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Classification of Die Casting Top Out Faults and Improvement Plan for Mold Structure

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  • Release time: 2026-11-07

Classification of Die Casting Top Out Faults and Improvement Plan for Mold Structure
Pin sticking, misalignment, and piercing are high-frequency faults in die-casting mass production. Design defects in the mold ejection system account for more than half of the causes of the faults. Xinfeng Machinery has sorted out, investigated, and optimized its ideas.

1、 The core cause of deformation and jamming of the top pin
The stability of operation is determined by the clearance between the top pin, the hardness of the heat treatment, and the wear of the guide sleeve. The conventional single-sided clearance control of the top pin is 0.008-0.015mm. If the clearance is too small, it will expand and lock due to heat, and if the clearance is too large, aluminum material will enter and cause flying edge jamming. This type of fault accounts for 44% of top problems. Continuous production of die casting molds requires inspection of the ejector pin components every 15000-20000 mold cycles.

2、 Defects caused by unreasonable layout of ejection points
The ejection points are concentrated at thin-walled single points, and uneven ejection force can cause deformation and piercing of the casting. Alloy wheel molds for wheel hubs require uniform arrangement of ejector pins at multiple points in a circular shape. When the thickness difference of the casting is large, the synchronization deviation of the ejector pin exceeds 0.2mm, which is prone to distortion and scrap. Many simplified molds reduce the number of ejector pins, lower processing costs, and sacrifice mass production stability.

3、 Aluminum adhesion on the surface of the top pin accelerates wear and failure
The surface of the mold cavity and top pin was not cleaned in time due to aluminum adhesion, and the aluminum layer was squeezed and scratched on the top pin, causing rapid damage to the mating surface. The AlTiN coating can reduce the tendency of the ejector pin to stick to aluminum. The ejector pin material is selected as SKD61 quenched to HRC50-52, balancing toughness and wear resistance. The hardness of the top pin exceeds HRC54 and its toughness decreases, making it easy to break under impact.

4、 Comparison of Characteristics of Low Pressure Casting Top Out Systems
Low pressure casting has a slow cooling rate, smaller shrinkage and clamping force, and a lower demand for pushing force than die-casting molds. The low-pressure wheel hub mold has a larger fault-tolerant space for setting the ejection stroke and ejection force curve, and the average frequency of ejector pin failures is about 37% lower than that of die-casting molds. The priority of low-pressure mold seal and liquid lifting pipe failures is higher than that of ejector failures.

5、 Common Misconceptions in Overseas Factory Operations and Maintenance
The operator encountered difficulties in the ejection process and directly increased the ejection force, resulting in successful demolding in a short period of time. However, this continued to cause bending of the ejector pin and deformation of the casting. The die and mold ejector system is a consumable component, and it is a safe solution to purchase molds with spare ejector pins. Google's "die casting ejector pin failure" is suitable for attracting on-site maintenance engineers.

FAQ
How to deal with the top pin locking urgently? After shutting down and cooling down, disassemble and clean the burrs, check the gaps, and spray high-temperature lubricating grease.

What should I do if the top pin breaks inside the mold cavity? Remove the residual section with an electric spark, replace it with a new ejector pin, and repair the fitting gap.

What type of grease is used for top pin lubrication? Special high-temperature top pin lubricating grease, ordinary butter has high temperature carbonization, carbon deposition, and sticking.

Where is the top pin of the wheel hub mold usually arranged? The back of the wheel rim and the position of the flange should avoid the appearance surface to prevent top marks.

Is the clearance between the top pins of low-pressure molds the same as that of die-casting? The temperature change under low pressure conditions is moderate, and the gap value can be slightly smaller than that of the die-casting ejector pin.

Can the mold be repaired if the top mark is too deep? Partial polishing, fine adjustment of top pin height, and replacement of inserts in severe cases.

How many spare ejector pins are recommended for a set of molds? 3-5 spare ejector pins are provided for vulnerable points to reduce downtime waiting periods.

Is there a difference between MIM mold ejector and die-casting ejector? MIM feeding is soft, with low top force and finer top pins, requiring higher synchronization accuracy.

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