CNC Knowledge: Sheet metal processing process of high-strength titanium alloy porous skin parts

Considering the difficulty of cutting large size, high strength and difficult to machine titanium alloy skin parts, we iteratively researched various sheet metal processing methods, reconstructed the original process flow and solved the problem of cold drawing by introducing laser cutting, CNC milling and other processing methods. The processing accuracy problems caused by springback and the processing difficulties of manual milling of high-strength materials have optimized the production efficiency of various difficult-to-process links and reduced the processing time.

1

Preface

In the production and processing of sheet metal skin parts, the cutting process is mainly manual cutting. For the production and processing of aluminum alloy materials, cutting and processing of plates with a thickness of less than 3.0mm is more suitable, but the overall production efficiency and production precision are weak. With the increasing demand for high precision and high performance in aeronautical products, the application of titanium alloys, aluminum-lithium alloys, stainless steel and other materials is gradually increasing the processing time required for cutting parts with complex shapes, irregular contours, porous and. high strength materials are long. Treatment is more difficult. Large-size fuselage skin parts processed from titanium alloy materials have high strength and large tensile rebound deformation. It is extremely difficult to obtain precise shapes by cold drawing. Due to the need to consider some process margin compensation during laser cutting and CNC cutting, the production efficiency of parts is reduced.[1-6]. This article takes large-sized titanium alloy cold-drawn skin parts as an example. Based on the consideration of process compensation, the time required for different sheet metal processing processes is comprehensively compared, and the process flow is optimized based on the verification results. improve the efficiency of difficult-to-machine titanium alloy skin parts. Production efficiency and manufacturing precision. After actual production verification, the processing problem of typical difficult-to-machine titanium alloy skin parts shown in Figure 1 was solved, and the main difficulties in cutting and processing were eliminated through iterative optimization of the process flow, the whole thing. Product processing time has been significantly reduced compared to before optimization.

a) Appearance

b) Porous structure

Figure 1 Typical difficult-to-machine titanium alloy skin parts

2

Problems of processing complex and porous titanium alloy skin parts

Titanium alloy skin parts have many holes, and some holes have special shapes such as L-shaped, oval and grooved shapes. The number of openings in parts is distributed between 21 and 24, and there are multiple positioning marks and mutual coordination relationships in the assembly process. This part is extremely difficult to process and has low production efficiency. In the process of cutting workpieces, the operator must first pre-position, mark each hole and the contour line of the workpiece, roughly cut the contour and find the positioning points of each opening, and then accurately mark the lines, then finish milling. manually. The production process is long and processing takes a long time. Table 1 lists the actual processing time required for each station in actual production. The average actual processing time required for the four types of skin parts is relatively long, 33.75 hours. In most cases, 2 or 3 people are needed for collaborative processing, resulting in low production efficiency.

Table 1 Actual processing time required for each position in real production (unit: h)

3

Optimization and reconstruction of process methods

From the actual processing time required for each station shown in Table 1, it is easy to see that the time required for cutting (roughing and fine milling) accounts for 78% of the bottleneck process, that is- i.e. the key point to improve the process. the efficiency of the organization of product production is the decisive link. In order to solve the problem of difficult cutting, it is planned to introduce the CNC cutting method, reconstruct the process flow, and gradually and iteratively optimize the process method. Introduce laser cutting for optimization. Since there are many coordination relationships between cutting the hole position of the part and assembly, and the springback of cold drawing causes large deviations in the shape accuracy of the part, a margin is kept during the implementation process to avoid the generation of scrap.

By optimizing the link of manual cutting with laser cutting, the effective processing time required by the cutting station has been reduced. Table 2 lists the actual processing time required by each station after the first optimization of the treatment process. 1 and Part 2 The total processing time required has been reduced by 21.9% and the total processing time required for Parts 3 and 4 has been reduced by 16.9%. However, the processing time required for parts is still long, and the remaining margin results in a large workload for precise manual marking and manual fine milling, the labor intensity is too high.

Table 2 Actual processing time required for each station of the laser cutting method (unit: h)

The production and processing time of these four parts of skin is still too long. The second process method was optimized for CNC milling, which reduced the workload of marking, rough cutting and fine milling to the contour line alone, while the hole position and size were ensured by CNC milling to guarantee precision. The process audit revealed that the processing time required for the entire process has rebounded, with the main stations affected being manual shape cutting and manual fine milling of shapes. Table 3 lists the effective processing time required for each station after optimizing the CNC milling process method. Compared to the first optimization results, the total processing time required for parts 1 and 2 increased by 8%, and the total processing time required for parts 3 and 4 increased by 1.7%. Analyzing the reasons for the increase in effective processing time, the main reason is that CNC milling time > total time reduced by optimization of other CNC workstations, surface adjustment and linkages. inspection takes a lot of time and requires additional adjustments.

Table 3 Actual processing time required for each station of the CNC milling method (unit: h)

Combined with the optimization results of the laser cutting method, in the third process optimization, the manual cutting shape link of the CNC milling method was optimized into the laser cutting shape. Laser rough cutting can minimize the margin of the workpiece milling process. On the one hand, it reduces the time required for manual roughing of the shape, and at the same time, it also indirectly greatly increases the processing time of manual fine milling of the workpiece. the shape. Table 4 lists the effective processing time required for each station of the laser + CNC milling method. Comparing the optimization results, it is found that the overall optimization effect is obvious, and the total product processing time is reduced by 37.5% and 40.8% respectively. compared to before optimization.

Table 4 Actual processing time required for each station of laser + CNC milling method (unit: h)

4

Conclusion

This paper targets the cutting difficulties and low production efficiency of titanium alloy porous skin parts, reconstructs the process flow, and gradually optimizes the processing method. With the aim of maintaining the machining allowance, different sheet metal processing methods were checked, the time required for the process was comprehensively compared, and the optimal process flow was determined. Finally, a method combining laser roughing of the exterior shape and CNC. Inner hole milling was used to resolve the issue. The problem of difficult machining of parts is eliminated and the machining time is greatly reduced.