For explanation of injection pressure, speed, position, time, temperature, please check!

Time:2020-07-14 10:38:23 / Popularity: / Source:

molded product 

1. Pressure

Operating pressure provided by pressure system (oil pump) of injection molding machine or servo motor is mainly used in various operating programs such as injection devices, melt adhesive devices, mold opening devices, ejection devices, shooting table devices, core pulling devices, etc. After inputting relevant parameters on the control panel of injection molding machine, processor converts them into signals for actions of each program, thereby controlling pressure required for execution of each action program.
Principle of pressure setting is:
Corresponding strength to overcome resistance of action, but to match speed of action, parameter value needs to be adjusted accordingly.

2. Speed

According to above-mentioned pressure, required activity speed (flow rate of system hydraulic oil) to complete each action program is divided into basic levels of speed: slow flow 0.1-10, slow speed 11-30, medium speed 31-60, high speed 61-99.

1. Control of injection speed

It is applied to different product structures and materials to set size value, which is not distinguished here (engineering/general plastics, crystalline/non-crystalline plastics, high temperature/low temperature plastics, soft rubber/hard plastic). It is easy to confuse audio-visual, and make a more understandable explanation. Injection speed is a process element that is more difficult to control in injection molding. Unlike other process elements, Numerical setting of injection speed mainly follows following points:
Depending on fluidity of material, such as PP, LDPE, TPE, TPR, TPU, PVC and other soft plastics, fluidity is better, cavity resistance during filling is small. In general, a lower injection speed can be used to fill cavity.
Commonly used medium-viscosity plastics such as ABS, HIPS, GPPS, POM, PMMA, PC+ABS, Q glue, K glue, HDPE, etc. have slightly poorer fluidity, and require low gloss in product appearance or moderate thickness (wall thickness or bone thickness of more than 1.5MM), injection speed can be filled at a medium speed, otherwise filling speed should be appropriately increased according to product structure or appearance requirements.
Engineering plastics such as PC, PA+GF, PBT+GF, LCP, etc. have poor fluidity. Generally, high-speed injection is required when filling, especially for materials with increased GF (glass fiber). If injection speed is too slow, floating fiber (silver pattern on the surface) of product will be serious.

2. Control of melt speed

This parameter is one of the most easily overlooked processes in daily work, because most colleagues believe that this process has little effect on molding, and parameters can be adjusted to make products. However, in the injection molding, melt parameters are as important as injection speed. Melt speed can directly affect melt mixing effect, molding cycle and other important links.

3. Speed control of mold opening

Different parameters are mainly set for different mold structures. For example, two-plate flat molds adjust high-speed mold clamping before starting low-pressure mold clamping and adjust to rapid mold opening after product leaves mold cavity to effectively improve production efficiency.
However, when adjusting speed of mold unlocking, mold with slider needs to determine fast and slow switching of mold opening and closing according to height and structure of slider.

4. Control of ejector pin speed

Mainly depends on demolding condition of product, in principle, as fast as possible on the premise of ensuring that product does not appear top white, top height, or deformation, otherwise it is necessary to adjust parameters appropriately according to actual situation. Of course, under general circumstances, the first adjustment of ejector pin speed should be a low-medium speed (15%-35%), which can effectively extend service life of ejector pin and cylinder.
injection molding parameters 

3. Location

Switching point between speed of each action, high and low pressure

1. Control of injection position

In debugging of injection molding parameters, position of injection needs to be adjusted according to unit weight and structure of product. When considering unit weight of product to adjust position, it is often said how much material product requires.
For example, a product has a single weight of about 50G and is produced using a 90T injection molding machine. Theoretical injection quantity of this model is 120G, melting stroke is 130MM, and approximate weight of each MM melt is theoretical injection quantity 120G/melting stroke 130MM =0.92G, that is, product's injection distance is 50*0.92=46MM. If end position of material is set at 60MM, then quality of product is basically OK when material is shot to 14MM.
Of course, above is a matter of experience, a little bit of deviation, because screw compression ratio calculation formula in the book is not followed, which is too complicated, I believe most colleagues can't count.

2. Control of position of injection

In general, it is understood that melt distance is set in response to required amount of material for molded product. Most colleagues ignore three-stage switching position of melt and only focus on end position of melt;
Molded product of general difficulty do not need to switch between fast and slow speed or high and low back pressure when adjusting position of melt, and desired product quality can still be achieved. However, in production of color masterbatch, high heat-sensitive plastics, proper adjustment of melt speed and back pressure adjustment position can better control product quality.

3. Position control of mold opening

Set switching point mainly to meet needs of speed of unlocking mold
Under normal circumstances, switching point of mold opening speed is that molded product is slow before it leaves mold cavity (about 5-15MM), and then rotates quickly, which can effectively shorten time required for mold opening, and finally rotates slowly (ie, mold opening buffer position) Generally, it is better to start switch from 20-40MM away from required mold opening end position (end position depends on the product structure and whether manipulator is used), which can effectively extend service life of injection molding machine and stability of mold opening action.
Structural factors of some special molds, such as three-plate mold or core-pulling mold, mold opening speed needs to be determined according to actual situation. For example, because product cavity is on the middle plate, three-plate mold first acts on nozzle plate during mold opening. After runner is separated from product, male and female molds are separated again, so 1-2 switching points need to be added at the position of mold opening, which is medium speed-slow speed-high speed-slow speed. Machines with larger tonnage can add more switching points as needed. In short, quality of molded product is not affected during mold opening process and movement process is stable.
Setting of clamping position mainly depends on the structure of mold
For example: when mold clamping speed is switched, plane mold structure (that is, parting surfaces of front and back molds are all flat, no slider/core pulling, and no penetration structure) can be directly used for "fast-medium speed-low pressure-high pressure" with 4 positions.
Switching principle of its position is:
Fast stroke of mold clamping is about 70% of stroke of mold opening. (Quick termination position of three-plate mold depends on structure size of mold). Main function is to shorten mold clamping cycle. Back to middle speed, acting on deceleration buffer of high-speed mold clamping, (because it will switch to low-voltage protection after mid-speed).
End position of mode-locking medium speed is very important. It determines starting position of mode-locking low-voltage protection. Some old colleagues are very vague about mode-locking low-pressure. They think it seems that any setting can be used to lock mold, but it is not. If low-pressure setting of mold clamping is improper, protection function will be completely lost, which is fatal to fully automatic production of mold.

4. Control of ejector pin position

In theory, ejection length of ejector pin is twice height of back mold cavity (ie, mold core), but in actual operation, it is not necessary to set position completely according to this method, specifically for convenience of taking out product. However, when adjusting position of ejector pin for the first time, length of ejector pin needs to be gradually increased, first ejecting 50% of stroke of ejector pin of mold, and then depending on state of product during production process.
molded product 

4. Temperature

Necessary conditions for plastic melting and mold heating

1. Temperature control of feed tub

Generally speaking, plastics with different properties have their relatively standard molding temperatures, such as:
ABS=(distinguish high impact material 230-260, low impact material 190-230),
PVC=(distinguish high density 160-200, low density 140-180),
PE=(distinguish between high density 240-300 and low density 180-230),
TPE= (distinguish between high density 170-200 and low density 140-180),
TPR= (distinguish between high density 170-200 and low density 140-180),
TPU= (distinguish between high-density 160-200 and low-density 120-160)
PBT+fiber=240-280. In addition, molding temperature of adding flame retardant (ie fire retardant) is 20-30 degrees lower than that of ordinary materials.
Specific use temperature depends on production situation, because molding temperature directly affects fluidity, viscosity, mold temperature, color, shrinkage rate, and product deformation of plastic.

2. Control of mold temperature

Mold temperature mainly depends on flowability of different plastics. It is simple to understand that it is a key process to overcome poor flowability. For example, PC material and PA+fiber material have poor fluidity, and flow resistance during filling process is large, which requires a fast injection speed for filling.
In addition, for production of PC transparent materials and plastic parts, in order to improve bad problems of product surface gas lines, rainbow marks and internal bubbles, a higher mold temperature is required. If mold temperature is lower when producing fiber reinforced materials, surface silver thread will appear ( Floating fiber). Under normal circumstances, you can refer to following data to adjust mold temperature:
ABS=30-50 (products with high surface quality requirements or need to control degree of deformation can be increased to 60-110 degrees)
PC=50-80 (products with high surface quality or thin wall can be increased to 85-140 degrees)
HIPS=30-50 (transparent PS and products with high surface quality requirements can be increased to 60-80 degrees)
PMMA=60-80 (thin wall products and products with high surface quality requirements can be increased to 80-120 degrees)
PP=10-50, PE=10-50 (high-density or thin-walled products can appropriately increase mold temperature)
Rubber (TPE, TPR, TPU) = 10-50,
PA, PBT=30-60 (high surface quality requirements and materials with glass fiber can be increased to 70-100)
molded product 

5. Time

Time of each action

1. Control of filling time, including injection time and holding time

Injection time
Generally required products are as short as possible when quality is qualified, because injection time directly affects internal stress and production cycle of product. In principle, the thinner adhesive position of product, the shorter injection time. On the contrary, thick-walled product needs to be extended as appropriate to control shrinkage problem.
In addition, use of multi-segment products with large switching speeds requires a long injection time. Setting of injection time also needs to be set according to volume of product (the larger product, the longer injection time). Production needs to be considered here. Plastic properties, such as: general plastic ABS, when product wall thickness is 2.0MM, injection speed is moderate, and temperature of material tube is moderate, flow rate is about 65 mm/sec in ongitudinal direction (different mold structures or processes have different flow rates).
Holding time
In principle, holding time mainly controls shrinkage of product surface and product structure size, but when control method of holding time is fully grasped, deformation of product can also be adjusted by using dwell.
Generally, use of holding pressure to control product shrinkage depends on shrinking position of product. Not all shrinkage can be solved by holding pressure, such as: shrinkage position is at the end of melt filling. Using holding pressure to control shrinkage will cause excessive stress near nozzle position, resulting in top white, sticky mold, or product warpage.

2. Eject delay time

Mainly control residence time when thimble is ejected, which is convenient for robot to pick up  product.

3. Core pulling time

Control operation time of core-pulling device of injection molding machine (mainly used to control movement stroke with time). If core-pulling is controlled by induction switch to control core-pulling stroke, core-pulling time can be omitted.

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