Injection molding is to mold molten plastic into a closed mold with a lower temperature through a nozzle under high pressure. Both thermoplastics and thermosetting plastics can be injection molded. In the production of packaging containers, it can mainly produce various box-type packaging containers, such as various turnover boxes and small boxes. For box-type packaging containers, the following aspects should be considered in structural design.
Wall thickness of container
The design of wall thickness mainly considers three aspects: one is thickness; the other is uniformity; the third is smooth transition.
① Thickness: The wall thickness of the container is mainly determined by its use, type of plastic, structure, etc. For thermoplastics, it should not be less than 0.6mm, usually 2 ~ 4mm. For thermosetting plastics, because of its poor fluidity, the thickness should be larger, 1.6 ~ 2.5ram for small parts and 3.2 for large parts ～ 8mm, the maximum does not exceed 10mm.
② Uniformity: The uniformity of the wall thickness has a great influence on the quality of the container. If the thickness difference of a container is too large, it will cause uneven shrinkage and cause defects such as deformation and cracks. Therefore, the structure should be designed with equal thickness as much as possible.
③ Gently transition: In some containers, some parts must have different thicknesses due to structural requirements, such as the corners of the container. At this time, a gentle transition should be used to avoid sudden cross-sections.
2. Increase stiffness
Plastic is relatively flexible, and the rigidity of the container made is poor, and the turnover box container sometimes has a large load capacity. Therefore, various structural measures should be taken to improve the rigidity.
① Adding ribs: The ribs can enhance the strength and rigidity of the container. The basic requirements for stiffeners are as follows: the number should be large, the wall thickness should be thin, the height should be short, and there should be sufficient slope. toughness;
② Improve the shape: Box-shaped containers are mostly rectangular thin-walled parts, which are easy to deform. Various strengthening measures should be taken to slightly convex the four side walls of the container to increase the rigidity. It is a band shape on the side wall to prevent distortion. Reinforcement; edge enhancement to prevent mouth deformation at the edge of the container; bottom reinforcement designed to be corrugated and arched at the bottom of the container.
③ Reasonable support: The bottom area of the box-shaped container is large, but it is not reasonable to use the entire bottom surface as a support. Because the bottom is slightly arched, it cannot be leveled. Therefore, the surface support should be changed to a linear or point support, and a convex edge support (that is, a line Support); raised foot support (ie point support); the height of the protrusion is generally 0.3 ~ 0.5mm.
④ Corner: The corner is the intersection of two or three faces. No matter what the shape of the container is, the corners must be rounded at the intersection. This can greatly increase the rigidity of the container and improve the plastic filling model. It can disperse stress and reduce deformation.
3. Draft angle
In order to facilitate the demoulding of the molded part, a suitable demoulding slope must be considered when designing the container. The demolding gradient is too small, the demolding is difficult, and the surface of the container is damaged; if the demolding angle is too large, the dimensional accuracy is affected.
The demolding gradient varies with the shape of the plastic part, the type of plastic, mold structure, surface roughness, and molding method. Generally speaking, the commonly used slope of plastic parts in the direction of demolding is 1º ~ 1.5º, and the minimum is not less than 0.5º.
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