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The CNC Machining Technology for automobile transmission parts
2020-08-14

The CNC machining of automobile transmission parts is divided into three parts, the first part: gears; the second part of shaft parts; the third part: shell parts.


Part 1: Gear

1. Gear machining process

According to different structural requirements, the main technological process of gear parts processing adopts forging blank → normalizing → finishing turning → gear shaping → chamfering → hobbing → shaving → (welding) → heat treatment → grinding → pairing and dressing.

Generally, the teeth are no longer processed after heating, except for the main-minus-slave teeth or parts that customers require to be ground.


Part 2 Shaft Parts

1. Shaft process

Input shaft: forging blank→normalizing→finishing machining→gear rolling→drilling→gear shaping→chamfering→gear hobbing→gear shaving→heat treatment→grinding→grinding.

Output shaft: forging blank→normalizing→finishing machining→gear rolling and hobbing→gear shaving→heat treatment→grinding→pairing trimming.

2. Specific process flow

(1) Forging billet

Hot die forging is a widely used blank forging process for automotive gear parts. In the past, hot forged and cold extruded blanks were widely used. In recent years, cross wedge rolling technology has been widely promoted in shaft processing. This technology is particularly suitable for making blanks for more complex stepped shafts. It not only has high precision, small subsequent machining allowances and high production efficiency.

(2) Normalizing

The purpose of this process is to obtain the hardness suitable for subsequent gear cutting and prepare the organization for the final heat treatment, so as to effectively reduce the 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 differences in hardness and uneven metallographic structure, which directly affects machining and final heat treatment.

(3) Finish turning processing

In order to meet the positioning requirements of high-precision gear machining, the precision turning of the gear blanks all use CNC lathes. The inner hole and the positioning end face of the gear are processed first, and then the other end face and outer diameter are processed simultaneously. It not only guarantees the verticality requirements of the inner hole and the positioning end surface, but also ensures the small size dispersion of the mass production of tooth blanks. Therefore, the precision of the gear blank is improved and the processing quality of the subsequent gears is ensured.


Part 3: Shell parts

1. Process

The general process flow is milling the bonding surface → machining process holes and connecting holes → rough boring bearing holes → fine boring bearing holes and positioning pin holes → cleaning → leak test detection.

2. Control method on process

(1) Fixture

The machining process of the transmission housing takes "vertical machining center processing. 10# process + vertical machining center processing 20# process + horizontal machining center processing 30# process" as an example. Three sets of machining center fixtures are required to avoid workpieces. For the clamping deformation, factors such as tool interference, flexible operation, multiple pieces and one clamping, and rapid switching must also be considered.

(2) Tool aspect

In the manufacturing cost of auto parts, tool costs account for 3% to 5% of the total cost. The modular structure of the composite tool has the characteristics of high precision, reusable tool holder and low inventory, and is widely used. It can greatly shorten the processing time and improve labor efficiency. Therefore, when the accuracy requirements are not high and the standard tools can achieve better processing results, try to use standard tools 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 further improve processing accuracy and production efficiency.



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