Explanation of injection pressure, speed, position, time, temperature

Time:2022-08-02 08:39:23 / Popularity: / Source:

1. Pressure

Action pressure provided by pressure system (oil pump) of injection molding machine or service motor is mainly used in various action procedures such as injection device, glue melting device, mold unlocking device, ejector device, shooting table device, and core pulling device. After inputting relevant parameters on control panel of injection molding machine, processor converts them into signals for each program action, thereby controlling pressure required for execution of each action program.
Principle of pressure setting is:
Corresponding strength to overcome resistance of action, but parameter value needs to be adjusted accordingly to match speed of action.

2. Speed

Cooperate with above pressure to complete movement speed (flow of hydraulic oil in system) required for each action program. Basic level of speed is divided into: slow flow 0.1-10, slow speed 11-30, medium speed 31-60, high speed 61-99.

1. Control of injection speed

Control of injection speed is applied to different product structures and materials to set size and value. It will not be distinguished here (engineering/general plastics, crystalline non-crystalline plastics, high temperature/low temperature plastics, soft/hard plastics) , it is easy to confuse audio-visuals, make an easy-to-understand explanation. Injection speed is a process element that is difficult to control in injection molding. Unlike other process elements, there are standard data for reference (will be introduced in detail later).
Numerical setting of injection speed mainly follows following points:
According to fluidity of material, such as PP, LDPE, TPE, TPR, TPU, PVC and other soft plastics, fluidity is good, and cavity resistance is small when filling. Generally, 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 poor fluidity. In the case where product appearance glossiness is not high or product meat thickness is moderate (product wall thickness or bone thickness is 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 during filling, especially for materials with GF (glass fiber) added. If injection speed is too slow, it will cause serious floating fibers (surface silver streaks) on the surface of product.
injection pressure 

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, but in 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. Control of mold opening and locking speed

Different parameters are mainly set for different mold structures. For example, two-plate flat molds can adjust high-speed mold clamping before starting mold clamping and low pressure, and adjust to fast mold opening after product is released from mold cavity, which can effectively improve production efficiency.
However, when adjusting speed of mold opening and locking for molds with row positions, it is necessary to switch speed of mold opening and locking according to height and structure of slider. Special mold structure and core-pulling mold are explained in following chapters due to their complex structure.

4. Ejector speed control

It mainly depends on demoulding status of product. In principle, it should be 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, in general, the first adjustment of ejector speed should be at medium and low speed (15%-35%), which can effectively prolong service life of ejector pin and ejector pin cylinder.

3. Location

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

1. Control of injection position;

In debugging of injection molding parameters, injection position needs to be adjusted according to unit weight and structure of product. When adjusting position considering unit weight of product, it is often said how much glue is needed for product.
For example: unit weight of a product is about 50G, which is produced by a 90T injection molding machine. Theoretical injection volume of this model is 120G, and melting stroke is 130MM. Melt weight per MM is about theoretical injection volume of 120G÷melting stroke of 130MM. =0.92G, that is, distance of product is 50×0.92=46MM. If melting end position is set at 60MM, product quality is basically OK when injection reaches 14MM.
(Of course, above is based on experience, there is a bit of deviation, because it is too complicated to calculate screw compression ratio according to formula in the book, I believe most colleagues can't calculate it). As for how to use injection position to control undesirable phenomena of various molded products, it will be explained in detail in following chapters.

2. Control of melting position;

Generally speaking, it is understood that glue distance is set in response to required amount of glue injection of molded product. Most colleagues ignore three-stage switching position of glue, and only focus on the end position of glue;
Molded products of general difficulty do not need to switch between fast and slow speeds or high and low back pressure when adjusting melting position, and required product quality can still be achieved. However, in production of color masterbatches and plastics with high heat sensitivity, adjustment position of melting speed and back pressure can be properly switched, which can better control quality of products.

3. Position control of mold opening and locking

Mainly set switching point according to needs of mold opening and locking speed
Under normal circumstances, switching point of mold opening speed is slow speed before the molded product leaves the mold cavity (about 5-15MM), fast rotation afterward, which can effectively shorten time required for mold opening, and slow speed at the end(ie, mold opening buffer position), and it is better to start switch 20-40MM away from required mold opening termination position (termination position depends on product structure and whether a manipulator is used), which can effectively prolong service life of injection molding machine and stability of mold opening action.
Structural factors of some special molds, such as three-plate molds or core-pulling molds, mold opening speed should be determined according to actual situation. For example, since product cavity of three-plate mold is on middle plate, nozzle plate is moved first when mold is opened, male and female molds need to be separated after nozzle runner is separated from product. Therefore, 1-2 switching points need to be added to mold opening position, which is medium speed-slow speed-high speed-slow speed. For machines with larger tonnage, more switching points can be added as needed. In short, quality of molded products is not affected during mold opening process and movement process is stable.
Setting of clamping position mainly depends on structure of mold
For example: plane mold structure (that is, parting surfaces of front and rear molds are flat, no slider/core pulling, no insertion structure), when clamping speed is switched, 4-stage position can be directly used to perform "fast-medium-speed-low pressure- high pressure",
Switching principle of its position is:
Fast mold clamping stroke is preferably about 70% of mold opening stroke. (Quick termination position of three-plate mold depends on structure and size of mold). After turning at medium speed, it acts as a deceleration buffer for high-speed mold clamping, (because it will switch to low-voltage protection function after medium speed is passed).
End position of mode clamping medium speed is very important. It determines starting position of mode clamping low voltage protection. Some senior colleagues are very vague about low pressure of mold clamping, thinking that it is possible to lock mold with any setting, but it is not.   about mode clamping low voltage. If low-voltage setting of mold clamping is improper, protection function will be completely lost, which is fatal to fully automatic production mold.
injection pressure 

4. Control of thimble position;

Theoretically, ejection length of ejector pin is twice height of mold cavity (ie, mold core) behind mold, but in actual operation, it is not necessary to set position completely by this method, which is mainly to facilitate removal of product. However, when adjusting position of ejector pin for the first time, it needs to be gradually lengthened. First, 50% of stroke of ejector pin of mold should be ejected, and then it depends on removal of product during production process.

4. Temperature

Necessary conditions for plastic melting and mold heating

1. Control of temperature of material pipe;

In general, plastics of 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 high density 240-300, low density 180-230),
TPE= (distinguish high density 170-200, low density 140-180),
TPR= (distinguish high density 170-200, low density 140-180),
TPU= (distinguish high density 160-200, low density 120-160)
PBT+fiber=240-280, and molding temperature of adding flame retardant (ie, fireproof material) is 20-30 degrees lower than that of ordinary material.
Specific use temperature depends on production situation, because molding temperature directly affects fluidity, viscosity, mold temperature, color, shrinkage, product deformation, etc. of plastic.

2. Control of mold temperature;

Temperature of mold is mainly determined by fluidity of different plastics. It is simply understood that it is key process to overcome poor fluidity. For example, fluidity of PC material and PA+fiber material is poor, their flow resistance during filling process is large, so a faster injection speed is required for filling.
In addition, when producing PC transparent plastic parts, higher mold temperature is required to improve defects such as air pattern on the surface of product, rainbow prints and internal bubbles. If mold temperature is low when producing fiber-filled materials, surface silver lines (floating fibers) will appear. In general, you can refer to following data to adjust mold temperature:
ABS=30-50 (products that require high surface quality or need to control degree of deformation can be increased to 60-110 degrees)
PC=50-80 (products with high surface quality requirements or thin-walled products 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-walled 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 (materials with high surface quality requirements and glass fiber can be increased to 70-100)

5. Time

Time for each action

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

Injection time
Generally, the shorter product is, the better quality is. Because injection time directly affects internal stress and production cycle of product, in principle, the thinner glue level of product, the shorter injection time. On the contrary, in order to control shrinkage problem of thick-walled products, it is necessary to extend injection time as appropriate.
In addition, use of multi-stage and high-speed switching products requires a longer injection time. Setting of injection time also needs to be set according to volume of product (the larger product, the longer injection time is required). Here, properties of plastic used for production should also be considered, such as: general plastic ABS, when product wall thickness is 2.0MM, injection speed is moderate, and material tube temperature is moderate, longitudinal flow rate is about 65 mm/s (different mold structures or processes have different flow rates).
Compress time
In principle, pressure holding time mainly controls surface shrinkage of product and product structure size, but when control method of holding pressure time is fully grasped, holding pressure can also be used to adjust deformation degree of product.
Here, I will briefly explain use of pressure-holding to control shrinkage of product. Generally, use of pressure-holding to control shrinkage of product depends on shrinkage position of product. Not all shrinkage can be solved by pressure-holding, such as: shrinkage position is at the end of melt filling, and using holding pressure to control shrinkage will cause excessive stress at the position near nozzle, resulting in top white, sticking to mold, or warping of product.

2. Thimble delay time

It mainly controls residence time when ejector pin is ejected, which is convenient for manipulator to pick up product.

3. Core pulling time

Control action time of core-pulling device of injection molding machine (mainly used to control action stroke with time).
4. Low-voltage time and setting method of clamping mode will be explained in detail in following chapters

Go To Top