Pressure forming is used when greater definition, variety of surface textures, small radii, and molded vents and pockets might be required. Pressure forming is generally more expensive than vacuum forming, but tooling costs are only a fraction of the cost of other methods.
Molds that are female (negative) should be aluminum and preferably water-cooled. Parts designed for short runs or prototype may be made of epoxy or wood, depending on complexity of shape, depth of draw.
Dimensions – Tolerances
Please see the sheet titled “Standard Manufacturers’ Tolerances” for guidelines.
Draft angles for female (negative) aluminum molds should be 2° – 4° to prevent lockup of part in mold. Deep parts or complex configurations, texturing on the tool side, may require more draft angle.
Radii and Fillets
Radii and Fillets may be less than in vacuum forming. Sharp corners may be attained on shallow draw areas. Keep in mind that larger fillets and radii make stronger, stiffer parts and create thicker corners.
As in vacuum forming, material starting thickness will become thinner when a part is formed. However, the amount of thinning will depend upon shape, size, depth of the draw, radii and fillets. For any special design considerations in pressure forming, please contact Mayfield Plastics’ engineering team.