The auxiliary equipment of the injection molding machine can effectively realize the automation of molding. In particular, the device is needed to protect the mold from damage due to the complete release of the plastic part
(1) Pneumatic demoulding device
The pneumatic demoulding device is nothing more than a direct ejector of compressed air that forces the plastic part to demold during mold opening, controlled by a cam electric valve. This action interval can be controlled by a timer. Many molds are equipped with a pneumatic demoulding mechanism. The precise positioning of the cam is controlled by an electric valve to determine the predetermined movement position of this demoulding mechanism, which coincides with the trajectory of the mechanical demolding movement regarded as a "molding assistant", that is, overlapping .
Another way to use compressed air as a "mould release assistant" is to insert a pneumatic valve driven by a cam. Generally, compressed air cannot be used directly as a "molding assistant", especially in the case of very light plastic parts, the air in the compression knitting room will blow the product through the workshop. For this reason, a (temporarily connected) air nozzle is now commonly used whose air flow is about the same as that of a hair dryer. This gentle air flow will push the plastic parts into the suction collector under the mold.
(2) Pneumatic stripper
The picture shows that people are commonly known as the "pneumatic broom" pneumatic unpacker, it is another device that makes it difficult to demold plastic parts. Pneumatic broom is placed on the injection molding motor template φ equipped with a rubber sheet. (It can also be replaced by a brush with a little reward) This way, when descending, the mold closing surface can be gently wiped, that is, the extended terminal part of the demolding device touches Plastic parts that have not fallen off cause them to move effectively.
Then the pneumatic broom rises, then stops at the starting position to control the start of a new cycle, and the injection mold continues to lock the mold. Then, it is controlled by a directional pulse from the injection mold to complete the mold opening action to control its descent.
For the part that is adhered and bound in the cavity of the injection molding model (that is, the elastomer part), it can also be equipped with a "pneumatic broom" with a rotating brush, which is driven by compressed air and peeled off.
3) Periodic repetitive balancing device
Cycle repetition balancer is another assistant for product automation. The micro-control of the transmission parts of the machine city, called the mechanical balancer, is nothing more than an easy-to-move tray. When it falls into the plastic part to make it move, it will touch the micro switch. The weight of the impact base is adjusted by a weight to balance the displacement of the plastic parts touching it. If a multi-type ray is used and the plastic parts hit the tray at the same time, this device cannot send out the actual data of plastic iron. Therefore, this device is limited to simple multi-cavity injection moulding to make plastic parts fall off at the same time.
The piezoelectric block is demolded, and the impact surface under the mold acts on the piezoelectric sensor, which will improve this situation. The appropriately amplified sensor signal will control the succession of the next cycle. The advantage of this off-module control is that the next cycle starts immediately after an object weighing less than 1 gram falls off. If this control is adopted for the above-mentioned multi-cavity mold, the same disadvantages of the above-mentioned mechanical balancer will still occur.
The electromechanical balancer is the most suitable and safest method for measuring the shedding of plastic parts because after each injection molding actually weighs the molding material, this electronic device synthesizes information and synchronizes the next cycle with the injection molding machine control start.
Therefore, according to the type of balancer, the actual weighing can be completed, and the weight error within the range of 0,5 grams can be obtained. This type of standardized balancer can be weighed up to 3000 grams.
The lag time before the next injection cycle due to weighing is in the range of 0.7 seconds; but in general it is not practical, because the automatic ℃ operation period is always given the closing lag, which is counted as a tenth of a second, so that When plastic parts are separated from the injection molding surface, in short, safe production will completely compensate for the time lost from self-robbing, because such reliability is the greatest protection for expensive multi-cavity molds. If something more than 1 gram is left in a mold with 24 cavities, the electronic device will make the cycle run? When the injection molding machine stops, the mold is protected from any damage.
These balancers have additional advantages; they can also play a role in controlling the quality of continuously molded products.
If the calculated weight of 14 plastic mold parts is 36 grams, and a cavity is not fully filled, the electronic device will show that the plastic parts weigh 3 grams. This difference will interrupt the subsequent cycle and immediately issue an alarm signal, and the technician will rush to the scene to identify the accident and remedy it.
The installation slide of this electronic device on the injection molding machine introduces the demoulded plastic parts into the balancer tray, completes the above weighing, and then opens the tray to let the objects fall into the turnover box.The shape of the balance tray can be seen on the right side of the bottom photo; the left side is The weight adjusted with the weight of the plastic part, the middle is the impact gauge and adjuster.
(4) Photocell
One or more types of photocells are also used for demoulding control of plastic parts. For mechanical and piezoelectric balancers, as a single-cavity mold for observation, or in most cases, the kind of mold that the plastic parts can fall at the same time instead of separately, the effectiveness of this photocell is 100%. It is impossible to observe the demolding state of transparent plastic parts using photoelectric cells; for this reason, people prefer the mechanical demoulding control device.
5) Ultrasonic system
The ultrasonic system is also used as a device for observing the shedding of plastic parts. The attempts made so far have been limited to observing single-cavity molds.
For the nominal weight completed by the electromechanical balancer, the cycle repeats lags in exchange for absolute mold safety, except that the injection molding machine uses a low-pressure mold clamping device. This not only protects the mold, but also the main method of ensuring quality control. In any case, from a long-term perspective, due to the reduction in downtime and repairs, its benefits offset the price paid. Moreover, there is no need for special personnel to observe and inspect complex and expensive multi-cavity molds.
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