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Development of Lightweight Tubing

Development of Lightweight Tubing

Creating Pipe from Round Bar (Hollowing Out Round Bar to Reduce Weight)

The steering system that transmits movement of an automobile’s steering wheel to the vehicle’s wheels includes parts such as the steering shaft and rack bar. These parts can be made hollow.

(1) Aim of creating hollow parts
The aim of creating hollow parts is not only to reduce weight but also to increase productivity and simplify production processes.

Part Aim of hollowing Effect
Steering shaft Weight reduction Weight reduction rate: 15 – 55%
Rack bar Process simplification Weight reduction rate: 10 – 60%
Weight reduction

(2) Approaches to the creation of hollow rack bars

Type Material Part manufacturing method Weight
Cylinders Rack gear cutting
Current Round bar (S45C) Gun drilling Cutting out teeth
I Cold finished seamless steel tube (S45C) Same as above 10%
II Same as above Cold press forming
(thinner walls)
Cold barrel shape forming Cutting out teeth 40%
III Electric resistance welded steel tube (0.30 – 0.40% C) Same as above Cold tooth profile forming 60%

(3) Representative examples of commercialization

Part Pipe dimensions Pipe standards Mechanical properties of material
Steering shaft
21.7~31.8φ×2.6~3.2t Equivalent to STKM15A TS≒540~610N/mm2
Rack bar 25~40φ×3~5t Sumitomo standards

Creating High Strength Steel Tube to Reduce Weight

The propeller shaft or drive shaft of an automobile is an important part that transmits the engine’s motive force to the wheels.

In the past, steel tube at the level of 500 N/mm2 was used for these parts, but demand for lighter vehicles and enhancement of output power has resulted in the use of high strength steel tube at the level of 700 N/mm2 or 800 N/mm2.