What Are the Design Techniques of Gravity Die Casting?

If you need to manufacture components with complex parts, you typically choose gravity die casting. Gravity die casting is common in industrial applications within the defense and medical fields, and it has many benefits—but what exactly are these benefits, and how does the method work?

How does gravity die-casting work?

As a metal casting China company, we would like to introduce to you that gravity die casting produces castings by pouring molten metal into permanent iron or steel molds. The only force used to fill the mold cavity is gravity, so filling can be controlled by tilting the mold. This process produces what's called "cold castings," which promote solidification in specific areas of the metal mold. Using iron or steel molds, gravity die casting has lower production accuracy and costs for aluminum and zinc castings compared to sand casting, and it has better surface finish and mechanical properties. Gravity die casting's mold cost is only a small part of the cost required for die casting, and rapid cooling provides excellent mechanical properties. Also, non-turbulent filling can ensure production of gravity die castings with minimal porosity, which can be heat-treated.

Design techniques for gravity die casting

Unlike semi solid metal casting, gravity die casting is a reproducible process that’s primarily used for producing medium-sized, dimensionally accurate non-ferrous metal castings, with the most common being aluminum, zinc, and bronze alloys. What are the techniques for designing castings with problem-free geometry?

Designed for the performance you need

Unnecessary heavy sections will increase material usage and weight, while also prolonging filling and cooling times. However, keep in mind that the minimum wall thickness is three millimeters and may require more depending on the cross-sectional area.

Avoid isolated heavy sections

These may lack metal flow, resulting in shrinkage defects such as internal tears, as well as stress concentration. Consider using pockets to thin out cross-sections, but be aware that this can lead to inconsistent shrinkage.

Add ribs to increase strength

Optimize weight reduction for the entire assembly by using reinforcements to strengthen thin walls, manage heat distribution, improve metal flow, and strengthen sprue positions.

Use draft in gravity die casting

The draft is a slight taper introduced to the mold cavity's side to aid in releasing the casting from the mold. For example, for aluminum box sections, the draft angle must be 2° on walls perpendicular to the parting surface or parallel to sliding planes.

Consider how shrinkage affects the release

As casting metals to recover to ambient temperature, they often shrink towards the nominal center. This helps a component release from the mold at the outer edge but often locks the inner mold part. Gravity die casting avoids this by using larger drafts in situations where shrinkage locking can occur.

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