Machining process

High strength steels for automobile beams have high strength and good bending performance, which is suitable for manufacturing beam parts. The machining processes related to automotive frames include cutting, punching, stamping, bending, and rolling, etc. It should be taken into account during the design that the plasticity and formability of high-strength automobile frame steel decreases while strength increases. Also, the more springback and distortion should be taken into consideration during the design of die and parts when high strength steels are used. Besides, when high strength steels are sheared, improper shearing gaps will cause a bad sheared edge and then cause the cracking during the formation. Poor shearing area will also be the source of fatigue cracking. Die or blade made up of inappropriate material will be easy to wear or even tipping.

In rolling and bending, the impact of bending radius, bending angle and edge shearing quality should be considered. The forming and blanking pressure rises considerably when the high-strength automobile frame steel is used. So it is recommended that the equipment be re-checked to make sure that the capacity of the stamping equipment and the capacity of the punching equipment meet the requirements.

 

Punch forming process versus roll forming process

1. Punch forming	• Big capacity punching machine (more than 5000 tons) • Big investment • Variable cross section beams can be made • Holding time should be increased to eliminate the possibilities of springback • Sheets of different lengths are needed for beams of different lengths • Big inventory
2. Roll forming	•Only constant cross section beams can be made •Small investment •No need to store various length sheets •Small inventory

Bending

Recommended hardness of bend mold materials is 56~58HRC.

The overbending angle for the offset of springback can refer to the processing parameter for 355MPa grade beam steels. Every 100MPa higher will need1^omore.

Radius R of corner of male mould of the bending machine:

3~6mm Steel sheet	R ≥ 1.2t
≥ 6mm Steel sheet	R ≥ 1.6t

(t: thickness of steel sheet); radius R of corner of female mould of the bending machine is decided by the sheet thickness, normally：

Shearing and punching

Hardness of tool material for shearing and punching 700MPa class high strength beam steels: 58~60HRC

Shearing tool gap for 700MPa class high strength beam steels:

8~10% of the thickness when the sheet is 5mm thick

10.5~13% of the thickness when the sheet is 8mm thick

 

Hot cutting

Plasma cutting is recommended

A steel-made wheel is made up of two parts, namely, the rim and the disk. The main processing technique for rim is roll forming. Punch forming and spin forming are usually applied for the disc. Punch forming is mainly used for discs of passenger cars, while discs of commercial cars are usually punch-formed (with inner tire) or spin-formed (without inner tire).

The plasticity of the high strength wheel steel will decrease with the increase of strength. So the analysis of the formability of rims and discs has become necessary to check the reasonability of their formation distribution in every process. The application of the high strength wheel steel will lead to more springback. Besides, attention should be paid to shearing quality. If the shearing quality is too poor, the rim edge tends to crack during expanding, and an inferior cross section of the disc after punching makes it vulnerable to cracking during flanging. Furthermore, such inferior cross sections tend to cause further fatigue cracking. The capacity of the former and the punch should be checked to make sure it can meet the requirements.