Materials for laser welding Laser welding

Summary

  • Laser welding is a technique that exploits the transparency of plastics to laser light. In this technique, laser light irradiating a target body (made of resin or plastic) generates heat at the interface between the body and a separate absorber layer to create welded junctions.
  • The transmission/absorption approach to resin welding involves a combination of two resin materials: one light-transmitting resin (the transmitter) and one light-absorbing resin (the absorber).
  • Among the various techniques for realizing plastic junctions,  laser welding excels in handling miniature components while avoiding contamination and offering extensive flexibility regarding the appearance and shape of processed products.
  • Laser welding offers many advantages and has a growing track record of practical successes. Asahi Kasei recommends our engineering plastics specialized for use in laser welding.

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What is laser welding?

Laser welding is a technique that exploits the transparency of plastics to laser light. In this technique, laser light irradiating a target body (made of resin or plastic) generates heat at the interface between the body and a separate absorber layer to create welded junctions.

Laser welding mechanism and process

The transmission/absorption approach to resin welding involves a combination of two resin materials: one light-transmitting resin (the transmitter) and one light-absorbing resin (the absorber).

Typical setup for laser welding

Typical setup for laser welding

Typical setup for laser welding

  • The transmitter is placed atop the absorber and laser light irradiates this two-layer stack from above (laser irradiation).
  • The laser passes through the transmitter and is absorbed in the absorber, generating heat (absorption/photothermal conversion).
  • This heat generation causes the absorber to expand, transmitting heat to the absorber/transmitter interface (heat transfer).
  • This heat induces melting in the transmitter, resulting in formation of a welding pool and welded junction (solidification).

Advantages of laser welding

Laser welding is one of many available techniques for junction formation and welding of resins and plastics; other approaches include hot-plate welding, vibration welding, ultrasonic welding, adhesive junctions, snap-to-fit junctions, and screws or bolts.

 

Among the various techniques for realizing plastic junctions, laser welding excels in handling miniature components while avoiding contamination and offering extensive flexibility regarding the appearance and shape of processed products.

Advantages of laser welding

  • Damage-free. Welded parts are not directly subjected to vibrations, ultrasonic waves, or other stimuli, ensuring no mechanical damage to circuit boards and other internal precision components.
  • Reduced product footprints facilitate miniaturization. Space is saved by eliminating fastening components such as screws or snap-fit joints.
  • Welded products are attractive in appearance and suitable for high-end designs. The welding process produces few burrs and no abrasion residue.
  • Suitable for welding ultra-miniature components. Non-laser-irradiated components experience no thermal impact.
  • Eliminates the problem of resin-powder contamination commonly observed in vibration welding and ultrasonic welding. Also eliminates the problem of adhesive degradation because there is no adhesive, yielding strong, hermetic joints with long lifetimes.
  • Silent and vibration-free. The welding process generates no noise or vibrations, making it extremely workplace-friendly.
Advantages of laser welding

Laser-weldable materials

In principle, laser welding is applicable to any thermoplastic resin. The key point is the transmissivity of the transmitter resin to laser light of the relevant wavelength.

 

In general, laser welding requires the transmitter resin to exhibit a transmissivity of around 20% or greater; below this threshold, the transmitter resin absorbs too much of the laser light and begins to melt. Most of  natural resin materials are white or transparent and can generally exhibit sufficient transmissivity to allow laser welding, although this is depends on the thickness of the material.

 

Laser welding typically uses diode lasers or YAG lasers as sources, producing light at wavelengths in the 800-1200 nm range, slightly longer than visible light wavelengths. Welding is possible as long as the materials involved exhibit adequate transmissivity and absorptivity in this wavelength regime; thus, appropriate selection of pigments and laser absorbers allows even colored resin products to be welded. The following table lists a few common combinations.

Laser-weldable materials and combinations

Laser-weldable materials and combinations

Asahi Kasei’s Recommended Solutions

Asahi Kasei’s LEONA™ SN series: Polyamide resins featuring excellent laser transparency

For laser-welding applications, Asahi Kasei recommends our LEONA™ SN series. LEONA™ SN-series are halogen- and red phosphorus-free flame retardant polyamide resins featuring excellent laser transparency and capable of forming strong laser-welded joints.

What are LEONA™ SN series, next generation halogen & red phosphorus free flame retardant polyamide series?

Asahi Kasei’s LEONA™ polyamide resins are engineering plastics featuring high strength and rigidity, and excellent thermal and chemical resistance. These materials may be strengthened by reinforcing with glass fibers or other fillers, improving strength, rigidity, durability, and dimensional stability.

 

LEONA™ SN-series are halogen & red phosphorus free flame retardant polyamide resins. These materials not only feature excellent laser transparency and the ability to form strong laser-welded junctions, but also offer superior performance in several other areas: high strength, high rigidity, compliance with the UL94 V-0 (0.75 mm) flammability standard, and (CTI) 600V (PLC 0) tracking resistance.

LEONA™ SN-series feature excellent laser transparency and the ability to form strong laser-welded joints

Even when compared to other non-halogen flame-retardant polyamide resins, LEONA™ SN-series stand out for their high laser transparency and their laser-welded joint strength. These materials also retain their high laser transparency and joint strength when subjected to specialized black colorization, featuring a highly attractive deep-black appearance.

Laser transmission properties of LEONA™ SN-series resins

For laser light with a wavelength 940 nm, we compared the transmittance of SN11B—a LEONA™ SN-series with 25% glass-fiber reinforcement—to that of a general non-halogen flame-retardant polyamide (also with a glass-fiber content of 25%). The results showed that the transmittance of SN11B is approximately 2 times greater for natural-colored material and 3-4 times greater for black-colored material.

Laser transmittance (wavelength: 940 nm)

Laser transmittance (wavelength: 940 nm)

In laser welding, large quantities of energy pass through materials to arrive at the site of welded joints. LEONA™ SN-series offer the following advantages:

 

  • Allow high-speed welding to improve manufacturing throughput.(See the video below.  Caution: Please note the strong light in this video.)
  • Can be welded by low-power lasers.
  • Material surfaces do not acquire an unattractive burned appearance.

Comparison of welding speeds: LEONA™ SN series (left) vs. general non-halogen flame-retardant polyamide (right)
(Caution: Please note the strong light in this video.)

Strength of laser-welded joints with LEONA™ SN-series

The figure below illustrates the excellent joint strength of compound parts formed by laser welding with LEONA™ SN-series.

Joint strength vs. power consumption for laser-welded joints

Joint strength vs. power consumption for laser-welded joints

Deep-black appearance of LEONA™ SN-series (in case of specialized laser-transmitting black colorization)

Compared to general non-halogen flame-retardant polyamide, LEONA™ SN-series with specialized black colorization, which transmits only laser light feature high laser-light transmittance and high joint strength.

 

Moreover, in comparison to general non-halogen flame-retardant polyamide, LEONA™ SN-series with specialized black colorization feature an attractive deep-black appearance that makes them ideal for applications demanding stylish designs. The deep-black appearance of LEONA™ SN-series is due to the smoothness of their surfaces, which are free from microscopic surface roughness that gives rise to diffuse light reflection.

Appearance of laser-welded test pieces and magnified surface views

Appearance of laser-welded test pieces and magnified surface views

  • Click here to download the Leona ™ SN series document

LEONA™ laser-welding case study

Using LEONA™ SN-series to reduce the size and weight of a battery case

Switching to LEONA™ polyamide (PA) as the material for a battery case allowed the case to be manufactured via laser welding, reducing its size and weight.

Conventional welding methods such as vibration or ultrasonic welding entail significant vibrations that may damage sensitive components inside the case. Also, the use of screws or other fasteners requires that some portion of the case be dedicated to bosses or other fastener housings, increasing its spatial footprint. The use of laser welding eliminates such fasteners while avoiding damage to components inside the case, reducing its size and weight.

batterycase
  • Click here for more information on Materials for automobile batteries.
  • Click here for more information on Materials for rechargeable batteries.

Eliminating unattractive “burned”-looking regions in welded surfaces of electronic components

One promising application made possible by the improved laser transmittance of flame-retardant resin grades is laser welding of electronic components, for which conventional welding techniques are difficult to apply. The ability to weld components with lower laser power reduces the emergence of unattractive “burned”-looking regions in welded surfaces.

Laser welding of electronic components with flame-retardant resin grades

Laser welding of electronic components with flame-retardant resin grades

  • Click here for more information on Materials for Connectors

Other potential applications

Valves, pumps, electric parking brakes, ECU cases, vehicle-mounted cameras, and more

 

 

For more information on Asahi Kasei’s materials and grades for laser welding, please contact us via the link below. In particular, please feel free to contact us regarding any design questions or concerns you may have regarding various types of laser welding.


We would like to talk to you about Asahi Kasei’s laser-weldable engineering plastics. Please contact us to ask any questions, discuss any concerns, and request samples.

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