When we adjust machine, we often sigh: If mold is transparent, it will be fine! In this way, you can see entire filling process of melt, see how and when defects occurred. When we design a certain glue injection process, whether glue injection process is actually completed according to envisaged requirements, whether starting point is set correctly, we hope to be able to see.

 

In fact, it is impossible to directly see melt filling process without high-tech equipment. But there is an indirect method. Using this technique, every operator can be as clear as if he saw filling process, method is very simple.

We only need to increase injection time every second, one injection for each additional second, then arrange unfilled injected pieces in order, so that you can clearly see filling process of melt until cavity is filled. If you want to take a closer look at a key position, only 0.1 second per injection will increase at this key position, so you can see clearly.
It is even easier if you just want to see if the starting point is not accurate. You only need to adjust the pressure and speed of the next stage to 0, and you can see where starting point is, instead of using method of increasing every second to observe slowly.
It should be reminded here that since melt will have a little inertial expansion after injection stops, actual shape of injected part when injection is stopped will be slightly different from the moment when injection is stopped. Actual starting point should be earlier than injection you see.
This technique can be said to be something that every injection technician must learn to use, otherwise it is impossible for adjustment technology to be greatly improved, let alone reach level of advanced technology.

So-called "positioning injection" method is a tuning method that evolved from our commonly used fast shot glue to lower-level slow shot glue. This method is to adjust slow speed and pressure of next stage to zero, so that rapid injection of previous stage will stop immediately when it reaches a set starting position, allowing pressure stored in cavity to be naturally released, and it is used for final filling of cavity and pressure holding. Usually starting point is set at the point where it just fills cavity, then adjusts to move forward and backward according to actual situation.
In the commonly used adjustment technique of "fast-turn and slow-shot glue", three levels of slow speed, fast speed, and starting position are all interrelated and affect each other, so those with inexperience are not easy to hold.

1. "Position injection" method because pressure and speed of latter stage are cancelled, two factors are missing. Therefore, only pressure and speed of previous stage need to be adjusted, starting point is moved forward and backward appropriately, adjustment becomes easier, it can be set more accurately, which is easier for beginners to hold.
2. In production, when we encounter certain raw materials and parts that cannot be produced at a slower speed, such as large parts, thin-walled parts, large PC parts, etc. Once they start slow injection, injection molded parts will be uneven or have pinches or vibrations. Therefore, they must be shot to end quickly. "Positioned shot" method is a good choice. Therefore, injection molded parts will not cause problems such as cracking, topping, and sticking due to excessive injection. On the contrary, in order to prevent problems such as criticizing and disapproving, we can use this tuning 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 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 criticism and disapproval.
What are limitations of "positioned injection" method?
Of course, it is not a panacea, it cannot completely replace tuning technique of "fast turn and slow shot glue". For example, when air is trapped, it is difficult to solve problem by using "positioned injection" method, but it is much easier to use "fast turn and slow injection method".
In any case, being able to use it flexibly will definitely become another magic weapon for you to solve difficult problems.

 

Slow first and then fast injection, that is, first-stage slow injection, when it reaches a set position, second-stage fast injection, starting point is usually set in the early stage of filling when cavity is first injected. According to different problems, sometimes it is necessary to switch to second stage when a small part of glue (about 10-15MM) is inserted, some need to be transferred to second stage when glue is a little bit (about 3MM), and sometimes it is necessary to switch to second stage before glue is fed.
With the first-level slow-spraying glue, melted glue can be filled smoothly from beginning, which is beneficial to prevent air trapping, gas lines and explosion-proof shooting, spiral or folding (snake-shaped) glue injection. Secondary fast injection is helpful to overcome resistance to ensure filling, reduce temperature drop of melt, prevent dull color and material shortage of injection molded parts.

Using this tuning technique, it can often be used to solve many problems such as water breath patterns and bullshit patterns, or to solve some conflicting problems, as follows:
It is used to solve problem of bullshit patterns and water trapping patterns on thick and large pieces. For example: 1. Number one problem in toy injection molding is bullshit pattern and water trapping of thick PVC parts. 2. It is used to solve problem of easy to produce air lines or jet lines at water inlet. For example, water inlet breath pattern of PC parts is difficult. 3. Solve problem of burnt glue and dull color around water inlet. 4. It is used to prevent other problems when it needs to fill mold quickly to get whole material. For example, problem of air lines or shooting lines around water inlet.
Of course, in the production, adjuster can also add several injection levels in this process in order to solve some other problems that arise during injection process according to actual situation. For example, when there is an air mark in the middle of injection molded part, a slow injection level must be added during rapid injection process, and then switch back to fast injection after filling position where gas pattern is generated. Since rapid injection is easy to cause air trapping, scorching and frontal problems, a slow and low pressure filling and pressure holding process is required in late injection period.
This tuning technique can be said to be one of several commonly used tuning techniques that are indispensable in injection molding production. Whether it will be used, whether it is used well or not, has essential differences in terms of level of technology.

First fast and then slow, that is to say, use first level of fast injection, and when it reaches a certain set position, then second level of slow injection. This secondary starting point is generally set at late stage of injection and filling, which is close to end of filling.

Use of one-stage fast glue injection can maintain melt temperature, overcome cavity resistance, and facilitate smooth filling. Second-level slow-spraying glue is beneficial to exhaust and melt glue to solve trapped air, prevent problem of cracking and shrinking. Using this technique can also solve many difficult and conflicting problems for us:

It can be used to solve air trapping problem of injection molded parts. Including "dead corners" trapped air and "backpack" trapped air problems. 2. It is used to solve problem that same mold is caused by imbalance of water in each cavity of mold. 3. It can also be used to solve problems such as front-end, white-out or shrinkage. 4. It can also be used to solve problem of difficult filling.

Of course, adjuster in production can also add several injection levels to injection process of "fast first and then slow" according to actual situation, in order to solve other problems in filling process. It is also possible to add a slow speed stage before fast injection to solve problems of nozzle position and air lines, all of which are higher and more advanced applications of this technique.
In fact, in a complex multi-stage glue injection process, two techniques of "first slow then fast" and "fast first and slow later" may actually be combined into one, but each is still working on its own. When there are relatively few problems, there are actually more obvious differences and emphasis, so they are divided into two techniques to discuss, so that we can understand differently and use them in conflict.

Sometimes, when solving problems such as pinning, water trapping, and bull dung piles, there will be such a situation: pressure or speed is reduced by one level, pinning or bull dung marks can be solved, but at the same time, there will be new problems such as uneven material; when pressure or speed is raised to one level, old problems will reappear, problems such as uneven materials will no longer exist. At this time, I really hope that pressure or speed of injection molding machine can be fine-tuned by half.

It is impossible to actually adjust half-level, but we found that purpose of fine-tuning can be achieved by adjusting melt temperature of plus or minus 2-5 degrees.
When temperature is increased, fluidity of melt will become better and filling will be faster, which has same effect as increasing pressure or speed; on the contrary, reducing temperature is like reducing injection pressure and speed.