Application of Laser Welding Technology in Metal Parts
This page explains how laser welding joins metal parts, which joint designs and materials it suits, and where the process stops making sense. It is written for design engineers and buyers who need to pick a joining method before releasing a drawing.
How the beam actually joins two parts
The beam is focused to a spot a few tenths of a millimeter wide. Power density at that spot runs high enough to melt the metal in a controlled pool. Two modes matter on the shop floor. Conduction mode melts the surface and heat travels down by conduction, which gives wide, shallow, smooth welds. Keyhole mode pushes power density higher, vaporizes a narrow channel through the melt, and the beam deposits energy deep into the joint.
Choosing between the two comes down to penetration and appearance. Conduction mode suits foils, battery tabs, and cosmetic seams where a smooth bead matters more than depth. Keyhole mode reaches deeper in a single pass, so it fits structural brackets, sensor housings, and tube-to-fitting joints. Both run fast, and both keep the heat-affected zone narrow compared with arc processes.
Fiber lasers dominate production work today. A 1 kW to 3 kW source covers most thin-sheet jobs at travel speeds of several meters per minute. Spot size, focal position, shielding gas, and travel speed are the four settings an operator tunes first. Get the focal position wrong by a few tenths and the weld either sits on the surface or blows through.
Joint designs that work, and ones that fight the process
Laser welding likes gaps measured in hundredths of a millimeter. A butt joint between two sheared edges usually needs a tight fit-up, or the beam passes through the gap and never bridges the two parts. Lap joints tolerate more variation because the beam melts into the lower sheet. For a lap seam, a small gap at the start of the weld helps gas escape and cuts porosity.
Fillet and T-joints are common on housings and brackets. The beam can be angled to melt both walls, but the vertical wall reflects part of the energy away. That reflection is why operators tilt the head 10° to 15° from vertical on reflective metals. It also keeps spatter out of the optics.
Dissimilar thickness is a normal case, not an edge case. A 0.5 mm lid on a 3 mm base welds well if the beam is offset toward the thicker side and the power is set for the thin part. Flip the offset and the lid vaporizes before the base reaches melting temperature.
What does not work: wide gaps, heavy mill scale, and joints buried deep inside a closed cavity. If the beam cannot see the seam, no parameter set will fix it.
- 1Butt jointTight fit-up required, gap under roughly 0.1 mm
- 2Lap jointForgiving, good for dissimilar thickness
- 3Fillet or T-jointTilt the head on reflective metals
- 4Hidden seamSkip laser welding, pick another process
Which metals weld cleanly under a laser
Stainless steel is the easiest family. Grades 304, 316L, and 17-4PH (SUS630) weld with good penetration and little post-weld cleanup. Austenitic grades stay ductile in the weld zone. Martensitic grades such as 420 and 440C harden as they cool, so preheat or a post-weld temper may be needed if the joint carries load.
Aluminum is workable but less forgiving. It reflects a large share of the beam at room temperature, conducts heat away fast, and forms an oxide skin that melts at a much higher temperature than the base metal. Higher power, a tighter focus, and clean oxide removal before welding are the usual answers. Alloys 6061 and 5052 weld well; 7075 is prone to hot cracking and is a poor candidate.
Copper and brass need even more power because of reflectivity, and green or blue wavelength sources are sometimes used for thick copper. Titanium welds cleanly but must be shielded with argon on both sides, since it picks up oxygen and nitrogen above roughly 400 °C and turns brittle.
Plated parts bring their own issue. Zinc and nickel coatings vaporize in the beam and can leave porosity in the weld. Machining the plating back from the joint edge, or welding before plating, avoids most of it.
Laser welding against the processes it usually replaces
Rough guidance for thin and medium sheet metal work. Final choice depends on joint access, volume, and cosmetic requirements.
| Process | Heat input | Typical section | Watch out for |
|---|---|---|---|
| Laser welding | Very low, narrow HAZ | 0.1 mm to 3 mm | Tight fit-up, reflective metals |
| TIG welding | High, wide HAZ | 0.5 mm and up | Distortion, slow travel speed |
| Resistance welding | Local, contact based | 0.2 mm to 2 mm | Electrode wear, access both sides |
| Electron beam welding | Very low, deep penetration | 1 mm to 50 mm | Vacuum chamber required |
| Adhesive bonding | None | Any | Cure time, temperature limit |
Where laser welding sits in a CNC workflow
Most parts we see are not welded as a stand-alone operation. They are machined first, welded, then finished or re-machined at the joint. The reason is simple: welding moves metal. A seam that has to hold ±0.005 mm after welding usually needs a cleanup pass, because shrinkage pulls the two sides together by a few hundredths of a millimeter.
A common sequence for a sensor housing starts with 5-axis machining of the body and the lid, laser welding around the perimeter, then a light face cut on the mating surface and a leak test. The weld provides the seal. The final cut provides the flatness.
For prototypes, laser welding lets us assemble a part from simpler machined pieces instead of cutting a deep pocket with a long reach tool. That often shortens the first-article cycle and lowers the risk of tool deflection. On production runs, the same joint may move to die casting or a one-piece machined design if volume justifies it.
We keep both capabilities under one roof. Turning, milling, welding, and inspection in the same plant means the joint tolerance is owned by one team, not split across two suppliers.
Common questions
Can laser welding hold the same tolerance as CNC machining?
Not by itself. The weld pool shrinks as it cools, which pulls the joint together. Expect a shift in the range of a few hundredths of a millimeter on thin sheet.
If the drawing calls for tighter geometry, plan a post-weld machining pass or a fixture that constrains the parts through cooling.
Does laser welding work on dissimilar metals?
Sometimes. Steel to stainless, copper to brass, and aluminum to steel can all be joined, but each pair forms a different intermetallic layer at the interface.
Those layers can be brittle. A peel or bend test on the actual pair is the only reliable check before committing to production.
How much gap can the process tolerate?
On a butt joint, keep the gap under roughly 0.1 mm for a 1 mm section. Wider gaps need filler wire or a different joint design.
Lap joints are more forgiving because the beam melts into the lower sheet, so a small gap at the seam start is acceptable and even helpful.
Will welding distort a thin part?
Less than TIG or MIG, but not zero. The heat-affected zone is narrow, yet the shrinkage still adds up over a long seam.
Tack the part first, alternate weld direction, and use a heat sink if flatness matters. A final skim cut removes what remains.
Can we inspect a laser weld without cutting the part?
Visual and dye penetrant checks catch surface defects. For internal porosity, X-ray or ultrasonic inspection is the usual route.
We can also run a leak test on sealed housings, which is often the fastest functional check for a welded sensor body.
What surface finish should the weld area have before welding?
Clean and dry. Oil, coolant residue, and heavy oxide all cause porosity or spatter.
For aluminum, remove the oxide layer within a few hours of welding. For plated parts, machine back the coating near the seam.
Send us the drawing and we will tell you if laser welding fits
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