The Application Of Forging Process In Automotive Lightweighting

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The Application Of Forging Process In Automotive Lightweighting

With the rapid development of forging technology, material flow simulation, and other technologies making forging process can be used more for the manufacture of complex parts. The application of FINA simulation technology enables process coordination control during component forging by providing more possibilities for lightweight applications in automotive products.

Lightweight of the Engine System

For advert hybrids, the linkage of the engine system is generally made of micro-alloy steel 3MnVS3 with a tensile strength of 850MPa. At present, there are also applications of new micro-alloy steel, which tensile strength can reach 1160MPa, to reduce the cross-section of the shaft to achieve a weight loss of 51 grams. However, the safety factor is yet to be improved.
Camshafts are generally solid shafts made of cast iron material, and Tekfor proposes a lightweight solution for forged cams, i.e., using tubes formed with internal high pressure as camshafts, which can effectively reduce weight by 400%. However, its strength and wear resistance is yet to be further verified.
In the crankshaft, traditional materials such as high-strength steel, micro-alloy steel, and besi-body steel can also be used. At the same time, no additional heat treatment is required after forging to ensure longer service life.

In addition, lightweight design and manufacturing solutions for engine systems are constantly being researched and developed. Hatebur proposes to build crankshafts from individual part faces, which can be easily forged. Schuler expands this concept by proposing to connect parts by shrinking mates. Trumpf goes a step further, recommending a hollow shaft neck, which is then laser-welded to connect to individual forged parts.

Lightweight Transmission and Powertrain

hollow shafts of rotor shaft need to be connected to the relevant components by pressure. Therefore, large wall thicknesses are generally required. The new lightweight solution is designed to reduce overall quality by increasing bearing bending torque and a larger diameter design.
For the universal section on the outside of the half shaft, a lightweight design of 50CrMnB5-3 (H50)1.7136 steel forging is used, The core layer strength produced by heat forging is higher than that of inductive quenched carbon steel, which improves the carrying capacity of the surface.
The connecting flanges of the output and half-axis of the drive shaft can achieve 10% weight loss through forging processes and deeper cavity designs while producing cost-effectively. The connection between the inside and outside of the constant speed drive shaft is achieved by the solid shaft, which is controlled by die forging into a hollow structure.

Lightweight of the Electric Rear Axle

The first lightweight solution mentioned in this application area is to increase the four cone teeth in the differential to six, as shown in Figure 3. This allows the torque transfer distribution on the side of the gear to be twice as effective and the entire system to be designed to be smaller.
The input gears are fixed to the outside of the differential housing, and Hirschvogel’s proposal achieves material savings below the root of the tooth in areas where torque is transferred to fewer teeth. In addition, weight reduction between mounting holes is achieved by perforating during forging to produce contour drilling.
Like the connecting rod, the higher quenching and cost-effective surface hardened steel 16MnCrV7-7 (H2)1.8195 allows for further gear carrying capacity with higher gear strength. Daido recommends its DCDG steel for gear components, which exhibits up to 40% pit strength and 20% root fatigue strength, allowing for smaller and lighter sizes.
Timken Steel proposes that components made of ME-grade surface hardened steel can withstand loads of up to 300 MPa on the side when using super steel. Depending on the load status of the component, the mass can be reduced by 10% to 30%.
Input gears typically use multiple threaded fasteners to connect to differential drives, and Trumpf proposes laser welding to save 1 kg of material.
The carriers of the differential-connected end-plate frames are generally made of cast iron and weigh 6.56 kg. Bharat Forge, Hammerwerk Fridingen, Hirschvogel, and Losasco recommend the use of lighter materials, which are expected to reduce weight by 10 to 20 percent. Hirschvogel and Leiber recommend switching to forged aluminum, which can reduce weight by 30%.

The lightweight of the Chassis

In terms of stabilizing rods, Benteler proposes a lightweight solution for thick-walled pipes,  Larger wall thicknesses are used in high-load curved areas, and thinner wall thicknesses are used in low-load areas. With this load-guided design, the stabilizer bar can save 1.55 kg of weight. Voestalpine proposes the use of high-strength spring steel to manufacture stabilizers for lightweighting.
Damper strut bearings are complex assembly parts that include multiple connected steel plates and can be reduced by approximately 200 grams in weight by the use of forged aluminum alloys.
Yamanaka proposed replacing the original steering gear shaft with hollow fittings, using a hollow forging process. JFE recommends the use of high-strength steel in gears for lightweighting.

Steering sections and wheel frames made of forged aluminum alloy have similar strength values to components made of cast iron, resulting in the same stiffness level only with small geometric optimizations during forging. Therefore, from the forging point of view, the geometric optimization of the components will be conducive to improving quality.
The rear lateral strut has changed from the original steel plate welding to the design of forged aluminum alloys and reinforced elements, enhancing the design’s flexibility. Although Yang’s modulus is low, weight reduction can be achieved while vertical stiffness is increased.
In terms of hubs, Cotarko recommends drilling holes in flanges or on forging presses based on the lightweight idea that rotating symmetrical components can remove material from the outside of the circle. At the same time, a lightweight design proposal is proposed to replace the brake disc connections with the star arm of the hub, which saves assembly space in the entire width and has significant

lightweight design potential.Lightweight Design Case for Commercial Vehicles

Through the study of the above lightweight scheme, the heavy truck is designed by the forging process. This includes transmission, driveshaft, and other components.  the main idea of lightweight design is to design high wall thickness in high-load areas and minimize materials such as thin-wall design, perforation design, etc., in low-load areas.
For components weighing 10.32 kg, approximately 29% weight loss can be achieved. The connection flanges of the driveshaft are mainly designed as rotating symmetrical components. From a forging point of view, it is easy to remove material in areas that are subject to smaller loads, resulting in lighter components.
Significant weight reductions can be achieved in the drive area, such as the design of the intermediate shaft, even when rotation symmetry is maintained. Linamar Seissenschmidt recommends converting from a solid shaft to a hollow shaft, using a tubular forging process to produce hollow structures. Richard Neumayer proposes structural optimization of transmission gears for quality savings near shafts.
Kamax sees the lightweight potential of the fastener head by using internal hexagonal components, which also provides an advantage during assembly. The use of high-strength materials with a strength rating of 15.9U can also significantly reduce weight, taking into account issues such as hydrogen and brittle resistance.
Lightweight can also be achieved by using the high-strength steel with good hydrogen brittleness of the new Nikko. To sum up, the study found that the heavy truck has a weight loss potential of up to 124 kg.

The conclusion

Although forging is an ancient metal forming technology, with the development of technology, it has a good future in the field of automotive lightweighting. The process is suitable for both industrial-grade production and small-volume experimental research. The lightweight development of automobile manufacturing can be realized through mutual promotion and cooperation between materials and production technology. Of course, this requires the cooperation and promotion of enterprises in the field of materials and forging processes.

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