Design of hot pressing die for support
The design of hot pressing die for bearings is a special technology for forming bearing parts (such as bridge bearings and mechanical bearings) at high temperatures. It is suitable for high-strength alloy structural steel (such as 40CrNiMoA) with a thickness of 10-50mm, die steel and other materials. It can realize the integral forming of bearings with complex shapes. The dimensional accuracy of the formed parts can reach IT11 level, the surface roughness is below Ra3.2μm, and the mechanical properties (such as tensile strength and impact toughness) meet the design requirements. The core is to heat the blank to the forging temperature (800-1200℃) through the heating system of the mold, and plastically deform the material under pressure to fill the mold cavity, thereby obtaining the desired shape. Thermal coupling analysis is required in the early stage of design to determine the optimal heating temperature, insulation time and forming pressure to ensure that the material is fully deformed without overheating or overburning.
The mold structure consists of an upper mold, a lower mold, a heating system, a guide mechanism, and an ejector. The upper and lower molds are made of H13 hot-work die steel, hardened to HRC 44-48. The working surfaces are nitrided (0.1-0.2mm thick) to enhance wear resistance and high-temperature oxidation resistance (withstanding temperatures exceeding 1200°C). The heating system utilizes electric heating elements or induction heating devices, evenly distributed within the mold (50-100mm apart). These elements maintain a temperature uniformity of less than ±10°C on the working surface of the mold within a range of 800-1000°C. The guide mechanism utilizes high-temperature-resistant guide pins and sleeves (material: 3Cr2W8V) with a clearance of 0.1-0.2mm to ensure accurate guidance even at high temperatures.
Controlling hot pressing process parameters is crucial. The heating temperature is determined by the material: 850-950°C for 40CrNiMoA steel and 1050-1150°C for high-speed steel. The holding time is calculated based on the billet thickness (1-1.5 minutes per millimeter) to ensure uniform heating of the material. Forming pressure is calculated based on the projected area of the part (15-30 kN per square centimeter) and is applied using a hydraulic press with a pressure control accuracy of ±1%. The holding time is 10-30 seconds to ensure that the material fully fills the mold cavity. After hot pressing, parts undergo isothermal annealing (650-700°C for 4-6 hours) to eliminate residual stresses caused by hot pressing and reduce hardness (HB200-250) for subsequent processing.
The cooling and lubrication system is the guarantee for the normal operation of the mold. A cooling water channel is set inside the mold. After hot pressing is completed, cooling water (water inlet temperature <30°C) is introduced to reduce the mold temperature to below 500°C. The cooling rate is controlled at 5-10°C/second to avoid cracks in the mold due to rapid cooling. Lubrication uses high-temperature grease (dropping point > 1200°C) or glass lubricant to form a lubricating film on the contact surface between the blank and the mold to prevent the material from sticking to the mold and reduce mold wear.
Commissioning and maintenance must be carried out strictly in accordance with specifications. During mold trials, inspect the form integrity and dimensional accuracy of parts. Sample three parts per batch and test the surface hardness using a durometer (deviation must be