Waveguide for plastic welding, arrangement for plastic welding, a welding method as well as a manufacturing method of a waveguide

A positive waveguide for plastic welding, comprising:

• an entry end defining an entry face for laser light,
• an exit end defining an exit face for laser light as well as
• a first and a second inner face which are arranged between the entry end and the exit end, which are arranged opposite to each other and by means of which laser light can be reflected, wherein
• a first distance between the entry end and the exit end defines a length of the waveguide and a second distance between the first and the second inner face defines the thickness of the waveguide, and
• the first inner face comprises a continuously curved concave shape which is part of a first spiral so that a radius of the first spiral from a point of origin of the first spiral to the first inner face varies continuously along the waveguide,
• the second inner face comprises a continuously curved convex shape which is part of a second spiral so that a radius of the second spiral from a point of origin of the second spiral to the second inner face varies continuously along the waveguide, wherein
• the thickness of the waveguide decreases continuously from the entry end in the direction of the exit end and
• an angle in the range of 30° to 150° is enclosed between the entry end and the exit end, wherein
• a first direction vector of a first straight line extending from the first inner face to the point of origin of the first spiral extends in the direction of the second inner face and
• a second direction vector of a second straight line extending from the second inner face to the point of origin of the second spiral extends away from the first inner face and
• the point of origin of the first spiral is different from the point of origin of the second spiral.