For inexperienced customers entering the injection molding industry, often consult our company's customer service: How can I improve my injection molding machine in one day? For this problem, we first understand the operating procedures of the injection molding machine:
1. The action program of the injection molding machine: nozzle forward→injection→hold pressure→pre-molding→reverse→nozzle backward→cooling→mould opening→ejection→needle withdrawal→door opening→door closing→mould closing→nozzle forward
2. Injection molding machine operation project: Injection molding machine operation project includes three aspects: control keyboard operation, electrical control cabinet operation and hydraulic system operation. The selection of injection process action, feeding action, injection pressure, injection speed, ejection type, temperature, current, and voltage monitoring of each section of the barrel, adjustment of injection pressure and back pressure, etc. are carried out respectively.
3. Action selection in the injection process: General injection molding machines can be operated manually, semi-automatically or fully automatically. Manual operation is in a production cycle, each action is realized by the operator flipping the operation switch. Generally, it is only used when the test machine adjusts the mold; in the semi-automatic operation, the machine can automatically complete the action of a work cycle, but after each production cycle, the operator must open the safety door, remove the workpiece, and then close the safety door before the machine can continue. One cycle of production; in fully automatic operation, the injection molding machine can automatically enter the next work cycle after completing a work cycle. There is no need to stop the machine for control and adjustment during normal continuous work. However, it should be noted that if fully automatic operation is required, semi-automatic or fully automatic operation is generally selected during normal production. At the beginning of the operation, the operation mode (manual, semi-automatic or fully automatic) should be selected according to the production needs, and the manual, semi-automatic or fully automatic switch should be toggled accordingly. The semi-automatic and fully automatic working procedures have been determined by the circuit itself. The operator only needs to change the speed and pressure, the length of time, the number of thimbles, etc. on the electric cabinet, and it will not be caused by the operator adjusting the wrong buttons. Make the work process chaotic. When each action in a cycle is not properly adjusted, manual operation should be selected first, and after confirming that each action is normal, semi-automatic or fully automatic operation should be selected.
4. Pre-plasticizing action selection: According to whether the injection seat retreats before and after pre-plastic feeding, that is, whether the nozzle leaves the mold, the injection molding machine generally has three options.
(1)Fixed feeding: The nozzle is always stuck into the mold before and after pre-molding, and the injection seat does not move.
(2) Front feeding: the nozzle is pressed against the mold for pre-plastic feeding. After the pre-plasticizing is completed, the injection seat will move back and the nozzle will leave the mold. The purpose of choosing this method is to use the injection hole of the mold to assist the nozzle during pre-molding to prevent the melt from flowing out of the nozzle when the back pressure is high. After pre-molding, it can prevent the nozzle and the mold from contacting for a long time to produce heat transfer and affect them. The relative stability of their respective temperatures.
(3) Post-feeding: After the injection is completed, the injection seat retreats, the nozzle leaves the mold and then preforms, and then the injection seat advances after the preformation. This action is suitable for processing plastics with a particularly narrow molding temperature. Because the nozzle and the mold have a short contact time, the loss of heat and the solidification of the melt in the nozzle hole are avoided. After the injection is finished and the cooling timer finishes, the pre-plastic action starts. The screw rotates to melt and squeeze the plastic to the front of the screw head. Due to the role of the check valve at the front end of the screw, the molten plastic accumulates at the front end of the barrel, forcing the screw back. When the screw retreats to a predetermined position, the pre-plasticization stops and the screw stops rotating. This is followed by a retraction action, which means that the screw makes a slight axial retreat. This action can relieve the pressure of the melt gathered at the nozzle and overcome the "salivation" caused by the imbalance of the pressure inside and outside the barrel. phenomenon. If there is no need to retract, the retract stop switch should be adjusted to the appropriate position, so that the same time the pre-plastic stop switch is pressed, the retract stop switch is also pressed. When the screw retreats to the stop switch, the retraction stops. Then the betting began to retreat. When the injection seat retreats until the stop switch is pressed, the injection seat stops retreating. If a fixed feeding method is used, attention should be paid to adjusting the position of the travel switch. Generally, the fixed feeding method is adopted in the production to save the time of the injection seat advance and retreat and speed up the production cycle.
5. Injection pressure selection: The injection pressure of the injection molding machine is adjusted by the pressure regulating valve. In the case of the adjusted pressure, the high and low pressure oil circuits are turned on and off to control the injection pressure in the early and late stages. There are three pressure options for ordinary medium-sized injection molding machines, namely, high pressure, low pressure, and first high pressure and then low pressure. High-pressure injection is realized by passing high-pressure oil into the injection cylinder. Due to the high pressure, the plastic enters the cavity under high pressure and high speed from the beginning. During high-pressure injection, the plastic enters the mold quickly, and the pressure gauge of the injection cylinder rises quickly. Low-pressure injection is realized by passing low-pressure pressure oil into the injection cylinder. The reading of the pressure gauge rises slowly during the injection process, and the plastic enters the cavity at low pressure and low speed. The first high pressure and then the low pressure is achieved by controlling the pressure of the pressure oil passing into the cylinder from time to time according to the actual requirements of the plastic type and the mold. In order to meet the requirements of different plastics with different injection pressures, the method of replacing screws or plungers with different diameters can also be used, which not only satisfies the injection pressure, but also gives full play to the production capacity of the machine. In large-scale injection molding machines, there are often multi-stage injection pressure and multi-stage injection speed control functions, which can better ensure the quality and accuracy of the product.
6. Selection of injection speed: Generally, there are fast-slow knobs on the control panel of injection molding machines to meet the requirements of injection speed. In the hydraulic system, a large flow oil pump and a small flow pump are provided for supplying oil at the same time. When the oil circuit is connected to a large flow, the injection molding machine realizes rapid mold opening and closing, rapid injection, etc., when the hydraulic oil circuit only provides a small flow, various actions of the injection molding machine proceed slowly.
7. Selection of ejection form: The ejection form of the injection molding machine has two types: mechanical ejection and hydraulic ejection. Some are also equipped with a pneumatic ejection system. There are two types of ejection times: single and multiple. The ejection action can be manual or automatic. The ejection action is started by the mold opening stop limit switch. The operator can achieve this by adjusting the ejection time button on the control cabinet as required. The ejection speed and pressure can also be controlled by the switch on the control cabinet, and the back and forth distance of the thimble movement is determined by the travel switch.
8. Temperature control: the temperature measuring thermocouple is used as the temperature measuring element, and the temperature measuring millivoltmeter is used as the temperature control device, which directs the on and off of the current of the barrel and the mold electric heating ring, and selectively fixes the temperature of each section of the barrel and the mold temperature. Table 5 lists the molding processing temperature ranges of some plastics for reference. The barrel electric heating ring is generally divided into two stages, three stages or four stages of control. The ammeter on the electrical cabinet respectively shows the size of the current of each section of the electric heating coil. The reading of the ammeter is relatively fixed. If the reading of the ammeter is found to be low for a long time during operation, it may be that the heating coil has malfunctioned, or the wire is in poor contact, or the heating wire is oxidized and thinned, or a certain heating ring is burned out. Both will increase the resistance of the resistors connected in parallel with the circuit and decrease the current. When the ammeter has a certain reading, you can simply use a plastic strip to wipe the outer wall of the heating ring one by one, and see whether the material is melted or not to judge whether a certain heating ring is energized or burned.
9. Mold clamping control: Mold clamping is a huge mechanical thrust to close the mold tightly to resist the huge opening force of the mold caused by the high pressure injection of molten plastic during the injection molding process and the filling of the mold. Close the safety door, each travel switch will give a signal, and the mold-clamping action will start immediately. First, the movable template is started at a slow speed. After a short distance, the control rod pressing block that originally held the slow switch is released, and the movable plate rotates to advance quickly. When advancing close to the end of the mold clamping, the other end of the control rod presses the slow switch again, and the movable plate rotates at a slow speed and advances at a low pressure at this time. In the process of low-pressure mold clamping, if there are no obstacles between the molds, they can be smoothly closed until the high-pressure switch is pressed. The high-pressure switch is to straighten the hinge of the machine to complete the mold clamping action. This distance is very short, generally only 0.3~1.0mm. The mold clamping termination limit switch is touched as soon as the high voltage is turned on. At this time, the action stops and the mold clamping process ends. The clamping structure of the injection molding machine has a full hydraulic type and a mechanical linkage type. Regardless of the structure, the clamping force is implemented by the connecting rod being completely straightened. The straightening process of the connecting rod is the process in which the movable plate and the tail plate are stretched apart, and it is also the process in which the four tie rods are stretched under force. The size of the clamping force can be known from the highest value of the oil pressure gauge at the moment of clamping the mold. If the clamping force is large, the maximum value of the oil pressure gauge will be high, and vice versa. Smaller injection molding machines do not have a clamping oil pressure gauge. At this time, it is necessary to judge whether the mold is really tight according to the straightening of the connecting rod. If the connecting rod of a certain injection molding machine is easily straightened when the mold is closed, or "almost" fails to straighten, or one of the several pairs of connecting rods is not fully straightened, expansion will occur during injection molding, and the part will be molded. There will be flashing or other problems.
10. Mold opening control: When the molten plastic is injected into the mold cavity and cooling is completed, the mold opening action is followed to take out the product. The mold opening process is also divided into three stages. In the first stage, the mold is opened slowly to prevent the part from tearing in the mold cavity. The second stage is to open the mold quickly to shorten the mold opening time. The third stage is to open the mold slowly to reduce the impact and vibration caused by the inertia of the mold opening.
If you understand the above injection molding machine operation process, then it is natural to improve the injection molding machine.