How to adjust the size of the fixture for the lsr injection molding machine | Lsr injection molding machine suppliers

Aug 23, 2021

SIZING THE CLAMP

The first thing to consider is the most obvious: The platen size must meet space requirements of the mold. Secondly, when specifying a clamping system that utilizes tiebars you need to review the distance between tiebars, and when specifying a tiebarless clamping system you must pay attention to the frame or drop-out width. This specification is particularly important if the parts are going to be brushed out of the mold or ejected and allowed to drop into a chute below the machine. A tiebarless system offers greater flexibility for auxiliary equipment such as core-pulls or robot movements into the molding area.

When specifying the size of clamping unit, it’s most important to remember that the clamp force must be able to overcome the expansion of silicone during vulcanization (curing). The standard rule for silicone is to allow 2 to 3 tons/in.² of projected part area. Additional items to consider for clamp size specification are part cross section and mold construction. Because LSR material expands significantly during cure, you may want to consider higher clamping forces for molding parts with a very thick cross section. For parts with a thin cross section (0.005 to 0.010 in.), such as diaphragms, the opposite is also true. Although such thin parts may have a very large surface area, the expansion of the silicone at such thinness is limited. The rate of expansion can also be controlled, to a certain extent, by processing with lower mold temperatures and extended cure times.

Mold construction must also be taken into account when determining the required clamp force. The clamp force must be high enough to maintain the correct force distribution across the cavity land. This is particularly important to consider when specifying a machine for a multi-cavity mold to produce very small articles. The total surface area of the part may be very small, so you must instead consider the cavity insert size. Also, use of preloaded cavities and/or spring washers may have an impact on the required clamp force. It is best to consult with your toolmaker and machine supplier together. For these reasons, the machine size for LSR molding is most often based on platen dimensional requirements instead of clamp force—which makes the tiebarless design a good option.

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