Injection molding machine adjustment is an essential skill for injection molders. Although many adjustment techniques are based on theory, they rely on experience. Today, editor summarizes following effective adjustment methods for your reference:

When we adjust machine, we often sigh: It would be great if mold was transparent! In this way, we can see the entire filling process of molten glue, see how and when defects are produced. When we design a certain injection process, we hope to be able to see whether injection process is actually completed according to requirements of concept, whether starting point position is set correctly, and so on. Transparent injection mold model, in fact, it is impossible to directly see molten plastic filling process without high-tech equipment. Using this technique, every machine operator can see filling process as clearly as if they were watching it, and method is very simple to say. Just increase injection time by one second! We only need to increase injection time by one second, one second per bet, then arrange parts that are not aligned in order, so that we can clearly see filling process of molten glue until cavity is filled. If you want to see more carefully at a key position, just increase each bet by 0.1 second at this key position, and you can see it clearly. If you just want to see if starting point is accurate, it is even simpler. Just set pressure and speed of next level to 0, and you can see where starting point is, without having to use method of increasing time by one second to observe slowly. It should be noted that since molten plastic will have a little inertial expansion process after injection stops, actual molded part will have a little difference from shape at the moment when injection stops. Actual starting point should be earlier than visible part. This skill can be said to be something that every injection molding technician must learn to use, otherwise machine adjustment technology cannot be greatly improved, let alone reach level of advanced technology.

 

So-called "positioning injection" method is a machine adjustment method evolved from commonly used fast injection to next level slow injection. This method is to adjust slow speed and pressure of next level to zero, so that fast injection of previous level stops immediately when it reaches a certain set starting position, so that pressure stored in cavity is naturally released, it is used to make final filling of cavity and pressure maintenance. Usually, starting point is set at the point where cavity is just filled, then forward and backward movement is adjusted according to actual situation. In commonly used "fast to slow injection method" machine adjustment technique, slow speed, fast speed and starting point level position are interrelated and affect each other, so it is not easy for those who are not experienced to grasp it. What are advantages of "positioning injection" method?
1. "Positioning injection" method eliminates pressure and speed of next level, which reduces two influencing factors. Therefore, it only needs to adjust pressure and speed of previous level, move starting point slightly forward and backward. Machine adjustment becomes easier, and it can be set more accurately, which is easier for beginners to master.
2. In production, when we encounter some raw materials and parts that cannot be produced by slow injection, such as large parts, thin-walled parts, large PC parts, etc., once they use slow injection, injection molded parts will be uneven or have clipping or vibration lines, so they must be shot quickly to the bottom. "Positioning injection" method is a good choice. Therefore, injection molded parts will not have problems such as batching, top whitening, and mold sticking due to excessive injection. On the contrary, in order to prevent batching, top whitening and other problems, we can use this machine adjustment technique to help solve them.
3. In fact, this technique can solve many problems if used well. When there is a shrinkage problem in injection molded parts, as long as front stage pressure is appropriately increased and starting point is slightly moved forward, general shrinkage problem can be solved. Unless shrinkage problem is quite serious, there will be no problems such as front and backlash.
What are limitations of "positioning injection" method?
Of course, it is not omnipotent and cannot completely replace "fast turn slow injection" machine adjustment technique. For example, when there is air trap, it is difficult to solve problem using "positioning injection" method, while it is much easier to use "fast turn slow injection" method. In any case, being able to use it flexibly will surely become another magic weapon for you to solve difficult problems.

Slow-first-fast-later injection, that is, first use first-level slow injection, and when it reaches a certain set position, start second-level fast injection. Starting point is usually set at the early stage of filling when injection is just started. Depending on different problems, sometimes it is necessary to turn to second level when a small part of glue is injected (about 10-15MM), sometimes it is necessary to turn to second level when glue is injected a little (about 3MM), and sometimes it is necessary to turn to second level before glue is injected. Using first-level slow injection, molten glue can be filled smoothly at the beginning, which is conducive to preventing air entrapment, air marks and explosion-proof injection, spiral or folded (snake-shaped) injection. Second-level fast injection is conducive to overcoming resistance to ensure filling, reducing temperature drop of molten glue, preventing problems such as dumb color and material shortage of injection molded parts. What problems can it solve? This machine adjustment technique can often be used to solve many problems such as gas lines and cow shit lines at water inlet, or solve some conflicting problems, as follows: Used to solve cow shit lines and water inclusion problems of large and coarse parts. For example: number one problem of toy injection molding is cow shit lines and water inclusion problems of thick and large PVC parts.
2. Used to solve problem of gas lines or spray lines that are easy to produce at water inlet. For example, gas line problem of water inlet of PC parts.
3. Solve problems of oil spraying, burning glue and matte color around water inlet.
4. When fast filling is required to discharge material, it is used to prevent other problems. For example, gas lines or spray lines appearing around water inlet, etc. Of course, in production, machine adjuster can also add several injection stages in order to solve some other problems generated during injection process according to actual situation. For example, when there is a gas mark at a certain position in the middle of injection molded part, a slow injection stage should be added during fast injection process, gas mark position should be filled and then switched back to fast injection. Since fast injection is prone to cause air entrapment, burning and batch front problems, a slow and low-pressure filling and pressure holding process is required in the later stage of injection. This machine adjustment technique can be said to be one of several common machine adjustment techniques that are indispensable in injection molding production. Whether it can be used or not, and whether it is used well or not, has an essential difference in terms of high and low technical levels.

 

Fast-first-slow, that is, first use a first-level fast injection, and when it is shot to a certain set position, then start a second-level slow injection. This second-level starting point is generally set at the end of injection molding, that is, close to the end of molding. What problems can it solve? Using a first-level fast injection can maintain temperature of melt, overcome cavity resistance, and facilitate smooth molding. Second-level slow injection is conducive to exhaust and melt absorption to solve air entrapment, prevent batching and shrinkage problems. Using this technique can also solve many difficult and contradictory problems for us: it can be used to solve problem of air entrapment of injection molded parts. Including "dead corner" air entrapment and "back bag" air entrapment.
2. Used to solve problem of batching, shrinkage or uneven material discharge in same mold caused by unbalanced water inflow in each cavity of mold.
3. It can also be used to solve problems such as batching, top whitening or shrinkage.
4. It can also be used to solve problem of difficult filling. Of course, in production, machine adjuster can also add several injection stages in this "fast first and slow later" injection process according to actual situation to solve other problems in filling. It can also add a slow stage before fast injection to solve problem of air marks at water gate level. All of these are higher and more advanced applications of this technique. In fact, in a complex multi-stage injection process, two techniques of "slow first and fast later" and "fast first and slow later" may actually have been combined into one, but each still plays its own role. When there are fewer problems, there are actually more obvious differences and emphasis, so they are divided into two techniques to discuss so that we can distinguish and understand and use them in a competitive manner.

Sometimes, when solving problems such as batching, water marks, and cow shit piles, following situation often occurs: by reducing pressure or speed by one level, batching or cow shit marks problems can be solved, but at the same time, new problems such as uneven material flow will appear; by increasing pressure or speed by one level, old problems will appear again, and problems such as uneven material flow will no longer exist. At this time, I really hope that pressure or speed of injection molding machine can be fine-tuned by half a level. How to achieve fine-tuning?
It is impossible to adjust half a level in practice, but we found that purpose of fine-tuning can be achieved by adjusting melt temperature by plus or minus 2-5 degrees. When temperature is increased, fluidity of melt will be better, and filling will be faster, just like effect of increasing pressure or speed; on the contrary, lowering temperature is like reducing injection pressure and speed.