What are the five elements of injection molding
1. Temperature: barrel temperature, material temperature, mold temperature, drying temperature, oil temperature, ambient temperature, etc.
2. Pressure: injection pressure, holding pressure, back pressure, demolding pressure, mold opening pressure, mold clamping pressure, etc.
3. Time: injection time, holding time, cooling time, drying time, measurement delay time, etc.
4. Speed: injection speed, carriage return speed, mold opening and closing speed, demolding speed, etc.
5. Location: measurement position, ejection position, mold opening position, etc.
The temperature of the screw barrel is set according to the performance of different plastic materials. The barrel temperature is generally 10 ° C-30 ° C higher than the melting point of the plastic. It must be noted that due to different synthesis methods or types of additives, the materials provided by different manufacturers will also have different melting points and allowable residence times in the barrel.
The mold temperature is generally cooled by circulating water when setting. However, when producing products with high precision dimensions or high surface quality, a mold temperature machine that can accurately control should be used according to process requirements.
In molding, the injection stroke must first be determined. In theory, the injection stroke can be calculated as follows:
S1 = 4 （CVp + Va） / ρDs2
In the formula: injection stroke Vp-product volume ρ-resin density C-number of cavities Va-gate volume Ds-screw diameter
In actual production, if the total weight of "product + gate" is known, the following formula can be used to calculate the injection stroke S1 = (M / Mmax) · Smax + (5 ~ 10) mm
S1 in the formula: injection stroke, mm M-"product + gate" total weight, g Mmax-maximum injection amount of injection molding machine, g / Smax-maximum injection stroke of injection molding machine
Due to the different geometry of the runner system and the various parts of the mold, in order to meet the product quality requirements, different parts have different requirements on the flow state of the filled melt (mainly the pressure and speed during flow). In an injection process, when the screw advances the melt to the mold, it is required to achieve different pressures and speeds at different positions, which is called multi-stage injection molding.
Generally, it is more scientific to set at least three or more injections when molding plastic parts, that is, the first section is at the main flow path, and the second section is from the runner to the gate. The third segment, the remaining part is the fourth segment, the weight position method can be used to determine the switching position of each segment;
In actual production, the multi-stage injection process parameters should be scientifically analyzed and reasonably set according to product quality requirements, runner structure, and mold exhaust conditions.
Usually, it can be set by debugging and observation method. Set the pressure / speed required to find the switching position during injection to 0, observe the position of the melt and the defect status of the product, and gradually adjust until a reasonable position is found. . However, in the process of debugging and observation, attention must be paid to the demolding condition of the under-injected product, so as to avoid mold sticking due to under-injection in some recessed parts of the mold.