Exhaust pipe head mold design
Exhaust pipe header die design is a specialized mold technology for forming automotive exhaust pipe ends. It’s suitable for machining steel pipe ends into specific shapes (such as bellmouths, flanges, and special-shaped connections) to meet the sealing connection and airflow guidance requirements of the exhaust system. Exhaust pipe headers are typically made of 2-5mm thick stainless steel (such as 304, 409L) or heat-resistant steel (such as 1Cr18Ni9Ti). After forming, the roundness tolerance of the end must be less than 0.5mm, the flange flatness must be less than 0.3mm/m, and defects such as cracks and wrinkles must be avoided. Initially, the mold cavity dimensions must be determined based on the exhaust pipe diameter (φ50-φ150mm) and the forming angle (30°-90°). For example, if an 80mm φ exhaust pipe is to be machined into a 90° elbow, the mold cavity radius should be 0.5mm larger than the pipe diameter to allow for welding margins.
The die structure consists of a bulging punch, a forming die, a clamping mechanism, and a heating device. The bulging punch is made of H13 hot-work die steel, hardened to a hardness of HRC 48-52. The working surface is nitrided (0.1-0.2mm thick) to enhance wear resistance and high-temperature oxidation resistance (withstanding temperatures exceeding 600°C). The punch head is designed to reflect the shape of the exhaust pipe head, with a corner radius of 5-8 times the material thickness (15-24mm for 3mm thick material) to prevent cracking during forming. The forming die is a split-piece structure consisting of two halves, opened and closed by a hydraulic cylinder. The die cavity is hardened with a nickel-based alloy (HRC 35-40) for enhanced impact and wear resistance.
Coordinated control of heating and forming is a key technical feature of exhaust pipe head molds. For stainless steel, localized heating of the pipe end (304 stainless steel to 800-900°C) is required before forming. This is achieved using a medium-frequency induction coil (50-100kW). The heating zone should be 1.5 times the forming length (150mm for a 100mm forming section), with a temperature uniformity tolerance of less than ±20°C. Forming force is calculated based on material thickness and deformation. For 3mm thick stainless steel, the bulging force is approximately 80-120kN. This is provided by a hydraulic system with a pressure control accuracy of ±1MPa and a holding time of 5-10 seconds to ensure sufficient plastic deformation of the material.
Positioning and clamping mechanisms ensure accurate forming position. A three-jaw centering chuck clamps the center of the exhaust pipe with a centering accuracy of ±0.1mm. The chuck jaws are bonded with high-temperature-resistant rubber (resistant to 200°C) to prevent damage to the pipe surface. The pipe end is positioned using a stop rod with a positioning accuracy of ±0.5mm. Adjustable bolts accommodate varying forming lengths (50-200mm). For bent exhaust pipe heads, an anti-twist mechanism is required. Guide rollers are installed on both sides of the mold to limit pipe rotation during the forming process (rotational error <1°).
Commissioning and maintenance require adaptation to high-temperature environments. During mold trials, measure the dimensions of the finished die. Sample 10 pieces per batch. If roundness is out of tolerance, adjust the die clearance (±0.1mm). If cracks occur, reduce the heating temperature or extend the hold time. During routine maintenance, clean the oxide scale from the punch surface every 200 strokes and repair minor scratches with specialized sandpaper (80# grit). Check the insulation of the induction coil weekly to prevent short circuits. When storing the mold for an extended period, apply high-temperature anti-rust oil (resistant to 300°C) to the forming surface and open the die to its maximum position to prevent deformation of the sealing ring under prolonged pressure.
