The pressure sensor can be installed in the injection molding machine nozzle, hot runner system, cold runner system and mold cavity, it can measure the plastic injection molding machine, filling mold, pressure and cooling process from the injection molding machine nozzle to Plastic pressure somewhere between the mold cavities. This data can be recorded in a monitoring system for real-time adjustment of the molding pressure and checked after molding or to eliminate failures in the production process. It is worth mentioning that this collected pressure data can be a common process parameter for this mold and this material. In other words, the data can be used to guide production on different injection molding machines (using the same mold). Only the pressure sensor installed in the cavity is discussed here.
Types of Pressure Sensors Currently, there are two types of pressure sensors used in mold cavities, namely flat and indirect types. The flat-type sensor is inserted into the cavity by drilling a mounting hole behind the cavity. The top of the sensor is flush with the surface of the cavity (as shown in Figure 1). The cable is passed through the mold and outside the mold. Surface monitoring system interfaces are connected. The advantage of this type of sensor is that it will not be disturbed by the pressure during demolding, but it is easily damaged at high temperatures, causing installation difficulties.
Indirect sensors are classified into two types: sliding and button type. Both of them can transfer the pressure exerted by the plastic melt on the ejector or the fixing pin to the sensor on the die ejector plate or moving platen. Slide sensors are usually mounted on the ejector plate under the existing pusher pin. When performing high-temperature molding, or when using a low-pressure sensor for a small ejector pin, a sliding sensor is generally mounted on a movable platen of the mold. At this time, the ejector pin works through the ejector sleeve or uses another. Transit pin (as shown in Figure 2). The transition pin has two roles. First, it can protect the sliding sensor from the ejection pressure when using the existing ejector. Another effect is that it allows the sensor to be protected from the rapid acceleration and deceleration of the ejector plate when the production cycle is short and the ejection speed is high.
The size of the pusher pin on the top of the sliding sensor determines the size of the desired sensor. When multiple sensors need to be installed in the cavity, it is best for the mold designer to use the same size pins for them to avoid the molder's setting errors or adjustment errors. Because the top pin acts to transmit pressure to the sensor, different pins are used for different products.
In general, the button sensor should be fixed in a recess in the mold, so that the sensor's installation position must be the most interesting position for the processing personnel. To disassemble this sensor, you must open the template or perform some special design on the structure in advance.
Depending on the position of the button sensor in the mold, it may be necessary to install a cable hub on the stencil. Compared with sliding sensors, button sensors provide more reliable pressure readings. This is due to the fact that the button sensor is always fixed in the recess of the mold and does not move in the borehole like a sliding sensor. Therefore, button sensors should be used as much as possible.
Pressure sensor mounting position If the pressure sensor is installed in the correct position, it can provide the molder with the most useful information. With some exceptions, the sensors used for process monitoring should normally be installed in the back third of the cavity, and the sensors used to control the molding pressure should be installed in the first third of the cavity. For extremely small products, pressure sensors are sometimes installed in the flow path system, but this will make the sensor not monitor the pressure of the gate. It should be emphasized that when the injection is insufficient, the pressure at the bottom of the cavity is zero, so the sensor located at the bottom of the cavity becomes an important means to monitor the lack of injection. With the use of digital sensors, sensors can be installed in each cavity, and only one network cable is required for connection from the mold to the injection molding machine. In this way, as long as the sensor is installed at the bottom of the cavity and no other process control interface is needed, the problem of insufficient injection can be eliminated.
Under the above premise, the mold design and manufacturer must also determine which of the cavity inside the cavity the pressure sensor is placed on, as well as the location of the wire or cable outlet. The design principle is that the wires or cables cannot move freely after they pass out of the mold. It is common practice to attach a connector to the mold base and then use another cable to connect the mold to the injection molding machine and auxiliary equipment.
The important role of the pressure sensor The mold manufacturer can utilize the pressure sensor to carry on the rigorous tryout to the mold that will deliver to use, in order to improve the design and processing of the mold. The molding process of the product can be set and optimized on the basis of the first trial or second trial. This optimized process can be used directly in subsequent trials, reducing the number of trials. With the completion of the trial mold, not only the mold has reached the quality requirements, but also the mold manufacturer has obtained a set of validated process data. This data will be delivered to the molder as part of the mold. As a result, mold makers provide molders with more than just a set of molds, but rather a solution that combines molds and process parameters that fit into the mold. Compared with simply providing molds, this scheme has increased its intrinsic value. Not only will the cost of the trials be greatly reduced, but it will also shorten the trial time.
In the past, after the moldmakers had been told by their customers that molds often had problems such as poor filling and inaccurate key dimensions, they could not know the status of the plastics in the molds. They could only guess the causes of the problems based on experience. Not only will it make detours, but sometimes it will not solve the problem completely. Now they can accurately determine the crux of the problem based on the analysis of the state of the plastic in the mold (as shown in Figure 4) collected by the molder from the pressure sensor.
Although not every mold requires a pressure sensor, each mold can benefit from the information provided by the pressure sensor. Therefore, all molders should understand the important role of pressure sensors in optimizing injection molds. Those mold makers who believe that the use of pressure sensors play a key role in manufacturing precision molds can enable their customers to produce products that meet quality requirements more quickly, while also promoting their mold design and manufacturing techniques.
