Injection molding product testing and inspection
Injection molding product testing and inspection is a critical step in ensuring that plastic part quality meets design requirements and application standards. This process runs throughout the entire production process, including incoming raw material inspection, in-process testing, and finished product inspection. Scientific and rational testing methods can promptly identify defects and quality risks in plastic parts, preventing substandard products from entering the market. This also provides a basis for optimizing production processes, improving production efficiency and product qualification rates. Injection molding product testing and inspection involves multiple aspects, including dimensional accuracy, appearance quality, mechanical properties, and chemical properties. Appropriate testing methods and standards must be selected based on the intended use and quality requirements of the plastic part.
Raw material testing is the first line of defense in injection molding product quality control, as its quality directly impacts the subsequent molding process and part quality. Raw material testing primarily includes visual inspection, performance testing, and composition analysis. Appearance inspection focuses on observing the uniformity of the raw material’s color, the presence of impurities, and the consistency of particle size. Granular raw materials should be prohibited from use if they exhibit signs of agglomeration, discoloration, or foreign matter. Performance testing includes measuring melt flow rate (MFR), density, tensile strength, and impact strength. These indicators reflect the raw material’s processing and mechanical properties, ensuring they meet molding requirements. For example, polypropylene raw materials used in structural parts must be tested for tensile strength exceeding 20 MPa and impact strength that meets the requirements of the intended use environment. Composition analysis verifies that the raw material’s chemical composition complies with regulations to prevent the use of counterfeit or inferior raw materials or the mixing of materials. Methods such as infrared spectroscopy and thermogravimetric analysis can be used for this purpose.
Online inspection during the production process is a crucial means of promptly identifying quality issues and preventing widespread defects. It primarily involves visual inspection, dimensional testing, and process parameter monitoring. Visual inspection can be performed using either manual or machine vision systems to examine plastic parts for surface defects such as scratches, dents, bubbles, flash, and burn marks. Manual visual inspection offers high flexibility but is less efficient and susceptible to human error. Machine vision systems, using high-definition cameras and image recognition algorithms, can quickly and accurately identify various surface defects, making them suitable for inspection in large-scale production. Dimensional inspection typically uses tools such as calipers, micrometers, and gauges to measure key dimensions of plastic parts. For parts requiring higher precision, a coordinate measuring machine (CMM) is also required for comprehensive dimensional inspection to ensure compliance with the tolerances specified in the drawing. Process parameter monitoring collects real-time data on parameters such as injection pressure, holding pressure, melt temperature, and mold temperature to determine whether they fluctuate within set ranges. If anomalies are detected, process parameters are adjusted promptly to prevent quality degradation caused by out-of-control parameters.
Finished product inspection is the final quality checkpoint before injection molded products enter the market. This requires comprehensive and systematic testing of plastic parts to ensure they meet customer requirements and relevant standards. Inspection items vary depending on the part’s intended use. For structural parts, dimensional accuracy, mechanical properties, and assembly performance are prioritized; for exterior components, surface quality, color consistency, and gloss are emphasized. Food-grade or medical-grade plastic parts also require hygienic and chemical safety testing, such as heavy metal content and volatile organic compound (VOC) emissions. For example, plastic parts used in food packaging must comply with the national food safety standard GB 4806.7-2016, testing for excess residue and potassium permanganate consumption. Finished product inspection typically utilizes sampling, with the sampling plan determined based on batch size and quality requirements. Unqualified batches require full inspection or rework until they meet quality standards.
The selection and maintenance of testing equipment are crucial to the accuracy and reliability of test results. Commonly used testing equipment for injection molded products includes coordinate measuring machines (CMMs), universal testing machines (UTMs), impact testing machines, colorimeters, gloss meters, and projectors. CMMs enable precise three-dimensional measurement, making them suitable for dimensional inspection of complex plastic parts with measurement accuracy up to 0.001mm. Universal testing machines are used to test mechanical properties such as tension, compression, and bending. By applying varying forces, deformation and fracture patterns are recorded and corresponding mechanical properties calculated. Colorimeters and gloss meters are used to measure the color and surface gloss of plastic parts, ensuring consistent appearance across batches. To ensure the accuracy of testing equipment, regular calibration and maintenance are required. Calibration plans should be developed in accordance with the equipment’s instruction manual and relevant standards, performed by qualified personnel, and calibration results should be recorded and archived. Operators should also receive professional training and be familiar with the equipment’s operating procedures and precautions to avoid distorted test results due to improper operation.
Standards and specifications for testing and inspection of injection molded products are essential for ensuring the orderly conduct of testing. Different industries and regions may have different standard requirements. Commonly used international standards include ISO (International Organization for Standardization) and ASTM (American Society for Testing and Materials), while domestic standards include GB (national standards) and QB (industry standards). Companies should select appropriate standards for testing based on the sales market and usage scenarios of their plastic parts. For example, plastic parts exported to Europe may need to comply with ISO 9001 quality management system and related product standards, while plastic parts for the domestic automotive industry must meet standards such as GB/T 17200-2008, “Quality Inspection Methods for Plastic Injection Molded Products.” Furthermore, companies can develop internal quality standards, incorporating specific customer requirements to create more stringent testing specifications and enhance product competitiveness. Strict adherence to testing standards and specifications ensures the fairness and authority of test results, providing strong assurance of product quality.
