In today's competitive environment, moldmakers are no longer just modelers—they must be versatile problem-solvers who can address a wide range of questions. For instance, when users ask, "What shrinkage should we use?" the moldmaker needs to act as an expert. When asked, "How high is the mold temperature and what is the heating rate?" they must take on the role of a craftsman. And when asked, "Is there a way to demold other products?" they need to function as an automation engineer. In the past, such a multi-faceted skill set was rare, but with the integration of pressure sensors, mold manufacturers now have this capability.
Pressure sensors can be installed in various parts of the injection molding system, including the nozzle, hot runner, cold runner, and cavity of the mold. These sensors measure the pressure of the molten plastic from the nozzle all the way to the cavity during the injection, filling, holding, and cooling phases. The collected data can be recorded in a monitoring system, allowing for real-time adjustments to the molding pressure or post-molding inspection to identify and resolve production issues. Notably, this pressure data becomes a standard process parameter for a specific mold and material, enabling consistent performance across different injection molding machines. Here, we focus specifically on the installation of pressure sensors within the cavity.
There are two main types of pressure sensors used in cavities: flat-mounted and indirect. Flat-mounted sensors are inserted into the cavity by drilling a hole behind it, with the top of the sensor flush with the cavity surface (as shown in Figure 1). The cable exits through the mold and connects to an external monitoring system. One advantage of this type is that it is not affected by demolding forces, but it is vulnerable to damage under high temperatures, making installation challenging.
Indirect sensors come in sliding and button styles. Both transmit the pressure exerted by the molten plastic on the ejector pin or fixed pin to the sensor located on the ejector plate or moving plate. Sliding sensors are typically mounted on the ejector plate beneath an existing push pin. During high-temperature molding or when using small top pins, these sensors are often placed on the moving die, where the push pin acts through an ejector sleeve or transition pin (as shown in Figure 2). The transition pin serves two purposes: it prevents interference from demolding pressure and ensures the sensor isn't affected by rapid movements of the ejector plate during fast cycles.
The size of the top pin determines the size of the sensor required. When multiple sensors are needed in a single cavity, it’s best for the mold designer to use uniform-sized top pins to avoid setup or adjustment errors. Since the pin transfers pressure from the melt to the sensor, different products may require different pin sizes.
Button-style sensors are mounted in a recess within the mold, making their placement a key consideration for mold designers. To remove them, the mold template must be opened, or special structural designs must be made in advance. Depending on the location of the button sensor, a cable box may also need to be installed on the mold template. Compared to sliding sensors, button sensors provide more reliable pressure readings because they remain fixed in the mold’s dimple, rather than moving within a bore. Therefore, button sensors are preferred whenever possible.
The placement of pressure sensors significantly impacts the information they provide. Sensors for process monitoring are typically installed in the last third of the cavity, while those used for pressure control are placed in the first third. For small parts, sensors may be installed in the runner system, though this limits their ability to monitor gate pressure. It's important to note that if injection is insufficient, the pressure at the bottom of the cavity will be zero, making sensors placed there essential for detecting underfill. With digital sensors, each cavity can be monitored individually, requiring network cables to connect the mold to the injection machine. This setup allows for direct detection of insufficient shot without additional controls.
Mold designers must decide where to place the pressure sensors and how to route the wires or cables. The design principle is that once the cables exit the mold, they should not move freely. A common practice is to attach a connector to the mold base and then use another cable to link the mold to the injection machine and auxiliary equipment.
Pressure sensors play a critical role in improving mold quality. Moldmakers can use them to conduct rigorous testing before delivering molds, helping refine both design and manufacturing processes. By optimizing the molding process based on test results, future trials can be minimized, reducing costs and time. Once the test pattern is complete, the mold not only meets quality standards but also provides proven process data that is delivered to the molder. This adds value beyond just providing a mold—it offers a comprehensive solution that combines the mold with optimized parameters. This approach enhances efficiency and reduces trial-and-error.
In the past, moldmakers could only guess at the causes of issues like poor filling or incorrect dimensions due to limited visibility into the mold’s internal conditions. Now, with pressure sensor data, they can accurately analyze the state of the plastic and quickly identify and resolve problems.
While not every mold requires a pressure sensor, all molds can benefit from the insights they provide. Therefore, it’s crucial for moldmakers to understand the importance of pressure sensors in optimizing injection molds. Those who integrate pressure sensors into their manufacturing process enable their customers to produce high-quality products faster and improve their own design and production techniques.
Sealed Standoffs,Sealed Studs,Waterproof Fasterner,Water Resistant Studs
Dongguan Tiloo Industrial Co., Ltd , https://www.sales-fastener.com