Cracks are among the most dangerous and unpredictable defects in injection molds. They often form silently in cavities, cores, slides, inserts, gate areas, and cooling channels due to fatigue, stress concentration, improper heat treatment, corrosion, or mechanical impact. Once cracks expand, they can cause sudden mold failure, product defects, flash, scratches, or even safety risks during production. Systematic and regular inspection is essential for preventive maintenance, risk control, and extending the overall service life of molds. Early detection of microcracks can prevent catastrophic damage and costly production downtime.
Visual and Magnifying Glass InspectionVisual inspection is the simplest and most widely used preliminary method in mold workshops. Before checking, the mold must be thoroughly cleaned of oil, residue, carbon deposits, and plastic buildup to ensure clear observation. A strong light source from an oblique angle helps highlight surface cracks by creating shadows. A magnifier of 5–20x is used to detect fine cracks in stress‑concentrated areas such as sharp corners, R‑angle roots, gates, ejector pin holes, insert seams, and parting lines. This method is fast and cost‑free but cannot detect internal or extremely fine closed cracks, so it should only be used as the first step in a complete inspection process.
Penetrant TestingPenetrant testing is the most practical and reliable method for detecting surface‑opening cracks. It is highly sensitive and works well on complex surfaces, curved cavities, deep corners, and hard‑to‑reach areas. The process involves thorough cleaning and drying, applying penetrant, allowing sufficient dwell time for liquid to enter cracks, removing excess fluid, and applying white developer. Cracks appear as sharp red lines, clearly showing location, length, and shape. It is widely used in mold shops for routine maintenance, repair verification, and pre-production inspection, especially for precision molds where microcracks must be excluded.
Magnetic Particle TestingMagnetic particle testing is suitable for ferromagnetic mold steels including S136, H13, 718, and NAK80. It detects both surface and near‑surface defects that are invisible to the naked eye. When magnetized, cracks create magnetic flux leakage that attracts magnetic particles, forming visible indications. This method is fast, reliable for large areas, and commonly used for mold bases, structural components, and large cores. Demagnetization is required afterward to prevent iron chip adhesion during production. It is especially effective for detecting fatigue cracks in high-stress areas.
Ultrasonic TestingUltrasonic testing is used for internal defects such as deep cracks, inclusions, porosity, and heat treatment cracks. It uses high-frequency sound waves to reflect off internal discontinuities, allowing accurate assessment of defect depth, size, and location. It is ideal for large mold blocks, high‑life precision molds, and critical structural components. However, it requires experienced operators and is less effective on highly complex cavity surfaces with many curves and ribs. It is often used during mold manufacturing, after heat treatment, and during long-term service evaluation.
Industrial Endoscope InspectionEndoscopes are specialized tools for inspecting deep cavities, cooling channels, runner systems, ejector holes, and other hidden areas unreachable by visual inspection. The flexible, ultra-fine probe reaches internal surfaces and displays real-time high-definition images, enabling detection of internal cracks, corrosion, blockages, and material buildup. It has become essential for complex, deep-cavity molds, hot runner molds, and large automotive molds. Regular endoscope inspection helps maintain internal system health and prevent unexpected failures.
Recommended Inspection ProcedureA complete and effective inspection combines visual checking, penetrant testing, magnetic particle testing, ultrasonic testing, and endoscope inspection where necessary. Start with external observation, move to surface defect detection, then check internal conditions. Early detection prevents catastrophic failure, reduces scrap rates, and improves overall production stability. Establishing a regular inspection cycle based on mold usage intensity is highly recommended for continuous production safety.
ConclusionEffective crack detection ensures mold reliability and production stability. Combining visual, penetrant, magnetic particle, ultrasonic, and endoscope methods allows comprehensive evaluation of surface and internal conditions. Regular and systematic inspection helps identify microcracks before they expand, supports accurate maintenance decisions, and reduces the risk of sudden mold failure. A complete inspection system extends service life, reduces downtime, improves product quality, and lowers overall production costs for injection molding facilities.
