Actual case   
Number of cars. CNC. External grinding. Wire cutting   《Eccentric shaft》

A. Material：  SCM420 alloy structural steel. High hardenability. No temper brittleness. Good weldability. The tendency to form cold cracks is small. Good machinability and cold plasticity. Generally used in quenched and tempered or carburized and quenched state. Used for manufacturing in non-corrosive media and working. The temperature is lower than 250 degrees C. In a medium containing a mixture of nitrogen and hydrogen. In the working high-pressure pipe and various fasteners. Higher grade carburized parts. Such as: bushings. gear shafts. smooth shafts. eccentric shafts. etc.... heat treatment, quenching 880 degrees, water cooling, oil cooling 500 degrees.

B. Difficulty. Process improvement and solution：

1. The material of this product is SCM420, which must be quenched and tempered at 28/30°. After that, the carburized surface layer is 1MM/1.5MM.

Process: Before roughing the SCM420 material, make a 28/30° quenching and tempering. After the quality is confirmed and the hardness is OK. In rough machining, the outer diameter and step allowance should be 0.3/0.4MM on one side. The carburized surface layer is required to be at least 1.2MM on one side.

2. This shaft is an eccentric shaft. The steps of ø45.5 and ø32 are 2MM 0/-0.018. The bottom of the steps is less than R0.2. At 32MM, there is a width 8 MM0/+0.02*depth 4*length 18. Keyway. In the eccentric direction.

Process: ①The shape margin is greater than 5MM. The length should be extended by 10MM for eccentric process reservation. ②Leave 0.3mm on one side for all shapes before roughing. At the same time, keep 0.3mm on the steps. Convenient for carburizing. 3MM center hole is punched at both ends, and the center angle is 60°. ③Eccentric position. Need to use "milling machine" to open the thick keyway. "Width 7.5*Depth 3.5*Length 17.5MM." Use this to find direction. ④ Use CNC 3-axis machine. Auxiliary tool three-jaw chuck. Clamp to the ø32.5MM position. Open the thick eccentric position ø58.5MM. Connect to the bottom step. At the same time, two eccentric center holes should be punched. It is convenient for subsequent cylindrical grinding.

3. The outer diameter tolerance is 0/-0.018. The step tolerance is 0/-0.03. The runout is within 0.01. The keyway tolerance is 0/+0.02. At the same time, the smoothness of 0.8 is guaranteed. Total length tolerance 0/-0.05.

Process: ①The single side of the carburized layer is 1.2MM. "Technical requirements, deformation should not be greater than 0.05" Carburized layer at the length process position. ② Use "External Grinding" to process the first outer diameter of the top two ends to roughen. The allowance of one side is +0.1/+0.15. ③Clamp the two ends in two steps with the number of cars. Complete the control chief. Within tolerance 0/-0.02. Choose hardened blade 65° "R0.1 tip" ④The second pass uses external grinding. Use a dial indicator at the top position to adjust the deviation tolerance. It is best to use "60# grinding wheel" for fine grinding to ensure smoothness 0.8. ⑥ Machining with "Milling Machine", find the highest point of eccentricity. Processing 8MM 0/+0.02*Deep 4*Length 18.Keyway. The width dimension can be tested by block gauge. ⑦Examine the outer diameter, step, eccentricity, healthy groove, smoothness... ⑧In the process of wire cutting. ⑨Number of car control length. Chamfering.

Three elements of cutting
1. Line speed Vc
The length of the blade moving on the machined surface of the workpiece per minute. Representation unit: m/min. The specific performance of the linear speed in the cutting process is mainly the spindle speed.
The conversion formula is：S=VcX1000/3.14D
D：Cutting diameter of workpiece

2. Depth of cut ap
The distance from the surface of the workpiece to be processed to the surface of the processed workpiece, expressed in units：mm。

3. Feed rate
The distance that the workpiece moves in the cutting direction for each revolution of the workpiece, expressed in units：mm/r。

Feed rate
1. In the turning process, each time the workpiece rotates, the amount of advancement of the turning tool is the feed amount.
2. The feed amount has a great relationship with the surface roughness of the machined surface. The feed is usually determined according to the surface roughness requirements.
1) The feed amount should be greater than the width of the chamfer, otherwise the chip cannot be broken, generally Take about twice the width of the chamfer
2) With a large feed rate, the thickness of the chip layer increases, and the cutting force increases.
3) A large feed rate requires a larger cutting power
3. The influence of the feed rate
1) The feed rate is small, the back wear is large, and the tool durability is quickly reduced
2) The feed rate is large, the cutting temperature rises, and the flank wear increases , But its impact on tool durability is smaller than cutting speed.
3) Large feed rate and high machining efficiency
4) Feed rate between 0.1-0.4, which has a greater impact on the flank face Small, depending on the specific situation. The empirical formula f thick=0.5*tool nose radius

Relationship between chip breaking and feed rate and chamfer width:

The relationship between chip breaking and feed rate and chamfer width: