What Key Items Should Be Tested for Injection Mold Trial Samples in China
Injection trial molding is an important process to verify mold structure, material adaptability and molding technology. Test results of trial samples are used to judge whether the mold meets mass production requirements, identify defects in advance and reduce quality risks in later mass production. Test items cover appearance, dimension, assembly, material performance and other dimensions.
Appearance Defect Inspection
Visually check the overall surface state of samples to find various molding defects, including sink marks, bubbles, silver streaks, burn marks, weld lines, flow marks, flash, ejection whitening, scratches, short shots and cold material spots. Focus on appearance surfaces, assembly contact surfaces and customer-specified visible areas, record the position, size and severity of defects, and distinguish whether defects are caused by molds, raw materials or process parameters. Meanwhile, check whether gate residue and demolding marks exceed the allowable range.
Dimension and Tolerance Inspection
Measure dimensions marked on the 2D product drawing, including overall length, wall thickness, hole diameter, boss positions, buckles, positioning structures and other key dimensions, with priority control of assembly-related tolerances. Measuring tools such as calipers, micrometers and height gauges and projectors are adopted. Measurement is carried out after the samples are placed at room temperature for stress release to avoid data deviation caused by high temperature of freshly demolded samples. For multi-cavity molds, samples from each cavity are measured separately to count dimensional differences among cavities, judge the balance of cavity machining, record product shrinkage and check whether it matches the shrinkage compensation design of the mold in the early stage.
Assembly Matching Verification
Carry out assembly tests between trial samples and mating parts, check plugging and unplugging, buckling, screw assembly, gaps and steps. Test repeated opening and closing of buckles and undercut assembly to check whether assembly is too tight, loose, stuck or abnormal noise occurs. Inspect the overall steps after product assembly, evaluate the matching effect of appearance, simulate assembly under actual use conditions, and find hidden dangers such as interference and inaccurate positioning of structural design.
Structural Strength and Functional Test
Conduct simple functional tests for stressed structures. Repeated assembly tests are performed on buckles and boss positions to assess risks of fracture and creep. Simple pressing tests can be carried out for shell products to observe cracking and deformation. If the product has special requirements such as sealing or light transmission, corresponding simple functional verification is conducted simultaneously to judge whether structural strength meets working conditions and identify hidden risks of embrittlement caused by excessive internal stress.
Internal Stress Inspection of Materials and Molded Parts
Check whether stress whitening exists on samples. Solvent immersion can be used to screen residual internal stress when necessary. Products with excessive internal stress are prone to cracking in later use or assembly. Verify raw material grades to confirm no material mixing, check whether materials degrade or scorch, compare basic characteristics of materials after molding, and judge whether settings of drying and barrel temperature are reasonable.
Demolding and Deformation Evaluation
Observe warpage, twisting and depression of samples after demolding, record deformation direction and amount, and judge whether deformation comes from uneven cooling, ejection force or molecular orientation. Check whether products have sticking, pulling, tearing and other demolding damage, evaluate whether ejection mechanism, demolding draft and polishing state meet production requirements, and analyze whether mold structure or process parameters need adjustment for improvement.
Evaluation of Weld Lines and Venting Effect
Locate all weld line positions on products, check the depth of weld lines and assess weld line strength. Confirm whether weld lines fall on key areas such as stress-bearing and sealing positions. Observe burn marks and trapped gas defects, judge whether the position and depth of vent grooves are sufficient, and evaluate whether the mold venting system can meet the demand of stable molding.
Weight Stability Inspection
Weigh single samples and compare weight differences of samples from the same multi-cavity mold. Weight fluctuation can directly reflect the stability of filling and packing. Higher weight usually means excessive packing pressure or flash, while lower weight generally indicates insufficient filling. Continuous multi-shot sampling and weighing are performed to judge the width of the process window and evaluate quality fluctuation risks during mass production.
