Pores and bubbles: tiny pores that appear on the surface or inside of a product. Pores are usually formed due to poor mold exhaust or excessive moisture in the plastic, which prevents gas from being expelled in a timely manner during injection molding; Bubbles are caused by the inclusion of air or the production of gas during the melting process of plastic. During inspection, the surface of the product can be observed from different angles in a well lit environment, and touched by hand to feel for any dents or protrusions.

Flying edge: also known as burr, is a thin sheet like residue formed at the edge of the product when molten plastic overflows from the parting surface of the mold or the gap between the core and the cavity during injection molding. Minor burrs can be removed by trimming, but severe burrs can affect the assembly accuracy and appearance quality of the product. During inspection, check if the edges of the product are neat and if there are any excess plastic protrusions.

Weld mark: A linear mark formed when two or more strands of molten plastic converge in a mold cavity and cannot be completely fused due to factors such as temperature and pressure. Welding marks can affect the strength and appearance of the product. Observe whether there are obvious linear marks on the surface of the product, especially around corners, holes, and other areas that are prone to weld marks.

Scratches and abrasions: Surface damage caused by contact with hard objects during the production, transportation, or storage of products. Scratches are usually thin and deep, while abrasions appear as rough surfaces with signs of wear. During inspection, carefully examine the surface of the product for any irregular lines or worn areas.

Color and luster

Uniformity of color: Qualified injection molded products should have uniform and consistent colors without obvious color differences. If the plastic raw materials are mixed unevenly, and the injection temperature or pressure is unstable, it may cause color difference in the product. Place the product on a white background and observe from different angles whether its color is consistent.

Glossiness: According to the design requirements of the product, its surface should have a certain glossiness. Excessive or insufficient glossiness may affect the appearance of the product. The glossiness is related to the type of plastic, the smoothness of the mold surface, and the injection molding process parameters. It is possible to determine whether the glossiness of the product meets the requirements by comparing it with standard samples or using a glossiness meter for measurement.

Dimensional accuracy check

Key dimension measurement

Length, width, height: Use measuring tools such as calipers and micrometers to accurately measure the key dimensions of the product. Compare the measurement results with the dimensions on the design drawings to determine if they are within the allowable tolerance range. For example, for some precision electronic component casings, the dimensional tolerance may be required to be within ± 0.05mm.

Aperture and spacing: For products with holes, it is necessary to measure the aperture and spacing. The measurement of aperture can be done using a plug gauge, while the measurement of hole spacing can be done using a caliper or specialized measuring tool. Ensure that the aperture and spacing meet the design requirements to ensure the assembly performance of the product.

dimensional stability

Comparison of different batches: Measure the dimensions of different batches of the same product and observe whether the dimensions are stable. If there is a significant fluctuation in size, it may be caused by unstable injection molding process parameters, mold wear, or changes in raw material properties. Products with poor dimensional stability may experience poor fit during assembly.

Environmental factors: Consider the size changes of products under different environmental conditions. For example, some plastic products may expand or contract in high temperature or humid environments. It is possible to measure the dimensions of products and evaluate their dimensional stability by simulating different environmental conditions.

performance testing

Mechanical properties

Tensile strength: The product is subjected to a tensile test using a tensile testing machine, and the maximum tensile force it can withstand during the tensile process is measured to calculate the tensile strength. Tensile strength reflects the ability of a product to resist tensile failure. Products with different purposes have different requirements for tensile strength, for example, some structural components require high tensile strength.

Bending strength: Use a bending testing machine to conduct a bending test on the product and measure the maximum bending stress it can withstand during the bending process. Bending strength reflects the ability of a product to resist bending deformation. For some products that require bending loads, such as plastic parts of furniture, bending strength is an important performance indicator.

Impact strength: The product is subjected to impact testing using an impact testing machine to measure its resistance to damage under impact loads. Products with high impact strength are not easily broken when subjected to external impact, making them suitable for situations where they may be subject to accidental collisions.

Thermal performance

Heat deformation temperature: Heat the product under a certain load and measure the temperature at which it begins to deform. The hot deformation temperature reflects the ability of a product to maintain shape stability in high temperature environments. For some products that need to be used in high-temperature environments, such as plastic parts around car engines, the thermal deformation temperature is a key performance indicator.

Heat aging resistance: Place the product in a high temperature environment for a certain period of time to observe changes in its performance and appearance. Products with good heat aging resistance will not experience significant deterioration in performance and appearance during long-term high-temperature use.

CHEMICAL

Corrosion resistance: Soak the product in different chemical media and observe whether it will undergo corrosion, discoloration, deformation, and other phenomena. Products with good corrosion resistance are suitable for use in environments containing chemicals, such as plastic parts of chemical equipment.

Solvent resistance: Use different solvents to wipe or soak the product, and check whether its surface will dissolve, bubble or discolor. Solvent resistance is an important performance indicator for some products that may come into contact with solvents, such as cosmetic packaging containers.

Material verification

Material composition analysis

Infrared spectroscopy analysis: Using an infrared spectrometer to analyze the composition of the product and determine the type of plastic used. Different plastics have different infrared spectral characteristics, and by comparing them with standard spectra, the material composition of the product can be accurately determined.

Thermogravimetric analysis: Using a thermogravimetric analyzer to measure the mass changes of products at different temperatures, in order to analyze the thermal stability and composition of their materials. Thermogravimetric analysis can help determine whether fillers, plasticizers, and other components have been added to the product.

Material performance compliance

Check material certificates: The supplier is required to provide material certificates for the raw materials used in the product, and check whether the performance indicators of the materials meet the design requirements. Material certificates usually include information on the physical, chemical, and mechanical properties of materials.

Comparison standard requirement: Compare the material properties of the product with relevant national standards, industry standards, or enterprise standards to determine whether it meets the requirements. For example, plastic products used in contact with food need to comply with the material requirements in the national food safety standards.

Process trace inspection

Injection mark

Position and size: Check whether the position of the injection port is reasonable and whether it will affect the appearance and performance of the product. The size of the injection molding port should be moderate. If it is too large, it may cause obvious marks on the product at the injection molding port, while if it is too small, it may affect the filling effect of the plastic. Observe whether the injection port marks are smooth and whether there are any residual plastic or burrs.

Post processing: Check if the injection port marks have undergone appropriate post processing, such as grinding, polishing, etc. Good post-processing can make the injection molding marks less obvious and improve the appearance quality of the product.

mold mark

Top pin marks: Top pins are components used in molds to push products out of the mold cavity, leaving marks on the surface of the product. Check whether the top needle marks are uniform, whether the depth is consistent, and whether there are obvious depressions or protrusions. Excessive depth of needle marks may affect the appearance and strength of the product.

Parting line marks: The parting line is the position of the mold parting surface, and there may be traces on the product at the parting line. Observe whether the parting line traces are clear and neat, and whether there are any flying edges or misalignment phenomena. The processing quality of parting line traces reflects the manufacturing accuracy of the mold and the level of injection molding technology.