Thermoforming
Thermoforming is a one sided process that starts with a flat sheet. All mold features will translate through the part and be present on the non-mold side as well. The dimensionally critical side of the part should face the mold.
Draft Angles
Draft is the amount of taper on a sidewall of a thermoformed part. Larger draft angles will produce more consistent wall thicknesses. The recommended minimum draft angles are 2 degrees for female molds and 3 degrees for male molds.
Radii
Larger Radii make better quality parts. The minimum recommended radius is equal to the starting material thickness. In a female, pressure formed part, a much smaller radius (approximately 0.030”) is achievable.
Draw Ratio
Draw refers to the ratio of height to width of the part at any location. A draw ratio of less than 1 to 1 is preferable. Deeper draw ratios may be achieved with special techniques.
Texture
Texture can provide a consistent appearance and a more durable surface finish. The thermoplastic sheet can be textured prior to thermoforming or the part can be pressure formed in a textured mold. A pressure form mold can add multiple textures as well as non-textured areas to a single part.
Undercuts
An undercut is an area where the plastic is trapped in the mold so the part cannot release. Undercuts are designed into parts for various reasons, including hiding trimmed edges. Most undercuts require specialized tooling with moving components.
Dimensions
The mold side of the part is controlled while the other side will vary. Drawings should be dimensioned to the mold side of the part.
Tolerances
Standard Hole to Hole Tolerance: +/- 0.015” up to 12”, +0.001” per inch above 12” Standard Forming and Trimming Tolerance: +/-0.030” up to 12”, +/-0.060” from 12” to 60”, +0.001” per inch above 60”.
Stiffness/Rigidity
Formed in details such as ribs, domes and other features can be added to a part to increase rigidity. This can often lead to a reduction in material thickness, which is a cost benefit.
