Plastic welding is one of the main methods of thermoplastic plastic secondary processing. Plastic welding can be divided into hot plate welding, laser welding, induction welding, friction welding, ultrasonic welding, high frequency welding, hot air welding etc.
The main welding principle of plastic laser welding is “transmission welding”. The laser (wavelengths 800 to 1950 NM) penetrates the upper layer, and is absorbed in the depth range of 0.1-0.5mm below the lower layer, and then laser radiation is converted to heat.
As the two layers of material are clamped together during the welding process, the material is heated to expand and heat is transferred from the absorbent layer to the transmissive layer. Under the synergistic effect of the internal expansion force and the external fixture pressure, the upper layer and the lower layer material are fully fused to complete the solid welding of the upper and lower parts.
Almost all of the thermoplastic can be used laser welding —- ABS, PP, PS, PA, PVC, PBT, etc., and the welding strength can reach the base material strength.
Plastic laser welding can not be used as shown below splicing welding, because the plastic melting temperature is low and mobility is poor. In this welding method, the welding strength and sealing can not be guaranteed.
The following diagram shows the penetration welding, and there is a theoretical welding possible, but in the actual welding process, the compression force, laser refraction and other issues is difficult to handle.
Plastic laser welding as a new type of welding, it has begun to replace some of the traditional plastic welding. At the same time, a variety of new welding methods and new materials are suitable for laser welding have also been developed.
The influencing factors on the quality of the laser welding
Plastic laser welding requires a combination of laser transmission material and laser absorption material. In the natural conditions, the general thermoplastic material is transparent to the laser, but the absorbent effect can be achieved by an additive (e.g., carbon black).
“Laser Transparency” is different from “Optical Transparency”, the laser wavelength belongs to the laser spectrum that human eye is not visible. In fact, many plastic laser welding applications only need the upper layer transparent to the laser. As a result, some materials that transparent under the laser but heavy color under the human eye are developed for plastic laser welding.
Material thickness, crystal properties, glass fiber content, other additives (such as flame retardants) may affect the laser transmission effect of the material. Generally need to ensure that more than 20% of the laser energy through the upper layer absorbed by the lower layer to obtain a good welding effect. Low laser transmission effect will make the upper layer first decomposition during the process of welding.—— UW has the professional measurement equipment to complete the material’s laser transmission test.
For the bottom layer absorption effect, the main way is to add carbon black, and other additives have less influence on the bottom absorption effect.
Material’s laser transmission test machine
Material color is also an important factor to affect the laser welding, usually transparent + black is the most simple combination, which can get the great laser welding process.
In color plastic, the pigment or dye content is very important. When the pigment content is low, the fusion depth of the laser is relatively large, but the material itself does not form thermal damage. The resulting expansion volume can extend the melt contact time and ultimately increase the welding strength. Therefore, the absorption rate and the transmittance of materials can be adjusted by adding a filler or a pigment.
PMMA and other non-crystalline thermoplastic plastic has a good transmission effect for the laser, on the contrary, PA, PBT, POM and other semi-crystalline thermoplastics, even in the natural conditions will absorb and reflect a part of the laser energy.
The most commonly used additive for white plastic is titanium dioxide (highly reflective material). Because white will reflect most of the laser rather than absorb, so white is not ideal for laser welding material color. Titanium dioxide type, addition volume, laser wavelength and specific process control are key factors to affect the ability of white materials welding.
Plastic laser welding requires a combination of “laser-transparent” and laser-absorbing materials, but all black standard materials can absorb certain lasers. In order to achieve the black and black materials. The lower black layer shall adopt PA66. BASF’s Ultramid A3WG6 LT (PA66) material has a black appearance and laser penetration, with the addition of carbon black PA66 material can achieve good laser welding.
Plastic laser welding in the structure is different from the traditional ultrasonic welding, because the different heat source and conduction mode, the laser welding requires flat and flat contact to complete the welding process.
Similar to ultrasonic welding, plastic laser welding generally use T-type connector, but the welding position to be used in flat and flat contact.
A: Light transmission material
B: Light absorbing material
C: Inside fixture
D: Outside fixture
E: Welding convex platform with the allowable collapse space
F: Material overflow area
G: Cover to avoid laser angle
H: The thickness of the light transmission layer
For high hardness, small product deformation parts, usually use the inside fixture (C) or the outside fixture (D), conversely need both to press fit. In the quasi-simultaneous welding process, welding convex platform melted would collapse because of fixture pressure. The welding collapse can achieve better welding strength and overcome certain deformation error of the material.
Because the laser beam is tapered, laser transmission material should avoid the laser path. Semi-crystalline plastic can absorb the laser, with this material to do the cover should consider the thickness of the laser layer ( the larger the thickness, the smaller laser penetration energy) .
For the circle structure shown below, don’t need the welding convex platform structure, but should ensure the material with the interference fit. During the welding process, the internal expansion of the material could complete the required compression process.
Plastic laser welding is suitable for various industrial applications, according to different sizes and shapes of products, UW laser can provide two methods : contour welding and quasi-simultaneous welding.
During the contour welding process, the laser welding head or product driven by the XYZ axis, the laser running along the welding trajectory. In whole process , partial materials melted, and have no overflow materials. As the material welding surface without the overall melting process, the welding product height change small at the end.
The contour welding requires that the welding position of the upper and lower materials be fully fit, and the lager deformation will increase the design difficulty of the welding fixture.
The contour welding can be adapted to larger product sizes and complex 3D structures, and can be quickly switched between different products.
The quasi-simultaneous welding is a more efficient welding method. When welding scanner lens guide laser beam at a speed of more than 5 m/s along the welding path high-speed movement, which make the whole welding surface heat melting gradually. Under the action of the fixture pressure, the entire welding convex platform have a certain collapse.
The quasi-simultaneous welding is similar to the traditional plastic welding, the weld seam position has molten outflow and the height of the product decreases.Due to the material collapse, so can overcome the material deformation.
The quasi-simultaneous welding can be adapted to product sizes is generally not more than 200mm * 200mm, and is usually used for planar welding. As a result of the overall heating, the efficiency is higher than the contour welding.
The program uses XYZ three-axis workbench, with double Y-axis and double-W axis, to achieve loading and welding at the same time. Suitable for mass production of round plastic welding of suction bag.
| Welding type | Plastic welding |
| Laser power | 120W |
| Spot shape | Round |
| Weld width | 1.5mm |
| Welding method | Contour welding |
| Position method | CCD & red |
| Welding speed | 30-100mm/s |
| Welding range (X*Y1*Y2*Z*R1*R2) mm |
200*400*400*400*R1*R2 |
| Control method | Industry PC |
| User interface | UW welding software |
| Power input | AC220V±10%50/60Hz |
| Machine size | 1600w×1819d×2259h(mm) |
| Weight | Determined by design(Kg) |
| Cooling type | Water cooling |
| Working temperature | 10-30℃ |
| Working humidity | 30%-75% |
| Application areas | Round light plastic |
Plastic is easy to mold into a complex shape structure, which widely used in industrial applications, such as auto parts, medical equipment, electronic sensors etc.
Auto parts
(Contour welding)
Auto meter
(Quasi-simultaneous welding)
Auto sensor
(Contour welding)
Electronic brake
(Contour welding)
Packing tape
(Contour welding)
Suction bag
(Contour welding)
Repeat reliable welding
No vibration welding
Clean and no pollution