Application of sensor in die industry

Application case of pressure sensor in injection mold:

Today's competitive environment requires mold makers not only to mold, but also to have the ability to be versatile when faced with many problems raised by users, such as when users ask "what shrinkage rate should we use? ", they need to act as plastic experts; When asked, "What is the mold temperature we need and what is the heating rate?" They need to be artisans; And when asked, "Is there any other way to demoulder?" They also need to act as automation engineers. In the past, such generalists did not exist, but now with the help of pressure sensors, mold manufacturers can provide this capability.

The pressure sensor can be installed in the injection molding machine's nozzle, hot runner system, cold runner system and mold cavity. It can measure the plastic pressure somewhere between the injection molding machine's nozzle and mold cavity during injection, filling, pressure holding and cooling. This data can be recorded in the monitoring system for real-time adjustment of molding pressure and for post-molding inspection or troubleshooting during production. It is worth mentioning that the collected pressure data can be used as general process parameters for the mold and material, in other words, the data can be used to guide production on different injection machines (using the same mold). Only the pressure sensor installed in the cavity is discussed here.

Type of pressure sensor

At present, there are two types of pressure sensors used in the cavity, namely the paperback type and the indirect type. The flat-mounted sensor is inserted into the mold cavity by drilling a mounting hole behind the mold cavity. The top of the sensor is flush with the surface of the mold cavity, and the cable passes through the mold and is connected to the monitoring system interface located on the outer surface of the mold. The advantage of this sensor is that it will not be disturbed by the pressure during demoulding, but it is easily damaged under high temperature conditions, making installation difficult.

The indirect type sensor is divided into sliding type and button type. They all transmit the pressure of the plastic melt applied to the ejector or fixed pin to the sensor on the ejector plate or moving plate. The sliding sensor is usually mounted on a ejector plate under an existing push pin. For high temperature molding, or for low pressure sensors for small pin pins, the sliding sensor is generally mounted on the mold's moving form, where the push pin ACTS through the ejector sleeve or another transition pin is used. The transition pin has two functions. One is to protect the sliding sensor from the pressure of the stripper in the case of an existing ejector. Another function is when the production cycle is short and the stripping speed is fast, it can make the sensor not affected by the fast acceleration and deceleration of the ejector plate.

The size of the push pin at the top of the sliding sensor determines the size of the sensor required. When multiple sensors need to be installed in the mold cavity, the mold designer needs to use the same size pin on them to avoid setting errors or tuning errors by the mold manufacturer. Since the function of the pin is to transmit the pressure of the plastic melt to the sensor, different sizes of the pin are required for different products.

In general, the button sensor is fixed to a recess in the mold, so that the sensor must be installed in the position of the most interest to the processor. To remove the sensor, the template must be opened or some special design must be made in advance on the structure.

Depending on the location of the button sensor in the mold, a cable collector may be required on the template. Compared with the sliding sensor, the button sensor has reliable pressure readings. This is because the button sensor is always fixed in the cavity of the mold, unlike the slide sensor which can move within the borehole. Button sensors should therefore be used whenever possible.