AWS WHC-5.08:2015

Plastics
Scope : made in one step by pouring the heated polymer into a cooled mold. The most common molding methods are injection molding or a press forming operation. Welding is performed in microseconds, which results in high productivity. Raw materials, petroleum, and natural feedstocks are abundant for the production of plastics. Most natural feedstocks are biologically-based and renewable, often derived from plant oils. While only a small fraction of crude oil is converted into polymeric materials, polymers have a significantly higher value than fuels; this contributes to the reduction of fuel consumption through weight reduction in aerospace and other transportation applications. Polymers are commonly produced from renewable materials. The infrastructure for recycling is widespread, with the result that new products are being developed around a steady supply of recyclable materials. Recycling is mandatory in many countries for manufactured items after they have served the original purpose. Diverting recycled materials to possibly less demanding applications in a new product, as is usually the case, takes supply pressure off virgin feedstocks. This cultural shift means the welding engineer may be challenged with welding mixed or recycled materials rather than new materials. Welding conditions for recycled materials may not be the same as for new materials same because of variations in overall purity. The welding of all thermoplastic material is based on fusion processes. On heating, the thermoplastic softensor melts, or both, and forms a fusible layer on the faying surfaces of the workpieces.