Injection processing product deformation, bending, distortion is mainly due to the phenomena of flow direction of plastic molding shrinkage is bigger than the vertical direction, make each parts to different warp shrinkage rate, and because of the injection molding inevitably in the internal parts have larger residual internal stress caused by warping, these are caused by the deformation of high stress orientation.
Inadequate or uneven cooling
Jacking force of ejector rod often deforms the formed parts when the ejector is not fully cooled. The strategy is to fully cool in the cavity, such as complete hardening before ejection. Also can reduce the mold temperature, lengthen the cooling time. However, some of the mold local cooling is not sufficient, in the usual molding conditions can not prevent deformation. In this case, it should be considered to change the path of cooling water, the position of cooling water channel or add cooling pin holes. In particular, it should be considered not to use water cooling, but to use air cooling and other methods.
Plunger caused
Some parts of bad demoulding, forced demoulding with the top of the deformation. For plastic parts that are not easily deformed, instead of deformation, cracks are generated. For ABS and polystyrene parts, this deformation is manifested by the whitening of the parts to be pushed (see cracking, crack, microcrack and whitening). The elimination method is to improve the polishing of the mold, so that it is easy to demoulding, sometimes using demoulding agent can also improve demoulding. The most fundamental improvement method is grinding core, reducing the demoulding resistance, or increase the draft Angle, in the part of the ejection is not easy to add ejection rod, and change the ejection way is more important.
Caused by molding strain
The deformation caused by forming strain is mainly caused by the difference in the direction of forming shrinkage and the change of wall thickness. Therefore, the difference of shrinkage rate in the direction can be reduced by increasing the mold temperature, raising the molten material temperature, reducing the injection pressure and improving the flow condition of the casting system. However, if only the forming conditions are changed, most of them are difficult to be corrected. At this time, the position and number of sprue need to be changed.
Sometimes it is necessary to change the configuration of the cooling channel; The longer laminated parts are easier to deform, and sometimes it is necessary to change the part design of the parts to set reinforcing bars on the back side of the upwarped side. The use of auxiliary cooling to correct this distortion is mostly effective. When this is not possible, the design of the die must be corrected. Among them, the most important is to pay attention to make the wall thickness of products consistent. As a last resort, the molds are corrected in the opposite direction by measuring the deformation of the product.
Crystalline plastics
Shrinkage of resin, generally crystallization resin (such AS polyformaldehyde, nylon, polypropylene, polyethylene and PET resin, etc.) than non-crystallization resin (such AS PMMA resin, polyethylene, polystyrene, ABS resin and AS resin, etc.) deformation, in addition, because the glass fiber reinforced resin has fiber alignment, deformation is also large.
Due to the narrow temperature range of melting point, most deformation occurs and is often difficult to correct. The crystallinity of crystalline plastics varies with the cooling speed, that is, the sharp cooling crystallinity decreases and the molding shrinkage decreases, while the slow cooling crystallinity increases and the molding shrinkage increases. A special corrective for the deformation of crystalline plastics utilizes this property.
In fact, the correction method is used to make the dynamic and static mold has a certain temperature difference. Is to take the other side of the warping strain temperature, can be corrected deformation. Sometimes the temperature as high as more than 20 ℃, but it must be very evenly distributed. It must be pointed out that in the design of crystallized plastic molding parts and molds, if no special measures to prevent deformation are taken in advance, the parts will be unable to be used due to deformation, only to make the molding conditions meet the above requirements, most cases still can not correct the deformation.
The method of warping
A simple way to correct an article taken from a mold is to place the article to be corrected on the tool to which it is to be warped and to place the weight where the weight should be placed. Or the warping products on the straightener, together into the products hot water near the temperature of thermal deformation, simply straightened by hand. But should pay attention to the temperature of hot water can not be too high, otherwise it will make the deformation of products more calendar harm.
|
苏公网安备32050602012411号
