Titanium alloy high strength sheet metal processing

In view of the difficulty of cutting large-sized, high-strength and difficult-to-machine titanium alloy skin parts, we conducted iterative research on 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 process methods. The processing accuracy problems caused by springback and the processing difficulties of manual milling of high-strength materials optimize the production efficiency of various difficult-to-process links and reduce processing time.

In the production and processing of sheet metal skin parts, the cutting process is mostly manual cutting. For the production and processing of aluminum alloy materials, the cutting and processing of plates with a thickness of less than 3.0mm is more suitable, but the overall production efficiency and production accuracy are low. With the increasing demand for high precision and high performance in aviation 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 is long. Processing is more difficult. Especially large-size fuselage skin parts processed from titanium alloy materials have high material strength and large tensile rebound deformation. It is extremely difficult to achieve precise shapes by cold drawing. Because a certain process margin compensation needs to be considered during laser cutting and CNC cutting, the production efficiency of parts is reduced [1-6]. This article takes large-size titanium alloy cold-drawn skin parts as an example. On the premise of considering 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 to improve the efficiency of difficult-to-machine titanium alloy skin parts. Production efficiency and manufacturing accuracy. After actual production verification, the processing problem of the typical difficult-to-machine titanium alloy skin parts shown in Figure 1 has been solved, and the main difficulties in cutting and processing have been eliminated. Through iterative optimization of the process flow, the total product processing time has been greatly shortened compared with before optimization.

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

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

product	Manual marking	rough cut by hand	precise line drawing	Manual fine milling	total processing time
Part 1	3	7	4	18	32
Part 2	3	7	4	18	32
Part 3	3.5	8	4	20	35.5
Part 4	3.5	8	4	20	35.5

Table 1 Effective processing time required for each station in actual production (unit: h)

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

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

product	Manual marking	Laser cutting allowance	precise line drawing	Manual fine milling	total processing time
Part 1	3	6	4	12	25
Part 2	3	6	4	12	25
Part 3	3.5	6	4	16	29.5
Part 4	3.5	6	4	16	29.5

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

The production and processing time of these four skin parts is still too long. The second process method was optimized to CNC milling, which reduced the workload of marking, rough cutting and fine milling to only the outline line, while the hole position and hole size were ensured by CNC milling to ensure accuracy. Process verification found that the processing time required for the entire process has rebounded, with the main affected stations being manual cutting of shapes 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 with 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 > the total time reduced by the optimization of other work stations. CNC positioning, surface adjustment and inspection links take a long time and require further adjustment.

product	Manual contour lines	Rough cut shape by hand	Accurately draw contour lines	Hand-finished milled shape	CNC Milling _	total processing time
Part 1	2	3	2	10	10	27
Part 2	2	3	2	10	10	27
Part 3	2.5	3.5	3	13	8	30
Part 4	2.5	3.5	3	13	8	30

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

Combined with the optimization results of the laser cutting method, in the third process optimization, the manual rough cutting shape link of the CNC milling method was optimized into the laser rough cutting shape. Laser rough cutting can minimize the milling process margin of the part. On the one hand, it reduces the time required for manual rough cutting of the shape, and at the same time, it also indirectly greatly increases the processing time of manual fine milling of 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 with before optimization.

product	Manual contour lines	Laser rough cutting shape	Accurately draw contour lines	Hand-finished milled shape	CNC Milling _	total processing time
Part 1	2	2.5	1.5	4	10	2 0
Part 2	2	2.5	1.5	4	10	2 0
Part 3	2.5	3	2.5	5	8	twenty one
Part 4	2.5	3	2.5	5	8	twenty one

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

This article aims at the cutting difficulties and low production efficiency of titanium alloy porous skin parts, reconstructs the process flow and gradually optimizes the process method. On the premise of retaining the machining allowance, different sheet metal processing methods were verified, the time required for the process was comprehensively compared, and the optimal process flow was determined. Finally, a method of combining laser rough cutting of the outer shape and CNC milling of the inner hole was used to solve the problem. The problem of difficult machining of parts is eliminated and the machining time is significantly reduced.