1. Pressure
The action pressure provided by the pressure system (oil pump) or servo motor of the injection molding machine is mainly used in various action procedures such as injection device, melting device, mold opening and locking device, ejection device, injection table device, and core pulling device. After the control panel of the injection molding machine inputs relevant parameters, the processor converts them into signals for each program action, thereby controlling the pressure required for the execution of each action program.
The principle of pressure setting is: the corresponding strength to overcome the resistance of the action, but the parameter value needs to be adjusted accordingly to match the speed of the action.
2. Speed
Cooperate with the above pressure to complete the required activity speed (the flow rate of system hydraulic oil) of each action program. The basic speed levels are divided into: slow flow 0.1-10, slow speed 11-30, medium speed 31-60, and high speed 61-99.
1. The control of injection speed is applied to different product structures and materials to set the size values. We will not distinguish them here (engineering/general plastics, crystalline/amorphous plastics, high temperature/low temperature plastics, soft rubber/hard plastics) It is easy to confuse people. To give a more understandable 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).
The numerical setting of the injection speed mainly follows the following points:
Depends on the fluidity of the material; soft plastics such as PP, LDPE, TPE, TPR, TPU, PVC and other soft plastics have good fluidity and have small cavity resistance when filling. Generally, a lower injection speed can be used for filling. 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. When the product appearance gloss is not required or the product thickness is moderate (product When the wall thickness or bone thickness reaches 1.5MM or more), the injection speed can be filled at a medium speed. Otherwise, the filling speed needs to be appropriately increased according to the product structure or appearance requirements.
Engineering plastics such as PC, PA+GF, PBT+GF, LCP have poor fluidity and generally require high-speed injection during filling, especially materials with added GF (glass fiber). If the injection speed is too slow, the surface of the product will be damaged. The floating fiber (silver streak on the surface) is serious.
2. Control of melting speed;
This parameter is one of the most easily overlooked processes in daily work, because most colleagues believe that this process has little impact on molding, and products can be produced by adjusting the parameters at will. However, in injection molding, the melt parameters are the same as those of the injection molding process. The glue speed is equally important. The melt speed can directly affect the melt mixing effect, molding cycle and other important links.
3. Control of mold opening and locking speed;
Setting different parameters mainly for different mold structures, such as adjusting high-speed mold clamping before starting low mold clamping pressure for a two-plate flat mold and adjusting to rapid mold opening after the product leaves the mold cavity can effectively improve production efficiency. However, when adjusting the speed of mold opening and locking for molds with rows of rows, the speed and speed of mold opening and locking must be determined according to the height and structure of the rows. Special mold structures and core-pulling molds are explained in the following chapters due to their complex structures.
4. Control of thimble speed;
It mainly depends on the demoulding condition of the product. In principle, it should be as fast as possible on the premise of ensuring that the product does not appear white, high, or deformed. Otherwise, the parameters need to be adjusted appropriately according to the actual situation. Of course; under normal circumstances, the first time to adjust the demoulding The true speed should be medium to low speed (15%-35%), which can effectively extend the service life of the ejector pin and ejector cylinder.
3. Location
Switching points between fast and slow speed, high and low pressure of each action
1. Control of injection position;
During injection molding parameter debugging, the injection position needs to be adjusted according to the unit weight and structure of the product. When adjusting the position by considering the unit weight of the product, it is often said that the amount of glue required for the product,
For example: a product has a unit weight of about 50G and is produced using a 90T injection molding machine. The theoretical injection volume of this model is 120G and the melting stroke is 130MM. The approximate melt weight per MM is the theoretical injection volume of 120G÷the melting stroke of 130MM. =0.92G, that is, the injection distance of this product is 50×0.92=46MM position. If the melt end position is set at 60MM, then the product quality is basically OK when the injection reaches 14MM.
(Of course, the above is based on experience, and there are some deviations, because the screw compression ratio calculation formula in the book is not followed. It is too complicated, and I believe most colleagues cannot calculate it.) As for how to use the injection position to control various moldings Defects in the product.
2. Control of melt position;
Generally speaking, it is understood that the melt distance is set in response to the required injection amount of the molded product. Most colleagues ignore the three-stage switching position of the melt and only focus on the melt end position. Of course; for molded products of ordinary difficulty, the melt position must be adjusted It is not necessary to switch between fast and slow speed or high and low back pressure, and the required product quality can still be achieved. However, when producing color masterbatch and highly heat-sensitive plastics, it is better to appropriately switch the melt speed and back pressure adjustment position. to control product quality.
3. Position control of mold opening and locking;
The switching point is mainly set according to the needs of mold opening and locking speed.
3.1 Under normal circumstances, the switching point of mold opening speed is slow speed before the molded product leaves the mold cavity (about 5-15MM), then fast speed, which can effectively shorten the time required for mold opening, and finally slow speed (i.e. mold opening buffer). Position, generally 20-40MM away from the required end position of mold opening, it is better to start switching (the end position depends on the product structure and whether a robot is used), which can effectively extend the service life of the injection molding machine and the stability of the mold opening action).
The structural factors of some special molds, such as three-plate molds or core-pulling molds, the mold opening speed needs to be determined according to the actual situation. For example, the three-plate mold has the product cavity on the middle plate. When opening the mold, the first action is on the nozzle plate, and the nozzle needs to be After the runner is separated from the product, the male and female molds are separated again, so 1-2 switching points need to be added at the mold opening position, which are medium speed-slow speed-high speed-slow speed. Machines with larger tonnage can be adjusted as needed. Add a few more switching points, in short, the quality of the molded products will not be affected during the mold opening process and the movement process will be smooth.
3.2 The setting of the clamping position mainly depends on the structure of the mold. For example: the flat mold structure (that is, the parting surfaces of the front and rear molds are both flat, no slider/core pulling, no insertion structure) switches at the clamping speed. You can directly use the 4-position position to perform "fast-medium speed-low pressure-high pressure". The switching principle of the position is: the fast mold clamping stroke is preferably about 70% of the mold opening stroke. (The quick end position of the three-plate mold depends on Depends on the structural size of the mold), its main function is to shorten the mold clamping cycle. After the medium speed, it acts as a deceleration buffer for high-speed mold locking (because it will switch to the low-voltage protection function after the medium speed)
The end position of the mold clamping medium speed is very important, as it determines the starting position of the mold clamping low voltage protection. Some experienced colleagues are very confused about the mold clamping low voltage and think that the mold can be locked by any setting. In fact, this is not the case. If the mold clamping low pressure is set improperly, its protective function will be completely lost, which is fatal to fully automatic mold production.
4. Control of ejector pin position;
Theoretically, the ejection length of the ejector pin is twice the height of the mold cavity (i.e., the mold core) behind the mold. However, in actual operation, it is not necessary to set the position exactly according to this method. Specifically, it is mainly to facilitate the removal of the product. However, when adjusting the ejector pin position for the first time, it is necessary to gradually lengthen it. First, 50% of the mold ejector pin stroke must be ejected, and then it depends on the removal status of the product during the production process.
4. Temperature
Necessary conditions required for plastic melting and mold heating
1. Control of material tube temperature;
Generally speaking, plastics with different properties have relatively standard molding temperatures, such as: ABS= (distinguish between 230-260 for high-impact materials and 190-230 for low-impact materials), SAN=180-220, HIPS=180- 220, POM=170-200, PC=240-300, ABS/PC=230-260, PMMA=200-230, PVC= (distinguish high density 160-200, low density 140-180), PP=180-230 , PE= (distinguish between high density 240-300 and 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) PA=230-270, PA+fiber=250-300, PBT=200-240, PBT+fiber=240-280. In addition, the molding temperature of adding flame retardants (i.e. fire retardant materials) should be 20-30 degrees lower than ordinary materials. The specific use temperature depends on the production situation, because the molding temperature directly affects the fluidity, viscosity, mold temperature, color, shrinkage rate, product deformation, etc. of the plastic.
2. Control of mold temperature;
The mold temperature mainly depends on the fluidity of different plastics. A simple understanding is that it is the key process to overcome poor fluidity. For example, PC materials and PA+ fiber materials have poor fluidity, and their flow resistance during the filling process is large, so they need to be faster. The glue injection speed is used for filling.
In addition, when producing PC transparent plastic parts, a higher mold temperature is required to improve surface air marks, rainbow marks, internal bubbles and other undesirable problems. When producing fiber-added materials, if the mold temperature is low, silver streaks will appear on the surface ( floating fibers).
Under normal circumstances, you can refer to the following data to adjust the mold temperature:
ABS=30-50 (Products with high surface quality requirements or deformation control can be raised to 60-110 degrees) PC=50-80 (Products with high surface quality requirements or thin-walled products can be raised to 85-140 degrees) HIPS= 30-50 (transparent PS and products with high surface quality requirements can be raised to 60-80 degrees)
PMMA=60-80 (thin-walled products and products with high surface quality requirements can be raised to 80-120 degrees) PP=10-50, PE=10-50 (high-density or thin-walled products can increase the mold temperature appropriately) Rubber (TPE, TPR, TPU)=10-50,
PA, PBT=30-60 (materials with high surface quality requirements and glass fiber added can be increased to 70-100)
5. Time
The time each action takes to execute
1. Control of filling time;
Including injection time and holding time
1.1. Injection time:
Generally speaking, if the quality of the product is qualified, the shorter the better. Because the injection time directly affects the internal stress and production cycle of the product, in principle, the thinner the glue position of the product, the shorter the injection time. On the contrary, for thick-walled products, the control time is The shrinkage problem requires extending the injection time as appropriate.
In addition, products that use multiple stages and have a large range of fast and slow switching require a longer injection time. The setting of the injection time also needs to be set according to the volume of the product (the larger the product, the longer the injection time required). Production also needs to be considered here. Use plastic properties, such as: general plastic ABS, when the product wall thickness is 2.0MM, the injection speed is moderate, and the material tube temperature is moderate, the longitudinal flow rate is about 65 mm/second (the flow rate is different for different mold structures or processes).
1.2. Pressure holding time:
In principle, the holding time mainly controls the surface shrinkage of the product and the structural size of the product. However, after fully mastering the control method of the holding time, the holding pressure can also be used to adjust the deformation of the product (therefore, the adjustment process is a precision adjustment process, which will be discussed later. The chapter details the adjustment method).
Here I will briefly explain how to use holding pressure to control product shrinkage. Generally, the choice of using holding pressure to control product shrinkage depends on the shrinkage position of the product. Not all shrinkage can be solved by holding pressure, such as: shrinkage The position is at the end of melt filling. Using holding pressure to control shrinkage will cause excessive stress near the nozzle, causing top whitening, mold sticking, or product warping and deformation.
2.Thimble extension
Time; mainly controls the dwell time of the ejector pin when it is ejected, so as to facilitate the robot to pick up the product.
3. Core pulling time;
Control the action time of the core-pulling device of the injection molding machine (mainly used to control the action stroke by time). If the core-pull of the core-pulling stroke is controlled by an induction switch, the core-pulling time does not need to be set.
