Most plastic parts and car by injection molding, since these plastic member itself has a high design accuracy, so that these members can not use a conventional plastic injection molding, but must be precision injection molding techniques. In order to ensure the performance of precision plastic car parts, quality and reliability, injection molding of high quality, in line with the requirements of the product design of plastic products, plastic materials must, injection molds and injection molding process equipment and continuous improvement.
The main factors affecting the precision injection molding
Determination is based on precision injection molding precision injection molding products, namely products dimensional tolerances, geometric tolerances and surface roughness. To make precision injection molding must have a number of related conditions, and most essential is a plastic material, injection mold, injection molding machine and process these four basic factors. Design of plastic products, should be selected first plastic material and the plastic injection molding and precision can be performed must be selected those with high mechanical properties, dimensional stability, good creep resistance, resistance to environmental stress cracking of the material. Secondly, the choice should be based on plastic material, finished size precision, piece weight, quality and selection of the desired mold structure suitable injection molding machine. In the process, the factors that affect the precision injection products, mainly from the precision molds, mold shrinkage, as well as ambient temperature and humidity variation width products and so on.
In precision injection molding, the mold is one of the keys to obtain the required quality of precision plastic products, precision injection mold should earnestly comply with the product size, shape and precision requirements. But even if the mold precision, uniform size, the actual size of its molded plastic products also because of the amount of shrinkage differences inconsistent. Therefore, effective control of plastic shrinkage in precision injection molding technique is very important.
Mold design is reasonable or not will have a direct impact on plastic shrinkage due to the mold cavity size is plus size estimated by the plastic shrinkage obtained, and shrinkage is recommended by the manufacturer of plastic or plastic manual within a range of values, it is not only the form of the mold gate, gate location and distribution, but also to plastic crystal orientation.
Plastic shape, size, and distance to the location of the gate. Effect of plastic shrinkage mainly heat shrinkage, contraction phase transition, orientation shrinkage, shrinkage and elastic recovery, compression and other factors, and these factors with precision injection molding products, conditions or operating conditions. Therefore, the relationship must be considered in the design of molds and injection conditions of these factors and the apparent factors such as injection pressure and the mold cavity pressure and filling speed, injection melt temperature and mold temperature, mold structure and the form and distribution of the gate and the effect of the gate cross-sectional area, wall thickness, the plastic material content of the reinforcing filler, plastic material crystallinity and orientation and other factors. Also due to the above factors different plastic materials, other molding conditions such as temperature, humidity, continued crystallization, internal stress change after molding, the injection molding machine varies.
Since the plastic injection molding process is a process of the ED from the solid powder or pellets to liquid melt solid products change. From the pellets to melt, and then from the melt to the article, in the middle to go through the role of temperature field, stress field, flow field and density field, etc., under the combined effect of these fields, different plastics thermosetting or thermoplastic, crystalline or non-crystalline, and other enhanced or non-enhanced with a different type of polymer morphology and rheological properties. Any of the above factors will affect the field of physical and mechanical properties of plastic products, size, shape, accuracy and quality of appearance. Thus, the intrinsic link process factors and performance polymers, plastics and morphology between manifests itself through the plastic. These analyzes clearly intrinsically linked to the injection molding process to develop a reasonable, rational design according to drawings and manufacture molds, injection molding as well as a reasonable choice of equipment are important. Precision injection molding and injection pressure on the ordinary injection molding and injection rates are different, often using precision injection injection high-pressure or ultrahigh-pressure, high-speed injection molding to obtain a smaller shrinkage. Taking these various reasons, in addition to considering the design elements of the general mold design precision injection mold when, we must also consider the following points: ① appropriate mold dimensional tolerances; ② prevent mold shrinkage error; ③ injection to prevent deformation; ④ prevent releasing deformation; ⑤ mold manufacturing error is minimized; ⑥ prevent mold accuracy error; ⑦ maintain the precision molds.
Prevent mold shrinkage error.
Because of shrinkage due to the injection pressure changes, therefore, for a single cavity mold, the mold cavity pressure cavity should be consistent; as for multi-cavity mold, the mold cavity pressure should be a difference between the cavity is small. In the single-cavity or multi-cavity multi-gate gate case, you must at the same injection pressure injection, so that the cavity pressure is the same. Therefore, we must ensure that the location of the gate balance. In order to make consistent pressure in the cavity of the mold cavity, it is preferable that the gate at the entrance to the pressure consistent. The gate pressure equalization flow path and the flow resistance related. So, before the gate pressure equilibrium, should be balanced so that the circulation. Since the melt temperature and mold temperature have an impact on actual shrinkage, so the design of precision injection mold cavity, in order to facilitate the identification of molding conditions, we must pay attention to the arrangement of the cavity.
These are the cars precision plastic molding mold design points.
