Hollow stabilizer bar manufacturing method

Abstract

A method for manufacturing a hollow stabilizer bar, including the preparation of a tube blank, comprising: selecting steel for tensile testing; determining the tensile strength, characteristic parameters, target elongation coefficient, and target cross-sectional area reduction rate of the steel before tube extraction based on the target tensile strength; determining the relationship between the outer diameter and thickness of the tube blank; selecting the target tube blank size; selecting the steel size; and high-frequency welding the target tube blank.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a hollow stabilizer bar for automobiles, and more particularly to a method for manufacturing a hollow stabilizer bar for automobiles with seam welding. Background Technology

[0002] The traditional process for high-frequency welded tube blanks of hollow stabilizer bars for automobiles (CN109423580 and CN110038913) involves the following steps: tube fabrication -> annealing heat treatment -> heading -> pickling -> film saponification -> tube drawing (1-3 times depending on the tube blank size) -> head and tail trimming -> normalizing heat treatment -> straightening -> flaw detection -> cutting. The annealing heat treatment after tube fabrication aims to improve the weld microstructure, making it closer to the base material to facilitate subsequent tube drawing. The normalizing heat treatment after tube drawing aims to adjust the material microstructure to meet mechanical performance requirements.

[0003] In terms of heat treatment processes, hollow stabilizer bars require extremely high surface quality, with no excessively thick decarburized layer or microcracks to ensure their fatigue resistance. Traditional heat treatment uses continuous furnaces or batch furnaces, holding the temperature above the A1 or A3 metamorphic point of the steel for a period of time to alter the material microstructure. The higher the temperature or the longer the holding time, the more severe the surface decarburization and oxidation. Existing processes often use atmosphere protection to reduce decarburization and oxidation, relatively increasing production costs.

[0004] In terms of surface treatment processes, traditional heat treatment is followed by pickling to remove the overheated oxide layer on the surface, and then saponification is performed to create a dense lubricating film on the surface, providing lubrication during pipe drawing. The solutions treated by phosphating and saponification must be neutralized and purified before being discharged to reduce the risk of pollution.

[0005] In terms of tube drawing process, the traditional method involves multiple drawing steps, with process annealing required between each drawing step. This makes it difficult to improve the tensile strength of the tube after drawing and also incurs higher production costs. Summary of the Invention

[0006] To reduce the number of tube extractions, one embodiment of the present invention proposes a method for manufacturing a hollow stabilizer bar. Regarding the preparation of the tube blank, the method includes: selecting a steel material and its target tensile strength; obtaining a tensile relationship between the cross-sectional area reduction rate and tensile strength of the steel material, and a tensile strength *a* before tube extraction, using a tensile test; performing curve fitting based on lnY=lna+n*lnX using this tensile relationship, where Y is the tensile strength of the steel material and X is an elongation coefficient corresponding to the cross-sectional area reduction rate of the steel material, to obtain a characteristic parameter *n* of the steel material; obtaining a target elongation coefficient of the steel material based on the target tensile strength, the tensile strength *a* before tube extraction, and the characteristic parameter *n*; obtaining a target cross-sectional area reduction rate *RA* based on the target elongation coefficient; and obtaining a tube blank thickness relationship t*(Dt)=(1-RA)** t0*(D0-t0) yields a relationship between D0 and t0, where D is the target outer diameter of the steel after it has been made into a tube blank and then drawn into a tube, t is the target wall thickness of the tube blank after drawing, D0 is the outer diameter of the tube blank, and t0 is the thickness of the tube blank. Based on this relationship between D0 and t0, a target tube blank size is selected. Based on the target tube blank size, a target steel size is selected, the steel is rolled into shape, and then high-frequency welded into the target tube blank. Attached Figure Description

[0007] Figure 1 This is a flowchart of one embodiment of the present invention, showing a method for manufacturing an automotive stabilizer bar.

[0008] Figure 2 As one embodiment of the present invention, a graph showing the relationship between cross-sectional area reduction rate and tensile strength.

[0009] Figure 3 This is a schematic diagram illustrating the use of curve fitting to obtain the characteristic parameters of steel, as one embodiment of the present invention.

[0010] Figure 4 This is a flowchart of one embodiment of the present invention, showing a method for manufacturing an automotive stabilizer bar.

[0011] Figure 5 This is a schematic diagram of a high-frequency welding apparatus according to one embodiment of the present invention.

[0012] Figure 6 This is a schematic diagram of a tube embryo according to one embodiment of the present invention.

[0013] Figure 7 As one embodiment of the present invention, a comparison table of mechanical properties of tube blanks before and after induction heat treatment is provided. Detailed Implementation

[0014] refer to Figure 1A method for manufacturing a hollow stabilizer bar for automobiles, regarding the preparation of the tube blank, includes the following steps in one embodiment: Step 10, selecting steel, performing a tensile test after induction heat treatment; Step 11, obtaining the tensile relationship between the reduction of cross-sectional area and tensile strength of the steel, and the tensile strength before tube extraction; Step 12, obtaining the characteristic parameters of the steel through curve fitting based on the governing equation; Step 13, obtaining the target elongation coefficient of the steel; Step 14, obtaining the target reduction of cross-sectional area of ​​the steel; Step 15, obtaining the relationship between D0 and t0, where D0 is the outer diameter of the tube blank and t0 is the thickness of the tube blank; Step 16, selecting the target tube blank size; Step 17, selecting the steel size; Step 18, high-frequency welding to form the target tube blank.

[0015] Step 10: Select manganese-boron steel as the steel for the hollow stabilizer bar of the automobile and the target tensile strength of the steel. In one embodiment, the steel comprises, by mass percentage: carbon C: 0.20-0.40%, silicon Si: 0.15-0.40%, manganese Mn: 1.1-1.5%, aluminum Al: 0.01-0.06%, chromium Cr: 0.05-0.3%, titanium Ti: 0.01-0.06%, boron B: 0.001-0.005%, phosphorus P limited to less than 0.02%, sulfur S limited to less than 0.01%, nitrogen N limited to less than 0.01%, and the remainder consisting of iron Fe and unavoidable impurities.

[0016] In one embodiment, the above-mentioned steel is rolled into a tube by high-frequency welding, which is the tube blank. (See reference) Figure 6 The tube blank includes base material 1 and weld bead 2. (Reference) Figure 7 The tube blanks were subjected to induction heat treatment at two different temperature ranges: 700–830°C and 830–960°C, followed by tensile tests. Figure 7 The comparison table of mechanical properties of the tube blank before and after induction heat treatment shows that both induction heat treatments at different temperature ranges can make the mechanical properties of weld 2 and base material 1, such as tensile strength, yield strength, and elongation, tend to be consistent. Specifically, weld 2 shows a significant increase in elongation and a substantial improvement in ductility after induction heat treatment. In one embodiment, the tensile strength 'a' before tube drawing is obtained by tensile testing after induction heat treatment of the tube blank.

[0017] In steps 11 and 12, in one embodiment, tensile tests are performed on the tube blank after induction heat treatment for different cross-sectional area reduction rates to obtain the tensile relationship between the cross-sectional area reduction rate and tensile strength. The relationship diagram is shown in the figure below. Figure 2 RA1, RA2, RA3, RA4, and RA5 represent the cross-sectional area reduction rates from smallest to largest. Figure 2In the diagram, the solid lines represent the data of the base material in the tube blank, and the dashed lines represent the data of the weld bead. In one embodiment, when the shrinkage rate is 0, the intercept on the Y-axis is the tensile strength 'a' of the steel before tube drawing.

[0018] Using the governing equation Y=a*X n Let Y be the tensile strength, and X be the elongation coefficient of the tube blank. Define X = 1 / (1 - RA), where RA is the reduction rate of cross-sectional area. We can obtain lnY = lna + n * lnX, where n is a characteristic parameter of the tube blank. For different reduction rates, taking the logarithm of the tensile strength and elongation coefficient yields... Figure 3 The experimental data (solid line) is then used for curve fitting. The slope of the fitted straight line (dashed line) is the characteristic parameter n of the tube embryo.

[0019] Step 13: Using lnY=lna+n*lnX, based on the tensile strength a before tube extraction and the characteristic parameter n of the tube blank obtained by curve fitting, as well as the target tensile strength, the target elongation coefficient can be obtained.

[0020] Step 14: Using the elongation coefficient X=1 / (1-RA) of the tube blank, the target cross-sectional area reduction rate of the tube blank can be obtained.

[0021] Step 15: Based on the tube blank thickness relationship t*(Dt)=(1-RA)*t0*(D0-t0), the relationship between D0 and t0 is obtained, where D is the target outer diameter of the steel after tube blanking, t is the target wall thickness of the tube blank after tube blanking, D0 is the outer diameter of the tube blank, and t0 is the thickness of the tube blank. In one implementation, the steel and the target tensile strength after tube blanking are selected. Through the above process, the tensile strength a of the steel before tube blanking, the characteristic parameter n of the steel, the target elongation coefficient, and the target cross-sectional area reduction rate can be obtained. Then, the target cross-sectional area reduction rate is substituted into RA in this relationship, and combined with the target outer diameter D and the target wall thickness t, the relationship between D0 and t0 can be obtained.

[0022] Step 16: Based on the relationship between D0 and t0, select the target size of the tube blank and the corresponding target steel size. This could involve selecting t0 and then fabricating a mold based on the corresponding D0; or selecting D0 and then choosing the steel thickness for the tube blank based on the corresponding t0. In this way, the diameter of the high-frequency welded pipe can be derived from the steel strip thickness, allowing for the selection of an appropriate pipe-making mold. Alternatively, an appropriate steel strip thickness can be purchased based on the pipe diameter corresponding to an existing pipe-making mold. In one embodiment, the required steel coil thickness can be ordered from the steel mill using an existing pipe-making mold, or the tube blank diameter can be determined based on the thickness of an existing steel coil, and then a pipe-making mold can be developed.

[0023] Step 17: The steel that meets the target steel dimensions is rolled into shape and then high-frequency welded into the target tube blank. In this way, the tube blank dimensions can be obtained by reverse engineering from the required dimensions and mechanical properties of the finished product.

[0024] refer to Figure 4 A method for manufacturing a hollow stabilizer bar for automobiles, in one embodiment, includes: step 200, tube fabrication; step 201, first induction heat treatment; step 202, heading; step 203, oil immersion lubrication; step 204, tube drawing; step 205, cutting; step 206, second induction heat treatment; step 207, straightening; step 208, flaw detection; step 209, short tube; and step 210, rust prevention.

[0025] Step 200, after the steel coil is formed, refer to... Figure 5 The left side of the tube blank 30 is an open tube heated by high-frequency induction heating by induction coil 34. Due to the skin effect and proximity effect, the heat is concentrated on both sides of the open end. The material is fused together by the extrusion of rollers 31, 32, and 33 on the right side. Then, the weld beads generated after extrusion are scraped off by internal and external scraping devices, resulting in smooth inner and outer surfaces and uniform wall thickness at the weld seam. The welded tube, after internal and external scraping, is rolled by rollers in the sizing section to control the outer diameter and straightness. After sizing, the high-frequency welded tube is inspected for weld quality by an online detection device to ensure there are no cracks or insufficient fusion. Finally, it is cut to the required length by a flying saw, transported to the unloading table for stacking and bundling, awaiting subsequent heat treatment.

[0026] Step 201 involves a first induction heat treatment to anneal the tube blank. Induction heating is used with 1-3 turns of the induction coil at a frequency of 3-30 kHz. The steel tube is heated to a heat treatment temperature of 700-960°C, and then passed through the coil at a fixed rate followed by natural air cooling. After annealing, the tube blank weld seam does not exhibit any loose iron structure; instead, it consists of granular iron and ferrite with uniform mechanical properties. After heat treatment, it possesses the following mechanical properties: tensile strength 500-650 MPa, yield strength 350-500 MPa, elongation ≥25%, and the following microstructure characteristics: grain size better than grade 8, surface decarburized layer thickness ≤40 μm, and surface oxide layer thickness ≤10 μm. In one embodiment, the steel tube is heated to two different temperatures: 700-830°C and 830-960°C. The test results show that after heat treatment with the above two sets of parameters, the mechanical properties of the weld are close to those of the base material, and both sets of parameters can achieve the purpose of weld optimization.

[0027] Step 202: Reduce the diameter of the steel pipe head so that the reduced diameter steel pipe head can enter the drawing die, making it easier to clamp during pipe pulling and preparing for drawing.

[0028] Step 203: Due to the use of induction heat treatment, the heating time is extremely short, and there is no oxide layer on the surface due to overheating. Before tube drawing, the tube is directly immersed in drawing oil for lubrication. Phosphating and saponification treatments are not performed, and tube drawing is carried out directly by oil drawing.

[0029] Step 204, the tube drawing process, involves placing the annealed, headed, and lubricated steel tubes onto a horizontal tube drawing machine. The length of the steel tubes before drawing is 4-7 meters, with 1-3 tubes drawn at a time. A single-pass drawing process is used, with a shrinkage rate of 25-35% and a drawing speed of 10-25 m / min. The length of the drawn steel tubes is 6-10 meters. The straight tubes after drawing meet the following dimensional accuracy requirements: outer diameter tolerance + / -0.10 mm, wall thickness tolerance + / -0.10 mm, roundness tolerance within 0.08 mm, and surface roughness Ra 3.2 or less. They also meet the following mechanical properties: tensile strength 800-900 MPa, yield strength 500-780 MPa, and elongation ≥ 8%. After the pipe was drawn, the straight pipe was flattened to 86% of its original diameter before cracking occurred; after the pipe was flared to 38% of its original diameter, cracking occurred.

[0030] Step 205: Cut to remove the length of the end that has been cut off.

[0031] Step 206: Second induction heat treatment for fine-drawn tube annealing. The finely drawn straight tubes that meet the dimensions are treated using induction heating at an induction frequency of 3-30kHz, heated to a heat treatment temperature of 500-750°C, and annealed. The annealed straight tubes possess the following mechanical properties: tensile strength 550-750MPa, yield strength 350-500MPa, elongation ≥15%, and the following microstructure characteristics: grain size better than grade 8, surface decarburized layer thickness ≤40µm, surface oxide layer thickness ≤10µm, and the following dimensional accuracy: outer diameter tolerance + / -0.10mm, wall thickness tolerance + / -0.10mm, roundness outer diameter tolerance ≤0.08mm, straightness ≤1mm / 1m, and surface roughness Ra ≤3.2. After heat treatment, the straight pipe was flattened to 50% of its original diameter before cracking occurred; after flaring, the flaring rate reached 32% and no cracking occurred, meeting the acceptable specification of 28%.

[0032] Step 207, in one embodiment, involves using multiple roller dies for straightening.

[0033] Step 208, in one embodiment, uses eddy current and ultrasonic waves to perform non-destructive testing on the inner and outer surfaces of the steel pipe.

[0034] Step 209: Cut the steel pipe to the final specified delivery length.

[0035] Step 210: Perform rust prevention treatment.

Claims

1. A method for manufacturing a hollow stabilizer bar, comprising: Select a type of steel and its target tensile strength; use a tensile test to obtain the tensile relationship between the reduction of cross-sectional area and the tensile strength, and the tensile strength a before tube extraction; use this tensile relationship to perform curve fitting based on lnY=lna+n*lnX, where Y is the tensile strength of the steel and X is the elongation coefficient corresponding to the reduction of cross-sectional area of ​​the steel, to obtain the characteristic parameter n of the steel; Based on the target tensile strength, the tensile strength a before tube drawing, and the characteristic parameter n, the target elongation coefficient of the steel is obtained; based on the target elongation coefficient, the target reduction rate RA of the cross-sectional area is obtained; based on the tube blank thickness relationship t*(Dt)=(1-RA)* t0*(D0-t0), the relationship between D0 and t0 is obtained, where D is the target outer diameter of the steel after tube drawing, t is the target wall thickness of the tube blank after tube drawing, D0 is the outer diameter of the tube blank, and t0 is the thickness of the tube blank; based on the relationship between D0 and t0, the target tube blank size is selected; based on the target tube blank size, the target steel size is selected, the steel is rolled into shape, and then high-frequency welded into the target tube blank.

2. The method as described in claim 1, wherein the step of selecting the tube blank size based on the relationship between D0 and t0 includes selecting D0 and then purchasing product steel based on t0.

3. The method as described in claim 1, wherein the step of selecting the tube blank size based on the relationship between D0 and t0 includes selecting t0 and then making a mold based on D0.

4. The method of claim 1, after high-frequency welding to form the tube blank, further includes: The tube blank is subjected to a first induction heat treatment, then directly immersed in oil for lubrication, and then drawn into a tube.

5. The method of claim 4, wherein the first induction heat treatment step comprises heating to 700-960°C at an induction frequency of 3K-30KHz.

6. The method of claim 4, wherein the first induction heat treatment step of the tube blank includes forming a surface decarburized layer with a thickness of less than 40 μm and a surface oxide layer with a thickness of less than 10 μm on the tube blank, and the following microstructure characteristics: grain size better than grade 8, and the following mechanical properties: tensile strength of 500-650 MPa and elongation of more than 25%.

7. The method of claim 4, wherein the tube blank drawing step includes achieving the target reduction rate RA of the cross-sectional area in one drawing, a surface roughness Ra of less than 3.2, and the following mechanical properties: tensile strength of 800-900 MPa and elongation of more than 8%.

8. The method of claim 4, wherein after the tube drawing step, the tube blank is further subjected to a second induction heat treatment.

9. The method of claim 8, wherein the second induction heat treatment step comprises heating to 500-750°C at an induction frequency of 3K-30KHz.

10. The method of claim 8, wherein the second induction heat treatment step of the tube blank includes forming a surface decarburized layer with a thickness of less than 40 μm and a surface oxide layer with a thickness of less than 10 μm on the tube blank, and the following mechanical properties: tensile strength 550-750 MPa, yield strength 350-500 MPa, elongation ≥15%, and the following microstructure characteristics: grain size better than grade 8.

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