Shaft forging machining process
(A), the function and structure of shaft features
1, function: to support transmission parts (gears, pulleys, etc.), transmission torque, load bearing, and to ensure that the workpiece mounted on the spindle or rotary tool with a certain accuracy.
2, Category: their structure and shape of the precision shaft, and can be divided into the optical axis, stepped shaft, hollow shaft axis and shaped (including the crankshaft, camshaft, and the eccentric shaft, etc.) four categories.
The type of graph axis
a) axis b) hollow shaft c) axle d) stepped shaft e) spline shaft f) Cross-axis g) eccentric shaft
h) Crankshaft i) convex shaft
In terms of length and diameter of the shaft in proportion to the points, can be divided into rigid shaft (L / d <12 =, and a flexible shaft (L / d> 12) categories.
3, surface characteristics: cylindrical, bore, taper, thread, spline, horizontal hole
(B) of the main technical requirements:
1, the dimensional accuracy
Is the main shaft journal surface, which affects the precision rotary axis and work status. Journal diameter of accuracy is usually based on their requirements IT6 ~ 9, sophisticated journal up to IT5.
2, the geometric shape accuracy
Journal geometry accuracy (roundness, cylindrical), the general public should be limited to nearly the diameter range. High precision of the geometry, can be provided in part drawing on the allowable tolerances.
3, the location accuracy
Mainly refers to the drive assembly relative to the parts with the journal bearing journal bearing assembly concentricity, usually used with the journal bearing journal of the radial circular bound to represent; according to use requirements to a high accuracy is 0.001 ~ 0.005mm, while the general accuracy of the axis is 0.01 ~ 0.03mm.
There are also external cylindrical surface of the face concentricity and axial alignment with the vertical axis line requirements.
4. Surface roughness
According to the work surface part of different parts may have different surface roughness values, such as general machine tool spindle bearing journal surface roughness Ra0.16 ~ 0.63um, with the journal surface roughness Ra0.63 ~ 2.5 um, with the machine operating speed increases and improvement in the level of precision, shaft surface roughness requirements will also be getting smaller and smaller.
(C), material and rough shaft
Reasonable selection of materials and provides technical requirements for heat treatment, to improve the strength and service life of shaft parts are important, while the processing of the shaft have a great impact.
1, the shaft parts of the material
Generally used 45 steel shaft, according to different working conditions of heat treatment using different specifications (such as normalizing, quenching, quenching, etc.) to gain some strength, toughness and wear resistance.
Accuracy and speed of the medium-high shaft, the choice of 40Cr and other alloy steel. Type of steel and surface hardened by quenching and tempering treatment, the mechanical parts with high energy. High precision shafts, sometimes with a bearing steel and spring steel 65Mn GCrls and other materials, they are hardened by quenching and tempering and surface treatment, with higher wear resistance and fatigue resistance.
For high speed and heavy load conditions, such as working under the shaft, the choice of 20CrMnTi, 20MnZB, 20Cr and other low-carbon steel with magic or 38CrMoAIA nitride. Low carbon steel by carburizing quenching with high surface hardness, impact toughness and center strength, heat distortion is very small.
2, the shaft parts of the rough
Shaft parts of the rough material most commonly used is the rod and forgings, only certain large, complex structure of the axis only by casting.
(D), the pre-processing of shaft
Round before in machining parts to deal with the rough pre-processing. Pre-processing, including correction, and cutting off end and drill the center hole.
1, calibration: calibration bar blank in the manufacturing, transportation and deformation generated in the process to ensure the uniform allowance and reliable clamping feed. Correction can be carried out in a variety of presses.
2, cut: when rough bar, should be cylindrical in before turning off the desired length. Saw off the bow on the bite, high hardness to cut off the bar with a sheet in the machine on the cutting wheel.
3, cut the center hole drilling end: processing center hole is the most common shaft positioning surface, the center of the drilled hole to ensure no deviation, should be cut and then drilled the center hole end.
4, the shortage of car: If the axis is to the rough forgings or large castings, you need to shortage of vehicles processed to reduce the error of the rough shape of a foreign surface, so that subsequent processing operations even more than King.
Second, the typical process of spindle parts
Shaft processing technology for its purpose, structure and shape, technical requirements, the size of the output differ. The axis of the preparation process of order is the most commonly encountered in the production process work.
(A) of the main issues shaft machining
Shaft processing the main problem is how to ensure that the size of the machined surface accuracy, surface roughness and the location between the major surface accuracy.
Shaft line of processing the typical process is as follows:
Rough pre-processing and heat treatment → → → Turning cylindrical keyway milling grinding heat treatment → other →
(B) CA6140 Spindle Process Analysis
1, CA6140 technical conditions of the spindle
(1), supporting the technical requirements of the journal
Two main shaft bearing journal A, B roundness tolerance of 0.005 mm, 0.005 mm runout tolerance, two conical bearing contact with the journal of the 1:12 ratio> 70%, surface roughness Ra0.4um. Bearing journal diameter by IT5-7 level precision manufacturing.
Requirements of the roundness of cylindrical shaft, for the general accuracy of the machine, and its tolerance is usually not more than 50% of size tolerance, for improving the accuracy of machine tools, not more than 25%, for high-precision machine tools, they should be 5 to 10 %, respectively.
(2), the technical requirements of cone
Spindle taper (Morse 6) on the bearing journal A, B beat, near shaft tolerance 0.005mm, 300mm at the end of tolerance of off-axis 0.01 mm, cone contact rate> 70%, surface roughness Ra0 .4 um, hardness requirements HRC48.
(3), the technical requirements of a short cone
Short taper spindle bearing journal on the A, B of the radial runout tolerance 0.008mm, face D to the journal A, B's face runout tolerance 0.008mm, cone and the end of the roughness are Ra0.8um.
(4), empty set of technical requirements for gear journal
Empty set of gear journal bearing journal on the A, B of the radial tolerance of 0.015 mm.
(5), the thread technical requirements
This is used to limit associated with the clamping nut must face runout requirements. Therefore in the processing of the spindle thread, you must control the axis line and the thread surface journal bearing axis coaxial line, the general provision does not exceed 0.025mm.
As can be seen from the above analysis, the main spindle bearing journal surface finish is two, cone, cone and short front end, and installed all the journal and other gear. The journal itself is the size of support to ensure the accuracy, geometry accuracy between the two coaxial journal bearings, the bearing journal and the mutual position of other surface accuracy and surface roughness, it is the key to spindle machining.
(C), CA6140 spindle machining process d), the spindle machining process analysis
1, spindle blank manufacturing methods and heat treatment
Volume: large; Material: 45 steel; blank: die forging
In the single and small batch production, the shaft parts of the rough rolled bar is often used.
Large difference in diameter stepped shaft, in order to save materials and reduce the amount of labor machining, forging is often used. Single and small batch production of the stepped shaft generally use the free forging, large volume production in the forging is used.
(2) heat treatment
45 steel, the quenching (235HBS) after, and then the local high-frequency quenching, can make the local hardness HRC62 ~ 65, then after appropriate tempering, can be reduced to the hardness required (for example, the provisions of CA6140 Spindle HRC52) .
9Mn2V, which is about 0.9% of a carbon manganese vanadium alloy tool steel, hardenability, mechanical strength and hardness than 45 steel is superior. After appropriate heat treatment, the applicable dimensional accuracy of precision machine tool spindle stability requirements. For example, universal cylindrical grinding machine M1432A head frame and wheel spindle on the use of this material.
38CrMoAl, which is a medium carbon alloy steel, nitride, due to nitriding temperature is lower than the quenching temperature 540-550 ℃, less deformation, high hardness (HRC> 65, center hardness of HRC> 28) and have excellent fatigue resistance, so the high-precision semi-automatic cylindrical grinder MBG1432 the head frame and wheel axle shaft are using this steel.
In addition, the precision and speed for the medium-high shaft, multi-use 40Cr and other alloy steel, quenched and tempered steel, and such high-frequency quenching, with high mechanical properties, can meet the requirement. Some pieces also use ball bearing steel shaft, such as spring steel, such as 66Mn GCr15 and other materials. The quenched and tempered steel and surface hardened, with a high resistance to abrasion and fatigue resistance. When asked in high-speed and heavy load conditions, the work of the shaft parts, can choose 18CrMnTi, 20Mn2B and other low carbon magic, the steel material hardened by carburizing with high surface hardness, toughness and heart Ministry of strength, but deformation caused by heat treatment for large than 38CrMoAl.
Where the requirements of the local high-frequency hardening of the spindle, the previous procedure to be arranged quenching (normalizing some steel is used), when the rough large margin (eg, forging), after conditioning on the Rough, semi- Before fine car to car because of rough to the internal stress generated when the elimination of the quenching and tempering; when the rough small margin (eg, bar), quenching can be rough on the car (the equivalent of forging a semi fine car) before. High-frequency quenching treatment after the general on the semi-finish turning, the spindle hardened only partial, so accuracy is required without hardening part of the process, such as threading, milling, keyway and other processes, are arranged in the local quenching and coarse after grinding. For high precision spindle in the local quenching and aging treatment needed after coarse grinding, so that the spindle microstructure and stress state to remain stable.
2, the choice of locating datum
On the solid shaft parts, precision datum is the top hole, to meet the benchmarks and benchmark coincidence unity, while for the hollow shaft as the CA6140A, in addition to the top hole in the cylindrical journal surface and both also used in turn to each other benchmarks.
3, the processing stage of the division
Spindle during processing and heat treatment processes of the manufacturing processes will produce different degrees of processing errors and stress, and therefore by stage of processing. Spindle is basically divided into the following three processing stages.
(1), roughing stage
1) The preparation of rough rough handling, forging and normalizing
2) rough cut the excess part of the face milling, drilling cylindrical center hole and the shortage of vehicles, etc.
(2), semi-finishing stage
1) Semi-finished steel before the heat treatment of 45 commonly used for quenching in order to achieve 220 ~ 240HBS.
2) semi-finishing car technology cone (cone positioning) Semi-finish turning and drilling deep holes and other cylindrical face.
(3), finishing phase
1) before finishing the local high-frequency hardening heat treatment
2) before finishing processing of coarse positioning of various cone, cylindrical coarse grinding, milling, keyways and splines, and threading and so on.
3) cylindrical grinding and finishing inside and outside the cone surface to ensure the accuracy of the most important axis.
4, the processing order of the arrangements and processes to determine
And within a hollow shaft cone characteristics, taking into account the journal bearing, general journal and the inner cone surface of the processing order of major, may have several options.
① → rough outer surface of the outer surface finishing drilling deep → → → taper cone roughing finishing;
② → rough outer surface of tapered bore drilling deep rough → → → finishing the outer surface of tapered bore finishing;
③ → rough outer surface of tapered bore drilling deep rough → → finishing → cone outer surface finishing.
CA6140 lathe spindle for processing the order for such an analysis can be used for comparison:
The first program: rough cone, due to use over the outer surface has been finished for precision datum, will destroy the outer surface accuracy and roughness, so this option should not be used.
The second program: the cylindrical surface finishing, but also re-plug in the cone block, this would undermine the accuracy of cone. In addition, in the processing of cone will be processed when the error is inevitable (the grinding cone conditions satisfactory conditions than with cone grinding the block itself will result in errors such as cylindrical surface and the different axis of the inner cone Therefore the program should not be used.
The third solution: finishing hole in the cone, although should have been finished off with a cylindrical surface as a fine base level; but cone finishing allowance is very small, less grinding force; same cone The finishing hole has been at the axis of the final stage of processing, the accuracy of external circular surface has little effect; with the processing order of the program can be used cylindrical surface and tapered bore each other benchmarks used interchangeably, can gradually increase the coaxial degrees.
After this comparison shows that, like the CA6140 spindle axis of processing of such order to the third program better.
Through analysis and comparison of the program can also be seen that the surface of shaft parts order processing has to a large extent on the conversion and positioning benchmarking. When the rough part processing, precision reference is chosen, the processing sequence to be roughly determined. Because each stage is always the first positioning surface processing, that process must first prepare for the process behind the locating datum used. For example, the spindle CA6140 process, beginning to play center hole end milling. This is fine for the rough and semi-trucks for vehicle positioning cylindrical base; semi-finish turning and cylindrical deep holes for the positioning for the benchmark; semi-finish turning cylindrical hole for the cone before and after the processing preparing a positioning reference. In turn, the front fitted with cone cone top after plugging holes, and this semi-finishing and finishing after the cylindrical base for positioning; and the last mill benchmark positioning cone is a good journal on the grinding process surface.
Process to determine the order according to processing, should have information on two principles:
1) the positioning surface processes in the process to be arranged before the processing. For example, deep processing arrangements in the outer surface so rough after the car is to have a journal as a more accurate positioning surface to ensure uniform wall thickness deep hole machining.
2) the processing of the surface to be crude, refined separately, after the first crude refined, multiple processing, in order to gradually improve its accuracy and roughness. Major surface finishing should be arranged in the end.
In order to improve the organization and processing properties of metal heat treatment processes and arrangements, such as annealing, normalizing, etc., should normally be scheduled before machining.
In order to improve the mechanical properties of parts and the elimination of internal stress and the arrangements for heat treatment process, such as quenching, aging, etc., should generally be arranged in rough after finishing before.
5, mass production and small batch production process in comparison
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