In general, engaged in injection molding industry for many years the customer most have the ability to judge and to select the appropriate production of injection molding machine. But in some cases, the customer may require manufacturers to assist injection molding machine which can decide to adopt a specification, and even customers may only the sample of the product or idea, and then ask the manufacturer whether the machine can produce, or what kind of model is more suitable. In addition, some special products may require a special mix of devices such as accumulator, closed loop, injection compression etc, to more efficient production. Therefore, how to decide the suitable injection molding machine to produce, is a very important problem. The following information is provided to the reader reference.
Usually the important factors influencing the injection machine choice, including mold products, plastic, molding requirements, therefore, to collect or have the following information in must be selected before: die size (width, height, thickness, weight), special design; the species and the quantity of used plastic (single raw material or a variety of plastic injection molding); appearance of the product size (length, width, height, thickness, weight); forming requirements, such as quality, production speed.
Information in the above can be obtained, according to the following steps to select the suitable injection machine:
1, elected to the type: by products and plastic machine and a series of decision.
Because there are many kinds of injection molding machine, thus begin the correct judgement of the products should be what kind of injection molding machine, or what a series of production, for example, is the general thermoplastic plastic or bakelite raw or PET feedstock, monochrome, multicolor, sandwich double color, or color mixing. In addition, some products need high stability (closed loop), high precision, super high firing rate, and high injection pressure or rapid production (multi loop) and other conditions, must choose the appropriate series production.
2, put down by the die size determination machine: "big column distance", "die thickness", "die minimum size" and "die pad size" is appropriate, to confirm whether the mold and put it down.
Mould width and height must be less than or at least one side is smaller than the big column spacing; the width and height of mold in the mold disc best size range; between the mold thickness mold thickness required between the injection molding machine; the minimum size of die mould width and height to be consistent with the recommendations of the injection molding machine, too small or not.
3, take that: by the mould and the finished product determine "whether opening stroke" and "supporting die stroke" enough to take out the finished products.
Opening stroke at least larger than the finished in switch mode direction two times the height of the above, and the need to contain the sprue length (sprue); support mould stroke will need enough ejection.
4, lock: products and plastic decided by "locking force" tonnage.
When the raw material with high pressure injection mold cavity will produce a supporting die strength, therefore the injection molding machine mold locking unit must provide adequate "locking force" make the mold should not be opened. The following calculation of clamping force demand:
The appearance of the finished product is obtained by projection area in the direction of the switch mode of finished products;
The projection area of the supporting die strength = finished in switch mode direction (cm2) #215; cavity number #215 mold pressure (kg/cm2);
In mold pressure with different raw materials and raw materials, generally 350 ~ 400kg/cm2;
Machine clamping force required is greater than the power of the supporting die, and to be on the safe side, machine clamping force usually need to be greater than the supporting die force more than 1.17 times.
So far has tentatively decided clamping unit specifications, models and roughly determine the tonnage, then must be made for the following steps, to confirm which one injection unit screw diameter compared with the required.
5, shot to the full: by the finished product weight and cavity number decision required "shot size" and select the appropriate "screw diameter".
The calculation of the weight of the product need to consider the cavity number (a few points of die);
For stability reasons, injection volume was 1.35 times more than the weight of the product, that is the weight of finished product for injection amount within 75%.
6, good shot: "judging by the plastic screw compression ratio" and "injection pressure" conditions.
Injection pressure plastics require higher some engineering and proper screw compression ratio design, have good forming effect, in order to make the product better shot, also need to consider the injection pressure needs and problems in the choice of screw compression ratio.
In general, the injection pressure of the screw diameter smaller can offer high.
7, shot fast: recognition and "injection speed".
Some products need high injection rate rapid fire out to steady forming, such as ultra-thin products, in this case, may need to confirm the machine injection rate and rate of fire is enough, whether to need to match the accumulator, closed loop control device. Generally speaking, under the same conditions, can provide a higher injection pressure screw usually firing rate is low, on the contrary, can provide lower injection pressure screw generally higher rate of fire. Therefore, the choice of screw diameter, injection volume, injection pressure and injection rate (injection speed), need cross consideration and choice.
In addition, also can use multi loop design, synchronous composite action to shorten the molding time.
After the above steps, the principle of injection molding machine can have decided to meet demand, but there may be some special problems must be considered, including:
The problem of size distribution:
In some special conditions, the customer mold or products may die of small volume but required a large amount of shooting, or die of large volume but required injection quantity is small, in this case, Standard Specification for manufacturers to preset may not be able to meet customer demand, and the need for the so-called "big small" with ", that is great wall small shot" or "small wall big shot". The so-called "Great Wall small shot" refers to the original standard clamping unit with smaller injection screw, on the contrary, "small wall big shot" is based on the original standard clamping unit of injection screw with larger. Of course, may also the clamping and injection were several levels in the match.
Fast machine or high-speed machine concept:
In practice, more and more customers will be required to buy the so-called "high speed machine" or "fast machine". Generally speaking, the purpose in addition to the product itself needs, most of the rest is to shorten the molding cycle, raise the output per unit time, thereby reducing the production cost, improve competitiveness. Usually, to achieve the above purpose, there are several practices:
Injection speed: the motor and pump to increase, or add the accumulator (plus the best of closed loop control);
Feed speed: the motor and pump will increase, or feeding hydraulic motors changed little, so that the screw speed speed up;
The multi loop system: double loop or three loop design, to synchronize compound action, shorten the molding time;
Increasing the mold water, enhance the cooling efficiency of Die & mould.
However, "there is no free lunch", although the upgrading and transformation of the performance of the machine can increase the production efficiency, but also tend to increase the investment cost and operation cost, therefore, benefit evaluation of pre investment must carefully measure, to yield the highest benefits to the most appropriate machine.