Heading forming process and die for high neck thin-walled flange forgings

To reduce the production cost of high neck thin-walled flange forgings, a new process of billet upsetting and forging flanges are proposed, and a product is used as an example, the process analysis and calculation are carried out, and the structure of the die forging and its working principle is briefly described.

0. Introduction

Flange connection has the advantages of reliable strength, good sealing, and convenient installation, disassembly, and maintenance, and it is widely used in the connection between chemical, petroleum, and other pipeline components. The forging process can effectively improve the organization of raw materials, and the streamlined distribution is reasonable; the forging performance is good, so the flanges are usually manufactured through the traditional processing process of forging billet, mechanical cutting, and heat treatment to obtain a product of qualified quality. In this paper, for a 304 stainless steel flanges for the transmission of low-pressure gas, after a comprehensive analysis of the product structure, quality requirements, production volume and forging characteristics, and other factors, proposed a new process of forging flange forgings with the pipe as a billet, upsetting, to obtain better economic and social benefits and enhance the market competitiveness of enterprises.

1. Process solution analysis

The flange sketch shown in Figure 1 belongs to the thin-walled high neck flange; that is, the thin wall thickness of the cylinder and high height characteristics are obvious. Its forging forming can use a variety of processes to achieve.

• (1) The use of free forging forming, through the material, pad ring upsetting, punching, reaming, rounding, and other processes to complete, this method has a large punching waste, forging size tolerance, more processes, and low production efficiency shortcomings.
• (2) The use of tire die forging flange forgings, using this method to improve production efficiency but also has a large punching scrap, forgings with a low dimensional accuracy of the disadvantages.
• (3) The use of die forging, although this method avoids the above disadvantages, the need for large tonnage die forging equipment and increase in the punching process, forging cost increases.

It can be seen that with the use of solid bars as billets, there are more processes, low productivity, low material utilization, and high cost problems. After reviewing the literature and analyzing the process calculation, this paper proposes a new process of upsetting and forging the pipe billet to form the flange, even if the pipe billet is upsetting a small deformation in the die to form the barrel of the flange. The other end is upsetting a large deformation to form of the flange, to obtain such flange forgings. The method is simple, with no even skin, and does not require large tonnage forging equipment, suitable for small and medium-sized enterprises, despite the higher cost of pipes and molds, but because of the forgings in large quantities, high production efficiency, so the production profit is still considerable.
According to the technical requirements such as dimensional accuracy and surface roughness of the parts, the machining allowance of 2.5 mm was added to the inner and outer surfaces of the forgings according to the literature, and the sketch of the flange forgings formed is shown in Figure 2. The overall closed die forging method is adopted, and the inner and outer die forging slope is taken as 1°.

Figure.1 Flange part sketch

Figure.2 Flange forging sketch

2. Billet size and equipment tonnage selection

The forging volume can be calculated from the dimensions shown in Figure 2.

Stainless steel seamless pipe specifications of the national standard, select the outer diameter Φ159mm, the wall thickness of 20mm pipe as a billet, under the material length.

Compared with the forging dimensions, the height of the free end of the pipe billet in the die chamber is:

The ratio of the free end height to the wall thickness of the pipe is:

The forging conditions are satisfied, so the forging forming process is feasible.
The sawing machine is used to ensure the dimensional accuracy of the billet; a medium frequency induction furnace is used to reduce skin oxidation in the heating process. The forging temperature range is 1100℃-950℃.
Because the stroke of the friction press changes with the deformation force of the forging, multiple strikes can be implemented, and there is an ejector device, so the closed die forging is usually carried out on the friction press—this flange forging deformation force formula calculation.

Formula: K for the material coefficient, kN/cm²; q for the degree of deformation coefficient; A forging area, cm².
For the high neck thin-walled flanges, take K = 150kN/cm²; for the flange part deformation degree is medium, take q = 1.3. The relevant parameters into the formula (1) calculation, . So choose a 400t friction press for forging production.

3. Die structure

The die forging used on the friction press usually adopts a die holder structure with a guide device, and this paper adopts a guide barrel die holder structure type, as shown in Figure 3. The upper punch sleeve 2 is fixed on the upper die holder 1 through the fixing plate 3 and is connected by countersunk holes and screws to form the upper die; the lower die 5 and the lower die sleeve 4 form a pre-stressed combined concave die structure, which enhances the strength of the lower die, and is fixed on the lower die holder 8 through countersunk holes and screws; the core 6 plays the dual role of forming the inner diameter of the forging and the top part. Therefore, core 6 is designed as a movable forming part, and after the die is released, the core is pressed out of the die to separate the forging. The core is pressed out of the die to separate the forgings.
The die structure is simple, the upper punch set, lower die, and core are made of 5CrMnMo hot work die steel, and the rest are made of 40Cr, which is low cost.

Figure.3 Structure of upsetting die
1 – upper die holder; 2 – upper punch bushing; 3 – fixed plate; 4 – lower die bushing; 5 – lower die; 6 – core (ejector); 7 – ejector rod; 8 – lower die holder

4. Conclusion

The use of billet upsetting flange forgings, less process, and the required equipment tonnage is small and very suitable for producing stainless steel flange forgings with a narrow forging temperature range. The process has high production efficiency, and low cost, has a certain application value in actual production, and also has a certain reference value for the production of other similar parts.
Author: Gao Dongsheng