of filler metal used as due to improper fitting, incorrect torch handling distance etc. as it might lead to a lack of fusion and improper penetration issues.
Craters must be avoided to prevent excessive cracking in the weld.
Sugaring occurs on the backside of the base metal due to oxidation of the metal.
Poor constructed bead occurs when too much of an amperage is supplied to the weld bead.
A very long arc is not ideal as it increases overall heat leading to a heavy distortion of the metal.
Avoid the presence of unwanted heat, fire, or any kind of sparks.
Stay away from the blowpipe or as torch as it releases flames of high temperatures that burns anything close to it.
The fuel cylinders must be taken care of as they might leak if not taken care of while transporting them.
The entire welding setup must be set at a place that is very far away and isolated from any kind of human crowds.
Once a welding process is completed, any kind of combustible material available around that place must be eradicated from that place immediately, be it fuel, wood, plastic, papers etc.
Walls must be well-insulated with fire and heat resistant materials that does not allow contaminants to be released to the outside world directly.
Stick Welding Concerns:
Selection of an AISI-SAE 1015 to 1025 steels Sulphur content way less than 0.035% is essential for a good weld in this Stick-Welding process.
Make sure that the welding arc angle used by the electrodes is in the range of zero to 15 degrees.
Even though buildup of weld in the joints provides strength to the metal, it increases distortion and overall shape disturbances.
Large electrodes are used for welding thick metals using a heavy amount of current supplied and with higher deposition rates.
Slag formation will be prevalent if correct amperage and voltage is not supplied along with proper welding method.
If we do not maintain a mediocre amperage, we would get a convex-shaped bead or else a narrow weld bead.
Basic testing of the welds is required in commercial products to verify whether a weld is good or bad. Weld quality on plastics can be analyzed by using:
Mechanical Testing: Tensile, Shear, Push, Peel, Impact, Drop, etc.
Imaging: CT Scanning, X-Ray and much more to be known.
Dimensional Analysis: Height, Gap, Deformation, etc.
Leak and Burst Testing: Water, Air, Helium, Hydraulic Fluid, etc.
Welds are typically quality tested based on the function it performs and under conditions that are the same or more severe than those unexpectedly encountered by the welded metals. Testing techniques are listed below:
Gas Weld Testing
Back Bend Test
Fluorescent Penetrant Test
Physical Weld Testing
Nick Break Test
Acid Etch Test
Tensile Strength Test
Guided Bend Test
Free Bend Test
Magnetic Particle Test
Acoustic Emission Testing
Gamma Ray Testing
Apart from all these visual and electronic tests done on the welded metal, there are two types of surface inspection done on them using other methods. They are:
Contact-type Surface Inspection
Non-Contact type Surface Inspection
Magnetic Test (MT): This type of surface inspection is possible on metals whose surfaces are highly magnetic as that of iron and steel. When magnetic particles of 2 to 3 mm are spread on the weld metal, it accumulates in the pores and hence when it is magnetized it behaves like a magnet along the weaker poles of discontinuity.
Penetration Test (PT): Highly penetrable liquids which are glossy in nature are poured on these weld that easily penetrates and shows all the available pores in the metal surface.
Here, laser light is allowed to pass through a cylindrical lens having a large beam to focus on the surface of the target.
The reflected light is used to process an image on the metal surface that identifies changes in position and also measure the shape changes.
The LJ-X8000 Series has a wide dynamic range that provides accurate displacement changes without allowing any gloss or light reflection to affect it adversely.
The set of equipment used for this process is:
2D Ernostar lens
The deposit of filler metal from a welding process along any joint is termed as a ‘weld bead’. Just like welding metal in several ways, there are various types of weld beads to be used in joints too. They are:
The stringer bead is a straightforward natural bead where one drags the weld along the joint and fills gaps if any and this provides an amazing weld.
Stringer beads are generally not wide enough and hence can be welded in any position as required.
For vertical metal line-up a ‘push’ operation using the bead must be done on the weld and directing the heat supplied to the weld away from it constantly during the cooling process will cool it down faster.
Weave beads are used to weave a joint from side to side that too for wider joints between two metal members.
This is the fastest mechanism to be done on a thick stock.
There are three methods to execute weave beads which are zig-zag, crescent and curlycue techniques.
It also helps in the prevention of undercutting and cracks in the weld. Moreover, it also reduces heat absorbed by the welded joint.
A semi-circle weave can also help in the prevention of this overheating problem.
Steep pockets and joints can be filled using a triangular weave bead.
Whip Motion Weld:
A stick welder generally performs something known as a ‘whip motion’ on any open grove joint which is on the root pass.
It is always the first welding operation done while using a stick weld. Typical stick welds are low-carbon steels that are labeled as E6010 and E6011.
This whipping motion allows one to maintain the keyhole size that is essential for complete penetration of the electrode rod.
The rate of whipping is characterized by the amount of heat supplied and obtained by the weld.
Two of the most important characteristics of a weld bead are its height and width. Either if the height of the bead is too much or if the bead is too narrow in width, then good fusion of subsequent weld passes will not be possible. Travel speed and weld current supplied optimize the weld bead width adversely. The current applied is directly proportional to the bead width. Whereas, travel speed and weld size are inversely proportional to one another.
What is the strongest type of weld?
The best method (or) type used for the particular project (or) welding job and the thickness and application used will determine the quality and strength of the welded metal. When heavier steel sections and joints contain multiple welded passes with many layers of beads will make it less obvious that the joint is cracked-open or even broken. SMAW is generally ideal for heavy and thick steels having high carbon content in them.
Can you weld over an existing weld?
It is highly possible to weld over an existing weld. But a lower setting and concentration are essential on the heavier piece along with a low volt and high amperage setting.
Why do welds rust first?
The welds are the first areas of any welded metal to get rusted. As welds generally have a large number of movements and forces applied to it, they tend to accumulate water (moisture) and oxidize to form rust faster. Finishing the weld with some anti-oxidant compound is a must or else rust can easily occur in that region. Even if the welding material used is of some metal alloy, then it might lead up to some galvanic activity and finally rust-up heavily.
How long does a weld last?
10-20 years is the maximum limit for a weld that is corrosion-resistant, non-stabilized ferritic, stress-resistant metals.
What is the hardest metal to weld?
Aluminum is considered as one of the most robust and corrosion-resistant metals as it has various powerful physical and chemical properties. Yet welders hate aluminum as it heats up to a very high temperature without glowing or showing any kind of a burning indication.
Why is my weld beading up?
When insufficient amounts of heat/ voltage are applied to the weld metal via rods, a ‘rope’ shaped bead is obtained that indicates that the heat supplied is too less for the welded metal.
Do you push or pull a weld?
Pushing a MIG welding tool provides a stronger weld due to the increased fusion of larger amounts of filler metal to the joints. Pulling, on the other hand, provides a deeper penetration on the base metal and isn’t essential for any kind of aesthetic looks. After all, the external looks of a weld do not define how strong or quality-ensured the final product is.
Sean Coby is a welder par excellence and well respected among the welding community in Woodbridge, VA. He prides himself to be the fabricator and mechanic in the automotive/ diesel industry for the past more than eight years now. As the chief editor of his https://weldinginfocenter.com, he shares his experience to be safe during welding and to take proactive steps for becoming a successful welder like him.