Plastic molding expertise

1. Five major elements:
1. Temperature: heating ring, thermocouple. If the thermocouple is broken, the actual temperature is high, which is easy to produce undesirable phenomena such as color difference and burning.
2. The quality of plastic injection molding is related to the adjustment of machine parameters.
2, 1 speed: the speed of the product with thicker meat needs to be changed from slow to fast and then slow (that is, the multi-stage molding process specially introduced later), and the thin product needs to be quickly maintained and then depressurized.
2, 2 pressure: should be adjusted according to the injection volume and demolding situation, add back pressure (to be appropriate, generally not more than 10bar) can make the measurement accurate.
2, 3 time: according to the premise of not affecting the quality of the finished product to strive for high efficiency.
2, 4 position: the displacement stroke of various actions, the precise position of the various action modes and pressure and speed completed in a certain section of the stroke.
2. Injection Engineering:
1. Filling: The material (resin) in the molten state is shot out of the mold and fills the entire molding cavity.
2. Gate closure (pressure packing): The function of pressure holding is to make up for the volume shrinkage caused by the cooling and solidification of materials in the mold and the role of maintaining secondary pressure.
3. Cooling: The plastic in the mold is further cooled and solidified to the extent that the product can be smoothly demolded. In order to maintain a high speed of each molding strip in the injection process, it is also necessary to grasp the change state of the molten material and the shrinkage of the cooling and curing of the filled material, that is, it is necessary to understand the melting point, properties and shrinkage ratio of the material.
Third, the key items of injection program control:
1. Speed segmentation control (rate of fire); 2. Pressure segmentation control (injection pressure); 3. Control (measurement) of plastic filling amount in the mold; 4. Material temperature (molten state) such as screw back pressure or speed. A. Program control of the rate of fire: the injection stroke is divided into three to four sections, each section plays an appropriate rate of fire, and the control method is: slow down the rate of fire when the molten material begins to pass through the glue, increase the rate of fire in the filling molding stage and then reduce the rate of fire at the end of filling, this method can prevent the burr to eliminate the flow marks at the gate part, reduce the residual stress of the molded product, and prevent the mold core from shifting. B. Control of injection pressure: it is divided into injection pressure and secondary pressure (holding pressure) control (whether the injection pressure change timing is appropriate or not, it is an important factor to prevent excessive molding pressure from being applied to the mold, prevent excessive burr or insufficient filling, etc.). C. Automatic correction of buffer amount: pre-adjust the measurement near the end of the injection stroke, so that a small amount of molten material due to the front end of the screw for buffering, according to the filling situation in the mold and then add pressure secondary pressure or three pressure to replenish the appropriate material to the mold, this method can prevent the finished product shrinkage and sag, or adjust the supplement of the molding shrinkage material.
Fourth, controlling the rate of fire can receive the following effects:
(1) The muzzle velocity is small to prevent mold deformation (such as eccentric, etc.); The small end speed prevents overfilling (burr), which can effectively control the occurrence rate of product defects and improve production efficiency.
(2) The correct holding pressure switching position can prevent burrs, and can be formed with small clamping force and large molded products.
(3) Prevent various undesirable phenomena, expand the operating space, and reduce the defective rate.
(4) After passing through the gate, it is accelerated to prevent jet phenomenon (i.e. flow marks) and silver filigree.
(5) Deceleration near the gate can stabilize the solidification layer of the finished product and prevent the defects of cloth grain.
(6) The deceleration of the thick part of the meat can also stabilize the solidification layer and prevent the shortcomings of cloth grain.
(7) The flow of meat thick products is irregular and slowly accelerated, and acceleration at the place where the jet is generated can make the jet disappear and eliminate the flow marks.
(8) The rate of fire position can be changed, which can change the welding position, that is, the bad parts of the product can be improved by switching the rate of fire position.
Fifth, the control effect of holding pressure pressure:
(1) During cooling, the holding pressure is reduced to prevent the appearance of burrs, thereby reducing the residual pressure and improving quality.
(2) After filling, the holding pressure drops to the stability of the solidification layer and then adds pressure (thick meat, small clamping force, and the molding of molded products with large clamping force can prevent cloth grain and shrinkage).
(3) After the completion of the plastic filling stroke, if the holding pressure switching point can be effectively grasped, the dimensional accuracy of the molded product can be stable, and the reduction of stress residue in the molded product is extremely important to improve many undesirable phenomena.
(4) Pressure holding stroke: After the plastic is filled with the mold hole, the plastic is injected into the gate before solidification, to prevent the accompanying plastic counterflow caused by the shrinkage and sagging phenomenon of the molded product, so the pressure holding is used to continue to apply pressure to the gate to prevent undesirable phenomena.