Mechanical parts - Application examples Mechanical parts Mechanical parts Engineering materials are more metal materials, with high strength, good toughness, high fatigue resistance and excellent performance, used to manufacture all kinds of important machine parts and engineering structural parts.
First, the machine tool parts selection analysis
A wide variety of machine tool parts, according to the structural characteristics, function and load characteristics can be divided into: shaft parts, gear parts, machine tool rails.
1, the machine tool shaft parts selection
Machine tool spindle is the most important axis of the machine parts. Different types of machine tools, spindle operating conditions are not the same. According to the work load of the spindle size and type, can be divided into four categories:
(1) light-load spindle. The working load is small, the impact load is not big, the axle neck part attrition is not serious, for example the ordinary lathe main axle. This kind of axle is generally made of 45 steel, quenched and tempered or normalized, in the requirements of wear-resistant parts of the use of high-frequency surface hardening strengthening.
(2) in the spindle. Medium load, wear more serious, have a certain impact load, such as milling machine spindle. Usually quenched and tempered with alloy steel, such as 40Cr steel, quenched and tempered, requiring wear-resistant parts of the surface hardened to strengthen.
(3) heavy-duty spindle. Work load, wear and shock are more serious, such as the work load of the combination of machine tool spindle. General use 20CrMnTi steel manufacturing, carburizing, quenching.
(4) high-precision spindle. Some machine tool spindle work load is not large, but the precision is very high, heat deformation should be minimal. Work should be very minor wear and tear, such as precision boring machine spindle. General use 38CrMoAlA special nitriding steel manufacturing, after quenching and tempering treatment, the nitriding and size stabilization treatment.
In the past, almost all of the main shaft is made of steel, and now the light load and medium-load spindle has been made of ductile iron.
2, machine tool parts selection
Machine gear according to the working conditions of the shell is divided into three categories:
(1) light-load gear. Rotational speed is generally not high, most of the 45 steel manufacturing, normalizing or quenching treatment.
(2) the gears. General 45 steel manufacturing, normalizing or quenched and tempered, and then high-frequency surface hardening to strengthen, to improve the bearing capacity and wear resistance. For large-size gear, you need to use 40Cr and other alloy quenched and tempered steel manufacturing. General machine tool live transmission system and the feed system of gear, most of this fall.
(3) heavy-duty gear. For some of the larger load, especially the high speed and withstand greater impact load gears are mostly 20Cr, 20CrMnTi isoturized steel manufacturing. Carburized, quenched after use. For example: the transmission of some important transmission gears.
3. Selection of Machine Guide
The accuracy of the machine tool rail has a great impact on the accuracy of the whole machine. Must be to prevent the deformation and wear, so the machine tool rails are usually made of gray cast iron, such as HT200 and HT350 and so on. The wear resistance of gray cast iron is better under lubricating conditions, but the abrasive wear resistance is worse. In order to improve the wear resistance, the surface of the rail can be quenched.
Second, the tractor and auto parts selection analysis
1, engine and transmission system components selection
These two parts include a considerable number of parts. Among them, a large number of gears and a variety of shafts, as well as work under high temperature parts, such as intake and exhaust valves, pistons and so on. They are more important timber is currently based on experience are generally used to selection. For different types of cars and different production plants, the engine and transmission system selection is not the same. Should be based on the specific parts of the working conditions and the actual failure mode, through a large number of calculations and tests to select the appropriate material.
2, to reduce the car's weight selection
With the increasing shortage of energy and raw material supply, people demand more and more energy-saving. Reducing the dead weight can increase the vehicle's weight utilization coefficient, reduce the material consumption and fuel consumption, which is of great significance in resource, energy saving and economic value.
Reduce the weight of selected materials, than the traditional timber should be lighter and can guarantee the performance of the business. For example, with aluminum or magnesium alloy instead of cast iron, the weight can be reduced to the original 1/3 to 1/4, but does not affect its performance; the use of new dual-phase steel plate instead of ordinary low carbon steel production car Stamping parts, you can use a relatively thin plate to reduce weight, but that does not reduce the strength of components; in the body and some less important structural parts, the use of plastic or fiber reinforced composite material instead of steel, can also reduce the weight, reduce Energy consumption.
Third, the typical examples of the selection of parts
1, machine tool spindle
Machine tool spindle is typical of the torsion - bending composite shaft, it is not subject to stress (medium load), the impact load is not large, if the use of plain bearings, journal requirements of wear. So most of the 45 steel manufacturing, and quenched and tempered, the journal by the surface hardening to strengthen. When the load is 40Cr and other low-alloy structural steel to manufacture.
Selection of the spindle spindle results are as follows:
Material: 45 steel.
Heat treatment: the overall quenching and tempering, shaft and taper hole surface hardening.
Performance requirements: the overall hardness NB220 ~ HB240; journal and the hole hardness HRC52.
Process route: forging → normalizing → roughing → quenching and tempering → finishing → surface hardening and low temperature tempering → grinding.
The shaft work stress is very low, the impact load is not, 45 steel yield limit of up to 400MPa or more, fully meet the requirements. Now some of the machine tool spindle can be made of ductile iron.
2, the tractor axle
Automotive axle is a typical shaft by the torque, but the work stress, and subject to considerable impact load, its structure shown in Figure 5. The maximum diameter of 50mm or so, with 45 steel manufacturing, even if the water quenching can only make the surface hardening depth of 10% radius. In order to improve the hardenability, and quenching in the oil to prevent deformation and cracking, medium and small car axle generally used 40Cr manufacturing, heavy vehicles with 40CrMnMo high hardenability such as steel manufacturing.
Example: 45 iron axle axle
Material: 40Cr.
Heat treatment: the overall quenching and tempering.
Performance requirements: rod HRC37 ~ HRC44; disk outer cylindrical HRC24 ~ HRC34.
Process route: cutting → forging → normalizing → machining → quenching and tempering → disc drilling → grinding spline.
3, machine tool gear
Machine gear working conditions are better, the work is not the force, speed medium, smooth and no strong impact, so the tooth surface strength, strength and toughness of the heart requirements are not too high, generally 45 steel manufacturing, the use of high-frequency Hardened surface hardening, tooth surface hardness up to HRC52 or so, which is bending fatigue or surface fatigue is sufficient. Gear quenched and tempered, the heart can ensure that there are about HB220 hardness and greater than 4kg? M / cm2 of the impact toughness, to meet the work requirements. For some of the gears require a higher, alloy quenched and tempered steel can be used (such as 40Cr, etc.) manufacturing. At this time the heart strength and toughness have increased, bending fatigue and surface fatigue resistance are also increased.
Example: ordinary lathe bed gear drive gear.
Material: 45 steel.
Heat treatment: normalizing or quenching, high frequency hardening and low temperature tempering.
Performance requirements: gear heart hardness HB220 ~ HB250; tooth surface hardness HRC52.
Process: Cutting → Forging → Normalizing or Annealing → Roughing → Tempering or Normalizing → Finishing → High Frequency Quenching → Low Temper Tempering (La spline hole) → Grinding.
4, tractor gear
Tractor gear working conditions than the poor gear machine, in particular, the main drive system gears, they are more stress, overload and impact of frequent, so the material requirements are higher. As the bending and contact stress is great, with high-frequency hardening to strengthen the surface can not guarantee the requirements, so the tractor's important gear with carburizing, quenching to strengthen treatment. Therefore, these gears are generally alloy steel carburizing 20Cr or 20CrMnTi and other manufacturing, in particular, the latter in China tractor gear production in the most widely used. In order to further improve the durability of the gear, in addition to carburizing, quenching, but also can be used to deal with surface treatment such as shot peening process. Shot peening, the tooth surface hardness can improve HRC1 ~ 3 units, durability can be increased 7 to 11 times.
Example: Tractor rear axle cone drive gear.
Material: 20CrMnTi steel.
Heat treatment: carburizing, quenching, low temperature tempering, carburizing layer depth of 1.2mm ~ 1.6mm.
Performance requirements: tooth surface hardness HRC58 ~ HRC62, heart hardness HRC33 ~ HRC48.
Process line: cutting → forging → normalizing → cutting → carburizing, quenching, low temperature tempering → grinding processing.
Selection of the above types of parts, can only be used as a mechanical parts selection analogy when the reference. Many of which are the result of long-term experience. Experience is very important, but only by experience can not get the best results. In the specific selection, but also refer to the relevant mechanical design manual, engineering materials manual, combined with the actual situation of primaries, important parts in the primary, the need for strength calculation check to determine the size of parts, the need to review the selected material Hardenability is to meet the requirements, and determine the heat treatment technical conditions. A good way to do this is to make a quantitative analysis of the materials available for the part, based on the working conditions and failure modes of the part, and then make a final decision on the selection of materials based on experience.
