Why Your Welds Lack Fusion — And How to Fix It

Ever looked at a weld and thought, “How is this even holding?”
That’s exactly what we said when we came across a weld that had survived for over 20 years — despite severe lack of fusion.

Let’s break down what went wrong… and how you can fix it.

🚩 What Is Lack of Fusion in Welding?

Lack of fusion happens when the weld metal doesn’t properly bond to the base material — or doesn’t melt into the previous weld pass. Instead of becoming one solid unit, the parts stay separate with weak points hidden beneath the bead.

It looks like the weld is there… but it isn’t doing its job.

🔍 What Causes Lack of Fusion?

Here are the most common reasons:

✅ Low Amperage
Not enough heat to penetrate the metal and create full fusion.

✅ Improper Wire Speed
Too slow or too fast and the arc can’t maintain a steady pool.

✅ Poor Travel Speed or Technique
Moving too fast, or inconsistent angles, prevents proper bonding.

✅ Dirty Base Material
Even though the weld might "stick," paint, rust, and grease block true fusion.

🧯 How to Fix It — The Right Way

Here’s how to guarantee better fusion:

🔧 1. Match Your Amperage to the Material Thickness
Use a welding chart or calculator. For mild steel, 1/8" thick, aim for 140–160 amps.

🔧 2. Adjust Wire Speed Accordingly
Balance it with amperage — too fast will pile up spatter; too slow will starve the arc.

🔧 3. Watch the Molten Pool
Don’t just move the gun. Ride the pool and ensure both sides are melting together.

🔧 4. Clean the Surface Properly
Grinding off paint and rust is the first step. Wipe off oil and moisture, too.

🔧 5. Use the Right Gun Angle and Stick-Out
Keep a 10–15° push angle with ⅜" stick-out for MIG.

🧠 Final Thought

A clean-looking bead means nothing if there’s no fusion underneath.

Don’t just weld it. Fuse it.

📚 Learn more, watch examples, and shop trusted welding tools on our site:
👉 ProgressiveWeldingSolutions.net