Development of high-strength iron-based powder metallurgy shifting lever

The rapid growth of China's automotive industry has created significant opportunities for the development and application of iron-based powder metallurgy products. As technological advancements continue to improve the performance of these materials, there is a clear trend toward producing high-strength, high-density, and complex-shaped structural components. The development of high-strength iron-based powder metallurgy parts not only expands the range of applications in the automotive sector but also enhances the efficiency and durability of critical components. **Product Analysis** Shift swing levers are essential structural components used in automotive transmissions, requiring high precision and mechanical strength. Through extensive testing and analysis of the part’s structural and dimensional requirements, our company developed a comprehensive production plan. This included selecting the appropriate materials, optimizing the manufacturing process, and designing specialized molds. As a result, we successfully produced a high-strength powder metallurgy shift lever that meets all specified standards (see Figure 1). The mechanical properties of the product fully comply with the technical requirements outlined in Table 1. Figure 1: Shifting Lever Structure Powder metallurgy involves pressing metal powders under high pressure within a mold cavity to achieve the desired density and shape, followed by sintering to form the final product. As the applied pressure increases, so does the product density, especially when exceeding 6 g/cm³, where the required pressure rises significantly. Table 1: Mechanical Properties and Technical Requirements Currently, most structural parts require an overall density of approximately 6.8 g/cm³. However, certain areas of the shifting lever experience higher stress during operation, necessitating localized high strength and hardness. Increasing the overall density to meet this requirement would lead to a substantial rise in production costs. To address this, we employed a localized copper infiltration technique, which enhances the density and mechanical properties of specific regions without increasing the overall cost. This method was successfully implemented in the production of the shifting lever. **Preparation Process** Based on the design of the shifting lever, a blanking diagram was created, and the preparation process was carefully planned, as shown in Figure 2. 1. **Powder Preparation** The main raw materials include water-atomized Fe powder, 200 μm 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 to ensure homogeneity. 2. **Pressing** The shifting lever was pressed using a 100-ton dry powder hydraulic press. A "one up and two down" mold structure was used, allowing for two-stage pressing to achieve a compact density of 6.85–7.0 g/cm³. Due to the complex geometry, secondary sintering and machining (such as chamfering, drilling, and deflashing) were performed to ensure uniform density across the component. Figure 2: Preparation Process 3. **First Sintering** The green compacts were sintered in a YS-105 conveyor-type furnace at 1120°C for 30 minutes. 4. **Rough Milling** Excess material was removed using a CNC milling machine to prepare the part for further processing. 5. **Secondary Copper Sintering** Copper infiltration was used to reduce porosity and enhance the mechanical properties of the part. A total of 1.5 grams of pure copper powder was placed on the infiltrated substrate and sintered at 1120°C. 6. **Heat Treatment** Carbonitriding was applied to improve surface hardness and wear resistance. The part was heated to 820°C for 30 minutes in a protective atmosphere of NH3 decomposition gas, then quenched in oil and tempered at 120°C for 30 minutes. Metallographic analysis confirmed the desired microstructure after heat treatment (see Figure 3). Figure 3: Metallographic Structure After Heat Treatment (500×) **Testing and Results** To measure the green and sintered densities, a drainage method was used on an electronic analytical balance, with paraffin sealing to prevent pore interference. Each density value was averaged from three samples prepared under identical conditions. Hardness tests were conducted using a Rockwell hardness tester, with five measurement points per sample. The crushing strength test was performed on a universal testing machine at a controlled loading speed of ≤0.03 t/s, using a custom inspection tool. The results are summarized in Table 2. Table 2: Performance Test Results **Conclusion** Through detailed product analysis, process optimization, and rigorous testing, we have successfully developed a high-performance powder metallurgy shift lever. Installation tests confirmed that the part meets all required performance specifications, demonstrating the potential of advanced powder metallurgy technologies in the automotive industry.

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