Study on Machining Performance of Laser Rapid Prototyping TA15 Titanium Alloy (2)

Rapid prototyping of laser rapid forming TA15 titanium alloy

The organization of the material is one of the important factors affecting the machining process. Fig. 3 is a longitudinal section macroscopic morphology of the laser rapid prototyping TA15 titanium alloy along the deposition growth direction. The layer-by-layer melting deposition trace corresponding to the surface "fish scale" shape is clearly seen from the figure. Further high-magnification microstructure analysis (Fig. 4) shows that the laser rapid prototyping TA15 titanium alloy has an ultra-fine "net basket" special microstructure, and its α-sheet is fine, the sheet bundle orientation is randomly diverse, and it has rapid solidification structure characteristics. This is the solidification microstructure of laser rapid prototyping titanium alloy with excellent comprehensive mechanical properties.

Figure 3 OM photo of typical microstructure of laser rapid prototyping TA15 titanium alloy

The hardness of the material is one of the important factors affecting the cutting process. The cross-section and longitudinal section microhardness distribution of the laser rapid prototyping TA15 titanium alloy material are shown in Fig. 5. It can be seen that the microhardness value distribution is uniform and stable, and is HV350 to HV400.

Fig. 5 Microhardness distribution of laser rapid prototyping TA15 titanium alloy

At the same time, the results show that the microhardness values ​​of different thickness test pieces and along different directions do not fluctuate greatly, and the macro hardness test results are also relatively uniform and stable, which is HRC40~HRC44. The insensitivity of the microhardness of the laser rapid prototyping titanium alloy to the wall thickness and shape and the uniformity of the hardness distribution inside the material provide stable and favorable conditions for the subsequent cutting process.

Cutting performance of laser rapid prototyping TA15 titanium alloy

1 Tool material and tool geometry selection

Due to the low thermal conductivity, low plasticity and high metal adhesion tendency of titanium alloy, it has a great influence on tool life. The selection of tool materials should mainly be based on the reduction of cutting temperature and viscosity reduction. Generally, a tool material having good red hardness, high flexural strength, high wear resistance, good thermal conductivity, and poor affinity with titanium alloy should be selected.

In this paper, the typical structure of laser rapid prototyping TA15 titanium alloy I-beam aircraft is taken as the object, and the cutting effect of different tools is compared. The results show that the selection of tool materials and tool geometry parameters for laser rapid prototyping titanium alloy can basically follow the selection of forgings. However, due to the special surface topography of laser rapid prototyping titanium alloy parts, during the process of milling the surface oxide layer, Cutting materials such as high-cobalt high-speed steel (such as W2Mo9Cr4V4Co8) or aluminum high-speed steel (such as W6Mo5Cr4V2Al) are used to reduce costs.

In the research of milling of laser rapid prototyping TA15 titanium alloy aircraft components, it is found that the milling cutter can be ground according to the situation of wear and chip removal, and the geometric parameters of the milling cutter can be changed to improve the cutting performance. The use of indexable tools and carbide single-blade milling, roughing requires the tool front and rear corners to be smaller, the finishing angle requires the tool rake angle, back angle, helix angle to be larger or the teeth are denser, and Reduce the cutting edge length as much as possible. The tool structure parameters of the laser rapid prototyping TA15 titanium alloy aircraft components are shown in Table 1.

2 Selection of cutting parameters

Laser rapid prototyping TA15 Titanium alloy material selection parameters are basically the same as forgings, the general principle is high cutting speed, medium feed per tooth fz, small axial depth of cut ap and appropriate large radial depth of cut ae However, a large depth of cut is required when milling the surface layer to avoid surface undulations, bond hard oxide particles and surface osmotic hard layers to sharp wear and "cutter" chipping.

The milling parameters of the laser rapid prototyping TA15 titanium alloy short beam members in the machining of the surface layer and normal roughing are shown in Table 2 (the tool material is Y330A).

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