Process setting of injection molding

Game controller injection molding manufacturer before molding, plastic must be fully dried. When materials containing water enter the mold cavity, silver ribbon-like defects will appear on the surface of the product, and even hydrolysis will occur at high temperatures, causing material degradation. Therefore, the material must be pre-treated before molding so that the material can maintain appropriate moisture.

1. Setting mold temperature (a) Mold temperature affects the molding cycle and molding quality. In actual operation, it is set from the lowest appropriate mold temperature of the material used, and then adjusted appropriately according to the quality status. (b) Correctly speaking, mold temperature refers to the temperature of the mold cavity surface when molding is being carried out. In the mold design and molding process condition setting, it is important not only to maintain the appropriate temperature, but also to make it evenly distributed. (c) Uneven mold temperature distribution will lead to uneven shrinkage and internal stress, which makes the molding port prone to deformation and warping. (d) Increasing mold temperature can achieve the following effects; 1. Increase the crystallinity and more uniform structure of the molded product. 2. Make the molding shrinkage more sufficient and reduce the post-shrinkage. 3. Improve the strength and heat resistance of the molded product. 4. Reduce residual internal stress, molecular orientation and deformation. 5. Reduce flow resistance during filling and reduce pressure loss. 6. Make the appearance of the molded product more shiny and good. 7. Increase the chance of burrs on the molded product. 8. Increase the chance of depression near the gate and reduce the chance of depression far from the gate. 9. Reduce the degree of obvious bonding line 10. Increase cooling time.
Metering and Plasticization (I) In the molding process, the control of the injection volume (metering) and the uniform melting of the plastic (plasticization) are performed by the plasticizing unit of the injection molding machine. 1. Barrel Temperature Although about 60~85% of the melting of plastic is due to the heat energy generated by the rotation of the screw, the melting state of the plastic is still greatly affected by the temperature of the barrel, especially the temperature near the front area of ​​the nozzle. When the temperature of the front area is too high, dripping and threading when removing the product are likely to occur. 2. Screw speed (screw speed) (1) The melting of plastic is generally due to the heat generated by the rotation of the screw. Therefore, if the screw speed is too fast, the following effects will occur: 1) Thermal decomposition of plastic. 2) Shortening of glass fiber (fiber-reinforced plastic). Accelerated wear of the screw or barrel. (2) The setting of the rotation speed can be measured by the size of its circumferen-tial screw speed: Circumferen-tial speed = n (rotation speed) * d (diameter) * π (pi) Usually, for plastics with low viscosity and good thermal stability, the circumferential speed of the screw rod can be set to about 1m/s, but for plastics with poor thermal stability, it should be as low as about 0.1. (3) In practical applications, we can try to lower the screw speed so that the rotary feeding can be completed before the mold is opened.

3. Back pressure (BACK PRESSURE) (1) When the screw rotates to feed, the pressure accumulated by the molten plastic pushed to the front end of the screw is called back pressure. During injection molding, it can be adjusted by adjusting the oil pressure of the injection hydraulic cylinder. Back pressure can have the following effects: 1) The molten plastic is melted more evenly. 2) The colorant and filler are dispersed more evenly. 3) The gas is discharged from the blanking port. 4) The feed is accurately measured. (2) The back pressure is determined by the viscosity of the plastic and its thermal stability. Too high a back pressure will delay the feeding time and increase the rotational shear force, which may cause the plastic to overheat. Generally, 5~15kg/cm2 is appropriate.

4. Suck back (decompression) (1) After the rod rotates and feeds, the screw is properly withdrawn to reduce the pressure of the molten plastic at the front end of the screw. This is called suck back, which can prevent dripping from the nozzle. (2) Insufficient back pressure may cause the main channel (SPRUE) to stick to the mold; too much back pressure may inhale air and cause air marks on the molded product.

Setting the number of stable molding (I) Pre-confirmation and preparatory settings 1. Confirm whether the material drying, mold temperature and heating tube temperature are correctly set and reach the processable state. 2. Check the action and distance setting of opening and closing the mold and ejection. 3. The injection pressure (P1) is set to 60% of the maximum value. 4. Set the holding pressure (PH) at 30% of the maximum value. 5. Set the injection speed (V1) at 40% of the maximum value. 6. Set the screw speed (VS) at about 60RPM. 7. Set the back pressure (PB) at about 10kg/cm2. 8. Set the back pressure at about 3mm. 9. Set the position of the holding pressure switch to 30% of the screw diameter. For example, for a φ100mm screw, set it to 30mm. 10. Set the metering stroke slightly shorter than the calculated value. 11. Set the total injection time slightly shorter and the cooling time slightly longer. (II) Manual operation parameter correction 1. Lock the mold (confirm the rise of high pressure), and the injection seat moves forward. 2. Inject manually until the screw stops completely, and pay attention to the stop position. 3. The screw rotates back to feed. 4. After cooling, open the mold and take out the molded product. 5. Repeat steps ⑴~⑷, and the screw will eventually stop at a position of 10%~20% of the screw diameter, and the molded product will not have short shots, burrs, whitening, or cracks. (III) Correction of semi-automatic operation parameters 1. Correction of metering stroke [metering end point] Increase the injection pressure to 99%, and temporarily adjust the holding pressure to 0, adjust the metering end point S0 forward until a short shot occurs, and then adjust it backward until a burr occurs, and use the middle point as the selected position. 2. Correction of injection speed Return PH to the original level, adjust the injection speed up and down, find out the individual speeds where short shots and burrs occur, and use the middle point as the appropriate speed [at this stage, you can also enter the parameter setting of multi-speed corresponding to appearance problems]. 3. Correction of holding pressure Adjust the holding pressure up and down, find out the individual pressures where surface depressions and burrs occur, and use the middle point as the selected holding pressure. 4. Correction of holding time [or injection time] Gradually extend the holding time until the weight of the molded product is obviously stable, which is a clear and appropriate choice. 5. Correction of cooling time Gradually reduce the cooling time and confirm that the following conditions can be met: (1) The molded product will not be whitened, convex or deformed when being ejected, clamped, trimmed or packaged. (2) The mold temperature can be balanced and stable. Simple calculation method for cooling time of products with a wall thickness of more than 4 mm: 1) Theoretical cooling time = S (1 + 2S) mold temperature below 60 degrees. (2) Theoretical cooling time = 1.3S (1 + 2S) …. mold temperature above 60 degrees [S represents the maximum wall thickness of the molded product]. 6. Correction of plasticizing parameters (1) Confirm whether the back pressure needs to be adjusted; (2) Adjust the screw speed so that the metering time is slightly shorter than the cooling time; (3) Confirm whether the metering time is stable, and try to adjust the gradient of the heating coil temperature. (4) Confirm whether there is dripping from the nozzle, whether there is a pigtail or sticking in the main channel, and whether there are air marks on the finished product, and adjust the nozzle temperature or the loosening distance appropriately. 7. Utilization of staged holding pressure and multi-stage injection speed (1) Generally speaking, injection should be carried out at high speed without affecting the appearance, but it should be carried out at a lower speed when passing through the gate and before switching to holding pressure; (2) Holding pressure should be gradually reduced to avoid excessive residual stress in the molded product, which may make the molded product easily deformed.