Tensile and Impact Spline Test Molds: Precision Tools for Material Mechanical Property Testing

In the field of material mechanical property testing, tensile spline test molds and impact spline test molds are core tooling for ensuring test data accuracy and standardizing material quality control. For R&D and production of polymers, composites, and metal powders, these molds produce test splines compliant with international (ISO 527, ISO 179) and domestic (GB/T 1040, GB/T 1043) standards, enabling measurement of key mechanical indicators like tensile strength and impact toughness. With advancing manufacturing demands for material performance and trends toward intelligent, green production, the design precision, manufacturing processes, and adaptability of these molds have become critical to linking material production and performance evaluation. This article analyzes their standard compliance, design-manufacturing technologies, application specifications, and development trends to provide actionable technical references for industry practitioners.

1. Core Positioning and Standard Adaptability of Molds

As basic tooling for material mechanical property testing, tensile and impact spline test molds are designed to ensure the accuracy and comparability of material strength data through standardized spline preparation. Both types of molds must strictly comply with international and domestic standards and serve as a key link between material production and performance evaluation.

1.1 Standard Orientation of Tensile Spline Test Molds

This type of mold is mainly designed based on material tensile performance testing standards, and is mainly compatible with the two systems of GB/T 1040.2-2006 (equivalent to ISO 527-2: 1993) and ASTM D638. For polymer materials such as plastics, the mainstream mold cavity is a 1BA dumbbell structure, and the dimensions need to be controlled within the range of a total length of 150mm, a parallel part length of 80±2mm, a width of 10±0.2mm, and a thickness of 4±0.2mm. The mold cavity tolerance must be strictly controlled within ±0.02mm; otherwise, the tensile strength test data deviation will exceed 5%, losing its reference value.

1.2 Standard Adaptation of Impact Spline Test Molds

Impact spline molds need to distinguish between simply supported beam and cantilever beam test scenarios, complying with ISO 179/GB/T 1043.1 and ISO 180/GB/T 1843 standards respectively. The general size of the simply supported beam impact spline is 80±2mm×10±0.2mm×4±0.2mm, and the notch depth must be precisely controlled to 1/3 of the sample thickness (1.33±0.1mm), with a notch angle of 45° and a bottom radius of 0.25mm; the cantilever beam impact spline mostly adopts the specification of 63.5±0.1mm×12.7±0.2mm×3.2±0.2mm. The notch processing accuracy directly affects the impact toughness data, and special structures are required to ensure no micro-cracks.

2. Key Technologies for Mold Design and Manufacturing

The design logic of both types of molds revolves around "spline accuracy guarantee" and "production efficiency optimization", but due to differences in testing requirements, there are significant differences in structural details and process requirements.

2.1 Key Structural Design Points

2.1.1 Tensile Spline Test Molds

The mold cavity should adopt a smoothly transitioning arc structure to avoid stress concentration leading to spline forming defects. The runner system preferably uses latent gates, and the diameter is adjusted according to material fluidity—PP material is usually 3-5mm, and PA6 material is 2-4mm to ensure uniform melt filling. For castable materials such as epoxy, the mold should be designed with special liquid retention ports and exhaust channels to reduce the spline bubble rate to below 1%. Multi-cavity molds must ensure that the length difference of each cavity runner is ≤2mm to ensure the dimensional consistency of parallel samples.

2.1.2 Impact Spline Test Molds

The core lies in the notch forming structure, usually adopting an embedded blade design. The blade hardness must be ≥HRC55, and the surface roughness Ra≤0.4μm. The mold should reserve a notch processing positioning datum, and the matching accuracy error with the subsequent notch making machine is ≤0.05mm. The cooling system should adopt uniformly distributed direct cooling channels to ensure uniform cooling rate of the spline and avoid residual stress affecting the impact test results.

2.2 Material and Process Selection Standards

2.2.1 Mold Material Matching

The mainstream materials are S136H stainless steel and H13 tool steel. The former is suitable for scenarios with high polishing requirements and can achieve a mirror effect (Ra≤0.2μm), while the latter extends the service life of the mold to more than 100,000 mold cycles due to its excellent wear resistance. For lightweight requirements or small and medium batch production, aluminum alloy 6061 can be used as an alternative, but the operating temperature must be controlled below 150℃.

2.2.2 Precision Manufacturing Processes

Cavity processing must adopt a composite process of CNC high-speed milling and electrical discharge machining (EDM). After nitriding treatment, the surface hardness can reach above HV1000, and the wear resistance is increased by 40%. Key dimensions need to be inspected by a coordinate measuring machine, and the inspection accuracy is ≤0.005mm. During mold assembly, the matching clearance between the guide pillar and guide sleeve should be controlled within 0.003-0.005mm to ensure mold clamping accuracy.

3. Production Application and Quality Control Specifications

The on-site use of both mold types requires aligning with material properties and molding equipment to establish standardized procedures, while strict quality control ensures spline validity.

3.1 Matching of Forming Process Parameters

3.1.1 Tensile Spline Preparation

Injection molds work with screw injection machines, requiring temperature fluctuation ≤±2℃ and pressure fluctuation ≤±1%. For PP materials: injection temperature 200-230℃, mold temperature 25-50℃; for PA6: 240-260℃ (injection), 60-80℃ (mold). Holding pressure: 40-60MPa, holding time 10-20s, cooling time 15-30s for full curing.

3.1.2 Impact Spline Preparation

Beyond basic injection parameters, control demolding speed (≤5mm/s via segmented ejection) to avoid notch damage. Notch processing must finish within 24 hours of forming, with cutter speed 500-1000rpm and feed rate 0.5-1mm/s.

3.2 Spline Quality Acceptance

3.2.1 Dimensional Inspection

Use a 0.02mm vernier caliper (length/width) and 0.001mm micrometer (thickness) for 100% key dimension checks; reject out-of-tolerance splines. Parallel sample dimension standard deviation must be <2%.

3.2.2 Appearance & Performance Check

Surfaces must be free of bubbles, flash, cracks, and obvious weld lines. Inspect notches with a 5-10x magnifier to ensure no micro-cracks. Prepare at least 3 parallel samples per test, with tensile strength RSD ≤5% and impact strength RSD ≤8%.

4. Technological Development Trends and Innovation Directions

4.1 Intelligent Upgrading

New molds integrate temperature/pressure sensors, monitoring the forming process in real time via IoT (data traceability ≥2 years). CAE simulation predicts cavity filling defects, cutting mold design cycles by over 30%.

4.2 Structural & Material Innovation

Modular design enables quick multi-standard spline switching via interchangeable cavities (mold change time ≤30min). Carbon fiber-reinforced composites reduce mold weight by 40% while maintaining high strength and wear resistance.

4.3 Green & Efficient Integration

Multi-cavity designs (up to 16 cavities) boost production efficiency by over 5x. Recyclable mold materials and optimized cooling systems cut energy consumption by 25%, meeting green manufacturing needs.