Design of Tail Pipe Beading Die
The design of the tail pipe rib pressing die is a forming technology for pressing reinforcing ribs on the outer surface of automobile exhaust tail pipes, air conditioning drain pipes and other pipes. By pressing annular or spiral ribs (height 0.5-3mm, width 2-10mm) on the surface of the pipe, the rigidity of the pipe is enhanced (bending strength is increased by 30%-50%), and it also has a decorative effect. The dimensional accuracy of the ribs after rib pressing is ±0.1mm, and the coaxiality error with the pipe is <0.2mm. It is suitable for stainless steel pipes and galvanized steel pipes with a diameter of φ20-φ100mm and a wall thickness of 0.8-2mm. In the early stage of design, the mold cavity needs to be determined according to the shape of the ribs. The annular ribs use a circumferential closed cavity, and the spiral ribs use a spiral groove cavity. The radius of the cavity fillet is 0.5 times the height of the ribs to avoid cracking of the pipe during rib pressing.
The mold structure consists of an upper rib punch, a lower material-carrying die, a positioning mechanism, an axial thrust device, and a guide mechanism. The rib punch is made of Cr12MoV steel, hardened to HRC 58-62, and polished to a working surface of Ra 0.4μm or less. The punch’s ribs are consistent with the design and are 0.05-0.1mm larger than the ribs (allowing for material springback). The material-carrying die is a split-piece structure, consisting of left and right halves, which open and close via a hydraulic cylinder. The inner diameter of the die is 0.1-0.2mm larger than the outer diameter of the pipe. The material is Cr12 (HRC 55-58), and the inner surface is hard-chrome plated (0.01mm thick) for enhanced wear resistance.
The coordinated control of compression force and axial thrust is a key technical issue. Compression force is calculated based on the projected area of the rib using the formula F = K × L × h × σs (K is a coefficient of 1.5-2.0, L is the rib circumference, h is the height, and σs is the yield strength). For example, for a φ50mm stainless steel pipe (h1mm, width3mm), compression force is approximately 8-12kN, provided by a hydraulic system with a pressure control accuracy of ±1%. Axial thrust, 10%-20% of the compression force (0.8-2.4kN), is applied by a cylinder to axially move the pipe, compensating for material flow during compression and preventing dents on either side of the rib. The parallelism error between the thrust direction and the pipe axis is less than 0.1mm/m.
The positioning and guiding system ensures the accurate position of the ribs. A three-claw centering chuck is used to position both ends of the pipe, with a centering accuracy of ±0.05mm. A rubber pad (thickness 1mm) is pasted on the surface of the chuck claw to prevent the surface of the pipe from being pinched. For multi-ribbed tail pipes, the servo motor controls the pipe rotation angle (annular ribs) or axial movement distance (spiral ribs), with a positioning accuracy of ±0.1mm and a spacing error of adjacent ribs of less than 0.2mm. The guiding mechanism uses a sliding guide pin and guide sleeve, with a guide pin diameter of 25-40mm and a matching clearance of 0.01-0.03mm, to ensure that the centering error of the rib pressing punch and die is less than 0.05mm.
The rib pressing process and mold maintenance need to adapt to the characteristics of the pipe. For stainless steel tail pipes, the rib pressing speed is controlled at 5-10mm/s, and the galvanized steel pipe is 10-15mm/s to avoid the coating falling off; the pipe surface needs to be pre-treated before rib pressing (remove oil and scale), and apply extreme pressure grease (dropping point > 180℃) to reduce mold wear. After every 1,000 pieces of work, check the wear of the ribs of the rib pressing punch (grind when the height decreases > 0.05mm), and polish with fine sandpaper (grit size 400#) when scratches appear on the inner hole surface of the die. Clean the debris between the ribs regularly to prevent indentations during rib pressing. The pressure sensor of the hydraulic system is calibrated once a month to ensure accurate force control.
