- Erstellt: 03-09-21
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Precision injection molding of high performance components requires primary error sources affected the molded component to be identified and isolated such that these errors can be reduced if needed. To systematically isolate and quantify the contribution of misalignment, thermal variation and component warpage to the accumulated error observed on the component, a methodology is presented and tested around an existing mold which produced parts with high dimensional variability. The mold featured two concentric guide pillars on opposite sides of the parting plane and rectangular centering block elements at three locations. Mold displacements at the parting plane were measured through the incorporation of three eddy-current linear displacement sensors. Thermal error sensitivity was investigated using FEM simulations such that the induced variability from thermal expansion and filling phase was identified and quantified. Finally, molded component warpage was isolated and quantified, again by the means of FEM simulation. The results were confirmed by using the mold on two injection molding machines to produce an array of parts whose key dimensions were measured.
Micro/nanostructured components play an important role in micro-optics and optical engineering, tribology and surface engineering, and biological and biomedical engineering, among other fields. Precision glass molding technology is the most efficient method of manufacturing micro/nanostructured glass components, the premise of which is meld manufacturing with complementary micro/nanostructures. Numerous mold manufacturing methods have been developed to fabricate extremely small and high-quality micro/nanostructures to satisfy the demands of functional micro/nanostructured glass components for various applications. Moreover, the service performance of the mold should also be carefully considered. This paper reviews a variety of technologies for manufacturing micro/nanostructured molds. The authors begin with an introduction of the extreme requirements of mold materials. The following section provides a detailed survey of the existing micro/nanostructured automotive mold components manufacturing techniques and their corresponding mold materials, including fixtures and mechanical parts methods. This paper concludes with a detailed discussion of the authors recent research on nickel-phosphorus (Ni-P) mold manufacturing and its service performance.
What is injection molding?
Injection molding is a manufacturing process which is commonly used to create plastic components.
Its ability to produce thousands of complex parts quickly makes it the perfect process for the mass production of plastic components. Essentially, the process involves the injection of plastic at high speed and pressure into a precision mechanical gear parts, which is clamped under pressure and cooled to form the final part.
By melting thermoplastic and injecting it into an aluminium mold at high speed and pressure, manufacturers can create multiple complex parts at once. When the parameters of the process are controlled correctly, there’s also little need for finishing and processing the manufactured part, making it more cost effective and efficient.
Although it’s one of the oldest manufacturing processes around, its speed and cost-efficiency is what continues to make it a popular choice with worldwide manufacturers. Today’s injection molding machines are fast, accurate and produce consistently high-quality components at scale.
How does injection molding work?
Although the process may seem simple, there are many elements involved which can alter and ruin the overall quality of the plastic component produced. In order to make a high-quality part, experienced manufacturers select the right thermoplastic (the material used to create the part), connector mold parts (which shapes the part), temperature and injection pressures to ensure the final part meets customer requirements.
Before we talk about the specific parameters that need to be controlled within the process, how does injection molding actually work?
Step 1: Feeding and heating the plastic
To start, a thermoplastic or combination of thermoplastics are fed into an injection molding machine. The plastics, which turn to liquid when heated, are fed into the hopper at the top of the machine in solid pellet form.
The pellets pass through the machine and into a temperature-controlled cylinder called the machine barrel. Here, the plastic pellets are heated until the thermoplastic is molten.
The temperature of the barrel and the plastic needs to be carefully monitored to make sure the thermoplastic doesn’t overheat and burn or scorch the final part.
Step 2: Pre-injection process
Before the molten plastic is injected, the tool, which is usually made up of a fixed half called the cavity and a moving half called the core, closes.
When closed, a clamp applies pressure to the tool, ready for the injection of the plastic.
The screw within the barrel of the machine also screws back to its set point so the plastic can enter the barrel, ready to be injected.
Step 3: Plastic injection
Once the clamp pressure is at an optimum level, the plastic is injected by the screw at high speed and pressure into the cavity. A gate inside the tool helps to control the flow of the plastic.
To make sure no damage is done to the final components, it’s important that the manufacturer monitors the injection pressure of the plastic and that they have the expertise to maintain and use the molds and tools correctly.
This ensures they are creating high-quality and consistent parts from their injection molding process, like packaging mold components.
Step 4: Forming the part
When the tool cavity is mostly full of liquid, a holding phase begins. This is where the part in held under high pressure so it can start to take its final form.
After a set holding time, the screw will screw back to its set point. This happens at the same time as the cooling phase of the cycle, which allows the thermoplastic to set in its final form.
Once the set cooling time has passed, the mold opens and ejector pins or plates push the new part out of the tool, and there are also custom mold components. These fall on to a conveyor belt ready to be finished and packed.
Step 5: Part finishing
Depending on the final application of the part, the molded component may require some finishing, including dyeing, polishing, or removing of excess material.
These processes are unique to each part and are completed before they’re packed and distributed to customers.
By picking and checking products by hand, as well as performing regular quality checks, experienced manufacturers can make sure they’re producing consistent, high-quality parts for their customers.