Lost foam casting method for automobile punching machine tool casting

Abstract

The invention relates to the field of full mold casting, and provides a lost foam casting method for an automobile punching machine tool casting, which comprises the following steps: firstly, melting scrap steel to 60% of required molten iron, then adding alloy raw materials except Fe, such as 3.3-3.9% of C, 2.3-2.7% of Si, 0.2-0.6% of Mn, 0.1-0.4% of Cr, 0.3-0.7% of Cu, 0.04-0.06% of Mg and 0.02-0.04% of Re, adding the scrap steel, and melting to obtain the molten iron with the required weight. And then the molten iron is subjected to spheroidizing and inoculation for the second time, so that the spheroidizing and inoculation effects are enhanced. And then the molten iron is poured through a stream inoculant funnel, three-time inoculation is achieved, nucleation cores are continuously supplemented for the molten iron, and recession is resisted. And after pouring, cooling is accelerated by introducing cold air into the bottom surface of the sand box, so that the nucleation rate is greatly increased, the growth time of graphite nodules is shortened, and the graphite refining effect is achieved.

Description

Technical Field

[0001] This invention relates to the field of lost foam casting, and more particularly to a lost foam casting method for automotive stamping machine castings. Background Technology

[0002] Ductile iron is widely used in the automotive industry due to its excellent casting performance, mechanical properties, and cost advantages, especially for various large mold parts such as fixtures, gauges, and chassis molds. The national standard GB / T 1348 requires QT550-5 material with a wall thickness of 30mm-60mm, demanding a tensile strength (Rm) ≥ 520MPa and an elongation (A) ≥ 4%. However, for modern automotive molds subjected to complex stresses and impact loads, a 4% elongation often means insufficient toughness reserve, making them prone to brittle fracture at stress concentration points and affecting service life. Therefore, it is necessary to significantly increase the elongation to over 12% while maintaining high strength (Rm ≥ 520MPa), thereby giving the mold a higher safety margin and fatigue resistance. For lost foam casting, ductile iron is suitable for large and complex parts, offering advantages such as precise casting dimensions, small machining allowances, and low production costs. However, the relatively slow cooling rate of this process, and the alloy composition of ductile iron, pose challenges to obtaining a high-toughness ferritic matrix. Therefore, solving the above problems is essential. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a lost foam casting method for automotive stamping machine castings, which solves the problems in the background art.

[0004] To achieve the above objectives, the present invention provides a method for lost foam casting of automotive stamping machine castings, comprising the following steps: Step 1: Weigh the alloy raw materials according to the following mass percentages: C 3.3-3.9%, Si 2.3-2.7%, Mn 0.2-0.6%, Cr 0.1-0.4%, Cu 0.3-0.7%, Mg 0.04-0.06%, Re 0.02-0.04%, Fe balance; wherein P≤0.06%, S≤0.04%; Step 2: Melt the scrap steel in the furnace, add the alloy raw materials (excluding Fe from Step 1), and melt them to obtain molten iron; Step 3, initial spheroidizing inoculation: Add a strong nucleating inoculant and a high-magnesium, low-rare-earth spheroidizing agent to the bottom of a ladle. Level the bottom of the ladle and cover it with a spheroidizing cover plate to prevent the spheroidizing agent and inoculant from being washed onto the surface of the molten iron when it is poured in. Then add the molten iron from step 2. After the spheroidizing cover plate dissolves, the spheroidizing agent and inoculant can react fully in the molten iron. Step 4, secondary spheroidizing and inoculation: Add spheroidizing agent and inoculant to the bottom of another ladle. Cover the bottom of the ladle with spheroidizing cover plate to cover the spheroidizing agent and inoculant. Then pour in the molten iron from the ladle in step 3 to complete the secondary spheroidizing and inoculation. Step 5, Pouring: The molten iron from the ladle in Step 4 is poured into the sand box mold through the pouring system. The mold leaves space for the test bar. At the same time as pouring, the inoculant funnel is opened to quickly complete the pouring and obtain the casting. The casting has a test bar on it. Step 6: Cool the casting inside the sand box. Once the casting temperature drops below 150°C, lift the casting out of the sand box. Step 7: Remove the test bar from the casting and perform tensile and metallographic tests.

[0005] Preferably, in step two, the alloy raw materials are added when the molten iron has melted to 60% of the required weight of molten iron, and then scrap steel is added and smelted until the required weight of molten iron is reached.

[0006] Preferably, after the smelting in step two is completed, the composition of the molten iron is sampled and tested. If it passes the test, the furnace temperature is raised to above 1520°C and left to stand at high temperature for 6-8 minutes. During the standing process, slag-collecting agent is sprinkled in the furnace to remove the slag and ensure the purity of the molten iron.

[0007] Preferably, in step three, the amount of spheroidizing agent and inoculant added during the first spheroidizing inoculation is 70% of the total amount of spheroidizing agent and inoculant; in step four, the amount of spheroidizing agent and inoculant added during the second spheroidizing inoculation is 30% of the total amount of spheroidizing agent and inoculant.

[0008] Preferably, the temperature of the molten iron in the ladle before pouring in step five is controlled at 1370±10℃.

[0009] Preferably, after pouring the ladle in steps four and five, the ladle is cleaned of slag by using a slag-collecting agent to remove the slag from the ladle.

[0010] Preferably, in step six, cold air is circulated through the bottom surface of the sand box to accelerate cooling.

[0011] Preferably, the inoculant is a ferrosilicon inoculant containing barium, strontium, and zirconium.

[0012] The beneficial effects of this invention are as follows: This invention adjusts the overall raw material formula, increasing the Si content to 2.3-2.7%. Si is a strong graphitizing element, promoting ferrite formation. The final Si content after inoculation is a key parameter for toughness. The high-silicon solid solution strengthening effect can increase the strength of ferrite, and the structural stability also greatly improves the toughness of the casting. The Mn content is 0.2-0.6%, segregating at the eutectic boundaries and stabilizing pearlite. Cr is a strong carbide-forming element, with a content of 0.1-0.4%, which can effectively increase the proportion and strength of pearlite, offsetting the strength decrease caused by reducing Mn and increasing Si, and is key to balancing strength and toughness. Both Mn and Cr have a good enhancing effect on tensile strength, but they have a counterproductive effect on the toughness of the casting. Therefore, based on our company's material composition, the content of both is reduced. Cu also stabilizes pearlite and refines the microstructure, with a lower segregation tendency than Mn. Its content is 0.3-0.7%. It works synergistically with Cr, slightly increasing pearlite without significantly impairing toughness. When Mn and Cr decrease, the Cu content should be increased to ensure the strength of the casting. P forms a brittle phase, reducing toughness; its content should be controlled below 0.06%. While both S and Mg promote spheroidization, excessive S content negatively impacts the matrix structure and produces large amounts of toxic gases; its content should be controlled below 0.04%. Mg, on the other hand, causes graphite distortion, negatively affecting tensile strength and toughness; its content is 0.04%-0.06%.

[0013] This invention involves melting scrap steel to 60% of the required amount of molten iron, then adding alloying materials (excluding Fe), and finally adding more scrap steel to melt the remaining molten iron to the desired weight. This ensures the uniformity of the alloying materials and scrap steel mixture. The molten iron then undergoes a second spheroidization and inoculation process, with 70% and 30% spheroidizing agent and inoculant added respectively to enhance the spheroidization and inoculation effects. The molten iron is then poured through a funnel containing the inoculant, achieving a three-stage inoculation process that continuously replenishes nucleation sites and combats fading. After pouring, accelerated cooling is achieved by circulating cold air through the bottom of the sand box, significantly increasing the nucleation rate and shortening the growth time of graphite spheres, thus achieving a refined graphite effect. The resulting castings exhibit refined graphite spheres, a spheroidization rate increased to level 2, an average elongation exceeding 13%, and a tensile strength exceeding 530 MPa. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 Metallographic testing of the present invention Figure 1 ; Figure 2 Metallographic testing of the present invention Figure 2 . Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0017] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0018] This embodiment provides a lost foam casting method for automotive stamping machine castings, including the following steps: S1, weigh the following alloy raw materials by mass percentage: C 3.9%, Si 2.7%, Mn 0.6%, Cr 0.4%, Cu 0.7%, Mg 0.06%, Re 0.04%, Fe balance; wherein P≤0.06%, S≤0.04%; adjust the existing QT550 material composition. The existing material has a tensile strength of 500MPa-520MPa and an elongation of only 4%-6%. Increase the Si content to 2.7%. Si is a strong graphitizing element, promoting ferrite formation. After inoculation, the final Si content is a key parameter for toughness. High silicon solid solution strengthening can increase the strength of ferrite, and the structural stability also greatly improves the toughness of the casting. The Mn content is 0.6%, segregating at the eutectic boundaries and stabilizing pearlite. Cr is a strong carbide-forming element, with a content of 0.4%, which can effectively increase the proportion and strength of pearlite, offsetting the strength decrease caused by reducing Mn and increasing Si, and is the key to balancing strength and toughness. Both Mn and Cr have excellent enhancing effects on tensile strength, but they have a negative effect on the toughness of castings. Therefore, the content of both is reduced based on our material composition. Cu also has the effect of stabilizing pearlite and refining the microstructure, and its segregation tendency is less than that of Mn. Its content is 0.7%. It works synergistically with Cr to increase pearlite slightly without significantly impairing toughness. When Mn and Cr are reduced, the content of Cu is increased to ensure the strength of the casting. P forms a brittle phase and reduces toughness, so it is controlled below 0.06%. Although S and Mg both promote spheroidization, excessive S has an adverse effect on the matrix microstructure and will produce a large amount of toxic gas, so it is controlled below 0.04%. Mg will cause graphite distortion, which will have an adverse effect on both tensile strength and toughness, so its content is 0.06%.

[0019] S2: The furnace melts scrap steel. When the molten iron reaches 60% of the required weight, S1 alloy raw materials other than Fe are added. Then, scrap steel is added and smelted until the required weight of molten iron is reached. The composition of the molten iron is sampled and tested to see if it meets the requirements before the furnace. If it passes the test, the furnace temperature is raised to above 1520℃ and allowed to stand at high temperature for 6-8 minutes. During the standing process, slag-collecting agent is sprinkled in the furnace to remove the slag and ensure the purity of the molten iron.

[0020] S3, First Spheroidizing Inoculation: Because the tapping temperature is higher than the ladle temperature, the tapping temperature of molten iron is controlled at 1500℃. Therefore, the amount of spheroidizing agent and inoculant added for the first spheroidizing inoculation is 70%. A strong nucleating inoculant and a high-magnesium, low-rare-earth spheroidizing agent are added to the bottom of a ladle. The bottom of the ladle is leveled and covered with a spheroidizing cover plate to prevent the spheroidizing agent and inoculant from being washed onto the surface of the molten iron when it is poured in. Then, the molten iron of S2 is added. After the spheroidizing cover plate dissolves, the spheroidizing agent and inoculant can fully react in the molten iron.

[0021] S4, Secondary spheroidizing and inoculation: Add spheroidizing agent and inoculant to the bottom of another ladle. Cover the bottom of the ladle with spheroidizing cover plate to cover the spheroidizing agent and inoculant. Then pour in the molten iron from the S3 ladle to complete the secondary spheroidizing and inoculation.

[0022] S5. After pouring the ladle, the slag inside the ladle must be cleaned thoroughly. Use a slag remover to clean the slag inside the ladle. The slag removal process should be quick to avoid excessive temperature loss, as prolonged slag removal will also lead to a decline in the incubation process.

[0023] S6, casting: Before casting, the temperature of the molten iron in the ladle is controlled at 1370℃. The molten iron from the S4 ladle is poured into the sand box model through the casting system for casting. The model leaves space for the test bar. At the same time as casting, the inoculant funnel is opened to quickly complete the casting and obtain the casting with the test bar. S7. Cool the casting inside the sand box by circulating cold air through the bottom of the sand box to accelerate cooling. Once the casting temperature drops below 150℃, remove the casting from the sand box. S8, remove the test bar from the casting, and perform tensile and metallographic testing. Metallographic testing includes... Figure 1 and 2 .

[0024] The inoculant is a ferrosilicon inoculant containing barium, strontium, and zirconium. These elements can form more and more stable heterogeneous nucleation cores, such as sulfur oxides and nitrides, significantly increasing the number of graphite spheroids. This invention uses barium silicon (FeSiBa), which has a better effect on preventing inoculation fading. A portion of the inoculant is added during the spheroidizing treatment for primary inoculation, another portion is added during the ladle turning process for secondary inoculation, and finally, a third inoculation is performed using in-flow inoculation. Through segmented treatment, nucleation cores are continuously replenished to the molten iron, combating fading.

[0025] The test bar was tested and the graphite spheres were refined, the spheroidization rate was increased to level 2, the elongation rate reached an average of over 13%, and the tensile strength was over 530 MPa.

[0026] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and many other variations of different aspects of the invention as described above exist, which are not provided in detail for the sake of brevity. Any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for lost foam casting of automotive stamping machine castings, characterized in that, It includes the following steps: Step 1: Weigh the alloy raw materials according to the following mass percentages: C 3.3-3.9%, Si 2.3-2.7%, Mn 0.2-0.6%, Cr 0.1-0.4%, Cu 0.3-0.7%, Mg 0.04-0.06%, Re 0.02-0.04%, Fe balance; wherein P≤0.06%, S≤0.04%; Step 2: Melt the scrap steel in the furnace, add the alloy raw materials (excluding Fe from Step 1), and melt them to obtain molten iron; Step 3, initial spheroidizing inoculation: Add a strong nucleating inoculant and a high-magnesium, low-rare-earth spheroidizing agent to the bottom of a ladle. Level the bottom of the ladle and cover it with a spheroidizing cover plate to prevent the spheroidizing agent and inoculant from being washed onto the surface of the molten iron when it is poured in. Then add the molten iron from step 2. After the spheroidizing cover plate dissolves, the spheroidizing agent and inoculant can react fully in the molten iron. Step 4, secondary spheroidizing and inoculation: Add spheroidizing agent and inoculant to the bottom of another ladle. Cover the bottom of the ladle with spheroidizing cover plate to cover the spheroidizing agent and inoculant. Then pour in the molten iron from the ladle in step 3 to complete the secondary spheroidizing and inoculation. Step 5, Pouring: The molten iron from the ladle in Step 4 is poured into the sand box mold through the pouring system. The mold leaves space for the test bar. At the same time as pouring, the inoculant funnel is opened to quickly complete the pouring and obtain the casting. The casting has a test bar on it. Step 6: Cool the casting inside the sand box. Once the casting temperature drops below 150°C, lift the casting out of the sand box. Step 7: Remove the test bar from the casting and perform tensile and metallographic tests.

2. The method for lost foam casting of automotive stamping machine castings according to claim 1, characterized in that, In step two, the alloy raw materials are added when the molten iron reaches 60% of the required weight of molten iron, and then scrap steel is added and smelted until the required weight of molten iron is reached.

3. The method for lost foam casting of automotive stamping machine castings according to claim 2, characterized in that, After the smelting in step two is completed, the molten iron is sampled and tested for composition. If it passes the test, the furnace temperature is raised to above 1520℃ and left to stand at high temperature for 6-8 minutes. During the standing process, slag-collecting agent is sprinkled in the furnace to remove slag and ensure the purity of the molten iron.

4. The method for lost foam casting of automotive stamping machine castings according to claim 1, characterized in that, In step three, the amount of spheroidizing agent and inoculant added for the first spheroidizing inoculation is 70% of the total amount of spheroidizing agent and inoculant; in step four, the amount of spheroidizing agent and inoculant added for the second spheroidizing inoculation is 30% of the total amount of spheroidizing agent and inoculant.

5. The method for lost foam casting of automotive stamping machine castings according to claim 1, characterized in that, In step five, the temperature of the molten iron in the ladle before pouring is controlled at 1370±10℃.

6. The method for lost foam casting of automotive stamping machine castings according to claim 1, characterized in that, After pouring the ladle in steps four and five, the ladle is cleaned of slag using a slag-collecting agent.

7. The method for lost foam casting of automotive stamping machine castings according to claim 1, characterized in that, In step six, cold air is circulated through the bottom of the sandbox to accelerate cooling.

8. The method for lost foam casting of automotive stamping machine castings according to claim 1, characterized in that, The inoculant is a ferrosilicon inoculant containing barium, strontium, and zirconium.

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