CN112458242A

CN112458242A - Laser bionic strengthening method for heavy-load titanium alloy die forging die

Info

Publication number: CN112458242A
Application number: CN202011182161.9A
Authority: CN
Inventors: 周倜; 陈震球
Original assignee: Jiangsu Baiornik Intelligent Technology Co ltd
Current assignee: Jiangsu Baiornik Intelligent Technology Co ltd
Priority date: 2020-10-29
Filing date: 2020-10-29
Publication date: 2021-03-09

Abstract

The invention relates to a laser bionic strengthening method for a heavy-load titanium alloy die forging die, wherein the die is made of 5CrNiMo, the die forging material is titanium alloy, the die forging temperature is 900 ℃, and the die forging pressure is more than 15000 tons; designing and preparing three bionic unit bodies which have different tissues, different structures, variable shapes and non-uniform gradient distribution with different hardness in different areas on the working surface of the base material by using a processing mode of laser primary fusing and secondary fusing; the unit body and the parent metal jointly form a coupling bionic functional surface with thermal fatigue resistance and erosion and abrasion resistance. The laser fusing method uses a laser with the energy density of 10.62-38.65J/mm2 and the scanning speed of 0.5-2 mm/s. The laser energy density is preferably 12.45J/mm2 and 37.67J/mm2, and the laser scanning speed is 1-5mm/s of the laser beam. The invention improves the surface strength and the abrasion resistance of the die, is easy to realize automatic production, saves human resources and prolongs the service life of the die.

Description

Laser bionic strengthening method for heavy-load titanium alloy die forging die

Technical Field

The invention belongs to the technical field of metal material surface strengthening, and particularly relates to a bionic strengthening method for the surface of a die forging die for manufacturing titanium alloy parts.

Background

Titanium is an important structural metal developed in the 50 s of the 20 th century, and titanium alloy has high strength, good corrosion resistance and high heat resistance. In the 50-60 s of the 20 th century, high-temperature titanium alloy for aircraft engines and structural titanium alloy for engine bodies were mainly developed. At present, the core components of military and some civil products are also made of titanium alloys.

At present, the main forming mode of titanium alloy parts is die forging forming, different temperatures are adopted for forging according to different sizes, the obtained forged piece is smooth in surface and accurate in size, and compared with other processing modes, the processing cost is low, and the steps are simple. Different forging methods and forging conditions can enable the forging piece to obtain different structural states and mechanical properties, the structural states and the temperature conditions have direct influence on the deformation behavior of the titanium alloy, and different processing modes can be adopted according to the required properties.

The conventional forging defects of the titanium alloy mainly comprise tissue overheating, uneven tissue, cavities, cracks and the like, are easy to find in the microscopic structure inspection or ultrasonic detection of the titanium alloy product, and are mainly formed by improper control of process parameters in the forging process of the titanium alloy product, so that the proper deformation rate, heating and forging temperature, pass deformation and cooling speed after forging are selected according to the titanium alloy materials with different characteristics in the forging process.

In the process of titanium alloys, the die is required to withstand significant impact pressures. The surface of the die cavity has complex shape and different depth, so that the stress on the surface of each die cavity is uneven. When the hot metal enters the cavity, the surface of the cavity is rapidly heated, namely tempering treatment is carried out, and the flowing blank generates scouring, extrusion and friction on the cavity, so that the die is softened and the abrasion is aggravated. In particular, titanium alloys have good ductility and are formed in a mold, and the titanium alloys often have a sticking effect similar to that of "chewing gum" on the mold surface. In the process, the surface roughness of the die is damaged, so that the forging is deviated, and the surface of the die is grooved. In addition, the die is subjected to cyclic thermal stress and abrasion in the repeated forging process, so that the die is subjected to plastic deformation such as thermal cracking, collapse and the like. The defects reduce the quality of the die, reduce the service life of the die, cause the die to lose efficacy and be scrapped, and cause great resource waste.

Since titanium alloys are very expensive and have very poor machinability, the die-formed titanium alloy parts are not machined and are die-formed in one step. The method puts a very high use requirement on the die, so that the use cost of the die is greatly increased, the die forging die for producing the common forge piece for 1000 die times can be used for producing the titanium alloy part for about 100 times, and the surface of the titanium alloy part is slightly damaged and judged to be invalid. If a method can be used for the titanium alloy die forging die, the viscous and corrosive wear effect of the titanium alloy die forging die on the surface of the die is reduced, the performance and the service life of the titanium alloy die forging die can be greatly improved by pretreatment, and a large amount of resources and production cost are saved. The natural observation shows that the soil animals such as the mole cricket, the dung beetle, the pangolin, the hippophae rhamnoides and the like can penetrate through the soil for a long time, and the body surface is not damaged. It has been found that non-smooth morphology exists on body surfaces that are subject to more compression and abrasion. Therefore, it is necessary to design a processing method to process a coupling bionic non-smooth model on the working surface of the mold to cope with fatigue and wear generated in the production process.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a bionic strengthening method for the surface of a die forging die for producing titanium alloy. The processing equipment is connected with a rotary worktable by a laser clamped by a mechanical arm with 6+3 degrees of freedom, and then laser coupling bionic strengthening treatment is carried out on the working surface of the titanium alloy die forging die so as to strengthen the surface of the die and prolong the service life of the die.

In order to solve the problems, the invention provides a titanium alloy die forging die with a coupling bionic surface. The working pressure of the die is 14000 tons, the working temperature is about 400 ℃, and the die is characterized in that the die is made of 5CrNiMo, and a bionic unit body is processed on the working surface of the die. The Vickers hardness of the bionic unit body is 55-60HRC, the shape of the bionic unit body is U-shaped, and the structure of the bionic unit body is refined martensite and ferrite; the average size of the crystal grains is about 0.5-5 μm and the crystal grains are closely and regularly arranged. The surface roughness of the processed die is about 6500, and the die has good quality.

The preparation method of the titanium alloy die forging die with the coupling bionic surface comprises the following steps:

the equipment for clamping the laser by using a mechanical arm scans a laser beam on the surface of the die by using a laser melting method, so that the surface of the die is melted and rapidly solidified to form a bionic unit body; the laser fusing method uses a laser with the energy density of 10.62-38.65J/mm2 and the scanning speed of 0.5-2 mm/s.

The laser energy density is preferably 12.45J/mm2 and 37.67J/mm2, and the laser scanning speed is 1-5mm/s of the laser beam.

The preparation method for performing coupling bionic treatment on the surface of the mold comprises the following steps:

the method comprises the following steps: pre-grinding and cleaning the surface of the die;

step two: by using the laser fusing method, a laser beam is scanned on the surface of the die along a preset track, so that the surface of the die is fused and rapidly solidified. Bionic unit bodies which are uniformly distributed and have refined grain structures are formed on the surface of the die.

The laser fusing method is adopted by the die, the power of a laser used by the die is 500W, the defocusing amount is 101mm, the laser frequency is 5Hz, the laser current is 105 mA-160 mA, the laser pulse width is 6-10ms, and the laser scanning speed is 1-5 mm/s.

The invention prepares the bionic unit body on the surface of the large titanium alloy die forging die made of 5CrNiMo, because the 5CrNiMo material has high carbon content, less alloy elements and poor thermal conductivity, when the energy is too low during laser melting, the laser melting area is too shallow to cause strengthening failure, and when the energy is too high, the molten pool is impacted to cause splashing in the continuous processing process, and deep pits or holes appear on the surface. Therefore, in the process of laser processing the unit body, if the parameter selection is not good, the processing is directly failed, not only can a good effect not be achieved, but also the surface of the die can be damaged, and the loss is caused for enterprises.

Therefore, only by controlling a single variable, experiments performed after changing parameters such as current, pulse width, frequency and the like can obtain a large amount of data, and the data show that proper parameters cannot be found by one-time fusing reinforcement, so that multiple times of fusing composite reinforcement are needed. After composite reinforcement, selecting parameters with better unit body performance from the composite reinforcement, carrying out repeated fine adjustment, and determining the energy density range, so that the hardness of the bionic unit body of the die reaches 58-60HRC, and the average size of crystal grains is about 3 mu m.

In order to solve the above problems, the laser bionic strengthening method for the titanium alloy die forging die of the present invention may adopt the following technical scheme.

Designing and preparing coupling bionic functional surfaces with different tissues on a working surface in different areas by using a laser melting processing mode, and is characterized in that the same area is subjected to strengthening treatment twice by using the laser melting mode, and a type I unit body and a type II unit body are respectively processed, wherein the type I unit body selects current of 90A, pulse width of 6ms, frequency of 10Hz, scanning speed of 1mm/s, and defocusing amount of +/-12-15 mm; the II type unit body selects current 145-160A, pulse width 8-10ms, frequency 5Hz, scanning speed 2-4mm/s and defocusing amount +/-7-8 mm. .

Designing and preparing coupling bionic functional surfaces with different tissues on a working surface in a subarea mode by using a laser fusion processing mode, wherein the fusion depth of a type I unit body is 0.3-0.4mm, the fusion width is 1.2-1.5mm, the tissue crystal grains in a fusion area are 3-5 mu m, the hardness is 53-55HRC, and the section of the fusion area is flat and moon-shaped; the type II unit body has the fusion depth of 1.0-1.4mm, the fusion width of 0.8-1.0mm, the structure crystal grains in the fusion zone of 0.5-2 μm, the hardness of 58-60HRC and the cross section of the fusion zone in a U shape. Only the II-type unit body can be obtained by secondary processing on the basis of the I-type unit body, and if the I-type unit body is not subjected to strengthening treatment, the splash can directly appear by directly using the processing parameters of the II-type unit body.

The method is characterized in that a laser melting processing mode is used for designing and preparing coupling bionic functional surfaces with different structures on a working surface in different areas, and the method comprises the following steps: the pitch of the type I unit bodies is 0.5mm, and the pitch of the type II unit bodies is 1 mm. Processing type III unit body in the middle of type II unit body, wherein the fusion depth of the unit body is 0.5-0.6mm, the width of the unit body is 0.6-0.8mm, and the structure crystal grain of a fusion zone is 3-5 μm. The distribution of the three types of unitary bodies is shown in FIG. 1.

The hardness of the bionic unit bodies can reach 502HV-620HV and is 30.4% -61.0% higher than that of the parent metal of the mould. So that in the area with smaller wear degree, the model can effectively block the development of fatigue crack and slow down the wear.

The coupling bionic functional surface with changeable shape is designed and prepared in different areas on the working surface by a laser melting processing mode, and is characterized in that the inclination angle of a striped bionic unit body is beta 1, the beta 1 is 30-60 degrees, a grid-shaped unit body is arranged, the included angle of a grid is beta 2, and the beta 2 is 45-90 degrees. The specific shape is shown in fig. 2.

The I, II and III type unit bodies have three main functions on the surface of a titanium alloy die forging die, the first function is to slow down the crack initiation and growth speed on the surface of the die, the hard phase fusing area, the secondary hard phase fusing area and the base metal are arranged in a gradient mode according to a design mode, the initiation stress of the crack is resisted in sequence according to the cracking direction of the crack on the surface of the die, the crack initiation time is slowed down, and the crack is prevented from expanding in a dam mode; the second major effect is to reduce the sticky wear of the die surface, and since the three unit bodies are slightly recessed from the surface of the mother body, a certain amount of graphite lubricant sprayed on the die surface will remain in the recessed portions of the unit bodies before each die forging. The residual graphite is helpful for increasing the lubrication of the surface of the die and is used as a lubricant for slowing down the friction wear of the titanium alloy forging on the surface of the die. The third function is to strengthen the wear resistance of the surface of the die, the hardness of the fused unit body is greatly improved, and the wear of the titanium alloy on the surface of the die can be effectively resisted.

The working principle of the invention is as follows:

the invention utilizes the bionic principle and adopts a laser melting method to prepare a stripe-shaped and grid-shaped bionic unit model with uniform distribution and refined grain structure on the working surface of a titanium alloy die forging die. The bionic unit body and the parent metal form a bionic body structure with alternate hardness and softness. The thinned bionic unit bodies not only improve the hardness, but also play a role in strengthening as pinning is formed on the surface of a die, and parent materials surround and connect the bionic unit bodies into a whole so that the stress on the surfaces of the bionic unit bodies is more uniform. The crack directions of the unit bodies and the surface cracking of the die are 45 degrees, 60 degrees or 30 degrees, so that the adhesion erosion abrasion of the titanium alloy to the surface of the die can be effectively resisted.

The invention has the beneficial effects that:

the invention adopts the surface treatment method of laser melting and consolidation, and combines a mechanical arm to flexibly process the surface of the die with a complex shape, thereby improving the surface strength of the die and the wear resistance of the die and prolonging the service life of the die. And by combining the mechanical arm with the laser, the automatic production is easy to realize, and the human resources are saved.

Drawings

FIG. 1 is the metallographic microstructure of the type I, II and III elementary bodies according to the invention.

FIG. 2 is a schematic diagram of the structural organization of the type I, II, III elementary bodies according to the invention;

FIG. 3 is a schematic view of the distribution of the type I, II, III elementary bodies of the present invention on the surface of the product.

Detailed Description

The details of the present invention are described below with reference to the accompanying drawings and specific embodiments.

The invention discloses a laser strengthening treatment method for the surface of an intelligent heavy-load titanium alloy die forging die. According to the bionic theory, the hardness is improved by preparing bionic unit body models with different appearances on the surface of the die by adopting a laser melting method, and the requirements of the die in the working state are better met. By preparing three fused and hardened unit bodies with different hardness on the surface of the mold and arranging the unit bodies in different modes, good impact resistance and resistance reduction self-lubricating effects can be obtained.

The 5CrNiMo steel has good toughness, strength and high wear resistance, and belongs to hot work die steel. The mechanical properties of the material are almost the same at room temperature and 500-600 ℃. The hardness of the alloy can be maintained at about HB300 even when the alloy is heated to 500 ℃. The steel is not sensitive to temper embrittlement due to the molybdenum content. After slow cooling from 600 ℃, the impact toughness decreases only slightly.

And preparing coupling bionic surfaces on the auxiliary forming surfaces on the two sides of the mold.

The invention firstly prepares a coarse stripe type I bionic unit body on the surface of a mould. The width of the coarse stripe bionic unit body is a1, and a1 is 1.2-1.5 mm; the depth is b1, and b1 is 0.3-0.5 mm; the distance between two adjacent unit bodies is c1, and c1 is 0.5-1 mm; the inclination angle of the stripe-shaped bionic unit body is beta 1, and the beta 1 is 30-60 degrees.

Preparing a II-type unit body on the surface of the I-type unit body in a secondary fusing mode at the center of each corresponding unit body, wherein the width of the II-type unit body model is a2, and a2 is 0.8-1.0 mm; depth b2, b2 is 1.1-1.4 mm; the distance between the centers of two adjacent stripe bionic unit bodies is c2, and c2 is 0.8-1.4 mm; the inclination angle of the stripe-shaped bionic unit body is consistent with that of the I-type unit body.

Processing a III type unit body aiming at the middle area of the I type unit body and the II type unit body, wherein the width of the III type unit body model is a3, and a3 is 0.6-0.8 mm; the depth is b3, and b3 is 0.5-0.6 mm; the distance between the centers of two adjacent bionic unit bodies is c3, and c3 is 1.2-1.6 mm; the inclination angle of the stripe-shaped bionic unit body is consistent with that of the I-type unit body.

The laser melting processing method is used for designing and preparing coupling bionic functional surfaces with different structures on the working surface in different areas, wherein: the pitch of the type I unit bodies is 0.5mm, and the pitch of the type II unit bodies is 1 mm. Processing type III unit body in the middle of type II unit body, wherein the fusion depth of the unit body is 0.5-0.6mm, the width of the unit body is 0.6-0.8mm, and the structure crystal grain of a fusion zone is 3-5 μm. The distribution of the three types of unitary bodies is shown in FIG. 1.

The coupling bionic functional surface with changeable shape is designed and prepared in different areas on the working surface by a laser melting processing mode, and is characterized in that the inclination angle of a striped bionic unit body is beta 1, the beta 1 is 30-60 degrees, a grid-shaped unit body is arranged, the included angle of a grid is beta 2, and the beta 2 is 45-90 degrees. The concrete shape is shown in figure 2, and the processing distribution schematic diagram of the type I, II and III unit bodies on the surface of the product is shown in figure 3.

The performance of the 5CrNiMo die surface after preparing the bionic unit body is shown in Table 1. The laser parameters and surface roughness are used as shown in table 2.

Performance of table 15 after preparation of bionic unit body on surface of CrNiMo die

TABLE 2 bionic unit body prepared on mould surface using laser parameters and surface roughness

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It should be understood by those skilled in the art that the foregoing embodiments are merely illustrative of the technical spirit and features of the present invention, and the present invention is not limited thereto but may be implemented by those skilled in the art.

Claims

1. A laser bionic strengthening method for a heavy-load titanium alloy die forging die is characterized by comprising the following steps: the die is made of 5CrNiMo, the die forging material is titanium alloy, the die forging temperature is 900 ℃, and the die forging pressure is more than 15000 tons; designing and preparing three bionic unit bodies which have different tissues, different structures, variable shapes and non-uniform gradient distribution with different hardness in different areas on the working surface of the base material by using a processing mode of laser primary fusing and secondary fusing; the unit body and the parent metal jointly form a coupling bionic functional surface with thermal fatigue resistance and erosion and abrasion resistance.

2. The laser bionic strengthening method for the heavy-duty titanium alloy die forging die according to claim 1, wherein the laser bionic strengthening method comprises the following steps: performing strengthening treatment on the same area twice by using a laser melting mode, and respectively processing a type I unit body and a type II unit body, wherein the type I unit body selects current of 90-110mA, pulse width of 6ms, frequency of 10Hz, scanning speed of 1mm/s and defocusing amount of +/-12-15 mm; the II type unit body selects current 145-160mA, pulse width 8-10ms, frequency 5Hz, scanning speed 2-4mm/s and defocusing amount +/-7-8 mm.

3. The laser bionic strengthening method for the heavy-duty titanium alloy die forging die according to claim 2, characterized in that: the fusion depth of the type I unit body is 0.3-0.4mm, the fusion width is 1.2-1.5mm, the structure crystal grain of a fusion area is 3-5 mu m, the hardness is 53-55HRC, and the section of the fusion area is flat and moon-shaped; the type II unit body has the fusion depth of 1.0-1.4mm, the fusion width of 0.8-1.0mm, the structure crystal grains in the fusion zone of 0.5-2 μm, the hardness of 58-60HRC and the cross section of the fusion zone in a U shape.

4. The laser bionic strengthening method for the heavy-duty titanium alloy die forging die according to claim 2 or 3, characterized in that: the pitch of the type I unit bodies is 0.5mm, and the pitch of the type II unit bodies is 1 mm. Processing type III unit body in the middle of type II unit body, wherein the fusion depth of the unit body is 0.5-0.6mm, the width of the unit body is 0.6-0.8mm, and the structure crystal grain of a fusion zone is 3-5 μm.

5. The laser bionic strengthening method for the heavy-duty titanium alloy die forging die according to claim 4, wherein the laser bionic strengthening method comprises the following steps: the width of the A-type stripe unit body model is 3.2-5.2 mm; the depth is 0.3-0.5 mm; the surface bulge is 0.1-0.2 mm, and the distance between two adjacent nearest unit bodies is 0.6-0.8 mm; the inclination angle of the stripe bionic unit body is consistent with the inclination angle of the longitudinal edge of the blade, and the width of the B-type stripe unit body model is 1.1-1.5 mm; the depth is 0.7-1.1 mm.

6. The laser bionic strengthening method for the heavy-duty titanium alloy die forging die according to claim 5, wherein the laser bionic strengthening method comprises the following steps: the inclination angle of the stripe bionic unit bodies is beta 1, the beta 1 is 30-60 degrees, the included angle of the grid is beta 2, and the beta 2 is 45-90 degrees.

7. The laser bionic strengthening method for the heavy-duty titanium alloy die forging die according to any one of claims 1, 2, 5 and 6, wherein the laser bionic strengthening method comprises the following steps: the method comprises the steps of pre-grinding and cleaning the surface of a die before laser melting, scanning a laser beam on the surface of the die along a preset track in the laser melting process to melt and quickly solidify the surface of the die, and forming a bionic unit body with uniformly distributed and refined grain structures on the surface of the die.

8. The laser bionic strengthening method for the heavy-duty titanium alloy die forging die according to any one of claims 1, 2, 5 and 6, wherein the laser bionic strengthening method comprises the following steps: the power of the used laser is 500W, the defocusing amount is 101mm, the laser frequency is 5Hz, the laser current is 105 mA-160 mA, the laser pulse width is 6-10ms, and the laser scanning speed is 1-5 mm/s.

9. The laser bionic strengthening method for the heavy-duty titanium alloy die forging die according to claim 8, wherein the laser bionic strengthening method comprises the following steps: the laser is held by a mechanical arm, and the mechanical arm enables laser beams to scan on the surface of the die according to preset tracks and preset distances.