CN108817871B

CN108817871B - Manufacturing process method of internal toothed plate of automobile VCR engine

Info

Publication number: CN108817871B
Application number: CN201810757874.XA
Authority: CN
Inventors: 王敏; 陈学慧; 张春; 奚建胜
Original assignee: Hubei University of Automotive Technology
Current assignee: Hubei University of Automotive Technology
Priority date: 2018-07-11
Filing date: 2018-07-11
Publication date: 2020-04-17
Anticipated expiration: 2038-07-11
Also published as: CN108817871A

Abstract

The invention discloses a manufacturing process method of an internal tooth toothed plate of an automobile VCR engine, wherein the toothed plate is made of chromium-molybdenum steel, and the manufacturing process adopts a low-temperature hot forging-cold finishing composite forming manufacturing process, and comprises the following steps in sequence: blanking, heating, blank making, low-temperature hot die forging, hot trimming, isothermal normalizing, shot blasting, surface lubricating treatment, cold finishing and electrochemical machining. In the heating procedure, the heating temperature of the blank is 100-200 ℃ lower than the conventional hot forging heating temperature, and the initial forging temperature of the blank is 1050 +/-30 ℃; the low-temperature hot die forging process is that the thermal expansion rate of a cavity of a hot forging die is designed according to 1.010-1.012 percent; the electrochemical machining process is to precisely machine the internal tooth surface after cold finishing. The invention overcomes the difficulty of processing the inner tooth surface, has the advantages of high precision, high efficiency, long service life of the die, stable process and the like, and is suitable for batch manufacturing of the toothed plate parts in the fields of automobiles, aerospace, machinery and the like.

Description

Manufacturing process method of internal toothed plate of automobile VCR engine

Technical Field

The invention relates to a manufacturing process method for manufacturing an internal toothed plate of an automobile VCR engine, belonging to the field of machining.

Background

In recent years, VCR (Variable Compression Ratio) engines have been the focus of attention of various automobile companies and research institutes because they have more excellent power performance, fuel economy and emission performance than the currently mainstream fixed Compression Ratio engines. The toothed plate is a key transmission part of a VCR engine, has high requirements on tooth profile precision and surface quality (5 grades in ISO1328 standard) in order to ensure the precision and the stability of piston motion, has an internal rack structure and narrow tooth space, belongs to a structure with an internal cavity difficult to machine, and is difficult to machine by adopting a traditional gear manufacturing method.

At present, forging and machining combined methods or precision forging processes are mostly adopted at home and abroad to manufacture internal rack structure parts. For the first method, machining is usually performed after heat treatment, and at the moment, the strength and hardness of the forged piece are high, machining is difficult, machining precision is difficult to guarantee, and a cutter is seriously abraded; especially when the internal tooth modulus is small, the tooth pitch is narrow and machining becomes impossible. With the second method, although less and inorganic machining of the tooth surface can be achieved, such as cold finishing gears, the tolerance level can reach ISO 13287-9 level, but it is still difficult to meet the manufacturing requirements of some high precision gears (ISO 13285 level or more).

The Chinese patent with the publication number of CN101695806B discloses a technology for processing a reverse gear of an automobile transmission by adopting warm forging-cold finishing and then shaving; the process is not suitable for manufacturing the internal toothed plate, but the process is not suitable for manufacturing the internal toothed plate because the tooth-shaped part of the internal toothed plate die is single-thin in structure and complex in stress, and the deformation resistance and the flowability of metal are high and poor at the warm forging temperature, so that the difficulty in filling the die cavity of the die with the metal and the short service life of the die are easily caused; the second reason is that the gear shaving processing is adopted to process an internal gear, meshing interference is easy to generate, the gear shaving precision can reach ISO 13286-7 grade at most, and the manufacturing requirement of a high-precision gear is difficult to meet.

The low-temperature hot forging is forging forming at the temperature of 100-200 ℃ lower than the conventional initial forging temperature of hot forging, so that the advantages of hot forging and warm forging are considered: the method can reduce the deformation resistance of the metal, improve the plasticity and the fluidity of the metal, prolong the service life of the die, reduce the generation of the oxide skin on the surface of the forged piece, and improve the geometric precision and the surface quality of the forged piece.

The electrochemical machining in the electrochemical machining is an efficient method for carrying out finish machining by utilizing high-speed local anodic dissolution of metal under the action of an external electric field to realize electrochemical reaction, the technology is not limited by a tooth surface structure and hardness, machining deformation and residual stress are avoided, the machining precision is high, the surface quality is good, the efficiency is high, the technology is particularly suitable for an inner cavity structure which is difficult to machine, and an effective way is provided for the high-precision machining of the internal toothed plate.

Disclosure of Invention

The invention aims to provide a manufacturing process method of an internal tooth toothed plate of an automobile VCR engine, which adopts chromium-molybdenum steel as steel and is characterized in that a low-temperature hot forging-cold finishing composite forming manufacturing process is adopted; the low-temperature hot forging-cold finishing composite forming process comprises the following steps of: blanking, heating, blank making, low-temperature hot die forging, hot trimming, isothermal normalizing, shot blasting, surface lubricating treatment, cold finishing and electrochemical machining;

in the heating process, the blank heating temperature is lower than the conventional hot forging heating temperature, the blank initial forging temperature is 1050 +/-30 ℃, and the die preheating temperature is 280 +/-20 ℃; coating a high-temperature anti-oxidation coating on the surface of the blank; the measures can reduce the depth of an oxide layer and a decarburized layer on the surface of the blank, and ensure the geometric precision, the surface quality and the mechanical property of the forging.

In the low-temperature hot die forging process, the thermal expansion rate of a cavity of the hot forging die is designed according to 1.010-1.012%; the reason is that the initial forging temperature of the blank is lower than the final forging temperature of the forge piece due to lower temperature of the blank during hot forging, so that the thermal expansion rate is lower than that of the conventional hot forging design;

the electrochemical machining process is electrolytic machining, namely, the inner tooth surface is subjected to finish machining after cold finishing, and the machining allowance is 0.1-0.2 mm; determining the structure and size of the electrochemical machining cathode according to the tooth shape and geometric dimension of the part, and adopting NaNO₃+ NaCl composite electrolyte, wherein NaNO is in the composite electrolyte₃And NaCl in 10-20 wt%, composite electrolyte at 25-40 deg.c and electrolytic machining speed of 0.6 x 10^-3～0.3×10^-2㎜/s。

The invention has the beneficial effects that: the internal toothed plate is manufactured by adopting a low-temperature hot forging-cold finishing composite forming process, and has the following advantages: 1) the precision is high: the low-temperature hot forging, cold finishing and electrochemical machining are combined, so that the internal tooth surface can reach the precision of more than 5 levels of ISO1328 standard; 2) the finish machining adaptability to the inner tooth surface is good: the electrochemical machining effectively overcomes the difficulty of machining the inner tooth surface, particularly the small-modulus inner tooth surface; 3) the service life of the die is long: the tooth-shaped part of the internal toothed plate die is single and thin in structure and complex in stress, and the die is short in service life and easy to lose efficacy by applying the traditional warm forging technology; the invention adopts the low-temperature hot forging technology with the initial forging temperature between the traditional warm forging and hot forging, can reduce the metal deformation resistance and improve the service life of the forging die; 4) the method is suitable for batch manufacturing: the whole manufacturing process has the advantages of few procedures, high efficiency and good process stability, and is beneficial to realizing batch manufacturing.

Drawings

Fig. 1 is a front view of a combustion rack of an automotive VCR engine.

Fig. 2 is a sectional view taken along line B-B in fig. 1.

Fig. 3 is a rear view of a combustion rack of an automotive VCR engine.

Detailed Description

The invention is further described below with reference to specific examples.

Example 1

The related object is a key transmission part, namely a combustion toothed plate, of the automobile VCR engine, and the key transmission part is fixedly connected with a piston during installation and is used for driving the piston to move in an engine cylinder; as shown in fig. 1-3, the combustion toothed plate 1 belongs to an internal toothed plate, and is made of chrome molybdenum steel 27CrMo4 (german brand), and flanges 2 (surrounding edges) are arranged on two sides of the front surface of the combustion toothed plate 1, so that a concave cavity is formed, the concave cavity is provided with 2 rows of internal toothed bar functional parts, each internal toothed bar functional part comprises four internal teeth 3, the internal teeth precision requirement is grade 5 according to ISO1328 standard, the modulus is 4.68mm, the total length of the toothed plate is 85mm, the total width is 68mm, the thickness is 36mm, and the tooth pitch is 14.7 mm; the manufacturing process method adopts a low-temperature hot forging-cold finishing composite forming manufacturing process, and comprises the following specific implementation procedures:

(1) blanking: sawing a round steel bar into blanks with the size of phi 45 x 105mm, flattening the end ports, and carrying out electronic weighing inspection;

(2) heating: heating the blank to 1150 +/-30 ℃ by adopting a medium-frequency induction heating method to ensure that the initial forging temperature when the blank is moved to a blank-making station is 1050 +/-30 ℃ and the preheating temperature of a die is 280 +/-20 ℃, and coating a high-temperature anti-oxidation coating on the surface of the blank to reduce the depth of an oxidation layer and a decarburized layer on the surface of the blank and ensure the geometric precision, the surface quality and the mechanical property of a forged piece;

(3) blank preparation: flatly placing the heated blank on a flattening station of a 20MN hot die forging press, and pressing the heated blank to be 14 +/-2 mm thick by utilizing a flattening die;

(4) hot die forging: and placing the flattened forge piece into a pre-forging and finish-forging station of a 20MN hot forging press for hot forging. When designing a die cavity, according to the measured statistical data, the expansion rate of the die cavity is 1.01%, and a pre-forging die cavity is 0.6mm deeper than a final forging die cavity so as to ensure the complete filling of tooth profile during final forging;

(5) hot trimming: after the final forging is demoulded, putting the final forging into an edge cutting die arranged on a 2.5MN punching machine, and carrying out hot edge cutting by using the waste heat of the final forging;

(6) isothermal normalizing: heating the forging to 900 +/-10 ℃ under protective gas, preserving heat for 100min, cooling to 680 +/-10 ℃ in a cooling chamber, preserving heat for 150min in an isothermal furnace, and finally air-cooling to room temperature; the hardness of the forging after isothermal normalizing is HB 160-200;

(7) shot blasting: removing an oxide layer on the surface of the forging;

(8) surface lubrication treatment: heating the forging to 100 +/-10 ℃, removing oil stains on the surface of the forging, and then soaking the forging into a polymer lubricating solution at 70 +/-10 ℃ to form a polymer lubricating layer on the surface of the forging, wherein the polymer lubricating layer plays a role in lubrication and friction reduction in subsequent cold finishing;

(9) cold finishing: shaping the forging by using a cold finishing die on a 1250-ton oil press, wherein the finishing allowance of the inner tooth surface is 0.2mm, and preparing for subsequent electrochemical machining;

(10) electrochemical machining: adopting electrolytic machining, carrying out fine machining on the inner tooth surface after cold finishing, wherein the machining allowance is 0.15mm, determining the structure and the size of an electrochemical machining cathode according to the tooth form and the geometric dimension of a part, and adopting NaNO₃NaCl composite electrolyte and NaNO in composite electrolyte₃And NaCl in 10 wt%, electrolyte temperature of 40 deg.c and processing speed of 1.2X 10^-3The mm/s and current density of 0.4A/mm can be obtained.

The manufacturing process method combines low-temperature hot forging, cold finishing and electrochemical machining, and can enable the internal tooth surface to reach the precision of more than 5 grade of ISO1328 standard; the obtained combustion toothed plate product completely meets the design requirements, provides a new manufacturing process method for the combustion toothed plate and is beneficial to realizing batch manufacturing.

Claims

1. A manufacturing process method of an internal tooth toothed plate of an automobile VCR engine adopts chrome-molybdenum steel as steel and is characterized in that a low-temperature hot forging-cold finishing composite forming manufacturing process is adopted; the low-temperature hot forging-cold finishing composite forming process comprises the following steps of: blanking, heating, blank making, low-temperature hot die forging, hot trimming, isothermal normalizing, shot blasting, surface lubricating treatment, cold finishing and electrochemical machining;

in the heating process, the blank heating temperature is lower than the conventional hot forging heating temperature, the blank initial forging temperature is 1050 +/-30 ℃, and the die preheating temperature is 280 +/-20 ℃; coating a high-temperature anti-oxidation coating on the surface of the blank; the measures can reduce the depth of an oxide layer and a decarburized layer on the surface of the blank, and ensure the geometric precision, the surface quality and the mechanical property of the forging;