Due to the complexity of the product structure and the special materials produced by insert molding, the details that need to be paid attention to in product design and mold design are determined. The insert molding process can not only be used for metal insert processing, but also as a means of holding continuous metal parts stamped on metal bands (hoops). By continuously supplying metal hoops to the mold, efficient injection molding can be achieved.
Guidelines for designing the thickness of insert molding products
Generally speaking, the average plastic thickness of 1.5mm can meet the filling flow characteristics and molding process requirements, and the combination of the insert and the plastic part is firm. The demoulding slope is larger than that of ordinary plastic parts. If the surface roughness of the product is poor, the friction force is large during demoulding.
Guidelines for shrinkage design of insert plastic products
The finished product of insert molding has a certain shrinkage rate. Since the insert part of the product does not shrink, it is necessary to shrink in sections and in different directions according to the area of the insert in the product to achieve the size requirements of the product. Most of the products with inserts do not shrink; only a small number of plastic parts made of plastic materials account for a small number. In most cases, the insert part does not shrink, while the other parts shrink in different amounts in the three directions of XYZ according to the product structure. Since the shrinkage rate is set in sections, the integration skills after the sections require a high level of design experience and level for the mold designer.
Practical Design and Manufacturing Guide for Insert Molds
Insert molding products are usually positioned by setting positioning bosses on the mold, and the insert needs to be accurately positioned in the X and Y directions. The insert positioning hole is preferably a flat hole, and it is best to avoid bending or stretching surfaces (such surfaces have poor precision and excessive deformation). The height of the positioning boss and the insert is 1.5-2 times the thickness of the insert. The head should have as large a taper as possible to facilitate the placement of the insert. The minimum height of the positioning boss is 3mm to facilitate the placement of the insert. For the elongated structure with a cantilever beam structure in the insert, the mold needs to be positioned auxiliary in addition to the main positioning. The auxiliary positioning boss is only used to correct the deformation during the placement of the insert to prevent die pressing. The side of the boss can be made into 0.1~0.2mm of material removal. The mold structure that uses the insert for sealing should be made as close to the break as possible to avoid being broken, especially for slender structures, to prevent die pressing.
After the insert is positioned in the mold, it needs to be fixed, because the insert may fall due to shaking during the closing process of the mold, causing die pressing. In the process of insert molding, suction cups are generally used to absorb inserts. The position of the suction cups to absorb inserts should be as flat as possible to avoid bending and stretching surfaces. If the positioning boss of the product produced by insert molding is symmetrical but the structure is not symmetrical, special attention should be paid to placing the insert in the opposite direction when placing the die. Therefore, it is necessary to add an anti-fool boss structure, and the anti-fool boss must be higher than the positioning boss. The temperature conditions of the insert molding process are generally: mold temperature is 65-120 degrees, and material temperature is within the range of 260-320 degrees. Of course, different raw material ratios have different temperature ranges. The material temperature of the material is an interval temperature, and the supplier will provide its upper and lower limit temperatures. The upper limit temperature indicates the temperature at which the material begins to carbonize and decompose, and the lower limit temperature indicates the temperature at which the material begins to flow. If the temperature is lower than the lower limit during molding, the material’s fluidity is insufficient, and insufficient plasticization of the molding screw is likely to cause the screw to break and the product cannot be filled normally. If the material temperature is higher than the upper limit, the viscosity decreases, it is easy to carbonize and produce gas, corrode the mold core and the molding machine screw, and the product is easy to be brittle, and it is difficult to pass the relevant mechanical property tests. The temperature of the mold needs to be adjusted within the temperature range of the material according to the structure of the product and the structure of the mold to find the optimal temperature.
Advantages and Limitations of Insert Molding
Insert molding has many advantages. It allows for relatively easy manufacturing of products that contain multiple materials or colors. It takes less time (and therefore costs less) to manufacture than other manufacturing methods that require transferring the part to an entirely different mold or machine. Insert molding reduces the need for assembly of the product by building the part in a step-by-step manner, which results in a more robust overall design. Insert molding is often the best manufacturing option for large production runs or products with multiple colors and multi-layer designs, but there are some limitations to be aware of. Similar to injection molding, insert molding has high upfront costs. The process uses metal to build and modify the mold, which is time-consuming and expensive. This means that customers need to produce a large number of parts to spread these costs.