Hydraulic bulging machine bulging force control system

I. Introduction

T-shaped pipe fittings are a kind of basic pipe fittings with a large application area in the industry, but the manufacturing process is mainly welding, hot drawing and plastic expansion. Produced by the above process, the product quality is low, the productivity is low, and the labor intensity is large. The best way to produce high quality T-tubes is currently the hydraulic bulging method, which requires a dedicated hydraulic bulging machine. In order to produce high-quality T-shaped pipe fittings, some advanced T-shaped pipe bulging machines have been introduced in China, and similar equipment has been developed. The 1250/850/850 bulging machine developed by Xi'an Heavy Machinery Research Institute is representative. The machine has oil cylinders in the up, down, left and right directions. The vertical cylinder is 12500kN, the left and right horizontal cylinders are 8500kN, and the bottom one has 3000kN. The main features of this equipment design and control are as follows:

(1) The whole control system is controlled by microcomputer, which has a high degree of automation, which helps to improve product quality and production efficiency.

(2) The forming force of this equipment is large, so the material, wall thickness and specification range of the T-shaped pipe fittings can be formed.

(3) It is equipped with a special deflation system to ensure the relative stability of the internal pressure of the pipe at the beginning of forming.

(4) 3000kN ejection cylinder can set a certain value of pre-ejection force through the liquid flow valve during the forming process, thereby reducing and avoiding the occurrence of cracking in the direction of the branch pipe when the T-shaped pipe is formed.

(5) equipped with a special booster system, ie supercharger. It can increase the pressure of ≤25MPa given in the hydraulic system by 8 times in the pressure of 1:8, so that the pipe is in the critical internal pressure state P at the initial stage of forming, which can avoid the horizontal cylinder direction when the internal pressure is too low. When moving forward, the pipe is wrinkled and becomes waste. At the same time, the supercharger can also be set to a 1:1 state.

The application effect of the 1250/850/850 bulging machine in practice is not satisfactory. When producing thick-walled carbon steel pipe fittings, the yield is close to 62%; when producing thin-walled copper alloy T-shaped pipe fittings, it cannot be formed at all. Observing the shaped T-piece, it was found that the branch pipe broke when the T-piece was just beginning to be deformed. In order to clarify the causes of waste generation, we analyzed the factors affecting the formation of T-pieces.

Second, factors affecting the formation of T-shaped pipe fittings

There are many factors affecting the formation of T-shaped pipe fittings, such as material, pipe specifications, forming speed, pipe end seal, mold finish and r angle, lubrication conditions, etc. However, through a large number of data verification and physical analysis, it is found that the bulging force and its control during the bulging process are the most critical factors. Different materials and different gauge pipes have a stable forming zone (safety zone) when forming T-shaped parts, as shown in Figure 1. Only when the bulging force is controlled to the safety zone can a qualified product be formed. If the pressure is lower than the B line in the safety zone, it will wrinkle. If it is higher than the A line in the safety zone, it will rupture. As can be seen from the specific situation of the waste product produced by the combination of FIG. 1 and the copper pipe member, the problem mainly changes during the deformation process in the bulging force P, and the axial compression causes the P to continuously rise. P is outside the range of line A in Figure 1, causing the branch to rupture. 1250/850/850 and some similar equipment can not dynamically correct and adjust the internal value of P during forming. This is the formation of low-strength, thin-walled metal pipe fittings (such as copper alloy pipe fittings) sensitive to changes in P. It is easy to cause the branch pipe to rupture and cause waste. Therefore, it is necessary to design a reasonable and feasible bulging Force Control System on the 1250/850/850 bulging machine so that the P inside the deformation process is controlled within a certain range.

Figure 1 Qualitative map of the safety zone of the bulging T-piece

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