Today's automakers face the need to increase the efficiency of electric vehicles. Manufacturers have addressed this issue from all angles: reducing weight, creating more efficient powertrains, and reducing noise. But the process is iterative and endless.
According to 3D Scientific Valley's market research, GKN has developed a 3D printed alloy steel material 20MnCr5 based on 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 for higher design freedom, more efficient and more integrated power system component manufacturing.
As early as 2018, GKN and Porsche used this material to develop additive manufacturing electronic drivetrain components. Recently, GKN revealed the mechanical properties of the 20MnCr5 material, as well as more details in the iterative design of additive manufacturing of the front transverse transmission part-differential case.
Lightweight-strong and durable
According to GKN, there are two important commercial steel materials in the field of powder bed laser melting (L-PBF) 3D printing technology: stainless steel and tool steel. These materials meet the requirements of tool manufacturing and medical device manufacturing due to their high corrosion resistance and high strength, but the cost on the market is moderate, with performance-driven mechanical characteristics, and high wear resistance and fatigue strength of steel-based 3D printing Materials are 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 considered to be one of the benchmark materials for surface hardened gears. This alloy steel material is used for powder bed laser melting 3D printing process, has moderate material cost, high strength and toughness, high fatigue strength, and can achieve excellent wear resistance through surface hardening.
Applications of this material include manufacturing highly stressed and wear-resistant gears and joint parts, spindles, gears and other mechanical parts.
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 extended to large-scale production applications. Parts manufactured through 3D printing allow engineers to complete design verification in weeks and move on to the next design iteration cycle.
During the production of 20MnCr5 material, internal stress may cause parts to deform, but through specific heat treatment, internal stress can be reduced.
As shown by the hardening curve, the gears for additive manufacturing have reached the quenching depth required for the tooth surface, but the tooth surface section shows a lower value. The figure above shows that the core hardness of the additive manufacturing gear is about 90 HV lower than the 16MnCr5 forged steel reference gear. Preliminary test results show that the low-pressure carburizing gear manufactured by additive has the potential to meet the current quality level of 16MnCr5 medium steel.
To verify the potential of powder and 3D printing technology, GKN and Porsche used 20MnCr5 3D printing materials to make the front lateral gearbox. For best results, they use 3D printing to make the component with the greatest potential for weight reduction-a differential case with a ring gear.
In conventional transmissions, the ring gear and differential case perform different functions within 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 manufacturing processes and assembly methods, the wide ring gear teeth are supported by a thin and sometimes eccentric disc that is connected to the differential case. The designer optimized the topology of the differential housing and defined the maximum available space in the transmission, removing all the internal contours needed for bevel gears, side shafts, bearings, etc.
According to the specifications and requirements of the transmission, all loads (bearings and gears) are applied to the package. CAD optimization tools provide a structure capable of withstanding all required loads. The final structure is designed based on the degree of freedom that additive manufacturing brings to the design. It cannot be produced using conventional manufacturing techniques, and additive manufacturing techniques may produce products that are close to computational structures.
Internal shapes are supported only by organic beams and structural systems that are essential for structural integrity, and these shapes cannot be processed by traditional methods. Although the powder bed laser melting 3D printing technology releases the design limitations of traditional technology, there are still some unique design limitations in this technology, such as the need to consider how to discharge unmelted powder material after 3D printing is completed. Plan when designing additive manufacturing components.
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.
Based on the original load requirements, calculations show that the following goals can be achieved:
Reduced weight by 13% (approximately one kilogram)
Change in radial stiffness reduced by 43%
Change in tooth stiffness in the tangential direction decreased by 69%
The use of it brings new possibilities for the production of lightweight and sturdy vehicle parts. As metal additive manufacturing continues to develop and become a mainstream process, this application can be extended not only to the field of prototypes or racing parts, but also to mass production.