Design tips and tricks for thin wall injection moulding
Injection moulding is a common and adaptable manufacturing technology that allows businesses to generate high-volume production runs at a cheap cost per part without losing quality. It is extremely reproducible and capable of creating strong components that fulfil precise mechanical and dimensional specifications.
Thin wall injection moulding can be used when a company has to make a plastic part with thin walls, such as certain automotive parts or smartphone cases. However, you must exercise extreme caution when developing goods with thin walls, as thin wall injection moulding presents additional obstacles. In this post, we’ll go over the fundamentals of thin wall injection moulding, common applications, and injection moulding design recommendations to help you get off on the right foot.
What is thin wall injection molding?
Thin wall injection moulding is a type of injection moulding that allows producers to build thinner and lighter parts while maintaining structural integrity. Companies can save material, increase productivity, achieve a lower cost-per-part, and reduce shipping-related fuel usage and carbon emissions by choosing thin wall injection moulding over standard injection moulding.
Cycle times are substantially faster for thin wall plastic components since there is less material to cool, resulting in shorter delivery lead times. In fact, a large reduction in wall thickness can sometimes cut cycle times in half, allowing businesses to get products into the hands of customers faster while saving money on operational costs. Furthermore, because thinner walls mean less plastic, businesses can save money on materials and, in the case of containers and packaging, provide more vacant space for the product.
However, there are a few drawbacks to thin wall injection moulding. For one thing, the injection process is more difficult. Higher pressure and faster moulding speeds are required to fill all of the thin cavities with molten material, avoid freezing off, and ensure the item comes out correctly. For example, although a component with conventional walls can be filled in two seconds, the identical part with 25% thinner walls may only take one second to fill. You may also need to take extra precautions and properly build gates to facilitate part ejection.
Manufacturing applications for thin wall injection moulding
When it comes to plastic packaging, manufacturers frequently turn to thin wall injection moulding since it can be used to construct everything from food-safe packaging to medical device packaging. Thin wall injection moulding is also used to make mobile phone components, plastic lids and containers, electronic housings, syringes, and medical device components. Thin wall injection moulding is used for components and component assemblies in the automotive, construction, appliance, and aerospace industries.
Design tips and tricks for thin wall injection moulding
Thin walls frequently generate material flow issues, which can result in unformed areas. Other common difficulties with thin walls include uneven cooling, distortion, cracks, variations in visual texture, and weak knit lines or fracture spots.
To prevent these issues and design the best possible part:
Pay close attention to your materials.
Material selection is always crucial in injection moulding, but it is critical for producing parts with thin walls. Some materials, such as polycarbonate (PC), are sticky, making it difficult to fill moulds with thin walls. Certain thermoplastics, such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), nylon (PA), and polypropylene (PP), will flow more easily through narrow parts of a mould. Liquid silicone rubber (LSR) also fills easily, although it may increase the danger of flash at the parting lines of your mould.
There is no one-size-fits-all material for thin wall injection moulding, therefore while comparing materials, consider your part’s shape and application requirements. Additionally, attempt to select a material that will not increase mould wear when injected at high speeds.
Consider the material of your mould.
In addition to considering the material of your product, you need carefully consider the material of your mould. While P20 steel is frequently used in traditional injection moulding applications, it may be insufficiently strong to handle the high pressures, wear, and erosion associated with injection moulding parts with thin walls. Instead, a more robust material, such as 718, H-13, D-2, or another strong steel, is required.
It is crucial to note that a tool made of a strong material may cost 30%-40% more than one made of P20. However, the increased performance and endurance of the tool easily offsets the added expense.
Have consistent wall thickness
Ensure that your design has constant wall thickness throughout. This allows for even cooling and aids in the prevention of warping, sink marks, flow lines, and short shots. Keep your wall thickness at 0.9mm (0.0354″) or more for the best results.
Include gussets or ribs in your design
If you need to strengthen or stiffen a part, you can incorporate ribs into its design. While ribs are typically half the thickness of the wall they support, if your wall is less than 1mm thick, your ribs may be as thick as your wall. Sink marks and read through may, however, be seen where the rib crosses the wall.
Inadequately built ribs can cause warping, sink marks, voids, and breaking, providing more difficulty than they’re worth. To avoid these issues, make ribs 60% of the wall thickness or less, maintain base radii modest, space ribs three times the wall thickness apart, and incorporate 1° of draught or greater.
Add gussets (or cross-support ribs) and follow the same set of recommendations to reinforce your thin rib wall without making your ribs thicker.
Radii should be included.
Sharp corners should be avoided in injection moulding because they can cause pieces to adhere to the tool during the ejection process. They also require more pressure to fill and can result in voids if there is insufficient pressure, thus radii and rounding out internal and external corners and edges are essential. Because the mould cavity in thin wall plastic injection moulding is so narrow, avoiding sharp corners and edges is even more important to ensure a smooth flow of material and a clean ejection.
Keep an eye on the temperature.
Mold temperature is critical to the injection moulding process and can have a significant impact on how the finished product looks and feels. A warmer mould helps the injected plastic to flow more smoothly, resulting in a smoother surface.
To keep the surface temperature of your mould as uniform as possible, insert non-looping cooling lines directly in your core and cavity blocks. Furthermore, attempt to improve coolant flow through your tool rather than decrease coolant temperature, and make sure the temperature difference between your delivery and return coolant is less than 10° F.
Gates should be carefully designed.
Since thin wall injection moulding needs greater injection rates and pressures, gates should be larger than the part’s walls to help reduce gate wear and material shear. Additionally, it will lessen or completely prevent freeze-off before packaging is finished. A gate well can lower stress at the gate and improve filling if your gate links to a thin wall with a pinpoint, hot-drop, or sprue.
Because thin-walled plastic parts shrink minimally, you may wish to increase the draft angles of reinforcing ribs, edges, and bosses.
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