Design of the Ejection System of Plastic Injection Mould-lytereng.com

Design of the Ejection System of Plastic Injection Mould

2022-09-21

Lyter Engineering_Design of the ejection system of plastic injection mold

A good mold reflects the comprehensive level of a plastic injection mould maker. A good design plastic injection mould requires continuous improvement of various technologies. Today we will talk about the ejection system of the mold.
Based on years of work experience, we have summed up the principles of ejectors arrangement: A, It cannot affect the appearance of the finished product; B. Ejection allows the finished product to be ejected at the most stressed point; C. Always try to arrange ejectors in the flat position of the finished product (avoid on the inclined or curved surface) D. Always arranged ejectors by the big steps of the part (beside the deep rib for example) E. Arranged at the overhang position where it is easy to be broken and deformed when the mold is opened) F. Use a set of ejectors as much as possible in the same mold.

1. Ejection stroke

The ejection stroke generally stipulates that the ejected product is 5~10mm away from the mold. When molding to produce plastic injection molded parts some barrel-shaped products with simple shapes and larger draft angles, the ejection stroke can be 2/3 of the depth of the finished product, as shown in the figure below.

2. The ejectors position

After cooling down, the plastic material will produce shrinkage stress on the steel parts, and there is a phenomenon of clinging. The thickness of the finished product on both sides of the hole-shape feature is the weakest, and the ejector should be set to eject it. The ejector should be set just below the vertical wall thickness of the finished product. In order to facilitate ejection. Ejectors are often arranged under the cross rib, which can be ejected and exhausted. When ejectors are arranged on inclined surfaces or curved surfaces, it is necessary to consider the key-in of the countersunk head and the tip of the ejector pins will slip during ejection.

3. Ejection types

A. The round ejector is the most common ejector components. It has the advantages of simple processing, good strength and long life. However, when the ejection surface of some products is relatively small, the shouldered ejector will be used. The shouldered ejector is mainly aimed at solving the problem that small ejector is not robust enough, to increases the strength of them.

B. Blade ejectors are mostly used where the ribs of some products cannot be used as round ejectors.

C. The sleeve ejector is mostly used in the screw columns and other similar positions on the product.

4. Ejection blocks:

In some molds, because the side wall of the product is too deep, it is easy to wrap the mold core insert and generate a large demoulding force. In order to make the finished product easy to demould, the ejector block is used together with ejector pins. And there is clearance on L section to ease the wear on the mold insert. When it is not easy to lay out ejector pins for such frame-shaped products, and this kind of products will be deformed when the ejection force is unbalanced, a combined ejection will be used for blocks and pins.