Ductile iron: Spherical graphite cast iron is obtained by spheroidizing molten iron close to gray cast iron with magnesium or magnesium alloy or other spheroidizing agents. Graphite is spherical, which greatly reduces the separability and cusp effect of graphite on the matrix. Ductile iron has high strength, wear resistance, oxidation resistance, shock absorption and small notch sensitivity.
Ductile iron camshafts are generally used in single-cylinder internal combustion engines, such as S 195 diesel engines. The nodular cast iron used for camshaft is QT600-3 or QT700-2, and the spheroidization degree is required to be Grade 2 (graphite spheroidization rate is 90-95%), and the graphite particle size is greater than Grade 6. Total hardness of camshaft HB230-280
Alloy cast iron: Manganese, chromium, molybdenum, copper and other elements close to the composition of gray cast iron are added to molten iron. So as to form an alloy with pearlite and reduce the amount of ferrite. Alloy cast iron camshafts are generally used for high-speed camshafts. Such as CAC480 camshaft, the overall hardness of camshaft HB263-3 1 1.
Chilled cast iron: generally used for surface chilling treatment of low alloy cast iron, so that the outer layer is white or pitted, and the center is still gray. Such as: 372 camshaft. The camshaft made of chilled cast iron is in dry friction or semi-dry friction working state, but it bears large bending and contact stress, which requires the surface of the material to be wear-resistant and high in strength, and the core still has certain toughness. At present, there are two kinds of chilled cast iron used in China: Cr-Mo-Cu chilled cast iron and Cr-Mo-Ni chilled cast iron. Microstructure of chilled layer: hardness HRC 45-52 of ledeburite+pearlite (sorbite) chilled cast iron. At present, the hardness of chilled cast iron in China is about HRC47.
Medium carbon steel: generally used for large engine camshafts. For example, the 6 102 engine is die forged, and part of it is used for motorcycle camshaft, so the molding is relatively simple. Generally, after die forging, annealing treatment is needed to facilitate mechanical processing. Typical process editor of camshaft machining 1. The rough machining of camshaft journal is grinded by centerless grinder. Edit this paragraph. There are two grinding methods of centerless grinder: through centerless grinding and cut-in centerless grinding. Through centerless grinding is generally used for single grinding wheel. Its guide wheel is a hyperboloid with a blade, which pushes the camshaft to move along the axial direction and is only used for grinding the optical axis. Cut-in centerless grinding is multi-wheel grinding (if it is single-wheel grinding, the grinding wheel is generally dressed into a special-shaped grinding wheel, such as grinding the spherical surface of a hydraulic tappet). For example, the existing 480 camshaft grinding can grind the stepped shaft, and the guide wheel is composed of multiple disks, so the workpiece cannot move along the axial direction. No matter which grinding method, the center of the workpiece is higher than that of the grinding wheel and the guide wheel. Generally, cutting grinding includes feeding station, grinding station, measuring station and measuring station. The linear speed of grinding wheel is 60m/s, the radial grinding allowance of journal can reach 3.5mm, the grinding time of single piece is 18s, and the working time of single piece is 25s. Machining camshaft with centerless grinder is a novel and unique new technology and method, but it has certain limitations, especially it is not easy to grind shoulders and end faces. Generally, it is not used to process many kinds of camshafts, but only used for single variety and mass production. If the camshaft is to be replaced, the guide wheel and grinding wheel must be replaced, and the spacing between grinding wheels needs to be readjusted. The dressing of plug-in centerless grinder generally adopts a single diamond dressing, and the route taken by the dresser is convex, and the difference between the segments of the dresser profile is equal to the difference between the segments of the camshaft journal. The grinding wheels used for rough grinding of camshaft journals all belong to cemented carbide series, with particle size of 60 and linear speed of 45m/. Second, milling the end face and drilling the center hole. The central hole edited in this section is the positioning benchmark for future processing procedures. When milling the end face, generally only five degrees of freedom can be defined, and two V-shaped blocks can define four degrees of freedom. The axial degree of freedom is the front end face or the rear end face of the 3# journal of camshaft (specific requirements should be put forward for this face in product design). At present, self-centering positioning clamping and dense tooth cutter head milling are widely used. The axial dimension ensures the approximate positioning reference dimension from the rear end face to the blank and the whole camshaft length. In view of the small size of the camshaft pulley journal, B5 center drilling is generally used when drilling the center hole, and φ 10 steel ball is used to check the hole depth after drilling, so as to ensure the size of the ball top and the rear end face and the distance between the tops of the two steel balls, which can ensure the consistency of future positioning. Third, the heat treatment of the camshaft Edit this heat treatment: put raw materials or semi-finished products in air or a specific medium, heat, keep warm and cool in an appropriate way to obtain the mechanical or technological properties that people need.
Classification of heat treatment: general heat treatment, chemical heat treatment and surface heat treatment.
Generally, nodular cast iron camshafts are austempered. The cooling medium is 10 and 20 spindles in oil salt bath or alkali bath. After quenching, it was tempered at a low temperature of140 C-250 C. After tempering, the microstructure was black acicular martensite with hardness HRC50-54.
Alloy cast iron and steel camshafts are generally quenched at medium frequency: the quenching frequency is 1000- 10000Hz, and 7000Hz is generally selected. Namely induction heating surface quenching. The principle is that the cam of the camshaft is put into the heating coil, and the cam is heated from the outer layer to the inner due to the skin effect of current, so that the surface structure at a certain depth is transformed into austenite, and then it is rapidly hardened. At present, the 480 camshaft adopts natural tempering, and the surface structure of the cam is acicular martensite.
The surface heat treatment of camshaft can greatly improve the torsional and bending fatigue strength of parts and the wear resistance of the surface.
Induction heating quenching has the advantages of small deformation, energy saving, low cost and high labor productivity. The quenching machine can be placed on the cold working production line for easy production management.
The power supply, transformer and induction coil need to be cooled during induction heating of 480 camshaft intermediate frequency quenching machine tool. The temperature of cooling water is required to be 25℃-30℃, and the temperature of quenching coolant is 53℃-62℃. If the machine itself cannot meet the requirements, an additional cooling device must be provided outside the machine to cool the cooling water. Four, camshaft deep hole processing editor. This section is L/D > in machining; The hole machining at 5 o'clock can be called deep hole machining. When drilling deep holes with ordinary twist drills, there are the following difficulties.
1. The drill bit is slender. The rigidity is poor, and the drill bit is easy to bend and vibrate during machining, so it is difficult to ensure the straightness and machining accuracy of the hole.
2. There are many chips, and the chip discharge channel is long and narrow, which is not easy to discharge.
3. Deep hole cutting fluid is not easy to enter, the cutting temperature is too high, the heat dissipation is difficult, and the drill bit is easy to break.
According to different technologies, deep-hole drilling can be divided into three types: drilling on solid objects, reaming and nesting, and drilling on solid materials is the most commonly used. For example, the deep holes for the 480 cam are all processed by double-headed gun drilling. The depth of each borehole is l/2+ 10 mm.
Gun drill drilling is a single-edge external chip removal type, which is generally suitable for processing φ2-φ20mm holes, L/D >; 100, surface roughness Ra 12.5-3.2mm, and accuracy H8-H 10. External chip removal single-blade deep-hole drill was first used to process barrel, so it is called gun drill, and it is also the only way to process φ2-φ6mm deep holes. The gun drill consists of a drill bit with a V-shaped cutting edge and a cutting fluid hole, a drill rod and a drill handle suitable for special equipment. High pressure cutting fluid (7MPa) is sent to the cutting area through the small hole of the drill bit for cooling, lubrication and chip removal, and then the chips and cutting fluid are discharged into the centralized cooling system along the V-shaped arbor. The drill bit is cemented carbide and adopts welding structure. The cutting amount is generally 0.06-0.1mm/r. In order to better control the damage degree of the tool, the tool adopts radial load feedback. Once the cutting force of the tool reaches a certain value, the tool will automatically return under the action of the numerical control system, thus avoiding the damage of the gun drill and improving the service life of the tool. Blunt tools can be replaced and sharpened again before use.
Generally, spindle oil is used as coolant for deep hole machining of camshaft. Although the cooling effect of oil is not as good as emulsion, the lubricating effect of oil is much better than that of coolant. V. Quick point grinding of spindle journal and editing of CBN grinding wheel This kind of quick point grinding is an advanced and efficient new technology for cylindrical grinding developed by German Iunco Company. The machine tool only needs two centers to position and clamp the camshaft, and does not need any clamping tools. Through the friction between the centers and the central hole of the camshaft, the workpiece is driven to move by the high-speed rotation of the front centers, which can realize the machining of grinding seven journals, one end face and one fillet with one grinding wheel after clamping the shaft parts at one time.
The grinding wheel is rapidly worn laterally, and the external dimensions of the camshaft to be ground will not change during the wear process. When grinding the end face, the grinding wheel can be inclined by 0.5, so that the contact surface between the grinding wheel and the workpiece is only 1/2 of the traditional grinding end face.
CBN has good thermal conductivity, which is 13 times that of cemented carbide and 3 times that of copper. In addition, CBN is far superior to diamond in thermal stability and chemical stability (diamond is easy to have affinity with iron cluster elements), can withstand the high temperature of 1300- 1500, and has great chemical inertia with iron cluster elements. CBN is an ideal tool for cutting ferrous metals.
CBN belongs to cubic system, and its physical properties such as hardness and strength are far superior to corundum and other series abrasives. In the grinding process, the wear of CBN itself is very small, and the cost of a single part is very small in the mass production process. The shape and size of grinding wheel change little, and its durability is high. The dressing frequency is about 1/20 of corundum series and the dressing amount is about 1/25 of corundum series. The grinding temperature between the grinding wheel and the workpiece is low, which can avoid the occurrence of workpiece cracks and grinding burns in the elastic deformation stage of grinding.
CBN has good chemical stability and heat resistance. It only reacts with carbon at 2000°C and easily reacts with water at high temperature. The durability of grinding wheel is high, and the utilization rate of machine tool can reach above 97%. Compared with ordinary grinding wheels, the efficiency can be improved by 600%-700%.
When the wear of the grinding wheel in the width direction accounts for 80% of the width of the grinding wheel, the grinding wheel will be dressed. The primary dressing amount is 0.006mm, and the primary dressing amount is 0.002 mm. Each dressing can grind 120 camshafts, and the linear speed of the grinding wheel is 120m/s, which can obtain high metal removal rate. Use cooling. It not only provides cooling liquid for grinding wheel and workpiece, but also provides better lubrication for grinding wheel and workpiece. At the same time, due to the adsorption of oil film, it can also prevent the surface of camshaft journal from oxidation and prevent the surface of workpiece from rusting after grinding. The supply of grinding liquid is the cooling liquid provided by spraying method, which can fully cool the grinding wheel, double the service life of the grinding wheel and more than double the metal removal rate. At the same time, the surface of the grinding wheel is washed by the method of coolant recoil to prevent the grinding wheel from being blocked, so that CBN particles can always cut the workpiece in a sharp state. In addition, the particle size of CBN is small, which is more than that of ordinary grinding wheel in cutting the camshaft journal per unit area. When the journal is cut, the elastic friction and deformation stages are small, so the elastic deformation and plastic deformation are small, which improves the surface roughness and prevents the surface from grinding burns and cracks caused by abrasive factors. In the abrasive cutting stage, the thermal stress and deformation stress are small.
Because of the high grinding speed, the grinding heat can not be transmitted into the deep part of the workpiece, and instantly gathers on the thin surface of the camshaft, forming chips and being taken away. The temperature of abrasive cutting point is above 1000℃, but only a few tens of degrees inside.
CBN grinding wheel is selected for grinding, which has sharp abrasive particles and small grinding force, so the calorific value of grinding area is small.
The microhardness of CBN is 7300—9000HV, the bending strength is 300MPa, the compressive strength is 800 800-1000 MPa, and the thermal stability is1250c-1350c.
The acoustic sensor is used to strictly limit the distance between the grinding wheel and the diamond roller, mainly to prevent the grinding wheel from colliding with the diamond roller during dressing. When the grinding wheel rack is fed longitudinally, a small gap is formed between the sensor probe and the grinding wheel. The grinding wheel rotates at high speed, compressing the air around the grinding wheel. According to the size of the air circulation channel, the air resistance sound is different, so as to judge the gap between the sensor and the grinding wheel and make feedback. Once the grinding wheel touches the diamond roller, the dresser will automatically dress the grinding wheel, and the sound sensor can judge the correctness of grinding wheel dressing according to the sharp sound.
Compared with resin binder, ceramic binder has stable chemical properties, heat resistance, acid resistance, alkali resistance, large porosity, difficult to generate heat when working, easy to fall off when grinding, small thermal expansion coefficient, high strength, good CBN geometry and easy dressing of abrasive.
CBN grinding wheel used for grinding the journal and end face of camshaft is only 4.5-5 mm thick, and it is attached to a rigid steel disk with good rigidity.
The ratio of workpiece speed to grinding wheel speed is 40/8000.
Feed-free grinding, that is, smooth grinding, can improve the geometric accuracy of workpiece and reduce the parameter value of surface roughness. The surface roughness decreases with the increase of polishing times, and the fine-grained grinding wheel is better than the coarse-grained grinding wheel.
Dressing of grinding wheel: Dressing usually includes shaping and sharpening. Shaping is to make the grinding wheel reach the required geometric shape and accuracy. The geometric shape of grinding wheel is realized by numerical control interpolation. Dressing is to remove the bonding agent between abrasive particles, so that the abrasive particles expose the bonding agent to a certain height, and form cutting edges and gaps between abrasive particles to accommodate chips.
Features of diamond roller grinding and dressing: high productivity: it only takes 2- 10 seconds to dress the diamond roller, and it can be dressed when replacing the camshaft without delaying the production rhythm. At the same time, due to the long service life of the diamond roller and short dressing time, the auxiliary time is greatly shortened, the consumption of a single workpiece is low, the precision of the diamond roller is high, and the surface quality of the dressed grinding wheel is also good.
The main component of mineral oil cooling liquid is light mineral oil, and an appropriate amount of oil-soluble antirust additives are added. In order to improve the lubrication performance of mineral oil, fatty acids and other oily additives are often added to improve the penetration and lubrication effect of mineral oil at low temperature and low pressure. The supply mode of mineral oil is spray method, which increases the supply pressure and the supply speed of grinding fluid, takes away the grinding heat quickly, breaks through the airflow of high-speed rotation of grinding wheel, makes grinding fluid enter the grinding area effectively and improves the grinding effect. Because of the small holes in the grinding wheel, the grinding fluid must be carefully filtered. Because the impurities such as abrasive chips and sand grains produced in the grinding process are increasing in the grinding fluid, the grinding fluid becomes dirty and smelly, which not only affects the quality of the grinding workpiece, but also harms the environmental hygiene. The filter used for quick spot grinding is a cylindrical paper filter. Processing and editing of intransitive verb cam In this section, the traditional cam processing adopts copying. Generally speaking, the intake and exhaust cams of a factory have a female profile, and there are several cams on the camshaft. This kind of machining is actually copying machining, and the machining error of master copying will be reflected in the finished cam. Specifically, it has the following defects.
1. The utilization rate of grinding wheel is also low. Take the 480 camshaft produced at present as an example. The linear speed of the grinding wheel of the copying machine tool is 60m/s, and the diameter of the newly replaced grinding wheel is φ760mm. But the grinding wheel must be replaced after it is used to φ7 10mm, otherwise the error of cam profile will increase and the grinding wheel will wear from φ760mm to φ7 10mm cam profile.
2. The electric frame of the workpiece headstock is a two-speed motor, and the camshaft can only rotate at a fixed speed. The linear velocity of several grinding points on the cam profile is different, and the cutting amount and grinding force per unit time are also different, which leads to errors in the processing of the cam profile and is prone to grinding burns and cracks. The contour error of cam grinding at constant speed is 0.036 mm. The profile error of cam variable speed grinding is 0.065438 0.02 mm.
3. The workpiece is supported on a cradle with a tail frame and a center frame, and the reciprocating swing momentum of the cradle mechanism affects the improvement of cam profile accuracy, roughness and production efficiency.
4. The same cam can only be used for the same camshaft, so it is only suitable for single variety production, otherwise it will be necessary to change the cam again, and flexible multi-variety production cannot be realized.
Modern CNC grinding camshaft machining has the following characteristics:
1. A set of numerical control devices (the latest ones in the world are Siemens 480D and FANAC2 10i) not only control the stepless speed change rotation and indexing of the workpiece spindle, but also control the reciprocating motion and lateral feed of the grinding wheel frame according to the lift and drop values of the cam profile.
2. The workpiece spindle is driven by a servo motor controlled by a numerical control device to realize stepless speed change transmission, which can not only realize different rotational speeds required by rough grinding and fine grinding, but also realize automatic speed change grinding of the workpiece spindle according to different cam curves per revolution. This can make the linear velocity, metal cutting amount and grinding force of each grinding point on the cam surface basically the same, which is very important to ensure the grinding quality of the cam surface.
3. The grinding wheel can realize high-speed and constant linear speed grinding. Such as 480 camshaft kopp grinder 80 m/s
4. It has great flexibility. CNC device can store 20 cam profile data and 9 grinding data. It meets the flexible production requirements of camshaft variety change.
5. The spindle of the grinding wheel adopts an internal balancing device, which replaces the previous hydraulic balancing device and mechanical balancing device, with high balancing accuracy, and the grinding wheel hardly shakes, thus improving the grinding accuracy of the cam profile.
6. Using diamond roller for dressing, and using sound velocity sensor to control the dressing amount of each grinding wheel during dressing, good grinding wheel dressing accuracy can be obtained, and after dressing each grinding wheel, the numerical control device can automatically remember and compensate.
7. Using CBN grinding wheel, the radius between the newly replaced new grinding wheel and the replaced waste grinding wheel is only 4.5-5mm, which ensures the consistency of cam profile. Seven. Chemical treatment of camshaft The chemical treatment in this paragraph is to put the metal in a certain chemical medium and generate a chemical coating on the metal surface through chemical reaction to obtain different properties such as decoration, corrosion resistance and insulation.
Chemical treatment generally includes oxidation treatment and phosphating treatment.
Advantages of phosphating treatment:
1. Generally speaking, the cam of camshaft should be phosphatized. The corrosion resistance of phosphating cam in the atmosphere is more stable than that of oxidation treatment. After phosphating, it can be filled with potassium dichromate solution and soaked in oil, which can further improve the corrosion resistance.
2. Phosphating film has many pores and strong adsorption capacity.
3. It has lubricity and antifriction.
4. It has high insulation.
Generally, after a period of running-in, the phosphating film at the peach tip falls off and becomes shiny, which is beneficial to the initial running-in of the cam and tappet. Generally speaking, the thickness of phosphating film of camshaft is 0.0025-0.006 mm In order to ensure the surface accuracy of camshaft, the surface roughness of cam before phosphating is required to be 0.6. Eight. Polishing and Editing of Camshaft This paragraph requires that the surface roughness of camshaft main journal and oil seal journal be 0.2, so the phosphating film on the surface of main journal and oil seal journal must be removed. In order to ensure the surface roughness of the main journal and the oil seal journal, they must be polished. In the polishing process, less heat is generated due to friction and grinding; Long heat dissipation time can effectively reduce the deformation and burn of the workpiece, mainly to improve the machining accuracy of the surface, so that the camshaft journal can obtain a smooth surface, but it can not improve the product size and geometric accuracy, and will not change the shape and position errors of the parts. According to the current technical level, the polishing abrasive belt is made of paper abrasive belt, the abrasive belt granularity is 280-320, the polishing liquid is kerosene, and the special tooling for polishing machine is made of hard resin. Nine. Inspection and Editing of Camshaft Due to the large contact stress between the cam and the tappet, it is not allowed to have any defects on the cam surface, so it is necessary to inspect the camshaft surface. Inspection is divided into two categories: magnetic particle inspection and fluorescent penetrant inspection, which mainly detect quenching cracks produced during cam quenching and grinding cracks produced during grinding. Inspection is also a nondestructive testing method. According to the current production level, fluorescent penetrant inspection is cleaner than magnetic particle inspection, because magnetic particle inspection needs to be equipped with magnetic suspension, and the field production is rarely kept clean, and some magnetic flux still flows on the camshaft after demagnetization. X. Cleaning and Editing of Camshaft In this section, the camshaft should not only clean the surface, but also clean the main oil passage and oil hole to prevent dirt such as iron filings from staying at the joint of the main oil passage hole and remove burrs from the oil hole orifice. Generally speaking, the cleanliness of a single camshaft is about 10mg. If the cleanliness exceeds the standard, it will accelerate the wear of engine parts and shorten the life of the engine. After cleaning, the camshaft will be blown dry. I hope it helps you,