Selection and installation of injection mold pressure sensor

Time:2021-11-16 08:48:51 / Popularity: / Source:

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

Type of pressure sensor

At present, there are two types of pressure sensors used in mold cavity, namely, flat-mounted type and indirect type. Flush-mounted sensor is inserted into cavity by drilling a mounting hole behind cavity. Its top is flush with surface of cavity, its cable passes through mold and connects to monitoring system interface located on outer surface of mold. .
Advantage of this kind of sensor is that it will not be disturbed by pressure during demolding, but it is easily damaged under high temperature conditions, causing difficulty in installation.
Indirect sensors are divided into two types: sliding type and button type. They can transmit pressure exerted by plastic melt on ejector or fixed pin to sensor on ejector plate of mold or movable mold plate. Sliding sensors are usually installed on ejector plate under existing pusher pins.
In high-temperature molding, or when low-pressure sensors are used for small ejector pins, sliding sensor is generally installed on movable platen of mold. At this time, pusher pin works through ejector sleeve or another transition pin is used.
Transition pin has two functions. One is that it can protect sliding sensor from interference of demolding pressure when existing ejector is used. Another function is that when production cycle is short and demolding speed is fast, it can make sensor not affected by rapid acceleration and deceleration of ejector plate.
Size of push pin on the top of sliding sensor determines size of sensor required. When multiple sensors need to be installed in mold cavity, mold designer should use ejector pins of same size for them to avoid setting errors or adjustment errors by molder. Because function of ejector pin is to transmit pressure of plastic melt to sensor, different products must use ejector pins of different sizes.
Generally speaking, button sensor should be fixed in a certain recess in mold, so that installation position of sensor must be the most interesting position of processing personnel. If you want to disassemble this kind of sensor, you must open mold plate or make some special designs on structure in advance.
Depending on position of button sensor in mold, it may be necessary to install a cable junction box on mold plate. Compared with sliding sensor, pressure reading of button sensor is more reliable.
This is because button sensor is always fixed in cavity of mold, unlike sliding sensor, which can move in borehole. Therefore, button sensors should be used as much as possible.

Installation location of pressure sensor

If pressure sensor is installed in correct position, it can provide molder with the most useful information.
Except for some special cases, sensor used for process monitoring should usually be installed in back third of cavity, sensor used to control molding pressure should be installed in the first third of cavity. For very small products, pressure sensor is sometimes installed in runner system, but this will make sensor unable to monitor pressure of gate.
It should be emphasized that when injection is insufficient, pressure at the bottom of cavity is zero, so sensor at the bottom of cavity becomes an important means to monitor insufficient injection. With use of digital sensors, sensors can be installed in each cavity, connection from mold to injection molding machine requires only one network cable.
In this way, as long as sensor is installed at the bottom of mold cavity, without any other process control interface, occurrence of insufficient injection can be prevented.
Under above-mentioned major premises, mold designer and manufacturer must also decide which cavity in cavity to place pressure sensor and location of wire or cable outlet. Design principle is that wires or cables cannot be moved freely after passing through mold.
General practice is to fix a connector on mold base, then use another cable to connect mold with injection molding machine and auxiliary equipment.

Important role of pressure sensors

Mold manufacturers can use pressure sensors to perform rigorous test molds on molds that are about to be delivered to improve design and processing of molds. Molding process of product can be set and optimized on the basis of the first trial or second trial. This optimized process can be directly used in subsequent mold trials, thereby reducing number of mold trials.
With completion of trial mold, not only mold meets quality requirements, but also mold manufacturer obtains a set of verified process data. These data will be delivered to molder as part of mold.
In this way, what mold manufacturer provides to molder is not just a set of molds, but a solution that combines mold and process parameters suitable for mold. Compared with simply providing molds, this solution has improved its intrinsic value. It not only greatly reduces cost of mold trial, but also shortens time of mold trial.
In the past, after being told by its users that molds often had problems such as poor filling and incorrect key dimensions, moldmakers had no way of knowing state of plastic in mold, so they could only guess cause of problem based on experience. Not only will it make detours, but sometimes it can't solve problem completely.
Now they can accurately determine crux of problem by analyzing information about plastic in the mold collected by the molder from the pressure sensor.
Although not every mold needs a pressure sensor, every mold can benefit from information provided by pressure sensor. Therefore, all mold makers should understand important role that pressure sensors play in optimizing injection molds.
Those mold makers who believe that use of pressure sensors play a key role in manufacture of precision molds can enable their users to produce products that meet quality requirements more quickly, while also promoting improvement of their mold design and manufacturing technology.

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