A method for preparing a small gauge tensile specimen

Abstract

This invention discloses a method for preparing small-sized tensile test specimens, comprising: ① sampling; ② pre-processing of the billet, clamping the aligned billet on a lathe fixture and turning it into a billet with a diameter of Ф8-12mm; ③ CNC program setting; ④ CNC machining, processing the round bar billet through rough turning, finish turning, chamfering, and cutting to finally produce small-sized tensile test specimens as shown below; ⑤ Grinding, further grinding the CNC-machined small-sized tensile test specimens using an external cylindrical grinder, with the final finished product size being Ф6±0.02mm. The purpose of this invention is to provide a method for preparing small-sized tensile test specimens to meet the requirements of European customers for testing the tensile properties of rails. This invention is characterized by its simple operation and ease of promotion.

Description

Technical Field

[0001] This invention belongs to the field of physical testing technology, and in particular relates to a method for preparing small-sized tensile specimens. Background Technology

[0002] Tensile testing is the most basic and commonly used test method for testing the mechanical properties of materials. By applying an axial tensile load to a standard specimen, it measures the core mechanical properties of the material, such as strength, plasticity, and elastic modulus, providing key data for material selection, product design, and quality inspection. It is applicable to almost all solid materials, including metals, plastics, rubber, and composite materials.

[0003] The design of tensile test specimens should follow the principle of smooth transition between the gauge length and the clamping section to avoid stress concentration at the transition point, which could lead to specimen fracture in the non-gauge length section. The core specimens are divided into two main categories: circular specimens and plate specimens. There are also special specimens for special materials such as pipes, wires, films, and rubber.

[0004] A European customer's order required tensile testing of the rails, but the required tensile specimen size was small and outside the scope of national standards. To meet the customer's requirements, this invention proposes a method for preparing small-sized tensile specimens, which is simple to operate and easy to promote. Summary of the Invention

[0005] To overcome the shortcomings of small tensile specimen size, which is outside the national standard range, the purpose of this invention is to provide a method for preparing small-sized tensile specimens to meet the requirements of European customers for testing the tensile properties of rails. This invention is characterized by its simple operation and ease of promotion.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a method for preparing small-diameter tensile specimens, comprising:

[0008] ① Sampling

[0009] When taking samples from the rail head, the sample axis must be strictly aligned with the rail rolling direction; sufficient machining allowance should be left on the sample to avoid insufficient subsequent machining;

[0010] ② Pre-processing of billets

[0011] The aligned blank is clamped on the lathe fixture and machined into a blank with a diameter of Ф8-12mm.

[0012] ③ CNC program settings

[0013] The diameter of the small tensile specimen is Ф6mm. The basic parameters of the program are written according to the diameter dimension, including the gauge length, transition arc, clamping section, and total length.

[0014] ④ CNC machining

[0015] The round bar billet is rough-turned, finish-turned, chamfered, and cut to finally process into small tensile test specimens with the following specifications: gauge length: Ф6±0.04mm, parallel length: 40mm, original gauge length: 30mm, transition arc: 10mm, clamping section: Ф8±0.05mm, length on both sides: 35mm, total specimen length: 120mm, end face chamfer: 0.5mm;

[0016] ⑤ Grinding

[0017] To ensure the accuracy of the outer diameter, surface finish, and cylindricity of the tensile specimens, the CNC-machined small-sized tensile specimens are ground again using an external cylindrical grinder. The final finished product size is Ф6±0.02mm.

[0018] Furthermore, the sample size is 150mm × 15mm × 15mm.

[0019] Furthermore, it is machined into a blank with a diameter of Ф10mm.

[0020] Further, the CNC machining process involves: loading a Ф10mm round bar blank into a soft jaw with a clamping length of 15-20mm; attaching a dial indicator to the lathe tool post with the indicator tip contacting the outer diameter of the blank; starting the spindle; adjusting the three-jaw chuck to ensure radial runout of the blank is ≤0.02mm; then, tightening the tailstock center against the center hole at the other end of the blank to eliminate radial movement. The machining process is as follows: rough turning → finish turning → chamfering and cutting.

[0021] Furthermore, the spindle speed is 500 r / min.

[0022] Furthermore, the grinding process involves using an external cylindrical grinder to grind small-sized tensile specimens, with the surface of the round bar ground to Ra 0.4~1.6μm.

[0023] Furthermore, ensure that the cylindricity is ≤0.02mm / m.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0025] The method of this invention for preparing small-sized tensile specimens solves the problem of complex processing of small specimens, while also meeting the GB / T 228.1 general tensile test standard. It takes into account the convenience of sampling, the representativeness of the test and the accuracy of the data, and meets the testing requirements of European customers. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings.

[0027] Figure 1This is a diagram of a small-size tensile specimen of the present invention. Detailed Implementation

[0028] A 200mm long section of heat-treated steel rail was cut from the rail beam factory to prepare a small-scale tensile test specimen:

[0029] ① Sampling

[0030] The first step is to clamp the rail on a high-speed band saw and cut off the entire rail head blank. The second step is to mark the sampling position on the cut rail head blank using a stretching tool. The third step is to cut the blank using a band saw, ensuring the sample axis is strictly aligned with the rail rolling direction. The blank size is 150mm × 15mm × 15mm, with sufficient machining allowance to avoid insufficient machining later.

[0031] ② Pre-processing of billets

[0032] Clamp one end of the cut blank onto a lathe fixture, and drill a 5mm deep center hole at the other end. Then, clamp the blank with the drilled center hole onto the lathe fixture and machine it into a Ф10mm blank.

[0033] ③ Write a program

[0034] The diameter of the small-sized tensile specimen processed in this study is Ф6mm. The basic parameters of the program were written according to the gauge length Ф6±0.04mm, parallel length 40mm, transition arc 10mm, clamping section Ф8±0.05mm, and clamping section length 35mm.

[0035] ④ CNC machining

[0036] Load a Ф10mm round bar billet into the soft jaws, with a clamping length of 15-20mm. Attach a dial indicator to the lathe tool post, with the indicator tip contacting the outer diameter of the billet. Start the spindle (500 rpm) and adjust the three-jaw chuck to ensure radial runout of the billet is ≤0.02mm. Then, tighten the tailstock center against the center hole at the other end of the billet to eliminate radial movement. Machining proceeds as follows: rough turning → finish turning → chamfering and cutting.

[0037] Rough turning: Turn the end face of the billet flat and rough turn the outer diameter to Ф10.4mm.

[0038] Precision machining clamping section: The clamping sections on both sides of the precision machining extend to Ф8±0.05mm, with a length of 35mm.

[0039] Precision turning of transition arcs: Machining 10mm transition arcs on both sides, smoothly transitioning from the clamping section Ф8mm to the gauge section Ф6mm.

[0040] Fine-machined gauge length section: Fine-machined gauge length section to Ф6±0.04mm, length 40mm.

[0041] Chamfering and cutting: Use a 3mm wide grooving tool to cut at Z-120.5mm, leaving a 0.5mm allowance for manual smoothing. Lightly grind the cut end face with a fine file to smooth the total length to 120mm.

[0042] ⑤ Grinding

[0043] To ensure the accuracy of the outer diameter, surface finish, and cylindricity of the tensile specimens, the CNC-machined small-sized tensile specimens need to be ground again. The small-sized tensile specimens are ground using an external cylindrical grinder. The surface of the round bar needs to be ground to Ra0.4~1.6μm, with a focus on ensuring that the cylindricity is ≤0.02mm / m, and ensuring that the finished product size is Ф6±0.02mm.

[0044] After the above-mentioned processes, the round bar blank is finally processed into the following small-sized tensile test specimens: gauge length Ф6±0.02mm, parallel length 40mm, original gauge length 30mm, transition arc 10mm, clamping section Ф8±0.05mm, length on both sides 35mm, total specimen length 120mm, and end face chamfer 0.5mm.

[0045] A random inspection was conducted on the small-sized tensile specimens processed by the method of this invention. The specimen diameter was 6.01 mm, the parallel length was 40.01 mm, the original gauge length was 30 mm, the transition arc was 10 mm, the clamping section diameter was 8.02 mm, the clamping section length was 35.03 mm, and the total specimen length was 120.02 mm, which met the requirements.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a small-sized tensile specimen, characterized in that, include: ① Sampling When taking samples from the rail head, the sample axis must be strictly aligned with the rail rolling direction. Leave sufficient machining allowance on the sample to avoid insufficient machining in subsequent processes; ② Pre-processing of billets The aligned blank is clamped on the lathe fixture and machined into a blank with a diameter of Ф8-12mm. ③ CNC program settings The diameter of the small tensile specimen is Ф6mm. The basic parameters of the program are written according to the diameter dimension, including the gauge length, transition arc, clamping section, and total length. ④ CNC machining The round bar billet is rough-turned, finish-turned, chamfered, and cut to finally process into small tensile test specimens with the following specifications: gauge length: Ф6±0.04mm, parallel length: 40mm, original gauge length: 30mm, transition arc: 10mm, clamping section: Ф8±0.05mm, length on both sides: 35mm, total specimen length: 120mm, end face chamfer: 0.5mm; ⑤ Grinding To ensure the accuracy of the outer diameter, surface finish, and cylindricity of the tensile specimens, the CNC-machined small-sized tensile specimens are ground again using an external cylindrical grinder. The final finished product size is Ф6±0.02mm.

2. The method for preparing small-size tensile specimens according to claim 1, characterized in that, The sample dimensions are 150mm × 15mm × 15mm.

3. The method for preparing small-size tensile specimens according to claim 1, characterized in that, The blank is machined into a Ф10mm blank.

4. The method for preparing small-diameter tensile specimens according to claim 1, characterized in that, The CNC machining process is as follows: A Ф10mm round bar blank is loaded into a soft jaw with a clamping length of 15-20mm. A dial indicator is attached to the lathe tool post, with the indicator tip contacting the outer diameter of the blank. The spindle is started, and the three-jaw chuck is adjusted to ensure that the radial runout of the blank is ≤0.02mm. Then, the tailstock center is tightened against the center hole at the other end of the blank to eliminate radial movement. The machining process is as follows: rough turning → finish turning → chamfering and cutting.

5. The method for preparing small-size tensile specimens according to claim 4, characterized in that, The spindle speed is 500 r / min.

6. The method for preparing small-size tensile specimens according to claim 1, characterized in that, The grinding process involves using an external cylindrical grinder to grind small-sized tensile specimens, with the surface of the round bar ground to Ra0.4~1.6μm.

7. The method for preparing small-diameter tensile specimens according to claim 6, characterized in that, Ensure cylindricity ≤ 0.02 mm / m.

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