What is Conduction Welding And Keyhole Welding?

Conduction welding uses a laser to melt the surface of the metal to create a shallow, wide weld. Keyhole welding, on the other hand, uses higher energy lasers to create deep, narrow welds by creating tiny holes in the metal. Both methods fall under the category of laser welding, which is widely used in aerospace, medical, energy and industrial applications, helping many industries to join metals. They are also used in electronics and semiconductor manufacturing.

Laser Welding Modes

Laser welding lets you join metals very accurately. A focused laser beam melts and joins metal surfaces. There are two main ways to do this: conduction welding and keyhole welding. Each way changes how the weld looks and how deep it goes.

Conduction Welding

Conduction welding is good for smooth and shallow welds. The laser heats the top of the metal. The heat spreads out through the metal. This makes a wide weld that is not very deep. People typically come to weld thin parts or workpieces where an aesthetically pleasing weld is desired.

Here is a table that compares conduction welding and keyhole welding:

Welding Mode	Energy Density (MW/cm²)	Characteristics
Conduction Welding	~0.5	Shallow and wide weld, heat moves by conduction, good for nice-looking welds.

Keyhole Welding

Keyhole welding uses much more energy. The laser is so strong it makes a small hole in the metal. This helps make welds that are deep and narrow. Suitable for thick metal or situations requiring a strong weld.

Keyhole welding:

Welding Mode	Energy Density (MW/cm²)	Characteristics
Keyhole Welding	>1.5	Deep and narrow welds, fast welding, makes a keyhole for better laser use.

How Modes Transition

You can change from conduction welding to keyhole welding by changing the laser settings. The switch does not happen at one exact point. It depends on many things:

• Power density changes how deep the laser goes.
• Beam diameter changes how the energy spreads out.
• Scanning speed changes how fast the heat moves.
• Recoil pressure pushes the melted metal and helps make the keyhole.
• Melt flow dynamics help shape the hole and the weld.
• Keyhole stability depends on the hole size and how steady the laser is.

You can change these things to get the weld you want. Laser welding lets you pick the best way for your project.

Conduction Welding Details

How It Works

Conduction welding uses a laser to join metals. The laser heats the top of the metal. The heat moves down into the metal. Only a thin layer melts. The weld pool gets very hot, close to melting. For example:

• Carbon steels melt at about 2500°F.
• Most weld pools reach around 2000°F.
• The temperature changes with metal and laser settings.

You can change how deep and wide the weld is. You do this by changing the laser power and how long you use it. You use less power than keyhole welding. The laser does not go through the metal. It makes a smooth and shallow weld.

Characteristics

Conduction welding makes a weld that is wider than deep. The weld bead looks smooth and flat. This type is good for thin materials or nice-looking welds. Here is a table with weld depth and width for stainless steel:

Weld Depth (mm)	Weld Width (mm)
0.25	0.1
0.33	0.115
0.194	0.09
Average Depth	0.2 - 0.3
Minimum Width	< 0.075

You see that conduction welding makes a shallow weld. The weld is usually wider than deep. This helps you not burn through thin metal.

You can pick different lasers and power for different metals and thicknesses. Here is a table to help you choose:

Material	Thickness Range	Recommended Laser Power	Common Applications
Carbon Steel	Up to 2mm	1000W	Automotive, Construction
Up to 8mm	2000W	Automotive, Construction
Stainless Steel	Up to 2mm	1000W	Food Processing, Medical Devices
Up to 5mm	1500W	Food Processing, Medical Devices
Up to 8mm	2000W	Food Processing, Medical Devices
Aluminum	Up to 2mm	1000W to 1500W	Aerospace, Transportation
Up to 3.5mm	2000W	Aerospace, Transportation
Up to 5mm	3000W	Aerospace, Transportation
Copper	Up to 1mm	1000W	Electrical, Plumbing
Up to 3mm	2000W	Electrical, Plumbing
Titanium	Up to 2mm	1000W	Aerospace, Medical
Up to 5mm	2000W	Aerospace, Medical
Thin Materials	0.3mm to 1mm	300W to 1000W	General Welding
1mm to 2mm	1000W	General Welding
Medium Thickness	2mm to 5mm	1000W to 1500W	General Welding
Thick Materials	5mm to 8mm	2000W to 3000W	General Welding
Over 8mm	Advanced Techniques	General Welding

You can also look at a chart for laser power settings for different metals and thicknesses:

Applications

Conduction welding is used in many industries. It works best for thin parts and when you want a nice finish. Here are some common uses:

Application Area	Description
Joining thin materials	Used for joining sheets with low material thickness, ensuring quick and low distortion welding.
Device housings	Corner welds on visible surfaces of device housings, providing aesthetic and functional benefits.
Electronics	Applications in electronics where smooth, pore-free seams are essential.

You often use conduction welding for copper and aluminum. These metals are used in electronics because they carry electricity well. You also see conduction welding in aerospace, medical devices, and food processing. You can join thin sheets fast and with little bending.

Pros and Cons

Conduction welding has many good points but also some limits. Here is a quick look:

Aspect	Conduction Welding	Keyhole Welding
Weld Penetration	Typically wider than deep, controlled by pulse length	Deeper penetration
Heat Input Control	Precise control of heat input, minimizes distortion	Less control over heat input
Quality of Weld	Enhances overall quality and reduces defects	Higher risk of defects
Process Type	Utilizes pulsed laser welding for controlled melting	Continuous wave laser for deep welds

You can control the heat very well. This means less bending and a better-looking weld. The process lowers the chance of gas bubbles and other problems. You often do not need extra finishing work. The welds look smooth and clean.

• You can control the weld shape well.
• You can join thin and delicate parts.
• You lower the chance of problems like bubbles or cracks.
• You save time on finishing.

But conduction welding does not work well for thick metal. The weld does not go deep. If you need a strong, deep weld, use keyhole welding instead.

Keyhole Welding Details

How It Works

Keyhole welding uses a powerful laser to melt and vaporize metal. The laser beam focuses on a small spot. This creates a tiny hole, called a keyhole, in the metal. The keyhole lets the laser energy go deep into the material. You get a weld that is much deeper than it is wide.

• The temperature near the keyhole wall can reach about 3000 K (about 4920°F). Sometimes, it even goes above the vaporization point of the metal.
• The pressure inside the keyhole is very high. This pressure helps keep the hole open while the laser moves along the joint.
• The laser power and how fast you move the laser both change how the keyhole forms and how deep the weld goes.

The vapor cavity, or keyhole, is the secret to deep penetration. The laser energy hits the front wall of the keyhole first. This makes the metal melt and vaporize quickly. The molten metal flows around the keyhole because of surface tension. The size of the keyhole changes as the pressure inside goes up and down.

Key Findings	Description
Keyhole Formation	The depth of the keyhole depends on how much laser energy hits the front wall.
Molten Pool Dynamics	Surface tension moves the melted metal around the keyhole.
Pressure and Energy	Changes in pressure inside the keyhole affect its size and the weld quality.

Characteristics

Keyhole welding gives you a deep and narrow weld. The aspect ratio, which is the depth compared to the width, usually ranges from 0.5 to 2.5. This depends on how fast you move the laser and how much power you use.

• You can weld thick materials, sometimes up to 25mm.
• The weld bead is narrow and goes deep into the metal.
• You get strong joints that can handle a lot of stress.

You may see some problems if the keyhole is not stable. If the keyhole wobbles or closes too fast, gas bubbles can get trapped. These bubbles turn into pores, which are tiny holes inside the weld. Pores can make the weld weaker.

• Porosityis a big problem in high-power laser welding. It can lower the strength of the weld.
• If the keyhole is not steady, you may get more pores.
• The type of shielding gas matters. Argoncan let bubbles form, but nitrogen helps keep the keyhole stable and reduces pores.

Applications

You can use keyhole welding for many jobs that need strong, deep welds. This method works best for thick metals and parts that must hold up under stress.

Material Type	Thickness Range
Stainless Steel	Up to 12mm
Titanium Alloys	Up to 16mm

Here are some common uses for keyhole welding:

Sector	Application Description
Medical Devices	Used for implantable devices and surgical tools. It keeps heat low to protect the metal.
Energy	Used in pipelines and power plants. It makes strong joints for systems under pressure.
Electronics	Used for small parts and seals. It keeps heat damage low and makes airtight joints.

You also find keyhole welding in aerospace, shipbuilding, and automotive work. It helps you join thick plates and make parts that must last a long time.

Pros and Cons

Keyhole welding gives you many benefits, but you should know about the risks.

Pros:

• You can weld thick materials with deep penetration.
• The welds are strong and narrow.
• You can use this method for high-strength and structural parts.
• The process works well for automated systems.

Cons:

• You can only use it in flat, horizontal, or vertical up positions.
• The process is sensitive to changes in settings.
• You need automated equipment for best results.
• If the keyhole is not stable, you may get pores that weaken the weld.

Comparison

Process Differences

Conduction welding and keyhole welding work in different ways. Conduction welding heats just the top of the metal. The laser melts a thin layer, so the weld is shallow. Keyhole welding uses much more energy. The laser melts and turns the metal into vapor. This makes a deep hole called a keyhole. The keyhole lets you weld deeper into the metal.

Here is a table that shows how the weld bead shapes and penetration profiles are not the same:

Welding Method	Weld Bead Shape	Penetration Profile
Keyhole Welding	Narrow, high aspect ratio	Deep, cylindrical cavity
Conduction Welding	Wider weld beads	Shallow penetration

Welding speeds and how deep the weld goes are also different:

Welding Mode	Penetration Depth	Welding Speed
Conduction Mode	Shallow	Lower
Keyhole Mode	Deep	Higher

Results and Applications

Conduction welding makes a round weld bead. It works best for thin metals and small parts. You get a smooth look and less bending. Keyhole welding makes a deep, skinny weld. These welds are strong and can take a lot of force.

• In conduction welding, the laser heats the surface but does not boil it. The weld is shallow.
• In keyhole welding, the laser boils the metal. This forms a keyhole and a deeper weld.
• Keyhole welds can be almost five times stronger than conduction welds.
• A keyhole weld can reach a tensile strength of 187.86 MPa and stretch by 24.76%.

In car factories, conduction welding joins surfaces with little depth. Keyhole welding is used on production lines, like making battery links for electric cars.

Welding Type	Characteristics	Typical Use Cases
Conduction Welding	Joins materials at the surface; softer method	Surface joining, thin parts
Keyhole Welding	Penetrates deep; faster method	Battery connections, thick parts, production lines

Choosing a Method

You should think about a few things before picking a welding method. Metal thickness is important. Conduction welding is best for plates under 1mm thick. Keyhole welding works better for plates over 3mm thick. The way the joint is made also matters. Conduction welding is good for lap or butt joints with small spaces. Keyhole welding can handle bigger gaps or tricky shapes.

Factor	Conduction Welding	Keyhole Welding
Thickness of Metal	Best for plates less than 1mm	Suitable for plates thicker than 3mm
Joint Design	Works well with small gaps	Better for large gaps or complex designs
Application Requirements	Low distortion, smooth finish	Strong, deep welds for high-stress jobs
Surface Conditions	Forgiving of irregularities	Sensitive to contaminants and irregularities

Both methods need good fit and joint prep. You must be very careful with the position, especially for butt joints. Conduction welding is great for small, delicate parts and when you want little heat damage. Keyhole welding is best for deep, strong welds. Always pick the method that fits your project.

You now understand how conduction welding and keyhole welding are different. The table below explains what happens with each method:

Welding Mode	Laser Power Threshold	Resulting Effect
Conduction Welding	0.5 MW/cm2	Less deep welds, but wider shape
Keyhole Welding	1.5 MW/cm2	Deeper welds, but more narrow

Use conduction welding when you have thin pieces or need to join tiny parts, like in electronics or medical tools. Pick keyhole welding for thick, strong metals, such as in cars or airplanes.