A four-position forging process for piston

Abstract

This invention discloses a four-station precision forging process for pistons. The process involves open billet preparation, open reverse extrusion, open skirt forging, and closed precision forging to complete the precision forging of the piston. The material is rationally distributed through three open forging stages, culminating in the final precision forging. This four-station precision forging process produces forgings with high precision, no flash, and complete filling of the piston skirt without closed extrusion. It also features low forming force, effectively reducing equipment tonnage, enabling continuous forging, and improving the die life at each station.

Description

Technical Field

[0001] The invention relates to the technical field of piston forging, in particular to a four-station precision forging process for a piston. Background Art

[0002] Forged pistons are widely used in heavy-duty vehicles, engineering machinery, marine and mining power generation. The manufacturing process usually includes welding, forging, casting, etc. With the increase of market demand, forged pistons have dense structure, high strength and good reliability. Therefore, forging has become the mainstream production process of pistons.

[0003] At present, the most advanced method of forging piston in China is the multi-step closed extrusion process, which can only fill the skirt of the piston through closed extrusion. There is flash on the top of the forging and it needs to be trimmed. The current forging process makes the forging die life short, the filling of the forging skirt is poor, and the equipment tonnage is large and the cost is high. Summary of the invention

[0004] The purpose of the present invention is to provide a piston four-station precision forging process in view of the technical defects existing in the prior art.

[0005] The technical solution adopted to achieve the purpose of the present invention is:

[0006] A four-station precision forging process for a piston, which completes the precision forging of the piston through open blanking, open reverse extrusion, open skirt forging, and closed precision forging. The material is reasonably distributed through three open forgings, and the precision forging is finally completed. Specifically, the following steps are included:

[0007] The blank is first heated to a predetermined temperature and then placed in a four-station die for forging:

[0008] One-step open upsetting: The blank is formed and upset by a one-station die to remove the oxide scale; the upper die of the one-station die is matched with two arcs of different arcs to distribute the metal material in advance in the length and width directions of the forging;

[0009] Two-step open reverse extrusion: The piston skirt contour is reversely extruded through the two-station die to complete the material distribution of the skirt. At the same time, the upper die punch of the two-station die is used to extrude the inner hole in the center of the skirt at the upper end of the forging;

[0010] Three-step open skirt top forming: formed by a three-station die. The upper mold cavity of the three-station die has no core in the middle. The outer side of the forging is a fully enclosed structure to restrict the metal material from flowing outward. Only the top of the skirt on the inner side of the forging is restricted by the die. During the forming process, the three-station die applies downward pressure, and the metal material in the three-station die is restricted to flow only inward. With the bottom of the two-step forging as support, the metal material slowly flows upward and inward, and finally forges the shape of the skirt top;

[0011] Four-step closed precision forging: forming is completed in a closed four-station mold. A convex core is set in the center of the mold cavity of the upper mold of the four-station mold, and the convex core is adapted to the size and shape of the inner hole inside the forging.

[0012] Among them, a two-station lower ejector rod is arranged at the lower mold center of the two-station mold.

[0013] Among them, a three-station upper ejector is arranged on the outer side of the top of the skirt of the corresponding forging in the upper die of the three-station die. The three-station upper ejector is shortened by 3-5mm according to the size of the forging to serve as a surplus material bin and reduce the stress on the three-station upper ejector.

[0014] Among them, a four-station upper ejector rod is arranged in the upper die of the four-station mold. The four-station upper ejector rod is shortened by 3-5mm according to the size of the forging, serving as a surplus material bin and reducing the force on the four-station upper ejector rod.

[0015] Among them, the first-station mold is an open structure, and its lower mold has a shallow groove-type first-station lower model cavity adapted to the diameter of the raw material. The center of the first-station lower model cavity has a positioning groove adapted to the top tip bottom size of the piston forging.

[0016] Among them, the lower mold of the two-station mold has a two-station mold cavity. The wall thickness of the forging formed in the two-step reverse extrusion process is smaller than the wall thickness of the piston forging at the corresponding position, and is reduced by 3-5mm on one side. The height of the extruded part formed is 10-20mm higher than the height of the piston forging.

[0017] Among them, the mold cavity size set in the upper mold of the four-station mold is the same as the size of the piston forging. When the mold is closed, the lower mold and the upper mold of the four-station mold are closed with a gap of 0.5mm.

[0018] Among them, the upper surface of the lower mold push rod of the two-station mold, the upper surface of the lower mold of the three-station mold and the upper surface of the lower mold of the four-station mold respectively have positioning grooves corresponding to the positioning grooves.

[0019] The invention completes the precision forging of the piston through open blanking, open reverse extrusion, open forging skirt, and closed precision forging. The material is reasonably distributed through three open forgings, and the precision forging is finally completed. The forging has high precision and no flash. It can fill the piston skirt without closed extrusion, and the forming force is small, which effectively reduces the tonnage of the equipment, can be forged continuously, and increases the mold life of each station. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of the forged piston targeted by the present invention.

[0021] Figure 2 It is a schematic diagram of the piston forging formed by the present invention.

[0022] Figure 3 1 is another schematic diagram of the piston forging formed by the present invention.

[0023] Figure 4 It is a schematic diagram of a four-station die for forming a piston forging according to the present invention.

[0024] Figure 5 It is a schematic diagram of a one-station mold of a four-station mold for forming a piston forging according to the present invention.

[0025] Figure 6 It is a first schematic diagram of an upper die of a one-station die for forming a piston forging according to the present invention.

[0026] Figure 7 It is a second schematic diagram of an upper die of a one-station die for forming a piston forging according to the present invention (a cross-sectional view taken along the AA line of the first schematic diagram).

[0027] Figure 8 It is a three-dimensional view of a one-station die for forming a piston forging according to the present invention.

[0028] Fig. 9 It is a schematic diagram of the lower die of a one-station die for forming a piston forging according to the present invention.

[0029] Fig.10 It is a schematic diagram of a two-station die for forming a piston forging according to the present invention.

[0030] Fig.11 It is a schematic diagram of the upper die of the two-station die for forming a piston forging according to the present invention.

[0031] Fig.12 It is a schematic diagram of the lower die of the two-station die for forming a piston forging according to the present invention.

[0032] Fig.13 It is a schematic diagram of a three-station die for forming a piston forging according to the present invention.

[0033] Fig.14 It is an initial schematic diagram of the three-station die for forming a piston forging according to the present invention after the two-station forming forging is loaded.

[0034] Fig.15 It is a schematic diagram of a four-station die for forming a piston forging according to the present invention.

[0035] Fig.16 It is a workpiece morphology change diagram during the piston forging forming process of the present invention.

[0036] Fig.17 It is a workpiece morphology change diagram in the cross-sectional form during the piston forging forming process of the present invention.

[0037] Description of reference numerals:

[0038] 1 is the piston top, 2 is the piston ring land, 3 is the piston pin hole, 4 is the oil return hole, and 5 is the piston skirt.

[0039] 6 is the piston pin retaining ring groove 7 is the oil ring groove 8 is the gas ring groove

[0040] 100 is a one-station mold, 200 is a two-station mold, 300 is a three-station mold, 400 is a four-station mold, 500 is an upper mold, and 600 is a lower mold.

[0041] 10 is an upper die of a station mold, and 11 is a lower die of a station mold

[0042] 20 is the upper die of the two-station die, 21 is the lower die of the two-station die, and 22 is the lower ejector of the two-station die.

[0043] 30 is the upper die of the three-station die, 31 is the lower die of the three-station die, and 32 is the upper ejector of the three-station die.

[0044] 40 is the upper die of the four-station die, 41 is the lower die of the four-station die, and 42 is the upper ejector of the four-station die.

[0045] 50 is a two-station forming forging. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0047] The four-station precision forging process for the piston of the embodiment of the present invention mainly comprises the following steps: heating - blank making - open reverse extrusion - open skirt forging - closed precision forging, a total of four process steps; Figures 2 to 3 As shown, the size of the final precision forging billet is ф75mm×180mm.

[0048] In order to realize the precision forging process of the present invention, a 1600-ton hot die forging press can be used, and a four-station die can be used for four-station continuous forging. During the forging process, after each station die is forged once, cooling water is first sprayed to cool the die, and then a lubricant is sprayed. The lubricant is oil-based graphite, which is evenly sprayed on the four-station die, and sprayed once for each forging. After forging, air is blown to clean the oxide scale remaining in the die.

[0049] During the forging process, the four-station die is preheated to about 300 degrees.

[0050] The process is as follows:

[0051] First, heat the steel billet to 1150-1180 degrees (440-460 degrees for aluminum alloy), and then put it into a four-station mold for forging:

[0052] The first step is upsetting: the purpose is to form upsetting and remove oxide scale. The upsetting upper die uses two arcs of different arcs to cross and match, and the material is distributed in advance in the direction of the length and width of the forging.

[0053] After forging is completed, the forging is taken out and compressed air is blown to blow out the oxide scale remaining in the lower die and cool and lubricate the die.

[0054] The second step is back extrusion: the purpose is to back extrude the piston skirt contour. This step completes the material distribution of the skirt.

[0055] Three-step skirt top forming: The top of the skirt is the most difficult position to form and is also the last place to be filled in the ordinary piston process. Usually, the metal will be filled here only after other positions of the closed cavity are completely filled.

[0056] The present invention forms the top of the skirt at the third station. As shown in the figure, the mold is fully surrounded on the outside to restrict the metal material from flowing outward, and only the top of the skirt is restricted by the mold on the inside. The metal material in the mold can flow inward but cannot flow outward. During the forming process, the mold applies downward pressure, and the forging is supported by the bottom of the two-step forging, and the metal material slowly flows upward and inward. Finally, the shape of the skirt top is forged.

[0057] Four-step closed precision forging: After the pre-forming in the first three steps, the material is distributed to the best state, and the final step is precision forging. The forging is completed in the closed mold, and the material distribution can theoretically achieve a completely full effect. Due to the error of raw material feeding, a circle of bins will be reserved at the bottom of the mold, between the upper and lower molds, to ensure that the error of the billet can be accommodated, as well as the deviation caused by the offset and tilt of the billet during the forging process.

[0058] Exemplarily, a four-station mold uses a four-station closed mold, such as Figure 4 As shown, it includes a one-station mold 100, a two-station mold 200, a three-station mold 300, a four-station mold 400, an upper mold plate 500, and a lower mold plate 600, which are placed on a hot die forging press, and the center position spacing of each station is the same. The mold closing height H is determined according to the bottom dead center position of the equipment slide.

[0059] Among them, a station mold 100 is a forming upsetting mold, such as Figure 4 As shown, it is composed of a one-station upper mold 10 and a one-station lower mold 11. It is an open structure. The upper mold is divided into a long side and a short side. The metal material is distributed according to the length and width direction of the forging cross section. It is composed of an arc R35-62 and a 130° arc surface, with a smooth transition in the middle. The diameter of the lower mold cavity is increased by 0.5mm on one side according to the original billet diameter, and the depth is 20mm. The conical tip is the same size as the tip of the piston forging top. The main purpose is to smoothly put it into the two-station mold 200 and position it accurately.

[0060] The two-station die 200 includes a two-station die upper die 20, a two-station die lower die 21 and a two-station die lower ejector 22. It is a reverse extrusion process, which reversely extrude the formed upset piece into the shape of an elliptical cup. The wall thickness of the reverse extruded piece in this process step is less than the wall thickness of the piston forging at the corresponding position, and the single side is reduced by about 3-5mm. The height of the reverse extruded piece in this process step is 10-20mm higher than the height of the piston forging.

[0061] The upper die is 3-5mm smaller than the inner hole of the piston forging, and the depth is about 30mm higher than the piston forging. The lower die draft angle is 6°, which is opposite to the outer angle of the piston forging.

[0062] The three-station die 300 includes a three-station die upper die 30, a three-station die lower die 31 and a three-station die upper ejector 32. The lower die is designed according to the size of the conical tip at the top of the piston forging. The upper die has a draft angle of 2°, no core in the middle, and the same angle as the outer contour of the piston forging. The lower die has the same size as the conical tip at the bottom of the piston forging. This die extrude the outer 6° of the two-station reverse extrusion into the reverse 2°. The outer side of the three-station forging changes with the shape of the die, the inner side flows freely, the wall thickness increases, and the height decreases.

[0063] The size of the four-station mold cavity is the same as that of the piston forging, and has a four-station mold upper ejector 42. When the mold is closed, the four-station mold lower mold 41 and the four-station mold upper mold 40 are closed with a gap of 0.5 mm.

[0064] It should be noted that the unit symbol for the parameters shown in the drawings of the present invention is mm.

[0065] This process is suitable for pistons of other sizes with consistent shapes, and is suitable for steel and aluminum pistons. Steel and aluminum forgings have different requirements for mold design. It can be used for equipment such as hot die forging presses and electric screw presses. It can be produced continuously and automatically, or each station can be forged individually.

[0066] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0067] Therefore, no matter from which point of view, the embodiments should be regarded as illustrative and non-restrictive, and the scope of the present invention is limited by the appended claims rather than the above description. Therefore, it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any figure signs in the claims should not be regarded as limiting the claims involved.

[0068] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. The four-station precision forging process for pistons is characterized by: The precision forging of the piston is completed through open blanking, open reverse extrusion, open forging skirt, and closed precision forging. The material is reasonably distributed through three open forgings, and the precision forging is completed at last. The specific steps include: The blank is first heated to a predetermined temperature and then placed in a four-station die for forging: One-step open upsetting: The blank is formed and upset by a one-station die to remove the oxide scale; the upper die of the one-station die is matched with two arcs of different arcs to distribute the metal material in advance in the length and width directions of the forging; Two-step open reverse extrusion: The piston skirt contour is reversely extruded through the two-station die to complete the material distribution of the skirt. At the same time, the upper die punch of the two-station die is used to extrude the inner hole in the center of the skirt at the upper end of the forging; Three-step open skirt top forming: formed by a three-station die. The upper mold cavity of the three-station die has no core in the middle. The outer side of the forging is a fully enclosed structure to restrict the metal material from flowing outward. Only the top of the skirt on the inner side of the forging is restricted by the die. During the forming process, the three-station die applies downward pressure, and the metal material in the three-station die is restricted to flow only inward. With the bottom of the two-step forging as support, the metal material slowly flows upward and inward, and finally forges the shape of the skirt top; Four-step closed precision forging: forming is completed in a closed four-station mold. A convex core is set in the center of the mold cavity of the upper mold of the four-station mold, and the convex core is adapted to the size and shape of the inner hole inside the final forging.

2. The four-station precision forging process for piston according to claim 1 is characterized in that: A two-station lower ejector rod is arranged at the lower mold center of the two-station mold.

3. The four-station precision forging process for piston according to claim 1 is characterized in that: A three-station upper ejector rod is arranged on the outer side of the top of the skirt of the forging in the upper die of the three-station die. The three-station upper ejector rod is shortened by 3-5mm according to the size of the forging to serve as a surplus material bin and reduce the force on the three-station upper ejector rod.

4. The four-station precision forging process for piston according to claim 1 is characterized in that: A four-station upper ejector rod is arranged in the upper die of the four-station mold. The four-station upper ejector rod is shortened by 3-5mm according to the size of the forging, serving as a surplus material bin and reducing the force on the four-station upper ejector rod.

5. The four-station precision forging process for piston according to claim 1 is characterized in that: The one-station mold is an open structure, and its lower mold has a shallow groove-type one-station lower mold cavity adapted to the diameter of the billet, and the center of the one-station lower mold cavity has a positioning groove adapted to the top tip bottom size of the piston forging.

6. The four-station precision forging process for piston according to claim 1 is characterized in that: The lower mold of the two-station mold has a two-station mold cavity. The wall thickness of the extruded part formed in the two-step open reverse extrusion process is smaller than the wall thickness of the piston forging at the corresponding position, and is reduced by 3-5mm on one side. The height of the extruded part formed is 10-20mm higher than the height of the piston forging.

7. The four-station precision forging process for piston according to claim 1 is characterized in that: The mold cavity size set in the upper mold of the four-station mold is the same as the size of the piston forging. When the mold is closed, the lower mold and the upper mold of the four-station mold are closed with a gap of 0.5mm.

8. The four-station precision forging process for a piston according to claim 5 is characterized in that: The upper surface of the second-station lower ejector pin of the lower mold of the two-station mold, the upper surface of the lower mold of the three-station mold and the upper surface of the lower mold of the four-station mold respectively have positioning grooves corresponding to the positioning grooves.

9. The four-station precision forging process for piston according to claim 1 is characterized in that: The draft angle of the two-station extrusion part is at the lower die of the two-station mold, which is a 6-degree draft angle from bottom to top; the draft angle of the three-station forging is at the upper die of the three-station mold, which is a 2-degree draft angle from top to bottom; the highest point of the two-station extrusion part can enter more than 1 / 2 of the depth of the upper die of the three-station mold.

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