Finding the correct holding pressure is critical for compacting products. Correct pressure in second stage should be within range of product parameters required to obtain a good Cpk (process capability index) product, and be at the center of it. Since holding pressure is set under conditions of gate sealing test, correct second-stage compaction and holding pressure values should be found through experiment, which is determined as center value of product processing parameter range.
First, check stability of first stage, and check whether there is insufficient mold filling or product shrinkage after first stage. Inspection process: set aside time in second stage and reduce holding pressure to low value allowed by equipment. Take care to avoid reducing holding pressure or holding pressure time to zero. If first stage is different from what was expected, then keep first stage unchanged. If no action is taken in second stage, it will lead to an error in first stage.
If first stage is stable, then start to increase holding pressure. Starting from low, it may only require a pressure of 1000 to 2000 psi for plastics. Check product every time holding pressure is increased; increase holding pressure in small increments until it is judged that quality of product reaches the best acceptable state. Produce a certain number of products whose quality requires preliminary testing. Label and put away.
Now continue to increase holding pressure until production has unacceptable flash, push rod action, adhesion or other problems that may cause damage to mold or product, or there are signs that processing cannot run under set high pressure conditions. Reducing pressure to maximum allowable process allows safe and efficient production. In addition, process a set of products for preliminary quality inspection. Affix logo and keep it away. Finally, a group of products are produced in the middle of pressure range just set.
Take out three groups of products obtained for quality control operations, and determine which group of products is unacceptable or acceptable through data generated by quality control. There are three possible answers:
All products are too big. This means failure because it indicates that wrong shrinkage was used when calculating cavity size. If they exceed high and low limit values of pressure range, it is difficult for any process change to make product size reach middle of required range.
All products are too small. This is still not good news, but at least it is "mold safety", which can be achieved by adjusting mold to make product within required range. In addition, it is difficult to return product to center of required range by changing process.
Some products are too small and some are too large. Now you can determine upper and lower limits of minimum DOE (design of experiment) by establishing possession data from obtained data. Within acceptable product range, use second-stage pressure experiment to determine center of product requirement range. This is right way to obtain a good process capability index Cpk Six Sigma quality.
Without data support, finger rule of 25%, 50% or 75% injection pressure will not work. This method will indicate that sometimes a low holding pressure is required, and sometimes a holding pressure that exceeds injection pressure is required. The only valid rule is: get data and let product determine!

 

Clamping process is generally divided into three or four stages, which is generally fast-slow-low pressure-high pressure;
Quick clamping, according to structure of mold, it is flat, or there is a slider. Different molds first set pressure/speed/position during rapid clamping, and set appropriate pressure/speed/position without affecting efficiency. Pay attention to principle of not only making mold smooth but also reflecting principle of fast clamping.
Low pressure---slow speed. This part is the most important. In jog state, set pressure to 0, slow down speed, and set position to 0, because machine itself has a bottom pressure, although pressure is 0, mold will still be closed. After mold is closed, because position is 0, high pressure cannot be raised. At this time, according to position of mold base displayed on main panel, change low pressure position to value displayed on panel;
For high pressure, generally speaking, it is necessary to set high pressure of mold clamping according to projected area of product and performance of material. After setting appropriate value, you need to adjust low pressure protection again, press previous step, and re-correct position of low pressure mold clamping. But it is guaranteed to be effective.
1. Under premise of ensuring mold clamping speed, low pressure mold clamping pressure should be set as low as possible, as long as it can reliably offset frictional resistance of mold clamping (frictional resistance between mold plate and large column, friction resistance of guide column and guide sleeve after movable and fixed mold contact, friction resistance of inclined guide column slider, friction resistance of movable mold plate and supporting parts, etc.).
2. It is necessary to set a sufficient low-pressure protection stroke (should be larger than size of product, or larger than size of gripper of manipulator if there is a manipulator), too large a low-pressure protection stroke will affect accurate setting of low-pressure protection pressure and low-pressure protection time, so setting should be reasonable.
3. After calculating actual time when low-voltage protection starts and ends, low-voltage time is set to be slightly greater than actual time (margin is less than 1 second to ensure that mold clamping action signal output is stopped in time when there is foreign matter). Principle of low-voltage protection is that within a certain low voltage time, computer cannot sample high voltage signal, and computer determines that there is a foreign body in mold cavity. At this time, computer should in principle stop mold-clamping signal output, simultaneously alarm and output mold-opening signal.
4. Set required clamping force first, and then set high-pressure clamping pressure proportionally. System pressure of machine with different clamping forces is same. Using this mechanism, clamping force can be accurately preset by setting high-pressure pressure.
5. Set high-pressure stroke position to be too large first. At this time, gradually reduce high-pressure stroke position based on experience, until high-pressure stroke cannot be raised or machine hinge cannot be straightened, then slightly adjust high-pressure stroke to make clamping force reliable. If there is a slider, protection position must be greater than height of slider guide post, and pressure should be as small as possible.
There is an inspection standard for low-pressure mold protection. Put a 0.5-2mm thick cardboard. If mold cannot be closed, it proves that you have set up successfully!