CN103009020B - Manufacturing method for steel cracking connecting rod - Google Patents

Abstract

The invention discloses a method for manufacturing a steel cracking connecting rod, which belongs to the field of engine component manufacturing. When casting the connecting rod blank, the preheated gray cast iron sheet is placed in the cavity of the connection part between the connecting rod body and the connecting rod cover, and the interface between the gray cast iron sheet and the molten steel is melted by the strong heat action of the molten steel during pouring After condensation, the gray cast iron sheet and steel are metallurgically combined to make a composite connecting rod blank; when implementing the cracking process, the connecting rod cracking tank is set in the middle of the gray cast iron sheet, and the brittleness of the gray cast iron material is used to realize the connecting rod body. It is separated from the brittle fracture of the connecting rod cover, and the natural three-dimensional concave-convex structure on the fracture surface ensures the precise positioning and assembly of the connecting rod body and the connecting rod cover. The invention can apply cracking connecting rods to various common steel materials to realize the brittle fracture separation of the connecting rod body and the connecting rod cover at normal temperature, without using mechanical grinding to process the joint surface, simplifying the manufacturing process and reducing the manufacturing cost.

Description

A kind of manufacturing method of steel cracking connecting rod

technical field

The invention belongs to the field of engine component manufacturing, and in particular relates to a manufacturing method of a steel cracking connecting rod.

Background technique

The connecting rod is one of the key components of the engine, and it is subjected to high-frequency alternating loads during its operation. Therefore, the connecting rod must have sufficiently high strength, stiffness and comprehensive mechanical properties. The traditional connecting rod adopts the split processing method. After the connecting rod blank is forged as a whole, the joint surface of the connecting rod body and the connecting rod cover is processed by sawing, milling, grinding, etc., and the positioning pin holes of the connecting rod cover and the bolts of the connecting rod body are finished. Complete the combination of the two after the hole. The traditional method has many procedures, low efficiency, high product rejection rate, and poor carrying capacity and quality stability. Therefore, cracking processing technology has gradually become the most promising new technology in the field of connecting rod manufacturing.

The low plasticity and brittleness of cast connecting rods are very suitable for the application of cracking processing technology, but the weight deviation of cast connecting rods is large, the mechanical properties are poor, and the fatigue strength is low, so its use is limited. At present, C70S6 high-carbon non-quenched and tempered steel developed in Germany is the most widely used in the production of cracking connecting rods, and SPLITASCO series high-carbon steels are developed in France. These materials have good crackability, but low yield strength and high hardness. Wears out quickly and the material is expensive. Domestic enterprises have successively developed vanadium-based, manganese-vanadium-based and manganese-vanadium-nitrogen-based non-quenched and tempered steels for connecting rods, typically 38MnVS, 40MnV, 48MnV, etc. However, there are still many problems in practical application: after cracking, the large end hole of the connecting rod is deformed excessively, the joint surface is obviously dislocated, the grain size of the fracture surface does not meet the meshing requirements, and even cracking cannot be opened, etc. These problems limit the high quality. Fabrication of cracked connecting rods.

In order to control the cracking quality of steel connecting rods and improve the qualified rate of cracking connecting rods, the current research on the cracking process of steel connecting rods mainly focuses on: (1) Controlling the carbon content of steel materials, adding microalloying elements Mn, S, Si, V, Cr, P, etc., and adjust the content of each component to meet the brittle fracture requirements; (2) optimize the split structure of the connecting rod, and use surface hardening treatment to form a split surface with a crystal interface; (3) ) put the steel connecting rod into liquid nitrogen deep cooling to change the ductility of the material and make it into a brittle state to realize the brittle fracture of the connecting rod; Irradiation changes the local austenite structure into martensite structure, and realizes the brittle fracture separation of the connecting rod. None of the above technologies can fundamentally solve the limitations of cracking technology on connecting rod materials, and it is impossible to apply medium carbon steel, ordinary forged steel, etc. to the manufacture of cracking connecting rods.

The application number is 201210111187.3, and the patent titled "A Manufacturing Method for Cracking Connecting Rod" proposes to manufacture connecting rods by artificially setting cracking surfaces in the connecting rod blank, that is, setting a layer of special metal foil in the mold cavity. , so that the molten metal reacts to form a brittle interface. This technology has the following problems: the metal foil has low strength and is easily oxidized. If the metal liquid level on both sides of the foil rises inconsistently, the filling is not stable, and the impact on the foil is large, the brittle interface formed in the casting will deviate from the predetermined position. Or the brittle interface cannot be formed, and subsequent splitting and dissection may not be possible.

The application number is 201210111190.5, and the patent titled "A Manufacturing Method for Composite Bimetallic Cracking Connecting Rod" proposes: first casting the connecting rod body and connecting rod cover, and then pouring the molten metal for cracking after pulling out the middle isolation plate to make a composite bimetallic cracking connecting rod. Connecting rod billets. This method is not practical for steel materials, because the steel material has a high melting point and is easy to stick to the mold, and the condensation and shrinkage of the metal will produce a large covering force on the isolation plate, making it difficult to remove the isolation plate smoothly.

In order to overcome the problems existing in the above-mentioned patented technology, the present invention proposes a method in which the gray cast iron sheet is cast inside the steel connecting rod, and the heat of the molten steel is used to metallurgically combine the gray cast iron sheet with the molten steel matrix material during casting to form a composite connecting rod. Cast slab; when the cracking process is implemented, the brittleness of the gray cast iron sheet is used to complete the splitting of the connecting rod body and the connecting rod cover. The manufacturing method of the steel cracking connecting rod proposed by the invention has the advantages of simple process, convenient operation and low manufacturing cost.

Contents of the invention

The purpose of the present invention is to provide a kind of steel connecting rod internal cracking problem for cracking common forged steel and medium carbon steel which can not be cracked, section deformation, crack bifurcation, etc. The method of casting gray cast iron is used to solve the limitation of cracking technology on the selection of connecting rod materials and improve the cracking quality of connecting rods.

Based on this purpose, the technical solution of the present invention is: a method for manufacturing a steel cracked connecting rod, which is characterized in that when casting the connecting rod blank, the preheated gray cast iron sheet is pre-placed on the connection between the connecting rod body and the connecting rod cover The cavity of the part; during pouring, the interface between the gray cast iron sheet and the molten steel is melted by the strong heat action of the molten steel, and after condensation, the gray cast iron sheet and the steel are metallurgically combined to make a composite connecting rod blank; A cracking tank is set up in the gray cast iron material area, and the cracking equipment is used to complete the brittle fracture of the connecting rod body and the connecting rod cover in the gray cast iron material area, and the natural three-dimensional concave-convex structure features on the fracture surface are used to complete the precise connection between the connecting rod body and the cover. Positioning and assembly.

A method for manufacturing a steel cracking connecting rod, the specific steps are:

A) When casting the connecting rod blank, place the preheated gray cast iron sheet 3 in the cavity of the connection part between the connecting rod body 1 and the connecting rod cover 2;

B) During pouring, the interface between the gray cast iron sheet 3 and the molten steel is melted by the thermal action of the molten steel, and after condensation, the gray cast iron sheet 3 is metallurgically combined with the steel to form a composite connecting rod blank;

C) Diffusion annealing/normalizing treatment;

D) The composite connecting rod blank made above may be forged, quenched and tempered;

E) Set up cracking tank 4 in the gray cast iron material area of the connecting rod, and use cracking equipment to make the connecting rod body 1 and connecting rod cover 2 complete brittle fracture in the gray cast iron material area;

F) Use the natural three-dimensional concave-convex structure features on the fracture surface of the brittle fracture section to complete the precise positioning and assembly of the connecting rod body-cover.

The connecting rod blank adopts sand casting, investment casting and lost foam casting.

The carbon content of the gray cast iron material is 2.2~4.0% by mass, the melting point is 1100~1300°C, and the thickness of the inlaid gray cast iron sheet is 0.1mm~10mm. In order to increase the bonding strength between the gray cast iron and the base metal, the inlaid gray cast iron sheet is made to include a front surface, a rear surface corresponding to the front surface and four sides, in which the side that directly contacts the connecting rod body and the connecting rod cover is cut There is a through V-shaped groove, or the side profile that directly contacts the connecting rod body and the connecting rod cover is made into a zigzag structure.

Preheat the mold before casting, so that the gray cast iron embedded in the mold is fully preheated to 400~900°C, so as to avoid interface cracks caused by thermal stress and phase transformation stress when the molten metal contacts with the gray cast iron, thereby improving Quality of metallurgical bonding at the interface between base metal and gray cast iron.

The method for manufacturing a cracked steel connecting rod is characterized in that the steps A) and B) are replaced by, when casting the connecting rod blank, first pour the connecting rod body 1 and the connecting rod cover 2 cavity Molten steel, when the molten steel is condensed to a semi-solidified state, the separator is removed, and gray cast iron molten iron is poured, so that the gray cast iron and steel are metallurgically combined to make a composite connecting rod blank.

The composite connecting rod blank made above may be processed by cracking process after being forged.

The manufacturing process of cracked connecting rod includes: casting connecting rod blank; diffusion annealing/normalizing; forging; quenching and tempering heat treatment; processing cracking groove, splitting and reassembly.

Beneficial effects of the present invention: (1) A layer of gray cast iron is inlaid and cast in the joint area of the connecting rod body and the connecting rod cover, and the low plasticity and brittleness of the gray cast iron are used to meet the technical requirements of the cracking process of the connecting rod, breaking through the impact of the cracking technology The limitation of connecting rod materials increases the optional range of connecting rod materials, reduces manufacturing costs, and can control the weight accuracy of connecting rods at 1.5%. (2) The cracking process is implemented in the gray cast iron material area of the connecting rod to reduce the cracking force during the cracking process, which can effectively improve the tearing, cracking, slag, fracture surface dislocation, and connecting rod that occur during the cracking process. Big head deformation and other issues. (3) Investment casting and lost foam casting are used to complete the precision forming of the cracked connecting rod. Its geometric shape and dimensional accuracy are close to the size of the finished connecting rod, which reduces processing costs, tool wear and energy consumption. (4) When designing the connecting rod structure, there is no need to consider the reserved cutting allowance and the grinding allowance of the joint surface, so the design of the connecting rod structure is simplified, and the machining accuracy and cost of the bolt holes are reduced.

Description of drawings

Fig. 1 Schematic diagram of connecting rod with gray cast iron insert.

Fig. 2 Flow chart of connecting rod lost foam casting process.

Fig. 3 Schematic diagram of connecting rod investment casting mold shell.

Figure 4 Flowchart of connecting rod investment casting.

In the figure, 1 connecting rod cover, 2 connecting rod cover, 3 gray cast iron sheet, 4 cracking tank, 5 connecting rod bolt, 6 riser, 7 sprue, 8 induction coil, 9 sand mold, 10 inner runner, 11 screw , 12 connecting rod formwork.

Detailed ways

The technical solution of the present invention will be further described below in conjunction with the examples, but it should not be understood that these examples are limitations to the technical solution.

Example 1:

Example 1 The connecting rod blank is manufactured by the lost foam casting process. The main material of the connecting rod is medium carbon steel 40Cr, which is moderately priced and easy to process. After heat treatment, it can manufacture connecting rod parts that withstand high loads and impacts. Due to its high toughness, brittle cracking cannot be achieved at room temperature and cannot be used for cracking Manufacturing of connecting rods. Gray cast iron chooses HT200, its plasticity and toughness are far lower than steel, and it is easy to be brittle and split. Its melting point is 1145~1250°C.

Figure 2 is the process diagram of the lost foam casting of connecting rods. The connecting rods are arranged vertically, with the big end of the connecting rod facing down and the small end facing up. And sprue 7 adopts the direct molding of wooden formwork. During mold manufacture, at first make the mold of the polystyrene foam mold of connecting rod, make the foam plastic mold of connecting rod with this mold again, then in the connecting rod body 1 of the foam plastic mold of connecting rod and connecting rod cover 2 A rectangular cavity is opened at the joint part to install the gray cast iron sheet 3, ensuring that the length of the gray cast iron sheet 3 exceeds the two sides of the connecting rod cover 2 by 3~10mm; Apply refractory coating, put it into a drying room with a temperature of 50°C to dry the pasted integral lost foam; bury the dried integral lost foam in dry sand, at a vibration frequency of 50~60HZ and an amplitude of 1- Vibrate within the parameter range of 2 mm, and use wooden molds to directly manufacture riser 6 and sprue 7 to complete the production of lost foam casting.

The gray cast iron sheet 3 is pre-cleaned with dilute hydrochloric acid to remove the surface scale, and coated with a layer of anti-oxidation protection agent on the outer surface, and then embedded in the connecting rod body 1 and the connecting rod cover 3 of the vanishing model. Before casting, put the entire sand mold into the induction coil, and use induction heating to preheat the connecting rod mold. During the preheating process, the foam plastic model is heated and vaporized. When the gray cast iron sheet 3 is preheated to 300~800°C, The molten alloy steel is poured into the mold until the riser is filled, and the molten steel is cast at a temperature 30-80°C higher than its liquidus temperature. After the casting is cooled, the whole sand mold is lifted out of the induction coil, and the sand is broken to take out the piece.

Through test analysis, it can be seen from the microstructure of the bonding interface that obvious metallurgical reactions have occurred at the interface, and the materials on both sides of the gray cast iron sheet are tightly bonded to the base metal without obvious cracks and holes. When implementing the cracking process, first, the big end hole of the connecting rod is roughly machined, a cracking groove 4 is set in the middle of the gray cast iron 3 of the connecting rod big end, and the connecting rod body 1 and the connecting rod cover 2 are separated by cracking equipment. The gray cast iron 3 inlaid in the connecting rod exhibits excellent brittleness during cracking, and the deformation of the big end hole of the connecting rod is small, and a dog-tooth staggered structure is formed on the section, which can realize the positioning surface of the connecting rod body 1 and the connecting rod cover 2, and complete two The precise fit of the person. Due to the inlay of gray cast iron, it effectively reduces the problems of unilateral tearing, failure to crack, and deformation of the big head hole when the connecting rod is cracked.

Example 2:

Example 2 An investment casting process is used to manufacture a steel connecting rod blank. The main material of the connecting rod is medium carbon steel 40Cr, which is moderately priced and easy to process. After heat treatment, it can manufacture connecting rod parts that withstand high loads and impacts. Due to its high toughness, brittle cracking cannot be achieved at room temperature and cannot be used for cracking Manufacturing of connecting rods. Gray cast iron chooses HT200, its plasticity and toughness are far lower than steel, and it is easy to be brittle and split. Its melting point is 1145~1250°C.

Using the investment casting process, firstly, according to the shape of the connecting rod to be manufactured, a wax mold of the connecting rod is made, and a rectangular cavity is opened on the connecting rod body 1 and the connecting rod cover 2 on the connecting rod wax model. To install the gray cast iron sheet 3, and bond the sprue rod and the inner runner on the wax mold of the connecting rod to make a wax mold module. Before the gray cast iron sheet 3 is embedded in the wax pattern, it should be cleaned with dilute hydrochloric acid to remove the surface scale, and a layer of anti-oxidation protective agent should be applied on the outer surface. The protective agent is boric acid or rare earth oxide; after the gray cast iron sheet 3 is embedded in the wax pattern Screw in the low-melting point screws 11 at both ends respectively, and extend the screws 11 out of the outer wall of the wax mold by 3~6mm; then dip the surface of the connecting rod module with a mixture of refractory water glass or silica gel and fine sand, and then paste, Sprinkle refractory sand to ensure that the surface sand layer is 2~5mm thick; after it is dry and solidified, heat the whole module to 60~80°C, remove the melted wax from the gate, and make the mold shell 12, As shown in Figure 3; before casting, the mold shell is heated to 700~900°C, and the smelted alloy steel is injected from the sprue, and the molten steel is cast at a temperature 30~80°C higher than its liquidus temperature. After condensation, a composite casting inlaid with cast iron sheets is formed, and the shell is manually removed and the riser is cut off.

Through test analysis, it can be seen from the microstructure of the bonding interface that obvious metallurgical reactions have occurred at the interface, and the materials on both sides of the gray cast iron sheet are tightly bonded to the base metal without obvious cracks and holes. When implementing the cracking process, first, the big end hole of the connecting rod is roughly machined, a cracking groove 4 is set in the middle of the gray cast iron 3 of the connecting rod big end, and the connecting rod body 1 and the connecting rod cover 2 are separated by cracking equipment. The gray cast iron 3 inlaid in the connecting rod exhibits excellent brittleness during cracking, and the deformation of the big end hole of the connecting rod is small, and a dog-tooth staggered structure is formed on the section, which can realize the positioning surface of the connecting rod body 1 and the connecting rod cover 2, and complete two The precise fit of the person. Due to the inlay of gray cast iron, it effectively reduces the problems of unilateral tearing, failure to crack, and deformation of the big head hole when the connecting rod is cracked.

Claims (4)

1. a manufacturing method of steel cracking connecting rod, is characterized in that, concrete steps are: A) When casting the connecting rod blank, place the preheated gray cast iron sheet (3) in the cavity of the connection part between the connecting rod body (1) and the connecting rod cover (2); the material of the gray cast iron sheet (3) The mass percentage of carbon content is 2.2-4.0%, the melting point is 1100-1300°C, the thickness of the gray cast iron sheet (3) is 0.1mm-10mm, and the gray cast iron sheet (3) is nickel-plated; B) During pouring, the interface between the gray cast iron sheet (3) and the molten steel is melted by the thermal action of the molten steel, and after condensation, the gray cast iron sheet (3) is metallurgically combined with the steel to form a composite connecting rod blank; C) Diffusion annealing/normalizing treatment; D) The composite connecting rod blank made above, quenched and tempered heat treatment; E) Set up a cracking tank (4) in the gray cast iron material area of the connecting rod, and use cracking equipment to make the connecting rod body (1) and the connecting rod cover (2) complete brittle fracture in the gray cast iron material area; F) Use the natural three-dimensional concave-convex structure features on the fracture surface of the brittle fracture section to complete the precise positioning and assembly of the connecting rod body-cover. 2. The manufacturing method of a kind of steel cracking connecting rod according to claim 1, characterized in that, the connecting rod blank adopts sand casting, investment casting or lost foam casting. 3. The manufacturing method of a steel cracking connecting rod according to claim 1 or 2, characterized in that a through V is cut on the side of the gray cast iron sheet (3) contacting the connecting rod body and the connecting rod cover shaped groove, or make the side contacting the connecting rod body and the connecting rod cover zigzag. 4. The manufacturing method of a cracked steel connecting rod according to claim 1, characterized in that, the steps A) and B) are replaced by, when casting the connecting rod blank, the connecting rod body (1) and Molten steel is poured into the cavity of the connecting rod cover (2). When the molten steel is condensed to a semi-solidified state, the separator is removed, and molten iron of gray cast iron is poured, so that the gray cast iron and steel are metallurgically combined to make a composite connecting rod blank.