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Research on Milling Method for Titanium Alloy Flange

Abstract: In the milling process of titanium alloy flange, it is necessary to overcome the problems of easy deformation of parts, high dimensional accuracy, low processing efficiency, and high tool consumption cost. This part needs to be studied in terms of cost control and reducing the risk of out of tolerance. Starting from the material characteristics of this type of part, this article describes the key points of tool selection, the design of tool path, and the process of parameter selection in the machining process. It analyzes how to improve the machining efficiency of titanium alloy parts, reduce deformation, and the possibility of out of tolerance. Preliminary research is conducted on the control method of cutting load during the machining process according to the milling method.

Keywords: titanium alloy; Flange plate; Easy to deform; Processing efficiency; Cutting load

Introduction to Part Structure and Processing Requirements

This article discusses the milling process of flange plates. A typical component has a set of positioning surfaces on both sides, with the front end connected to the engine fairing and the rear end connected to the engine fan disc. The holes and lace play a fixing and weight reducing role. The following are the requirements for the milling process. The structure of a flange is complex, and due to the specialized functions of most structures, high dimensional accuracy is required, making the machining of parts difficult. Due to the large machining allowance of this type of part, it is necessary to ensure effective control of deformation before and after machining. The surface quality requirements of the part are relatively strict, so the machining process is relatively complex. This makes the machining process of this part significantly different from traditional methods. The milling process of this part not only needs to meet strict aperture requirements, but also needs to ensure effective control of machining deformation during the removal of large excess. The angular relationship between each group of holes in the part is complex, and the positional requirements are high. There is a strict positional relationship between the holes and the lace. After processing, special processes such as shot peening must be carried out. During processing, the above characteristics must be internally controlled to meet the impact of subsequent special process on it, which brings difficulties to the machining of the part.

2. Material cutting performance and tool selection

2.1 Introduction to Material Characteristics

This part uses DMD0777 material, which is equivalent to domestic TC4 alloy. Compared with other metal materials, titanium alloy has characteristics such as small specific gravity, high thermal strength, good thermal stability and corrosion resistance. However, at the same time, titanium alloy material also has characteristics such as high hardness or high temperature hardness, large work hardening, poor thermal conductivity, high cutting temperature, easy adhesion with cutting tools, and high chemical activity. These characteristics of titanium alloy make it a difficult to machine material with poor machinability.

2.2 Selection of cutting tools

The selection of cutting tools requires attention to several main aspects:

(1) From the perspective of tool geometry, the back angle of the tool can usually be larger to reduce friction between the back face and the workpiece surface. The front angle should also be larger to make the tool sharper, enhance the strength of the tool head, reduce machining deformation, reduce machining hardening, and improve the quality of the machined surface.

(2) Considering the strength of the cutting edge, heat dissipation ability, wear resistance, surface quality, and processing efficiency, while ensuring the rigidity of the clamping and tool system, it is possible to appropriately increase the radius of the end of the milling cutter tip. This allows for a reduction in chip thickness while ensuring surface quality, thereby improving feed rate, and strengthening the strength, heat dissipation ability, and wear resistance of the cutting edge.

2.3 Selection criteria for cutting parameters for processing titanium alloys

The cutting amount of titanium alloy is similar to that of high-temperature alloys and some aviation stainless steel materials, and should be approached from the perspective of reducing cutting temperature, because controlling cutting heat is the primary means of protecting the tool. Due to the fact that surface roughness is independent of cutting line speed and cutting depth has little effect when cutting titanium alloys, the feed rate can be adjusted appropriately based on the shape and size of the cutting tool and the end edge arc structure when considering machining efficiency factors. Efforts are made to control the force state of the cutting tool during the cutting process through the thickness and width of the chips, in order to achieve the machining goal. When selecting the cutting amount, consideration should also be given to the cutting load borne by the tool and the part during the machining process. The primary method to reduce the cutting load is to reduce the cutting force. Light and fast cutting is beneficial for reducing the force during the machining process of the part, thereby reducing the deformation of the part. There are several methods to reduce cutting load. Firstly, small cutting depth and large feed rate can be selected. This method is more common in the cutting process using end edges. Due to its easy chip removal, convenient cooling, and lower overall tool load, this method can achieve a higher material removal rate while achieving machining goals. Secondly, the small cutting width and large feed method can be chosen. In order to reduce the load borne by the tool and achieve the same goal, when both methods can be applied, it is preferred to use the end edge for machining, because the direction of the tool's force is more inclined towards the axial direction of the tool, resulting in stronger rigidity. When the end edge is worn out and cannot be used, milling with the side edge can effectively utilize various positions of the tool, which is beneficial for reducing tool consumption. During the machining process of this part, both methods were applied to achieve a balance between machining efficiency and tool cost.

3. Design and machining process of milling tool trajectory for this part

3.1 General principles for tool path design

The lace structure requires a large amount of margin to be removed, making processing and process control difficult. The design of the cutting path has a significant impact on the machining of parts. Several difficulties in tool path design were overcome during the milling process of this part. Firstly, in order to achieve a higher material removal rate, it is necessary to have as much feed as possible during the tool application process. During the high feed application process, it is necessary to avoid the problem of cutting load changes at the corners. On the one hand, the method to avoid this problem is to cut in and out at low loads. On the other hand, at smaller corners, the cutting load should be adjusted through cutting parameters, that is, using the method of arc cutting in and out and the method of reducing speed at the corners. The process of tool trajectory design must consider each machining action during the machining process, effectively control the cutting load at each moment, in order to effectively exert tool performance and reduce tool wear. During the milling process, the forward milling method is always used for titanium alloys. Due to material performance reasons, the tool wear is significant during reverse milling, and the surface quality of the parts is poor.

3.2 Key points of the processing process

During the machining process, it is necessary to strictly follow the operating procedures. In order to meet the needs of batch production of parts and ensure stable quality, attention should be paid to multiple aspects during the machining process, including:

(1) The clamping length of the cutting tool needs to be strictly regulated, because in the process of highly efficient material removal, it often involves vibration issues of parts and tools. Although resonance can be avoided by adjusting parameters, in order to pursue cost reduction, the optimal processing conditions should be selected.

(2) The durability of cutting tools needs to be tested and statistically analyzed, as surface problems such as work hardening often occur during the processing of titanium alloy parts. This problem is often caused by the accumulation of cutting tools on the surface of the parts or the entry of chips into the cutting area. Therefore, blunt cutting tools cannot be used, and the number of parts processed by each tool must be clearly specified.

(3) The precision machining process must use new cutting edges and it is not allowed to replace the blades midway to avoid unstable effects on the quality of the parts caused by the size and sharpness of the blades.

(4) For integral hard alloy cutting tools, it is necessary to check whether the tools are sharp before processing, and tools with severe wear are not allowed to be used.

(5) During the installation of precision machining tools, it is necessary to check the tool deflection. If the tool deflection value exceeds 0.02, it will cause some characteristics to exceed the tolerance.

epilogue

Due to the reasonable and effective design of the machining process for this part, the stability of the margin removal process, and the proficiency in operating steps, the high efficiency, high quality, and low consumption of the machining process have been achieved. Through the development of this part, the requirements of the design drawings and relevant documents have been ultimately ensured, and the research on flange milling technology for this model has been successfully completed.

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