A method of near-net shape local additive manufacturing of a hydraulic cylinder barrel

Abstract

The application provides a hydraulic cylinder barrel near-net forming local additive manufacturing method, which comprises the following steps: step 1), adopting a hot-rolled steel pipe as raw material, shaping the cold-drawn steel pipe through annealing, pickling, phosphorization and soap kernel processes; step 2), sizing according to the size required by the design process; step 3), locally upsetting the cold-drawn steel pipe after sizing; step 4), performing a quenching and tempering treatment on the locally upset cold-drawn pipe; and step 5), supporting the inner hole, flattening the end face, chamfering, and turning the clamping head of the upset cold-drawn pipe after the quenching and tempering treatment, so as to determine the processing datum of subsequent scraping and fine turning. The method has the advantages of good comprehensive mechanical properties, high size precision, small machining allowance and high material utilization rate.

Description

Technical Field

[0001] This invention relates to the field of hydraulic cylinder manufacturing technology, and more specifically, to a near-net-shape partial additive manufacturing method for hydraulic cylinder barrels. Background Technology

[0002] The hydraulic support column and jacks are important components, with the outer and middle cylinders being key parts. The hydraulic support column bears a large load, and the outer and middle cylinders are typically made of high-strength, thick-walled hot-rolled steel pipes. The traditional processing method for locally upset pipes is as follows: length setting → locally upset → quenching and tempering → turning the inner hole → first end face chamfering → turning the outer diameter → rough boring → second end face chamfering → scraping and rolling.

[0003] The existing local upsetting process has a high forging temperature, which easily causes severe decarburization and oxide scale thickness of 1-2.5mm. It is prone to overheating or even burning, resulting in coarse grains and the formation of Widmanstätten and network ferrite. Subsequent quenching and tempering treatment is difficult to eliminate these defects, and it is difficult to control the mechanical properties of the upsetting region.

[0004] The reasons for this are twofold. First, the raw material for traditional locally upsetting tubes is hot-rolled tube, which has poor precision. This results in a large gap between the upsetting die and the forging, leading to low dimensional accuracy in the upsetting area. Second, the high forging temperature results in a thick oxide scale, which leads to poor surface quality in the locally upsetting area, making it difficult to guarantee dimensional accuracy.

[0005] Secondly, the straightness and roundness of traditional local upsetting of tubes are poor. The machining datum is determined by the inner hole or the outer circle, and the machining allowance needs to be increased to ensure the machining accuracy of the inner hole and the outer circle. The turning volume is large, there are many processes, and the machining efficiency is low.

[0006] On the other hand, traditional local upsetting of tubes has a large machining allowance, with an inner hole machining allowance of 9-13mm and an outer circle machining allowance of 10-15mm, resulting in low material utilization.

[0007] Therefore, the traditional local upsetting process for tubes suffers from problems such as large machining allowances, low material utilization, low processing efficiency, and unstable mechanical properties in the local upsetting zone. There is an urgent need to explore a new local upsetting process to reduce machining allowances, improve material utilization, increase processing efficiency, and enhance mechanical properties. This is of great significance for improving the performance of hydraulic cylinders, thereby extending the service life of hydraulic supports, and enabling the efficient operation of coal mining equipment underground.

[0008] In order to solve the above problems, people have been seeking an ideal technological solution. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by providing a near-net-shape local additive manufacturing method for hydraulic cylinder barrels that offers excellent overall mechanical properties, high dimensional accuracy, small machining allowance, and high material utilization.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is: a method for near-net-shape partial additive manufacturing of a hydraulic cylinder, comprising the following steps:

[0011] Step 1) Using hot-rolled steel pipe as raw material, the steel pipe is cold-drawn and shaped through annealing, pickling, phosphating and soaping processes. During the cold drawing process, the wall reduction is controlled between 2.5mm and 8mm, the outer diameter tolerance is between 0 and 0.8mm, and the inner diameter tolerance is ±0.3mm.

[0012] Step 2) Determine the length according to the design process requirements; cold-drawn tubes can be directly ordered to length due to their high dimensional accuracy.

[0013] Step 3) The cold-drawn steel pipe after being cut to length is partially upset. The heating temperature for partial upsetting is 980℃~1030℃, the initial forging temperature is 930℃~980℃, the final forging temperature is 860℃~890℃, and the cooling rate after forging is 0.5℃ / s~1.5℃ / s, to obtain the partially upset cold-drawn pipe.

[0014] Traditional local upsetting results in low dimensional accuracy after forging. The raw material is hot-rolled pipe, which has low precision. The gap between the upsetting die and the forging is also large. Furthermore, the high forging temperature generates a large amount of oxide scale, which affects the dimensional accuracy of the forged workpiece. Additionally, horizontal die forging suffers from poor raw material dimensional accuracy and incomplete die closure, leading to even worse dimensional accuracy after upsetting.

[0015] The optimized local upsetting process uses cold-drawn tubes as raw material. The cold-drawn tubes have high precision in both outer and inner diameters. The gap between the die inner diameter and the forging is less than 1.2mm, and the gap between the punch outer diameter and the forging is less than 0.8mm. The oxide scale generated at the low forging temperature is less than 0.3mm. The upsetting force is 1.8 times that of traditional local upsetting, ensuring that the workpiece dimensions are acceptable even at a lower forging temperature. The use of vertical closed-die forging eliminates the problem of incomplete die closure, further guaranteeing workpiece dimensional accuracy.

[0016] Traditional local upsetting processes involve heating temperatures of 1100–1200℃, initial forging temperatures of 1050–1000℃, and final forging temperatures of 950–1000℃. The high forging temperatures result in oxide scale thicknesses of 1–2.5 mm, severe decarburization of the workpiece surface, and the easy formation of Widmanstätten and network ferrite in the heated area, which are difficult to eliminate in subsequent heat treatment. The optimized local upsetting process uses heating temperatures of 980–1030℃, initial forging temperatures of 930–980℃, and final forging temperatures of 860–890℃. The lower forging temperatures reduce decarburization, avoid overheating and burning, and prevent the formation of Widmanstätten and network ferrite. The post-forging cooling rate is 0.5–1.5℃ / s. By controlling the cooling rate, the recrystallization nucleation rate is increased, and the grain size is refined.

[0017] Step 4) Perform quenching and tempering treatment on the locally upset cold-drawn tube. The austenitizing heating temperature is controlled at 870℃~880℃, preferably 873℃~878℃. The austenitizing heating holding time is (wall thickness * (1.2~1.4) min / mm);

[0018] Compared to traditional quenching and tempering (heating temperature between 850℃ and 860℃), the optimized quenching and tempering process increases the austenitizing heating temperature by 20℃ and reduces the holding time by 10-20 minutes compared to the traditional method (wall thickness * (1.6-1.8) min / mm). Increasing the austenitizing temperature improves superheat, increases the austenite nucleation rate, and increases the austenite growth rate. The austenite grain size depends on the ratio of nucleation rate to growth rate. The ratio of nucleation rate to growth rate is highest at an austenitizing temperature of 875℃. Reducing the holding time, while ensuring the austenite transformation is completed, can shorten the austenite grain growth time and refine the grain size.

[0019] The quenching and cooling process uses internal and external spraying of circulating water, and the workpiece temperature is 70℃~100℃ when the cooling is finished.

[0020] The quenching and cooling process adopts internal and external spraying of circulating water. By controlling the spraying water speed, nozzle density, and spraying time, the cooling rate of the inner and outer surfaces of the workpiece and the axial and radial directions is ensured to be the same and uniform.

[0021] The spray water temperature that the workpiece comes into contact with is consistently between 28 and 32°C, which increases the cooling rate of the workpiece's core, increases the depth of the hardened layer, and allows the material to acquire more martensite. Therefore, after austenitization, the austenite grains are fine, the martensite content is high after quenching, and the martensite laths are finer and more uniform.

[0022] The tempering temperature is 590℃~630℃, with the preferred temperature being 600℃~630℃. The tempering cooling adopts internal and external spraying of circulating water to ensure uniform cooling rate in the axial and radial directions of the workpiece. The workpiece temperature is 150℃~200℃ when the cooling is finished.

[0023] The tempering temperature is 590–630℃, which is 40–50℃ higher than the traditional tempering temperature. This results in a higher martensite content and finer, more uniform martensite laths in the workpiece. Therefore, a higher tempering temperature can be used to improve the material's plasticity and toughness while ensuring its strength. Tempering cooling also employs internal and external circulating water spraying, ending cooling when the workpiece temperature reaches 150–200℃. This reduces tempering brittleness, minimizes workpiece deformation, and ensures dimensional accuracy.

[0024] The material processing technology for non-local upsetting areas is cold drawing followed by quenching and tempering. Hot-rolled tubes are annealed and cold-drawn to form cold-drawn tubes. Compared to hot-rolled tubes, cold-drawn tubes, after plastic deformation, have grains that are elongated into flattened grains along the deformation direction, resulting in numerous slip bands, twin bands, and dislocations. During the austenitizing heating stage, both cold-drawn and hot-rolled tubes undergo recrystallization. In cold-drawn tubes, the grains are elongated, increasing the area of ​​grain boundaries and leading to an increase in defects such as slip, twins, and dislocations, thus increasing the nucleation rate. The recrystallized grains in cold-drawn tubes are finer than those in hot-rolled tubes. During the austenitizing stage, the recrystallized grains in cold-drawn tubes are fine, resulting in fine-grained austenite. Due to the reduction in austenite grain size, the martensite size decreases, and the width of the martensite lath bundles decreases. After tempering transformation, the martensite transforms into tempered sorbite, retaining the fine and uniform ferrite phase, with finely dispersed carbides distributed around the ferrite. Therefore, cold drawing reduces the grain size of austenitized grains, refines lath martensite, and makes tempered sorbite uniform and dense, thereby improving the strength and toughness of the material.

[0025] The material processing technology for the locally upset region is cold drawing → upset → quenching and tempering. The rapid heating rate during local upseting preserves defects such as flattened grains, numerous slip bands, twin bands, and dislocations present in cold drawing until the austenite transformation. Due to the low forging temperature and controlled cooling rate after forging, the grains are further refined, resulting in fine equiaxed pearlite and ferrite grains after forging. After quenching and tempering, uniformly distributed fine tempered sorbite is obtained. Therefore, the process of cold drawing → upset → quenching and tempering improves the strength and toughness of the material.

[0026] Step 5) Perform the following processes on the upset cold-drawn tube after heat treatment: expand the inner hole, flatten the end face, chamfer and turn the head to determine the machining datum for subsequent scraping and finishing.

[0027] Traditional machining methods typically include: fixed length → partial upsetting → quenching and tempering → turning the inner hole → first chamfering of the end face → turning the outer circle → rough boring → second chamfering of the end face → scraping and rolling.

[0028] Specifically, the inner hole is as follows: the outer circle of the left end is clamped, the outer circle of the non-upsetting area of ​​the right end of the center frame is clamped, and the right end face and the inner hole of the right end are machined 60-100mm. The center frame is then clamped in place with the inner hole of the right end, and the right end face and the inner hole of the right end are machined 60-100mm.

[0029] First flat end face chamfering: three-jaw support at both ends of the hole, machine the left and right end faces, chamfer, and check along the axial direction.

[0030] Outer diameter: For the outer diameter of the machined part, leave a radial allowance of 5-10mm in both the upset and non-upset areas.

[0031] Rough boring: Clamp the inner hole by positioning it with chamfered ends.

[0032] Second end face chamfering: The three-jaw chuck supports the holes at both ends, machine the left and right end faces, chamfer, and perform axial inspection. The improved process in this application includes: length setting → local upsetting → tempering → end face chamfering → scraping and rolling. End face chamfering: The three-jaw chuck supports the holes at both ends, machine the left and right end faces, chamfer, and perform axial inspection.

[0033] As can be seen, the number of processes has been significantly reduced. By controlling the dimensional accuracy of raw materials through cold drawing, controlling post-forging dimensional accuracy through low forging temperature and high die precision, and controlling post-tempering dimensional accuracy through internal and external water spraying, the dimensional accuracy of the workpiece is guaranteed. In the flat turning process, the machining datum can be determined by supporting the inner hole, reducing one turning of the inner hole, one turning of the end face and chamfering, one turning of the outer diameter, and one rough boring of the inner hole. The machining allowance has been reduced; the traditional machining process requires an inner hole machining allowance of 9–13 mm and an outer diameter machining allowance of 10–15 mm, while the optimized process requires only 3–5 mm for both inner holes and outer diameters. Material utilization has been improved; the traditional process has a material utilization rate of 70.92%, while the optimized process achieves 81.32%, an increase of 14.67%.

[0034] Based on the above, in step 1), the material selected for the hot-rolled steel pipe is 30CrMnSi.

[0035] Based on the above, in step 3), the local upsetting deformation is carried out by vertical closed die forging, and the heating method is medium frequency induction heating.

[0036] Based on the above, in step 4), during the quenching and cooling process, the spraying water velocity of the circulating water inside and outside is 5m / s to 10m / s, and the spraying time is 2.5min to 5min.

[0037] Based on the above, in step 4), during the tempering cooling process, the spraying water velocity of the circulating water inside and outside is 5m / s to 10m / s, and the spraying time is 30s to 60s.

[0038] This invention has outstanding substantive features and significant progress compared to the prior art. Specifically, this invention has the following advantages:

[0039] This invention adjusts the supply status of hydraulic cylinder barrels, optimizes the local upsetting process and molds, optimizes the process parameters of heat treatment, and puts forward special requirements for the cooling method, ultimately resulting in a significant improvement in the performance, precision and utilization rate of materials.

[0040] Instruction manual illustrations

[0041] Figure 1 This is a schematic diagram showing the process dimensions and structural principle of a hydraulic cylinder. Detailed Implementation

[0042] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0043] like Figure 1 As shown, using a hot-rolled pipe of 30CrMnSi material and a specification of Φ303*41mm as the raw material, a near-net-shape partial additive manufacturing method for hydraulic cylinder barrels is implemented, including the following steps:

[0044] Step 1) Anneal the hot-rolled steel pipe, then pickle, phosphate and saponify, shape the cold-drawn steel pipe, 3mm≤cold drawing wall reduction<4mm, outer diameter tolerance (0mm~0.8mm), inner diameter tolerance (±0.3mm).

[0045] In other embodiments, the cold-drawn wall reduction is controlled between 2.5 mm and 8 mm.

[0046] Step 2) Determine the length according to the dimensions required by the design process.

[0047] The outer diameter of the local upsetting zone is Φ324mm, such as... Figure 1 The D4 dimension in the figure refers to the outer diameter of the non-upsetting area, Φ300mm. Figure 1 The D2 dimension in the figure has an inner diameter of 226mm. If the d2 dimension has a local upsetting zone length of 130mm, then... Figure 1 The L2 dimension in the figure represents a total workpiece length of 1000mm. Figure 1 The L10 dimension is specified in the text. The standard length for cold-drawn tubes is Φ300*38×1085mm.

[0048] Step 3) Perform local upsetting on the cold-drawn steel pipe after it has been cut to length to obtain a locally upset cold-drawn pipe.

[0049] Local upsetting deformation is achieved using vertical closed-die forging with medium-frequency induction heating. The heating temperature is 980℃~1030℃, the initial forging temperature is 930℃~980℃, and the final forging temperature is 860℃~890℃. The upsetting force is 45000kN, and the cooling rate after forging is 0.5~1.5℃ / s. The inner diameter of the die is the nominal outer diameter of the locally upset cold-drawn tube plus 1mm, and the outer diameter of the punch is the nominal outer diameter of the locally upset cold-drawn tube minus 0.5mm. The upsetting force varies depending on the steel pipe specifications, as shown in the table below.

[0050] Φ190~Φ330 30～47 30000～48000 Φ330~Φ430 47～61 48000～82500 Φ430~Φ630 61～75 82500～120000

[0051] Table 1. Comparison of Steel Pipe Specifications, Upsetting Force, and Corresponding Wall Thickness

[0052] Step 4) Perform quenching and tempering treatment on the locally upset and cold-drawn tubes.

[0053] The austenitizing heating temperature is 875℃, and the holding time is 50 min. Quenching cooling uses internal and external circulating water spraying at a water velocity of 7-8 m / s for 3 min to ensure uniform axial and radial cooling rates. The workpiece temperature at the end of cooling is 70-100℃. Tempering temperature is 630℃, and the holding time is 4 h. Tempering cooling uses internal and external circulating water spraying at a water velocity of 7-8 m / s for 40 s to ensure uniform axial and radial cooling rates. The workpiece temperature at the end of cooling is 150-200℃.

[0054] In other embodiments, the austenitizing heating temperature is controlled at 870°C to 880°C, preferably at 873°C to 878°C.

[0055] (5) After the heat treatment, the upset cold-drawn tube is flattened and reversed, the inner hole is supported, the end face is flattened, the chamfer is made and the head is turned to determine the machining benchmark for subsequent scraping, rolling and precision turning.

[0056] This invention presents tensile and impact tests on the optimized cylinder additive manufacturing process and the traditional cylinder additive manufacturing process, respectively. The experiments show that the optimized locally upset cold-drawn tube has higher strength, plasticity, and toughness than the locally upset steel tube produced by the traditional processing process, as shown in the table below.

[0057]

[0058] Table 2 Comparison of the process in this application with traditional cylinder additive manufacturing processes.

[0059] In other preferred embodiments, in step 4), the austenite heating temperature is preferably between 870°C and 875°C, or alternatively between 875°C and 880°C; the tempering temperature is preferably >600°C and not higher than 630°C, and alternatively between 590°C and 600°C.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for near-net-shape partial additive manufacturing of a hydraulic cylinder barrel, characterized in that: Includes the following steps: Step 1) Using hot-rolled steel pipe as raw material, the material selected for hot-rolled steel pipe is 30CrMnSi. Through annealing, pickling, phosphating and soaping processes, the cold-drawn steel pipe is shaped. During the shaping process of the cold-drawn steel pipe, the wall reduction amount is controlled between 2.5mm and 8mm, the outer diameter tolerance is between 0 and 0.8mm, and the inner diameter tolerance is ±0.3mm. Step 2) Determine the dimensions according to the design and process requirements; Step 3) The cold-drawn steel pipe after being cut to length is subjected to local upsetting. The local upsetting deformation is carried out by vertical closed die forging and the heating method is medium frequency induction heating. The heating temperature for local upsetting is 980℃~1030℃, the initial forging temperature is 930℃~980℃, the final forging temperature is 860℃~890℃, and the cooling rate after forging is 0.5℃ / s~1.5℃ / s, to obtain the locally upsetting cold-drawn pipe. Step 4) Perform quenching and tempering treatment on the locally upset cold-drawn tubes. The austenitizing heating temperature is controlled at 873℃~878℃, and the austenitizing heating holding time is wall thickness * (1.2~1.4) min / mm. The quenching and cooling process uses internal and external spraying of circulating water, and the workpiece temperature is 70℃~100℃ when the cooling is finished. The tempering temperature is 600℃~630℃. The tempering cooling adopts internal and external spraying of circulating water to ensure uniform cooling rate of the workpiece in the axial and radial directions. The workpiece temperature is 150℃~200℃ when the cooling is finished. The material processing technology for the non-local upsetting area is cold drawing to quenching and tempering; Step 5) Perform the following processes on the upset cold-drawn tube after heat treatment: expand the inner hole, flatten the end face, chamfer and turn the head to determine the machining datum for subsequent scraping and finishing.

2. The near-net-shape partial additive manufacturing method for hydraulic cylinder barrels according to claim 1, characterized in that: In step 4), during the quenching and cooling process, the spraying water velocity of the circulating water inside and outside is 5 m / s ~ 10 m / s, and the spraying time is 2.5 min ~ 5 min.

3. The near-net-shape partial additive manufacturing method for hydraulic cylinder barrels according to claim 1 or 2, characterized in that: In step 4), during the tempering cooling process, the spraying water velocity of the circulating water inside and outside is 5 m / s ~ 10 m / s, and the spraying time is 30 s ~ 60 s.

4. The near-net-shape partial additive manufacturing method for hydraulic cylinder barrels according to claim 3, characterized in that: In step 4), the temperature of the spray water is maintained at 28℃~32℃.

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