Calculation of clamping force

A. Calculation of clamping force:

Supporting mold force = projected area of the finished product in the direction of the switching mold (cm²) × number of mold cavities × pressure in the mold (kg / cm²);

B. How to choose the right injection molding machine: 1MPa = 9.8kg / cm²

Choice of injection molding machine

1. Selecting the right type: The model and series are determined by the product and plastic.

Because there are many types of injection molding machines, it is necessary to correctly determine which injection molding machine or series of products should be produced at the beginning, such as general thermoplastics, bakelite materials, or PET materials. Color, two-color, multi-color, sandwich or mixed color, etc. In addition, certain products require conditions such as high stability (closed loop), high precision, super high rate of fire, high injection pressure, or rapid production (multi-loop), and must also choose the appropriate series to produce.

2. Lowering: Determine whether the “large column distance”, “die thickness”, “minimum die size” and “die plate size” of the machine are appropriate according to the die size to confirm whether the die can be placed. The width and height of the mold must be less than or at least one side is smaller than the inner distance of the large column; the width and height of the mold should preferably be within the size of the mold plate; the thickness of the mold must be between the thickness of the injection molding machine; the width and height of the mold Need to meet the minimum mold size recommended by the injection molding machine, too small will not work.

3. We can get: It is judged by the mold and the finished product whether the "opening stroke" and "holding stroke" are sufficient to take out the finished product. The mold opening stroke must be at least more than twice the height of the finished product in the direction of the opening and closing mold, and the length of the sprue must be included; the die travel must be sufficient to eject the finished product.

4. Locking: The "clamping force" tonnage is determined by the product and plastic. When the raw material is injected into the cavity under high pressure, a mold supporting force is generated, so the clamping unit of the injection molding machine must provide sufficient "clamping force" so that the mold will not be opened. The calculation of the clamping force requirements is as follows: the projected area of the finished product in the direction of the switching mold is obtained from the appearance size of the finished product; the supporting mold force = the projected area of the finished product in the direction of the switching mold (cm2) × number of cavities × pressure in the mold (kg / cm2 ); The pressure in the mold varies with the raw materials, generally 350 ~ 400kg / cm2 for the raw materials; the clamping force of the machine needs to be greater than the supporting force, and for the sake of insurance, the clamping force of the machine is usually greater than 1.17 times the supporting force. So far, the specifications of the clamping unit have been initially determined, and the tonnage of the model has been roughly determined, and then the following steps must be performed to confirm which screw diameter of the injection unit is more suitable.

5. Full injection: Determine the required "injection amount" from the weight of the finished product and the number of mold cavities and select the appropriate "screw diameter". To calculate the weight of the finished product, the number of mold cavities (one mold and several cavities) must be considered; for stability, the injection volume must be more than 1.35 times the weight of the finished product, that is, the weight of the finished product must be within 75% of the injection volume.

6, shot well: judge the "screw compression ratio" and "injection pressure" and other conditions from plastic. Some engineering plastics require a higher injection pressure and a suitable screw compression ratio design in order to have a better molding effect. Therefore, in order to make the finished product better injection, the need for injection pressure and compression ratio issues must be considered when selecting the screw. . Generally speaking, smaller diameter screws provide higher injection pressure.

7. Shooting fast: and confirmation of "shooting speed". Some finished products require high injection rate and rapid injection to stabilize the molding, such as ultra-thin finished products. In this case, it may be necessary to confirm whether the injection rate and injection speed of the machine are sufficient, and whether it needs to be equipped with pressure accumulators and closed-loop control devices. In general, under the same conditions, a screw that can provide a higher injection pressure usually has a lower rate of fire, and a screw that can provide a lower injection pressure usually has a higher rate of fire. Therefore, when selecting the diameter of the screw, the injection amount, injection pressure, and injection rate (injection speed) need to be cross-considered and selected. In addition, a multi-loop design can also be used to reduce the molding time by synchronizing the compound action.

Some special problems may also need to be considered again: the problem of size matching: in some special situations, the customer's mold or product may have a small mold volume but a large shot volume, or a large mold volume but a small shot volume, In this case, the standard specifications preset by the manufacturer may not be able to meet customer needs, and so-called "large and small shots", that is, "big wall small shot" or "small wall large shot". The so-called "big wall and small shot" refers to the original standard clamping unit with a small injection screw. On the other hand, "small wall and big shot" refers to the original standard clamping unit with a large injection screw. Of course, there may be several stages in clamping and injection.

Fast machine or high speed machine concept:

In practical applications, more and more customers will require the purchase of so-called "high-speed machines" or "fast machines". In general, in addition to the needs of the product itself, most of the purpose is to shorten the molding cycle, increase the output per unit time, and then reduce production costs and improve competitiveness. Generally, to achieve the above purpose, there are several methods: increase the injection speed: increase the motor and pump, or increase the accumulator (preferably closed-loop control); increase the speed of feeding: increase the motor and pump Larger or smaller feeding hydraulic motor, speed up the screw speed; Multi-loop system: adopt double- or triple-loop design to synchronize the compound action to shorten the molding time; increase the mold water circuit and improve the cooling efficiency of the mold.