Insufficient pressure can result in incomplete forming, poor detail reproduction, uneven wall thickness, and weak spots in the final product. The material may not properly conform to the mold, leading to defects like webbing or bridging between high points.

Excessive pressure can cause material thinning, especially in corners and deep draws. It may lead to tearing, increased cycle times (as the material needs more time to cool under pressure), and higher energy consumption. In vacuum forming, too much pressure can distort fine details or cause the mold to shift.

Stiffer materials (like PET and PVC) generally require higher forming pressures than more flexible materials (like PP and PS). The material's melt strength and elongation properties at forming temperature significantly influence the pressure needed for proper forming.

The safety factor accounts for variations in material properties, machine performance, and environmental conditions. It ensures reliable forming even with minor fluctuations in these parameters. A typical safety factor of 15-20% is recommended for most applications.

For large areas, consider segmenting the mold into multiple cavities, increasing sheet thickness, or using higher pressure machines. The pressure required increases with the square root of the forming area, so large areas can quickly require impractical pressure levels.

Start with the calculated pressure and perform test runs with your specific material batch and equipment. Measure part quality (wall thickness distribution, detail reproduction) and adjust the pressure as needed. Document successful settings for future reference.