Die Casting

Cracking in die casting is one of the most common problems in the industry. The cause is usually not a single factor, but the combined effect of material, mold, process, and part structure. With years of experience in die casting and injection molding, Haina shares its practical insights to break this issue down clearly.

Material. Die casting alloys are inherently brittle. Common alloys such as aluminum, zinc, and magnesium have far less ductility than steel. If the alloy composition is off, or too much recycled material is mixed in, toughness drops. If degassing during melting is incomplete, internal porosity and slag inclusions become stress concentration points — and cracks start right there under load.

Mold. The most common issue is uneven cooling. If local mold temperature is too high or too low, the casting shrinks inconsistently during solidification, generating internal stress. An poorly designed ejection system is also critical — too few ejector pins, wrong positions, or unbalanced ejection can force the part out before it has fully solidified, cracking it directly. Poor gate and runner design leads to uneven filling, local overheating, or cold shuts, and these weak areas are prone to cracking. At Haina, we focus on cooling layout and ejection balance during mold design and manufacturing to reduce cracking risk at the source.

Process. Temperature control is key. If pouring temperature is too high, grains become coarse and toughness drops; if too low, fluidity suffers and cold shuts form. If mold temperature is too low, cooling is too fast and internal stress is high; if too high, sticking and shrinkage porosity occur. Improper injection speed, intensification pressure, or holding time can also cause gas entrapment and shrinkage porosity, leading to cracks. Opening the mold too early — before the casting has fully solidified — also causes deformation and cracking.

Part structure. Abrupt wall thickness changes create stress concentration at the transition. Sharp corners, sharp edges, and narrow slots are stress concentration zones by nature. Without sufficient fillet transitions, or with walls that are too thin, filling becomes difficult and cracking is more likely. When taking on die casting projects, Haina conducts DFM analysis upfront to flag structural cracking risks and avoid repeated mold modifications later.

When troubleshooting, start by looking at crack location: cracks along ejector pin positions usually point to ejection issues; cracks at thick-to-thin transitions usually point to cooling and shrinkage; cracks near the gate usually point to filling and temperature issues.

In short: die casting cracking is essentially caused by restricted shrinkage during solidification, where internal stress exceeds the material's strength. Solving it requires looking at material, mold, process, and part structure together — changing just one area is often not enough. Haina provides one-stop service from mold design and die casting production to post-processing, helping customers control cracking risk from the source.

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