I-type forgings are one of the more common parts in the oil drilling industry, such as wellhead devices, oil trees and throttling, pressure and other equipment, the market demand is large.
The shape of this type of forgings has the following characteristics: the two ends of the flange and the intermediate cylinder coaxial, flange and intermediate connection cylinder diameter difference.
Status and analysis of the forging process
The current commonly used production process of I-shaped forgings is:
(1) Based on the roughing dimensions of the flange diameter of the product, on the basis of which the processing volume is directly forged into large cylindrical forgings, which are then formed by means of machining.
(2) A symbolic pulling and elongation process is added to the above production process to form the small central cylindrical part.
However, both of these processes have the following shortcomings:
(1) Low raw material utilization, in extreme cases less than 50 per cent (in the case of the products studied in this paper, the utilization rate of raw materials using the above production process (direct free forging) is only 74 per cent at its highest).
(2) The large amount of spare parts for processing and the high processing costs, resulting in high production costs and weak product profitability.
3) Long production cycle and low customer satisfaction rate.
In this article, we mainly study the forgings of the forging type, break through the limitations of the traditional production process, avoid the above problems, in order to reduce production costs, adapt to market rhythms, increase market competitiveness as the ultimate goal.
And we focus on the shape of such forgings from the design of the split die, using the tire die forging process production, to achieve the dimensional accuracy of the forged parts.
Process flow of I-shaped forgings
Since these forgings are mainly produced in small and medium batches, they are produced using the die forging process.
The over-investment in workwear and the large production costs make it difficult to improve market competitiveness, so a comprehensive analysis is considered. The research on the production process of splitting die can have the double advantage of both the precision of die forging products and the multiple varieties of small batches in the production of tire die forging.
The specific process flow diagram is shown in Figure 1.
Figure 1: Process flow diagram
The newly developed I-formed parts are 101.96kg in mass and 154kg in forged parts, and the complexity factor S = 0.53 according to the forging process calculation.
In the free forging process already belongs to the complex class of forgings, the design of the split die puts forward higher requirements.
Based on the part diagram provided by the user, the forgings are drawn according to the new process plan, close to the forgings process balance. The product has high dimensional accuracy and the part and forging diagrams are shown in Figure 2.
Figure 2 Diagram of parts and forgings
Forging process development
The forging process production plan is: the billet is first drawn and then the flange is formed by the tire die upsetting one end, and then the other flange is formed by the combination of the parting insert and the outer tube die.
With this forging process, the first upsetting process is equivalent to the blanking process of the second upsetting process, which can control the eccentricities of the forgings and the dimensional accuracy of the blanks.
After calculations, in the final parting die forging into shape, the quality of the forged parts and parting die quality combined more than 600kg, forging equipment to choose 3t free forging hammer.
Design basis of tire mold, split insert and sleeve mold
Tire mold design basis: cold forging diagram → hot forging parts → tire mold. The dimensions of the hot forgings are calculated as in formula (1).
In the formula: Lt is the forging size in the final forging temperature(mm); L is the size of the forged part in the cold state (mm); α is the material line expansion coefficient (1/C); t is the final forging temperature (°C).
For the oil industry forging materials (mainly: AISI4130, 410SS), the starting forging temperature is generally 1150 ℃, the final forging temperature is ≥ 860 ℃. For this forging operation process is relatively long, the final forging temperature is low, the cold shrinkage rate is appropriately reduced, usually taken as 1.2% – 1.4%.
The design of the sub-packing is based on the tire mold design process, with emphasis on the assembly of the sleeve mold in the design process, to avoid the situation that the assembly is not possible or difficult.
Design of tire mold and split mold
According to the established forging production process, the tire mold (Fig. 3), the split inserts (Fig. 4) and the sleeve mold (Fig. 5) were designed by combining the elements of the tire mold design.
Figure 3 tire mold
Figure 4 split insert
Figure 5 sleeves mold
Figure 3 shows the first upsetting die, which at the beginning of the design required an accurate calculation of the weight of the forged part. Otherwise, there will be a filling of the back parting free forging after upsetting.
The split inserts are shown in Figure 4. The design must take into account the fact that the split insert is located in the middle cylinder of the forged part after the forging has been formed, and to facilitate removal, a beveled groove is made at the split die interface to facilitate removal of the split insert after forging.
At the same time, the local optimization design was carried out, the design of the end face contacting the inside of the flange was 10 °, the inside chamfering was R20mm, and the contacting chamfering between the outside and the second upset sleeve die was R15mm.
The overall slope of the outside of the mould is the same as the slope of the inner cavity of the upsetting mould shown in Fig. 3, and the diameter is reduced by 1 mm on one side to facilitate placement in the cavity of the sleeve model shown in Fig. 5.
The sleeve die shown in Figure 5 is to ensure the size of the flange after upsetting, a2, a3 size is designed for hot forging part size, cavity slope free transition. Figure 6 shows a composite split die with split inserts and sleeve module.
Figure 6 split die
The combined tire mold is forged on 3TZ, and the bearing force is extremely great during the forging process. Therefore, in the design process, the overall thickness of the sleeve mold is thickened.
After the actual small batch production verification, the split-die forging process plan is feasible and successful, and has the process guarantee capability of mass production.
In this article, the new process method is used to produce I-shaped forgings, which saves 23% of raw materials than direct free forging. The new scheme produces I-shaped forgings that reach the process target value.
The forgings have the same level of technology as die forging. Compared with die forging or direct free forging, raw material consumption saves 20% to 40% of raw materials, lower production costs, and better process flexibility.