When titanium alloy meets thin-walled parts, it seems that the difficulty of machining 2mm thin walls is doubled on recognized difficult-to-machine materials, but after specific analysis, there can still be corresponding solutions:
PART
01
Analysis of titanium alloy thin-walled cavity parts
1.1 Part Size Analysis
The minimum rectangular profile size of the envelope cover plate parts is 567mmx426mmx56.5mm, and the overall appearance is a large arc surface thin-walled cavity structure, the wall thickness of the arc surface cavity is 2mm, and the thickness of the connecting shoulders at both ends is 6mm. In order to ensure the tightness of the cover plate and the box after installation, the flatness of the mounting surface of the cover plate parts is required to be 0.1mm.
Figure 1
1.2 Processing process analysis
The key processing part of the cover plate parts is the cavity, and the difficulty is to solve the flutter problem of the cover plate parts in the processing process due to the structural characteristics of the thin wall. Its overall structure is simple, the cover plate and the box installation surface have high flatness and surface quality requirements, the dimensional accuracy and surface quality requirements of the rest of the parts are not high, and all the processing processes can be completed on the CNC machining center.
Here the 570mmx430mmx60mm blank sheet is selected, and the processing of titanium alloy thin-walled cavity cover plate parts needs to carry out three processing steps: (1) convex cavity rough milling, finishing milling, that is, mounting hole processing, (2) concave cavity rough and fine milling, (3) mounting surface finishing.
PART
02
Processing technology and tooling scheme design
2.1 Convex cavity rough milling, finishing milling and mounting hole processing
The overall dimensions of the processing cover plate parts are 567mm±0.1mmx426m± 0.1mmx57mm, to ensure that the roughness of the surface of all the processed surfaces is Ra3.2Um, leave 0.5mm machining allowance in the thickness direction, and process 4 threaded holes of M16 deep 40 on the large plane as the fixed holes of the convex cavity processing process, 4 threaded holes are based on the symmetrical center point of the large plane, and the positioning size corresponds to the fixed holes of the aluminum-magnesium alloy 6061 tooling fixed on the workbench, so that the cover plate parts are adoptedThe positioning method of "one side and two pins" realizes positioning and clamping by means of screw clamping.
Fig.2. Roughing
Secondly, the convex cavity of the cover plate part and the installation of the step surface on both sides are processed. The four-flute end mill with high cobalt content is selected for the rough machining of the convex cavity and the roughing of the installation step surface on both sides, and the rough machining method of the parallel milling surface is shown in Figure 2. In the cutting process, the high-speed tool steel tool must maintain sufficient cutting fluid to prolong the service life of the tool.
Then, the convex cavity finishing adopts the polycrystalline cubic boron nitride ball nose milling cutter, and the streamline surface finishing method is shown in Figure 3, and the overall error is controlled within 0.012mm. Finally, the 16 mounting holes on the machining mounting surface (all of which belong to threaded connection holes) can be directly drilled with a cemented carbide drill bit such as 0.5mm to meet the processing requirements. After the end of this process, the burr should be removed, the sharp edge should be blunt, and the surface of the convex cavity should be polished, and there should be no obvious knife marks, so as not to affect the positioning and clamping of the next process.
Fig.3. Simulation of convex cavity finishing of parts
2.2 Cavity roughing and finishing milling and milling tooling
Fig. 4 is the milling tooling of coarse and fine milling of concave cavity. The concave surface of the tooling that is fixed on the workbench in the previous process is matched with the convex cavity of the cover plate part, and the two sides of the tooling are matched with the installation step surface at both ends of the cover plate part, so as to achieve precise positioning. The concave surface of the tooling is cleaned at the intersection of the plane and the plane, so as to avoid burrs or sharp edges affecting the positioning accuracy. Then use 10 M10 threaded holes on both sides of the tooling to complete the clamping and fixing of the cover plate parts and the tooling.
The roughing of the concave cavity of cover plate parts adopts the method of grooving, and the tool, cutting fluid and cutting parameters are basically the same as those of the convex cavity. The 4 M16 clamping holes in the previous process are easy to cause vibration damage to the tool during the milling process, and attention needs to be paid in cutting. The tool is the same as the milling data and the convex pocket finishing.
Figure 4
It is important to note that the following are the following:
(1) A natural failure treatment must be arranged between the roughing and finishing of the concave cavity of the cover plate parts, so as to completely release the internal stress generated by the cutting process and prevent the processing deformation;
(2) When finishing and clamping, the mating surface of the cover plate parts and the tooling should be replaced many times before and after, and the black grinding marks on all the mating surfaces in the tooling should be repaired repeatedly, so as to ensure that there can be no obvious gap between the positioning of the cover plate parts and the tooling mating surface;
(3) Remove the chips on the root and corner cleaning and mating surface of the tooling to avoid crushing the cover plate parts and affecting the surface quality;(4) When locking the screws on both sides, the left and right sides should be rotated symmetrically to avoid deformation caused by clamping force as much as possible.
2.3 Finishing the mounting surface
The main reason for the difference in flatness and surface roughness of the mounting surface after testing and processing is the tool mark or processing deformation, which requires re-finishing of the mounting surface.
Figure 5
The positioning datum and the clamping fixed surface should be selected on both sides of the parallel installation step surface of the cover plate part, the processing method of finishing milling is selected firstly, the processing method of fine grinding is selected, and the processing means of grinding are finally selected, and the processing process is continuously detected. Reserve a machining allowance of less than 0.5mm in the convex cavity machining process to achieve the accuracy requirements. After the processing is completed, the cover plate parts that have passed the inspection.
Titanium alloy TC4 belongs to the difficult-to-machine material, the cover plate parts belong to the structure of thin walls and cavities, the actual CNC machining uses the same tooling, and can be consistent with the overall process of the cover plate parts in the design; in the technical not only solves the clamping positioning, but also can skillfully overcome the 2mm thin-walled processing chatter, avoid the clamping force is too large, prevent deformation and other problems. In processing practice, the rational use of tooling can reduce costs, facilitate operation, save time and efficiency.