Design Guidelines: Liquid Silicone Rubber Molding
|SIZE||12 in. x 8 in. x 4 in.|
|VOLUME||26 cu. in.|
|DEPTH||No greater than 2 in. from any parting line; deeper parts are limited to a smaller outline|
|PROJECTED MOLD AREA||65.5 sq. in.|
Typically, Protolabs can maintain a machining tolerance of +/- 0.003 in. (0.08mm) with a linear tolerance of +/- 0.01 in./in. (0.01mm/mm).
|PM-F0||non-cosmetic, finish to Protolabs’ discretion|
|low-cosmetic, most toolmarks removed|
|600 grit stone, 10-12 Ra|
|PM-T1||SPI-C1 + light bead blast|
|PM-T2||SPI-C1 + medium bead blast|
|SPI-A2||grade #2 diamond buff, 1-2 Ra|
|MINIMUM FOR SHUT OFF||3°|
|MINIMUM FOR LIGHT TEXTURE (PM-T1)||3°|
|MINIMUM FOR LIGHT TEXTURE (PM-T2)||5°+|
While 1 degree of draft is common in LSR parts, zero draft can occasionally be tolerated on shallow parts. The nature of LSR allows the rules of draft to be stretched more so than thermoplastics, if mold construction permits.
Adding draft angles to design, even on LSR parts, helps facilitate ejection of a part from a mold, and improves overall moldability.
LSR molding has the ability to produce parts with undercuts. Many simple undercuts can be easily removed by the press operator without mechanical assistance. Each part will be reviwed on a case by case basis for feasibility.
Undercuts, such as those shown, can complicate and, in some cases, prevent part ejection, so eliminate them if possible.
Some part corners will have a radius rather than a sharp edge since we use an automated CNC milling process to make the mold for your parts. This typically does not require a change to your model, but resulting radii are identified before the mold is milled.