DE4432081A1 - Radiation welding of thermoplastics and non melting materials using laser light - Google Patents

Abstract

The parts to be connected are first interlocked or held together by internal stresses, locked into the correct end position, to bring the joint surfaces into contact. They are then irradiated to melt them together, and the bond is cooled. Blunt contacting surfaces may be joined, avoiding irradiation of surrounding edge regions. Laser light with a wavelength between 0.5 and 10.90 mu m, pref. between 0.70 and 10.64 mu m is used. To weld non-thermoplastics, their joining surfaces are coated with thermoplastic.

Description

The invention relates to a method for welding joining of Plastic parts using radiation energy.

Molded parts made of thermoplastics can be found under different welding processes are connected to each other, whereby many types of energy are used to melt the joining surfaces be set, e.g. B. warm gas, IR radiation, heated plates or Molded parts, friction by rotation or vibration, ultrasound and high-frequency electromagnetic fields.

For the series production of small molded parts up to approximately 150 mm Diameter, the ultrasonic welding process is preferred set because it is very economical with welding times of less than one second works economically. With larger molded parts, the vibration welding process with welding times of a few seconds before moves. The rotary friction welding process is based on rotationally symmetrical Parts limited, and heating element welding required long heating times.

The welding processes mentioned require special, sometimes very much elaborate tools for fixation and if necessary also for energy pouring, e.g. B. heating elements, sonotrodes etc., because ins high forces applied especially in the friction welding process Need to become. For ultrasonic welding and vibration will also weld the parts and, if necessary, in them included functional parts, e.g. B. Electronics through high acceleration forces and possibly damaged. With Heizele Mental welding is damage from heat radiation or con vection often cannot be excluded.

The present invention is accordingly the task reasons, a process for welding plastic parts to develop with the help of radiation energy, which without any directions for fixing the parts to be connected and without manoeuvrable facilities for introducing welding energy.

The solution to the problem is a method of the above Type in which according to the invention the parts to be connected first by positive locking or internal frictional connection in the right end fixed to each other and the joining surfaces in contact  brought and then exposed to radiation energy the.

Further details and advantages of the process according to the inven tion are shown schematically in the drawing from management examples described below.

Show it

Fig. 1 is a positive fixation of the joint to be joined parts and exposure to radiation energy

Fig. 2 the connection of butt joint surfaces by means of radiation energy.

The joining of molded parts made of thermoplastics by welding with high-energy radiation is easy to carry out if one joining part 1 ( FIG. 1) consists of radiation-absorbing material and the second 2 consists of radiation which is at least partially transparent but can be welded well to the first part.

Due to the high-energy radiation 3 , for example laser beams which penetrate through the permeable or partially transparent joining part onto the joining surface 4 of the absorbent joining part 1 , the latter is melted and also heats the joining surface of the non-absorbing part 2 , since the melt - due to the out expansion to a larger volume - is also able to bridge smaller gaps. Thus, when generating a sufficient melt volume, a welding pressure is built up from the inside. When the parts cool down, this pressure is reduced again.

When welding with high-energy beams, in contrast to other welding methods, such as vibration or ultrasound, only a small area of the joining zone is melted ( Fig. 2), the remaining joining zone acts as a spacer that absorbs the welding force applied from the outside. It is therefore important that no melt is lost due to flashing, so that no vacuoles or internal stresses due to shrinkage occur during cooling.

Furthermore, the avoidance of melt expulsion is of great advantage with regard to the appearance and function of the molded parts and saves any rework that would otherwise be necessary. Constructive measures, such as are necessary to cover the shoots, can also be omitted. For example, if the joining surfaces abut each other on all sides, an edge region 5 ( FIG. 2) not acted upon by the energy radiation is observed.

The mutual fixing of the joining parts 1 and 2 takes place according to the invention by positive locking, z. B. by snap connections or threads or internal frictional connection, such as screw connections or magnets. This fixation only needs to be dimensioned so that the locally occurring welding pressure, which moves along the seam contour with the beam guide, is absorbed. The parts can then be guided, for example by a robot, in such a way that the weld seam contour is always freely accessible from the high-energy beam. A fixation to be applied from the outside would grip both parts to be joined and would therefore considerably impede the beam guidance and mechanically stress the parts. The Relativgeschwin speed between the welding beam and the seam to be welded, i.e. the feed rate, depends on the material and its wall thickness as well as on the seam width and the beam power and is usually between 0.5 and 10 m / min.

Almost everyone is for welding with high-energy beams Suitable for thermoplastics. The permeability or absorption of the Radiation is both of the thermoplastic type and the additives, such as Fillers and pigments as well as wavelength and energy density of the rays used. To connect non-thermoplastic joining parts can do this with thermoplastic coatings on the joining surfaces the.

For the welding process according to the invention and the beams of an Nd: YAG laser that are preferably used for this purpose, the following are particularly suitable as permeable or partially permeable thermoplastics:
Polyolefins, polyamides, polyformaldehyde, PMMA, PBT, PET. Styrene polymers and copolymers, polysulfones and others are also suitable.

The required radiation absorption of thermoplastics is through various additives to the desired penetration depth adjustable. The most diverse colorants, ins especially soot or nigrosine in a concentration of 0.01 proven to 0.10%.

Other additives, for example glass fibers, glass balls and others Fillers increase the scatter of radiation in the parts and reduce the depth of penetration, but do not prevent completely penetration, so that even such materials are conditionally suitable for parts to be irradiated. This too filled thermoplastics can be adjusted using special additives  bar that they absorbed the high-energy radiation in the surface beers.

Laser beams are used as high-energy radiation, for example a wavelength between 0.50 and 10.90 microns, preferably between between 0.70 and 3 µm. The generation of radiation and their properties are described in the relevant literature ben. All laser sources must be used, the thermoplastics can heat, especially lasers in the infrared range emit. It is preferred for welding thermoplastics the Nd: YAG laser is used, but for many applications the CO₂ laser is also suitable.

With a combination of non-absorbent and absorbent material becomes the joining surface of the absorbent Irradiated lower part through the upper part and through the Absorption in the surface heated and melted. Here it is advantageous if the angle of incidence α is as small as possible is to minimize losses due to reflection.

When welding joining parts made of highly absorbent mate rialien and with butt welds is also a radiation in the welding plane possible. The seam width then corresponds to the on penetration depth of the beam.

Claims (4)

1. A method for welding plastic parts with the aid of radiation energy, characterized in that the parts to be connected are first fixed to one another in the correct end position by positive locking or internal frictional connection and the joining surfaces are brought into contact and then exposed to radiation energy until in the intended welding zone, the plastic parts are melted, thereby joining, and the plastic materials connected in this way are solidified by cooling. 2. The method according to claim 1, characterized in that at butt joint surfaces on all sides an edge area not affected by the energy radiation is observed. 3. The method according to claim 1 and 2, characterized in that as energy radiation laser beams of a wavelength between 0.50 and 10.90 µm, preferably between 0.70 and 10.64 µm be used. 4. The method according to claim 1 to 3, characterized in that for welding non-thermoplastic plastic divide these on the joining surfaces with thermoplastic art be coated material.