Plastic shell products injection mold design principles

All products are almost a process from scratch, ID-MD-mold-production, we must first have good ideas, product features, appearance, simply speaking, the product is first designed, the appearance is determined by the customer. , structural design, verification and then to mold manufacturing and production. Although all products should be perfect, but many times engineers have to succumb to reality, product design must meet the requirements of mass production, that is, to be able to achieve mold manufacturing. For example, a plastic mold is a tool that is moved by a plurality of inserts and a male and female mold to satisfy the molding of the product. Therefore, there must be sufficient space for movement between the plurality of inserts, and the plastic is pressed from the particles to the solution and then to the mold cavity. Molding in which the molecular form is constantly changing, the product also needs to comply with some guidelines in the design process.

Here we will come together to understand what principles should be paid attention to in the design of plastic shell products:

First, the wall thickness design principle

The basic design code for plastic materials depends on the external force of the product, whether it is supported by other parts, the number of columns to be supported, the number of extensions and the choice of plastic materials. The general thermoplastic wall thickness design should be based on 4mm. From an economic point of view, thick products not only increase material costs, but also increase production cycle and increase production costs. From the point of view of product design, the possibility of excessively thick products increasing the porosity of the product greatly impairs the rigidity and strength of the product.

The temperature of the plastic mold is lower than the melting temperature of the plastic material. When the plastic material just enters the mold from the nozzle, due to the lower temperature of the mold, a layer of crystal is formed on the surface of the mold, which is about 0.2MM, which can pass The space of the rubber is very small, it requires a very large injection pressure, and it is very likely that it will not be filled. Now some thin-wall injection molding technology is born. The ideal wall thickness distribution is undoubtedly the uniform thickness of the cut surface in any place, but it is inevitable that the wall thickness will change in order to meet the functional requirements. In this case, the transition from thick rubber to thin rubber should be as smooth as possible. Too sudden wall thickness transitions can result in dimensional instability and surface problems due to different cooling rates and turbulence. Product wall thickness and uniformity Plastic mold manufacturers will evaluate the mold development in the early stage to ensure that the product has a good appearance.

Second, the design principle of the reinforcement

The role of the ribs The ribs are an indispensable part of the plastic part. Ribs increase the rigidity and strength of the product without significantly increasing the cut area of the product. It is especially suitable for some plastic products that are often subjected to pressure, torsion and bending. In addition, the ribs act as internal cavity support cavities, which contribute to the influx of plastic into the part of the component. Design principle Reinforcing ribs are generally placed in the direction of extension of the non-contact surface of the plastic product. The position of the ribs should be selected in the direction of the product's large stress and large offset. It is also subject to some production considerations such as cavity filling and shrinkage. And demoulding, etc.

Third, the principle of column design

1. The pillar protruding rubber wall thickness is used to assemble the product, separate the objects and support other parts.

2. Hollow struts can be used to insert parts, tighten screws, etc. In the mold manufacturing process, the plastic mold factory usually adds craters to the top of the column to prevent the top of the column from shrinking due to excessive wall thickness.

Fourth, the design principle of the mouth

General size of the inverse wishbone design

A. The mouth is closely related to the anti-stop. The effect of the counter-stop is opposite to that of the stop, which prevents the B-shell from deforming outward and prevents the A-shell from retracting.

B. The anti-stop is made on the shell of the mother's mouth.

C. When designing the anti-stop, pay attention to the 8.0MM 公  at least 6.0MM from the unilateral buckle, because the buckle should be deformed.

Five, the principle of the buckle design principle

The design of the buckle is generally inseparable from the cantilever type; the so-called cantilever type actually uses the characteristics of the flexural deformation of the plastic itself to return to the original shape through elastic recovery.

Advantages: The buckle provides a product assembly method that is not only simple and fast, but also low in cost and high in reliability; the buckle is easy to assemble and disassemble, and the designer's assembly idea is fully utilized. Because the combination part of the buckle is formed at the same time when the finished product is produced, it is not necessary to cooperate with other fastening components such as screws and mesons during assembly. The assembly process of the buckle is also very simple, generally only requires one insertion action, no need for rotary motion or The work of positioning the product before assembly can be done by simply interlocking the two sides of the combination.

Disadvantages: The weakness of the buckle device is the two combined parts of the buckle. The hook-shaped extension and the flange portion are easily deformed after repeated use for many times. Because of the fatigue effect, the part of the bottom connected product is buckled. In the case of breakage, the buckle after the break is difficult to repair, which is more common in brittle or fiber-incorporated plastic materials. Because the buckle is molded at the same time as the product, the damage of the buckle is also the damage of the product. The remedy is to design the buckle device to be shared by multiple buckles at the same time, so that the overall device will not be unable to operate due to the damage of the individual buckles, thereby increasing the service life. Another weakness of the buckle device is that the tolerance of the relevant size of the buckle is very strict. The excessive position of the buckle is easy to form the buckle damage. On the contrary, if the position of the buckle is too small, the assembly position is difficult to control or the combined part is too loose. phenomenon.

In the design of the casing plastic products, due to the above principles, usually after the product is designed, some hand plates will be used to verify the overall appearance and structure of the product. If the overall feeling is satisfactory, you can start to choose the mold manufacturer, usually the plastic mold manufacturer. The structure of each plastic part will be reviewed and analyzed from the above aspects to ensure that the product meets the assembly, structure, strength and ensure the good appearance of the product, simplifying the product structure as much as possible, saving mold development cost and improving injection molding production efficiency. .