The rapid growth of China's automotive industry has created significant opportunities for the development and application of iron-based powder metallurgy products. As technology in this field continues to advance, these materials are increasingly being designed for high-strength, high-density, and complex-shaped components. The development of high-strength iron-based powder metallurgy parts is a key strategy to expand the use of powder metallurgy in automotive applications.
**Product Analysis**
Shift swing levers are critical structural components used in automotive transmissions, requiring high precision and mechanical strength. Through extensive testing and analysis of the part’s dimensional accuracy and structural performance, our company developed an optimized production plan. This included selecting appropriate materials, refining manufacturing processes, and designing molds, ultimately leading to the successful development of a high-strength shifting lever that meets all technical specifications (see Figure 1). The mechanical properties of the product fully satisfy the required standards (see Table 1).
Figure 1: Shifting Lever Structure
Powder metallurgy involves pressing metal powders under vertical pressure within a mold cavity, causing deformation and achieving a specific density. As the applied pressure increases, so does the product density, especially when reaching 6 g/cm³ or higher, where the required pressure rises significantly.
Table 1: Mechanical Properties and Technical Requirements
Currently, most structural parts require a density of around 6.8 g/cm³. However, certain areas of the shifting lever experience high stress during operation, requiring localized high strength and hardness. Increasing overall density to meet these demands would lead to higher production costs. Instead, we applied a localized copper sintering process to enhance the density and strength of specific regions, while keeping costs low. This method was successfully implemented in the production of the shifting lever.
**Preparation Process**
Based on the shape of the shifting lever, a blanking diagram was designed. The preparation process is illustrated in Figure 2.
**Powder Preparation**
The main raw materials include water-atomized Fe powder, 200 μm atomized Cu powder, and graphite powder. These were mixed in a 0.5-ton double-cone mixer for 20–30 minutes, then further blended in a 1.5-ton double-cone mixer for 30–50 minutes.
**Pressing**
The shifting lever requires pressing on a 100-ton dry powder hydraulic press. A “one up and two down†mold structure was used, with two-stage pressing achieved through post-pressing. This resulted in a compact density of 6.85–7.0 g/cm³. Due to the complex geometry, forming was challenging. To ensure uniform density, secondary sintering and copper infiltration were performed after machining steps such as chamfering, drilling, and deflashing.
Figure 2: Preparation Process
**First Sintering**
Sintering was carried out in a YS-105 conveyor-type sintering furnace at 1120°C for 30 minutes.
**Rough Milling**
A CNC milling machine was used to remove excess material from the green compact.
**Secondary Copper Sintering**
Copper infiltration is a common technique in powder metallurgy to reduce porosity and improve mechanical properties, particularly dynamic properties like impact toughness. After testing, 1.5g of pure copper powder was used as the infiltrant, placed on the substrate at 1120°C.
**Heat Treatment**
Carbonitriding was employed to enhance surface hardness and wear resistance. The part was heated to 820°C for 30 minutes in a mesh belt furnace under a NH3 decomposition atmosphere, with a carbon potential of 0.8%. It was then oil-quenched and tempered at 120°C for 30 minutes to relieve internal stresses and maintain high strength. Metallographic analysis showed a refined microstructure after heat treatment.
Figure 3: Metallographic Structure (500×)
**Testing and Results**
Green and sintered densities were measured using the drainage method on an electronic balance, with paraffin sealing to avoid pore interference. Each density value was averaged from three samples prepared under the same conditions. Local density was tested using the same method.
Hardness (HRA) was measured using a Rockwell hardness tester, with five points tested per sample and the results averaged.
Crushing strength was tested on a universal testing machine at a controlled loading speed of ≤0.03 t/s, using a special inspection tool. The test results are shown in Table 2.
Table 2: Performance Test Results
**Conclusion**
Through detailed product analysis, development methods, and preparation processes, the entire development cycle of the high-performance powder metallurgy shifting lever was thoroughly documented. Installation tests confirmed that the performance metrics of the shifting lever meet all required specifications.
FUJI Landing Door Series
Suzhou FUJI Precision Elevator Co.,Ltd , https://www.profuji.com