Method for testing impact fatigue of hard alloy tooth head

Abstract

The invention discloses a method for testing impact fatigue of a hard alloy tooth head, which comprises the following steps: setting an impact force close to the stress condition of the hard alloy tooth head under a real working condition by preparing a fixed contact area and simulating a corresponding rock impact condition. And the impact cycle times of the hard alloy tooth head under the corresponding working conditions are recorded through high-frequency impact with the set impact force. And finally, calculating a relatively accurate and reliable average impact fatigue life estimation value and an impact fatigue life lower limit estimation value according to statistical estimation of the fatigue life of a sixth point under given stress in GB / T 24176-2009 metal material Fatigue Test Data Statistical Scheme and Analysis Method. The metal material fatigue test national standard is combined with the hard alloy detection, so that the finally output data is more accurate and reliable.

Description

Technical Field

[0001] This invention relates to the field of alloy testing technology, and more specifically to a method for testing the impact fatigue of cemented carbide tooth tips. Background Technology

[0002] As the teeth of industry, cemented carbide is used as the main cutting component in the tooth position of cutting tools. Under actual working conditions, it is subjected to intermittent, high-frequency impacts. Practice has shown that the impact strength is far less than the strength limit of cemented carbide, but it can still cause it to break. This is because the dynamic impact fatigue performance cannot be equated with static performance indicators such as strength and toughness.

[0003] The prior art CN101608990A discloses a method for testing the impact fatigue of cemented carbide, which utilizes... This technique uses the impact force of free fall to perform cyclic impacts, achieving the effect of impact cycling. The final output is the number of impact cycles and the impact energy. However, this technique cannot simulate impact effects according to different working conditions. The final output data can only be compared internally and cannot provide a true evaluation of the performance of cemented carbide under corresponding working conditions.

[0004] Therefore, this application utilizes an impact fatigue testing machine and a dedicated clamping mold to calculate the impact force based on the mining conditions, rock, and cutting tooth usage. The number of impact fatigue cycles of the sample is then determined through testing. Finally, the impact fatigue life of the cemented carbide sample is calculated with reference to GB / T24176-2009 Metallic Materials - Fatigue Testing - Data Statistical Scheme and Analysis Method. Summary of the Invention

[0005] In view of this, the present invention provides a test method for impact fatigue of cemented carbide teeth to solve the problems encountered in the background art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: 1. By preparing a fixed contact area and simulating the corresponding rock impact conditions, the impact force is set to approximate the stress condition of the cemented carbide tooth under real working conditions.

[0007] 2. By subjecting the carbide tooth to high-frequency impacts at a set impact force, the performance of the tooth under corresponding working conditions is recorded. The number of impact cycles.

[0008] Specifically, a test method for impact fatigue of cemented carbide tooth tips includes the following steps: (1) Prepare cemented carbide sample and impact pair. The cemented carbide sample is a cutting tooth with a cone shape with parabolic flow lines. A groove corresponding to the parabolic flow line cone of the cemented carbide sample is machined in the center of the impact pair. The impact pair uses ductile iron material QT600-3. (2) Fix the cemented carbide sample with the clamp of the impact fatigue testing machine and fix it with screws and self-locking anti-loosening washers. The teeth of the cemented carbide sample face down and are aligned with the groove of the impact pair. (3) Adjust the magnitude of the impact force; the magnitude of the impact force is calculated by the contact area between the ballistic flow line of the tooth head and the groove of the impact pair and the rock compressive strength under simulated rock conditions (the impact force value can also be obtained through simulation software). ; F—impact force used in the test; S—Contact area between the tooth tip and the attack pair; R—Rock compressive strength; (4) Start the impact fatigue testing machine, set the control mode to load control, and the command function to sine wave. The testing machine will start to allow the carbide tooth to impact the impact pair with the set impact force at a high frequency until the carbide breaks. The equipment will then stop and the number of impact cycles will be recorded. (5) According to GB / T 24176-2009 Metallic Materials. Fatigue Testing. Data Statistical Scheme and Analysis Method, the number of samples in each test group should be ≥7. In order to achieve better results, 28 samples are required. After obtaining the complete test results, the impact fatigue life of the sample group is calculated in the following order. (6) Referring to the statistical estimation of fatigue life under given stress in the national standard 6, prepare fatigue life data, x=logN. For n samples, plot the data according to the order from smallest to largest. Assign a sequence number to each data point. The failure probability of the i-th level can be estimated as: ; (7) Plot the values ​​of (x=logN, y=Pi) on normal probability paper, and perform linear fitting of the curve through visual inspection; (8) Determine X using the curve （10） and X （90） The estimates of the mean μ and standard deviation σ are calculated as follows: ; (9) Look up the k value in the standard by the number of tests and the confidence level, and then calculate the estimated value of the lower limit of fatigue life using the following formula: ; (10) Through N=10 xThe estimated average impact fatigue life and the estimated lower limit of impact fatigue life for this set of samples were calculated.

[0009] Preferably, the shape of the cemented carbide sample mentioned in step (1) does not have fixed requirements; a standard shape can be fixed based on the shape of the product itself. The impact pair groove can correspond to the shape of the sample mentioned above.

[0010] In step (2), the self-locking anti-loosening washer adopts a combination of spring anti-loosening washer and double-layered self-locking anti-loosening washer, which is more secure.

[0011] The impact force calculation in particular (3) can also be replaced by finite element simulation software such as ANSYS, which is more accurate and reliable.

[0012] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: This invention enables more accurate and scientific stress setting for corresponding working conditions, and better results in determining the performance of cemented carbide when impacting rocks. Furthermore, by referencing national standard fatigue research and analysis methods, the final fatigue data output is more accurate.

[0013] Specifically, 1. Calculate the stress on the carbide tooth under real working conditions to more accurately simulate the actual use of the tooth.

[0014] 2. Combining finite element simulation technology with dynamic testing of cemented carbide material properties allows the test samples to... The product is in a more accurate operating condition.

[0015] 3. Combining national standards for fatigue testing of metallic materials with testing of cemented carbide results in a final output... The data is more accurate and reliable. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the sample testing structure provided by the present invention.

[0018] Figure 2 This is a diagram showing the stress on the alloy tooth tip in ANSYS finite element simulation.

[0019] Figure 3 This is a schematic photograph illustrating the experimental process.

[0020] Figure 4 The curve is the fatigue data fitting curve for Example 1.

[0021] Figure 5 The curve is the fatigue data fitting curve for Example 2.

[0022] in, Figure 1 middle: 1—Impact fatigue testing machine fixture; 2—Hard alloy sample; 3—Fixing screw; 4—Self-locking anti-loosening washer; 5—Impact pair. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 (1) Prepare sample group 1, a total of 7 samples, with a sample diameter of 7 mm and a parabolic flow line contact area of ​​173.3 mm². 2 ; (2) Impact pairs were prepared using ductile iron QT600-3, and the central groove was machined to correspond to the parabola of the sample. (3) Fix the sample and impact pair using clamps; (4) The simulated impact condition is F15 granite with a compressive strength of 150 MPa. According to the formula, F = 173.3 * 150 = 25.995 KN is calculated. This data is verified by finite element simulation. Figure 2 The data is correct; (5) Start the impact fatigue testing machine, set the control mode to load control, the load to 26KN, the command function to sine wave, the testing machine starts high-frequency impact until the cemented carbide breaks, the equipment stops, and the number of impact cycles is recorded as shown in Table 1. (6) Record data for a set of 7 samples in accordance with national standards; (7) Calculate the failure probability Pi as shown in Table 1; (8) The fitted curve on the normal probability paper is as follows: Figure 4 ; (9) The estimated mean μ and standard deviation σ were obtained by calculation, and μ = 4.755 and σ = 0.887; (10) The value of k is 1.282. The estimated value of the lower limit of fatigue life is Xmin = 3.618. (11) The average impact fatigue life of this group of samples was estimated to be 56,885 cycles and the lower limit of impact fatigue life was estimated to be 4,152 cycles.

[0025] Table 1. Number of impact cycles in Example 1

[0026] Example 2 The testing method is the same as in Example 1. Sample group 2 consists of 7 samples with a diameter of 7 mm and a contact area of ​​173.3 mm² for the parabolic flow lines. 2 The simulated working condition is F15 granite with a compressive strength of 150MPa. It is fixed in the upper clamp using a combination of spring anti-loosening washers and double-layered self-locking anti-loosening washers. The toothed head faces the groove of the impact pair. Figure 2 Simulations showed that the impact force on the carbide tooth tip was approximately 25 kN, which was further verified by formula calculation to be 26 kN. Impact fatigue testing was then initiated until all seven samples fractured, and the number of impact cycles was recorded as shown in Table 2. The data were then fitted to... Figure 5 The curve was calculated to have a value of 5.246 = 0.61, and the k value was found to be 1.282. The estimated average impact fatigue life of experimental group 2 was 176,198 cycles, and the estimated lower limit of impact fatigue life was 29,092 cycles.

[0027] Table 2. Number of impact cycles in Example 2

[0028] Experiments show that the impact fatigue testing and analysis method of cemented carbide of the present invention can detect the impact fatigue performance of cemented carbide of different materials relatively accurately and reliably. The impact fatigue life of the cemented carbide sample of experimental group 2 is much greater than that of experimental group 1, and the impact fatigue performance of cemented carbide of experimental group 2 is better.

[0029] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0030] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for testing the impact fatigue of cemented carbide tooth tips, characterized in that, Includes the following steps: (1) Prepare a cemented carbide sample and an impact pair. The cemented carbide sample is a cutting tooth with a cone shape with parabolic flow lines. A groove corresponding to the cone shape of the parabolic flow lines of the cemented carbide sample is machined in the center of the impact pair. (2) Fix the cemented carbide sample with the clamp of the impact fatigue testing machine and fix it with screws and self-locking anti-loosening washers. The teeth of the cemented carbide sample face down and are aligned with the groove of the impact pair. (3) Adjust the magnitude of the impact force; (4) Start the impact fatigue testing machine, set the control mode to load control, and the command function to sine wave. The testing machine will start to allow the carbide tooth to impact the impact pair with the set impact force at a high frequency until the carbide breaks. The equipment will then stop and the number of impact cycles will be recorded. (5) Based on the statistical estimation of fatigue life under given stress in point 6 of GB / T 24176-2009 Metallic Materials. Fatigue Testing. Data Statistical Scheme and Analysis Method, calculate the estimated value of relative average impact fatigue life and the estimated value of the lower limit of impact fatigue life.

2. The method for testing impact fatigue of cemented carbide tooth tips according to claim 1, characterized in that, The impact pair uses ductile iron material QT600-3.

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