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Plastic Injection Mold Design

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Plastic injection mold design plays a very important role in success of a mold build.

A good injection mold design can save much time and money for develop the mold.

We can say all the manufacturing are built on the basis of the plastic injection mold design, that is why Creative will make DFM report and hold plastic injection mold design meetings to optimize the product and mold structure. A good mold designer should follow the base points of mold design.

Here are some base points of plastic injection mold design.

1.Steel Selection

The selection of tool steel will depend on the quantity and quality of parts to be produced. For high volume production, the initial expense of quality tooling is a sound investment.

A wide variety of tool steels are available for injection mold construction. Soft metals, such as aluminum and beryllium copper, can be used for prototype parts or short production runs up to 10,000 parts.

Some part designs may benefit from the use of higher thermal conductivity materials such as beryllium copper. This material is less durable than steel and may hob or wear faster than steel if used at the parting-line. Beryllium copper can be used for inserts, slides or cores to increase heat transfer rates and reduce cycle times. In cases where there is a long draw core, a fountain-type bubbler may be beneficial.

2.Sprue and Sprue Puller Design

The sprue should have sufficient draft, from 1° to 3° to minimize drag and sprue sticking. Longer sprues may require more taper (3° - 5°), as shown in Figure 1. Typically, the sprue diameter should be slightly larger than the nozzle diameter. Permanent surface lubricant treatments have also been used successfully

3.Conventional Runner Design

A balanced runner configuration is critical to achieve uniform part quality from cavity to cavity. In a balanced runner system, the melt flows into each cavity at equal times and pressure. The runner balance can be designed by using computer mold-flow analysis programs and verified by performing short-shot studies.

An unbalanced runner may result in inconsistent part weights and dimensional variability. The cavity closest to the sprue may be overpacked and flashing may occur. As a result of overpacking, parts may also develop high molded-in stresses, which lead to warpage.

4.Gate Design and Location

Most conventional gating types are suitable for processing plastic material. The type of gate and the location is the most important things of mold design.

Part packing

Gate removal or vestige

Part cosmetic appearance

Part dimensions, including warpage.

5.Mold Venting

Mold venting is critical to the quality and consistency of the finished part. Venting is required to allow the air in the sprue, runner and cavity to leave the tool as the melt flows into the cavity. Inadequate venting may cause short-shots, poor surface appearance, or weak weld-lines. Potential air traps in the part design can be predicted by flow simulation software. Once the tool has been built, short-shot studies can be used to find the critical venting areas.

If you want to know more about basics of injection mold design, please feel free to contact us.

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