Forming process method for maraging steel end socket shell

Abstract

The invention discloses a maraging steel end socket shell forming process method, and relates to the technical field of metal material plastic forming. The method comprises the steps that the blanking size and the extension force of a blank are calculated according to a target shell, and the sizes of a male die and a female die of an extension die are calculated; selecting a press machine according to the stretching force, and calculating the stretching times; blanking is conducted according to the blanking size, solid solution is conducted, and then stamping is conducted; and after appearance inspection and flaw detection are conducted on the stamped extension piece, machining forming is conducted. According to the method, the blanking size of a part blank, the working size of the die and the stamping force (extension force) required by working are calculated and determined before stamping, so that a proper press machine is selected, and after the press machine is determined, the extension frequency is determined, so that the forming quality is better guaranteed. A plate blank before stamping is heated in a vacuum furnace during solid solution, and an oil cooling mode is selected for rapid cooling after heating is finished.

Description

Technical Field

[0001] This invention relates to the field of metal material plastic forming technology, specifically to a process method for forming a martensitic aging steel head shell. Background Technology

[0002] Solid rocket motor combustion chamber head shells are typically formed from ultra-high strength steels such as T250, D406A, and D6AC through machining or stamping. They are characterized by a hemispherical overall structure, thin shell walls (2mm-5mm), and subsequent welding and other processing after stamping. There are few publicly reported studies on the stamping forming methods for T250 maraging steel head shells. After heat treatment and solution treatment, T250 maraging steel achieves a hardness of 28HRC-36HRC, equivalent to the hardness of 30CrMnSiA after quenching and tempering. At this point, the yield strength reaches over 880MPa, and the tensile strength reaches 1100MPa-1300MPa. After aging treatment, the material hardness reaches 48HRC-53HRC, and the tensile strength reaches 1710MPa-1860MPa. Typically, the plastic forming of T250 steel is carried out under solution treatment conditions, while the final machining is performed under aging conditions. Regardless of the conditions, the high strength of T250 steel poses significant challenges to the heat treatment and stamping processes before stamping, compared to other ultra-high strength steels.

[0003] When T250 martensitic aging steel head shells are formed by stamping, the raw material is sheet metal, and the heat treatment state is solution treated. The solution heat treatment of the sheet metal before stamping has a significant impact on the dimensional accuracy of the head shell. Improper control of the heat treatment process and parameters can lead to the final dimensional accuracy of the head shell failing to meet design requirements. QJ20574-2016, "Heat Treatment Process Requirements for T250 Martensitic Aging Steel," lists the process flow for typical engine parts. The overall stamping process is as follows: 1. Sheet metal blanking - 2. Solution treatment - 3. Stamping - 4. Machining - 5. Aging - 6. Machining. Referring to the relevant process requirements in QJ20574, the sheet metal process is as follows: After the furnace temperature reaches 820℃~860℃, the sheets are stacked and loaded into the furnace, held at 820℃~860℃ for 90min~120min, and then removed from the furnace and air-cooled. Following the above process, after solution treatment of the end cap shell blank, uneven air cooling results in inconsistent hardness with a difference greater than 2 HRC. This leads to significant diameter expansion at the edge of the end cap shell after stamping, a phenomenon known as "flanging." Furthermore, surface oxidation and contamination of the sheet metal result in poor smoothness, introducing other new defects during the stamping process. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technology, this invention provides a forming process for martensitic aging steel head shells. Before stamping, this invention calculates and determines the blanking dimensions, die working dimensions, and required stamping force (drawing force) to select a suitable press. Once the press is determined, the number of drawing operations is determined to better ensure forming quality. The sheet metal blank is heated in a vacuum furnace during solution treatment before stamping, and then rapidly cooled using oil cooling after heating.

[0005] The purpose of this invention is to provide a process for forming martensitic aging steel head shells, used for forming hemispherical head shells, comprising the following steps: Calculate the blanking dimensions and drawing force based on the target shell, and calculate the dimensions of the punch and die of the drawing die; Select the press based on the stretching force and calculate the number of stretching cycles; Cut the material according to the blanking dimensions, perform solution treatment, and then stamp it. After inspecting the appearance and flaw detection of the stamped parts, they are machined into shape.

[0006] Preferably, the blank cutting dimensions are based on the blank diameter, which is calculated using the equal area method, i.e., the area of ​​the blank before drawing is equal to the area of ​​the drawn part. The specific blank diameter calculation is as follows: D=1.13

[0007] In the formula, D is the blank diameter; F is the surface area of ​​the drawn part.

[0008] Preferably, the dimensions of the punch and die of the drawing die are calculated using the following formula: punch size: l =(l1 +0.4△)-

[0009] Die size: l =(l2 +0.4△+Z)+

[0010] In the formula, l The dimensions of the working part of the punch; l For the working part of the die; l1 l2 represents the minimum limiting dimension of the inner shape of the drawn part. Δ is the minimum limit dimension of the drawn part's shape; △ is the workpiece tolerance; Z is the double-sided clearance between the punch and die of the drawn part. , These are the manufacturing tolerances for the punch and die, respectively.

[0011] Preferably, the formula for calculating the tensile force is: P= d t K

[0012] In the formula, d t is the diameter of the workpiece; t is the thickness of the workpiece. K represents the tensile strength of the material. This is the correction value for the extensibility coefficient.

[0013] Preferably, the number of extensions is determined, and the conditions for one extension are as follows: h≤(0.5~0.7)d In the formula, h is the height of the drawn part; d is the diameter of the drawn part.

[0014] Preferably, during the stamping process, stamping is performed according to the determined working dimensions of the drawing die, the press, and the number of drawing cycles.

[0015] Preferably, during solution treatment, after loading the blank into the furnace, the temperature is raised to 820℃~860℃ and held for 90min~150min, followed by oil cooling.

[0016] Preferably, the thickness of the blank is 2mm to 5mm, and a subsequent trimming allowance of 5mm to 15mm is added during blanking.

[0017] Preferably, the stamping process includes: Fix the mold on the press, adjust the gap between the die and the punch to make it suitable for stamping hemispheres of different plate thicknesses, and tighten the die and the punch. Clean the working surfaces of the die and punch thoroughly and apply lubricant. Clean the surface of the stamping blank, apply grease, and place the blank into the die cavity; Adjust the working pressure of the press according to the theoretically calculated tensile force, and then perform the stamping.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a forming process for martensitic aging steel head shells. It provides a systematic and comprehensive study of the stamping process for T250 martensitic aging steel, including the dimensions of the sheet blank, heat treatment before stamping, working dimensions of the stamping die, selection of the press, and determination of the number of drawing passes. This method has been applied to the actual manufacturing of solid rocket engine head shells. The sheet blank solution treatment in this invention utilizes vacuum oil cooling, avoiding surface oxidation caused by heating in air and improving surface quality. Because the cooling rate is fast and uniform, the precipitation of the second phase is suppressed, ensuring uniform microstructure and hardness after solution treatment, and solving the edge-flaking phenomenon of existing processes. Through theoretical calculations and numerous experimental explorations and studies, this invention has determined the stamping process for T250 martensitic aging steel head shells, resulting in head shells with better dimensional accuracy and consistency. Attached Figure Description

[0019] Figure 1 This is a cross-sectional view of the hemispherical head shell described in this invention; Figure 2 This is a process flow diagram of the hemispherical structure head shell described in this invention; Figure 3 This is a cross-sectional view of the shell of a hemispherical structure head provided in Example 1; Figure 4 This is a cross-sectional view of the shell of a hemispherical structure head provided in Example 2. Detailed Implementation

[0020] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0021] The purpose of this invention is to provide a forming process for T250 martensitic aging steel head shells, eliminating defects such as "flanging" during the stamping process, solving the problem of difficult dimensional accuracy control after stamping, and applying it to the hemispherical forming of combustion chamber head shells for various engine models. See also... Figure 1 The figure shows a cross-sectional view of the hemispherical head shell of the present invention.

[0022] To achieve the above objectives, the present invention provides a process for forming martensitic aging steel head shells, used for forming hemispherical head shells, comprising the following steps: Calculate the blanking dimensions and drawing force based on the target shell, and calculate the dimensions of the punch and die of the drawing die; Select the press based on the stretching force and calculate the number of stretching cycles; Cut the material according to the blanking dimensions, perform solution treatment, and then stamp it. After inspecting the appearance and flaw detection of the stamped parts, they are machined into shape.

[0023] The blank cutting dimensions are based on the blank diameter, which is calculated using the equal area method, meaning the area of ​​the blank before drawing is equal to the area of ​​the drawn part. The specific blank diameter calculation is as follows: D=1.13

[0024] In the formula, D is the blank diameter; F is the surface area of ​​the drawn part.

[0025] The dimensions of the punch and die of the drawing die are calculated using the following formulas: punch size: l =(l1 +0.4△)-

[0026] Die size: l =(l2 +0.4△+Z)+

[0027] In the formula, l The dimensions of the working part of the punch; l For the working part of the die; l1 l2 represents the minimum limiting dimension of the inner shape of the drawn part. Δ is the minimum limit dimension of the drawn part's shape; △ is the workpiece tolerance; Z is the double-sided clearance between the punch and die of the drawn part. , These are the manufacturing tolerances for the punch and die, respectively.

[0028] The formula for calculating tensile force is: P= d t K

[0029] In the formula, d t is the diameter of the workpiece; t is the thickness of the workpiece. K represents the tensile strength of the material. This is the correction value for the extensibility coefficient.

[0030] The number of extensions is determined, and the condition for one extension is: h≤(0.5~0.7)d In the formula, h is the height of the drawn part; d is the diameter of the drawn part.

[0031] During the stamping process, the stamping is carried out according to the working dimensions of the drawing die, the press, and the number of drawing cycles.

[0032] During solution treatment, after loading the blank into the furnace, heat it to 820℃~860℃ and hold it for 90min~150min. After holding, oil cooling is performed.

[0033] The thickness of the blank is 2mm to 5mm, and a subsequent trimming allowance of 5mm to 15mm is added when cutting the blank.

[0034] The stamping process includes: Fix the mold on the press, adjust the gap between the die and the punch to make it suitable for stamping hemispheres of different plate thicknesses, and tighten the die and the punch. Clean the working surfaces of the die and punch thoroughly and apply lubricant. Clean the surface of the stamping blank, apply grease, and place the blank into the die cavity; Adjust the working pressure of the press according to the theoretically calculated tensile force, and then perform the stamping.

[0035] For example, see Figure 2 The diagram illustrates a stamping process for T250 martensitic aging steel head shells. Before stamping, the blank dimensions, die working dimensions, and required stamping force (drawing force) are calculated and determined to select a suitable press. Once the press is selected, the number of drawing passes is determined to better ensure forming quality. The sheet metal blank is heated in a vacuum furnace during solution treatment before stamping, and then rapidly cooled using oil cooling after heating.

[0036] Specifically, the following steps are included: Step 1: Calculation and blanking of sheet metal blank. The unfolded dimensions of the blank are calculated using the equal area method, meaning the area of ​​the blank before drawing is equal to the area of ​​the drawn part. The formula for calculating the blank diameter is as follows: D=1.13

[0037] In the formula, D is the blank diameter (mm); F is the surface area of ​​the drawn part (mm²). 2 ); Step 2: Heat treatment of sheet blanks. After the sheet blanks are cut, they are heated in a vacuum furnace, and then rapidly cooled using oil cooling after heating.

[0038] Step 3: Calculate the design dimensions of the punch and die of the drawing die. The calculation formula is as follows: punch size: l =(l +0.4△)-

[0039] Die size: l =(l +0.4△+Z)+

[0040] In the formula, l The dimensions of the working part of the punch; l Δ is the dimension of the working part of the die; l is the minimum limit dimension of the outer and inner shape of the drawing part; △ is the workpiece tolerance; Z is the double-sided clearance between the punch and die of the drawing part. , These are the manufacturing tolerances for the punch and die.

[0041] Step 4: Calculate the tensile force and select the required press tonnage. The formula for calculating the tensile force is as follows: P=Lt K = d t K

[0042] In the formula d t is the diameter of the workpiece; t is the thickness of the workpiece. The tensile strength of the material (kg / mm) 2 ); K This is the correction value for the elongation coefficient; Step 5: Determine the number of repetitions. Conditions for one repetition: h≤(0.5~0.7)d In the formula, h is the height of the drawn part (mm); d is the diameter (mean diameter) of the drawn part (mm).

[0043] Step 6: The sheet blank after solution treatment in Step 2 is stamped and formed according to the working dimensions of the stamping die, the press, and the number of drawing cycles determined in Steps 3, 4, and 5.

[0044] Step 7: Inspect the appearance of the head shell, perform dye penetrant testing, and check for cracks on the inner and outer surfaces.

[0045] Step 8: Machin the head shell according to the design drawings, including the height and inner diameter of the shell, and the outer diameter φD ± 0.10. The invention is further characterized in that, In step 1, the blank material is T250 martensitic aging steel plate with a thickness of 2mm to 5mm. The calculated blank diameter must be supplemented with a subsequent trimming allowance of 5mm to 15mm during blanking.

[0046] After the sheet metal blank is cut in step 1, rubber plates are placed on both ends of the lathe to tighten the outer diameter φD±0.10.

[0047] In step 2, the solution treatment of the sheet blank is carried out in a vacuum furnace oil quenching furnace. The process parameters are as follows: after loading the furnace, the temperature is raised to 820℃~860℃, held for 90min~150min, and then oil cooled after the holding time is completed.

[0048] In step 2, the sheet blank undergoes solution heating and oil cooling processes. Special fixtures are used to ensure that the sheet blank is flat and does not deform after heat treatment.

[0049] In step 2, the hardness of the sheet blank after solution treatment should not exceed 32 HRC.

[0050] In step 6, the mold is fixed on the press, the gap between the concave and convex dies is adjusted to suit the stamping of hemispheres with different plate thicknesses, and the concave and convex dies are tightened; the working surfaces of the concave and convex dies are cleaned and lubricated; the surface of the stamping blank is cleaned, lubricated, and the blank is placed in the concave die; the working pressure of the press is adjusted according to the theoretically calculated pressure, and stamping is carried out.

[0051] The sheet metal blank is cooled by oil cooling, which can ensure rapid cooling of the blank and obtain a supersaturated solid solution structure. The hardness of the blank is no greater than 32 HRC and is uniform, with a hardness difference of no more than 2 HRC. This prepares the structure for subsequent stamping processes and eliminates the phenomenon of flanging after stamping caused by large differences in the hardness of the blank.

[0052] The sheet metal blank is subjected to vacuum solution heating and oil cooling to achieve rapid cooling, ensuring uniform cooling of the sheet metal before stamping. The use of specialized fixtures reduces heat treatment deformation and facilitates dimensional accuracy control during the stamping process.

[0053] To further illustrate the stamping process method for martensitic aging steel provided by the present invention, specific embodiments are described in conjunction with the present invention.

[0054] Example 1 See Figure 3 As shown, a certain head shell has a wall thickness of (2±0.1) mm.

[0055] a) Figure 3 Blank dimensions are determined by: Figure 3 We know that the area of ​​the extended surface consists of three parts: the area of ​​the straight segment f1, the area of ​​the curved segment f2, and the area of ​​the ellipsoid f3, i.e., F = f1 + f2 + f3 =

[0056] In the formula, f1 = 2πrh = 6.28rh = 6.28 × 166 × 15.6 = 16262.7 f2 = π(dl + 2rh) = 3.14 × (139.79 × +2×15.5×13.51)=9029.6 f3 = πdh = 3.14 × 158.3 × 4 = 1988.2 Substituting F=27280.5 into the formula, we get D=φ187; Considering the installation and clearance errors of the drawing die, it is difficult to ensure that the large end face is flush after drawing, so additional machining steps are required to achieve the desired result. Figure 1 Therefore, the blanking size is adjusted to D=φ202.

[0057] b) Figure 3 Determining the dimensions of the working part of the drawing die: Depend on Figure 3 It can be determined that: l = 158.3, Δ = 0.2. =0.080, =0.12, Z=(1~1.1)t=2~2.2, take 2.1. Calculated: lt= 158.3 (punch working size), la=160.6 (die working size).

[0058] c) Calculation of tensile strength of T250 steel and selection of press Depend on Figure 3 It can be determined that d1 = 158.3, t = 2. =102~104, K =0.45. According to P=Lt K =πd1t K The calculation yields P = 46.077 (tons), and the Y32-200 four-column universal hydraulic press was selected for the experiment.

[0059] d) Figure 3 Number of times the part is drawn: Depend on Figure 3 Given: h=35, d=158.3, (0.5~0.7)d=(0.5~0.7)×158.3 =79.15~110.81, we know that: h<(0.5~0.7)d, so it can be drawn into shape in one step.

[0060] e) Figure 3 Part stamping results Cutting 5mm thick plates, cutting dimensions The sample was 202-0.2-0.1mm thick and underwent vacuum solution treatment and oil cooling at a temperature of 830℃. After heating, it was oil cooled, and the hardness was measured to be 28HRC~31HRC after being taken out of the furnace. All dimensions of the stamped head shell parts were qualified, and the inner surface was checked with a template and matched. The surface quality was good, with no defects such as bulges or wrinkles. The flaw detection and machining inspections were qualified.

[0061] Example 2 See Figure 4 As shown, a certain head shell has a wall thickness of 5mm.

[0062] a) Figure 4 Blank dimensions are determined by: Figure 4We know that the area of ​​the extended surface consists of two parts: the area of ​​the straight segment f1 and the area of ​​the ellipsoid f2, i.e., F = f1 / f2. +f =

[0063] In the formula f =2 ab = 6.28 × 85 × 367 = 195904.6 f = dh = 3.14 × 367 × 20 = 23047.6 Substituting F=218952.2 into the formula, we get D= 528 Considering the installation and clearance errors of the drawing die, it is difficult to ensure that the large end face is flush after drawing, so additional machining steps are required to achieve the desired result. Figure 4 Therefore, the blanking size is adjusted to D= 540.

[0064] b) Figure 4 Determining the dimensions of the working part of the drawing die: Depend on Figure 4 It can be determined that: l = 392 / 80, Δ = 0.2. =0.080, =0.12, Z=(1~1.1)t=5~5.5, take 5.25. Calculation yields: l =392 / 80 (punch working dimension), l =397.45 / 85.45 (working dimensions of the die).

[0065] c) Calculation of tensile strength of T250 steel and selection of press Depend on Figure 4 It can be determined that: d =392, t=5, =102~104, K =0.45. According to P=Lt K =πd t K The calculation yields P = 285.256 (tons), and the Y32-630 four-column universal hydraulic press was selected for the experiment.

[0066] d) Figure 4 Number of times the part is drawn: Depend on Figure 4Given: h=105, d=392, (0.5~0.7)d=(0.5~0.7)×392 =196~274.4, we know that: h<(0.5~0.7)d, so it can be drawn into shape in one step.

[0067] e) Figure 4 Parts stamping and inspection Cutting 5mm thick plates, dimensions The diameter of the end cap was 540-0.2-0.1mm. Vacuum solution treatment and oil cooling were performed at a solution temperature of 850℃. After heating, oil cooling was completed. The hardness after removal from the furnace was measured to be 29HRC~32HRC. The dimensions of the stamped end cap shell parts were qualified. The inner surface was checked with a template and found to be in good agreement. The surface quality was good, with no defects such as bulges or wrinkles. Flaw detection and machining inspections were passed.

[0068] This invention describes preferred embodiments and their effects. However, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to include both the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for forming a martensitic aging steel head shell, characterized in that, For the molding of hemispherical structure head shells, the following steps are included: Calculate the blanking dimensions and drawing force based on the target shell, and calculate the dimensions of the punch and die of the drawing die; Select the press based on the stretching force and calculate the number of stretching cycles; Cut the material according to the blanking dimensions, perform solution treatment, and then stamp it. After inspecting the appearance and flaw detection of the stamped parts, they are machined into shape.

2. The forming process method for martensitic aging steel head shells according to claim 1, characterized in that, The blank cutting dimensions are based on the blank diameter, which is calculated using the equal area method, meaning the area of ​​the blank before drawing is equal to the area of ​​the drawn part. The specific blank diameter calculation is as follows: D=1.13 In the formula, D is the blank diameter; F is the surface area of ​​the drawn part.

3. The forming process method for martensitic aging steel head shells according to claim 1, characterized in that, The dimensions of the punch and die of the drawing die are calculated using the following formulas: punch size: l =(l1 +0.4△)- Die size: l =(l2 +0.4△+Z)+ In the formula, l The dimensions of the working part of the punch; l For the working part of the die; l1 l2 represents the minimum limit dimension of the inner shape of the drawn part. Δ is the minimum limit dimension of the drawn part's shape; △ is the workpiece tolerance; Z is the double-sided clearance between the punch and die of the drawn part. , These are the manufacturing tolerances for the punch and die, respectively.

4. The forming process method for martensitic aging steel head shells according to claim 1, characterized in that, The formula for calculating tensile force is: P= d t K In the formula, d t is the workpiece diameter; t is the workpiece thickness; K represents the tensile strength of the material. This is the correction value for the extensibility coefficient.

5. The forming process method for martensitic aging steel head shells according to claim 1, characterized in that, The number of extensions is determined, and the condition for one extension is: h≤(0.5~0.7)d In the formula, h is the height of the drawn part; d is the diameter of the drawn part.

6. The forming process method for martensitic aging steel head shells according to claim 1, characterized in that, During the stamping process, the stamping is carried out according to the working dimensions of the drawing die, the press, and the number of drawing cycles.

7. The forming process method for martensitic aging steel head shells according to claim 1, characterized in that, During solution treatment, after loading the blank into the furnace, heat it to 820℃~860℃ and hold it for 90min~150min. After holding, oil cooling is performed.

8. The forming process method for martensitic aging steel head shells according to claim 1, characterized in that, The thickness of the blank is 2mm to 5mm, and a subsequent trimming allowance of 5mm to 15mm is added when cutting the blank.

9. The forming process method for martensitic aging steel head shells according to claim 1, characterized in that, The stamping process includes: Fix the mold on the press, adjust the gap between the die and the punch to make it suitable for stamping hemispheres of different plate thicknesses, and tighten the die and the punch. Clean the working surfaces of the die and punch thoroughly and apply lubricant. Clean the surface of the stamping blank, apply grease, and place the blank into the die cavity; Adjust the working pressure of the press according to the theoretically calculated tensile force, and then perform the stamping.

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