Choosing a suitable injection molding machine is crucial in the injection molding process. From a cost perspective, choosing a large-scale machine means a sharp increase in production costs. Starting with a small-scale injection molding machine could be disastrous for the project. Imagine if a company doesn't have the appropriate production equipment; they will be unable to complete the project delivery during the trial molding stage, especially the trial production stage. This is because the automotive industry requires specific production equipment for trial production according to IATF 16949 standards. Of course, other industries such as electronics and home appliances are easier to solve; they can simply find a supplier.
From a product quality perspective, large-scale injection molding machines also bring many problems. For example, insufficient product strength, color difference, scorching, and trapped air are common issues. Conversely, even if a small-scale injection molding machine has sufficient mold capacity, it may be difficult to fully mold the product, potentially leading to problems such as burrs (also known as flash), short shots, and warping due to increased pressure from unresolved short shots.
So, how should one choose an injection molding machine in the early stages of product development? What factors should be considered when choosing an injection molding machine?
I. Clamping Force Calculation
How is the force calculated? Generally, we calculate the required clamping force by adding the projected area of the product in the ejection direction to the projected area of the runner. Note that the projected area of the product is not the length * width in the ejection direction, but rather the area of the through holes needs to be deducted. Then, we combine this with the average pressure per unit for different raw materials to calculate the required clamping force!
As shown in the diagram below: Clamping Force Calculation = Total Projected Area * Number of Cavities * Average Cavity Pressure per Unit / 0.8
II. Mold Capacity Calculation
What does mold capacity mean? Literally, mold capacity refers to the amount of space the mold is within the clamping unit of the injection molding machine. The length and width of the mold consider the spacing between the machine's purlins, while the mold height considers the opening and closing angle of the two plates of the injection molding machine.
Indeed, many times the product is too small. The required clamping force T calculated from the projected area is very small. For example, electronic connector products have a very small projected area, so the calculated force is usually very small. If the machine is too small and the mold dimensions are too large, it may not fit into the injection molding machine.
However, this doesn't mean calculations are unnecessary. On the contrary, they are even more crucial. Designers need to know the required clamping force for their molds. This provides technical support for subsequent trial molding and production.
III. Calculation of Glue Storage Capacity
What factors need to be considered when selecting an injection molding machine regarding glue storage capacity?
The output volume is an easily overlooked aspect. Often, considering that the mold can fit and the pressure is sufficient, people assume they've found the most suitable machine specifications. However, screw glue storage capacity is also a critical factor. Since the screw is usually an optional accessory, adjusting the screw diameter changes the glue storage capacity. A key issue here is material density. Injection molding machine suppliers often provide grammage based on PP material. If the volume of glue storage capacity cannot be found, it needs to be calculated.
Injection volume per mold = {[(Product weight * number of cavities + runner weight) * 1.06 / raw material density] / injection volume of the injection molding machine} * 100%
Raw material dwell time = Total injection volume of the injection molding machine / [(Product weight * number of cavities + runner weight) * 1.06 / raw material density] * molding cycle
In summary, when selecting an injection molding machine, the following should be considered:
First: The mold dimensions should match the machine, and the injection area should be within the machine's template range;
Second: The required clamping force should be less than 80% of the machine's maximum pressure;
Third: The injection volume should prioritize the 20%~80% injection capacity range;
If you're planning to buy an injection molding machine, whether new or used, feel free to contact me. I will help you choose the most suitable model.
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