Chapter 5 Mold Testing 5.1 Testing Process As indicated in Fig 5-1 is a typical testing process for injection molds. After assembling the molds, the bench workers shall begin PSI(Pre-Shipping Inspection) to check preliminarily whether there are obvious problems inconsistent with the design requirement, whereafter starts the testing, which may be any one of the testings for To, T1, T2 and T3. Each testing usually conducts 30 to 40 times of molding After each testing, the testing workers shall complete the Tir (Tryout Issue Report)to describe the various problems existing in the testing process and suggestions for solution. Subsequently, the quality inspection department shall make a TVR(Tooling Verify Report) on the plastic parts obtained from testing. As for the problems detected in TiR and TVR, it is necessary to search the tiR and TvR problem database in the enterprise database for corresponding standard problems and the sol Meanwhile, problems beyond the existing problem database shall be analyzed and programmed, so that the problem database can be further expanded and perfected The tir made by the testing workers and the TvR made by quality inspection department shall be the basis for determining whether the molds meet customers'requirements. If the requirements have not been reached, the MPI(Manufacture Processing Instruction) shall be made, whereby the factory shall instruct mold repairing and conduct re-assembly as well as re-testing until the requirements are met. The customers shall issue the approval certificate thereafter and shipment of molds shall be ultimately completed, thereby transferring into the formal injection mass production
Chapter 5 Mold Testing 5.1 Testing Process As indicated in Fig.5-1 is a typical testing process for injection molds. After assembling the molds, the bench workers shall begin PSI (Pre-Shipping Inspection) to check preliminarily whether there are obvious problems inconsistent with the design requirement, whereafter starts the testing, which may be any one of the testings for T0, T1, T2 and T3. Each testing usually conducts 30 to 40 times of molding. After each testing, the testing workers shall complete the TIR (Tryout Issue Report) to describe the various problems existing in the testing process and suggestions for solution. Subsequently, the quality inspection department shall make a TVR (Tooling Verify Report) on the plastic parts obtained from testing. As for the problems detected in TIR and TVR, it is necessary to search the TIR and TVR problem database in the enterprise database for corresponding standard problems and the solutions whereto. Meanwhile, problems beyond the existing problem database shall be analyzed and programmed, so that the problem database can be further expanded and perfected. The TIR made by the testing workers and the TVR made by quality inspection department shall be the basis for determining whether the molds meet customers’ requirements. If the requirements have not been reached, the MPI (Manufacture Processing Instruction) shall be made, whereby the factory shall instruct mold repairing and conduct re-assembly as well as re-testing until the requirements are met. The customers shall issue the approval certificate thereafter and shipment of molds shall be ultimately completed, thereby transferring into the formal injection mass production
PSI Testing Expanding? TIR TVR Qualified? Approval from customer Problem database lole MPI Mold shipment g hov 5.2 PSI After completing mold assembly, the bench workers shall begin PSI(Pre-Shipping Inspection)to check preliminarily whether there are obvious problems inconsistent with the design requirement. For instance, the pre-shipping inspection for injection molds of a company falls into six parts, i.e. injection molding system, slide system, ejection system, hot and cold medium channel system, positioning system and other aspects, wherein the six parts can be decomposed into several branches and each branch must undergo self-detection and re-check etc, as indicated in Table 5-1 Table 5-1: pre-shipping report of plastic injection mold Inspection Content Method hether the sprue bush, runner and gate are processed as IPQC Whether the date code and the cavity No are consistent IPQC Injection Molding Whether it is necessary to intake air and if necessaryEyeballing
Fig.5-1: mold testing flow 5.2 PSI After completing mold assembly, the bench workers shall begin PSI (Pre-Shipping Inspection) to check preliminarily whether there are obvious problems inconsistent with the design requirement. For instance, the pre-shipping inspection for injection molds of a company falls into six parts, i.e. injection molding system, slide system, ejection system, hot and cold medium channel system, positioning system and other aspects, wherein the six parts can be decomposed into several branches and each branch must undergo self-detection and re-check etc, as indicated in Table.5-1. Table 5-1: pre-shipping report of plastic injection mold Subject Content Inspection Method Whether the sprue bush, runner and gate are processed as per the engineering drawings. IPQC Whether the date code and the cavity No. are consistent with requirement. IPQC Injection Molding Whether it is necessary to intake air and if necessary Eyeballing PSI Testing TIR TVR MPI Expanding? Problem database Assembly Mold repair Qualified？ Approval from customer Mold shipment Yes No No Yes No Expanding? Yes No
System whether it has completed Whether test on the hot runner is oK Control box Whether the electromagnetic valve switch for the needle Eyeballing valve hot runner has been assembled Whether the nameplate of the hot runner has been correctlyEyeballing Slide System mold block have been sufficiently processed and lubricated Whether the slide briquetting, the endurance mold block,On-site the stop pin and the retum spring have been correctly Detection assembled Whether the slide can glide smoothly Whether the thimble has been left out or assembledEyeballing Whether the oil slot of angle pin has been sufficiently Eyeballing System Whether the angle pin and the thimble can return smoothly. On-site hether top of the thimble towers above the moving moldEyeballing surface(0.05mm-0.10mm) Whether top of the angle pin is lower than the movingEyeballing mold surface(0.02mm-0.05mm) Whether the hot and cold medium channel leak(dwell for On-site Detection Cold Medium Whether blind bolt of the mold plate for testing water hasEyeballing
whether it has completed. Whether test on the hot runner is OK. Temperature Control Box Whether the electromagnetic valve switch for the needle valve hot runner has been assembled. Eyeballing System Whether the nameplate of the hot runner has been correctly assembled. Eyeballing Whether the slide briquetting and the oil slot of endurance mold block have been sufficiently processed and lubricated. Eyeballing Whether the slide briquetting, the endurance mold block, the stop pin and the return spring have been correctly assembled. On-site Detection Slide System Whether the slide can glide smoothly. On-site Detection Whether the thimble has been left out or assembled reversely. Eyeballing Whether the oil slot of angle pin has been sufficiently processed. Eyeballing Whether the angle pin and the thimble can return smoothly. On-site Detection Whether top of the thimble towers above the moving mold surface (0.05mm—0.10mm) Eyeballing Ejection System Whether top of the angle pin is lower than the moving mold surface (0.02mm—0.05mm) Eyeballing Whether the hot and cold medium channel leak (dwell for 30 minutes) On-site Thermal and Detection Cold Medium Channel Whether blind bolt of the mold plate for testing water has been removed. Eyeballing
System Whether entrance/exit of the hot and cold medium channel Eyeballing are marked Whether connector of tubes has been assembled Eyeballing er block and been assembled Whether all screws are secure Sampling System ctIon Whether the thimble requiring anti-reverse is provided IPQC with an anti-reverse unit. Whether all problem points listed in the MPI have been IPQC Whether all parts have been assembled. Eyeballing Miscellaneous Whether the interposing space of the moving and fixedEyeballing molds over the parting line has been aired for 0.5mm. Whether the oil stain and smudge on the mold seat, core Eyeballing ave been Whether the wedge block is assembled Eyeballing 5.3 TIR After PSI starts the testing, after which the testing workers shall fill in the tiR and meanwhile the problems shall be brought into and analyzed within the range of the TiR standard problem database. wherein the analysis include the problem points, description of problem points, origin of problem as well as modification countermeasures etc. If it is beyond the problem database, consideration need be made on whether the current problem database shall be expanded. Common testing problems and countermeasures are as follows 1. Cannot Be Sufficiently Filled The plastic melt condenses and solidifies before it can smoothly fill in the cavity part far away from e gate or that with thin section, the cavity therefore is insufficiently filled and the shape and structure of the molded products are incomplete, which is intrinsically due to the low fluidity and poor filling capacity of the plastic melt. The extrinsic cause, however, is due to the large resistance against filling and the insufficient filling power. Specific causes thereof are as follow The plastic melt is provided with high flow viscosity, resulting in poor flow and filling capacity; 2 The plastic melt has poor plasticity, excessively low temperature for plastication and unbalanced melt temperature, which altogether result in the poor melt fluidity;
Whether entrance/exit of the hot and cold medium channel are marked. System Eyeballing Whether connector of tubes has been assembled. Eyeballing Whether the positioning block and positioning ring have been assembled. Eyeballing Whether all screws are secure. Sampling Inspection Positioning System Whether the thimble requiring anti-reverse is provided with an anti-reverse unit. IPQC Whether all problem points listed in the MPI have been settled. IPQC Whether all parts have been assembled. Eyeballing Whether the interposing space of the moving and fixed molds over the parting line has been aired for 0.5mm. Eyeballing Whether the oil stain and smudge on the mold seat, core and cavity have been cleaned. Eyeballing Miscellaneous Whether the wedge block is assembled Eyeballing 5.3 TIR After PSI starts the testing, after which the testing workers shall fill in the TIR and meanwhile the problems shall be brought into and analyzed within the range of the TIR standard problem database, wherein the analysis include the problem points, description of problem points, origin of problem as well as modification countermeasures etc. If it is beyond the problem database, consideration need be made on whether the current problem database shall be expanded. Common testing problems and countermeasures are as follows: 1. Cannot Be Sufficiently Filled The plastic melt condenses and solidifies before it can smoothly fill in the cavity part far away from the gate or that with thin section, the cavity therefore is insufficiently filled and the shape and structure of the molded products are incomplete, which is intrinsically due to the low fluidity and poor filling capacity of the plastic melt. The extrinsic cause, however, is due to the large resistance against filling and the insufficient filling power. Specific causes thereof are as follows: ① The plastic melt is provided with high flow viscosity, resulting in poor flow and filling capacity; ② The plastic melt has poor plasticity, excessively low temperature for plastication and unbalanced melt temperature, which altogether result in the poor melt fluidity;
3 Mold temperature is overlow or unbalanced, temperature of some parts is too low and temperature of melt injected into the cavity drops too fast; a The flow of melt in the mold is too long or too complicated, the resistance against filling is and the filling is not smooth, even resulting in stagnation 6 Temperature of the nozzle is too low and the cold-slug well of feed system is improperly set resulting in jam and stagnation when the front cold material of melt enters the cavity 6 During the filling, molds are not sufficiently aired and the gas has not been discharged in time thereby resulting in the expansion of filling resistance O The actual quantity of injection for the injection machine is too small and the melt required filling is insufficient, thereby directly resulting in material shortage in the cavity; 8 The injection stroke of screw is ended and the plastic stocked in the plastication room is scarce, resulting in poor transmission of injection pressure and insufficient post-stage power of filling: 9 Injection rate of screw is excessively low, the injection pressure is overlow and the filling power is insufficient (0 Wall thickness of products is uneven and the filling resistance is (10 Wall of products is too thin and the filling resistance is large; above all, temperature of melt drops too fast when it flows through and the hertz increases Solutions O Use plastics with low viscosity and sound fluidity or adjust prescription of plastics and reduce iscosity of melt 2 Improve barrel temperature, increase injection pressure, raise melt temperature to reduce erection degree, and improve plastication quality 3 Improve mold temperature and uniformity thereof, raise nozzle tem nd properly cold-slug well Increase dimension of the runner and gate and properly set gate position to avoid overlong flow during filling and overlarge loss of pressure when the melt enters cavity; 5 Properly design mold exhausting scheme and change number of position of gate as well as position of parting line when necessary to achieve sound exhausting effect; 6 Select proper injection machine and correctly adjust screw injection stroke to ensure sufficient actual quantity of injection; meanwhile, it should be ensured that the melt stored in the plastication room at the front of the screw can perfectly transmit pressure. Check the plastic raw material in the hopper of injection machine in due course to see whether it is sufficient Increase injection pressure, injection rate and the filling power of melt; meanwhile, check whether the non-return valve on the screw is damaged to avoid pressure caused by the counterflow of melt as well as loss of melt during injection; 8 Improve structure of plastic parts and design of wall thickness, reduce complication of structure, improve uniformity of wall thickness and properly design wall thickness to reduce structural resistance during the melt filling stroke 2. Welding mark The thread mark formed at the front confluence of two or more melt flows in the cavity is called welding mark or welding line. Usually, apart from low mechanical intensity, such defect as depression and aberration may also occur at places where welding mark appears For plastic parts with holes and inserts or those of complicated structure and with uneven wall
③ Mold temperature is overlow or unbalanced, temperature of some parts is too low and temperature of melt injected into the cavity drops too fast; ④ The flow of melt in the mold is too long or too complicated, the resistance against filling is large and the filling is not smooth, even resulting in stagnation; ⑤ Temperature of the nozzle is too low and the cold-slug well of feed system is improperly set, resulting in jam and stagnation when the front cold material of melt enters the cavity; ⑥ During the filling, molds are not sufficiently aired and the gas has not been discharged in time, thereby resulting in the expansion of filling resistance; ⑦ The actual quantity of injection for the injection machine is too small and the melt required for filling is insufficient, thereby directly resulting in material shortage in the cavity; ⑧ The injection stroke of screw is ended and the plastic stocked in the plastication room is scarce, resulting in poor transmission of injection pressure and insufficient post-stage power of filling; ⑨ Injection rate of screw is excessively low, the injection pressure is overlow and the filling power is insufficient. ⑩ Wall thickness of products is uneven and the filling resistance is large; ⑩ Wall of products is too thin and the filling resistance is large; above all, temperature of melt drops too fast when it flows through and the hertz increases. Solutions: ① Use plastics with low viscosity and sound fluidity or adjust prescription of plastics and reduce viscosity of melt; ② Improve barrel temperature, increase injection pressure, raise melt temperature to reduce erection degree, and improve plastication quality; ③ Improve mold temperature and uniformity thereof, raise nozzle temperature and properly set cold-slug well ; ④ Increase dimension of the runner and gate and properly set gate position to avoid overlong flow during filling and overlarge loss of pressure when the melt enters cavity; ⑤ Properly design mold exhausting scheme and change number of position of gate as well as position of parting line when necessary to achieve sound exhausting effect; ⑥ Select proper injection machine and correctly adjust screw injection stroke to ensure sufficient actual quantity of injection; meanwhile, it should be ensured that the melt stored in the plastication room at the front of the screw can perfectly transmit pressure. Check the plastic raw material in the hopper of injection machine in due course to see whether it is sufficient; ⑦ Increase injection pressure, injection rate and the filling power of melt; meanwhile, check whether the non-return valve on the screw is damaged to avoid pressure caused by the counterflow of melt as well as loss of melt during injection; ⑧ Improve structure of plastic parts and design of wall thickness, reduce complication of structure, improve uniformity of wall thickness and properly design wall thickness to reduce structural resistance during the melt filling stroke. 2. Welding Mark The thread mark formed at the front confluence of two or more melt flows in the cavity is called welding mark or welding line. Usually, apart from low mechanical intensity, such defect as depression and aberration may also occur at places where welding mark appears. For plastic parts with holes and inserts or those of complicated structure and with uneven wall