Processing method for eliminating crankshaft grinding delayed cracks

Abstract

The invention provides a machining treatment method for eliminating crankshaft grinding delayed cracks. The machining treatment method comprises the steps that a crankshaft is pretreated; the crankshaft is subjected to primary cold spraying treatment, so that a pure titanium spraying layer is formed on the surface of the crankshaft; the crankshaft is subjected to secondary cold spraying treatment, so that a titanium-based self-lubricating spraying layer is formed on the outer side of the pure titanium spraying layer of the crankshaft; and the crankshaft is subjected to ultrasonic rolling, so that the spraying layer on the outer portion of the crankshaft is densified. According to the machining treatment method for eliminating the grinding delayed cracks of the crankshaft, the grinding delayed cracks can be blocked, diffusion of the grinding delayed cracks is inhibited, and therefore the service life of the crankshaft is prolonged, and the reliability of the crankshaft is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of crankshaft processing, and in particular relates to a processing method for eliminating delayed cracks in crankshaft grinding. Background Art

[0002] The crankshaft is one of the core motion conversion components of a diesel engine. It is typically made of high-strength alloy steel. During operation, the crankshaft converts the reciprocating linear motion of the pistons in the diesel engine into its own continuous rotational motion, thereby driving the subsequent load.

[0003] Because the crankshaft journal needs to bear a large load during actual use, the machining quality of the journal will directly affect the service life of the crankshaft. In the prior art, those skilled in the art will first heat treat the crankshaft to obtain good material structure and properties, and then grind it to control its surface machining accuracy. However, due to the residual stress and structural transformation caused by the heat treatment, the crankshaft journal surface is prone to grinding-delayed cracking. When the crankshaft generates a large amount of frictional heat due to continuous high-load operation, the cracks will gradually expand and extend, thereby affecting the service life and reliability of the crankshaft. Summary of the Invention

[0004] In view of this, the present invention aims to propose a processing method for eliminating crankshaft grinding delayed cracks, so as to achieve the purpose of extending the service life of the crankshaft and improving the reliability of the crankshaft.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0006] A processing method for eliminating delayed cracks in crankshaft grinding, comprising:

[0007] After the crankshaft is ground, it is pre-treated to remove any attachments on the outside of the crankshaft.

[0008] The crankshaft is subjected to a first cold spraying treatment using titanium powder as a solid phase material and a mixture of nitrogen and helium as a gas phase material, so as to form a pure titanium spray layer on the surface of the crankshaft;

[0009] The crankshaft is subjected to a second cold spraying treatment using a mixture of titanium powder and nanographite as the solid phase material and a mixture of nitrogen and helium as the gas phase material, so that a titanium-based self-lubricating spray layer is formed on the outer side of the pure titanium spray layer of the crankshaft;

[0010] The crankshaft is subjected to ultrasonic rolling to densify the spray coating on the outside of the crankshaft.

[0011] Furthermore, the pretreatment includes ultrasonic cleaning and / or low-temperature plasma cleaning.

[0012] Furthermore, after the crankshaft is pre-treated to remove the attachments on the outside of the crankshaft, the processing method for eliminating crankshaft grinding delayed cracks further includes:

[0013] The crankshaft is subjected to micro-arc oxidation treatment to form a ceramic oxide film with a thickness of 5 μm on the surface of the crankshaft.

[0014] Furthermore, the first cold spraying treatment of the crankshaft using titanium powder as a solid phase material and a mixture of nitrogen and helium as a gas phase material to form a pure titanium spray layer on the surface of the crankshaft includes:

[0015] Using titanium powder with a particle size of 15μm to 25μm and a sphericity greater than 90% as the solid phase material, and a mixed gas formed by 70% nitrogen and 30% helium as the gas phase material, the crankshaft is subjected to the first cold spraying treatment under the conditions of pressure of 3.5MPa, temperature of 300℃, solid phase material conveying rate of 30g / min, spraying distance of 35mm and solid phase material spraying speed greater than 620m / s, so that a pure titanium spray layer with a thickness of 5μm to 20μm and a porosity of less than 1.5% is formed on the surface of the crankshaft.

[0016] Furthermore, the crankshaft is subjected to a second cold spraying treatment using a mixture of titanium powder and nanographite as a solid phase material and a mixture of nitrogen and helium as a gas phase material, so that a titanium-based self-lubricating spray coating is formed on the outer side of the pure titanium spray coating of the crankshaft, comprising:

[0017] A mixture of titanium powder and nano-graphite is used as the solid phase material, and a mixed gas formed by 70% nitrogen and 30% helium is used as the gas phase material. The crankshaft is subjected to a second cold spraying treatment under the conditions of a pressure of 3.5 MPa, a temperature of 300°C, a solid phase material conveying rate of 30 g / min, a spraying distance of 35 mm, and a solid phase material spraying speed greater than 620 m / s, so that a titanium-based self-lubricating spray layer with a thickness of 5 μm is formed on the outer side of the pure titanium spray layer of the crankshaft.

[0018] Furthermore, in the mixture of titanium powder and nanographite, the nanographite accounts for 1 wt% to 2 wt%, and the particle size of the titanium powder is 15 μm to 25 μm, and the sphericity is greater than 90%.

[0019] Furthermore, the ultrasonic rolling of the crankshaft to densify the spray coating on the outside of the crankshaft includes:

[0020] The crankshaft was subjected to ultrasonic rolling under the process parameters of a static pressure of 200N and an amplitude of 10μm, so that the spray coating on the outside of the crankshaft was densified.

[0021] Compared with the prior art, the processing method for eliminating delayed cracks in crankshaft grinding created by the present invention has the following advantages:

[0022] The present invention provides a processing method for eliminating delayed grinding cracks on crankshafts. This method forms a pure titanium spray coating on the crankshaft surface through a first cold spraying process, and forms a titanium-based self-lubricating spray coating on the outer surface of the pure titanium spray coating through a second cold spraying process. The spray coating is then densified by ultrasonic rolling to achieve a good treatment effect on the crankshaft surface, extending the service life and reliability of the crankshaft. After the crankshaft is processed using this method, the spray coating formed by the two cold spraying processes can promote the early closure of delayed grinding cracks, thereby eliminating the risk of failure caused by crack propagation during use of the crankshaft. Secondly, the low elastic modulus of the pure titanium spray coating can reduce the transmission efficiency of grinding stress and absorb energy through plastic deformation of the spray coating, thereby inhibiting the propagation of cracks. Furthermore, the in-situ lubrication mechanism of the titanium-based self-lubricating spray coating allows nanographite to precipitate under the action of frictional heat to form a transfer film, thereby significantly reducing the friction coefficient of the crankshaft journal, reducing the heat generation of the crankshaft under continuous high-load conditions, and further inhibiting the propagation of delayed grinding cracks. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 A schematic flow chart of a processing method for eliminating delayed cracks in crankshaft grinding according to an embodiment of the present invention;

[0025] Figure 2 This is a schematic structural diagram of the crankshaft according to an embodiment of the present invention after the second cold spraying treatment.

[0026] Description of reference numerals:

[0027] 1: crankshaft;

[0028] 2: Pure titanium spray coating;

[0029] 3: Titanium-based self-lubricating spray coating. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0031] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0032] In the prior art, crankshafts are usually made of high-strength alloy steel. This embodiment will be specifically described using a crankshaft made of 34CrNiMo6 as an example.

[0033] After crankshaft production, technicians typically perform induction hardening on the crankshaft journal to achieve a surface hardness of 58HRC. The journal neck is then ground to ensure good surface finish. However, due to residual stress and structural transformation, the journal surface is prone to grinding-delayed cracking. These cracks cannot be detected immediately after grinding. Only when the crankshaft is subjected to continuous high-load operation, when friction between the crankshaft and the bearing generates a large amount of heat, will the cracks gradually propagate, ultimately affecting the crankshaft's service life and reliability.

[0034] To solve this problem, this embodiment provides a processing method for eliminating delayed cracks in crankshaft grinding. Figure 1 The flowchart of the processing method for eliminating delayed cracks caused by crankshaft grinding is shown in the figure. As shown in the figure, the processing method for eliminating delayed cracks caused by crankshaft grinding specifically includes the following steps:

[0035] Step 110: After the crankshaft is ground, pre-process the crankshaft to remove attachments on the outside of the crankshaft.

[0036] After the crankshaft is ground, grease, oxide layers, or other contaminants will inevitably be deposited on its surface. To prevent these deposits from affecting the subsequent cold spraying process, the crankshaft is pre-treated to remove any deposits on its exterior.

[0037] Optionally, pretreatment may include ultrasonic cleaning and / or low-temperature plasma cleaning. Ultrasonic cleaning utilizes the cavitation, acceleration, and straight-through flow of ultrasound in a liquid to disperse, emulsify, and remove contaminants (e.g., grease) attached to the crankshaft's exterior. Low-temperature plasma cleaning involves impacting the crankshaft's surface with plasma at temperatures below 80°C to remove oxide layers or other deposits.

[0038] In addition, as an optional implementation of this embodiment, in order to improve the adhesion effect of the spray layer formed by the subsequent cold spraying process, after pre-treating the crankshaft and removing the external attachments of the crankshaft, the processing method for eliminating the crankshaft grinding delayed cracks can also add the following steps:

[0039] The crankshaft is subjected to micro-arc oxidation treatment to form a ceramic oxide film with a thickness of 5 μm on the surface of the crankshaft.

[0040] It should be noted that micro-arc oxidation (MAO) is a surface treatment method that forms a modified ceramic coating on a workpiece surface through the transient high temperature and high pressure generated by arc discharge, by matching and adjusting electrolyte and electrical parameters. In this embodiment, the ceramic oxide film formed on the crankshaft surface through MAO provides a base for subsequent cold spraying, facilitating the formation of a reliable spray coating from the solid-phase material during cold spraying.

[0041] Step 120 : Using titanium powder as a solid-phase material and a mixture of nitrogen and helium as a gaseous-phase material, the crankshaft is subjected to a first cold spraying treatment to form a pure titanium spray layer on the surface of the crankshaft.

[0042] After the pretreatment of the crankshaft is completed, the crankshaft is subjected to two cold spraying treatments in this embodiment so that the outer surface of the crankshaft is formed as follows: Figure 2 The two-layer spray coating structure shown in the figure has a pure titanium spray coating 2 formed on the outside of the crankshaft 1, and a titanium-based self-lubricating spray coating 3 formed on the outside of the pure titanium spray coating 2. The pure titanium spray coating 2 and the titanium-based self-lubricating spray coating 3 are used to seal the grinding-delayed cracks on the crankshaft 1, thereby extending the service life and reliability of the crankshaft.

[0043] The first cold spraying treatment should use titanium powder as the solid phase material and a mixture of nitrogen and helium as the gas phase material to form a pure titanium spray layer on the surface of the crankshaft. Specifically, during the first cold spraying treatment, the particle size of the titanium powder should be 15μm to 25μm, and the sphericity should be greater than 90%, and the nitrogen and helium in the gas phase material should account for 70% and 30% respectively. In addition, when cold spraying, the pressure should be 3.5MPa, the temperature should be 300℃, the solid phase material delivery rate should be 30g / min, the spraying distance should be 35mm, and the solid phase material spraying speed should be greater than 620m / s. Under the above process conditions, the spray gun should reciprocate and scan the surface of the crankshaft at a constant speed until a pure titanium spray layer with a thickness of 5μm to 20μm and a porosity of less than 1.5% is formed on the surface of the crankshaft.

[0044] Because the pure titanium spray coating has a lower elastic modulus, it can reduce the transmission efficiency of grinding stress. When the crankshaft is subjected to stress load, the plastic deformation of the pure titanium spray coating can also absorb energy, thereby inhibiting the expansion of cracks and avoiding grinding delay crack propagation.

[0045] Step 130 , using a mixture of titanium powder and nanographite as a solid phase material and a mixture of nitrogen and helium as a gas phase material, the crankshaft is subjected to a second cold spraying treatment to form a titanium-based self-lubricating spray layer on the outer side of the pure titanium spray layer of the crankshaft.

[0046] After the first cold spraying process is completed, the crankshaft is subjected to a second cold spraying process in this embodiment. The second cold spraying process uses a mixture of titanium powder and nanographite as the solid phase material and a mixture of nitrogen and helium as the gas phase material to form a titanium-based self-lubricating spray layer on the outer surface of the pure titanium spray layer of the crankshaft.

[0047] Specifically, during the second cold spraying process, in the mixture of titanium powder and nanographite, the proportion of nanographite should be 1wt% to 2wt%, the particle size of the titanium powder should be 15μm to 25μm, the sphericity should be greater than 90%, and the nitrogen and helium in the gas phase material should account for 70% and 30% respectively. In addition, during the cold spraying, the pressure should be 3.5MPa, the temperature should be 300℃, the solid phase material delivery rate should be 30g / min, the spraying distance should be 35mm, and the solid phase material spraying speed should be greater than 620m / s. Under the above process conditions, the spray gun should reciprocate and scan the surface of the crankshaft at a constant speed until a titanium-based self-lubricating spray layer with a thickness of 5μm is formed on the outside of the pure titanium spray layer of the crankshaft.

[0048] Because the titanium-based self-lubricating spray coating has an in-situ lubrication mechanism, it allows nanographite to precipitate under the action of frictional heat, forming a transfer film. When the crankshaft is in operation, the transfer film can significantly reduce the friction coefficient of the crankshaft journal and reduce the heat generation of the crankshaft under continuous high-load conditions, thereby further inhibiting the propagation of grinding-induced cracks.

[0049] It's important to note that before cold spraying the crankshaft, the gas source should be activated to preheat it to the set temperature. The solid-phase material delivery system should then be activated and the delivery rate adjusted to a stable level. The crankshaft can then be cold sprayed to ensure a high-quality coating.

[0050] Step 140: ultrasonically roll the crankshaft to densify the spray coating on the outside of the crankshaft.

[0051] After the second cold spraying process, to improve the quality of the sprayed coating, this embodiment applies ultrasonic rolling to the crankshaft, densifying the sprayed coating on the crankshaft's exterior. Ultrasonic rolling is a metal surface treatment technology that combines ultrasonic mechanical vibration with static rolling. Ultrasonic rolling can cause nanoscale plastic deformation of the workpiece surface, significantly reducing surface roughness and forming a reinforced surface layer with compressive stress, resulting in improved wear resistance, fatigue strength, and corrosion resistance.

[0052] Optionally, during ultrasonic rolling, the process parameters can be set to a static pressure of 200N and an amplitude of 10μm. Under these process parameters, a more reliable bond is achieved between the crankshaft's outer wall, the pure titanium spray coating, and the titanium-based self-lubricating spray coating. Furthermore, a denser film is formed on the outermost surface of the titanium-based self-lubricating spray coating, thereby enhancing the crankshaft's surface treatment.

[0053] This embodiment provides a processing method for eliminating delayed cracks caused by crankshaft grinding. A pure titanium spray layer is formed on the crankshaft surface through a first cold spray treatment, and a titanium-based self-lubricating spray layer is formed on the outside of the pure titanium spray layer through a second cold spray treatment. The spray layer is then densified by ultrasonic rolling, so that the crankshaft surface obtains a good treatment effect and the service life and reliability of the crankshaft are extended.

[0054] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A processing method for eliminating delayed cracks in crankshaft grinding, characterized in that: include: After the crankshaft is ground, it is pre-treated to remove any attachments on the outside of the crankshaft. The crankshaft is subjected to a first cold spraying treatment using titanium powder as a solid phase material and a mixture of nitrogen and helium as a gas phase material, so as to form a pure titanium spray layer on the surface of the crankshaft; The crankshaft is subjected to a second cold spraying treatment using a mixture of titanium powder and nanographite as the solid phase material and a mixture of nitrogen and helium as the gas phase material, so that a titanium-based self-lubricating spray layer is formed on the outer side of the pure titanium spray layer of the crankshaft; The crankshaft is subjected to ultrasonic rolling to densify the spray coating on the outside of the crankshaft.

2. A processing method for eliminating delayed cracks in crankshaft grinding according to claim 1, characterized in that: The pretreatment includes ultrasonic cleaning and / or low-temperature plasma cleaning.

3. The processing method for eliminating delayed cracks in crankshaft grinding according to claim 1, characterized in that: After the crankshaft is pre-treated to remove the attachments on the outside of the crankshaft, the processing method for eliminating crankshaft grinding delayed cracks further includes: The crankshaft is subjected to micro-arc oxidation treatment to form a ceramic oxide film with a thickness of 5 μm on the surface of the crankshaft.

4. The processing method for eliminating delayed cracks in crankshaft grinding according to claim 1, characterized in that: The first cold spraying treatment is performed on the crankshaft using titanium powder as a solid phase material and a mixture of nitrogen and helium as a gas phase material to form a pure titanium spray layer on the surface of the crankshaft, including: Using titanium powder with a particle size of 15μm to 25μm and a sphericity greater than 90% as the solid phase material, and a mixed gas formed by 70% nitrogen and 30% helium as the gas phase material, the crankshaft is subjected to the first cold spraying treatment under the conditions of pressure of 3.5MPa, temperature of 300℃, solid phase material conveying rate of 30g / min, spraying distance of 35mm and solid phase material spraying speed greater than 620m / s, so that a pure titanium spray layer with a thickness of 5μm to 20μm and a porosity of less than 1.5% is formed on the surface of the crankshaft.

5. The processing method for eliminating delayed cracks in crankshaft grinding according to claim 1, characterized in that: The second cold spraying treatment of the crankshaft using a mixture of titanium powder and nanographite as a solid phase material and a mixture of nitrogen and helium as a gas phase material to form a titanium-based self-lubricating spray coating on the outer side of the pure titanium spray coating of the crankshaft includes: A mixture of titanium powder and nano-graphite is used as the solid phase material, and a mixed gas formed by 70% nitrogen and 30% helium is used as the gas phase material. The crankshaft is subjected to a second cold spraying treatment under the conditions of a pressure of 3.5 MPa, a temperature of 300°C, a solid phase material conveying rate of 30 g / min, a spraying distance of 35 mm, and a solid phase material spraying speed greater than 620 m / s, so that a titanium-based self-lubricating spray layer with a thickness of 5 μm is formed on the outer side of the pure titanium spray layer of the crankshaft.

6. The processing method for eliminating delayed cracks in crankshaft grinding according to claim 1, characterized in that: In the mixture of titanium powder and nanographite, the nanographite accounts for 1 wt% to 2 wt%, and the particle size of the titanium powder is 15 μm to 25 μm, and the sphericity is greater than 90%.

7. The processing method for eliminating delayed cracks in crankshaft grinding according to claim 1, characterized in that: The ultrasonic rolling of the crankshaft to densify the spray coating on the outside of the crankshaft includes: The crankshaft was subjected to ultrasonic rolling under the process parameters of a static pressure of 200N and an amplitude of 10μm, so that the spray coating on the outside of the crankshaft was densified.

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