What are the most important die casting design tips? - assemblean

Die casting is a very economical process for the large-scale production of metallic castings. With die casting, you can produce complicated shapes with high accuracy, thin wall thicknesses and smooth surfaces that require little finishing. Efficient die casting production starts with the part design. That's why there are die casting design tips you should follow.

Mould design

The first important die casting design note concerns the mould design. The mould must be able to withstand high pressure in the manufacturing process and allow smooth part production.

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To do this, you should keep in mind during the design that the part can be easily removed from the mould without damage. Therefore, consider features such as parting lines at the beginning of your part design.

Fillets and radii

Fillets and radii are other important design features in die casting. They allow you to create smooth transitions between surfaces and avoid stress build-up. This affects the strength, durability and appearance of your parts.

Die casting design tips for fillets and radii:

• The size and shape of fillets and radii are application specific, but should not be smaller than 1mm.
• Larger radii are recommended for areas with higher loads.
• To prevent stress accumulation, avoid sharp corners and edges.
• Be aware of the radius when two surfaces meet, as these can affect the strength of the joint.
• Use fillets and radii throughout the design to maintain the strength and smoothness of the component.

Add draft angles aligned with the mould opening direction. This will ensure that your part can be removed from the mould without damage to the surface. Usually they range from 1 to 3 degrees, but can be greater for more complex parts.

Wall thickness

When designing the wall thickness, consider the desired stiffness, strength and weight of your product. The wall thickness affects the cooling time of the mould and the pressure that can be applied to the mould.

The wall thickness is application specific and depends for example on the mould size, the material used and the production processes.

Some minimum wall thicknesses for castings are:

• Magnesium: 1.016 - 2.54 mm
• Aluminium: 1.016 - 2.032 mm
• Zinc: 0.381 - 0.889 mm

Ribs and outside corners

You can use ribs to reinforce component walls and increase stiffness. They also allow you to distribute loads more evenly and thus prevent deformation. With outside corners you can create sharp transitions between surfaces.

The thickness of ribs and outside corners is also application-specific. For example, thicker ribs are important for components that are under heavy loads.

Add ribs to the thinnest wall first so that this component does not become too thin. In addition, the spacing between ribs should be evenly distributed.

Another design tip: Avoid outside corners to prevent stress accumulation. If outside corners are necessary, their radius should be as large as possible to reduce stress.

Windows and holes

Windows and holes allow fluids to flow through or create a connection between two parts. You should consider them when designing your part so that they do not affect the strength and stability of the final product.

In most cases, windows are rectangular in shape and are located at the top or side of the mould. Holes, on the other hand, can take different shapes and lie anywhere in the mould.

Windows and holes should be rounded or fluted and located away from sharp corners and edges. In addition, windows and holes on the side of the mould may require demoulding bevels with larger angles.

Finished features

Some features are usually only possible after the castings have been cast. This finishing is an additional process step that increases production time and production costs.

If post-machining is necessary, follow these die casting design tips:

• Try to add as few reworked features as possible to keep costs comparatively low.
• Design the features to be as simple and accurate as possible.
• Choose the location of the features so that as little material as possible has to be removed.
• The tolerances of the features should be realistic and achievable.
• You can also add reworked features by inserting cores in the design phase. Cores create internal components in the casting by creating holes and other features in the final casting.

Parting lines

One feature that can be machined during finishing is the parting line. This is the line where the two halves of the mould meet. It is usually at the top or side of the part. The parting line is important in the design of the die cast part as it is where a visible seam will be created on the final product.

Make sure the parting line is where it is least visible. Also note the thickness of the line. This is because lines that are too thin can cause the part to break when it is removed, while parting lines that are too thick can cause uneven surfaces and imperfections in the final product.

Often there is also extra material that settles on the parting line. This extra material is called flash and can be removed during finishing.

Surface treatment grades

The final step in the casting process is the surface treatment. The type of treatment depends on the area of application of your end product.

It is divided into different grades:

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Grade 1 (Utility Grade) - for basic use.

Grade 1 is also called Utility Grade. This surface after casting does not need any cosmetic treatment and this grade is best suited for castings with coatings.

Grade 2 (Functional Grade) - functional & simple

The 2nd grade is the Functional Grade. It is used for grinding and painting and therefore for castings with decorative coatings.

Grade 3 (Commercial Grade) - for commercial use

Grade 3, also called Commercial Grade, is suitable for electrostatically painted and custom surface treatment. It is mainly used for structural components that are used under high loads.

Grade 4 (Consumer Grade) - for end-user use.

As grade 4 is intended for consumer use, the surface does not have any disturbing defects. Therefore, this grade is suitable for decorative end products.

Grade 5 (Superior Grade) - for special quality requirements

The 5th grade has a micrometre-precise application of the coating. It is best suited when the end products are bearings for seals and gasket seats.

More die casting design tips with us

If you have any further questions about design tips, we will be happy to assist you with your die-casting production. assemblean offers you the complete die-casting process with its own foundry and a wide range of materials. Request your quote online or by and in consultation with you we will realise a manufacturable solution.

Before we get into the specific design tips, let’s take a look at the primary principles that make for successful die casting:

• The molten metal can easily flow through the mold, filling it to produce a solid part.
• The metal solidifies evenly and quickly.
• The part ejects without damaging itself or the tooling.
• The part design minimizes the complexity of the tooling required.
• The part function is prioritized over its shape.
• Tolerances should be kept as open as possible without affecting the fit, form, or function.

By keeping these principles in mind and utilizing the tips below, you will be well on your way to producing a design that can be reliably and economically made. If you have an upcoming die casting project, feel free to start a quote with us today! Our representatives and subject matter experts are here to help guide you through the process and help answer any questions you may have.

Implementing both fillets and radii in your design can be beneficial in several ways. Firstly, they help the metal evenly flow through all areas of the part and reduce concentrated areas of heat around corners and transitions. These are also important features to prevent cold shuts, caused when the metal begins solidifying before it has completely filled the mold cavity. Components that cool evenly lessen the stress on the tooling, thus increasing its lifetime and reducing maintenance. Fillets can also reduce stress concentrations, especially where intersecting features would otherwise create sharp corners. Here are some further guidelines when it comes to adding fillets and radii:

• Add fillets or radii to sharp edges and corners.
• The deeper the corner or pocket, the larger the fillet should be.
• Fillets create smooth transitions between features that promote metal flow and structural integrity. Radii should be generous on intersecting features.
• Constant-radius fillets help maintain edge continuity and smoothness of the part.
• Draft angles are required when the fillet is perpendicular to the parting line. The draft of the intersecting surface will determine the amount of draft needed.

When it comes to wall thicknesses, the most crucial aspect is uniformity. Keeping the walls of the part uniform will help promote metal flow and uniform cooling. Areas with uneven wall thicknesses can cause different shrinkage rates, leading to defects in the part, such as sink marks or cracks. Here are some other considerations to make when it comes to wall thicknesses:

• Molten metal flows more freely with thicker walls.
• Certain alloys such as zinc can produce parts with thinner walls.
• Avoid prominent protruding features that significantly increase wall thickness, which can cause uneven and slower cooling rates.

Ribs are structural features that provide several benefits in die cast parts. Their primary purpose is to provide additional rigidity and strength, especially to areas with thin walls. Ribs also assist the molten metal flow, allowing it to reach and fill connected areas more quickly.

Adding corings, such as the space between ribs or walls, helps reduce material as a metal-saver and provides better cast parts. The purpose of coring is to displace the casting alloy, reducing material usage and resulting in a lighter-weight part. With the proper use of ribs and coring, you can avoid areas of concentrated heat caused by excessive material buildup while also reducing the weight of the part and maintaining its strength. When incorporating ribs and cored features into your design, it’s essential to keep the following in mind:

• Designers should add ribs onto thin-walled sections.
• Design for an odd number of ribs to better distribute internal stresses and avoid forming thick intersections.
• Add fillets to ribs and edges of metal savers to reduce sharp corners and assist with metal flow.
• Avoid having too many ribs too close together, as this can affect the effectiveness of metal savers.
• Include generous draft on the sides of metal saver pockets to assist with mold release and prevent tool wear.

Special consideration should be given to hole and window features, as they present their own unique challenges with the die casting process. The inside surfaces of holes and windows tend to adhere to surfaces of the steel die during the cooling process. This can impact the ejection mechanism and make it harder to release the part from the die, contributing to tool wear and part defects. Additionally, holes and windows can impede metal flow through the casting. Additional techniques such as bridge features or runners can be used for larger windows to ensure proper metal flow; however, this can add extra steps and cost to trim out these features after casting. If your design requires holes and windows, the design guidelines below will help keep your part manufacturable:

• Holes and windows require the highest draft compared with other features.
• Perimeters of holes and windows should be filleted.
• In some cases, it may be better to post-machine holes; however, this will add manufacturing time.

Parting lines are where the die halves meet and interface with each other. When designing your parts, the parting line locations are one of the first aspects to consider. Parting lines can be straight or broken depending on the geometry and die components required to create them. When it comes to the parting line locations, here are the key aspects to consider:

• Parts with straight parting lines will usually be less expensive than one that requires broken parting lines since less complex tooling is needed.
• Quality along parting lines is more difficult to control; therefore, you should avoid having it cross critical or tight tolerance features.
• Parting lines often exhibit flash, a thin web or fin of material that occurs due to the clearances needed for die operation. Flash is removed during trimming, and it should be easily accessible.

The as-cast external surface finish classification should be specified in your design. The class you choose can significantly influence the end cost as higher-grade finishes require additional steps and a more sophisticated die design. That said, you should aim to select the lowest classification that meets your intended application to yield lower costs.

The North American Die Casting Association (NADCA) has guidelines to help you classify your surface finishing requirements in a general sense. Please reference the chart below for these classification guidelines. Note that this is useful for general type classification, and final finish quality requirements are agreed upon between the customer and manufacturer.

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