Technical document

  1. 你的位置
  2. HOME
  3. News
  4. Technical document

Custom Processing Key Points of Standard Mechanical Test Specimen

2026-04-30 11:36:26 Plastic Molds
Standard mechanical test specimens are benchmark samples for performance testing such as tensile, bending, impact and hardness of plastic materials. They adopt national standard, ISO and ASTM standard sizes, covering PP, ABS, PC, PA, PEEK and various modified engineering plastics. The dimensional accuracy, surface flatness, internal defect-free and consistency of injection molding process of specimens directly determine the accuracy, repeatability and comparability of mechanical test data. Custom processing must be strictly standardized from standard selection, mold structure, injection molding process, post-processing control and dimensional accuracy control to ensure each batch of specimens meet the qualification requirements of laboratory testing.

1. Standard Specification Selection and Structural Dimension Control

Customizing mechanical test specimens must first clarify the implementation standards, commonly including GB/T, ISO and ASTM three major systems. The length, width, thickness, arc transition and clamping section size of tensile specimen, cantilever beam impact specimen, simply supported beam impact specimen and bending specimen corresponding to different standards have strictly fixed parameters, which cannot be modified at will. Tensile specimens focus on controlling the width and thickness of the middle parallel section and the transition arc radius; impact specimens need to accurately control the V-shaped notch angle, depth and bottom arc radius. Deviation of notch size will directly cause large fluctuation of impact strength data.

injection mould

The wall thickness of the specimen must be uniform as a whole, without thickness difference, shrinkage depression and local glue accumulation. Reinforcement positions, splicing traces and gate residues are not allowed in the parallel test section. Confirm the material shrinkage rate in the early stage of customization, advance shrinkage compensation in mold design to avoid dimensional tolerance exceeding after molding; unify the glue feeding position, set the gate in the non-test stress area, avoid tensile, bending and impact key sections, and prevent gate stress and weld lines from affecting mechanical performance test results.
2. Mold Processing and Cavity Precision Design of Specimen MoldMechanical specimen mold is the core to ensure the consistency of samples. The cavity must adopt high-precision engraving and mirror polishing, with tight parting surface without flash burr, to eliminate edge overflow and scratch and size deviation of specimens. The mold cavity adopts integral mold insert structure to reduce insert splicing gaps and avoid weld lines and raised parting lines; the mold surface is mirror polished to ensure the specimen surface is smooth without lines, scratches and bubbles, meeting the requirements of appearance and mechanical stress.
The mold cooling water channels are arranged conformally and evenly to ensure consistent cooling speed of each part of the whole specimen, reduce internal stress, warping and bending deformation, and prevent uneven clamping of deformed specimens and large dispersion of test data. Multi-cavity molds must achieve balanced runner and synchronous glue feeding, with high consistency of size, temperature and filling between cavities, avoiding excessive performance difference of specimens in the same batch. The thimble layout avoids the test stress section, adopts concealed ejection without thimble dent and whitening stress point.

3. Key Points of Injection Molding Process Parameter Control

Injection molding of mechanical specimens must adopt stable and solidified process parameters, and random adjustment of machine parameters is prohibited. Raw materials are fully dried in advance to remove moisture and avoid bubbles, silver streaks and delamination. Modified glass fiber materials control drying temperature and time to prevent glass fiber precipitation and material degradation. Adopt low-speed and medium-pressure stable filling to avoid internal stress and uneven molecular orientation caused by high-speed injection molding, resulting in distorted data of tensile strength and elongation at break.

Set reasonable holding pressure and holding time to make up shrinkage in place and eliminate shrinkage depression, while avoiding excessive residual stress caused by over holding pressure. The cooling time is sufficient, and the mold is opened and ejected after the specimen is completely shaped to prevent bending and distortion deformation caused by early demolding. For the same brand and batch of raw materials, fix barrel temperature, mold temperature, back pressure and injection speed parameters. Do not change the proportion of recycled materials or mix raw materials of different batches during production to ensure high unity of mechanical properties of specimens.

injection mould

4. Post-processing, Cutting and Trimming and Environmental Aging Specification

The injection molded mechanical specimens have residual internal stress and cannot be directly tested on the machine. They need to be placed at constant temperature and aged according to material requirements to release molding internal stress and stabilize molecular structure and size. Gate and runner residual materials of specimens are neatly cut with special tooling. Manual breaking and excessive polishing are prohibited to avoid micro-cracks and edge chaps at the incision affecting impact and tensile test results.

Slight surface burrs can only be finely polished and trimmed. Do not polish the test stress section and notch position; the notch of impact specimen is uniformly processed by special standard milling machine to ensure full compliance of angle, depth and radian. Manual trimming is prone to size deviation and micro-cracks. Finished specimens are classified and placed flat for storage to avoid bending deformation caused by stacking and extrusion. Before testing, place them in constant temperature and humidity laboratory for a sufficient time to eliminate the interference of temperature and humidity on test data.

Summary

The core of custom processing of standard mechanical test specimens lies in four major links: accurate standard matching, high-precision mold cavity, stable injection molding process and standardized post-processing aging. Strictly follow GB, ISO and ASTM dimensional specifications, do a good job in mold precision and uniform cooling of water channels, solidify injection molding parameters to reduce internal stress and molding defects, cooperate with professional cutting, notch processing and constant temperature aging treatment. It can ensure uniform size, intact appearance, no bubbles and weld lines inside the specimen, making the mechanical tensile, bending and impact test data true, reliable and repeatable, meeting the application requirements of material research and development, incoming material testing, formula modification and third-party laboratory certification.

injection mould

Home
Product
News
Contact