Air slip forming

Figure A.7 Air-slip forming process. (Courtesy of Dow Chemical Company)...

E. Air-slip forming is similar to vacuum snap-back except that heated sheet is billowed up and mold rises to meet It. 

Vacuum air-slip forming (Fig. 10-12) is used to reduce thinning in deep-drawn items. The polymer is prestretched in a bubble shape prior to forming. When the bubble is evacuated, it drops around the mold. 

Develop a model to describe the vacuum air-slip forming (Fig. 10-12). Use the concepts of Chapter 2 to help in this endeavor. Illustrate how you would apply this for a sheet made out of polymethyl methacrylate. 

Air-slip forming bubble assist vacuum forming (qv). 

The air slip process uses a positive pressure billow sheet pre-stretch that is generated by the movement of a male mold towards the heated sheet that is clamped across a pressure chamber. The mold platen acts as a piston in the chamber and drives a volume of air ahead of it that serves to billow the sheet. At the full extent of its forward travel, the mold periphery seals against the sheet frame, and forming is completed by drawing a vacuum through ports in the mold. 

A polymer, typically polyacrylic acid of molecular weight 450 000, was dissolved in millipore water to a concentration of 1 mg ml at a pH of 4. A small amount of this solution was deposited on a clean glass cover slip and dried in air to form a thin polymer film. The substrate was then rinsed with water to leave only the strongly adsorbed molecules. An AFM tip was then brought down onto the surface in a 1 mM KNO3 solution. As the tip touched the surface, the... 

I. Combination plug-assist and air-slip is recommended in forming complex parts with high ridges. 

Once a stable de-aired slip h2 been formed it is desirable to pump it through 2 nylon filters with openings of 40 pm and 10 pm to remove agglomerates and coarse particles. 

The use of hydrostatic slideways - in which pressurized oil or air is employed - completely eliminates stick-slip and reduces friction to very low values but there are disadvantages in the form of higher costs and greater complication. 

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