Injection mold test matters needing attention
Injection molding trials are a critical verification step before a mold is officially put into production. This process requires rigorous control of every detail to accurately assess mold performance and determine optimal process parameters. Improper operation during the trial process can not only distort trial data but also damage the mold or equipment, impacting subsequent production plans. Therefore, during trial molds, it is crucial to adhere to scientific operating procedures, paying close attention to mold operating conditions, changes in product quality, and the stability of process parameters. Promptly identifying and documenting any issues will provide a reliable basis for mold optimization and mass production.
During the initial mold trial, parameter adjustments should be made gradually to avoid damage to the mold or part due to sudden parameter changes. For the first injection, use a low injection pressure (approximately 70% of the estimated pressure) and a slow injection speed (30-50 mm/s). Observe the melt filling the cavity, then gradually increase the pressure and speed until the cavity is just full. Each parameter adjustment should be made individually, and the adjustment should be limited to a single factor: injection pressure should be increased or decreased by no more than 10 bar, injection speed by no more than 20 mm/s, and temperature by no more than 5°C. This ensures that the impact of these parameters on part quality can be accurately assessed. For example, if part material is missing during the mold trial, the injection pressure should be gradually increased rather than increasing both pressure and temperature simultaneously. Otherwise, it will be difficult to distinguish between insufficient pressure and insufficient fluidity. During the initial mold trial, close attention should be paid to the mold opening and closing movements to ensure that moving parts such as guide pins, guide bushings, and ejector mechanisms are not binding, and that there are no leaks in cooling water, hydraulic oil, or other lines. This will prevent equipment abnormalities from impacting the mold trial process.
Comprehensive inspection of product quality is a core task of mold trial, requiring assessment across multiple dimensions, including appearance, dimensions, and mechanical properties. Appearance inspection focuses on defects such as missing material, flash, bubbles, scorch marks, silver streaks, and water ripples. The location and morphology of the defects should be recorded, and the causes analyzed. Missing material may indicate insufficient pressure or poor venting; flash may indicate insufficient clamping force or excessive injection pressure; and bubbles may indicate insufficient drying of the raw material or poor venting. Dimensional inspection requires the use of tools such as calipers, micrometers, and coordinate measuring machines to measure key dimensions of the part (such as length, width, thickness, and aperture). These dimensions are then compared to the design drawings, and dimensional deviations are calculated to determine whether the mold’s machining accuracy and plastic shrinkage meet requirements. For complex structural parts, assembly testing is required to check clearances with other components and functional performance, such as the snap fit and shaft-hole fit accuracy. Mechanical property testing (such as tensile strength and impact strength) requires sampling according to standards and testing with laboratory equipment to ensure compliance with operational requirements. All test data must be carefully recorded and compiled into a mold trial report to provide a basis for mold improvements.
Real-time monitoring of mold status is an essential component of the mold trial process. Pay attention to abnormal signals such as mold temperature, sound, and vibration. During mold trial, use an infrared thermometer to monitor the temperature distribution of various parts of the mold to ensure that the cooling water circuits are functioning properly and that the temperature differential is within ±5°C. If any localized temperature rises, this could indicate a blockage in the circuit or uneven heating, requiring prompt inspection. Listen for the sounds of the mold opening, closing, and injection. Normally, these should be smooth mechanical movements. Any unusual noises (such as metallic clanging or squealing) could indicate insufficient lubrication of the guide pins and sleeves, loose components, or interference. Immediately stop the machine for inspection to prevent damage. Observe mold vibration. Excessive vibration during mold closing could indicate uneven clamping force or insecure mold installation. Recheck the mold securement and clamping parameters. Regularly clean the cavity and runners during mold trial to remove plastic residue and oil contamination to prevent impact on subsequent product quality inspections.
Data recording and analysis during the mold trial must be systematic and comprehensive to provide a basis for subsequent process optimization and mold improvement. Each mold’s process parameters (such as injection pressure, speed, temperature, holding time, cooling time, etc.) and the corresponding part quality should be recorded. Correlations between these parameters and quality should be established to identify the optimal parameter range. For example, the shrinkage of the part at different holding pressures can be recorded to determine the holding pressure range that achieves acceptable dimensions. Mold operating data, such as mold opening and closing times, injection time, and cycle time, should be recorded to calculate production efficiency and assess mold suitability. Any issues that arise should be categorized and analyzed: mold structural issues (such as improper gate placement or insufficient venting) should be reported to the mold design department for revision; process parameter issues (such as degradation caused by excessive temperatures) should require parameter adjustments; and raw material issues (such as excessive impurities) should require raw material replacement or enhanced pretreatment. After the mold trial, all data should be compiled into a comprehensive report that includes the purpose, process, results, issues, and recommendations. This report should be reviewed by relevant personnel to determine whether mold modifications or process parameter optimization are necessary.
Mold maintenance and review after the mold trial are crucial steps to ensure the continued effectiveness of the trial. After the trial, the mold must be thoroughly cleaned to remove plastic residue from the cavity and runners. The parting and molding surfaces must be wiped with alcohol and inspected for scratches and wear. Moving parts, such as guide pins, guide bushings, and the ejector mechanism, should be lubricated to prevent rust and seizure. Vulnerable parts, such as the mold’s fastening bolts and cooling nozzles, should be inspected to ensure they are free of looseness or damage. Based on the issues identified in the trial report, a mold improvement plan should be developed, clearly defining the modifications, responsible individuals, and completion deadlines. These modifications may include adding venting slots, adjusting gate dimensions, and repairing worn parts. The optimal process parameters identified during the trial should be consolidated and a standard operating procedure (SOP) compiled to provide a basis for mass production. A trial review meeting should be held to share experience, analyze the causes of any problems, and prevent recurrence in subsequent trials. Post-trial review and improvement efforts can significantly improve mold reliability and production efficiency, reducing quality risks during mass production.
