Injection molding is a common manufacturing process for high-volume production. It involves injecting molten material into a mold, which cools and hardens before being ejected from the machine. The process offers numerous benefits, including fast production and its ability to produce complex part designs. However, for the success of any final product, one should consider variables like wall thickness.
The walls of injection molded parts must be thick enough to ensure strength and durability for the application of the piece. However, when the wall thickness is too thick, the parts may have defects like shrinkage marks and bubbles. The walls also need not be too thin; this usually makes filling cavities difficult due to the molten resin’s flow resistance. The right wall thickness is essential to avoid defects during and after manufacturing.
What is the minimum wall thickness required on a plastic part?
You need to answer several other questions to help you determine how thick or thin a product’s walls should be. Below are the things to ask yourself when exploring the idea of wall thickness.
- Is the wall used for structure?
- Will thick wall molding offer sufficient strength and stiffness?
- How will thin walls affect the application of the part?
- Will the type of resin affect the thinness of the wall?
Your answers to these questions, alongside other variables, will help you determine whether a thick wall will compromise the integrity of your product or improve its function. Establishing how thin or thick the walls should be is a familiar challenge people face when designing injection molded parts. Fortunately, there are standards for the wall thickness of parts specific to certain materials.
Variables to consider when deciding on wall thickness
When deciding on wall thickness, you also want to consider other variables such as flow rate, material composition, and part yield. Knowing more about these elements will help you decide on wall thickness. Here is an elaboration of each variable.
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Material composition
The material composition can be the sole distinguishing factor in wall thickness due to a material’s stiffness and strength. Stiffness refers to how far parts can bend when pressure is applied, while strength is a part’s ability to resist fracturing when pressure is applied. The strength and stiffness of parts vary depending on the thickness. Parts with thinner walls bend more and are more likely to break. For stiffness and strength to work in your favor, you should determine the thickness of your part depending on the material composition.
- Flow rate
How fast or slow molten flows into a mold partly depends on the material composition; this also affects the manufacturing process. Injection molding involves high pressure, meaning thin wall areas can cause flow rate issues regardless of the material used. Consequently, one may incur costly flaws such as sink marks and voids. Proper wall thickness will help you avoid extra production costs arising from the need for more pressure.
- Part yield
Part yield refers to the ratio of good to bad parts; thin walls contribute to low part yield, making it essential to consider part yield before budgeting and manufacturing. For instance, you produced four parts, and two came out perfect. However, one of the remaining two has a void, and the other broke during the process. That would mean the production had a 50% part yield.
The manufacturer will have to discard extra pieces to achieve the minimum wall thickness. Unfortunately, the costs of trial and error usually fall on the person or the company paying to get the parts made.
Also Read: Aluminum Die Casting in The Automotive Industry
Importance of uniform thickness
Maintaining uniform thickness in parts allows the molten plastic to flow easily and fill the cavity. When there’s no uniformity in wall thickness, the thick sections cool way after the thin sections, causing shrinking. Consequently, stress builds at the boundary area between the two sections; the narrow section has hardened, so it doesn’t yield, while the thick section can yield. This can cause warping and twisting and, in severe cases, cracks.
Sometimes design limitations can make it impossible to achieve uniform wall thickness. But you can maintain uniform thickness by removing plastic from the thick area (coring) or using support structures like gussets.
The best way to ensure proper thickness for your parts is by working with an experienced manufacturer. That ensures you cost-effectively produce your parts and enhance your product quality.
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