Production Process Guidance of Leaf Springs－Shot Peening (Part 7)

Production Process Guidance of Leaf Springs

－Shot Peening (Part 7)

1. Definition:

Relying on the action of centrifugal force, shot peening is to use a motor to drive a impeller body to rotate, and a large number of the steel shots with a diameter of 0.2 ~ 3.0mm are thrown to the concave surface of the leaf spring to remove the surface oxide skin, so as to make the appearance clean and prepare for the painting work. At the same time, through the shot peening process, the spring has a certain plastic deformation, the internal stress is eliminated, and the service life of the leaf spring is improved.

2. Application:

Each leaf of leaf springs.

3. Operating procedures:

3.1. Inspection before shot peening

Before shot peening for the springs , check the inspection qualification mark of the previous process of springs, which must be qualified, the shot peening process can be allowed to start.

3.2. Selection of steel shots

Shot peening adopts Ф1.2-1.4mm manganese steel wire or Ф0.8-1.2mm cast steel shot. The proportion of steel shots that meets the standard shall not be less than 75%, otherwise, the steel shot separation device on the shot blasting machine should be properly adjusted to screen shots to make it reach the standard value.

The hardness of steel shots is between HRC50-55, the geometric shape is close to a sphere, without sharp edges and corners. If cutting steel wire shots are used, the optimum value of the shot height should be equal to its diameter, and the maximum value should be less than 1.5 times the diameter of the steel wire.

Control of steel shot flow:

The shot peening flow is based on the turbine galvanometer reaching 40-45A, the voltage is 380V and the traveling speed of the conveyor chain is about 0.08-0.098m/s. Otherwise, the steel shot flow shall be adjusted to reach the specified shot peening intensity to ensure the reduction of shot peening camber height, so as to stabilize the process camber height.

3.3. Control of shot peening strength

The shot peening strength must be qualified, with the coverage of shot peening ≥ 95%, measured by the camber height reduction of springs, or the measured value of Almen C test piece ≥ 0.18C.

3.4. Shot peening inspection

1) Appearance inspection of springs after shot blasting: the surface of flat bars is silver white after shot blasting. Touch with your hands, it is flat and smooth, without pricking feeling, and with a certain temperature, and the sprayed surface is densely and evenly covered with ejection marks.

2) The process camber detection of springs after shot peening must meet the process requirements. The camber δ of a spring is measured as shown in Figure 1.2.3 below

(Fig. 1. Camber measurement of eye rolled leaf)

(Fig. 2. Camber measurement of eye wrapped leaf)

(Fig. 3. Camber measurement of others leaf)

3) The coverage rate of shot peening must reach more than 95%.

4) Shot peening strength ≥ 0.18c.

3.5. Material Management

The shot peened springs shall be stacked neatly. It is forbidden to place them at will, resulting in surface bruises. The inspection qualification marks shall be made and the work transfer cards shall be pasted.

4. Inspection standards of shot peening (Refer to the standard: GB/T 19844-2018 / ISO 18137: 2015 MOD Leaf Spring - Technical Specifications):

Measurements according to figure 1 and figure 2, the inspection standards of shot peening are shown in table 1 below.

Compiled by  WONDEE Autoparts

2022-4-26