Die forging method for connecting rod body of medium-speed diesel engine for dual-fuel ship with 450 mm cylinder diameter

Abstract

The invention belongs to the field of casting, and discloses a die forging method for a medium-speed diesel engine connecting rod body for a dual-fuel ship with the cylinder diameter of 450 mm. The die forging method comprises the following steps that S1, a steel ingot is heated, specifically, the steel ingot is heated in a natural gas heating furnace; s2, forging: upsetting and drawing out the steel ingot twice on a pressing machine; s3, blanking: blanking according to the size required by the process; s4, round billet heating is conducted, specifically, the round billets blanked in the S3 are heated; s5, blank manufacturing, wherein a blank with a large head, a rod part, a conical part and a small head is freely forged on a 3t hammer; s6, blank heating, wherein the blank is heated; and S7, die forging is conducted, specifically, the blank heated in the step S6 is placed in a die cavity, and one-time die forging forming is conducted. The die forging method is simple in process, short in flow, low in consumption and low in cost, and the die-forged connecting rod body is regular in appearance, small in needed forming force, high in material utilization rate and good in metal streamline.

Description

Technical Field

[0001] The invention belongs to the field of casting, in particular to a die forging method for a connecting rod body of a dual-fuel marine medium-speed diesel engine with a cylinder diameter of 450mm. Background Art

[0002] The connecting rod shape of a 450mm cylinder diameter dual fuel medium speed diesel engine is as follows Figure 8 As shown, it includes the middle rod and the flat square head and ball head at both ends, weighs 380kg, and the horizontal projection area is 271189mm 2 It has the characteristics of heavy forging weight and large projection area. At present, free forging is adopted in China, that is, a flat square is forged at each end and then the two ends are directly turned to produce the shape. This process has a long processing cycle, high processing cost, serious material waste, large processing allowance, long working hours, high processing cost, discontinuous internal fiber structure and poor mechanical properties.

[0003] The die forging process can effectively improve the mechanical properties, but it is only suitable for connecting rods with lighter weight and smaller specifications. For example, the "Engine Connecting Rod Die Forging Process and Die" in "Mechanical Engineer" (December 2007) publicly records the current die forging process as follows: raw material inspection → bar cutting and blanking → medium frequency induction heating → roll forging → initial forging → final forging → trimming → punching → thermal correction → residual heat quenching → tempering → delivery to the warehouse. When die forging is applied to the connecting rod body of a 450mm cylinder dual-fuel medium-speed diesel engine with heavy weight and large projected area, the following problems still exist:

[0004] 1) For connecting rods with large volume and specifications, due to the large cross-section, if the heating speed and the insulation temperature at each stage are not properly controlled, stress cracks are likely to occur inside the material;

[0005] 2) In the die forging process, in order to ensure smooth metal flow and full filling of the cavity, two die forgings including pre-forging and final forging are usually required. Otherwise, the metal flow will not be smooth, resulting in incomplete filling of the cavity. This is especially true for connecting rods with heavy weight and large projected area. During the production process, the connecting rod of a 450mm cylinder dual-fuel medium-speed diesel engine weighs 380kg and has a horizontal projected area of ​​271189mm. 2 , far exceeding the specifications of existing die-forged connecting rod bodies. According to the traditional die-forging process, at least one pre-forging is required before final forging. The production process is long, the energy consumption is high, and the mold manufacturing cost is high.

[0006] 3) Since the connecting rod body of a diesel engine is an uncommon special-shaped structure, folding is easily generated at the thin-thick connection of the ball head end during the die forging process.

[0007] Therefore, there are still difficult-to-overcome technical problems in the current die forging process for preparing the connecting rod body of a 450mm cylinder diameter dual-fuel medium-speed diesel engine. Summary of the invention

[0008] The purpose of the present invention is to provide a die forging method for a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine connecting rod body with a simple process, short flow, low consumption, low cost, regular shape of the die-forged connecting rod body, small required forming force, high material utilization rate and good metal streamline in view of the above-mentioned situation.

[0009] The method of the present invention comprises the following steps:

[0010] S1. Ingot heating: The ingot is heated in a natural gas heating furnace;

[0011] S2. Forging: The steel ingot is upset and stretched twice on a press;

[0012] S3. Cutting: Cutting according to the size required by the process;

[0013] S4. Round billet heating: heating the round billet cut in S3;

[0014] S5. Billet making: A billet having a big head, a rod, a cone and a small head is forged by free forging on a 3t hammer;

[0015] S6. Billet heating: heating the billet;

[0016] S7. Die forging: placing the blank heated in step S6 in a die cavity and performing one-step die forging.

[0017] In the step S1, the steel ingot is first heated to 500-550°C and kept warm for 2 hours, then the heating rate is controlled to be ≤60°C / h and heated to 780-820°C and kept warm for 2 hours, and finally the heating rate is controlled to be ≥80°C / h and heated to 1230-1250°C and kept warm for 6 hours.

[0018] In the step S2, the ratio of the height to the diameter of the steel ingot after the second upsetting is 0.65-0.75, and the diameter of the billet after the second drawing is consistent with the diameter of the big end of the billet.

[0019] In step S3, the weight of the material is 1.05-1.08 times the weight of the connecting rod;

[0020] In step S4, the round billet is first heated to 700-750° C. and kept warm for 2 hours, and then heated to 1050-1100° C. and kept warm for 3 hours;

[0021] In step S5, the diameter of the large end of the forged billet is 0.76-0.85 times the diameter of the flat square head of the connecting rod body, the diameter of the rod of the billet is consistent with that of the connecting rod body, the angle between the taper of the billet and the rod is 160-165°, and the diameter of the small end of the billet is 0.65-0.7 times the diameter of the ball head of the connecting rod body.

[0022] In the step S5, the tapered portion of the blank is formed by using an anvil, and the taper of the tapered surface on one side of the lower portion of the anvil is consistent with the taper of the tapered portion of the blank.

[0023] In step S6, the blank is heated to a temperature of 1130-1170° C. and kept warm for 5 hours.

[0024] In step S7, a hydraulic press is used to perform a die forging process, the upper die is connected to the press beam, the lower die is placed on the press walkway, the upper mold cavity and the lower mold cavity are symmetrical up and down, the upper cavity at the bottom of the upper die is consistent with the shape of the upper part of the connecting rod body, and the lower cavity at the top of the lower die is consistent with the shape of the lower half of the connecting rod body.

[0025] The present application aims at solving the problems existing in the background technology. By designing a reasonable blank shape, the connecting rod body can be directly forged in one step after the blank is made by free forging without the need for a pre-forging process.

[0026] 1) Optimization of drawing length: In order to meet the needs of subsequent free forging, the height to diameter ratio of the steel ingot after the second upsetting is controlled to be 0.65-0.75, and the diameter of the billet after the second drawing is consistent with the diameter of the big end of the billet; further, after years of experiments and research, it is found that as long as the billet size parameters after free forging are strictly controlled, it can be die-forged in one time without the need for two or more die forgings. Therefore, on the one hand, a billet with a big head, a rod, a conical surface and a small head is prepared by free forging, and on the other hand, the diameter of the big head of the billet is limited to 0.76-0.85 times the diameter of the flat square head of the connecting rod body, the rod of the billet is consistent with the diameter of the rod of the connecting rod body, the angle between the cone and the rod of the billet is 160-165°, and the diameter of the small head of the billet is 0.65-0.7 times the diameter of the ball head of the connecting rod body. By controlling the above ratio, the heated billet can be forged in one step in the hydraulic press, effectively reducing the number of forging times. This is an unprecedented innovation in the preparation of the 450mm cylinder diameter dual-fuel medium-speed diesel engine connecting rod body with heavy weight and large projected area.

[0027] 2) Optimization of heating conditions: In step S1, the heating process of the steel ingot before forging is carried out by graded heating. The first heating is to 500-550℃ to make the temperature of the steel ingot uniform and reduce temperature stress. The second heating is to 780-820℃ to make the structure completely transformed into austenite and reduce the structure stress. Finally, it is heated to 1230-1250℃ to achieve good plasticity and low deformation resistance of the steel at this temperature. In the second heating, the heating rate is controlled to be ≤60℃ / h to avoid heating too fast. There are temperature stress and organizational stress in the heating process. If the heating rate is too fast, cracks will be generated inside. In the third heating, the heating rate is controlled to be ≥80℃ / h, hoping to heat up quickly to reduce energy consumption. In step S4, when heating the round billet before blanking, graded heating is also adopted. The round billet is first heated to 700-750℃ and kept warm for 2h to reduce temperature stress, and then heated to 1050-1100℃ and kept warm for 3h to make the organization completely austenitized, so as to meet the requirements of deformation plasticity and organization in the subsequent blanking steps. Finally, in step S6, the billet before die forging is heated to 1130-1170℃ at one time and kept warm for 5h, so as to reduce the oxide scale of the billet and avoid excessive grain growth, and make the billet have lower deformation resistance and better plasticity, which is convenient for one-time die forging.

[0028] The invention has the advantages of simple process, short flow, low consumption and low cost. The die-forged connecting rod body has a regular shape, small forming force, high material utilization rate and good metal streamline, and is particularly suitable for preparing a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a front view of the special anvil of the present invention;

[0030] Figure 2 It is a front view of a connecting rod blank of the present invention;

[0031] Figure 3 A half-section front view of the upper mold of the present invention;

[0032] Figure 4 A bottom view of the upper die of the present invention;

[0033] Figure 5 A top view of the lower mold of the present invention;

[0034] Figure 6 It is a diagram of the use state of the upper mold and the lower mold of the present invention;

[0035] Figure 7 A half-section front view of a die-forged connecting rod body of the present invention;

[0036] Figure 8 A top view of a connecting rod body forged by die forging according to the present invention;

[0037] Fig. 9 This is a graph showing the grain size of the connecting rod surface prepared in Example 1;

[0038] Fig.10 This is a graph showing the grain size of the connecting rod surface prepared in Example 2;

[0039] Fig.11 This is a graph showing the grain size detection on the surface of the connecting rod body prepared in Example 3.

[0040] Among them: anvil 1, cone surface 1.1, upper die 2, cavity 2.1, lower die 3, cavity 3.1, blank 4, big head 4.1, rod 4.2, cone 4.3, small head 4.4, connecting rod body 5, flat square head 5.1, rod 5.2, ball head 5.3. DETAILED DESCRIPTION

[0041] The method of the present invention is further explained below with reference to the accompanying drawings:

[0042] Reference Figure 1 , the conical surface 1.1 at the lower right side of the anvil 1 is consistent with the conical portion 4.3 of the blank 4; Figure 3 and Figure 4 The bottom of the upper mold 2 has a cavity that is consistent with the upper half of the connecting rod body 5, and is symmetrical with the cavity 3.1 of the lower mold 3 about the parting surface. Figure 5 The top of the lower mold 3 has a cavity 3.1 that is consistent with the lower half of the connecting rod body 5, and is symmetrical with the cavity 2.1 of the upper mold 2 about the parting surface.

[0043] Embodiment 1:

[0044] Reference Figure 2 , S1. Ingot heating: first heat the ingot to 500℃, keep it warm for 2h, then control the heating rate to ≤60℃ / h and heat it to 800℃, keep it warm for 2h, finally control the heating rate to ≥80℃ / h and heat it to 1230℃, keep it warm for 6h;

[0045] S2. Ingot forging: After the holding time is sufficient, the ingot is taken out of the furnace for the first upsetting, and the ratio of the height to the diameter of the ingot after upsetting is controlled to be 0.68. It is drawn for the first time, and the ratio of the length to the diameter after drawing is controlled to be 2.5. It is upsetting for the second time, and the ratio of the height to the diameter of the ingot after upsetting is controlled to be 0.65. It is drawn for the second time, so that the diameter of the billet after drawing is consistent with the diameter of the big end 4.1 of the billet.

[0046] S3. Cutting material from sawing machine: the cutting weight is 1.07 times the weight of connecting rod body 5;

[0047] S4. The round billet is heated to 730°C for 2 hours, and then heated to 1100°C for 3 hours.

[0048] S5. Forge a blank 5 with a big head 5.1, a rod 5.2, a taper 5.3 and a small head 5.4 required for die forging on a 3t hammer, wherein the diameter of the big head 4.1 of the connecting rod body blank is 0.85 times the diameter of the flat square head 5.1 of the connecting rod body 5, the diameter of the rod 4.2 of the blank is consistent with the diameter of the rod 5.2 of the connecting rod body 5, the angle between the taper 4.3 and the rod 4.2 of the blank is 162°, and anvil 1 is used for forming. The taper of the cone surface 1.1 on the lower right side of the anvil 1 is consistent with the taper of the taper 4.3 of the blank 4, and the diameter of the small head 4.4 of the blank is 0.65 times the diameter of the ball head 5.3 of the connecting rod body 5.

[0049] S6. Heat the blank to 1170°C and keep it at this temperature for 5 hours.

[0050] S7. Reference Figure 6 , connect the upper die 2 to the 80MN press, place the lower die 3 on the press walkway, place the heated blank 4 in the lower mold cavity 3.1, and the press walkway moves and automatically aligns with the upper die 2. At this time, the upper die 3 is pressed down. When the upper die 2 contacts the lower die 3, the die forging is completed. Lift the upper die 2, and the press walkway moves out the lower die 3 containing the connecting rod body 5, take out the connecting rod body 5, and the die forging is completed.

[0051] The connecting rod body forged by the method of the present invention has no folds or cracks on the surface, is smooth, has a fully filled cavity, and has mechanical properties and grain size that meet the requirements.

[0052] Table 1 Mechanical properties of connecting rod body in Example 1

[0053] Re / MPa Rm / MPa A / ％ Z / ％ AKv2 / J Required value ＞500 800-950 ≥14 ≥40 ≥20 Measured value 707 864 16.5 65 128 148 131

[0054] The grain size is required to be ≥ level 5, and the actual measured value is level 8.

[0055] Embodiment 2:

[0056] S1. Ingot heating: first heat the ingot to 550℃, keep it warm for 2h, then control the heating rate to ≤60℃ / h and heat it to 820℃, keep it warm for 2h, finally control the heating rate to ≥80℃ / h and heat it to 1250℃, keep it warm for 6h;

[0057] S2. Ingot forging: After the holding time is sufficient, the ingot is taken out of the furnace for the first upsetting, and the ratio of the height to the diameter of the ingot after upsetting is controlled to be 0.65. It is drawn for the first time, and the ratio of the length to the diameter after drawing is controlled to be 2.0. It is upsetting for the second time, and the ratio of the height to the diameter of the ingot after upsetting is controlled to be 0.66. It is drawn for the second time, so that the diameter of the billet after drawing is consistent with the diameter of the big end 4.1 of the billet.

[0058] S3. Cutting material of sawing machine: the cutting weight is 1.05 times the weight of connecting rod body 5;

[0059] S4. The round billet is heated to 700°C for 2 hours, and then heated to 1080°C for 3 hours.

[0060] S5. Forge a blank 5 with a big head 5.1, a rod 5.2, a taper 5.3 and a small head 5.4 required for die forging on a 3t hammer, wherein the diameter of the big head 4.1 of the connecting rod body blank is 0.76 times the diameter of the flat square head 5.1 of the connecting rod body 5, the diameter of the rod 4.2 of the blank is consistent with the diameter of the rod 5.2 of the connecting rod body 5, the angle between the taper 4.3 and the rod 4.2 of the blank is 165°, and anvil 1 is used for forming. The taper of the cone surface 1.1 on the lower right side of the anvil 1 is consistent with the taper of the taper 4.3 of the blank 4, and the diameter of the small head 4.4 of the blank is 0.68 times the diameter of the ball head 5.3 of the connecting rod body 5.

[0061] S6. Heat the blank to 1130°C and keep it at this temperature for 5 hours.

[0062] S7. Reference Figure 6 , connect the upper die 2 to the 80MN press, place the lower die 3 on the press walkway, place the heated blank 4 in the lower mold cavity 3.1, and the press walkway moves and automatically aligns with the upper die 2. At this time, the upper die 3 is pressed down. When the upper die 2 contacts the lower die 3, the die forging is completed. Lift the upper die 2, and the press walkway moves out the lower die 3 containing the connecting rod body 5, take out the connecting rod body 5, and the die forging is completed.

[0063] The surface of the connecting rod body has no folds or cracks, the surface is smooth, and the cavity is fully filled.

[0064] Table 2 Mechanical properties of connecting rod body in Example 2

[0065] Re / MPa Rm / MPa A / ％ Z / ％ AKv2 / J Required value ＞500 800-950 ≥14 ≥40 ≥20 Measured value 710 878 18.5 62 154 159 103

[0066] The grain size is required to be ≥ level 5, and the actual measured value is level 8.

[0067] Embodiment 3:

[0068] S1. Ingot heating: first heat the ingot to 520℃, keep it warm for 2h, then control the heating rate to ≤60℃ / h and heat it to 780℃, keep it warm for 2h, finally control the heating rate to ≥80℃ / h and heat it to 1240℃, keep it warm for 6h;

[0069] S2. Ingot forging: After the holding time is sufficient, the ingot is taken out of the furnace for the first upsetting, and the ratio of the height to the diameter of the ingot after upsetting is controlled to be 0.70. It is drawn for the first time, and the ratio of the length to the diameter after drawing is controlled to be 2.2. It is upsetting for the second time, and the ratio of the height to the diameter of the ingot after upsetting is controlled to be 0.75. It is drawn for the second time, so that the diameter of the billet after drawing is consistent with the diameter of the big end 4.1 of the billet.

[0070] S3. Cutting material from sawing machine: the cutting weight is 1.08 times the weight of connecting rod body 5;

[0071] S4. The round billet is heated to 750°C for 2 hours, and then heated to 1050°C for 3 hours.

[0072] S5. Forge a blank 5 with a big head 5.1, a rod 5.2, a taper 5.3 and a small head 5.4 required for die forging on a 3t hammer, wherein the diameter of the big head 4.1 of the connecting rod body blank is 0.80 times the diameter of the flat square head 5.1 of the connecting rod body 5, the diameter of the rod 4.2 of the blank is consistent with the diameter of the rod 5.2 of the connecting rod body 5, the angle between the taper 4.3 and the rod 4.2 of the blank is 160°, and anvil 1 is used for forming. The taper of the cone surface 1.1 on the lower right side of the anvil 1 is consistent with the taper of the taper 4.3 of the blank 4, and the diameter of the small head 4.4 of the blank is 0.7 times the diameter of the ball head 5.3 of the connecting rod body 5.

[0073] S6. Heat the blank to 1160°C and keep it at this temperature for 5 hours.

[0074] S7. Reference Figure 6 , connect the upper die 2 to the 80MN press, place the lower die 3 on the press walkway, place the heated blank 4 in the lower mold cavity 3.1, and the press walkway moves and automatically aligns with the upper die 2. At this time, the upper die 3 is pressed down. When the upper die 2 contacts the lower die 3, the die forging is completed. Lift the upper die 2, and the press walkway moves out the lower die 3 containing the connecting rod body 5, take out the connecting rod body 5, and the die forging is completed.

[0075] The surface of the connecting rod body has no folds or cracks, the surface is smooth, and the cavity is fully filled.

[0076] Table 3 Mechanical properties of connecting rod body in Example 3

[0077] Re / MPa Rm / MPa A / ％ Z / ％ AKv2 / J Required value ＞500 800-950 ≥14 ≥40 ≥20 Measured value 718 879 17 61 138 139 125

[0078] The grain size is required to be ≥ level 5, and the actual measured value is level 8.

Claims

1. A die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine, characterized in that: The following steps are involved: S1. Ingot heating: The ingot is heated in a natural gas heating furnace; S2. Forging: The steel ingot is upset and stretched twice on a press; S3. Cutting: Cutting according to the size required by the process; S4. Round billet heating: heating the round billet cut in S3; S5. Billet making: A billet having a big head, a rod, a cone and a small head is forged by free forging on a 3t hammer; S6. Billet heating: heating the billet; S7. Die forging: placing the blank heated in step S6 in a die cavity and performing one-step die forging.

2. A die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine according to claim 1, characterized in that: In the step S1, the steel ingot is first heated to 500-550°C and kept warm for 2 hours, then the heating rate is controlled to be ≤60°C / h and heated to 780-820°C and kept warm for 2 hours, and finally the heating rate is controlled to be ≥80°C / h and heated to 1230-1250°C and kept warm for 6 hours.

3. The die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine according to claim 1 is characterized in that: In the step S2, the ratio of the height to the diameter of the steel ingot after the second upsetting is 0.65-0.75, and the diameter of the billet after the second drawing is consistent with the diameter of the big end of the billet.

4. The die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine according to claim 1, characterized in that: In step S3, the weight of the material is 1.05-1.08 times the weight of the connecting rod; 5. The die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine according to claim 1, characterized in that: In step S4, the round billet is first heated to 700-750° C. and kept warm for 2 hours, and then heated to 1050-1100° C. and kept warm for 3 hours; 6. The die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine according to claim 1, characterized in that: In step S5, the diameter of the large end of the forged billet is 0.76-0.85 times the diameter of the flat square head of the connecting rod body, the diameter of the rod of the billet is consistent with that of the connecting rod body, the angle between the taper of the billet and the rod is 160-165°, and the diameter of the small end of the billet is 0.65-0.7 times the diameter of the ball head of the connecting rod body.

7. The die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine according to claim 1, characterized in that: In the step S5, the tapered portion of the blank is formed by using an anvil, and the taper of the tapered surface on one side of the lower portion of the anvil is consistent with the taper of the tapered portion of the blank.

8. The die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine according to claim 1, characterized in that: In step S6, the blank is heated to a temperature of 1130-1170° C. and kept warm for 5 hours.

9. The die forging method for a connecting rod body of a 450mm cylinder diameter dual-fuel marine medium-speed diesel engine according to claim 1, characterized in that: In step S7, a hydraulic press is used to perform a die forging process, the upper die is connected to the press beam, the lower die is placed on the press walkway, the upper mold cavity and the lower mold cavity are symmetrical up and down, the upper cavity at the bottom of the upper die is consistent with the shape of the upper part of the connecting rod body, and the lower cavity at the top of the lower die is consistent with the shape of the lower half of the connecting rod body.

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