Choose the most suitable injection molding machine

  • Detail

Select the appropriate injection molding machine

usually, the important factors that affect the selection of injection molding machine include mold, product, plastic, molding requirements, etc.

mold size (width, height, thickness), weight, special design, etc

type and quantity of plastics used (single raw 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

1. Select the right type: the model and series are determined by products and plastics

since there are many kinds of injection molding machines, it is necessary to correctly judge which kind of injection molding machine or series this product should be produced at the beginning, such as general thermoplastic or bakelite raw materials or PET raw materials, monochrome, two-color, multicolor, sandwich or mixed color, etc. In addition, some products require conditions such as high stability (closed loop), high precision, ultra-high firing rate, high firing pressure or rapid production (multi loop), and appropriate series must also be selected for production

2. Placement: determine whether the "large column spacing", "mold thickness", "minimum mold size" and "mold disk size" of the machine are appropriate according to the mold size, so as to confirm whether the mold can be placed

the width and height of the mold should be less than or at least one side less than the inner distance of the large column

the width and height of the mold should preferably be within the size range of the mold disk

the thickness of the mold should be between the mold thickness of the injection molding machine

the width and height of the mold should meet the minimum mold size recommended by the injection molding machine, and it can't be too small

3. Take out: determine whether the "mold opening stroke" and "mold supporting stroke" are enough to take out the finished product from the mold and the finished product

the mold opening stroke should be at least twice the height of the finished product in the mold opening and closing direction, and the length of the sprue should be included; The mold supporting stroke should be enough to eject the finished product

4. Locking: the tonnage of "clamping force" is determined by the product and plastic

when raw materials are injected into the mold cavity with high pressure, a mold supporting force will be generated, so the mold locking unit of the injection molding machine must provide enough "mold locking force" to prevent the mold from being supported. The mold locking force demand is calculated as follows:

the projection area of the finished product in the direction of the switching mold is calculated from the appearance size of the finished product

mold supporting force = projected area of finished product in the direction of mold opening and closing (cm2) × Number of mold holes × In mold pressure (kg/cm2)

the pressure in the mold varies with the raw material. Generally, the raw material is 350 ~ 400kg/cm2

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 usually needs to be greater than 1.17 times of the supporting force

so far, the specification of the clamping unit has been preliminarily determined, and the tonnage of the model has been roughly determined. Then, the following steps must be carried out to confirm which injection unit has a screw diameter that meets the requirements

5. Full injection: determine the required "injection amount" by the weight of the finished product and the number of mold holes, and select the appropriate "screw diameter"

the number of mold holes (several holes in a the first mock examination) should be considered when calculating the weight of the finished product

for the sake of stability, the injection amount should be more than 1.35 times the weight of the finished product, that is, the weight of the finished product should be within 75% of the injection amount

6. Good injection: determine the "screw compression ratio" and "injection pressure" and other conditions from the plastic

some engineering plastics need higher injection pressure and appropriate screw compression ratio design to have better molding effect. Therefore, in order to make the finished product shoot better, the needs of injection pressure and compression ratio should also be considered when selecting screws

generally speaking, the screw with smaller diameter can provide higher injection pressure

7. Fast shooting: and confirmation of "shooting speed"

some finished products require high ejection rate and rapid ejection to form stably, such as ultra-thin finished products. In this case, it may be necessary to confirm whether the ejection rate and velocity of the machine are sufficient, and whether it needs to be equipped with pressure accumulators, closed-loop control and other devices. Generally speaking, under the same conditions, the screw that can provide higher jet pressure usually has a lower jet speed, on the contrary, the screw that can provide lower jet pressure usually has a higher jet speed. Therefore, when selecting the screw diameter, the injection volume, injection pressure and injection rate (injection speed) need to be cross considered and selected

in addition, multi loop design can also be adopted to shorten the forming time by synchronous compound action

some special problems may also have to be considered in terms of whether the verified experimental machine is qualified:

size matching:

in some special cases, the customer's mold or product may be small in size but need a large amount of shot, or the mold may be large in size but need a small amount of shot. In this case, the standard specifications preset by the manufacturer may not meet the customer's needs, It is necessary to connect the main switch to the power supply, which is called "size matching", that is, "large wall small shooting" or "small wall large shooting". The so-called "big wall small injection" refers to using the original standard clamping unit with a smaller injection screw, on the contrary, "small wall large injection" refers to using the original standard clamping unit with a larger injection screw. Of course, there may also be several levels of difference between clamping and shooting

concept of fast machine or high-speed machine:

in practical application, more and more customers will ask to buy the so-called "high-speed machine" or "fast machine". Generally speaking, its purpose is to shorten the molding cycle and increase the output per unit time, so as to reduce production costs and improve competitiveness, except that if the mechanical properties cannot meet the needs of the product itself. Generally, there are several ways to achieve the above purpose:

faster injection speed: increase the motor and pump, or add a pressure accumulator (it is best to add closed loop control)

faster feeding speed: increase the motor and pump with 46 # or 68 # anti-wear hydraulic oil, or reduce the feeding oil pressure motor to speed up the screw speed

multi loop system: adopt double loop or three loop design to synchronously carry out composite action and shorten forming time

increase the mold water path and improve the cooling efficiency of the mold

Copyright © 2011 JIN SHI