The right tool for your business – PART 1
Ad-Vance Engineering Ltd
Specialist precision engineering company, based in Northern Ireland, specializing in bespoke injection molding tools.
Your tool is one of the most significant investments in injection moulding. Injection moulding tools serve as the means to shape your component within an injection moulding machine.
To ensure consistent production of high-quality parts in the required quantities, several factors must be taken into account when it comes to your moulding tooling. These include:
When developing a plastic part, it is critical to consider its "mouldability". Without first inspecting the design, a part intended for 3D printing may not necessarily be suitable for injection moulding.
Design considerations include the following:
Material & Texture
Choosing a surface finish can have both aesthetic and functional benefits. Surface finishes?can increase the product's appeal to?customers and improve product functionality by adding features such as greater durability, scratch resistance, and grip.
When designing?a component, all aspects must be considered, including the surface finish. If the surface finish?is critical to the design of a component, it must be considered throughout the tool design stage, since it can affect the cost of the tooling project.
Wall Thickness
Because of the filling?of polymer into the mould and the weight of a part, wall thickness influences injection moulding cycle time. A thicker wall thickness takes longer to mould, weighs more, and as a result?costs more to mould.
Another consideration for wall thickness is the variation in thickness throughout your design. Injection moulding favours uniform wall thickness. If one section of a part is somewhat thicker than the others, a sink mark will emerge in that spot.
Non-uniform wall thicknesses can also cause warping. The moulding wall will cool and shrink at different rates.
A blend transition from one wall thickness to another can help to reduce stress in the part.
Ribs
Instead of increasing wall thickness, add ribs to strengthen mould walls, which can help eliminate defects?like warping, sinking, and voids.
Ribs are vertical features?that offer structural integrity and are often located 90 degrees from the mould wall. Ribs are 50-60% thinner than the connecting wall; thick ribs are prone to shrinkage. Sink marks can also be caused by ribs that are too?thick.
Bosses
Bosses, like ribs, serve to maintain structural integrity. They are used for?additional components, such as screws and inserts.
Attach Bosses to the mould walls for further strength, or add gussets if that is not possible. This is comparable to the ribs described above, and the same wall thickness rules apply.
Draft Angles
Vertical walls in injection moulding contract?and get?caught in the mould, requiring additional force to remove the moulding. This can damage the ejector pins or, worse, the mould.
It is preferable to create walls with a little slant or draft angle. This makes it easier to eject the mould, even when it is at an angle.
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Radii
Sharp corners in moulding are not recommended, just like draft angles. They cause?weakness at the corners and reduce flow in the mould due to the abrupt change in direction.
Eliminating sharp edges in favour of rounded corners increases 'mouldability' by allowing more material to flow through the mould and making the corners less prone to get stuck when being ejected.
Undercuts & Coring
Some design elements will interfere with the tool's ejection mechanisms. In some cases, the material and design are flexible enough to be ejected from the mould. Avoid stripping undercuts in parts made of rigid materials like PC and Nylon.
Most undercuts cannot be moulded without extra assistance. Sliders and cores are examples of mechanisms that can be added to the tool, increasing its cost and complexity.
Snap fittings, for example, are used to attach plastic pieces together; they can be formed by inserting slots into the moulding to allow side cores to create the design or by moving?the feature to the edge.
Additionally, lifters are used?to create?undercuts; a lifter moves at an angle in tandem with the ejector pins, pushing the part away from the feature and outward as the pins force it off.
Size
The size of the item or numerous parts?has an impact on mould size, which impacts cost and machine compatibility. Consequently, the unit price.
After you have inspected your part, it is time to consider the mould tool itself.
The type of tool steel used is determined by several factors, including the material, quantity required, and surface finish.
Aluminium is a popular material for prototype moulds because it is inexpensive and available in small quantities. Aluminium has a limited durability in injection moulding.
A prototype mould, for example, might be used to determine whether the moulding generated is fit for purpose before proceeding to production moulding tools, which need a bigger investment.
P20 Steel is commonly used for general applications and materials such as ABS, PP, HDPE, LDPE, and low-volume operating projects. There is also a harder version of P20 steel.
Hardened steel, such as H13, will be used?for more aggressive polymers including nylon, acrylic, or?glass-filled.
Stainless steel is another type of tool material that can be employed. This tool steel is suitable for extremely corrosive materials like PVC. As previously stated, stainless steel is essential to create high-gloss surface finishes.
If you've got this far, find out how else we can help you:
LinkedIn: Ad-Vance Engineering Ltd
Phone: 028 9262 2933
Email: [email protected]