Design of the Inclined Wedge Internal Expansion Trimming Die
The design of the inclined wedge internal expansion trimming die is a special die developed for the trimming of the mouth of cylindrical and cup-shaped parts (such as bearing sleeves and hydraulic cylinder barrels). The expansion block is driven by the inclined wedge to expand from the inside of the part to the outside, and the trimming process is completed in cooperation with the external trimming die. It can ensure that the verticality error of the part after trimming is less than 0.1mm/m, and the flatness of the mouth is less than 0.05mm. It is suitable for alloy structural steel, stainless steel and other materials with a thickness of 3-10mm. Its core advantage is that the expansion block is supported inside the part during trimming to avoid deformation of thin-walled parts due to radial force. The trimming accuracy is 30%-50% higher than that of the traditional external pressure trimming die, which is suitable for mass production. In the early stage of design, the number of expansion blocks (usually 3-6 blocks) needs to be determined according to the inner diameter of the part. The circumferential diameter of the expansion block after expansion is 0.1-0.2mm larger than the inner diameter of the part to ensure reliable tightening.
The mold structure consists of an inclined wedge drive mechanism, an internal expansion component (expansion block, expansion core), a trimming die, a reset spring and a guide mechanism. The inclined wedge is made of Cr12MoV steel, with a quenching hardness of HRC58-62, a bevel angle of 30°-45°, and a surface roughness of Ra0.8μm or less; the expansion block is made of W18Cr4V high-speed steel, with a quenching hardness of HRC62-65, and a wear-resistant alloy (thickness 0.5-1mm) is welded on the working surface to improve wear resistance. The expansion core is a conical structure (the taper is consistent with the angle of the inclined wedge). The inclined wedge pushes the expansion core downward to expand the expansion block radially. The matching clearance between the expansion blocks is 0.05-0.1mm to ensure uniform expansion. The trimming die is made of cemented carbide (YG15), with a sharp edge, and the radial clearance with the expansion block is 5%-8% of the material thickness (0.25-0.4mm for 5mm thick material) to ensure a smooth trimming section.
The coordinated control of the tensioning force and the trimming force is the key technology. The tensioning force needs to be greater than the radial force during trimming (usually 1.2-1.5 times the trimming force). For example, the trimming force of a 5mm thick 45 steel part is 80kN, and the tensioning force needs to reach 96-120kN, which is achieved by adjusting the angle of the wedge and the tonnage of the press. The expansion stroke of the expansion block needs to be precisely controlled, usually 0.5-1mm larger than the wall thickness of the part to ensure that there is no radial displacement of the part after tensioning (displacement <0.03mm). The cutting edge height of the trimming die is 3-5 times the material thickness (15-25mm for 5mm thickness) to enhance the rigidity of the cutting edge and avoid chipping during trimming.
Applicable scenarios and process limitations must be clearly defined. The inclined wedge internal expansion trimming die is suitable for cylindrical parts with an inner diameter of 50-300mm and a height of 100-500mm. It is not recommended for parts with smaller inner diameters (less than 50mm) because the limited number of expansion blocks makes uniform expansion difficult. Regarding trimming process parameters, the trimming speed should be controlled within 10-30mm/s. Excessive speeds can increase the impact between the expansion block and the inclined wedge, shortening its lifespan. For high-strength steel parts, annealing treatment (600-650°C for 2 hours) is required before trimming to reduce the hardness to below HB200 and minimize edge wear.
The guidance and reset system ensures precise movement. The wedge and die holder are guided by sliding guides (with a clearance of 0.01-0.03mm). A guide groove is located at the bottom of the expander block, which mates with the guide key on the lower die holder (with a clearance of 0.02-0.04mm) to prevent the expander from swinging. The reset system utilizes multiple coil springs (10-20mm in diameter) distributed around the expander block. After trimming is complete, the expander retracts and resets, with a reset time of less than 0.5 seconds, ensuring a smooth cycle.
During debugging and quality control, attention should be paid to the uniformity of tightening. During the mold trial, the change in the inner diameter of the part after trimming should be measured (the allowable change is less than 0.05mm). If the ovality is out of tolerance, the size consistency of the expansion block should be adjusted (the error is less than 0.02mm). After every 1,000 pieces of work, check the wear of the expansion block and the trimming die. When there are dents on the surface of the expansion block, use a grindstone to grind it. When the wear of the die edge is greater than 0.1mm, replace it. During maintenance, it is necessary to clean the iron filings between the expansion blocks every week, and apply high-temperature grease (temperature resistance above 150°C) on the contact surface of the wedge and the expansion core to ensure smooth movement. When stored for a long time, the expansion block needs to be retracted to the minimum position, and anti-rust oil should be applied to the contact surface to avoid rust and stagnation.
