Forming processes thermoforming

This is an extension of the cold forming process. It uses thermoformed B-stage thermoset reinforced plastic (RP) skin to improve surface and other characteristics to a cold molded thermoplastic. The mold is closed and the fast, room temperature curing RP plastic system hardens. The finished product has the smooth TP-formed sheet. 

Dow s patented scrapless forming process is identified as the SFP process. An extruder produce a biaxially oriented sheet (Chapter 5). In turn the sheet is slit and cut into square blanks. These blanks are heated and pressed into circular disc with a lip. Immediately or latter after reheating, the disc is thermoformed into a shape such as a cup. 

Sheet is thermoformed into a product by one of the forming process. To reinforce or rigidize it, one side that is usually the back surface of the formed sheet receives a spray-up of reinforced plastic (Chapter 15). 

Laminating lends itself to the manufacture of resilient products with a large flat surface area and excellent surface properties. These products can be converted to their final form by thermoforming and insert molding. This method avoids the use of paint with its negative side effects, that is, the influence of solvents on the physical properties of the injection-molded part (tension and plasticizing effect). The lamination process also circumvents the optical problem of flow and weld lines. 

Thermoforming has close similarities with vacuum forming, except that greater use is made of air pressure and plug assisted forming of the softened sheet. The process is invariably automated and faster cycle times are achieved than in the vacuum forming process. Only thermoplastic sheet can be processed by this method. 

Polyethylene, polyvinyl chloride and polypropylene are easily worked utilizing ordinary wood or metal working hand and power tools. Being thermoplastic, these materials can be easily thermo-formed as well as cut, sawed, drilled and tapped. In the heat forming process, electric ovens are generally used which can maintain good thermal control. Of the three thermoplastics, polypropylene requires the more finite thermal control. Table III provides approximate time and temperature relationship required for thermoforming these three plastics. 

However, they can also be transfer or compression molded, solid state formed or thermoformed. PC is the matrix phase in most of these blends. The impact modifier can be PE, ABS or acrylic copolymer, e.g., MBS. The blends show good processability, heat resistance, ductility, HDT, high modulus, impact, tensile and flexural strength over a wide temperature range, good adhesion, solvent, chemical, and UV resistance. They can be painted, hot stamped, metallized and plated. Some blends (containing PB as impact modifier) may have poor weatherability. The blends are mainly used in the automotive industry. 

This review on vacuum thermoforming can be related to most of the other forming processes. With a vacuum system a sheet is subjected to heat to meet its optional processing temperature, or technique that forces it against the shape of a mold. The hot, pliable material is moved rapidly to the mold (for example, by gear drives) and/or is moved by an air pressure differential, which holds it in place as it cools. When the proper set temperature is reached, the formed part can be removed and still retain its shape. 

This term refers to the normal method of most thermoforming processes in which a material is formed at a temperature above the melting point in semicrystalline polymers or above the softening point in amorphous polymers. See Pressure Forming, Vacuum Forming and Thermoforming,... 

Thermoforming is one of the simplest, most economical plastic-forming processes. There are numerous variations of the thermoforming process, but most involve heating... 

Keywords thermoforming, solid-phase pressure forming (SPPF), vacuum forming, pressure forming, processing window, viscoelasticity, residual stress, sagging, shrinkage, quality control. 

Formability. Materials with a broad softening range, such as PS and PC, can be thermoformed into deep-draw package shapes. Crystalline polymers, eg, HDPE and PP, are more difficult to thermoform, but solid-phase forming processes below the melting point are possible. Multilayer semirigid barrier containers are made by Shell s Solid Phase Pressure Forming Process and the patented Dow... 

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