Key Notes for Customization of Plastic Test Specimen Molds
2026-05-19 10:38:35
Plastic Molds
Plastic test specimen molds are special precision molds dedicated to producing various standard tensile, impact, bending and flame retardant test samples. The manufacturing precision, internal structural design and processing technology level of molds directly affect specimen forming quality and final material test data accuracy. Slight unreasonable design and processing deviation in mold customization will lead to large test data errors and mass unqualified specimens. In the whole process of customizing national standard, American standard, European standard and non-standard special test specimen molds, comprehensive strict control must be implemented covering standard parameter verification, structural design optimization, mold steel selection, machining precision control, cooling and exhaust layout and final trial molding acceptance to avoid various hidden quality risks in advance.
1. Strict Verification of Implementation Standards and Dimensional ParametersStandard classification verification must be completed first in the early customization stage to accurately distinguish different system specifications of GB national standard, ASTM American standard and ISO European standard. Core data such as tensile specimen models, impact specimen notch styles, standard thickness grades and fixed gauge lengths are confirmed one by one. Similar specimens of different standards have tiny dimensional differences, and mixed use of standards will directly cause finished specimens unable to match test equipment for normal use.
2. Core Points of Integral Mold Structural Design
Balanced multi-cavity layout design is preferred, and common specimen molds mostly adopt stable four-cavity and six-cavity symmetrical arrangement modes. The design ensures consistent melt flowing speed and unified forming temperature in each cavity, realizing stable consistency in size and physical properties of all specimens in the same batch and avoiding single-cavity independent forming deviation. Reasonable planning of gate installation positions is essential. Side gates are preferentially selected for tensile specimens to stay away from stress-bearing test areas and prevent gate traces from interfering with normal fracture positions in tensile tests. Gates of impact specimens are arranged away from reserved notch positions to avoid concentrated welding lines at weak stress positions and ensure authentic and effective impact test results.
3. Selection Criteria of Custom Mold Steel Materials
For conventional general modified plastics and ordinary raw material forming molds, 718H pre-hardened mold steel is selected for cavities and cores. This material features convenient deep processing and excellent comprehensive polishing performance, with high cost performance, fully meeting long-term stable use demands of conventional laboratory small and medium-batch production. When customizing molds for high-wear raw materials such as glass fiber reinforced and carbon fiber reinforced plastics, high-hardness mirror mold steel including NAK80 and S136 must be adopted. Such materials have strong wear resistance and corrosion resistance, which can effectively avoid cavity surface pulling damage in long-term production and stably maintain high finish of specimen surfaces. Standard 45# refined steel plates are uniformly used for mold bases to strengthen overall mold rigidity, prevent integral datum position deviation after repeated mold opening and closing, and maintain long-term stable specimen forming size. Ejector pins, small inserts and other vulnerable accessories are uniformly made of high-quality SKD61 steel to improve wear resistance and reduce daily replacement frequency of vulnerable parts.
4. Customization Requirements for Cooling and Exhaust SystemsTest specimens are mostly slender thin structural parts. Cooling pipelines need to be evenly arranged closely attached to cavity outer walls to realize synchronous heat dissipation in all areas, rapidly dissipate injection molding residual heat, effectively reduce internal residual stress of specimens, and restrain post-forming warping, bending and size shrinkage deformation. Key optimization is implemented on exhaust structures at melt converging positions, specimen terminal ends and corner dead zones. Precision shallow-depth exhaust grooves are professionally opened to rapidly discharge air gathered inside cavities, avoiding internal bubbles, surface burning, material shortage and silver line defects, and ensuring dense and flawless internal tissue structure of finished specimens. Independent optimized exhaust design is carried out at reserved notch positions of impact specimens to prevent loose internal material tissue caused by local air trapping and avoid excessive fluctuation of final impact test data.
5. Control of Machining Precision and Surface TechnologyProfessional precision numerical control equipment is adopted for integral core finishing processing. All arc structures, right-angle positions and standard gauge sections are integrally formed at one time to minimize later manual trimming links and reduce dimensional errors caused by human intervention. High-grade smooth polishing treatment is implemented inside all cavities to ensure smooth and flawless surfaces without processing tool marks and surface scratches. The formed test specimens have flat and tidy appearance, fully meeting laboratory visual acceptance standards. High-precision finishing and fitting treatment are carried out on parting surfaces to ensure tight fitting and reliable sealing, completely block injection molding overflow flash, reduce later manual trimming and polishing workload, and keep neat and unified edge outlines of all finished specimens.
6. Design Specifications of Ejection and Demolding Structures
Single-point centralized ejection mode is abandoned for slender long-strip test specimens. Multiple tiny ejector pins are evenly distributed for dispersed force bearing ejection to effectively avoid surface whitening, integral deformation and even fracture damage of specimens in the ejection process. Scientific and reasonable demolding inclination is formulated. Excessively large inclination will cause obvious size deviation at both ends of specimens, while excessively small inclination will lead to difficult demolding and surface pulling damage. Unified standard demolding gradient is formulated in strict accordance with the industry universal design specifications of test specimens. Smooth demolding optimization treatment is completed inside molds to reduce internal cavity friction resistance, realizing stable demolding production adapting to forming characteristics of different raw materials such as PP, PA, PC and ABS.
7. Reserved Space for Raw Material Adaptation and Injection Technology
Commonly used production raw material types need to be notified in advance during mold customization. Distinguishing design is carried out according to hygroscopic raw materials, high-fluidity raw materials and high-viscosity raw materials to targeted adjust internal flow channel size and cavity feeding width, matching different material forming characteristics. Sufficient adjustable reserved space is set in mold internal design for injection molding production technology, realizing flexible switching of injection speed, mold temperature and holding pressure parameters. It can meet both low-temperature low-speed stable forming demands and high-temperature high-efficiency high-speed injection production conditions, covering forming demands of various types of modified plastics. Structural optimization is carried out from the mold end for specimens requiring later stress relief treatment to reduce internal stress generation sources in advance and lower the probability of later irreversible deformation of finished products.
8. Trial Molding Acceptance and After-sales Confirmation StandardsFull-standard formal trial molding inspection must be completed after mold manufacturing. Various size data such as overall length, thickness, width and reserved notch specifications of trial-produced specimens are measured comprehensively to confirm whether all indicators fully comply with detection standards, and targeted fine adjustment and modification are implemented for unqualified positions. Continuous multi-batch trial production verification is conducted to stably inspect hidden problems such as long-term dimensional fluctuation, appearance color difference and abnormal forming defects of specimens, and formal delivery can be arranged only after all indicators reach the standard.
9. Other Practical Customization DetailsInstallation matching specifications are confirmed in advance according to actual used injection molding equipment, including equipment tonnage tie rod spacing and positioning ring standard size, to avoid finished molds unable to be installed and put into use normally. Clear demand classification is made between small-batch trial molds for laboratory temporary use and formal large-scale mass production molds. Simplified structure design is adopted for trial molds to control comprehensive cost, while structural reinforcement treatment is implemented for mass production molds to extend overall service life. If it is necessary to produce color difference comparison specimens and color matching test samples, reserved optimization design is completed in advance for internal forming technology space to ensure consistent size and stable performance of finished specimens with different color formulas.
