Burn through is a common issue that can occur when MIG welding thinner metals. It happens when the welding arc melts a hole completely through the base metal. Preventing burn through requires careful technique and proper settings on your MIG welder.
Got No Time? A Quick Answer for You:
To prevent burn through when MIG welding:
- Wear proper protective equipment like welding helmet, jacket, gloves.
- Clean and prepare the metals by removing rust, paint, grease.
- Set your welder to lower amperage and voltage settings.
- Use smaller diameter filler wire suitable for base metal thickness.
- Maintain proper arc length, avoid excessive weaving motions.
- Control travel speed – not too fast or slow.
- Use copper backup bars or chilled metal to dissipate heat.
- Allow proper preheat and interpass cooling of metals.
Following basic technique and adjusting welder settings for thinner materials will help prevent burning holes through your weld joints.
Why Burn Through Happens During MIG Welding
Burn through occurs when the intense localized heat of the MIG welding arc melts away too much of the base metal, creating a hole. Some common causes of burn through include:
- Excessive amperage setting – Too high amps overheats the metal, melting holes through it.
- Fast travel speed – Moving too quickly along the weld joint causes inadequate penetration and fusion.
- Improper arc length – Excessive arc length increases voltage, causing a hotter arc. Too short an arc concentrates heat in a small area.
- Thin materials – Thinner gauge metals require lower heat input to avoid burn through.
- Poor gas shielding – Inadequate shielding allows weld contamination leading to excess heat buildup.
- Lack of fusion – Poor joint preparation or dirty metals can limit fusion, resulting in burn through.
- Excessive weaving – Too much side-to-side torch motion dwells the arc over one spot too long.
How To Prevent Burn Through When MIG Welding
Preventing burn through requires controlling the heat input to the base metal. Here are the best tips to avoid burning holes when MIG welding:
1. Wear Proper Protective Equipment
MIG welding requires proper protective gear to stay safe from sparks, spatter, and arc flashes:
- Welding helmet – Use a quality auto-darkening helmet with proper lens shade for the amperage used. This protects eyes and face from UV and infrared light.
- Welding jacket and gloves – Wear thick, fire-resistant leather gloves and a jacket made of leather or specialized fabrics like Nomex to prevent burns.
- Other PPE – Use fire-resistant ear plugs, leather steel-toe boots, apron, etc. Remove lighters, matches, and flammable items from pockets before welding.
2. Clean and Prepare Metals Thoroughly
Grind, clean, and fit up metals properly to ensure good heat flow and prevent burn through:
- Remove rust, mill scale, paint – Use angle grinders, wire wheels, or sandblasting to strip metals to bare, clean surface.
- Bevel thick sections – Grind a proper groove angle and depth on thicker sections to control penetration.
- Gap joints – Leave 1/16″ gap on thin materials for full weld penetration to edges.
- Clamp pieces – Use vise-grip clamps, magnets, vices, or jigs to hold metals securely and prevent heat sink.
3. Set Machine For Lower Amperage and Voltage
Adjust welder parameters down to prevent overheating thinner gauge metals:
- Reduce amperage to match filler wire size and metal thickness. Use 100-150 amps on 24 gauge, up to 200-250 amps on 1/8″ and thicker.
- Lower voltage to reduce arc energy. 18-22V is suitable for thin materials. Higher voltages increase chances of burn through.
- Set wire feed speed just fast enough to maintain a steady arc and proper bead shape.
:pro_tip: Slow down wire speed if you see burn through starting – this reduces heat input.
4. Choose Proper Filler Wire Size
Match the diameter of the electrode wire to the thickness of the base metal:
- Use 0.023-0.024″ wire for 24 gauge sheet metal.
- 0.030″ wire works for 18-20 gauge metals.
- For 1/8-1/4″ stock, step up to 0.035-0.045″ wire.
Smaller wire sizes put less current into the weld, preventing overheating. Oversized filler wire adds excess heat and increases chances of burn through.
5. Maintain Correct Arc Length
Hold a consistent arc gap of ~1/8-3/8″ between contact tip and workpiece:
- Avoid excessive arc length – Higher voltage causes overheating and lack of fusion.
- Prevent short arcs – Concentrated heat buildup leads to burn through, especially on thin materials.
- Use a MIG gun liner – Helps regulate and steady your arc length as you weld.
Keep the arc tight and centered on the joint without long gaps or short burying into the weld puddle.
6. Control Travel Speed
Move along the weld at an even speed, neither too fast or too slow:
- Go slower on thinner materials – Allows adequate heating of the joint without excess penetration.
- Avoid stop-start motion – Dwelling in one spot overheats the metal. Maintain steady travel.
- For fillet welds, focus on each side separately – Quick back-and-forth weaving overheats the center.
- On gaps, slow down at the start/end – Skipping over edges can cause burn through.
:editor_note: The right travel speed depends on many factors. Test different speeds on scrap pieces to dial in your technique.
7. Use Copper Backup Bar
For heavy penetration welds, use a copper or aluminum bar clamped opposite the weld:
- Copper rapidly conducts heat away from the underside of the joint.
- Prevents “soaking” through of excess concentrated heat.
- Ideal for situations where backside is inaccessible, like some fillet welds.
- Can be chilled even further by immersing bottom of bar in water bath.
8. Allow Proper Cooling Time Between Passes
Let the metal cool adequately between weld passes to prevent overheating:
- Slow down with multiple pass welds – Earlier passes add preheat for later ones.
- Peen each weld layer – Helps remove heat-affected zone for next pass.
- For thicker materials, allow a few minutes between passes for the metal to cool.
- Avoid excessive overlap between beads – Weld pile-up retains heat.
:pro_tip: Use a temp gun or crayon to verify interpass temperature before depositing the next weld layer.
9. Learn Proper MIG Welding Technique
Develop skill using proper MIG welding technique to prevent burn through:
- Keep arc centered on joint – Weaving too wide overheats edges.
- Use forehand welding method – Focuses heat from wire tip in direction of travel.
- Avoid lingering in one spot – Keep welding torch moving.
- Make stringer beads – No excessive weave or whip patterns.
- Tune angle of torch 15-45° from vertical – Directs heat into the joint.
With practice, you’ll gain muscle memory to weld automatically with good technique. Get comfortable welding thinner materials without burn through.
Mistakes To Avoid That Cause Burn Through
It’s also helpful to be aware of common mistakes that can result in burn through so that you can watch out for them:
- Lack of fusion – Not fully melting base metal causes inadequate mixing and penetration.
- Welding dirty, contaminated metals – Paint, oil, mill scale get trapped in the weld and lead to voids.
- Using excessive wire stickout – More than 1/2″ causes arcing problems and inefficient heat transfer.
- Overwelding – Depositing more filler metal than required overheats the weld zone.
- Poor welding position – Avoid overhead or vertical down positions. Use flat or horizontal welds.
- Insufficient gas flow – Low flow rates causes turbulence and weld contamination.
- Uneven welding surface – Gaps or holes in joint draw arc energy and penetrate through.
- Poor ground clamp connection – Inadequate electrical contact concentrates current density.
How To Fix Burn Through Damage
Despite your best efforts, you may still get an occasional burn through while learning. Here’s how to fix it:
- Clean out the hole – Grind to remove slag and enlarged hole.
- Fill hole with weld – Use smaller filler wire and lower heat to fill up the damaged area.
- Add reinforcement plate – For larger holes, weld on a cover patch or plug.
- Peen while hot – Hammering helps dense up the weld rework areas.
- Blend repair – Grind, sand, and polish to even out the patched section.
With care, you can fill a burn through successfully while maintaining weld integrity. Preventing them in the first place is always preferable.
Tips To Prevent Burn Through Summary
Here’s a quick summary of the top tips for avoiding burn through when MIG welding:
- Adjust machine settings lower – Reduce voltage, amperage for material thickness.
- Pick appropriate filler wire size – Smaller than base metal.
- Wear proper protective gear – Leathers, auto hood, gloves, etc.
- Allow cooling between weld passes – Manage interpass temperature.
- Maintain proper arc length and angle.
- Use suitable travel speed – Adjust for material thickness.
- Employ backup bars – Copper, aluminum to dissipate heat.
- Develop proper welding technique – No excessive weaving.
- Prepare materials well – Clean, beveled, tight-fit joints.
Preventing Burn Through In MIG Welding
With the right techniques and practice, burn through is a manageable issue when MIG welding thinner gauge metals. Adjusting your machine settings appropriately for the material thickness and following solid technique will go a long way towards preventing unwanted holes in your welds.