We weld thresholds using a semi-automatic machine: from preparation to finishing

Car thresholds are one of the most vulnerable parts of the body, subject to corrosion, mechanical damage and wear. Over time, even relatively new cars may develop through holes, rust spots or deformations that require urgent repairs. Semi-automatic welding - the most effective way to restore thresholds, allowing you to achieve a strong and durable seam at minimal cost.

In this article we will analyze the entire process in detail: from diagnosing damage and choosing equipment to finishing and anti-corrosion protection. You will find out what electrodes and gas it is better to use, how to properly prepare the metal, what mistakes beginners most often make and how to avoid them. The material will be useful for both novice car enthusiasts and experienced craftsmen who want to systematize their knowledge.

We will pay special attention safety precautions - Working with a semi-automatic machine requires strict rules to be followed to avoid burns, electric shock or fire. We will also consider alternative repair methods (for example, using fiberglass or cold welding) and cases where professional help is indispensable.

1. Diagnosis of damage: when welding is needed and when you can do without it

Before taking up the welding machine, it is necessary to assess the extent of damage to the thresholds. Not all defects require radical intervention - sometimes local repairs or anti-corrosion treatment are sufficient.

The main signs in which welding is required:

• 🔹 Through holes - even small holes (with a diameter of 5 mm) will expand over time due to corrosion and vibration.
• 🔹 Heavy rust, eating through the metal (the so-called “red hole”).
• 🔹 Deformations after an accidentwhen the threshold is bent or has creases that violate the rigidity of the body.
• 🔹 Peeling or destruction of the factory seam (often found on cars older than 10 years).

If the damage is superficial (minor corrosion, scratches, paint chips), you can do without putty, primer and painting. However, it is important to remember: even small pockets of rust left unattended will turn into through holes in 1–2 years due to constant exposure to moisture and reagents.

⚠️ Attention: On vehicles with a galvanized body (for example, Volkswagen, Audi, Skoda after 2010) corrosion spreads more slowly, but this does not mean that the thresholds do not need repair. Galvanizing only protects against surface rust, and mechanical damage requires welding.

For an accurate diagnosis, use:

• 🔦 Flashlight and mirror - to inspect the inside of the threshold through the technological holes.
• 🔧 Screwdriver or awl - to check the strength of the metal (if the tool fails, welding is inevitable).
• 📏 Ruler or feeler gauge - to measure the depth of corrosion.

2. Selection of equipment and consumables

To weld thresholds with a semi-automatic machine, you will need not only the machine itself, but also a number of auxiliary tools. The strength of the seam and the safety of work depend on their quality.

2.1. Semi-automatic welding machine: what parameters are important

An inverter semi-automatic machine with the following characteristics is suitable for body work:

• 🔌 Supply voltage: 220 V (for garage) or 380 V (for professional workshops).
• 🔢 Current range: 30–160 A (for thin body metal, 60–100 A is sufficient).
• ⚡ PV (on duration): not less than 60% at maximum current.
• 💨 Possibility of working with gas: it is necessary to have a reducer and a hose for argon or carbon dioxide.

Popular models for beginners:

• 🔧 Svarog EASY MIG 180 — optimal price/quality ratio, suitable for the garage.
• 🔧 Resanta SAIPA-160 - a budget option with good reviews.
• 🔧 Blueweld Prestige MIG-200 - for professionals, supports aluminum welding.

2.2. Welding gas: carbon dioxide vs argon

Two types of gases are used for welding thresholds:

Parameter	Carbon dioxide (CO₂)	Argon (Ar) or Ar+CO₂ mixture
💰 Cost	2–3 times cheaper	More expensive, but more economical
🔥 Seam quality	Rougher seam, lots of spatter	Smooth seam, fewer defects
🔧 Suitable for	Thick metal (from 1.5 mm)	Thin metal (0.8–1.2 mm)
⚡ Welding speed	Slower due to frequent cleaning stops	Faster, less post-processing

For thresholds of most passenger cars (metal thickness 0.8–1.2 mm) is optimal mixture of argon and carbon dioxide (80% Ar + 20% CO₂). It provides a stable arc and minimal spatter.

2.3. Electrode wire: diameter and composition

For bodywork, wire with a diameter of 0.6–0.8 mm made of low carbon steel (grade SV-08G2S or ER70S-6). Thicker wire (1.0 mm) is only suitable for rough work (e.g. frame repairs).

Important: the wire must be clean and dry. It must be stored in an airtight container, as moisture causes the seam to become porous.

The wire is free of rust and oil|The gas cylinder is validly tested|The nozzle and tip are the correct diameter|The ground cable is not damaged-->

3. Preparing the threshold for welding: the key to quality repairs

Improper preparation is the main cause of poor welds, metal burning and re-corrosion. This stage takes up to 70% of the time of the entire repair, but you cannot save on it.

3.1. Removing body kits and cleaning the surface

Before welding you must:

1. Remove plastic linings, door seals and other interfering elements.
2. Clean the threshold from dirt, oil and old paint using sandblaster or a wire brush.
3. Degrease the surface acetone or antisilicon.

To remove rust use:

• 🔨 Angle grinder (grinder) with a petal circle.
• 🧹 Sandblasting - the most effective method, but requires special equipment.
• 🧴 Rust converter (for example, Tsinkar) - for small lesions.

⚠️ Attention: If the threshold has multilayer structure (for example, at Toyota Land Cruiser or Nissan Patrol), you cannot weld it without disassembling it. There may be amplifiers or soundproofing inside that could be ignited by sparks.

3.2. Cutting rusty metal and preparing edges

Through holes or heavily rusted areas need to be cut completely, rather than brewing on top. To do this:

1. Draw the outline of the cut-out area with chalk or a marker, stepping back 10–15 mm from the edge of rust.
2. Cut metal Bulgarian with cutting wheel thickness 1.0 mm.
3. Sand the edges at an angle 45° for better penetration.

If the hole is small (up to 5 cm), you can do without the insert by welding it with a “patch” of sheet metal thick 0.8–1.0 mm. For large defects you will need cut out the insert according to the shape of the cutout and weld it overlapping or butt welding.

How to make a template for insertion?

Cut a stencil from cardboard or thick paper to the shape of the hole, then transfer it to the metal. For a precise fit, use tin snips or a jigsaw. The insert must fit under the existing metal to 10–15 mm for secure fastening.

3.3. Protection of neighboring elements

Before welding, cover:

• 🚗 Door glass - with a damp cloth or a special screen.
• 🔋 Wiring - if it passes next to a threshold (for example, on VAZ 2110 or Renault Logan).
• 🎨 Paintwork - masking tape or aluminum foil.

Don't forget about fire safety: There should be no flammable materials (gasoline, oil, rubber seals) near the welding site.

4. Setting up a semi-automatic machine and threshold welding technique

Correct machine settings are the key to an even seam without burns. For body metal thickness 0.8–1.2 mm The following parameters are recommended:

Parameter	Meaning	Note
🔌 Voltage (V)	18–22 V	The thinner the metal, the lower the voltage.
⚡ Current (A)	60–90 A	For wire 0.8 mm.
🌀 Wire feed speed	3–5 m/min	Selected experimentally based on the sound of welding.
💨 Gas consumption (l/min)	8–12	If there is wind or draft, increase to 15.

The technique of welding thresholds has its own nuances:

1. Burner angle: 10–15° in the direction of movement (as when writing with a ballpoint pen).
2. Arc length: 3–5 mm. An arc that is too long leads to spattering, while a short arc leads to wire sticking.
3. Travel speed: uniform, without delays. The optimal speed is when the seam looks like “scales”.
4. Welding order: Start at the edges of the insert, then move towards the center to minimize distortion.

For thin metal use spot welding (short seams length 10–15 mm at intervals 2–3 cm), rather than a continuous seam. This reduces the risk of burn-through and warping.

4.1. Common mistakes and how to avoid them

Even experienced welders sometimes make mistakes that spoil the result:

• 🔥 Burn through metal - occurs due to too high a current or slow movement of the torch. Solution: Reduce the current by 10-15 A and increase the speed.
• 💥 Excessive splashing - Causes: long arc, wet wire or incorrect gas. Solution: check the settings and replace consumables.
• 🌀 Uneven seam - a consequence of an unstable hand or an incorrect angle of the torch. Solution: Practice on a scrap piece of metal.
• 🔗 Lack of penetration — the seam did not penetrate deep into the metal. Solution: Increase the amperage or decrease the driving speed.

⚠️ Attention: On vehicles with aluminum thresholds (for example, Jaguar XJ or Audi A8) semi-automatic welding requires special wire (ER4043) and argon as a shielding gas. Attempt to weld aluminum with carbon dioxide will lead to porosity in the weld!

5. Treatment of the seam after welding: grinding and anti-corrosion protection

The weld is only half the job. Without proper post-processing, it will quickly become covered with rust, and the repair will have to be repeated.

5.1. Cleaning the seam and leveling the surface

After welding:

1. Remove slag (frozen metal splashes) using scarpel hammer or a wire brush.
2. Sand the seam Bulgarian with petal circle (P80–P120), then sander with sandpaper (P240–P400).
3. Check the threshold geometry ruler or template — it should not protrude or fall in relation to the body.

To level deep depressions, use automotive putty (for example, Novol Plus or 3M Gold). Apply it in thin layers (no more than 2–3 mm at a time) to avoid cracks.

5.2. Anti-corrosion treatment: what to choose

After grinding, the threshold must be protected from corrosion. Options:

• 🛡️ Primer for metal (for example, Reoflex or Body 960) - applied in 2-3 layers.
• 🖌️ Anti-gravel coating (for example, Dinitrol 479) - for the lower part of the threshold.
• 🔴 Movil or cannon fat — for the internal cavity of the threshold (applied through technological holes).
• 🎨 Painting — final layer (choose the color according to the car code).

Pay special attention hidden cavities. After welding, treat them anticorrosive in aerosol (for example, Noxudol 700) or wax composition (Tectyl). To do this, use a flexible nozzle that allows you to reach hard-to-reach places.

5.3. Leak test

After the anti-corrosive coating and paint have completely dried, check the threshold for leaks:

• 💦 By water - water the threshold with a hose under pressure. If there are untreated areas inside, moisture will seep in.
• 🔍 Endoscope — for inspection of the internal cavity (can be rented at a car service center).

If leaks are detected, repeat the treatment with anticorrosive or sealant (Terostat).

6. Alternative methods of repairing thresholds: when welding is not suitable

It is not always possible or necessary to cook thresholds. In some cases, it is more appropriate to use alternative methods.

6.1. Cold welding and epoxy compounds

Suitable for:

• 🔧 Small cracks (up to 3–5 cm).
• 🔧 Temporary repairs (for example, before selling a car).
• 🔧 Metal thickness less 0.8 mm, which is difficult to cook.

Popular formulations:

• 🧴 Poxipol — two-component epoxy resin.
• 🧴 Abro Steel - cold welding with metal filler.
• 🧴 Loctite 9466 - for aluminum thresholds.

Application technology:

1. Clean and degrease the surface.
2. Apply the composition in a layer 2–3 mm, extending beyond the edges of the crack.
3. Once cured (15-30 minutes), sand and paint.

⚠️ Attention: Cold welding is temporary solution. The service life of such repairs is 1–2 years, after which full welding will be required. Do not use it on load-bearing body parts!

6.2. Fiberglass and polyester resins

This method is suitable for cosmetic repairs small holes (up to 2 cm) on non-load-bearing sections of the threshold. Procedure:

1. Cut out the rusty metal and clean the edges.
2. Stick on the inside of the threshold fiberglass, soaked polyester resin (for example, Fiberglass Resin).
3. After hardening (24 hours), putty and paint.

Advantages of the method:

• ✅ Does not require welding equipment.
• ✅ Suitable for thin metal.

Disadvantages:

• ❌ Low strength - cannot withstand loads when driving off-road.
• ❌ Over time, it may peel off due to vibrations.

6.3. When is the best time to turn to professionals?

Some cases require the intervention of an experienced bodyworker:

• 🚗 The threshold is load-bearing element (for example, on pickup trucks or SUVs).
• 🔥 Damage affects spars or body reinforcements.
• 🔧 Necessary completely replacing the threshold (for example, on BMW E39 or Mercedes W210, where the thresholds are integrated into the body).
• 🎨 Required maintaining factory geometry (important for premium cars).

The cost of professional repair of thresholds in a car service:

Type of repair	Cost (RUB)	Due date
Local welding (1–2 holes)	3 000–6 000	1 day
Replacement of the threshold section (30–50 cm)	8 000–15 000	2–3 days
Complete replacement of the threshold (with painting)	20 000–40 000	3–5 days

7. Tips for caring for thresholds after repairs

To delay repeat repairs, follow these recommendations:

• 🚿 Wash thresholds in winter at least once every 2 weeks to remove salt and reagents. Use contactless car wash or manual cleaning with a soft brush.
• 🛡️ Apply extra protection autumn: liquid locker (for example, Turtle Wax) or anti-gravel film.
• 🚗 Avoid parking on grass or soil - moisture from the ground accelerates corrosion.
• 🔧 Check drainage holes in the thresholds (most cars have them). If they are clogged with dirt, water will accumulate inside.

For additional protection you can install:

• 🛡️ Plastic or aluminum trims - they protect against sand and stones.
• 🧲 Magnetic footrests — temporary protection when traveling outdoors.
• 🎨 Vinyl wrap - for example, 3M Scotchgard.

FAQ: Frequently asked questions about welding thresholds

🔧 Is it possible to cook thresholds with a regular inverter (not semi-automatic)?

Technically it is possible, but it is highly not recommended. Inverter (manual arc welding) produces a less neat seam, heats the metal more and requires a highly qualified welder. For thin body metal (0.8–1.2 mm) semi-automatic is preferable, as it allows you to control the current strength and wire feed speed.

If there is no other choice, use electrodes with a diameter 1.6–2.0 mm (for example, ANO-21) and weld spot seams with mandatory cooling of the metal between passes.

🔥 How to avoid burns when welding thin metal?

Burns occur due to excess heat. To avoid them:

• Reduce the current to 50–60 A (for metal 0.8 mm).
• Use pulse mode welding (if your machine has one).
• Brew short seams (1–2 cm) with breaks for cooling.
• Place under the area to be welded copper or aluminum plate - it will remove heat.

🛠️ Do you need to cook the thresholds from the inside?

Desirable, but not always possible. If there is access to the inside of the threshold (for example, through technological hatches), double welding (outside and inside) significantly increases the strength of the seam. However, on many modern cars, the internal cavity of the threshold is closed with amplifiers or sound insulation, and it can only be reached after complete disassembly.

In such cases, limit yourself to external welding, but be sure to treat the internal cavity anticorrosive in aerosol through drainage holes.

🎨 Is it possible to paint thresholds immediately after welding?

No. Between welding and painting there should be at least 24 hoursso that the metal cools and stabilizes. Otherwise, the paint may crack due to internal stress. Optimal sequence:

1. Welding and seam cleaning.
2. Anticorrosive treatment