Today's car manufacturers are facing the need to increase the efficiency of electric vehicles. Manufacturers have solved this problem from all angles: reducing weight, creating more efficient power transmission systems, and reducing noise. However, this process is iterative and endless.
GKN developed the 3D printed alloy steel material 20MnCr5 according to the characteristics of powder bed laser melting (L-PBF) additive manufacturing technology. This material can withstand high wear and load, and combined with the functional integration achieved by 3D printing to further reduce weight, the application direction is higher design freedom, more efficient and more integrated power system components.
As early as 2018, GKN and Porsche used the material to develop additively manufactured electronic drivetrain components. Recently, GKN revealed the mechanical properties of 20MnCr5 material, as well as more details of the two parties in the design iteration of the additive manufacturing of the front transverse transmission component-differential housing.
Lightweight, strong and wear-resistant
According to GKN, in the field of powder bed laser melting (L-PBF) 3D printing technology, there are two important commercial steel materials: stainless steel and tool steel. These materials meet the requirements of tool manufacturing and medical device manufacturing with their high corrosion resistance and high strength, but the market is moderate in cost, has performance-driven mechanical characteristics, and has high wear resistance and fatigue strength of steel-based 3D printing The material is still very limited.
GKN has developed a 20MnCr5 alloy steel material that can meet the requirements of the automotive industry. 20MnCr5 alloy steel is a medium-strength steel that can be surface-hardened and is generally regarded as one of the benchmark materials for surface-hardened gears. This alloy steel material is used in the powder bed laser melting 3D printing process. It has moderate material cost, high strength and toughness, and high fatigue strength. It can achieve excellent wear resistance through surface hardening.
The application direction of the material includes manufacturing gears and joint parts, main shafts, gears and other mechanical parts with high stress and wear resistance.
20MnCr5 material opens up a new space for additive manufacturing for the automotive industry. The automotive industry can first use this material for prototype manufacturing, and then confirm whether it can be expanded to large-scale production applications. Parts manufactured by 3D printing allow engineers to complete design verification in a few weeks and enter the next design iteration cycle.
In the process of 20MnCr5 material production, internal stress may cause parts to deform, but through specific heat treatment, internal stress can be reduced.
Additive manufacturing gears have reached the required hardening depth of the tooth surface, but the tooth surface section shows a lower value. The core hardness of additive manufacturing gears is about 90 HV lower than that of 16MnCr5 forged steel reference gears. Preliminary test results show that the low-pressure carburizing gears manufactured by additive have the potential to meet the current steel quality level of 16MnCr5.
In order to verify the potential of powder and 3D printing technology, GKN and Porsche used 20MnCr5 3D printing materials for the manufacture of front lateral gearboxes. For the best benefit, they used 3D printing technology to manufacture the component with the greatest potential for weight reduction-a differential housing with a ring gear.
In a conventional transmission, the ring gear and the differential case perform different functions in the transmission. The ring gear is made of special steel and then hardened and ground to ensure accuracy. The differential housing is usually cast to transfer torque from the ring gear to the center bolt and bevel gear.
Due to the manufacturing process and assembly method, the wide ring gear teeth are supported by thin and sometimes eccentric discs, which are connected to the differential case. The designer carried out topology optimization of the differential housing and defined the maximum available space in the transmission, removing all internal contours required for bevel gears, side shafts, bearings, etc.
According to the gearbox specifications and requirements, all loads (bearings and gears) are applied to the package block. CAD optimization tools provide a structure that can withstand all required loads. The final structure is designed based on the degrees of freedom that additive manufacturing brings to the design, and cannot be produced using conventional manufacturing techniques, which may produce products close to the computing structure.
The internal shapes are only supported by organic beams and structural systems that are essential for structural integrity, and these shapes cannot be processed by traditional methods. Although powder bed laser melting 3D printing technology releases the limitations of traditional technology on design, there are still some unique design limitations of this technology. For example, it is necessary to consider how to discharge unmelted powder material after 3D printing is completed. Planning is carried out when the design of additive manufacturing components is carried out.
The final finite element analysis showed a very uniform stress level and allowed the wall thickness to be reduced. Due to equipment limitations, this was not possible before.
According to the original load requirements, the calculation shows that the following goals can be achieved:
· 13% weight reduction (about one kilogram)
· Radial hardness change reduced by 43%
· Change in tooth stiffness in the tangential direction is reduced by 69%
· Inertia reduced by 8%
According to GKN, the powder bed laser melting 3D printing technology is used with 20MnCr5 material, which brings new possibilities for the production of lightweight and robust vehicle components. As metal additive manufacturing continues to develop and become a mainstream process, the application can be expanded not only to the field of prototypes or racing components, but also to mass production.