Thin-wall molding


Overview

The term "thin-wall" is relative. Conventional plastic parts are typically 2 to 4 mm thick. Thin-wall designs are called "advanced" when thicknesses range from 1.2 to 2 mm, and "leading-edge" when the dimension is below 1.2 mm. Another definition of thin-wall molding is based on the flow-length-to-wall-thickness ratios. Typical ratios for these thin-wall applications range from 100:1 to 150:1 or more.


Typical applications
Thin-wall molding is more popular in portable communication and computing equipment, which demand plastic shells that are much thinner yet still provide the same mechanical strength as conventional parts.


Processing
Because thin-wall parts freeze off quickly, they require high melt temperatures, high injection speeds, and very high injection pressures if multiple gates or sequential valve gating are not used. An optimized ram-speed profile helps to reduce the pressure requirement.

Due to the high velocity and shear rate in thin-wall molding, orientation occurs more readily. To help minimize anisotropic shrinkage in thin-wall parts, it is important to pack the part adequately while the core is still molten.

Molders should watch for excessive residence time, melt temperatures, or shear-all of which can cause material degradation.


Design
We recommend you design you part with styling lines and curved surfaces to boost stiffness and enhance part aesthetics. Impact strategies involve using unreinforced plastic housing to absorb the load or using filled thermoplastics to transfer it. For either case, you'll need to fasten internal components snugly, and avoid stress concentration and sharp notches.

Large gates, greater than the wall thickness, are generally used to ensure sufficient material flow during packing.


Computer simulation
To accurately simulate thin-wall molding under high pressure, high injection speed, and fast cooling conditions users should specify the following: