1, insufficient or uneven cooling When the ejection is not fully cooled, the top thrust of the top bar often causes the molded workpiece to deform, so the release will be deformed if the mold is not sufficiently cooled. The solution is to fully cool in the mold cavity, and so on completely hardened rear can be ejector. It can also reduce the mold temperature and prolong the cooling time. However, the partial cooling of some molds is not sufficient, and sometimes it is not possible to prevent deformation under normal molding conditions.
This situation should consider changing the path of cooling water, the location of cooling water channel or additional cooling tip hole, especially should consider not water cooling, using air cooling and so on.
2, the top bar causes Some parts of the release of poor, the use of the top bar forced demoulding caused by deformation. Plastic parts that are not easily deformed are not deformed but produce cracks. For ABS and polystyrene parts, this deformation is manifested by the whitish expression of the part being pushed (refer to cracking, crack, micro-splitting and whitish). The elimination method is to improve the mold polishing, so that it is easy to release, and sometimes the use of Mold release agent can also improve the demoulding.
The most fundamental improvement method is to grind the core, reduce the release resistance, or increase the draft tilt, in the not easy to top out the site to add the top bar, and change the top-out way is more important.
3, caused by forming strain The deformation caused by forming strain is mainly due to the difference in the direction of molding shrinkage and the change of wall thickness. Therefore, increasing the mold temperature, increasing the melt temperature, reducing the injection pressure, improving the flow conditions of the pouring system can reduce the shrinkage in the direction of the difference.
However, only changing the molding conditions are most difficult to rectify, then you need to change the location and number of gate, such as forming a long bar to be injected from one end. Sometimes it is necessary to change the configuration of the cooling water channel, the longer thin parts are more prone to deformation, sometimes need to change the local design of the workpiece on the back of the side to set the reinforcing rib. It is mostly effective to use auxiliary tool cooling to correct this deformation. When it cannot be rectified, the design of the mold must be corrected. Among them, the most important thing is to pay attention to the consistency of the product wall thickness.
In the last resort, we have to correct the mold by measuring the deformation of the product and correcting it in the opposite direction.
4, crystalline plastic
Large shrinkage resin, generally crystalline resin (such as POM, nylon, polypropylene, polyethylene and PET resin, etc.) than non-crystalline resin (such as PMMA resin, polyethylene, polystyrene, ABS resin and as resin, etc.) of the deformation of large, in addition, because the glass fiber reinforced resin has a fiber, deformation is also large. Due to the narrow temperature range of the melting point most of the deformation, and often difficult to correct. The crystallinity of crystalline plastics varies with the cooling rate, that is, the sharp cooling crystallinity decreases, the molding shrinkage decreases, and the crystallization rate of slow cooling increases, and the molding shrinkage is increased.
The special correction method for the deformation of crystalline plastics is the use of this-property. In fact, the correction method used is to make the dynamic, static mode has a certain temperature difference. is to take the other side of the warp to create a strain on the temperature, you can correct the deformation. Sometimes this temperature difference of up to 20 ℃, but must be very evenly distributed.
It must be pointed out that in the design of crystalline plastic molded parts and molds, if not in advance to take special measures to prevent deformation, the workpiece can not be used due to deformation, only the molding conditions to meet the above requirements, most of the situation still can not correct the deformation.
5, the method of correcting the warp of the product
Products removed from the mold if it is to be corrected, the simple way to correct the products on the corrective tool, in the warping of the place with heavy, but must clearly determine the weight of the same position placed. Or put the warp products on the straightening device, together with the heat deformation temperature near the hot water, simple to straighten with the hand.
But pay attention to the hot water temperature can not be too high, otherwise it will make the deformation of the product more damage.
Do not leave any marks on the product after warping correction. Causes of warpage, bending and twisting of molded parts and prevention measures