How To Avoid A Lack Of Fusion In Welding

Table of Contents > 1. What is a Lack of Fusion in Welding?     1.1 Types of Lack of Fusion     1.2 How to Detect a Lack of Fusion? 2. What Causes a Lack of Fusion?     2.1 Lack of Current     2.2 Improper Joint Preparation     2.3 Incorrect Welding Parameters     2.4 Incorrect Welding Technique     2.5 Magnetic Arc Blow 3. How to Prevent a Lack of Fusion in Welding     3.1 1. Increase the amperage     3.2 2. Prepare the joint before welding     3.3 3. Adjust the speed according to amperage     3.4 4. Employ proper welding technique     3.5 5. Deal with magnetic arc blow     3.6 6. Choose a suitable welding method 4. Quick Table of Causes and Solutions for Lack of Fusion 5. 🧐How To Avoid A Lack Of Fusion In Welding FAQ

As a beginner or a new welder, you will occasionally encounter welding defects. While some surface irregularities pose more aesthetic issues, there are structural defects that can affect the integrity of the weld.

A lack of fusion is a structural welding defect that occurs when the weld metal doesn't correctly fuse with the base metal. This defect creates discontinuities that create weak spots in the welds.

In this article, we will thoroughly explain this defect and teach you how to avoid a lack of fusion in welding. Without further ado, let's explore more.

What is a Lack of Fusion in Welding?

A lack of fusion is a welding defect that occurs when the weld metal doesn't correctly fuse with the base metal. Instead of creating a uniform surface, a small gap or void, similar to a crack, forms between the weld and sidewall, the previous weld bead in the multi-pass application, or the weld and root pass.

A Lack of Fusion in Welding
Source: https://www.kemppi.com/

Lack of fusion is a severe welding defect that affects uniformity in the weld's metallurgical, mechanical, and physical attributes. Internal voids or gaps create a weak spot in the weld, which is likely to fail under stress and pressure.

In welding literature, incomplete fusion, together with cracks, is one of the leading causes of weld failure. Compared to other weld defects, a lack of fusion is as harmful as cracks, lack of penetration, internal porosity, or inclusions. However, it is more severe than spatter, accidental arc strikes, overlap, or excessive reinforcement.

Source: https://www.madearia.com/

Types of Lack of Fusion

There are several types of incomplete fusion welding defects. The type and location of the lack of fusion can distinguish them.

The three basic types of lack of fusion are:

1. Pure lack of fusion

2. Open lack of fusion

3. Non-metallic inclusions lack of fusion

Pure lack of fusion is a structural defect. It forms once the molten weld metal meets the base metal, which hasn't adequately melted during the welding procedure. A small joint forms between the solid and the liquid phase, creating a flat face and discontinuity. This gap poses a risk of weld failure and compromises the structural integrity of the weld.

An open lack of fusion occurs inside the weld and during the multi-pass procedure. Internal stresses produced during weld solidification and cooling create a gap between the two passes. The weld faces separate in an irregular shape, creating an internal defect and a weak spot.

Oxide or non-metallic inclusions often follow a lack of fusion. If the oxide layer does not melt, the inclusions occur evenly across the entire surface of the lack-of-fusion defect. If the oxides melt, the inclusions become spherical.

Micrographs of lack-of-fusion defect: (a) lack of fusion with unmelted oxide inclusions, (b) lack of fusion with melted oxide inclusions.
Source: https://www.researchgate.net/

Based on the location of the weld defect, we are seeing the following types of incomplete fusion:

• Lack of side wall fusion: This defect arises between the side wall of the parent metal and the weld metal.

• Incomplete inter-run fusion: This defect forms between the two passes (two weld beads) in the multi-pass welding.

• Lack of root fusion: This defect occurs when the weld metal doesn't correctly fuse with the root opening in root-pass welding.

Types of Incomplete Fusion
Source: https://technoweld.com.au/

How to Detect a Lack of Fusion?

There are several methods welders use to detect the lack of fusion in the weld. Some are easier to detect, while some require advanced testing methods. The most common ways to detect the incomplete fusion are:

• Visual inspection: You can visually detect some surface irregularities and signs of lack of fusion, such as gaps, cracks, or porosity. However, remember that visual inspection is limited to surface defects only.

Visual Detection of Surface Irregularities and Lack of Fusion
Source: https://www.onestopndt.com/

• Ultrasonic testing: Ultrasonic testing uses high-frequency sound waves to detect internal irregularities and defects, including lack of fusion. This is the most suitable of all the available non-destructive testing methods. It can detect most types of lack of fusion, with the exception of the pure lack of fusion.

• Radiographic testing: Radiographic testing uses X-rays to detect the internal lack of fusion. Testing can detect all voids or porosity in the weld, allowing welders to detect a lack of fusion that is not visible to the naked eye.

• Liquid penetrant testing: Welders use dye penetrants to detect surface irregularities and a lack of fusion in pressure vessels, tanks, and ships. The penetrants fill and pass through the voids created by a lack of fusion.

Liquid Penetrant Testing
Source: https://www.twi-global.com/

What Causes a Lack of Fusion?

Several factors, individually or combined, contribute to the formation of a lack of fusion. The leading causes of the lack of fusion are:

• Low current

• Narrow joint preparation

• Poor welding parameters

• Bad welding technique

• Magnetic arc blow

• Incorrect welding method

Understanding the causes of incomplete fusion is crucial to avoiding them. Here is a detailed explanation of how each factor contributes to the lack of fusion.

Image of a Lack of Fusion in Welding
Source: https://www.youtube.com/shorts/i5jyfEb6s4M

Lack of Current

The leading cause of the lack of fusion and penetration is the low amperage for the given metal thickness. A lack of current means low heat, which doesn't correctly burn and fuse two pieces of base metal.

While the current can melt the filler, it might be insufficient to melt the base metal. Failure to melt both the weld metal and the parent metal causes an incomplete fusion between them.

The current should also be sufficient for root-pass welding and multi-pass procedures. The final goal is to melt all parts of the equation so that they can fuse adequately and create a uniform structure.

MIG Root-pass Welding
Photo by @arclabsweldingschool (TikTok)

Improper Joint Preparation

Poor weld preparation causes various welding defects, including a lack of fusion, penetration, or porosity. Dirt, rust, oil, moisture, paint, or an oxide layer inside the weld joint, among others, can create non-metallic inclusions that follow incomplete fusion.

Narrow joint preparation also contributes to the lack of fusion. Narrow joints attract the arc to one side, causing a lack of side wall fusion on the other side of the joint.

In addition, a narrow joint preparation may prevent adequate access into the joint. Poor joint access encourages the flooding of the joint with molten weld metal. This issue typically occurs when the electrode or nozzle is too large for the prepared joint.

Source: https://welding.org.au/

Incorrect Welding Parameters

Welding parameters include a series of settings that can cause incomplete fusion when they are tuned incorrectly. We already mentioned welding amperage as the leading cause, but it is also related to welding speed, electrode choice, and more.

Correct amperage with incorrect welding speed can cause incomplete fusion. Even if you use enough amps, high speed reduces the overall heat input. As a result, you get a lack of penetration and fusion. Conversely, using low welding speed with correct amperage can cause excessive heat build-up and burn-through.

Additionally, a high current or too low a welding speed will cause weld pool flooding ahead of the arc. This combination results in poor or non-uniform penetration and fusion.

Weld Pool at Too Low Welding Speed
Source: https://www.youtube.com/watch?v=Xod-ByrxHg4&t=231s

Incorrect Welding Technique

A welding technique comprises various factors such as travel angle, working angle, electrode manipulation, etc. An incorrect combination of these factors can contribute to uneven welds and a lack of fusion.

Lack of sidewall fusion is common in wide joints, which require weave beads. While weaving, not spending enough time on the sides causes a lack of fusion between the sidewall and weld metal.

Ensure adequate sidewall coverage when weave welding.
Source: https://www.youtube.com/shorts/wOzWgxZ56-s

Magnetic Arc Blow

A magnetic arc blow is an issue that occurs when welding ferromagnetic steels. The problem occurs due to unbalanced conditions in the magnetic field surrounding the arc. The common unbalanced conditions are:

• Varying distances between the arc and workpiece connection (ground)

• Changes in the direction of the current as it flows from the electrode into the workpiece.

The effects of a magnetic arc blow cause an arc deflection. As a result, the arc doesn't follow the shortest path between the tip of the electrode and the base metal. Instead, it moves in front and back or rarely on the sides of the joint.

Straying away from the center of the joint causes weld build-up on the sides, in front or before the joint. This issue causes uneven distribution and a lack of sidewall or root fusion.

Arc Blow in Welding
Source: https://www.sinostoneltd.com/

How To Prevent A Lack of Fusion in Welding

After discussing the causes, you could already deduce some possible solutions for a lack of fusion. But, to put it more comprehensively, here are some tips and tricks. To avoid a lack of fusion in welding, you should:

1. Increase the amperage

2. Properly prepare the joints

3. Adjust the speed according to the amperage

4. Use the proper welding technique

5. Deal with magnetic arc

6. Choose a suitable welding method

Here are further explanations on how each factor can help you deal with incomplete fusion.

Stick Welding Process
Photo by @a1weldingclasses (TikTok)

1. Increase the amperage

A lack of heat is the leading cause of fusion failure. Therefore, increasing the amperage can help with this issue.

When setting up your welder, always follow the manufacturer's recommendations. Each machine is unique, so it has different amperage recommendations for the given metal thickness. Thus, you should read the manual before welding.

Another solution is to use a welder with smart functions. Machines such as YesWelder DP200 have intelligent parameter matching. The welder automatically adjusts voltage, current, and wire speed based on material and thickness. This feature is invaluable for beginners who need a head start in setting up the amperage and avoiding defects such as a lack of fusion or penetration.

Firstess DP200 Multi-Process MIG Welder

Keep in mind that smart settings give you a head start. However, you can still run a bit hot or cold, so if you still notice a lack of fusion, manually tune up the heat. Beware that too much heat can cause overheating and burn-through.

2. Prepare the joint before welding

Weld preparation is crucial in achieving the highest-quality, clean, and uniform welds. Although some methods, such as MMA (Stick) welding or Flux-core arc welding, can burn through light surface contamination, it is always better to clean the pieces before welding.

Removing oil, dirt, rust, or grease from the surface will yield clean welds. You won't have to worry about the porosity, non-metallic inclusions, or incomplete fusion inside the joint.

Clean Metal before Welding
Source: https://www.youtube.com/watch?v=CLh6kPC_RoI

Additionally, you should make sure your joints are wide enough for the given metal thickness. Narrow joints attract the arc to one side and cause a lack of sidewall fusion. Therefore, make sure your joints are wide enough to promote even weld metal distribution, fusion, and penetration.

Also, ensure your joints are wide enough for the electrode and nozzle diameter. Too large electrodes will cause joint flooding with the base metal and possibly incomplete fusion.

Ensure the joint is wide enough for the electrode.
Source: https://www.youtube.com/watch?v=DLspWWtNa-U

3. Adjust the speed according to amperage

The welding speed and amperage are closely related to achieving the strongest and uniform welds. If your amperage is suitable for the given thickness, but you still notice incomplete fusion, try reducing the speed.

Lower speed with proper amperage improves the heat input in the joint. The correct heat input is crucial in achieving adequate penetration and fusion.

If the applications call for a lower amperage, you can reduce the speed to improve heat input. Even though you have less heat, spending more time in one place will provide more heat. This heat will melt and fuse the weld metal and base metal to provide adequate fusion and penetration.

Like with amperage settings, do not overdo it. High amperage and low speed will cause burn-through and overheating. Additionally, moderate amperage with low speed can also do the same.

Burn-Through Due to Excessive Amperage
Source: https://www.researchgate.net/

4. Employ proper welding technique

A good balance between working angle, travel angle, electrode manipulation, and speed produces sound and uniform welds. Therefore, make sure you adjust the welding technique for your applications.

Use weaving beads when welding thicker and broader joints. Straight or stringer beads will not correctly fill the joint and provide proper fusion in these applications.

Types of Welding Beads
Source: WcWelding.com

When weaving, spend enough time on the joint sidewall. This will allow the weld pool to wash into the parent metal, improving sidewall fusion.

Additionally, the amount of weaving should be limited depending on the welding procedure specification. Limiting the arc energy input is crucial, particularly when welding alloy or high-notch toughness steels.

Weaving in Stick Welding
Source: https://www.youtube.com/watch?v=2Sv3f4NErnc&t=12s

5. Deal with magnetic arc blow

Arc blow can cause a number of welding problems, including excessive spatter, incomplete fusion, porosity, and lower weld quality. But there are several things you can do if you have to deal with a magnetic arc blow.

How Arc Blow Occurs
Source: https://www.canadianmetalworking.com/

First, you can change the position of the ground. Position the earth clamp so you always weld towards or away from it. That way, you can minimize the varying distances between the arc and the workpiece connection.

Additionally, arc blow is typical in DC welding. When Stick welding or manual metal arc welding, you can deal with arc blow by switching to AC current. Most electrodes support both AC and DC. But if they don't, you can always find a suitable AC alternative.

For example, E6010 is a DC-only electrode. So, if you notice an arc blow when using it, you can switch to E6011. This electrode shows similar performance, but you can use AC/DC to run it.

AC Stick Welding with E6011
Photo by @juanislas_1 (TikTok)

6. Choose a suitable welding method

Each welding method has its unique advantages and drawbacks. For example, TIG welding is the ideal method for thin, delicate, and exotic metals. Its heat control will help you produce the best results on sheet aluminum or steel, including the proper penetration, fusion, and weld quality.

TIG Welding Thin Metal
Photo by @rootsrockryan (TikTok)

Meanwhile, TIG welding can come short when welding thick stock. In these applications, TIG cannot produce enough heat, which can result in a lack of fusion and penetration. So, you should turn to Stick or Flux-cored welding when welding thick stock. These techniques are capable of outputting more amps and higher heat, which solves the fusion issues.

MIG welding is somewhere in between. It can produce proper fusion on most medium-thickness metals, including steel, stainless steel, and aluminum. Welders favor MIG for its low-skill requirements, which make it ideal for most home, hobby, and DIY applications.

MIG Welding Project
Source: https://www.youtube.com/shorts/4lj4Ozi4-JU

Quick Table of Causes and Solutions for Lack of Fusion

Here is a quick table of causes and solutions for the lack of fusion in welding, summarizing everything we said in this article.