In the die casting process, erosion is surface damage or material loss caused by high-velocity molten aluminum impacting the die surface. It is commonly seen in gates, runners, and sharp transition areas. This defect leads to rough surfaces, dimensional issues, and reduced die life, while increasing maintenance costs and scrap rates. Effective prevention requires optimized gate design, mold temperature control, and early identification through simulation.
This article will cover the types and mechanisms of erosion, common locations, root causes, consequences, detection methods, and proven solutions. Read on to learn how to prevent erosion and ensure high-quality aluminium alloy die casting parts.
Types and Mechanisms of Erosion
Impact Erosion
When molten aluminum hits the die cavity at high speed, it causes immediate material loss.
This most often occurs at the gate and inlet areas, especially when there are no splash blocks or guides.
The direct impact of molten aluminum quickly wears away the die surface.
Particle Erosion
Molten aluminum often contains tiny solid particles such as silicon, aluminum oxide, or inclusions.
These particles scrape the inner wall of the die during flow, gradually causing surface degradation.
The stronger the turbulence and the higher the particle concentration, the faster the areas susceptible to erosion will wear.
Cavitation Erosion
When the vapor bubbles formed in the low-pressure area of the mold cavity collapse, they will produce tiny high-energy jets, causing local erosion.
Usually occurs in areas with sharp flow changes or uneven mold temperature.
Common Locations of Erosion
Around the Gate and Runners
The molten aluminum enters the die casting mold cavity from the gate and runner, which is the first time it contacts the mold at high speed.
Without flow control design, high-speed molten aluminum will quickly corrode the mold surface, and this initial damage will continue to expand during the production process.
Mold Erosion in the Gating Area
Core and Thin-Wall Transition Areas
Molten aluminum will accelerate when passing through narrow areas or cores, forming high-pressure areas.
This concentrated speed will cause erosion at the core edge and thin-wall transition area, which will affect dimensional consistency over long-term use.
Sharp Angles or Small Radii
Narrow angles or curvatures in the mold will disrupt laminar flow and produce sudden velocity changes, which will cause turbulence and local flow separation, increasing the risk of erosion.
These areas need to be focused on during the mold design and simulation stages.
Flow Dead Spots Behind Complex Structures
Complex geometric structures such as inserts, ejectors, or products can interfere with the normal flow of molten metal.
On the back of these structures, the metal is prone to backflow or vortices, causing “flow dead spots”.
Turbulent flow in these areas scours the mold surface for a long time, which can easily cause chronic erosion in multiple directions.
Mold Erosion Defect in the Area of Flow Washouts
Root Causes of Erosion
Excessive Molten Aluminum Velocity
Setting injection parameters too high will significantly increase the impact energy.
If the gate design is poor or the filling time is too short, the molten aluminum will directly hit the mold, especially in small areas.
Sharp Mold Geometry Transitions
Sudden changes in wall thickness or direction in the mold will force the molten aluminum to accelerate or turn sharply, causing turbulence, pressure imbalance, and flow separation, which will cause erosion in high-stress areas of the mold.
Inadequate Cooling or Mold Temperature Control
An unbalanced cooling system will form hot and cold zones inside the mold. Hot zones are prone to cavitation, and cold zones may form inclusions or solidify prematurely, both of which will aggravate erosion.
Lack of Protection on the Mold Surface
Uncoated or untreated mold steel is very susceptible to wear under thermomechanical loads. Without surface treatments such as nitriding or PVD, high-stress areas will degrade rapidly.
Thermal Cycle Fatigue
The mold expands and contracts repeatedly during continuous heating and cooling, forming microcracks that expand under the impact of molten aluminum.
Once these cracks are formed, the development of erosion will be significantly accelerated, seriously shortening the service life of the mold.
Consequences of Erosion
Rough Casting Surface
Erosion forms small pits, scratches, or irregular wear areas on the mold surface.
These defects will be directly copied to the surface of the die casting parts, causing the casting to have a noticeable rough texture and reduced finish, affecting the appearance of the product and the subsequent coating quality.
Dimensional Deviation
After the mold cavity is eroded, its original geometric contour will gradually degrade. The dimensions of the casting begin to deviate from the design value after demolding.
The deviation may be enlarged at the least, or exceed the tolerance range at the most, resulting in poor assembly or functional failure.
Increased Welding Defects
Erosion causes rough and uneven mold surfaces, making it easier for molten aluminum to adhere and stagnate in local high-temperature areas, forming welding defects.
These metal deposits hinder the normal flow of metal, further damage the mold surface, and cause scars, pores, or structural weaknesses on the casting surface, reducing the quality of the finished product.
Shortened Mold Life
Once the mold is eroded, the damage will gradually deepen and expand with each production cycle, especially in high-impact areas.
This will cause the mold to enter maintenance frequently or even be scrapped prematurely, increasing unplanned downtime and mold replacement costs.
Increased Scrap Rate
Castings produced using eroded molds are more prone to various defects such as surface scratches, welding, deformation, or dimensional abnormalities.
These problems often exceed quality standards and are judged as unqualified products during factory inspection, resulting in increased scrap rates.
Erosion Detection Methods
Visual Inspection
Routine inspections should focus on high-risk areas such as gates and thin-walled areas. Signs of erosion include rough spots, pits, or dull surfaces.
Early detection can be made in time to avoid replacing the entire set of molds.
Microscope and X-Ray Inspection
Minor erosion or early microcracks cannot be seen by the naked eye.
High-resolution imaging tools, such as microscopes and X-rays, help identify surface wear or subsurface cracks early, allowing timely maintenance and reducing the risk of unexpected mold failure.
Erosion Prevention Strategies
Mold Flow Simulation
Use professional mold flow analysis software (such as AutoCAST, FLOW-3D) to simulate the mold, focusing on analyzing the flow rate and impact points of molten aluminum in areas such as gates, corners, and cores.
According to the simulation results, adjust the gate angle, add a buffer zone, or set a splash table to avoid high-speed molten aluminum directly hitting the mold surface.
Injection Speed Control
Set reasonable primary and secondary injection speed curves in the equipment control system.
Fill the main channel with medium speed at the beginning, and switch to low speed near the gate area to reduce the kinetic energy of the metal.
Combined with pressure sensor monitoring, speed fluctuations are corrected in real time to avoid sudden impacts.
Balanced Cooling System
Identify hot spots through thermal simulation during the mold design stage, and then arrange independent cooling circuits in these areas, such as parallel water channels or needle cooling channels.
Use a mold temperature controller to accurately control the coolant temperature to ensure that the temperature fluctuation of each mold is less than ±5°C.
High-Performance Mold Steel
During the design stage, steels with high thermal fatigue strength, such as H13 and H11, are preferred.
For gates, core inserts, and sharp corners, use mold steel that has been treated with secondary melting.
For ultra-high impact areas, powder high-speed steel can also be used, or replaceable carbide parts can be embedded in the mold.
Erosion-Resistant Coating
After the mold is manufactured, PVD or nitriding treatment is applied to the gate inlet, runner outlet, core front edge, and other areas prone to erosion.
The thickness is controlled in the range of 4-10 microns, taking into account both wear resistance and precision.
The surface condition is checked after every 150,000 molds are produced, and the coating is re-applied according to the wear condition.
Protective Lubricant
Select a high-temperature erosion-resistant release agent containing graphite, fluoride, or ceramic particles.
Spray it on the mold surface (especially the gate and core area) at regular intervals to form a heat-resistant film layer.
The automatic oil injection system controls the spray volume to avoid insufficient or excessive spraying that may cause sticking or contamination.
CEX Casting’s Capabilities in Erosion Control
Simulation-Assisted Mold Design
CEX Casting uses advanced mold flow analysis and DFM tools to predict high-risk erosion areas before mold opening.
By simulating the velocity and turbulence of the molten metal, the gate size, position, and flow direction are optimized to eliminate direct impact and ensure long-term stability of the mold surface.
Precision Cooling System
Our production line is equipped with an automated cooling system to maintain a uniform mold temperature for each mold.
Thermal sensors provide real-time feedback to prevent cavitation or fatigue in hot areas to reduce erosion wear.
Mold Inspection and Maintenance
Our in-house quality inspection laboratory regularly performs X-ray and microscopic inspections to detect early signs of erosion.
At the same time, the mold wear map is recorded and repaired or re-coated when necessary to keep the mold in good condition.
Conclusion
Erosion is a key defect in aluminium die casting components, which seriously threatens surface quality and mold life.
To effectively control erosion in high-pressure die casting, it is necessary to rely on precise mold design, stable process parameters, and material technology upgrades.
As a one-stop aluminum alloy die casting manufacturer, CEX Casting provides mold simulation design, cooling systems, and erosion-resistant coatings to reduce the risk of erosion comprehensively.
Contact us today to see how we can eliminate erosion defects and increase die life for your next die casting products.