Process guide
A sealed sensor housing with a circuit board inside does not like being shaken. Laser welding joins the lid to the base with no vibration, no particles, and no visible flash on the outside.
How it works
The weld forms where the two parts touch, below the surface.
Laser welding makes a transmission weld: light through the top part, heat in the joint. Ultrasonic welding needs a horn on an energy director. Solvent bonding softens the surface instead of melting it with light. Heat staking forms a post. Laser etching marks one surface. It does not join two parts.
In transmission welding, the two parts are clamped together. A laser beam passes through the upper part, which is transparent to that wavelength, and is absorbed by the lower part at the joint. The surface of the lower part melts, heat passes into the upper part where they touch, and the clamp pressure closes the gap as both sides melt and fuse.
The upper part does not have to look clear. It only has to let near infrared light through, and many black resins are made to do exactly that. So a black lid can be welded to a black base, with the difference sitting in the additives nobody can see.
Roles
Laser welding fuses a closed joint. Ultrasonic welding uses a horn. Laser etching only marks the surface.
| Page | Use it for |
|---|---|
| Laser welding (this page) | A weld through a light-passing top part |
| Ultrasonic welding | A horn and an energy director |
| Solvent bonding | A joint made by softening the surface |
| Heat staking | A molded post formed into a head |
| Laser etching | A mark, not a weld |
Beam paths
The choice follows joint shape and volume.
| Method | What moves | Fits |
|---|---|---|
| Contour | A single spot traces the joint line once | Large or varied parts; flexible, but the joint must already sit flat |
| Quasi simultaneous | Mirrors sweep the spot around the joint many times very fast | Most housings; the whole joint melts together and can collapse to close gaps |
| Simultaneous | Fixed diode arrays light the whole joint at once | High volume parts with a fixed shape; each design needs its own array |
| Mask | A wide beam passes a mask that shades everything except the joint | Fine, detailed joints such as microfluidic channels |
Design
The laser is forgiving in many ways and unforgiving about contact.
Alternative
Ultrasonic is the default for most plastic housings. Laser is what teams switch to when vibration, flash, or looks become a problem.
Keep reading
Other joining methods, and the parts laser welding shows up in.
The usual first choice for plastic housings.
Ultrasonic weldingWhen glue is the better joint.
Ultrasonic welding vs adhesiveHolding metal and boards with a melted post.
Heat stakingDissolving the joint instead of melting it.
Solvent bondingUsing a laser to mark, not to join.
Laser etchingSealed shells around electronics.
Sensor housingsEvery molding process and secondary operation.
All processesFAQ
Yes. The top part uses a colorant that looks black but lets near infrared light through, and the bottom part uses carbon black to absorb it. The pair has to be specified together.
With a special absorbing additive at the joint, or with lasers at wavelengths that clear plastics absorb. It is done in medical and microfluidic parts, but setup is more involved.
A well designed laser weld can be leak tight, which is why it is common on sensor and fluid housings. Whether it meets a given leak spec is proven by testing, not assumed.
No. Marking changes the surface color. Welding melts the joint between two parts, usually out of sight.
Welding fuses two parts at a joint. Laser etching marks one surface. They are not the same process.
When the horn can reach an energy director and the resins weld. Laser welding is the path when the joint is closed and the top part can pass the light.
Next step
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