Processing, thermoplastics weld lines

R. Selden, Effect of Processing on Weld Line Strength in Five Thermoplastics, Polymer Engineering and Science, 37,205-218 (1997)... 

The entanglement of the polymer chains at the weld line is related to their diffusion rate, which is a function of temperature and melt viscosity of the polymer [95]. The holding pressure in the cavity and the injection speed can also affect the weld line strength [96]. Many predictive models for the weld line strength of thermoplastic amorphous polymers in relation to the viscoelastic properties and processing conditions such as the melt temperature, the mold temperature, and the holding time, have been proposed [97-99]. 

Fig. 9-30A. Ultrasonic bonding of thermoplastic products is adaptable to complex high volume products as well as for simple pieces. Shown here is a semiautomatic slide table ultrasonic assembly system that uses standard welding heads and power supply to weld polystyrene automotive defroster duct assemblies. The high frequency vibration generated by the head generates heat at the weld line for bonding. Fast welds are achieved by this process. Courtesy Sonics Materials, Inc.)...

Flash - In welding thermoplastics, molten plastic that seeps out of the joint area during the welding process. In molding, surplus plastic attached to the molding along the parting line. Flash must usually be removed before parts are considered to be finished. 

Clearweld is a further enhancement of the transmission laser welding process that provides designers with a tool to laser weld clear, coloured or opaque thermoplastics. Clearweld uses materials capable of strong absorption in the NIR spectrum which impart minimal colour. It can be used in number of ways, including, but not limited to, a coating at the joint line, inclusion within the substrate or application as a consumable film. Compared with previous technologies, it offers complete freedom in the choice of colour, reflectivity and transparency of the work pieces at visible wavelengths. 

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