Method for the production of mechanical parts by means of a direct transfer die casting and mechanical part

Abstract

The application provides a method for manufacturing mechanical parts by using a direct transfer die casting die forging and the mechanical part. According to the structure size of a final forging blank, a die casting blank with a deformation of not less than 30% in a die forging process is designed through simulation analysis of the die forging process; the die casting blank is obtained by using a die casting die; when the die casting blank is demolded, the temperature of the die casting blank is in a preset demolding temperature window; the die casting blank after demolding is directly transferred to a die forging die within a preset transfer time window, and the die casting blank is not actively heated in the transfer process; the demolding temperature window and the transfer time window are determined in advance according to the wall thickness of the die casting blank and the temperature drop rate of the die casting blank in air, so that the die casting blank is naturally cooled to a preset die forging temperature window in the transfer process; and the die casting blank is formed by final forging by using a die forging die which is independent of the die casting die in the die forging temperature window. The application has the advantages of double improvement of material mechanical properties and product shape, energy saving and the like.

Description

Technical Field

[0001] This invention relates to the field of parts manufacturing technology, and more particularly to a method for manufacturing mechanical parts by die casting and direct feeding forging, as well as the mechanical parts themselves. Background Technology

[0002] Die casting is suitable for producing complex-shaped aluminum or magnesium alloy parts and yields good mechanical properties, while forging can achieve even higher mechanical properties. To combine the advantages of both, attempts have been made to integrate die casting and forging in existing technologies. For example, an integrated die casting and forging machine can be used to complete both die casting and forging sequentially within the same mold; or the die-cast part can be cooled and then reheated for forging. However, in integrated die casting and forging machines, the forging mold is subjected to high die casting temperatures (approximately 700°C in aluminum alloy production) for extended periods, leading to a significant reduction in mold life. Furthermore, the method of cooling before heating is not only energy-intensive and inefficient but also increases equipment investment and production cycle time.

[0003] Therefore, in the combined production of die casting and forging, how to avoid the forging mold from being subjected to the high temperature of die casting without additional heating, while effectively utilizing the residual heat of die casting, has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this application is to provide a method for manufacturing mechanical parts via die casting and direct feeding forging, as well as the mechanical parts themselves. This at least solves the problem of how to avoid the forging die being subjected to the high temperatures of die casting without additional heating, while effectively utilizing the residual heat from die casting.

[0005] On the one hand, a method for manufacturing mechanical parts by die casting and direct feeding forging is provided. Based on the final forging billet structure and dimensions, the structure and dimensions of the die casting billet with a deformation of not less than 30% during the forging process are determined through simulation analysis of the forging process. Die casting is performed using die casting molds to obtain die casting blanks; When the die-cast billet is demolded, its temperature is kept within a preset demolding temperature window; After demolding, the die-casting billet is directly transferred to the forging die within a preset transfer time window, without actively heating the die-casting billet during the transfer process; The demolding temperature window and the transfer time window are predetermined based on the wall thickness of the die-casting billet and its temperature drop rate in air, so that the die-casting billet naturally cools down to the preset forging temperature window during the transfer process. Within the forging temperature window, the die-cast billet is forged into its final shape using a forging die that is independent of the die-casting die.

[0006] In one optional embodiment, the pre-determination of the demolding temperature window and the transfer time window includes the following steps: Obtain the three-dimensional model of the final forging of the mechanical part to be manufactured, ensure the shape and size of the die-casting billet with a deformation amount of not less than 30% during the die forging process, and obtain the minimum wall thickness t_min of the die-casting billet. Based on the material thermophysical parameters of the die-cast billet, cooling experiments were conducted on samples with different wall thicknesses in an air environment, and the temperature drop rate function v(T,d) was obtained by fitting. Set the lower limit T_forge_low and the upper limit T_forge_high of the forging temperature window, and the upper limit Δt_max of the transfer time window; Solve for the range of values ​​of T_demold that allow the die-cast billet to cool from the demolding temperature T_demold to within the interval [T_forge_low, T_forge_high] during the transition time Δt≤Δt_max, and use this range as the demolding temperature window.

[0007] In one optional embodiment, the lower limit of the demolding temperature window is higher than the upper limit of the forging temperature window, and the temperature difference between the two is 30°C to 50°C; the upper limit of the transfer time window is no more than 15 seconds.

[0008] In one optional embodiment, the demolding temperature window is 460℃~510℃, the forging temperature window is 415℃~465℃, the transfer time window is ≤15 seconds, and the temperature drop during the transfer process is ≤45℃.

[0009] In one optional embodiment, ensuring that the temperature of the die-cast billet is within a preset demolding temperature window during demolding includes: A conformal cooling water channel is arranged inside the die-casting mold, and an electric regulating valve is installed at the inlet of the water channel; Temperature sensors are installed on the surface of the die-casting mold cavity to monitor the temperature of the die-casting billet in real time. When the temperature approaches the lower limit of the demolding temperature window, reduce the flow rate of the cooling medium or stop cooling. When the measured temperature falls within the demolding temperature window, the demolding action is executed.

[0010] In an optional embodiment, the method further includes the step of pre-setting a positioning protrusion or positioning recess on the non-forging load-bearing surface of the die-casting billet, and the step of setting a matching positioning structure on the lower die of the forging mold. When the die-casting billet is transferred to the forging die, the positioning protrusion or positioning recess cooperates with the positioning structure to achieve automatic centering and positioning of the die-casting billet.

[0011] In an optional embodiment, the method further includes the step of providing a temperature control structure on the die-cast billet, the temperature control structure comprising at least one of the following: Weight reduction grooves or holes are opened in the thick-walled areas of the die-cast billet to accelerate the cooling of that area; Temporary ribs are provided in the thin-walled areas of the die-cast billet to slow down the cooling of that area; The temporary ribs are crushed during the forging process, and the temperature control structure is used to homogenize the cooling rate of the die-cast billet during the transfer process.

[0012] In an optional embodiment, during the die forging step, no lubricant is sprayed on the surface of the die-cast billet, but only on the surface of the die forging die; and the die forging speed is controlled within the range of 5 mm / s to 50 mm / s, using medium-low speed die forging.

[0013] In one alternative embodiment, a temperature detection step is further included after the die-cast billet is transferred to the forging die and before final forging: Infrared thermometers were used to measure the temperature at multiple points on the surface of the die-cast billet. If the measured temperature is higher than the upper limit of the forging temperature window, the forging process will be paused and an alarm signal will be issued.

[0014] In another aspect, a mechanical part is provided, which is manufactured using the method described in any of the preceding methods.

[0015] The method provided in this application achieves direct, unheated transfer from die casting to forging by pre-setting a demolding temperature window and a transfer time window, and by utilizing the physical relationship between the wall thickness of the die-cast billet and the rate of temperature drop. On the one hand, the elimination of a reheating process saves investment in heating equipment and energy consumption; on the other hand, the die-casting mold and the forging mold are independent of each other, with the forging mold only contacting the billet cooled to approximately 400°C, avoiding prolonged exposure to high temperatures and significantly extending the lifespan of the forging mold. Therefore, the method provided in this application simultaneously solves two key problems: the need for additional heating and the vulnerability of forging molds to high temperatures. Furthermore, the die-casting process yields a casting billet with relatively fewer defects, offering a significant advantage over billets obtained through ordinary casting. Immediately forging the die-cast billet further improves the shortcomings of poorly dense casting structure, low impact resistance, and numerous pores, thereby obtaining a high-performance final product. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the method for manufacturing mechanical parts by die casting and direct forging according to an embodiment of this application.

[0017] Figure 2 This is a schematic diagram showing the structure and dimensions of a die-cast part prepared using the method provided in the embodiments of this application.

[0018] Figure 3 This is a schematic diagram showing the structure and dimensions of a mechanical part prepared using the method provided in the embodiments of this application.

[0019] Figure 4 This is a schematic diagram showing the structure and dimensions of a die-cast part before forging, prepared using the method provided in the embodiments of this application.

[0020] Figure 5 This is a schematic diagram showing the structure and dimensions of a forged mechanical part prepared using the method provided in the embodiments of this application. Detailed Implementation

[0021] Various embodiments and features of this application are described herein with reference to the accompanying drawings.

[0022] It should be understood that various modifications can be made to the embodiments described herein. Therefore, the above description should not be considered as limiting, but merely as an example of embodiments. Other modifications within the scope and spirit of this application will be apparent to those skilled in the art.

[0023] The accompanying drawings, which are included in and form part of this specification, illustrate embodiments of the present application and, together with the general description of the present application given above and the detailed description of the embodiments given below, serve to explain the principles of the present application.

[0024] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.

[0025] Please see Figure 1 This invention provides a method for manufacturing mechanical parts by die casting and direct forging, including: step S1, determining the structure and dimensions of the die casting billet with a deformation of not less than 30% during the die forging process based on the final forging billet structure dimensions through simulation analysis of the die forging process.

[0026] Step S2: Use a die-casting mold to perform die casting to obtain a die-cast billet.

[0027] Step S3: When demolding the die-cast billet, ensure that its temperature is within the preset demolding temperature window.

[0028] Step S4: Transfer the demolded die-casting billet directly to the forging die within a preset transfer time window, without actively heating the die-casting billet during the transfer process.

[0029] The demolding temperature window and the transfer time window are predetermined based on the wall thickness of the die-cast billet and its temperature drop rate in the air, so that the die-cast billet naturally cools down to the preset forging temperature window during the transfer process.

[0030] Step S5: Within the forging temperature window, the die-cast billet is forged into its final form using a forging die independent of the die-casting die (resulting in the final part, i.e., the mechanical part of this invention). Figure 2 As shown.

[0031] The method provided in this application achieves direct, unheated transfer from die casting to forging by pre-setting a demolding temperature window and a transfer time window, and by utilizing the physical relationship between the wall thickness of the die-cast billet and the rate of temperature drop. On the one hand, the elimination of a reheating process saves investment in heating equipment and energy consumption; on the other hand, the die-casting mold and the forging mold are independent of each other, with the forging mold only contacting the billet that has cooled to approximately 400°C, avoiding prolonged exposure to high temperatures and significantly extending the lifespan of the forging mold. Therefore, the method provided in this application simultaneously solves two key problems: the need for additional heating and the vulnerability of forging molds to high temperatures.

[0032] Please see Figure 4 In step S1, based on the final forging billet structure dimensions, the die-casting billet structure and dimensions with a deformation amount of not less than 30% during the die forging process are determined through simulation analysis of the die forging process.

[0033] In one optional embodiment, the shape and dimensions of the die-cast billet are determined by the following steps: Step S1: Obtain the 3D model of the final forging and calculate the total volume V_forge of the final forging based on the principle of constant volume. In metal plastic forming, the material volume remains essentially constant (density changes are ignored). Therefore, the volume of the final forging is equal to the volume of the die-cast billet.

[0034] Step S2: Set the volume distribution coefficient for the die forging process. Based on the required reduction of section ratio for each part of the final forging, distribute V_forge in reverse to the corresponding parts of the die-casting billet to obtain the preliminary volume distribution of the die-casting billet. Different parts of the final forging require different amounts of deformation during the die forging process. For example, load-bearing parts with high mechanical performance requirements require greater deformation (e.g., 50%), while simple connection parts allow for smaller deformation (e.g., 30%). Calculate the volume of each part of the die-casting billet in reverse according to the reduction of section ratio requirements.

[0035] Step S3: Perform finite element simulation of the forging process, aiming at deformation uniformity. Adjust the local shape of the die-cast billet to ensure that the equivalent strain of each part during forging is ≥30%, and the ratio of maximum strain to minimum strain is ≤1.5. Use plastic forming simulation software such as Deform and Forge to import the preliminary die-cast billet model and the final forging die model, and set parameters such as forging temperature (e.g., 440℃), friction coefficient (e.g., 0.3), and forging speed (e.g., 20mm / s). After running the simulation, extract the equivalent strain of each node of the billet. The equivalent strain of all nodes should be ≥0.3 (i.e., 30%), and the strain distribution should be uniform (maximum / minimum ≤1.5). If these requirements are not met, adjust the local shape of the die-cast billet, for example, by adding protrusions (to provide more material) in areas of insufficient deformation or adding pits (to reduce material) in areas of excessive deformation, until the constraints are met.

[0036] Step S4: Output the three-dimensional model of the die-casting billet that satisfies the above constraints.

[0037] In step S3, when the die-cast billet is demolded, its temperature is kept within a preset demolding temperature window.

[0038] When demolding the die-cast billet, its temperature is kept within a preset demolding temperature window. The demolding temperature window is a temperature range calculated in advance based on subsequent process requirements, ensuring that the billet has sufficient heat for subsequent natural cooling at the moment of demolding.

[0039] In step S4, the die-casting billet after demolding is directly transferred to the forging mold within a time window not exceeding the preset transfer time window, and the die-casting billet is not actively heated during the transfer process.

[0040] After demolding, the die-cast billet is directly transferred to the forging die within a preset transfer time window. During the transfer process, the die-cast billet is not actively heated (i.e., no external heat source such as a heating furnace or induction heating is used). The transfer time window is a maximum allowable transfer duration, such as 10 seconds or 15 seconds.

[0041] Please see Figure 5 In step S5, within the forging temperature window, the die-casting billet is forged into its final shape using a forging die that is independent of the die-casting die.

[0042] The demolding temperature window and transfer time window are predetermined based on the wall thickness of the die-cast billet and its temperature drop rate in air. Specifically, aluminum alloys with different wall thicknesses cool at different rates in air. Temperature drop rate curves can be obtained through experiments or simulations, and then the parameter combination that falls exactly into the temperature range required for die forging after a certain demolding temperature and a certain transfer time can be calculated.

[0043] Within the forging temperature window, a forging die, independent of the die-casting die, is used to forge the final shape of the die-cast billet. An independent die means that the die-casting die does not bear the high pressure of forging, and the forging die does not bear the high temperature of die casting, thus avoiding the problem of a sudden decrease in the lifespan of the forging die in an integrated forging machine due to prolonged exposure to the approximately 700°C high temperature of die casting.

[0044] In one optional embodiment, the pre-determination of the demolding temperature window and the transfer time window includes the following steps: Obtain the three-dimensional model of the final forging of the mechanical part to be manufactured, determine its minimum wall thickness t_min, and set the wall thickness d of the die casting billet. For example, it can be set to satisfy d≥max(t_min,5mm).

[0045] For example, if the thinnest part of the final forging is 3mm, the die-cast billet wall thickness should be at least 5mm; if the thinnest part of the final forging is 4mm, the die-cast billet wall thickness should be at least 6mm. This is to ensure that the die-cast billet wall thickness is sufficient to make the temperature control during the indexing process easy, and also to ensure that the deformation during the die forging process is sufficient to guarantee the quality of the final product.

[0046] Based on the material thermophysical parameters of the die-cast billet, cooling experiments were conducted on samples with different wall thicknesses in an air environment, and the temperature drop rate function v(T,d) was obtained by fitting.

[0047] For example, for A356 aluminum alloy, temperature-time curves were recorded for samples with wall thicknesses of 5mm, 8mm, and 12mm, and regression analysis was used to obtain... Functions of the form.

[0048] Set the lower limit T_forge_low and the upper limit T_forge_high of the forging temperature window, and the upper limit Δt_max of the transfer time window.

[0049] For example, the forging temperature window is set to 415~465℃, and Δt_max = 15 seconds.

[0050] Solve for the range of values ​​of T_demold that allow the die-cast billet to cool from the demolding temperature T_demold to within the interval [T_forge_low, T_forge_high] during the transition time Δt≤Δt_max, and use this range as the demolding temperature window.

[0051] For example, calculations show that when T_demold is between 460 and 510°C, the temperature drops to the range of 415 to 465°C after 15 seconds of natural cooling.

[0052] As an example, in the production of a certain aluminum alloy control arm, the minimum wall thickness of the final forged part is 4mm, so the wall thickness of the die-cast billet is set to 6mm. A sample of A356 material is taken, and the cooling curve is recorded in air at 25℃. The curve is then fitted to obtain... The forging temperature window is set to 420~450℃, and the transfer time is capped at 10 seconds. The calculated demolding temperature needs to be between 465~495℃. Therefore, the demolding temperature should be controlled between 465~495℃ in subsequent production.

[0053] This method provides a quantifiable window determination process, avoiding the blindness of trial and error based on experience. Through cooling experiments and function fitting, the matching relationship between demolding temperature and transfer time can be accurately calculated for different materials and wall thicknesses, making the natural cooling to the forging temperature inevitable rather than accidental, thus improving the stability and repeatability of the process.

[0054] In one alternative embodiment, the lower limit of the demolding temperature window is higher than the upper limit of the forging temperature window, and the temperature difference between the two is 30°C to 50°C; the upper limit of the transfer time window is no more than 15 seconds.

[0055] The lower limit of the demolding temperature window is higher than the upper limit of the forging temperature window, with a temperature difference of 30°C to 50°C. For example, if the upper limit of the forging temperature window is 465°C, then the lower limit of the demolding temperature window is at least 495°C (temperature difference 30°C) to 515°C (temperature difference 50°C). This temperature difference ensures sufficient room for temperature drop during the transfer process.

[0056] The upper limit of the transfer time window is no more than 15 seconds. That is, the total time from the start of demolding to the start of forging shall not exceed 15 seconds. This time limit is set based on the typical temperature drop rate of thick-walled parts in air (approximately 2~3℃ / second), ensuring that the temperature drop is within the range of 30~50℃.

[0057] For example, the temperature difference can be selected as 30℃, 35℃, 40℃, 45℃, or 50℃; the maximum transfer time can be selected as 5 seconds, 8 seconds, 10 seconds, 12 seconds, or 15 seconds.

[0058] As an example, a production line produces aluminum alloy brackets with a wall thickness of 3mm, and the required forging temperature window is 430~460℃. According to this claim, the lower limit of the demolding temperature window is at least 460+30=490℃, and the upper limit is at least 490+temperature difference range (e.g., if 40℃ is taken, the upper limit is 530℃). The actual demolding temperature is controlled within 490~530℃. The transfer time is set to 12 seconds, and the measured temperature drop is approximately 38℃, which meets the requirements.

[0059] By limiting the relative temperature difference and time upper limit, the method of this application simplifies the constraint relationship between demolding temperature, transfer time, and forging temperature into an easily controllable parameter range. Producers do not need to perform complex calculations; they only need to ensure that the demolding temperature is 30-50°C higher than the required forging temperature and that the transfer is completed within 15 seconds to stably obtain a qualified forging temperature. This reduces the difficulty of process implementation and improves production efficiency.

[0060] In one optional embodiment, the demolding temperature window is 460℃~510℃, the forging temperature window is 415℃~465℃, the transfer time window is ≤15 seconds, and the temperature drop during the transfer process is ≤45℃.

[0061] This range of values ​​is determined based on the experimental data in the disclosure document (see Temperature Connection Table 1). Among them, the lower limit of the demolding temperature of 460℃ ensures that the billet will not be lower than 415℃ after cooling within 15 seconds; the upper limit of 510℃ ensures that the temperature will not be higher than 465℃ after cooling (maximum temperature drop of 45℃).

[0062] Temperature Connection Table 1

[0063] For example, the demolding temperature can be selected from 460℃, 470℃, 480℃, 490℃, 500℃, and 510℃; the forging temperature can be selected from 415℃, 425℃, 435℃, 445℃, 455℃, and 465℃; the transfer time can be selected from 5, 8, 10, 12, and 15 seconds; and the temperature drop can be selected from 30, 35, 40, and 45℃.

[0064] In one optional embodiment, ensuring that the temperature of the die-cast billet is within a preset demolding temperature window during demolding includes: A conformal cooling channel is arranged inside the die-casting mold (the shape of the channel is consistent with the outline of the casting), and an electric regulating valve is installed at the inlet of the channel; Temperature sensors (such as thermocouples or infrared sensors) are installed on the surface of the die-casting mold cavity to monitor the temperature of the die-casting billet in real time. When the temperature approaches the lower limit of the demolding temperature window, reduce the flow rate of the cooling medium or stop cooling. When the measured temperature falls within the demolding temperature window, the demolding action is executed.

[0065] As an example, a die-casting machine produces aluminum alloy shells, with the demolding temperature window set at 470~490℃. The billet temperature is approximately 700℃ immediately after die-casting. The control system automatically increases the cooling water flow rate from 5L / min to 15L / min for rapid cooling; when the temperature drops to 475℃, the flow rate is reduced back to 8L / min; when the temperature drops to 472℃, the system determines that the temperature has entered the window, issues a demolding signal, and the ejector pin actuates to complete the demolding.

[0066] The method provided in this application achieves precise control of the demolding temperature through real-time temperature feedback and dynamic adjustment of the cooling medium flow rate, avoiding demolding temperature deviations caused by fluctuations in the cooling rate (such as changes in ambient temperature and mold temperature). Compared with traditional timed demolding, the method provided in this application can adaptively adjust the cooling rate to ensure that the billet temperature falls within a preset window during each demolding, providing a reliable prerequisite for subsequent natural cooling to the forging temperature.

[0067] In one alternative embodiment, die casting is performed using a multi-station die casting machine, the multi-station including at least a mold closing die casting station, a mold opening and part removal station, a spraying station, and a mold temperature control station; and at the same time as mold opening and part removal, the gate and flash are removed.

[0068] In this application, the die casting process employs a multi-station die casting machine, which includes at least four stations: a mold closing die casting station for filling and solidifying molten metal; a mold opening and part removal station for opening the mold and removing the die casting blank; a spraying station for spraying release agent or lubricant into the mold cavity; and a mold temperature control station for heating or cooling the mold to maintain a stable mold temperature. Furthermore, during mold opening and part removal, a trimming device (such as an in-mold trimming blade) is used to remove the gate and flash, avoiding the need for a separate gate removal process later.

[0069] As an example, a four-station rotary die-casting machine has a 6-second dwell time at each station. Station 1 completes die casting and solidification; after the rotary table rotates, station 2 opens the mold, ejects the billet, and simultaneously the cutter removes the gate and flash; station 3 sprays release agent onto the mold cavity; station 4 maintains the mold temperature at 200°C by circulating hot water through a mold temperature controller. This cycle continues, producing one die-cast billet every 24 seconds, matching the cycle time of the forging machine (approximately 20-30 seconds).

[0070] This application utilizes a multi-station layout to allow auxiliary operations such as cooling, spraying, and part removal of the die-casting mold to run concurrently with the die-casting process, significantly improving the die-casting cycle time and thus matching the rhythm of the forging process, avoiding waiting time for the forging machine. Simultaneously, the in-mold trimming technology eliminates the subsequent gate removal process, reduces workpiece turnover and secondary clamping, further shortening the total time from die casting to forging, and facilitating temperature control.

[0071] In an optional embodiment, the method further includes the step of pre-setting a positioning protrusion or positioning recess on the non-forging load-bearing surface of the die-casting billet, and the step of setting a matching positioning structure on the lower die of the forging mold. When the die-casting billet is transferred to the forging die, the automatic centering and positioning of the die-casting billet is achieved through the cooperation of the positioning protrusions or positioning recesses and the positioning structure.

[0072] In this embodiment, positioning features (protrusions or recesses) are pre-set on the die-casting billet, and corresponding mating structures (recesses or protrusions) are set on the lower die of the forging mold. When the die-casting billet is placed on the forging mold, the positioning features and the mating structures automatically engage, realizing automatic centering and positioning of the die-casting billet in the horizontal direction without manual adjustment.

[0073] Positioning features should be placed on the non-forging load-bearing surface of the die-cast billet (i.e., the area that will not be subjected to the main deformation force during the forging process), or on the surface of the scrap material that will be removed by subsequent machining, so as not to affect the performance of the final part.

[0074] This method solves the problem of rapid and accurate placement of high-temperature billets on forging dies. Since die-cast billets remain above 400°C after demolding, precise alignment is difficult when placed manually or by a robotic arm. Through a pre-set positioning structure, alignment is achieved immediately upon placement, improving positioning accuracy (ensuring uniform deformation) and shortening transfer time (requiring no adjustment), which is beneficial for temperature control.

[0075] In one optional embodiment, the method further includes the step of providing a temperature control structure on the die-cast billet, the temperature control structure comprising at least one of the following: Weight reduction grooves or holes are opened in the thick-walled areas of the die-cast billet to accelerate the cooling of that area; Temporary ribs are provided in the thin-walled areas of the die-cast billet to slow down the cooling of that area; The temporary ribs are crushed during the die forging process, and the temperature control structure is used to homogenize the cooling rate of the die-cast billet during the transfer process.

[0076] This application incorporates a temperature control structure on the die-cast billet to homogenize the cooling rate of the billet during transfer. Two types are included: weight-reducing grooves or holes: these are formed in the thick-walled areas of the die-cast billet. These grooves / holes increase the heat dissipation area, allowing the thick-walled areas to cool faster and preventing their temperature from being significantly higher than that of the thin-walled areas. Temporary ribs: these are formed in the thin-walled areas of the die-cast billet. The ribs increase the local heat capacity and reduce the heat dissipation area, causing the thin-walled areas to cool more slowly and preventing premature cooling. During the forging process, the temporary ribs are flattened or undergo plastic deformation, integrating into the part body or flowing into the flash groove, without affecting the final product.

[0077] As an example, a die-cast billet has a wall thickness of 12mm in the central region and 5mm in the edge region. Multiple 3mm diameter through holes are made in the thick-walled central region to accelerate heat dissipation; while annular ribs with a height of 2mm and a width of 3mm are placed in the thin-walled edge region to slow down heat dissipation. After a 10-second transfer, the temperature difference between the center and the edge is reduced from the original 40℃ to less than 10℃.

[0078] The method described in this application solves the problem of uneven billet temperature field caused by inconsistent temperature drop rates in regions with different wall thicknesses through a passive (no external energy required) structural design. The uniform temperature field makes the material flow more consistent during die forging, improves the uniformity of deformation, and ultimately improves the mechanical properties of the part (especially its fatigue resistance).

[0079] In one optional embodiment, in the forging step, the forging die includes an upper die and a lower die, the lower die is provided with at least one tapered guide post, and the upper die is provided with a corresponding guide hole; The die-casting billet is fitted outside the conical guide post, and the conical guide post guides the die-casting billet to be radially aligned when the mold is closed.

[0080] The guiding structure of the forging die consists of at least one tapered guide post in the lower die and a corresponding guide hole in the upper die. The die-casting billet is fitted over the guide post (i.e., the guide post passes through the through hole in the die-casting billet or surrounds its outer circumference). When the die is closed, the tapered guide post first enters the guide hole. Due to the self-centering effect of the tapered surface, it can guide the die-casting billet to automatically center in the radial (horizontal) direction. This guide post not only serves as a guide for the die but also as a positioning element for the billet.

[0081] The automatic centering function of the tapered guide pillars compensates for the insufficient precision of the robot arm's placement, ensuring that the die-casting blank is centered in the mold cavity every time the mold closes, thereby obtaining uniform deformation and symmetrical part shape. At the same time, this structure avoids the need for additional positioning devices that would occupy mold space.

[0082] In an optional embodiment, during the die forging step, no lubricant is sprayed on the surface of the die-cast billet, but only on the surface of the die forging die (e.g., the lubricant can be water-based graphite); and the die forging speed is controlled in the range of 5 mm / s to 50 mm / s, using medium-low speed die forging.

[0083] In this embodiment, no lubricant is sprayed on the surface of the die-cast billet (to avoid the lubricant affecting the temperature drop and forging quality); lubricant is only sprayed on the surface of the forging die. The lubricant forms a lubricating film at high temperature, reducing friction between the billet and the die. At the same time, the lubricant has a heat insulation effect, which can slow down the temperature rise of the die.

[0084] The forging speed is controlled within the range of 5mm / s to 50mm / s, which is considered medium-low speed forging. Normal forging speeds can reach over 100mm / s. Medium-low speed forging reduces deformation heat effects and avoids localized overheating that could lead to material overheating or coarsening of the microstructure.

[0085] For example, the forging speed can be selected as 5mm / s, 10mm / s, 20mm / s, 30mm / s, 40mm / s, or 50mm / s.

[0086] The method described in this application distinguishes between lubrication targets (die lubrication and billet lubrication), thus avoiding lubricant residue on the billet surface that could affect subsequent heat treatment or machining, while ensuring smooth demolding. Medium- and low-speed die forging effectively controls deformation heat, making the forging process nearly isothermal, preventing grain growth or cracks caused by localized overheating, and improving the internal quality of the parts.

[0087] In one alternative embodiment, after the die-cast billet is transferred to the forging die and before final forging, a temperature detection and compensation step is also included: Infrared thermometers were used to measure the temperature at multiple points on the surface of the die-cast billet. If the measured temperature is lower than the lower limit of the forging temperature window, the die-cast billet is sent to an emergency soaking furnace for short-term reheating until it is heated to within the forging temperature window before being taken out for die forging. If the measured temperature is higher than the upper limit of the forging temperature window, the forging process will be paused and an alarm signal will be issued.

[0088] Use an infrared thermometer to measure the temperature distribution at multiple points on the surface of the die-cast billet (e.g., the center, edges, and other key locations).

[0089] If the measured temperature is lower than the lower limit of the forging temperature window, it indicates that the natural cooling is excessive. In this case, the die-cast billet should be sent to an emergency soaking furnace for short-term reheating (e.g., heating for 5-10 seconds) to allow it to rise back to the window, and then the die-casting billet should be removed.

[0090] If the measured temperature is higher than the upper limit of the window, it indicates that the billet is overheated. At this time, the die forging is paused and an alarm is triggered. The operator then decides whether to wait for cooling or scrap the billet.

[0091] As an example, in one production run, a conveyor belt jam extended the transfer time to 20 seconds, causing the measured billet temperature to drop to 400℃, below the lower limit of 415℃. The control system issued a command, and the robotic arm delivered the billet to an adjacent emergency soaking furnace (set temperature 430℃). After heating for 8 seconds, the temperature rose back to 425℃, and the billet was then removed and forged normally. In another batch, due to a cooling system malfunction, the demolding temperature reached as high as 530℃, and after transfer, it remained at 490℃, exceeding the upper limit of 465℃. The system alarmed, suspended forging, and marked the billet as scrap.

[0092] The method described in this application provides tolerance for process fluctuations. Even in the event of anomalies (such as equipment failure or environmental changes), scrap will not be directly caused; instead, it can be salvaged through emergency reheating. Simultaneously, an over-temperature alarm mechanism prevents overheated billets from entering the forging die, avoiding damage to the die or the production of defective products. This improves the robustness of the production line and the yield rate.

[0093] In one alternative implementation, most of the forgings are directly fed to the die forging process. However, if the temperature is detected to be too low, an emergency soaking furnace is available to temporarily heat the forgings that do not meet the temperature requirements. Once the temperature is within acceptable limits, the forgings are then sent to the die forging process.

[0094] Before being transferred to the forging die, all die-cast billets pass through a tunnel-type soaking furnace. The soaking furnace is a continuous heating channel through which the billets pass at a constant speed, and the furnace temperature is constant (e.g., set to the center value of the forging temperature window, such as 440°C). By adjusting the residence time of the billets in the furnace (i.e., the conveyor belt speed) and the furnace temperature, the temperature of each billet is stabilized near the center value of the forging temperature window when it exits the furnace.

[0095] This method completely eliminates the influence of demolding temperature and transfer time fluctuations on forging temperature, ensuring a highly consistent temperature before forging (fluctuation ≤ ±5℃), which is beneficial to the stability of the forging process and the consistency of part quality. Although a soaking furnace is added, the investment is acceptable for mass production, and it still saves energy compared to the traditional "cooling and reheating" method (the soaking furnace only needs to maintain 440℃ instead of reheating to 700℃).

[0096] In one alternative embodiment, the die-casting mold cavity is provided with replaceable inserts, and the method further includes changing the inserts to alter the shape of positioning features or temperature control structures on the die-casting billet according to different final forging shapes.

[0097] Inserts are removable, partial cores in die-casting molds. The shape of their inner surfaces determines the specific geometry of the positioning features or temperature control structures on the die-cast blank. When producing different final forgings, only the inserts need to be replaced, without replacing the entire die-casting mold.

[0098] The method described in this application significantly reduces mold costs and production changeover time. Die-casting molds themselves are expensive (hundreds of thousands of yuan), while inserts are only a small fraction of that cost. By quickly replacing inserts, various specifications of parts can be flexibly produced, enabling flexible manufacturing of small batches and diverse products. Furthermore, the replaceability of the inserts makes it possible to optimize positioning and temperature control structures for different products without redesigning the entire mold.

[0099] On the other hand, a mechanical part is provided, which is manufactured using any of the methods described above.

[0100] Please see Figure 2 and Figure 3 , Figure 2 This is a schematic diagram showing the structure and dimensions of a die-cast part prepared using the method provided in the embodiments of this application. Figure 3 This is a schematic diagram showing the structure and dimensions of a mechanical part prepared using the method provided in the embodiments of this application. Figure 4 This is a schematic diagram showing the structure and dimensions of a die-cast part before forging, prepared using the method provided in the embodiments of this application. Figure 5 This is a schematic diagram showing the structure and dimensions of a forged mechanical part prepared using the method provided in the embodiments of this application.

[0101] The mechanical parts manufactured using this method combine the shape complexity of die casting with the high strength of forging. Because forging eliminates defects such as porosity and shrinkage cavities inherent in die casting and refines the grain size, the fatigue life and impact toughness of the parts are significantly improved. Simultaneously, due to energy and mold cost savings during the process, the parts offer higher cost-effectiveness and are particularly suitable for fields with high requirements for lightweighting and reliability (such as automotive and aerospace).

[0102] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for manufacturing mechanical parts by die casting and direct feeding forging, characterized in that, Based on the final forging billet structure dimensions, the die-casting billet structure and dimensions with a deformation amount of not less than 30% during the die forging process are determined through simulation analysis of the die forging process. Die casting is performed using die casting molds to obtain die casting blanks; When the die-cast billet is demolded, its temperature is kept within a preset demolding temperature window; After demolding, the die-casting billet is directly transferred to the forging die within a preset transfer time window, without actively heating the die-casting billet during the transfer process; The demolding temperature window and the transfer time window are predetermined based on the wall thickness of the die-casting billet and its temperature drop rate in air, so that the die-casting billet naturally cools down to the preset forging temperature window during the transfer process. Within the forging temperature window, the die-cast billet is forged into its final shape using a forging die that is independent of the die-casting die.

2. The method according to claim 1, characterized in that, The pre-determination of the demolding temperature window and the transfer time window includes the following steps: Obtain the three-dimensional model of the final forging of the mechanical part to be manufactured, ensure the shape and size of the die-casting billet with a deformation amount of not less than 30% during the die forging process, and obtain the minimum wall thickness t_min of the die-casting billet. Based on the material thermophysical parameters of the die-cast billet, cooling experiments were conducted on samples with different wall thicknesses in an air environment, and the temperature drop rate function v(T,d) was obtained by fitting. Set the lower limit T_forge_low and the upper limit T_forge_high of the forging temperature window, and the upper limit Δt_max of the transfer time window; Solve for the range of values ​​of T_demold that allow the die-cast billet to cool from the demolding temperature T_demold to within the interval [T_forge_low, T_forge_high] during the transition time Δt≤Δt_max, and use this range as the demolding temperature window.

3. The method according to claim 1, characterized in that, The step of ensuring that the temperature of the die-cast billet is within a preset demolding temperature window during demolding includes: A conformal cooling water channel is arranged inside the die-casting mold, and an electric regulating valve is installed at the inlet of the water channel; Temperature sensors are installed on the surface of the die-casting mold cavity to monitor the temperature of the die-casting billet in real time. When the temperature approaches the lower limit of the demolding temperature window, reduce the flow rate of the cooling medium or stop cooling. When the measured temperature falls within the demolding temperature window, the demolding action is executed.

4. The method according to claim 1, characterized in that, It also includes the steps of pre-setting positioning protrusions or positioning recesses on the non-forging load-bearing surface of the die-casting billet, and setting a matching positioning structure on the lower die of the forging mold; When the die-casting billet is transferred to the forging die, the positioning protrusion or positioning recess cooperates with the positioning structure to achieve automatic centering and positioning of the die-casting billet.

5. The method according to claim 1, characterized in that, The method also includes the step of providing a temperature control structure on the die-cast billet, wherein the temperature control structure includes at least one of the following: Weight reduction grooves or holes are opened in the thick-walled areas of the die-cast billet to accelerate the cooling of that area; Temporary ribs are provided in the thin-walled areas of the die-cast billet to slow down the cooling of that area; The temporary ribs are crushed during the forging process, and the temperature control structure is used to homogenize the cooling rate of the die-cast billet during the transfer process.

6. The method according to claim 1, characterized in that, During the die forging process, no lubricant is sprayed on the surface of the die-cast billet, but only on the surface of the die forging mold; and the die forging speed is controlled within the range of 5 mm / s to 50 mm / s, using medium and low speed die forging.

7. The method according to claim 1, characterized in that, After the die-cast billet is transferred to the forging die and before final forging, a temperature detection step is also included: Infrared thermometers were used to measure the temperature at multiple points on the surface of the die-cast billet. If the temperature is too high, an alarm will be issued first, followed by a delayed forging signal and a delay time. Once the delay time is up, forging will begin directly.

8. A mechanical part, characterized in that, The mechanical part is manufactured using the method described in any one of claims 1-7.

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