A diesel engine piston material, a diesel engine piston, a method of manufacturing the same, and a forging die

Abstract

The present application relates to the field of diesel engine piston forging, in particular to a diesel engine piston material, a diesel engine piston and a preparation method and a forging die thereof. The diesel engine piston material provided by the present application comprises the following components: Si: 14.1-18.3 wt%; Ni: 1.6-3.2 wt%; Fe: 0.8-1.6 wt%; Mg: 0.3-0.6 wt%; Cr: 0.01-0.05 wt%; Zn: 0.06-0.3 wt%; Ti: 0.02-0.2 wt%; Zr: 0.07-0.2 wt%; V: 0.1-0.18 wt%; Al: balance. The piston material is applied to piston preparation, the layered temperature of the forging part is maintained during the forging process, the deformation and forming performance of the piston material is improved, the linear expansion coefficient is reduced, the volume stability is improved, the thermal deformation amount is reduced, and the service life of the piston is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of diesel engine piston forging, in particular to a diesel engine piston material, a diesel engine piston and a preparation method and a forging die thereof. BACKGROUND

[0002] The shipping cost is much lower than that of cars, trains and airplanes. In the process of globalization of world trade, shipping has developed rapidly, and the use of ships has also increased significantly. According to statistics, 75% of global trade is completed by shipping. Diesel engines are widely used on ships because of their good economy, high reliability and long service life.

[0003] The piston and piston ring assembly is a core component of the diesel engine and one of the components with the most severe working conditions, which supports the piston, transmits combustion heat, controls the distribution of lubricating oil, and seals the gas in the combustion chamber. Due to the importance of the piston, whether the design is good or bad, or the precision during processing, has a direct impact on the economy, reliability, maintenance cycle and service life of the diesel engine.

[0004] Currently, large-bore marine diesel engines are developing from low power and low speed to high power and medium-high speed. During the use of the diesel engine, the piston skirt may be pulled, the pin hole and the outer circular surface may be abnormally worn, and other failure conditions may occur.

[0005] The invention patent "A passenger plane aluminum alloy piston seat precision forging forming method" (patent number 202310012597.0) proposes a passenger plane aluminum alloy piston seat precision forging forming method. The patent proposes an aluminum alloy forging process method. However, the following problems still cannot be solved:

[0006] 1) 4032 aluminum alloy belongs to a heat-treatable aluminum alloy in deformed aluminum, is a eutectic alloy of silicon-aluminum system, and the main components of the alloy are Al, Si, Cu, Mg, Ni, Zn, Cr, Mn, Fe, and other alloying elements, as shown in Table 1:

[0007] Table 1 Main chemical components of 4032 aluminum alloy (wt%)

[0008] Si Cu Mg Ni Fe Cr Zn Al 11-13 0.5-1.3 0.8-1.3 0.5-1.5 ≤1.0 ≤0.1 ≤0.25 balance

[0009] Although the 4032 aluminum alloy has excellent comprehensive mechanical properties, casting properties and machining properties, its relatively high linear expansion coefficient and poor volume stability seriously affect the application of the piston in high-power and medium-high-speed large-bore marine diesel engines, and the piston is prone to "piston pulling" phenomenon, and even may also have oil leakage and air leakage phenomenon.

[0010] 2) At present, the material used for the forging and pressing piston is 4032 aluminum alloy, the aluminum alloy has a narrow forging temperature range and good heat conductivity, the surface temperature of the forging directly contacted with the die reduces too fast in the forging process, which leads to the reduction of plasticity of the aluminum alloy, the increase of deformation resistance, the poor filling, the small deformation temperature range, the difficult forming, the need of larger striking force for forming, which is easy to cause the cracking of the forging, and when the temperature difference between the blank and the die is too large, the surface temperature of the blank reduces rapidly, a thick coarse grain layer is formed in the forging process, and the coarse grain defect cannot be eliminated in the subsequent heat treatment, thereby reducing the performance of the forging. It is needed to further optimize and adjust the forging die and the forging process according to the existing piston use conditions and development trend, so as to obtain superior organization and performance.

[0011] 3) At present, the skirt diameter of the high-power and medium-high speed large-bore ship piston is generally large, generally ≥170mm, and the pin seat part of the large-bore ship piston is thick, while the skirt is relatively thin, and the cross-section changes greatly along the center line direction, which is not easy to fill and form; the pin seat bottom end arc is small (R≤3mm), which is also not conducive to filling, and the skirt of the piston port also has stress concentration. Under the condition that the existing forging process and method are unchanged, the flowability of the aluminum alloy is poor in the deformation process, the metal is difficult to fill the die in the die forging forming, and folding defects are easily formed, the adhesion of the aluminum alloy is large, the workpiece is easily bonded to the die when the aluminum alloy is deformed greatly in the forging process, which causes the difficulty of demolding, the forged piece is easy to peel after demolding, even warping is produced, and the wear of the die is also increased.

[0012] 4) The draft angle of the inner wall of the piston pin seat is small, which is not conducive to the flow of the metal, and as the metal flows downward, upward and around, the contact area between the die and the metal continuously increases, the friction resistance also continuously increases, the flow resistance of the metal increases, therefore each step shows an upward trend, and when the piston is completely formed, the stress of the convex die reaches the maximum value, and the connection degree of the curved surface of the bottom of the piston pin seat and the inner bottom surface of the piston is not smooth enough, which hinders the flow of the metal, causes the poor circular arc line of the inner bottom surface of the piston, and produces small cracks. SUMMARY

[0013] Therefore, the technical problem to be solved by the present application is to provide a diesel engine piston material, a diesel engine piston and a preparation method and a forging die thereof.

[0014] The present application provides a diesel engine piston material, which comprises the following components:

[0015] Si: 14.1-18.3 wt%; Ni: 1.6-3.2 wt%; Fe: 0.8-1.6 wt%; Mg: 0.3-0.6 wt%; Cr: 0.01-0.05 wt%; Zn: 0.06-0.3 wt%; Ti: 0.02-0.2 wt%; Zr: 0.07-0.2 wt%; V: 0.1-0.18 wt%; Al: balance.

[0016] In one embodiment of the present application, the diesel piston material comprises the following components:

[0017] Si: 14.3 wt%; Ni: 2.8 wt%; Fe: 1.4 wt%; Mg: 0.3 wt%; Cr: 0.02 wt%; Zn: 0.09 wt%; Ti: 0.11 wt%; Zr: 0.07 wt%; V: 0.13 wt%; Al: balance.

[0018] In another embodiment of the present application, the diesel piston material comprises the following components:

[0019] Si: 16.2 wt%; Ni: 2.4 wt%; Fe: 1.2 wt%; Mg: 0.45 wt%; Cr: 0.03 wt%; Zn: 0.11 wt%; Ti: 0.15 wt%; Zr: 0.11 wt%; V: 0.1 wt%; Al: balance;

[0020] In another embodiment of the present application, the diesel piston material comprises the following components:

[0021] Si: 17.9 wt%; Ni: 1.6 wt%; Fe: 0.8 wt%; Mg: 0.6 wt%; Cr: 0.04 wt%; Zn: 0.3 wt%; Ti: 0.2 wt%; Zr: 0.18 wt%; V: 0.15 wt%; Al: balance.

[0022] In the diesel piston material of the present application, the elements Fe and Ni mainly exist in the form of alloy phase Al9FeNi, which mainly improves the thermal strength of the alloy, reduces the linear expansion coefficient of the alloy, and improves the volume stability of the piston. As shown in Figure 1 , Figure 1 is an alloy electron microscope microstructure diagram of the diesel piston material of the present application. When the elements Fe and Ni exist in the form of alloy phase Al9FeNi in the as-cast sample, the Al9FeNi phase is dispersedly distributed in the alloy matrix in the form of flexible skeleton. In some embodiments of the present application, the mass ratio of the elements Ni and Fe is (1.0-2.0): 1.

[0023] The diesel engine piston material is a new hypereutectic Al-Si alloy material, which is applied to the preparation of the diesel engine piston, can reduce the linear expansion coefficient, improve the piston volume stability, and reduce the thermal deformation amount of the piston in operation.

[0024] The application further provides a preparation method of the diesel engine piston, comprising the following steps:

[0025] The diesel engine piston blank is forged in the forging die, and is heat treated to obtain the diesel engine piston.

[0026] The diesel engine piston blank is composed of the diesel engine piston material. In some embodiments of the application, the upper part of the diesel engine piston blank is an elliptical cylinder, and the lower part is a positioning circular table, the lower surface of the positioning circular table is consistent with the lower inlay block positioning conical surface of the forging die, the rod blank is obtained after being formed by upsetting, and the roughness of the rod blank is less than or equal to 12.5 microns.

[0027] In order to make the material inside uniformly heated, eliminate the stress generated by heating, and make the material structure uniform, the rod blank needs to be heated to 480-520 DEG C, preferably 480-500 DEG C, and kept for more than 5 hours before being formed by upsetting. In some embodiments of the application, the rod blank after heating and keeping is formed by upsetting in the upsetting die by using the two-hammer forming method, the first hammer upsetting is performed at a speed of 383-426 m / min, the second hammer upsetting is performed at a speed of 502-534 m / min, and the diesel engine piston blank is obtained. The upsetting ratio of the upsetting forming is 1.2-2.2, and the upsetting deformation is 0.1-0.2. The temperature of the diesel engine piston blank obtained after the upsetting forming is 460-500 DEG C. The upsetting die is provided with a positioning cylindrical boss, which is used for forming the diesel engine piston blank into the shape of the diesel engine piston blank, is beneficial to positioning in the next forming process, makes the die punch and the blank material keep good coaxiality, and improves the coaxiality of the piston inner cavity and the skirt.

[0028] The diesel engine piston blank is first forged in the forging die. The temperature of the diesel engine piston blank before being formed by forging is 460-500 DEG C. In some embodiments of the application, the diesel engine piston blank obtained after the upsetting forming is placed in the forging die within 20 s, the first hammer forging is performed at a speed of 594-621 m / min, the second hammer forging is performed at a speed of 784-819 m / min, and the diesel engine piston blank is formed by forging at a strain rate of 0.28-0.69 s -1 .

[0029] The forging forming temperature of the diesel engine piston blank is 182-253 DEG C; specifically, the diesel engine piston blank is forged in a forging die with a temperature of 182-253 DEG C. The forging forming temperature of the thick side of the piston skirt of the diesel engine piston blank is 10-20 DEG C higher than that of the thin side; specifically, the temperature of the thick side of the piston skirt of the diesel engine piston blank in the forging die is 10-20 DEG C higher than that of the thin side. The forging forming temperature of the piston skirt of the diesel engine piston blank is 40-60 DEG C higher than that of the piston top; specifically, the temperature of the piston skirt of the diesel engine piston blank in the forging die is 40-60 DEG C higher than that of the piston top.

[0030] In some embodiments of the present application, the forging die is preheated to 182-253 DEG C before forging forming, and the temperature of the thick side of the piston skirt of the diesel engine piston blank in the die is 10-20 DEG C higher than that of the thin side, and the forging forming temperature of the piston skirt of the diesel engine piston blank in the die is 40-60 DEG C higher than that of the piston top. The temperature of other parts of the diesel engine piston blank is kept substantially constant during the whole forging forming process, and the forging forming temperature difference between the thick and thin sides of the piston skirt and the forging forming temperature difference between the piston skirt and the piston top improve the flowability of the piston skirt and the piston top, promote filling, thereby reducing coarse grain defects and improving the mechanical properties of the final diesel engine piston.

[0031] After the diesel engine piston blank is forged in the forging die, the blank is subjected to heat treatment to obtain a diesel engine piston. Specifically, the forged blank is subjected to solid solution treatment and artificial aging to obtain a diesel engine piston. The solid solution treatment comprises: heating to 475-485 DEG C, heating time 1.5-3 h, holding time 0.5-1 h; heating to 505-525 DEG C, heating time 0.5-1 h, holding time 3-4 h; water cooling within 25 s for 5-15 min. The artificial aging comprises: heating to 175-185 DEG C, heating time 1-3 h, holding time 7-8 h.

[0032] The present application provides a diesel engine piston prepared by the above preparation method. The diesel engine piston provided by the present application comprises a piston skirt and a piston top. The piston skirt of the diesel engine piston provided by the present application has an asymmetric structure on both sides with the piston central axis as the reference, the thickness of the pin seat on one side of the piston skirt is thicker, and the thickness of the pin seat on the other side is thinner. The piston top of the diesel engine piston provided by the present application is a trumpet-shaped piston top; the area ratio of the trumpet-shaped piston top to the piston skirt of the diesel engine piston is (0.35-0.55):1.

[0033] The present application also provides a forging die applied to the preparation method of the above diesel engine piston, which comprises a die body and a heating coil arranged in the die body; the heating coil is used for heating the thick-thin two sides of the piston skirt of the diesel engine piston blank and the piston top of the diesel engine piston blank. Specifically, the forging die provided by the present application comprises a punch, a top rod, an upper insert block, a lower insert block and a heating coil arranged in the lower insert block and uniformly distributed in a circle. As shown in Figure 2 , Figure 2 It is a front view of the forging die provided by the present application, Figure 2 The forging die comprises a top rod, an upper insert block 1, a lower insert block 2, a lower cushion 3, a top rod 4, a punch 5, a heating coil 201 arranged in the lower insert block and uniformly distributed in a circle, and a heat insulation plate 202 arranged on the heating coil 201, and the lower cushion 3 is arranged above the top rod 4; Figure 2 The diesel engine piston blank 6 arranged in the forging die is also included in the forging die, and the diesel engine piston blank 6 has a piston skirt 601 and a piston top 602. It should be noted that Figure 2 The diesel engine piston blank 6 shown in the figure has been formed and forged by the punch 5 and initially has the structure of the final obtained piston part, and the top view of the section is shown in Figure 3 , Figure 3 It is a top view of the section of the diesel engine piston blank 6 provided by the present application, and Figure 3 The piston skirt 601 and the piston top 602, 603 and 604 of the diesel engine piston blank 6 provided by the present application can be seen, and the piston skirt of the diesel engine piston blank 6 provided by the present application has an asymmetric structure on both sides with the piston central axis as the reference, the thickness of the pin seat on one side of the piston skirt is thicker, and the thickness of the pin seat on the other side is thinner, so that the piston skirt of the final obtained piston has an asymmetric structure on both sides with the piston central axis as the reference.

[0034] The lower insert of the forging die has a cavity for forming the diesel engine piston, and the upper part of the lower insert corresponds to the piston skirt and the piston top of the diesel engine piston blank. The heating coil of the forging die is used for heating the thick and thin edges of the piston skirt of the diesel engine piston blank and the piston top of the diesel engine piston blank; in particular, the heating coil heats the upper part of the lower insert, preheats the upper part of the lower insert to 182-253 DEG C, the temperature of the thick edge of the pin seat of the piston skirt corresponding to the upper part of the lower insert is 10-20 DEG C higher than that of the thin edge, and the temperature of the other parts of the blank is kept basically constant during the whole forging process, so that the temperature of the piston skirt is 40-60 DEG C higher than that of the piston top, and the flowability of the piston skirt is improved.

[0035] Further, since the diesel engine piston provided by the application has an asymmetric structure, the punch of the forging die also has an asymmetric structure, and stress concentration exists in the skirt of the piston port, as shown in Figure 4 , Figure 4 which is a structural schematic diagram of the piston punch. Therefore, the application provides a large circular arc with a radius R≥10 mm at the uppermost end of the piston skirt corresponding to the upper part of the lower insert of the diesel engine piston blank, and left and right flash grooves with different depths are provided according to the thickness of the piston pin seat (the flash grooves are asymmetrically designed), wherein the left flash groove is arranged at the thicker side of the piston skirt, and the right flash groove is arranged at the thinner side of the piston skirt, so as to improve the flowability of the flash of the forged piston skirt. As shown in Figure 5 , Figure 5 which is a side sectional view of the forging die, Figure 5 it can be known that the lower insert 2 of the forging die comprises a piston blank left flash groove 203, a piston blank right flash groove 204 and a large circular arc 205 with a radius R≥10 mm connected with the piston blank left flash groove 203; other symbols and Figure 2 are the same, and will not be described here.

[0036] Further, the upper part of the lower insert of the forging die has a trumpet-shaped recess, as shown in Figure 6 , Figure 6 which is a physical diagram of the piston blank produced by the forging die, and the trumpet-shaped recess is used for forming a trumpet-shaped piston top of the diesel engine piston blank, obtaining a diesel engine piston with a trumpet-shaped piston top, and making the area ratio of the formed trumpet-shaped piston top and the piston skirt be 0.35-0.55:1; the maximum diameter of the trumpet-shaped piston recess is greater than or equal to the maximum diameter of the punch of the forging die; and the uppermost part of the trumpet-shaped piston recess is a positioning conical surface consistent with the positioning conical surface of the diesel engine piston blank. In addition, the upper part of the lower insert of the forging die is provided with an annular extrusion groove, and three exhaust grooves are arranged on the annular extrusion groove.Figure 7 As shown, Figure 7 This is a detailed cross-sectional view of the lower insert 2 of the forging die and the diesel engine piston blank 6 described in this invention. Figure 7 The piston top 603 can be seen in the image; the area covered by the "+" sign represents the entire area of ​​the trumpet-shaped piston top 603 of the piston blank 6. Figure 7 The area covered by the long dashed lines represents the area of ​​the entire piston skirt of piston blank 6. Figure 7 207 represents extrusion groove 207; the plane indicated by the solid line in 208 represents the positioning conical surface of the upsetting blank; 209 represents the three vent holes set in the lower insert.

[0037] In addition, such as Figure 8 As shown, Figure 8 This is a schematic diagram of the draft angle of the inner wall of the piston pin seat. Figure 8 As can be seen from punch 5, the draft angle of the piston pin seat is relatively small. The aforementioned flared piston top 603 and three vent holes improve the flow of alloy metal, resulting in high forming quality of the piston inner cavity, free from defects such as cracks and flaking, and solving the problem of metal flow obstruction caused by the small draft angle of the piston pin seat inner wall.

[0038] This invention provides a diesel engine piston material, a diesel engine piston, a method for preparing the same, and a forging die. The diesel engine piston material provided by this invention comprises the following components: Si: 14.1–18.3 wt%; Ni: 1.6–3.2 wt%; Fe: 0.8–1.6 wt%; Mg: 0.3–0.6 wt%; Cr: 0.01–0.05 wt%; Zn: 0.06–0.3 wt%; Ti: 0.02–0.2 wt%; Zr: 0.07–0.2 wt%; V: 0.1–0.18 wt%; Al: balance. The diesel engine piston material provided by this invention is used in the preparation of diesel engine pistons. During the forging process, the forging parts maintain a delamination temperature, which improves the deformation capacity and formability of the diesel engine piston material, reduces the coefficient of linear expansion, improves the volumetric stability of the piston, reduces the amount of thermal deformation of the piston during operation, ensures uniform, stable, and reliable piston quality, and extends the service life of high-power and medium-to-high speed large-diameter marine pistons. Attached Figure Description

[0039] Figure 1 This is an electron micrograph of the alloy microstructure of the diesel engine piston material described in this invention;

[0040] Figure 2 This is a front cross-sectional view of the forging die described in this invention;

[0041] Figure 3 This is a top cross-sectional view of the diesel engine piston blank 6 described in this invention;

[0042] Figure 4This is a schematic diagram of the piston punch described in this invention;

[0043] Figure 5 This is a side cross-sectional view of the forging die described in this invention;

[0044] Figure 6 This is a photograph of a piston blank produced by the forging die described in this invention.

[0045] Figure 7 This is a detailed cross-sectional view of the lower insert 2 of the forging die and the diesel engine piston blank 6 described in this invention;

[0046] Figure 8 A schematic diagram of the draft angle of the inner wall of the piston pin seat;

[0047] Figure 9 Structural diagram of the upsetting die used in this invention;

[0048] Figure 10 This is a schematic diagram of the process for obtaining a diesel engine piston blank by upsetting the bar billet according to the present invention;

[0049] Figure 11 This is a metallographic image of the alloy forging of the diesel engine piston obtained in the present invention. Detailed Implementation

[0050] This invention discloses a diesel engine piston material, a diesel engine piston, a method for manufacturing the same, and a forging die. Those skilled in the art can refer to this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments; those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0051] The present invention first prepares the bar billet before forging to obtain the bar billet, then uses an upsetting die to upset the bar billet to obtain a diesel engine piston blank, and then puts the obtained diesel engine piston blank into the lower insert of a forging die that has been fixed in advance and the lower insert has been preheated, and then performs piston forming and heat treatment processes to obtain the diesel engine piston of the present invention.

[0052] The upsetting die used in this invention is as follows: Figure 9 As shown, Figure 9 The structural diagram of the upsetting die used in this invention is as follows: Figure 9It can be known that the upsetting die comprises an upper upsetting die 7, a lower upsetting die 8 and a positioning cylindrical boss 9 arranged on the lower upsetting die 8. The rod blank has a cylindrical shape. The rod blank is arranged on the positioning cylindrical boss 9, and the rod blank is formed by two hammer forming through the upper upsetting die 7, so that the diesel engine piston blank is obtained. Figure 10 As shown in the figure, Figure 10 The flowchart for forming the diesel engine piston blank through the rod blank made of the piston material is shown.

[0053] The forging die used in the application is the same as the above, and will not be repeated.

[0054] The rod blank made of the diesel engine piston material is used to prepare the diesel engine piston, and the specific components are shown in Table 2.

[0055] Table 2: Components of the blank made of the piston material (wt%)

[0056] element Si Ni Fe Mg Cr Zn Ti Zr V Al content 14.1～18.3 1.6～3.2 0.8～1.6 0.3～0.6 0.01～0.05 0.06～0.3 0.02～0.2 0.07～0.2 0.1～0.18 balance

[0057] The actual piston material components of the rod blank used in each embodiment and the comparative example are shown in Table 3.

[0058] Table 3: Components of the blank made of the piston material (wt%)

[0059]

[0060] The application will be further described in combination with the embodiments as follows:

[0061] Embodiment 1

[0062] The preparation of the diesel engine piston is carried out according to the following forging forming process steps:

[0063] 1) Preparation before forging: according to a certain proportion, the rod size is φ130*242mm, the end surface of the rod blank is turned, and the roughness is ≤12.5μm, so that the rod blank is obtained;

[0064] 2) Blank heating: the rod blank obtained in step 1) is heated before forging, which should be carried out in a box-type electric furnace. When the temperature of the product is 515℃, in order to make the material inside uniformly heated, eliminate the stress generated by heating, and make the material organization uniform, the temperature is kept for 5.5h;

[0065] 3) Die fixing: the punch is fixed on the upper insert block, and the upper insert block is fixed on the electric screw press. The lower insert block is fixed in the lower forging die positioning groove;

[0066] 4) Heating of the lower insert: The heating coil heats the upper part of the lower insert, preheating the upper mold of the lower insert to 245°C. The temperature of the thicker side of the piston skirt of the upper mold of the insert is kept 18°C ​​higher than the temperature of the thinner side. During the entire forging process, the temperature of other parts of the billet is kept basically constant, and the temperature of the piston skirt is 55°C higher than the temperature of the piston top, which improves the fluidity of the piston skirt.

[0067] 5) Upsetting: After the bar billet in step 2) is kept at 515°C for the specified holding time, it is placed in an upsetting mold and upset using an electric screw press. The process involves two hammer blows: the first blow speed is 400 m / min, and the second blow speed is 520 m / min. The upsetting ratio is 1.6, the upsetting deformation is 0.15, and the temperature after upsetting is 497°C. The upsetting mold is designed with a positioning cylindrical boss to address the existing problem of poor coaxiality of the blank. The details are the same as described above and will not be repeated. The upset blank is the diesel engine piston blank described in this invention, with an upper part that is an elliptical cylinder and a lower part that is a positioning cone consistent with the positioning cone surface of the lower insert of the forging mold. The details are the same as described above and will not be repeated.

[0068] 6) Piston Forming: Within ≤20s, the upset diesel engine piston blank is placed into the positioning conical surface of the lower insert mold, where an electric screw press performs forming forging. Forming is done with two hammer blows: the first blow speed is 600 m / min, and the second blow speed is 800 m / min. The forging is completed at a relatively low strain rate of 0.48s. -1 The bottom is formed.

[0069] 7) During the forging process, after each piece is forged, another billet should be hooked out of the furnace; multiple billets should not be hooked out at once. After every 20 forgings, the forgings should be inspected, and any abnormalities should be adjusted promptly. After each forging, the die cavity should be sprayed with a mixture of graphite and machine oil as a lubricant.

[0070] 8) The aluminum piston forging blank needs to be ground. The inner cavity and periphery of the blank are ground with a pneumatic grinding machine, and the frame is stacked for cooling.

[0071] Heat treatment process:

[0072] 9) Solution treatment: Heat to 480℃ for 2.5 hours and hold for 0.7 hours; heat to 520℃ for 0.8 hours and hold for 3.5 hours; transfer from the furnace to water in ≤25 seconds and water cooling time in 10 minutes.

[0073] 10) Artificial aging: Heat to 180℃ for 2 hours, hold for 7.5 hours to obtain the diesel engine piston described in this invention. Figure 11 As shown, Figure 11 This is a metallographic image of the alloy forging of the diesel engine piston obtained in the present invention.

[0074] Example 2

[0075] The preparation of the diesel engine piston is carried out according to the following forging forming process steps:

[0076] 1) Preparation before forging: blanking according to a certain proportion, the size of the bar blank is φ130*232mm, the end face of the bar blank is turned to a roughness of ≤12.5μm;

[0077] 2) Heating of the blank: the bar blank obtained in step 1) is heated before forging, which should be carried out in a box-type electric furnace, when heated to a temperature of 500℃ of the product, in order to make the material inside uniformly heated, eliminate the stress generated due to heating, and at the same time make the material organization uniform, the blank is kept for 6.0h;

[0078] 3) Fixing of the die: the punch is fixed on the upper insert, and the upper insert is fixed on the electric screw press. The lower insert is fixed in the lower forging die positioning groove;

[0079] 4) Heating of the lower insert: the upper part of the lower insert is heated by the heating coil, and the upper part of the insert is preheated to 212℃, the temperature difference between the thick and thin parts of the piston skirt of the upper part of the insert is kept at 15℃, and the temperature of the other parts of the blank is kept basically constant during the whole forging forming process, so that there is a temperature difference of 50℃ between the piston skirt and the piston top, and the flowability of the piston skirt is improved;

[0080] 5) Upsetting forming: when the bar blank in step 2) is kept at 500℃ for 6.0h, the bar blank is put into the upsetting die, and the electric screw press is used for upsetting forming, two hammer forming, the first hammer speed is 405m / min, the second hammer speed is 514m / min; the upsetting ratio is 1.9, the upsetting deformation is 0.18, and the temperature after upsetting is 484℃; the upsetting die is designed with a positioning cylindrical boss for solving the problem of the existing product that the blank coaxiality is poor, which is the same as the above, and will not be repeated. The blank after upsetting is the diesel engine piston blank of the present application, which is an elliptical cylinder in the upper part and a positioning conical surface consistent with the lower insert positioning conical surface of the lower insert of the forging die in the lower part, which is the same as the above, and will not be repeated.

[0081] 6) Piston forming: the diesel engine piston blank obtained after upsetting is put into the positioning conical surface in the lower insert die within ≤20s, and the electric screw press is used for forming forging, two hammer forming, the first hammer speed is 613m / min, the second hammer speed is 786m / min; the forging is formed at a lower strain rate of 0.64s -1 .

[0082] 7) In the forging process, after each piece is forged, a blank is hooked from the furnace, and more than one blank is not allowed to be hooked at a time. After 20 pieces are forged, the forgings are inspected once, and the adjustment is made in time if abnormalities are found. After each piece is forged, the die cavity is sprayed with a mixture of graphite and machine oil lubricating liquid once;

[0083] 8) The aluminum piston blank is polished, and the inner cavity and the periphery of the blank are polished by a pneumatic grinding machine, and the frame is cooled;

[0084] Heat treatment process:

[0085] 9) Solution treatment: heating to 485℃, heating time 3h, holding time 1h; heating to 525℃, heating time 1h, holding time 4h; transfer from the furnace to the water in ≤25s, water cooling time 15min;

[0086] 10) Artificial aging: heating to 185℃, heating time 3h, holding time 8h, to obtain the diesel engine piston of the application.

[0087] Example 3

[0088] The preparation of the diesel engine piston is carried out according to the following forging forming process steps:

[0089] 1) Preparation before forging: according to a certain proportion, the bar size is φ130*252mm, and the bar blank end face is turned to a roughness of ≤12.5μm;

[0090] 2) Blank heating: the bar blank obtained in step 1) is heated before forging, which should be carried out in a box-type electric furnace, and when heated to the product temperature of 520℃, in order to make the material inside uniformly heated, eliminate the stress generated by heating, and make the material organization uniform, the temperature is kept for 6.5h;

[0091] 3) Die fixing: the punch is fixed on the upper insert, and the upper insert is fixed on the electric screw press. The lower insert is fixed in the lower forging die positioning groove;

[0092] 4) Heating of the lower insert: the heating coil heats the upper part of the lower insert, and the upper part of the insert is preheated to 183℃, the temperature difference between the thick and thin parts of the insert is kept at 11℃, and the temperature of the blank is kept basically constant during the whole forging forming process, so that there is a temperature difference of 42℃ between the piston skirt and the piston top, and the flowability of the piston skirt is improved;

[0093] 5) Upsetting forming: after the bar blank in step 2) is kept warm for 520℃ for a warm-keeping time, the bar blank is put into an upsetting die, an electric screw press carries out upsetting forming, two hammer forming, the first hammer speed is 425 m / min, the second hammer speed is 532 m / min; the upsetting ratio is 1.3, the upsetting deformation is 0.12, and the temperature after upsetting is 503℃; the upsetting die is designed with a positioning cylindrical boss for solving the problem of poor coaxiality of the existing product, and the specific design is the same as above, which will not be repeated. The blank after upsetting is the diesel engine piston blank of the application, which is an elliptical cylinder in the upper part and a positioning conical surface consistent with the lower insert block positioning conical surface of the forging die in the lower part, and the specific design is the same as above, which will not be repeated.

[0094] 6) Piston forming: the diesel engine piston blank obtained after upsetting is put into the positioning conical surface in the lower insert block die within ≤20s, and an electric screw press carries out forming forging, two hammer forming, the first hammer speed is 620 m / min, the second hammer speed is 819 m / min; the forging is formed at a lower strain rate of 0.29s -1

[0095] 7) In the forging process, one blank is hooked out from the furnace after each forging, and multiple blanks are not allowed to be hooked out at one time. The forgings are checked once every 20 forgings, and adjusted in time if abnormalities are found. The die cavity is sprayed with a mixed lubricating liquid of graphite and machine oil once after each forging;

[0096] 8) The aluminum piston forging blank is polished, the inner cavity and the periphery of the blank are polished by a pneumatic grinding machine, and the frame is cooled;

[0097] Heat treatment process:

[0098] 9) Solid solution treatment: heating to 475℃, heating time 1.5h, warm-keeping time 0.5h; heating to 505℃, heating time 0.5h, warm-keeping time 3h; transferring from the furnace to water ≤25s, water cooling time 5min;

[0099] 10) Artificial aging: heating to 175℃, heating time 1h, warm-keeping time 7h, to obtain the diesel engine piston of the application.

[0100] Comparative Example 1

[0101] The diesel engine piston is prepared according to the following forging forming process steps:

[0102] 1) Preparation before forging: blanking according to a certain proportion, the forging bar adopts 4032 alloy, the size of the bar is φ130×232mm, the end face of the bar blank is turned, and the roughness is ≤12.5μm;

[0103] ​2) blank heating: the bar blank obtained in step 1) is heated before forging, which is carried out in a box-type electric furnace, and when heated to the product temperature of 500 DEG C, in order to uniformly heat the material inside, eliminate the stress generated by heating, and make the material structure uniform, the temperature is kept for 6.0h;

[0104] 3) mold fixing: the punch is fixed to the upper insert, and the upper insert is fixed to the electric screw press. The lower insert is fixed in the lower forging mold positioning groove;

[0105] 4) lower insert heating: the upper part of the lower insert is heated by the heating coil, and the upper part of the lower insert is preheated to 212 DEG C. The temperature difference between the thick and thin parts of the piston skirt of the upper part of the insert is kept at 15 DEG C, and the temperature of the other parts of the blank is kept basically constant during the whole forging process, so that there is a temperature difference of 50 DEG C between the piston skirt and the top of the piston, and the flowability of the piston skirt is improved;

[0106] 5) upsetting forming: when the bar blank in step 2) is kept at 500 DEG C for 6.0h, the bar blank is put into the upsetting die, and the electric screw press is used for upsetting forming, two hammer forming, the first hammer speed is 405 m / min, the second hammer speed is 514 m / min; the upsetting ratio is 1.9, the upsetting deformation is 0.18, and the temperature after upsetting is 484 DEG C; the upsetting die is designed with a positioning cylindrical boss for solving the problem of the existing product blank coaxiality difference, which is the same as the above, and will not be repeated. The blank after upsetting is the diesel engine piston blank of the present application, which is an elliptical cylinder in shape, and the lower part is a positioning conical surface consistent with the lower insert positioning conical surface of the forging die, which is the same as the above, and will not be repeated.

[0107] 6) piston forming: the diesel engine piston blank obtained after upsetting is put into the positioning conical surface in the lower insert die within ≤20s, and the electric screw press is used for forming forging, two hammer forming, the first hammer speed is 613 m / min, the second hammer speed is 786 m / min; the forging is formed at a lower strain rate of 0.64s -1 down forming.

[0108] 7) during the forging process, one blank is hooked out from the furnace after each forging, and multiple blanks are not allowed to be hooked out at one time. The forgings are inspected once every 20 forgings, and adjusted in time if abnormality is found. The die cavity is sprayed with mixed lubricating liquid of graphite and oil once after each forging;

[0109] 8) the aluminum piston forging blank is polished, and the inner cavity and the periphery of the blank are polished by a pneumatic grinding machine, and the frame is cooled;

[0110] Heat treatment process:

[0111] 9) solution treatment: heating to 485℃, heating time 3h, holding time 1h; heating to 525℃, heating time 1h, holding time 4h; transferring from the furnace to water in ≤25s, water cooling time 15min;

[0112] 10) artificial aging: heating to 185℃, heating time 3h, holding time 8h, to obtain the diesel engine piston of the present application.

[0113] Comparative Example 2

[0114] The preparation of the diesel engine piston is carried out according to the following forging forming process steps:

[0115] 1) preparation before forging: blanking according to a certain proportion, the size of the bar stock is φ130x232mm, the end face of the bar stock is turned to a roughness of ≤12.5μm;

[0116] 2) heating of the blank: the bar stock obtained in step 1) is heated before forging, which should be carried out in a box-type electric furnace, when heated to a temperature of 500℃ for this kind of product, in order to make the material inside uniformly heated, eliminate the stress generated due to heating, and make the material organization uniform, the holding time is 6.0h;

[0117] 3) mold fixing: the punch is fixed to the upper insert, and the upper insert is fixed to the electric screw press. The lower insert is fixed in the lower forging mold positioning groove;

[0118] 4) upsetting forming: after the bar stock in step 2) is heated to 500℃ for 6.0h, the bar stock is put into the upsetting mold, the electric screw press is used for upsetting forming, two hammer forming, the first hammer speed is 405m / min, the second hammer speed is 514m / min; the upsetting ratio is 1.9, the upsetting deformation is 0.18, and the upsetting temperature is 484℃; the upsetting mold is designed with a positioning cylindrical boss for solving the problem of the existing product that the blank coaxiality is poor, which is the same as the above, and will not be repeated. The blank after upsetting is the diesel engine piston blank of the present application, which is an elliptical cylinder in the upper part and a positioning conical surface consistent with the lower insert positioning conical surface of the forging mold in the lower part, which is the same as the above, and will not be repeated.

[0119] 5) piston forming: the diesel engine piston blank obtained after upsetting is put into the positioning conical surface in the lower insert mold in ≤20s, wherein the electric screw press is used for forming forging, two hammer forming, the first hammer speed is 613m / min, the second hammer speed is 786m / min; the forging is formed at a lower strain rate of 0.64s -1 .

[0120] 6) in the forging process, after forging each piece, a blank is hooked from the furnace, and more than one blank is not allowed to be hooked at a time. After forging 20 pieces, the forged piece is checked, and the adjustment is made in time if abnormality is found. After forging each piece, the die cavity is sprayed with mixed lubricating liquid of graphite and machine oil once;

[0121] 7) the aluminum piston forging blank is polished, the inner cavity and the periphery of the blank are polished by a pneumatic grinder, and the frame is stacked with cold;

[0122] Heat treatment process:

[0123] 8) solid solution treatment: heating to 485 DEG C, heating time 3h, holding time 1h; heating to 525 DEG C, heating time 1h, holding time 4h; transfer from the furnace to water in ≤25s, water cooling time 15min;

[0124] 9) artificial aging: heating to 185 DEG C, heating time 3h, holding time 8h, to obtain the diesel engine piston.

[0125] The diesel engine piston prepared by the above method is subjected to performance test and volume stability test, wherein the performance test is shown in Table 4, and the volume stability test is shown in Table 5:

[0126] Table 4: performance results of examples and comparative examples

[0127]

[0128]

[0129] Table 5: comparison of volume stability test of examples and comparative examples

[0130]

[0131] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any skilled person in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method of manufacturing a diesel piston, characterized in that, The method comprises the following steps: forging the diesel engine piston blank in a forging die to form a diesel engine piston; The diesel engine piston blank is made of a piston material; The piston material comprises the following components: Si: 14.1-18.3 wt%; Ni: 1.6-3.2 wt%; Fe: 0.8-1.6 wt%; Mg: 0.3-0.6 wt%; Cr: 0.01-0.05 wt%; Zn: 0.06-0.3 wt%; Ti: 0.02-0.2 wt%; Zr: 0.07-0.2 wt%; V: 0.1-0.18 wt%; Al: balance; The mass ratio of the Ni and Fe is (1.0-2.0):1; The forging temperature of the thicker side of the piston skirt of the diesel engine piston blank is 10-20 DEG C higher than that of the thinner side; The forging temperature of the piston skirt of the diesel engine piston blank is 40-60 DEG C higher than that of the piston top.

2. The method of manufacturing a diesel piston according to claim 1, wherein The forging temperature is 182-253 DEG C.

3. The method of manufacturing a diesel piston according to claim 1, wherein The heat treatment comprises solution treatment and artificial aging; The solution treatment specifically comprises: heating to 475-485 DEG C, heating time 1.5-3 h, holding time 0.5-1 h; then heating to 505-525 DEG C, heating time 0.5-1 h, holding time 3-4 h; water cooling within 25 s for 5-15 min; The artificial aging specifically comprises: heating to 175-185 DEG C, heating time 1-3 h, holding time 7-8 h.

4. The method of manufacturing a diesel piston according to claim 1, wherein The method comprises the following steps: After heating and holding the diesel engine piston material rod blank, the rod blank is forged in a upsetting die by a two-hammer forming method, first, the first hammer upsetting is performed at a speed of 383-426 m / min, and the second hammer upsetting is performed at a speed of 502-534 m / min, to obtain the diesel engine piston blank; the upsetting ratio of the upsetting forming is 1.2-2.2, and the upsetting deformation is 0.1-0.2; The obtained diesel engine piston blank is placed in a forging die within 20 s, first hammer forging is performed at a speed of 594 to 621 m / min, second hammer forging is performed at a speed of 784 to 819 m / min, the diesel engine piston blank is forged and formed at a strain rate of 0.28 to 0.69 s -1 , and then heat treated to obtain a diesel engine piston.

5. A diesel piston characterized by, The diesel engine piston is prepared by the method of any one of claims 1-4.

6. The diesel piston of claim 5 wherein, The piston top is a trumpet-shaped piston top; The area ratio of the trumpet-shaped piston top to the piston skirt of the diesel engine piston is 0.35-0.55:1.

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