Laser welding

Materials for laser welding

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.

旭化成のエンジニアリングプラスチック、ザイロン™、レオナ™、テナック™は、一般的にナチュラル材ー着色材の重ね合わせでレーザー溶着可能です（材料・グレード選定についてはお気軽にご相談ください）。
本ページでは、特にレーザー溶着加工に適した樹脂材料として、レオナ™SNシリーズをご提案します。レオナ™SNシリーズは、環境と安全を考慮したノンハロゲン・赤燐フリーの難燃ポリアミド樹脂で、レーザー透過性・接合強度に優れます。

レーザー透過性に優れたポリアミド樹脂 SNシリーズ

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

旭化成のポリアミド樹脂レオナ™ は強度・剛性、耐熱性、耐薬品性に優れたエンジニアリングプラスチックです。ガラス繊維のような充填材（フィラー）によって強化することで、強度・剛性、耐久性、寸法安定性が向上します。

レオナ™ SNシリーズは、環境と安全を考慮したノンハロゲン・赤燐フリーの難燃ポリアミド樹脂です。レーザー透過性・接合強度に優れ、さらに、高強度・高剛性、UL94 V-0（0.75mm）取得、耐トラッキング性（CTI）600V（PLC 0）と、優れた性能を有します。

Laser transmission properties of LEONA™ SN-series resins

レオナ™SNシリーズの中でも、ガラス繊維25%強化品であるSN11Bのレーザー透過率 (940nm)を、LEONA™一般的なノンハロゲン難燃ポリアミド樹脂（ガラス繊維含有量はSN11Bと同じ25%）と比較したところ、ナチュラル色で約2倍、黒色で3-4倍でした。

LEONA™ SN series laser transmittance (light wavelength: 940nm) — Laser transmittance (wavelength: 940 nm)

材料を透過して接合部位に到達するエネルギー量が多いため、レオナ™SNシリーズを用いたレーザー溶着加工には、

高速加工による生産性の向上が可能
（下記動画参照。※動画では強い光が出ますのでご注意ください。）
低出力レーザーでも加工可能
表面に焦げを発生させない

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

下図のとおり、レオナ™SNシリーズをレーザー溶着させた複合品は接合強度に優れています。

Laser welding output and bonding strength — Joint strength vs. power consumption for laser-welded joints

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

レオナ™SNシリーズは、レーザーのみを透過させる特殊黒着色を施した場合でも、一般ノンハロゲン難燃ポリアミド樹脂よりもレーザー透過率が高く、接合強度の高さも維持しています。
さらに、一般ノンハロゲン難燃ポリアミド樹脂よりも漆黒性に優れており、外観を重視される部品にも好適です。この漆黒性はレオナ™SNシリーズの表面平滑性に起因しており、LEONA™光を乱反射させる表面の微細な凹凸が少ないためです。

Appearance of laser-welded test pieces and magnified surface views

レオナ™ SNシリーズ
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LEONA™ laser-welding case study

バッテリーケースの小型化・軽量化

バッテリー（蓄電池）を納める筐体にポリアミド（PA）樹脂レオナ™を使用し、レーザー溶着加工を行うことで、筐体の小型化・軽量化が可能です。

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.

電装部品の溶着界面の焦げ低減

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

その他の想定用途

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

レオナ™ SNシリーズ
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Laser welding related information

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

1. Laser irradiation：The transmitter is placed atop the absorber and laser light irradiates this two-layer stack from above
2. Absorption/photothermal conversion：The laser passes through the transmitter and is absorbed in the absorber, generating heat
3. Heat transfer：This heat generation causes the absorber to expand, transmitting heat to the absorber/transmitter interface
4. Solidification：This heat induces melting in the transmitter, resulting in formation of a welding pool and welded junction

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.

Types, advantages, and disadvantages of welding and joining methods

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.