Design principle of ejection system
Product ejection is the last step of the injection process, the ejection quality will directly affect the quality of the product, and design should follow the principles.
(1) The principle of equilibrium layout: ejector pins must be evenly arranged in order to prevent the deformation of the product.The Symmetric product should be ejected by the ejector pins symmetrically arranged, the rib and boss should be ejected by the Symmetric pins layout
(2)The principle of aesthetic.The layout need attention to the aesthetic.The ejector pins marks should be on the place invisible after assembly. This is especially important for the transparent products. Any ejector pins would leave the marks on the products, and the continuous wear in the process will make those marks increasingly evident.
(3) The effective principle. The ejector pins should be arranged to the place for ejection where the max holding force occurs. Those places include the edge, corner, deep groove and deep boss…the ejection force should apply to the lowest area of parts, and the parts should be pushed instead of pulled out of the mould.
the ejection force should apply to the lowest area of parts
(4) Optimal location principle. Ejection force must apply on the location of the maximum ejection force need with good rigidity and strength, such as wall, ribs, boss bottom, side wall, the ejection pins diameter should be as big as possible to prevent deformation or damage of the product. Try to avoid ejection force acting on product thin plane to prevent the rupture, thru and white spots of product. The barrel products should adopt stripper plate instead of ejector pins for ejection.
(5) Safety first principle.In the mold with the slide core and the lifter, the ejector pins are arranged outside of projection plane of slide and the lifter. If it cannot be avoided, then design the ejector pin first reset mechanism.
(6) Other issues
Convenient design for the gate falling, and the ejector pins should be added at the corner of the gate..
A deep hole components(boss, positioning column, etc. ) generally need dowel pins or ejector pins on both sides of the column.
Solid pillar bottom need ejector pins for ejection, which can prevent the trapped gas and the spark relics remaining.
Plastic mold for PVC material couldn’t adopt ejector pins with groove top and PVC melt material couldn’t flow directly to the cavity. But PVC soft plastic doll mold (beryllium – Copper mold) could use this way, and design is convenient for gate removal and the balance product ejection. And the overflow groove is 2mm away from the edge of the cavity.
Distance between the ejector pins, support pillar and the cooling pipe should be 3 mm at least.
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