How to control the dimension of injection molded products? ( part three)
Third, the usual production control
The occurrence of geometrical fluctuations after the forming of plastic parts is a common problem and is a phenomenon that often occurs:
1. Control of material temperature and mold temperature. Different grades of plastics must have different temperature requirements. The poor fluidity of plastic materials and the use of two or more kinds of mixture will have different conditions. The plastics should be controlled at the optimal flow. Within the range of values, these are usually easy to do, but the control of the mold temperature is more complicated. Different geometry, dimension and ratio of wall thickness of the forming parts have certain requirements for the cooling system. The mold temperature is largely Controlling the cooling time;
Therefore, the mold should be kept at an allowable low temperature state as much as possible, so as to shorten the injection cycle, improve the production efficiency, and the mold temperature changes, then the shrinkage rate also changes, the mold temperature remains stable, and the dimensional accuracy is stabilized, thereby preventing the formed parts. Defects such as deformation, poor gloss, and cooling spots make the physical properties of the plastics optimal. Of course, there is a debugging process, especially the multi-cavity moldings are more complicated. Therefore, the mold temperature cannot be arbitrarily changed during the production process, and the mold temperature should be set within the recommended temperature range of the material.
2. Adjustment control of pressure and exhaust:
Proper injection pressure, the matching of clamping force should be determined when the mold is adjusted. The air in the cavity formed by the mold cavity and the core and the gas generated by the plastic must be discharged from the exhaust groove outside the mold. Poor gas will result in insufficient filling, resulting in weld marks or burns;
These three forming defects sometimes occur at the same place or in the same place. When there is a thick wall around the thin portion of the formed part, the shrinkage marks appear when the mold temperature is too low, and the burnt phenomenon occurs when the mold temperature is too high. Usually, weld spots will appear at the same time in the burned part. The exhaust groove is often neglected, and it is generally in a small state. Therefore, as long as no burrs are generated, the depth of the exhaust shoulder is as deep as possible, and the rear of the shoulder is opened. Larger venting groove, so that the gas passing through the shoulder can be quickly discharged outside the mold. If there is a special need to open the venting groove on the ejector pin, the reason is the same, one is that there is no flash, and the other is venting. It will work very well.
The depth of the exhaust shoulder is as deep as possible, and a large venting groove is formed at the rear of the shoulder so that the gas passing through the shoulder can be quickly discharged outside the mold, and if necessary, the vent groove is opened on the ejector pin. The reason is the same, one is that there is no flash, and the other is that it can work very well.
3. Supplementary shaping control of the dimension of injection molded parts
Due to the difference in shape and dimension of some plastic parts, deformation and warping may occur in different situations with the change of temperature and loss of pressure after demolding. At this time, some auxiliary fixtures can be adjusted to make timely adjustments after the forming parts are released. Remedial measures can be taken, and after it is naturally cooled and shaped, better correction and adjustment effects can be obtained. If strict management is ensured throughout the injection molding process, the dimension of the injection molded part is very well controlled.
Asia Billion is a high precision injection mould maker and precision injection molding companies in China. if you need a competitive supplier for precision injection mold and molding, we think we will be your good choice.
Contact us freely at :
Asia Billion Innovational Technology Limited