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Part 1: Gear and automotive suspension parts
1. Gear machining process
According to different structural requirements, the main technological process of gear parts processing is forging blanks → normalizing → finishing machining → gear shaping → chamfering → hobbing → shaving → (welding) → heat treatment → grinding → mesh trimming .
The teeth are generally not machined after the heat, except for the main and secondary teeth or the parts that the customer requires to grind the teeth.
2. Shaft process flow
Input shaft: forging billet → normalizing → finishing machining → tooth rolling → drilling → tooth shaping → chamfering → hobbing → shaving → heat treatment → grinding → meshing trimming.
Output shaft: forging billet→normalizing→finishing machining→grinding and hobbing→shaving→heat treatment→grinding→pairing trim.
3. Specific process flow
(1) Forging billet
Hot die forging is a widely used blank forging process for automotive gear parts. In the past, hot forging and cold extrusion blanks were widely used. In recent years, cross wedge rolling technology has been widely promoted in shaft processing. This technology is especially suitable for making blanks for complex stepped shafts. It not only has high precision, small post-processing allowances, but also high production efficiency.
(2) Normalizing
The purpose of this process is to obtain hardness suitable for subsequent gear cutting and to prepare the structure for final heat treatment, so as to effectively reduce heat treatment deformation. General normalizing is greatly affected by personnel, equipment and environment, making it difficult to control the cooling rate and uniformity of the workpiece, resulting in large dispersion of hardness and uneven metallographic structure, which directly affects machining and final heat treatment.
(3) Finishing machining
In order to meet the positioning requirements of high-precision gear processing, CNC lathes are used for the finishing of gear blanks. The inner hole and the positioning end face of the gear are processed first, and then the processing of the other end face and the outer diameter is completed simultaneously. It not only ensures the verticality requirements of the inner hole and the positioning end face, but also ensures that the size dispersion of large-scale tooth blank production is small. Thereby, the precision of the gear blank is improved, and the processing quality of the subsequent gears is ensured.
There are three main ways of positioning and clamping for shaft parts processing:
1. Positioning with the center hole of the workpiece: In the processing of the shaft, the coaxiality of each outer surface and end face of the part, and the verticality of the end face to the rotation axis are the main items of their mutual position accuracy. The design basis of these surfaces is generally Both are the center line of the shaft. If two center holes are used for positioning, it conforms to the principle of the coincidence of the datum.
2. The outer circle and the center hole are used as the positioning reference (one clamp and one top): although the centering accuracy is high, the rigidity is poor, especially when processing heavier workpieces, it is not stable enough, and the cutting amount should not be too large. During rough machining, in order to improve the rigidity of the part, the outer surface of the shaft and a center hole can be used as the positioning reference for processing. This positioning method can withstand a large cutting moment and is the most common positioning method for shaft parts.
3. Use the two outer circular surfaces as the positioning reference: When machining the inner hole of the hollow shaft (for example: machining the inner hole of the Morse taper on the machine tool), the center hole cannot be used as the positioning reference, and the two outer circular surfaces of the shaft can be used as the positioning reference. positioning datum. When the workpiece is the spindle of the machine tool, the two supporting journals (assembly datum) are often used as the positioning datum, which can ensure the coaxiality of the taper hole relative to the supporting journal, and eliminate the error caused by the misalignment of the datums.
Part II: Shell Parts
1. Process flow
The general process flow is milling joint surface → machining process holes and connecting holes → rough boring bearing holes → fine boring bearing holes and locating pin holes → cleaning → leak test detection.
2. Control method
(1) Fixtures
The machining process of the transmission housing is taken as an example of "Vertical machining center machining. 10# process + Vertical machining center machining 20# process + Horizontal machining center machining 30# process", three sets of machining center fixtures are required to avoid workpieces The clamping deformation should also be considered, such as tool interference, flexible operation, multiple pieces and one clamp, and rapid switching.
(2) Tool aspect
In the manufacturing cost of auto parts, tool cost accounts for 3% to 5% of the total cost. The composite tool with modular structure has the characteristics of high precision, reusable tool holder and small inventory, and is widely used. It can greatly shorten the processing time and improve labor efficiency. Therefore, when the precision requirements are not high and standard tools can achieve better processing results, standard tools should be used as much as possible to reduce inventory and improve interchangeability. At the same time, for mass-produced parts, the use of advanced non-standard composite tools for parts with high precision requirements can improve machining accuracy and production efficiency.
