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The important factors that often affect the choice of injection molding machine include molds, products, plastics, molding requirements, etc. Therefore, the following information must be collected or available before selection: mold size (width, height, thickness), weight, special design, etc.; The type and quantity of plastics (single material or multiple plastics); appearance size (length, width, height, thickness), weight, etc. of injection molded products; molding requirements such as quality conditions, production speed, etc.
After obtaining the above information, you can follow the steps below to choose the right injection machine:
1, choose the right type: Determined by the product and plastic models and series.
Since there are many types of injection machines, it is necessary to first determine exactly which type of injection molding machine or which series should be used to produce this product. For example, it is general thermoplastic plastic or bakelite raw material or PET raw material. Color, two-color, multi-color, sandwich or mixed color. In addition, some products require high stability (closed loop), high precision, ultra-high firing speed, high pressure or rapid production (multi-loop) conditions, and must also choose the right series to produce.
2. Put it down: Determine whether the â€œlarge pillar distanceâ€, â€œdie thicknessâ€, â€œminimum mold sizeâ€ and â€œdie plate sizeâ€ of the machine table are appropriate by the die size to confirm whether the die is released.
The width and height of the mold must be less than or at least one side smaller than the distance between the columns; the width and height of the mold should be within the mold disk size; the thickness of the mold should be between the mold thickness of the injection molding machine; the width and height of the mold Need to meet the injection molding machine recommended minimum mold size, too small will not work.
3, get out: From the mold and finished product to determine "open mold stroke" and "travel mold stroke" is enough to allow the finished product to be removed.
The opening stroke must be at least more than twice the height of the finished product in the direction of the switch die, and must include the length of the sprue; the die stroke must be sufficient to eject the finished product.
4. Locked up: The â€œmold clamping forceâ€ is determined by the product and plastic.
When the raw material is injected into the mold cavity with high pressure, it will produce a hold-up force, so the clamping unit of the injection molding machine must provide enough â€œclamping forceâ€ to prevent the mold from being opened. The clamping force requirement is calculated as follows:
Find the projected area of â€‹â€‹the finished product in the direction of the switch mode from the finished product appearance size.
Stretching force = projected area of â€‹â€‹the finished product in the direction of the switch mode (cm2) × number of cavity points × in-mold pressure (kg/cm2);
In-mold pressure varies with raw materials. General raw materials take 350 ~ 400kg/cm2;
The clamping force of the machine needs to be greater than the strength of the supporting mold, and for the sake of safety, the clamping force of the machine usually needs to be more than 1.17 times the strength of the supporting mold.
At this point, the dimensions of the die-clamping unit have been tentatively determined, and the number of tonnages of the model has been roughly determined. The following steps must then be performed to confirm which injection unit screw diameter is more desirable.
5. Shooting satiety: Determine the required â€œshot volumeâ€ from the finished product weight and the number of cavity points and select the appropriate â€œscrew diameterâ€.
Calculate the weight of the finished product to take into account the number of cavity points (a few points);
For stability reasons, the shot volume needs to be 1.35 times the weight of the finished product. That is, the finished product weight should be within 75% of the shot volume.
6, shot well: the plastic to determine the "screw compression ratio" and "injection pressure" and other conditions.
Some engineering plastics require high injection pressure and appropriate screw compression ratio design to have better molding effect. Therefore, in order to make the finished product shot better, the need for injection pressure and the compression ratio need to be considered when selecting the screw. .
In general, smaller diameter screws provide higher injection pressures.
7, shot faster: and "injection speed" confirmation.
Some finished products require high injection rate and rapid injection to stabilize molding, such as ultra-thin finished products. In this case, it may be necessary to confirm whether the injection rate and the injection rate of the machine are sufficient, and whether it needs to be matched with a pressure accumulator, a closed-loop control device, or the like. In general, under the same conditions, the screw that can provide higher injection pressure usually has a lower firing rate. Conversely, a screw that provides a lower injection pressure usually has a higher firing rate. Therefore, when selecting the screw diameter, the injection amount, injection pressure and injection rate (shooting speed) need to be cross-checked and selected.
In addition, multi-circuit design can also be used to shorten the molding time with synchronous compound action.
After the above steps, in principle, injection molding machines that meet the requirements can already be determined, but there are some special issues that may have to be considered, including:
In some special circumstances, the customer's mold or product may have a small mold size but require a large amount of shot, or the mold has a large volume but requires a small amount of shot. In this case, the standard specifications set by the manufacturer may not be able to Meet the needs of customers, and must carry out the so-called "size", which is "big wall shot" or "small wall shot." The so-called "big wall shot" refers to the original standard clamping unit with a smaller injection screw, and vice versa, "small wall shot" is the original standard clamping unit with a larger injection screw. Of course, it is also possible that there are several stages between clamping and ejection in the match.
The concept of fast machines or high-speed machines:
In actual use, more and more customers will demand the purchase of so-called "high-speed machines" or "fast machines." In general, its purpose is to reduce the molding cycle, increase the output per unit time, reduce production costs, and increase competitiveness, in addition to the needs of the product itself. In general, there are several ways to achieve the above objectives:
Faster injection speed: Increase motor motor and pump, or add pressure accumulator (preferably closed loop control);
Feeding speed is quickened: the motor and pump are increased, or the feed hydraulic motor is reduced, so that the screw speed is increased;
Multi-loop system: Double-loop or triple-loop design is adopted to perform compound actions simultaneously to shorten the molding time;
Increase the mould waterway and increase the cooling efficiency of the mould.
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