Mar 12,2026
Models Push Out System Failure Analysis and Improvement Strategies
Models Push Out System Failure Analysis and Improvement Strategies
Ejection system, Ejector pin, Sticking, Wear, Failure analysis
The pushout system is the final “level” in the mold that pushes the finished product out of the mold core. Its reliable operation directly determines whether production can proceed continuously. However, the pushout system is also one of the parts with the highest failure rate in the mold, with common problems including thimble jamming, thimble breaking, white top, unbalanced pushout, and so on. Deep analysis of these failure patterns and targeted improvement strategies are key to improving the reliability and lifespan of the mold.
Failure Mode 1: Thimble Stuck and Wear. During prolonged back-and-forth motion, friction occurs between the thimble and the thimble holes. Stuck occurs when the interval is too small, improper lubrication, or changes in the interval due to thermal expansion. Stuck can lead to a sharp increase in pushout resistance, which can cause the thimble plate to deform, the thimble to bend, and even break. The improvement strategies include: 1 Choosing the appropriate coordinated parity, usually H7/f6 or H7/g6, both to ensure smooth movement and to prevent melt infiltration; 2 Applying surface treatments to the dials, such as nitrogenation, chromium-hardened coating, or TiN coating, to improve surface hardness and abrasion resistance; 3 Designing a forced reset mechanism on the dial plate to ensure that the dial does not get stuck due to insufficient spring strength during the reset process; 4 For long-distance pushout, adding guide pillars and guide covers on the dial plate can ensure consistency in the direction of pushout.
Failure Mode 2: Thimble Break. Thimble break usually occurs on thin, long thimbles with smaller diameters, or in areas where top output is concentrated. The causes of fracture include: insufficient strength of the thimble itself (materials, improper heat treatment), excessive pushout resistance (product package tightness too great, insufficient moulding slope), excessive pushout journey causing the thimble to undergo bending stress, concentration of stress at thimble root, etc. Improved strategies: 1 Choose higher-strength thimble materials, such as powdered high-speed steel such as SKD61, ASP60; 2 Optimize moulding slope, reducing package tightness; 3 Increase thimble number, distributing top output; 4 Design large round corners at thimble roots, avoiding concentration of sharp-cornered stress; 5 For areas that are extremely breakable, replace round thimbles with flat thimbles or cylinders (case thimbles) to increase the bearing area.
Failure Mode 3: Top white and tip-out marks. Top white refers to white stress marks left by the thimble on the surface of the product, which in serious cases can lead to the product being scrapped. Top white usually occurs in cases where the removal slope is insufficient, the tip-out speed is too fast, or the thimble end surface has too small an area of contact with the product. Improved strategies: 1 Increase the removal slope, reducing packing tightness; 2 Increase the contact area of the thimble end surface with the product, such as using a flat thimble or a thicker thimble; 3 Increase bite or serrated lines on the thimble end surface, increasing friction, preventing the thimble from slipping; 4 Optimize the tip-out speed curve, adopting a slow-fast-slow tip-out method; 5 Add cooling circuits around the thimble, reducing the adhesion force of the product to the mold core.
Failure Mode 4: Unbalanced tip-out causes deformation of the product. When the thimble layout is asymmetrical, or some thimbles become invalid due to wear, the tip-out force will be uneven, causing the product to warp and deform during the tip-out process. Improved strategies: 1 In the CAE analysis phase, simulate the tip-out process and optimize the thimble layout to ensure that the tip-out force center overlaps with the product‘s geometric center; 2 Increase the number of thimbles to make the tip-out force distribution more uniform; 3 Add tip-out placings in areas prone to deformation to provide auxiliary support; 4 Use tip-out plate balancing mechanisms, such as synchronous tip-out of hydraulic cylinders, to ensure that all thimbles move in sync.
Preventive maintenance of the extrusion system is equally important. Regular inspection of the dendrites‘ wear, cleaning of dirt from the dendrites‘ holes, checking the exhaustion of the springs, and lubricating of the guide column guide covers are necessary measures to ensure the long-term stable operation of the extrusion system. For moldes with high life requirements, consider using guide covers with self-lubricating functions, or integrating straight-line bearings on the dendrites‘ plates to reduce friction and wear.
Through system failure analysis and improvement, the failure rate of the tip-out system can be minimized, ensuring that the mold remains as reliable as it was during millions of tip-out cycles.
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