A three-cylinder crankshaft press-bending die and a three-cylinder crankshaft machining method

Abstract

The application discloses a three-cylinder crankshaft bending die and a three-cylinder crankshaft machining method. The three-cylinder crankshaft bending die comprises an upper die and a lower die which are horizontally arranged along the front-back direction. The upper die is located above the lower die. The lower end of the upper die is concavely provided with an upper die cavity arranged along the front-back direction. The upper end of the lower die is concavely provided with a lower die cavity arranged along the front-back direction. The upper die cavity and the lower die cavity are vertically aligned and jointly form a forming cavity. The upper die and the lower die are pressed together to press and bend a bar placed between the upper die and the lower die along the front-back direction into a three-cylinder crankshaft blank. The upper die cavity and the lower die cavity are expanded at the positions corresponding to the three connecting rod necks of the three-cylinder crankshaft blank. In this way, the material corresponding to the three connecting rod necks of the bar is extruded more compactly under the extrusion of the upper die and the lower die.

Description

Technical Field

[0001] This invention belongs to the field of molds, and particularly relates to a three-cylinder crankshaft bending mold and a three-cylinder crankshaft processing method. Background Technology

[0002] The crankshaft is a crucial component of an automobile engine. Engines experience complex and variable stresses during operation, therefore, the crankshaft must possess excellent comprehensive properties, including strength, hardness, and impact toughness, to ensure normal operation under high loads. Microalloyed non-quenched and tempered steel, after forging or hot rolling, can achieve performance similar to quenched and tempered steel in terms of composition, and offers advantages such as energy saving, environmental friendliness, and low cost. It has gradually gained attention in the production of difficult-to-machine forgings such as crankshafts. However, under certain specific operating conditions, such as in mining truck engines, current non-quenched and tempered steel crankshafts are prone to fatigue damage, large grain size, and connecting rod journal fracture. In other words, the overall performance of non-quenched and tempered steel crankshaft forgings used in high-requirement applications still needs improvement. To address this challenge, optimizing post-forging cooling methods to improve the crankshaft grain size and thus enhance its mechanical properties is a common approach. However, the cooling regime has a relatively small impact on the grain size of forgings. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention discloses a three-cylinder crankshaft bending die with a simple structure that can control the flow characteristics of the crankshaft core material to improve the grain size level of the corresponding part, thereby enhancing the overall performance of the crankshaft and reducing the probability of crankshaft cracking.

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A three-cylinder crankshaft bending die includes an upper die and a lower die arranged horizontally in the front-back direction. The upper die is located above the lower die. The lower end of the upper die is recessed with an upper die cavity arranged in the front-back direction. The upper end of the lower die is recessed with a lower die cavity arranged in the front-back direction. The upper die cavity and the lower die cavity are aligned vertically and together form a cavity. The upper die and the lower die are pressed together to bend a bar stock placed between them in the front-back direction into a three-cylinder crankshaft blank. The upper die cavity and the lower die cavity are expanded at the three connecting rod necks of the three-cylinder crankshaft blank.

[0005] The beneficial effect of the above technical solution is that, under the extrusion of the upper and lower dies, the material at the corresponding three connecting rod necks of the bar stock will be squeezed more densely due to the presence of the upper and lower die cavities.

[0006] In the above technical solution, the three connecting rod necks of the three-cylinder crankshaft blank are, in order from the flange end to the small end, the first connecting rod neck, the second connecting rod neck, and the third connecting rod neck. The cavity has the same structure as the first and second connecting rod necks, but the projections of the two on the corresponding vertical planes in the left and right directions are symmetrically distributed.

[0007] The beneficial effect of the above technical solution is that it makes the first and third connecting rod journals of the three-cylinder crankshaft blank have the same shape, and the material density is similar.

[0008] In the above technical solution, the cavity is provided with a first overflow outlet on the right side corresponding to the first connecting rod neck, and the cavity is provided with a second overflow outlet on the left side corresponding to the third connecting rod neck.

[0009] The beneficial effect of the above technical solution is that it allows excess material at the first and second connecting rod necks to overflow through the first and second overflow ports, respectively.

[0010] In the above technical solution, the expansion depth of the upper mold cavity and the lower mold cavity on the right side of the first connecting rod neck is greater than the expansion depth on the left side, and the expansion depth of the upper mold cavity and the lower mold cavity on the left side of the third connecting rod neck is greater than the expansion depth on the right side.

[0011] The beneficial effects of the above technical solution are that it makes the thickness of the side of the first connecting rod neck and the second connecting rod neck that are far apart from each other greater, and the material is more concentrated, which is beneficial to the subsequent pre-forging and final forging.

[0012] In the above technical solution, the expansion width of the upper mold cavity and the lower mold cavity on the left side of the first connecting rod neck is greater than the expansion width on the right side, and the expansion width of the upper mold cavity and the lower mold cavity on the right side of the third connecting rod neck is greater than the expansion width on the left side.

[0013] The beneficial effect of the above technical solution is that it makes the width of the side where the first connecting rod neck and the second connecting rod neck are close to each other larger, which is beneficial to the subsequent pre-forging and final forging.

[0014] In the above technical solution, the cavity is closed on both the left and right sides corresponding to the second connecting rod neck.

[0015] The beneficial effect of the above technical solution is that when the bar stock is squeezed by the upper and lower dies, the material corresponding to the second connecting rod neck will flow to the first and third connecting rod necks.

[0016] The cross-sections of the upper and lower mold cavities described in the above technical solution are concave arc-shaped cavities.

[0017] The advantages of the above technical solution are that it has a simple structure and good preforming effect.

[0018] In the above technical solution, the closing points on the left and right sides of the upper and lower molds corresponding to the second connecting rod neck are mutually fitted stepped steps.

[0019] The beneficial effect of the above technical solution is that when the upper and lower molds are fitted together, the stepped steps on both sides can limit the left and right movement of the upper and lower molds.

[0020] The second objective of this invention is to provide a simple processing method for a three-cylinder crankshaft that can improve crankshaft quality.

[0021] To achieve the above objectives, the technical solution of the present invention is as follows: A method for machining a three-cylinder crankshaft, comprising the following steps:

[0022] Step 1: The non-quenched and tempered steel bar is heated to the set temperature by medium frequency induction heating;

[0023] Step 2: Place the bar stock processed in Step 1 onto the three-cylinder crankshaft bending die as described above and bend it to obtain a three-cylinder crankshaft blank;

[0024] Step 3: Place the three-cylinder crankshaft blank obtained in Step 2 on a pre-forging die for pre-forging treatment, and obtain a three-cylinder crankshaft pre-product;

[0025] Step 4: Place the three-cylinder crankshaft preform obtained in Step 3 on the final forging die for final forging, and then trim and cool it to finally obtain the finished three-cylinder crankshaft.

[0026] The advantages of the above technical solution are: it has high processing efficiency, and the upper and lower dies can make the material at the three connecting rod necks of the three-cylinder crankshaft more compact when bending the bar stock. It is also a three-cylinder crankshaft processing method with good forming effect during pre-forging and final forging.

[0027] In the above technical solution, the pressing speed of the three-cylinder crankshaft bending die, pre-forging die, and final forging die is 600-650 mm / s.

[0028] The beneficial effect of the above technical solution is that it ensures that the impact force of the three-cylinder crankshaft bending die, pre-forging die and final forging die is moderate at the corresponding pressing speed. Attached Figure Description

[0029] Figure 1 This is an elevation view of the three-cylinder crankshaft in this embodiment;

[0030] Figure 2 This is an end view of the flange end of the three-cylinder crankshaft in this embodiment;

[0031] Figure 3 This is a side view of the original three-cylinder crankshaft bending die and the bar stock being clamped together.

[0032] Figure 4 This is an end view of the original three-cylinder crankshaft bending die and the bar stock when they are clamped together.

[0033] Figure 5This is a schematic diagram of the original upper mold structure;

[0034] Figure 6 This is a schematic diagram of the original lower mold structure;

[0035] Figure 7 This is a side view of the three-cylinder crankshaft bending die in Embodiment 1.

[0036] Figure 8 for Figure 7 Sectional views at points AA, BB, and CC;

[0037] Figure 9 This is a cross-sectional view of the original three-cylinder crankshaft bending die at the three connecting rod necks;

[0038] Figure 10 This is a schematic diagram showing the grain size and distribution of the three-cylinder crankshaft connecting rod neck prepared in this embodiment;

[0039] Figure 11 A comparative diagram showing the material flow area in the core of the bar stock before and after optimization of the three-cylinder crankshaft bending die;

[0040] Figure 12 Figures showing the grain size results of various parts of the three-cylinder crankshaft before and after optimization of the bending die;

[0041] Figure 13 A schematic diagram comparing the grain size of a three-cylinder crankshaft before and after optimization of the bending die;

[0042] Figure 14 Graphs showing the flow and process analysis of the core material of a three-cylinder crankshaft before and after optimization of the bending die;

[0043] Figure 15 A comparative analysis of the forming process of a three-cylinder crankshaft before and after optimization of the bending die.

[0044] In the diagram: 1a, upper die; 1b, lower die; 11a, first overflow outlet; 11c, second overflow outlet; 12b, stepped step; 2, three-cylinder crankshaft; 21, connecting rod journal; 21a, first connecting rod journal; 21b, second connecting rod journal; 21c, third connecting rod journal; 22, flange end; 23, small end; 24, balance block; 25, main journal; 10, three-cylinder crankshaft bending die; 30, original three-cylinder crankshaft bending die; 3a, original upper die; 3b, original lower die; 31, longitudinal groove; 32, groove portion; 33, second protrusion portion; 34, first protrusion portion; 4, bar stock. Detailed Implementation

[0045] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0046] Several forms of the three-cylinder crankshaft 2 provided in the embodiments of the present invention are as follows: Figure 1 As shown, the middle part is the main journal 25, one end of the main journal 25 is an enlarged flange end 22, and the other end is a small end 23 with a reduced diameter. Three connecting rod journals 21 are arranged at intervals along the length of the main journal 25. The projection of the three connecting rod journals 21 in the plane perpendicular to the main journal 25 is evenly distributed in a circumferential direction. The two connecting rod journals 21 at both ends are respectively provided with balance blocks 24 on both sides of their slots. The structure of the balance blocks is similar to a fan-shaped structure.

[0047] The existing three-cylinder crankshaft manufacturing process involves the following steps: bar heating (using an induction furnace) – bending (using the existing three-cylinder crankshaft bending die 30) – pre-forging – final forging. However, the existing three-cylinder crankshaft bending die 30 consists of an upper die and a lower die. Both the lower ends of the upper die 3a and the lower die 3b have longitudinal grooves 31 arranged along the front-to-back direction. These grooves 31 are aligned to press the bar stock placed along the front-to-back direction. A first protrusion 34 is located in the middle of the lower end of the upper die 3a along the left-to-right direction, and a groove 32 is located in the middle of the upper end of the lower die 3b along the left-to-right direction. The groove 32 is aligned with the first protrusion 34. In conjunction with this, the original lower die 3b has two second protrusions 33 in the middle along the left and right direction. The two second protrusions 33 are distributed at intervals along the front and back direction, and the groove 32 is located between the two second protrusions 33. At the same time, the two second protrusions 33 are slightly recessed downward at the position corresponding to the longitudinal groove 31. When the original upper die 3a presses down, it will bend the bar at the groove 32 and the first protrusion 34. The two second protrusions 33 will also slightly bend the corresponding part of the bar. The three bending points on the bar correspond to the three connecting rod necks later.

[0048] Example 1

[0049] This embodiment provides a three-cylinder crankshaft bending die, including an upper die 1a and a lower die 1b arranged horizontally in the front-back direction. The upper die 1a is located above the lower die 1b. The lower end of the upper die 1a is recessed with an upper die cavity arranged in the front-back direction, and the upper end of the lower die 1b is recessed with a lower die cavity arranged in the front-back direction. The upper die cavity and the lower die cavity are aligned vertically and together form the cavity. The upper die 1a and the lower die 1b are pressed together to bend the bar stock placed between them in the front-back direction into a three-cylinder crankshaft blank. The upper die cavity and the lower die cavity are expanded at the three connecting rod necks of the three-cylinder crankshaft blank. This makes the material at the three connecting rod necks more compacted due to the presence of the upper die cavity and the lower die cavity under the extrusion of the upper die and the lower die.

[0050] In the above technical solution, the three connecting rod necks of the three-cylinder crankshaft blank, from the flange end 22 to the small end 23, are respectively the first connecting rod neck 21a, the second connecting rod neck 21b, and the third connecting rod neck 21c. The cavity has the same structure corresponding to the first connecting rod neck 21a and the second connecting rod neck 21b, but the projections of the two on the corresponding vertical planes in the left and right directions are symmetrically distributed. This makes the first connecting rod neck and the third connecting rod neck of the three-cylinder crankshaft blank have the same shape, and the material density is similar.

[0051] In the above technical solution, the cavity is provided with a first overflow outlet 11a on the right side corresponding to the first connecting rod neck 21a, and the cavity is provided with a second overflow outlet 11c on the left side corresponding to the third connecting rod neck 21c, so that the excess material at the first connecting rod neck and the second connecting rod neck can overflow through the first overflow outlet and the second overflow outlet respectively.

[0052] In the above technical solution, the expansion depth of the upper and lower mold cavities corresponding to the right side of the first connecting rod neck 21a is greater than the expansion depth of the left side, and the expansion depth of the upper and lower mold cavities corresponding to the left side of the third connecting rod neck 21c is greater than the expansion depth of the right side. This makes the thickness of the side of the first connecting rod neck and the second connecting rod neck that is far apart from each other greater, and the material is more concentrated, which is beneficial to the subsequent pre-forging and final forging.

[0053] In the above technical solution, the expansion width of the upper and lower die cavities corresponding to the first connecting rod neck 21a on the left is greater than the expansion width of the right side of the upper die cavity and the expansion width of the upper and lower die cavities corresponding to the third connecting rod neck 21c on the right is greater than the expansion width of the left side of the upper die cavity and the lower die cavity. This makes the width of the side of the first connecting rod neck and the second connecting rod neck that are close to each other larger, which is beneficial to the subsequent pre-forging and final forging.

[0054] In the above technical solution, the cavity corresponding to the second connecting rod neck 21b is closed on both the left and right sides, so that when the bar stock is squeezed by the upper and lower dies, the material corresponding to the second connecting rod neck will flow to the first connecting rod neck and the third connecting rod neck.

[0055] The cross-section of the upper and lower mold cavities in the above technical solution is a concave arc-shaped cavity, which has a simple structure and good preforming effect.

[0056] In the above technical solution, the closing points on the left and right sides of the upper mold 1a and lower mold 1b corresponding to the second connecting rod neck 21b are mutually fitted stepped steps 12b, so that when the upper mold and lower mold are in contact with each other, the stepped steps on both sides can limit the upper mold and lower mold to the left and right.

[0057] Because the three-cylinder crankshaft bending die provided in this embodiment has changed the structure of the three connecting rod necks in the cavity compared to the original three-cylinder crankshaft bending die, it can be specifically seen that... Figure 8(after improvement) and Figure 9 (Before Improvement) In the improved three-cylinder crankshaft bending die, when bending the bar stock, the material corresponding to the second connecting rod neck is shaped upwards, and the core material also flows towards the upper die. However, due to the increased volume at the first and third connecting rod necks, the bar stock at these locations experiences greater radial flow after being squeezed by the upper and lower dies, leaving more core material remaining at the first and third connecting rod necks. This prepares the material volume for subsequent pre-forging and final forging, resulting in less core material flowing to the second connecting rod neck. In addition, combined with the change in the direction of the second connecting rod neck, the volume of core material on the inner side or surface of the three connecting rod necks is reduced until the upper and lower dies reach the process closing height. The three-cylinder crankshaft bending die provided in this embodiment can reduce the volume of core material (due to the high impurity content and poor quality of the bar stock core material) flowing to or remaining on the inner side and surface of the connecting rod neck, thereby improving the grain size grade at the connecting rod neck, thus improving the mechanical properties of key parts at the connecting rod neck, and reducing the probability of surface cracks or fractures on the connecting rod neck surface. Since the core material of the bar stock is basically formed at each connecting rod neck during the bending process, the subsequent pre-forging and final forging have little impact on this specific part.

[0058] Based on the actual production process of the three-cylinder crankshaft, experiments and grain evolution simulation analysis were conducted. Samples were taken from the fracture crack area (the area where the core material flows to near the parting surface) and normal parts (middle and outer) in the connecting rod neck section of the three-cylinder crankshaft forging. The average grain size and microstructure of each sampling part were observed and compared with the finite element simulation results. Figure 10 The results and distribution of grain size evolution in the inner, middle and outer parts of each connecting rod neck of the three-cylinder crankshaft forging are shown. The microstructure of the crack in the non-quenched and tempered steel three-cylinder crankshaft is mainly pearlite and ferrite. Figure 10 (a) Comparison results of the first connecting rod journal of the three-cylinder crankshaft. The average grain size of the core material region (near the surface crack) is 151 μm, which does not meet the production process requirements (≤127 μm, grain size grade 3). At the same time, local mixed crystal phenomenon occurs, with large grain size areas (red areas) flowing to the inner side and surface of the connecting rod journal, while the average grain size of the middle and outer sides of the connecting rod journal are 112 μm and 63 μm, respectively, which meet the process requirements. Furthermore; Figure 10 (c) The average grain size at the crack in the third connecting rod neck is 148 μm (grain size grade 2.5), which does not meet the process requirements. The grain size is large and flows to the inner side of the connecting rod neck and even to the surface. In contrast, the average grain size in the middle and outer parts of the connecting rod neck is 112 μm and 75 μm, respectively, which meets production requirements. Combining the grain size results of the first connecting rod neck, it can be seen that the grain distribution of the first and third connecting rod necks is consistent. The inner sides of both the first and third connecting rod necks are also prone to crack defects. Furthermore... Figure 10(b) The grain size of the central material region is 147 μm, but the large grains did not flow to the connecting rod neck surface, and the average grain size of the central and outer parts is 102 μm and 31 μm, respectively, indicating that the grain size of the central material of the crankshaft forging flows to the region is relatively large.

[0059] The forging process for non-quenched and tempered steel three-cylinder crankshafts mainly includes medium-frequency heating, pre-forming bending, pre-forging, and final forging (subsequent processes include trimming, temperature-controlled cooling, and stacking cooling). This embodiment mainly optimizes the cavity structure of the three-cylinder crankshaft bending die. Since the three-cylinder crankshaft bending die is an independent die in the forging process of the three-cylinder crankshaft, it mainly achieves the pre-forming function of key or complex parts. Preforming can reduce the deformation of the three-cylinder crankshaft blank during the pre-forging process, ensuring that the pre-forging and final forging cavities are filled while reducing fatigue crack defects in the first and third connecting rod necks. Meanwhile, although the second connecting rod neck does not have core material outflow or crack defects, its pre-formed portion serves to position it for subsequent pre-forging and final forging. Therefore, this embodiment mainly optimizes the structure of the three connecting rod necks in the three-cylinder crankshaft bending die. Based on the inherent influence relationship between the pre-forming method of the three-cylinder crankshaft blank, the core material flow characteristics, and the grain size grade, the goal is to reduce the volume of core material at the inner parting surface of the connecting rod neck, thereby improving the grain size. The improved structure of the three-cylinder crankshaft bending die is as follows: Figure 7 and Figure 8 As shown, with Figure 9 Compared with the original three-cylinder crankshaft bending die, the improved three-cylinder crankshaft bending die structure controls the deformation at the three connecting rod necks and increases the volume of the cavity at the three connecting rod necks to store more bar stock. This is beneficial for crankshaft forming in the subsequent large deformation pre-forging stage, thereby achieving the purpose of controlling the flow characteristics of the bar stock core and improving the grain size.

[0060] The flow characteristics of the three-cylinder crankshaft core were simulated and analyzed using the finite element method with the bending die provided in this embodiment. Figure 11 The comparison of the flow area and volume of the core material at the connecting rod neck before and after adjustment of the bending die for a three-cylinder crankshaft forging shows that core material still flows to the inner side and surface of the first and third connecting rod necks, but more core material flows out of the crankshaft matrix, resulting in a relatively smaller volume of core material remaining inside the connecting rod necks. Simultaneously, the flow trend of the second connecting rod neck remains consistent with the previous state, with core material flowing to the inner side of the connecting rod neck but not to the crankshaft surface, resulting in a relatively smaller volume of core material. Based on this, it is shown that the three-cylinder crankshaft bending die provided in this embodiment can control the flow characteristics of the core material in the three-cylinder crankshaft blank through optimized preforming, thereby reducing the volume remaining or flowing to key parts of the crankshaft and improving the mechanical properties of the three-cylinder crankshaft.

[0061] Finite element simulation analysis of grain evolution was performed using the same forging process (bending, pre-forging, and final forging). Figure 12 The analysis results of grain size at various parts of the three-cylinder crankshaft using the bending die of this design show that the grain size of the inner, middle, and outer sides of the first connecting rod journal section is approximately 122 μm, 119 μm, and 99.7 μm, respectively; the grain size of the inner side of the second connecting rod journal is approximately 113.3 μm, the middle area is approximately 110.7 μm, and the outer part is approximately 94.2 μm; while the inner, middle, and outer parts of the third connecting rod journal are 125 μm, 119 μm, and 105.3 μm, respectively; and the grain size of the key parts (outer side of the first connecting rod journal, main journal, and flange end) tested according to the actual crankshaft production process requirements are 99.7 μm, 113.7 μm, and 97 μm, respectively.

[0062] To better compare the grain size and distribution before and after optimization, and to analyze the influence of core flow characteristics on grain size, the forging results of three-cylinder crankshaft blanks prepared by the original three-cylinder bending die and the improved three-cylinder bending die under the same process are compared. Figure 13 As shown, on the one hand, the optimized grain size of all connecting rod neck inner sides (the area where the core material flows and where fatigue cracks occur) of the three-cylinder crankshaft blank is relatively reduced due to the decrease in the volume content of the core material, which can appropriately improve the mechanical properties of this part and reduce the probability of crack initiation. Although the size of the middle and outer sides tends to increase, the overall grain size of each test part meets the production process requirement of less than 127μm (grain size level 3). On the other hand, the grain size of the connecting rod neck section of the original three-cylinder crankshaft bending die structure has a large gradient from the inside to the outside and the stratification is more obvious. However, the grain size of the three-cylinder crankshaft blank prepared by the improved three-cylinder crankshaft bending die in this embodiment has a more stable zigzag change, indicating that the overall grain size is more uniform and the mixed crystal phenomenon is reduced. Figure 13 (d) Based on the grain size results of the actual production and testing parts of the three-cylinder crankshaft blank, it can be seen from the figure that the optimized grain size is larger, but still meets the production requirements of grain size level 3. Combined with the above analysis results, it shows that the three-cylinder crankshaft bending die of this embodiment can affect the forging deformation and core material flow characteristics of the three-cylinder crankshaft blank. The reduction of core material volume will appropriately increase the grain size level of the corresponding part of the crankshaft matrix. The core material flow characteristics can be optimized by adjusting the preforming method to improve the grain size level, thereby improving the effectiveness of the mechanical properties of the three-cylinder crankshaft blank and providing guidance for actual production practice.

[0063] in, Figure 13 Figure (a) corresponds to the first link neck, Figure (b) corresponds to the second link neck, Figure (c) corresponds to the third link neck, and Figure (d) corresponds to the key part.

[0064] Example 2

[0065] This embodiment provides a method for machining a three-cylinder crankshaft, including the following steps:

[0066] Step 1: Heat the non-quenched and tempered steel bar to the set temperature (1200℃) using medium frequency induction heating;

[0067] Step 2: Place the bar stock processed in Step 1 on the three-cylinder crankshaft bending die 10 as described in Example 1 and bend it to obtain a three-cylinder crankshaft blank;

[0068] Step 3: Place the three-cylinder crankshaft blank obtained in Step 2 on a pre-forging die for pre-forging treatment, and obtain a three-cylinder crankshaft pre-product;

[0069] Step 4: Place the three-cylinder crankshaft preform obtained in Step 3 on the final forging die for final forging, and then perform edge trimming and cooling to finally obtain the finished three-cylinder crankshaft. This method has high processing efficiency, and the upper and lower dies can make the material at the three connecting rod necks of the three-cylinder crankshaft more compact when bending the bar stock. It also has good forming effect during pre-forging and final forging.

[0070] In the above technical solution, the pressing speed of the three-cylinder crankshaft bending die 10, the pre-forging die and the final forging die is 600-650 mm / s (preferably 630 mm / s), so that the impact force of the three-cylinder crankshaft bending die 10, the pre-forging die and the final forging die is moderate at the corresponding pressing speed.

[0071] The process of processing a three-cylinder crankshaft using the existing three-cylinder crankshaft bending die is as follows: The bar stock is heated to 1200℃ by medium-frequency induction heating for 3 minutes, and then conveyed to the existing three-cylinder crankshaft bending die by a conveyor belt for about 14 seconds. The existing upper die is forged towards the existing lower die by the forging press at a speed of about 630 mm / s, squeezing the bar stock until the distance between the surfaces of the existing upper and lower dies reaches the closed height, achieving the pre-forming purpose. Then, the crankshaft is manually clamped for about 2 seconds to change the die, and the three-cylinder crankshaft is bent. The crankshaft blank is clamped into the pre-forging die. The pre-forging die also reaches the closed height at a speed of 630 mm / s and extrudes the three-cylinder crankshaft blank. The bar fills the cavity of the pre-forging die. After the pre-forging die is opened, the three-cylinder crankshaft pre-product is obtained. The three-cylinder crankshaft pre-product is clamped and changed in 2 seconds and placed in the final forging die. The final forging die also reaches the closed height at a speed of 630 mm / s and extrudes the three-cylinder crankshaft pre-product. The pre-forging die is opened, and the three-cylinder crankshaft finished product is obtained. It can then undergo subsequent edge trimming, cooling and other processes.

[0072] The process of processing a three-cylinder crankshaft using the three-cylinder crankshaft bending die provided in this embodiment differs from the original three-cylinder crankshaft bending die processing process described above in that the three-cylinder crankshaft pre-product needs to be rotated 180° axially when placed in the pre-forging die.

[0073] By optimizing the cavity structure of the three-cylinder crankshaft bending die, this embodiment changes the cavity volume and pre-deformation amount at the first and third connecting rod necks. During the pressing of the upper and lower dies of the three-cylinder crankshaft bending die, the flow characteristics of the bar stock material can be altered, thereby changing the grain size grade of the corresponding parts. The specific reasons and advantages are discussed below: Figure 14 As shown in (a), the three-cylinder crankshaft blank bent using the three-cylinder crankshaft bending die of this embodiment needs to be rotated 180° axially before subsequent pre-forging. The three-cylinder crankshaft blank prepared by the original three-cylinder crankshaft bending die has a large warping angle at the second connecting rod neck, a downward forming direction, and a large bending depth, resulting in a large amount of bar stock from both sides concentrating towards the second connecting rod neck, causing a large volume of core material in this area. The three-cylinder crankshaft bending die of this embodiment allows the deformation at the second connecting rod neck to meet the forging position requirements for positioning the pre-forging section, while also causing the bar stock to form towards the upward die direction, making it difficult for core material to flow to the second connecting rod neck. In addition, it increases the pre-forming amount at the first and third connecting rod necks, causing more bar stock to be formed radially, thereby preventing more bar stock from flowing towards the area of ​​the second connecting rod neck, resulting in an elongated bar stock length after bending, thus reducing the volume of core material at the second connecting rod neck.

[0074] Figure 14 (b) To compare the flow results and forming directions at the core of each connecting rod neck section with the original three-cylinder crankshaft bending die and the three-cylinder crankshaft bending die of this embodiment, it is explained that while the volume of the material region at the core of the second connecting rod neck section in this embodiment is reduced, it is also relatively far from the surface of the forging. Since the deformation of the second connecting rod neck is relatively small in the subsequent forging process, the core material at this location is less likely to flow to the surface of the crankshaft connecting rod neck. In addition, the bending forming direction of the second connecting rod neck in the original three-cylinder crankshaft bending die is consistent with the subsequent pre-forging and final forging forming trend, while the bending forming directions of the first and third connecting rod necks are approximately 90° to the subsequent forming direction at this location. However, the subsequent forming direction of the connecting rod neck section of the three-cylinder crankshaft blank prepared by the three-cylinder crankshaft bending die provided in this embodiment is the same as the bending forming direction. This makes the bar stock flow relatively stable during the forging process of the connecting rod neck of the three-cylinder crankshaft, and also results in a more regular microstructure and grain arrangement, which is conducive to uniform grain distribution and reorganization and growth, thereby obtaining a higher grain size grade.

[0075] Figure 15This diagram illustrates the flow of core material in the first and third connecting rod necks of a three-cylinder crankshaft during the pre-forging and final forging process. In the original three-cylinder crankshaft bending die, the core material cross-section of the three-cylinder crankshaft blank was approximately circular at the beginning and early stages of pre-forging. However, the core material cross-section of the three-cylinder crankshaft blank corresponding to the improved three-cylinder crankshaft bending die in this embodiment is a flattened elliptical shape. The entire bar stock is pushed and forged through the die to the connecting rod neck cavity for forming, with excess waste forming flash and being discharged. The main reason for this is that the pre-forging and final forging dies contain a umbilicus structure at the first and third connecting rod necks [see physical example]. Figure 15 Figures (a) and (b) Figure 15 [Figure (a) shows the first connecting rod neck and Figure (b) shows the third connecting rod neck]. The protruding navel structure first contacts the bar stock during forging, causing excessive material reduction in the three-cylinder crankshaft blank at this point, which easily leads to fatigue defects and affects the forming quality. Combined with the forming flow direction of the connecting rod neck, the flat core material of the three-cylinder crankshaft blank in this embodiment can be left in excess or formed in the flash structure during pre-forging, which reduces the volume of material flowing to the inside of the connecting rod neck and makes it easier to be discharged with the flash at the navel. However, the circular cross-section structure of the original three-cylinder crankshaft bending die before the improvement causes a large amount of core material to be squeezed into the inside of the connecting rod neck during pre-forging. During the final forging process, it is not easy to be discharged due to the influence of the navel structure and tends to accumulate on the inside and the surface of the forging.

[0076] In the accompanying drawings, "before mold optimization", "before bending mold optimization" or "before bending mold optimization" all refer to the three-cylinder crankshaft blanks or finished products prepared using the original three-cylinder crankshaft bending mold, while "after bending mold optimization" or "after bending mold optimization" all refer to the three-cylinder crankshaft blanks or finished products prepared using the three-cylinder crankshaft bending mold provided in this embodiment.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A three-cylinder crankshaft bending die, comprising an upper die (1a) and a lower die (1b) horizontally arranged in the front-rear direction, wherein the upper die (1a) is located above the lower die (1b), the lower end of the upper die (1a) is recessed with an upper die cavity arranged in the front-rear direction, and the upper end of the lower die (1b) is recessed with a lower die cavity arranged in the front-rear direction, wherein the upper die cavity and the lower die cavity are aligned vertically and together form a cavity, the upper die (1a) and the lower die (1b) are pressed together to bend a bar stock placed between them in the front-rear direction into a three-cylinder crankshaft blank, characterized in that, The upper and lower mold cavities are expanded at the three connecting rod necks corresponding to the three-cylinder crankshaft blank. The three connecting rod necks of the three-cylinder crankshaft blank are, from the flange end (22) to the small end (23), the first connecting rod neck (21a), the second connecting rod neck (21b) and the third connecting rod neck (21c) respectively. The cavity has the same structure corresponding to the first connecting rod neck (21a) and the third connecting rod neck (21c), but the projections of the two on the vertical planes corresponding to the left and right directions are symmetrically distributed. The cavity is provided with a first overflow outlet (11a) on the right side corresponding to the first connecting rod neck (21a), and the cavity is provided with a second overflow outlet (11c) on the left side corresponding to the third connecting rod neck (21c). The expansion depth of the upper and lower mold cavities on the right side of the first connecting rod neck (21a) is greater than the expansion depth on the left side, and the expansion depth of the upper and lower mold cavities on the left side of the third connecting rod neck (21c) is greater than the expansion depth on the right side. The expansion width of the upper and lower mold cavities on the left side corresponding to the first connecting rod neck (21a) is greater than the expansion width on the right side, and the expansion width of the upper and lower mold cavities on the right side corresponding to the third connecting rod neck (21c) is greater than the expansion width on the left side.

2. The three-cylinder crank press bending die according to claim 1, characterized in that, The cavity is closed on both the left and right sides corresponding to the second connecting rod neck (21b).

3. The three-cylinder crank press bending die of claim 2, wherein, The cross-sections of the upper and lower mold cavities are concave arc-shaped cavities.

4. The three-cylinder crank press bending die of claim 2, wherein, The upper mold (1a) and lower mold (1b) have mutually fitting stepped steps (12b) at the left and right closing points corresponding to the second connecting rod neck (21b).

5. A method for machining a three-cylinder crankshaft, characterized in that, Includes the following steps: Step 1: The non-quenched and tempered steel bar is heated to the set temperature by medium frequency induction heating; Step 2: Place the bar stock processed in Step 1 on the three-cylinder crankshaft bending die (10) as described in any one of claims 1-4 and bend it to obtain a three-cylinder crankshaft blank; Step 3: Place the three-cylinder crankshaft blank obtained in Step 2 on a pre-forging die for pre-forging treatment, and obtain a three-cylinder crankshaft pre-product; Step 4: Place the three-cylinder crankshaft preform obtained in Step 3 on the final forging die for final forging, and then trim and cool it to finally obtain the finished three-cylinder crankshaft.

6. The three-cylinder crankshaft machining method according to claim 5, characterized in that, The pressing speed of the three-cylinder crankshaft bending die (10), the pre-forging die and the final forging die is 600-650 mm / s.

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