Injection Mold Ejector Pin Wear Inspection Standards

Ejector pins, as core ejection components of injection molds, are subject to repeated impact forces, friction resistance from molten plastic, high-temperature alternating stress and lateral demolding forces during long-term operation. Various types of wear such as abrasion, deformation, chipping and corrosion are prone to occur during continuous production, which directly affect the molding quality of plastic parts, the overall service life of molds and production line stability. This inspection standard is formulated around five core dimensions: appearance, dimension, fitting clearance, geometric accuracy and product defect reverse judgment. It also integrates wear grading judgment, standardized inspection procedures, preventive control requirements and differentiated implementation standards for molds of different precisions. It is applicable to general injection molds, precision electronic molds and special working condition molds for glass fiber and mineral filled materials. The document defines quantitative thresholds, grading rules and corresponding treatment methods, providing unified and implementable guidelines for on-site inspection, daily maintenance and component replacement, so as to avoid production failures and quality hazards caused by ejector pin wear.

Core Inspection Dimensions and Quantitative Standards

Appearance Inspection

Appearance inspection is the most convenient preliminary screening method that can be completed without precision measuring tools. It is suitable for daily mold inspection, shutdown maintenance and regular mold disassembly. Inspection shall be carried out on the working end, rod body, tail and fitting section of ejector pins by visual observation combined with a 5 to 10 times magnifying glass. Qualified ejector pins shall be free of obvious scratches, carbon deposits, rust, corrosion and chipping. The working end shall have clear edges and regular head fillets. Minor surface scratches and slight floating rust can be polished for continued use and classified as normal wear. Once obvious groove wear, dense pitting, end chipping, plastic sintering, oxidation peeling or wear depth of 0.02mm and above with wear area exceeding 30% of the working section appears, it shall be directly judged as moderate to severe wear. When the standard fillet wear of the ejector pin head exceeds 0.1mm, the end becomes blunt without edges or radial steps appear, it belongs to functional wear. Even if the dimension inspection does not exceed the standard, it shall be included in the key control scope to prevent molding defects caused by uneven stress during ejection.

Dimension Inspection

Dimension inspection is the core basis for judging ejector pin wear. Professional precision measuring tools such as micrometers, surface roughness meters and height gauges shall be used to measure the most severely worn positions compared with new part standard dimensions, and differentiated accuracy thresholds for general and precision molds shall be distinguished. The core indicators include three items. Firstly, diameter wear: measured at the extreme wear position of the fitting and working sections. For general molds, wear ≤0.01mm is slight, 0.01–0.02mm is moderate, and ≥0.02mm is severe. For precision electronic and medical plastic molds, diameter wear ≥0.01mm is considered excessive and requires immediate repair or replacement. Secondly, surface roughness: new ejector pins have a standard Ra value of 0.2–0.4μm. When roughness increases to Ra≥1.6μm, demolding resistance rises sharply, easily causing whitish marks, scratches and sticking, requiring polishing or replacement. Thirdly, length wear: end wear reduces effective length. When shortening exceeds 0.03mm, it breaks ejection balance, causing insufficient local force and skewed demolding, requiring timely replacement.

Fitting Clearance Inspection

The fitting clearance between ejector pins and pin holes is a key indicator affecting mold operation stability. Excessively small clearance causes jamming and abnormal noise, while excessively large clearance leads to melt overflow, flash and aggravated eccentric wear. The industry standard for new ejector pins is 0.01–0.015mm per side, with a total clearance of 0.02–0.03mm as optimal. Grading judgment: total clearance ≤0.02mm is slight wear within normal range; 0.02–0.04mm is moderate wear, repairable for general parts but requiring immediate replacement for precision parts; over 0.04mm is severe wear, requiring simultaneous pin replacement and hole maintenance to avoid bell-mouthing and inner wall scratches. Inspection shall also focus on pin hole openings. Bell-mouthing, overflow residue and scratches indicate synchronized wear, requiring full coaxiality inspection of the ejection system.

Geometric Accuracy Inspection

Geometric accuracy directly determines ejection synchronization for precision molds, long ejector pins and multi-cavity molds, which must be inspected using V-blocks, dial indicators and platform feeler gauges to prevent bending, eccentricity and excessive coaxiality deviation. Standards: axial runout ≤0.02mm is qualified; exceeding this value indicates bending deformation. Straightness inspection uses a standard platform, with clearance over 0.02mm/m indicating excessive bending. Excessive coaxiality deviation causes lateral stress during ejection, aggravating local wear and even scratching the mold cavity. Such defects have no repair value and require direct pin replacement, along with calibration of parallelism and coaxiality of ejector plates and return pins.

Product Defect Reverse Judgment

Ejector pin wear can be judged through molded part defects without mold disassembly, suitable for real-time production control. Under slight wear, plastic parts show only extremely slight whitish marks without cracks or scratches, with stable dimensions, allowing continued production with shortened inspection intervals. Under moderate wear, obvious whitish marks and local scratches appear, demolding resistance increases, and the ejection system produces slight noise, requiring immediate pin replacement for precision parts and temporary repair for small-batch trial production of general parts. Under severe wear, parts suffer cracking, edge chipping and dimensional deviation, with flash, jamming or seizure. Immediate shutdown and maintenance are required, with simultaneous inspection of cavity scratches to avoid expanded damage.

Wear Grading Judgment and Treatment Table

Preventive Inspection, Life Control and Standardized Procedures

Component Life and Preventive Replacement Standards

Service life and replacement cycles shall be differentiated based on ejector pin material, plastic characteristics and production conditions to avoid sudden wear failures. Standard SKD61 pins for unfilled materials recommend full inspection every 500,000 to 1,000,000 cycles and preventive replacement at 1,000,000 cycles. High-hardness SKH51 precision pins require key inspection every 300,000 to 500,000 cycles and replacement at 500,000 cycles. For highly abrasive glass fiber, mineral and ceramic filled materials, special inspection is required every 200,000 to 300,000 cycles with shortened replacement cycles. Titanium-coated or nitrided wear-resistant pins can be used to reduce wear frequency and extend service life.

Standardized Inspection Procedures

Daily inspection runs through the entire production process, focusing on ejection marks, whitish marks and flash status, monitoring abnormal noise and jamming, with immediate marking and recording of abnormalities. Weekly maintenance involves disassembling pins, inspecting appearance, ends and corrosion, thoroughly cleaning deposits and polishing minor scratches. Full-depth inspection is carried out at specified cycles, using micrometers to measure diameter and length, roughness meters to test finish, dial indicators to check coaxiality, and feeler gauges to measure fitting clearance, with final judgment based on grading standards. Closed-loop disposal is implemented after inspection: immediate replacement for any severe standard, decision based on precision for moderate standards, and record-keeping for slight wear.

This standard conforms to actual injection workshop operations with clear quantitative indicators and strong implementability, balancing differentiated requirements for general and precision molds. It defines wear thresholds and standardized maintenance procedures, effectively reducing downtime, ensuring molding quality and extending mold service life, suitable for daily maintenance, regular inspection and component management of various molds in the injection industry.