In general, customers who have been in the injection molding industry for many years have the ability to judge and choose the right injection molding machine to produce. However, under certain conditions, the customer may need the assistance of the manufacturer to decide which specification of the injection molding machine to use, even if the customer may only have sample or idea of â€‹â€‹the product, and then ask whether the manufacturer's machine can produce, or which model comparison Suitable for. In addition, some special products may need to be equipped with special devices such as accumulators, closed circuits, injection compression, etc., in order to produce more efficiently. This shows that how to determine the right injection molding machine to produce is an extremely important issue. The following information is provided to readers for reference.
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 making the selection:
Die size (width, height, thickness), weight, special design, etc.
The type and amount of plastic used (single material or multiple plastics);
The appearance size (length, width, height, thickness), weight, etc. of the injection molded product;
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€œmold thicknessâ€, â€œminimum mold sizeâ€ and â€œdie plate sizeâ€ of the machine table are appropriate by the mold size to confirm whether the mold is released.
The width and height of the mold must be less than or at least one side less than the distance between the columns;
The width and height of the mold are preferably in the range of the mold plate size;
The thickness of the mold must be between the mold thickness of the injection molding machine;
The width and height of the mold must conform to the minimum mold size recommended by the injection molding machine, too small.
3, get out: From the mold and finished product to determine "open mold stroke" and "support mold stroke" is enough to allow the finished product to be removed.
The opening stroke must be at least greater 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 needs to be sufficient to eject the finished product.
Lockable: The "mold clamping force" 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.
Supporting force = projected area of â€‹â€‹the finished product in the direction of the switching die (cm2) Ã— number of cavity points Ã— in-mold pressure (kg/cm2);
In-mold pressure differs depending on the raw material, and the general raw material is 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, shoot full: from the finished product weight and the number of cavity required to determine the "injection volume" and select the appropriate "screw diameter."
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.
Shoot well: Plastics determine "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.
â—† The concept of fast machine or high speed machine:
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:
â—†Increase injection speed: Increase motor motor and pump, or add pressure accumulator (preferably add closed loop control);
â—†Accelerate the feeding speed: Increase the motor motor and pump, or increase the feed hydraulic motor to make the screw speed faster;
â—†Multi-loop system: Double-circuit or triple-loop design is adopted to perform compound action synchronously and shorten the molding time;
â—† increase the mold water, enhance the cooling efficiency of the mold.
However, â€œthere is no lunch for lunchâ€, although the improvement and improvement of machine performance can increase production efficiency, it often increases investment costs and operating costs. Therefore, the evaluation of the benefits before investment needs to be carefully measured in order to use the most suitable machine. Type produces the highest benefits.
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