At present, the requirements for processing precision of aerospace products continue to increase, the overall structural parts in the aerospace field continue to increase, and the application of high-precision, thin-walled cavity parts in the aerospace product industry is becoming more and more extensive. In particular, the control of the machining accuracy of the components in the servo system is directly related to the requirements of multiple performance indicators in the weapon system. Such parts are generally processed from the entire titanium alloy blank, and the material removal rate is up to 85%. At the same time, a significant production feature of this type of parts is the variety, small batch size, and even single-piece production. This structural feature and production mode determine that its manufacturing technology has always been in an unstable state. Processing and manufacturing has always had long processing cycles, Difficulties such as high processing cost and difficult control of processing accuracy.
With the upgrading of weapon systems and the continuous improvement of performance, the parts of the current on-board servo system products tend to develop in a small size and with high precision, which places higher requirements on processing technology. At the same time, in order to pursue a small volume and high-precision structure, sometimes it is impossible to take into account the processing technology of the product. Therefore, a high-precision (dimension accuracy of 0.01mm or more) inner cavity cylindrical surface structural parts has appeared in the servo products. The mechanical processing of the structure is poor, and it is difficult to meet the accuracy requirements of parts using traditional casting and machining methods.
1. Process analysis of parts and formulation of process plans
(1) Analysis of parts structure and manufacturability.
A ball ring frame (see Figure 1) is made of titanium alloy TC4-M, which belongs to single-piece small batch production. The parts are precision machined parts. The external dimensions of the part are Sφ108mm and the wall thickness is 4mm. The requirements of geometric accuracy and dimensional accuracy are high. Because it is formed by monolithic cutting, it is easy to be deformed during processing, the material cutting performance is poor, and the manufacturability of the part structure is also poor, which brings great difficulty to the processing. Therefore, choosing a reasonable processing method and the correct tool has become the key to the quality assurance of processing.
(2) Formulation of processing technology plan.
Through the analysis of the structure of the spherical ring frame parts, the following technological process is formulated: blank → rough machining (machine cutting after removing the margin by wire cutting) → heat treatment aging → precision machining → cross-checking, the processing difficulty is the inner cavity cylindrical surface φ22 －0.002－0.010mm processing and the guarantee of shape and position tolerance, its structure and material processing technology is poor, and it cannot be machined by standard tools. Metal processing WeChat, the content is good, it is worthy of attention.
Through the analysis of the structure of the spherical ring frame parts, the following processing schemes are adopted for the cylindrical surface of the spherical ring frame φ22－0.002－0.010mm and the hole of φ20＋0.008＋0.002mm: the three-dimensional cutting process is carried out by clamping both sides of the front and back sides during roughing The cylindrical surface of the inner cavity has a margin of 1mm on one side. When finishing, a special boring tool is used in the five-axis machining center to process the cylindrical surface of φ22-0.002-0.010mm. The special boring tool can be fine-tuned with high precision, thereby ensuring φ22- The dimensional accuracy of the 0.002-0.010mm cylindrical surface, and the five-axis machining center is used to complete the processing of the φ22-0.002-0.010mm cylindrical surface and the φ20+0.008+0.002mm hole at a time, which ensures the coaxiality and perpendicularity tolerance requirements of the parts.
2. Design of special boring tool
(1) Analysis of material characteristics of parts.
The material of the ball ring frame parts is titanium alloy TC4-M, and its specific characteristics are as follows:
① Titanium alloy has poor thermal conductivity and is a poor thermal conductor metal material. During cutting, the contact area of the chip and the rake face is very small, which is particularly likely to cause thermal deformation of thin-walled parts.
②The titanium alloy has a low elastic modulus and large elastic deformation. The titanium alloy has an elastic modulus of 1078MPa (about 1/2 of steel). The workpiece has a large springback near the flank surface during cutting, resulting in the processed surface and the back blade. The surface contact area is particularly large. As a result, the geometry and precision of the machined parts are poor, the surface roughness value increases, and the tool wear increases.
③ Titanium alloy has high affinity and high cutting temperature. When cutting, titanium chips and the cut surface layer are engaged with the tool material, resulting in serious knife sticking, which is easy to cause strong bond wear of the tool. Titanium alloy has strong chemical activity at high temperature. When it is above 600℃, it will form a solid solution with oxygen and nitrogen. After absorbing the gas, the hardness of the titanium alloy surface will increase significantly, which has a strong wear effect on the knife. Therefore, the tools for processing titanium alloys are required to have high strength and high toughness, as well as high red hardness.
(2) Design principle of special boring tool.
Through the analysis of the material properties of the parts, combined with the structural characteristics of the parts, a boring cutter designed for φ22-0.002-0.010mm cylindrical surface processing is designed. The structure of the boring cutter is shown in Figure 2. 2. Fastening screw 4. Blade 3. The blade is installed in a square hole at one end of the cutter bar. The fastening screw fastens the blade on the cutter bar and connects the standard adjustable boring head to the machine tool spindle. The machined parts are fastened on the auxiliary tool of the CNC machining center, so that the machining part is perpendicular to the main shaft. The cylindrical surface of the inner cavity of the part is boring through the above-mentioned boring cutter. During the processing, the actual measurement size can be adjusted according to the actual standard. Adjust the boring head to fine-tune the blade to ensure the machining accuracy of the parts. The adjustable range of the standard adjustable boring head is within 0.06mm, and the fine-tuning precision of the diameter is above 0.002mm. The state during processing is shown in Figure 3.
(3) The design principle of the boring tool holder.
According to the material characteristics of the ball ring frame parts, the cutter bar should have high strength and good toughness. Therefore, the tool bar material is alloy tool steel CrWMn quenched and tempered material (32～35HRC), which is limited by the size of the inner hole of the ball ring frame parts. The diameter of the rod should be less than 19mm, and it should be equipped with a standard adjustable boring head interface, and the clearance should be controlled within 0.01mm.
(4) Design principle of boring cutter blade.
For the processing of titanium alloy materials, the blade material uses YL10.2 fine-grained cemented carbide scrap tools as raw materials, and is formed by wire cutting, and the front and rear angles are processed on the tool grinding machine. This kind of material has good thermal conductivity, which is conducive to the dissipation of heat and the reduction of cutting temperature. At the same time, it has good toughness and high red hardness. Metal processing WeChat, the content is good, it is worthy of attention.
When cutting titanium alloys, the tool clearance angle α0 is the most sensitive of all tool parameters, because the metal elastic recovery under the cutting layer is large and the machining hardness is large. Generally, a large clearance angle is used to make the cutting edge easily cut into the metal layer and reduce the flank. However, if the back angle is too small (less than 15°), metal adhesion will occur; and if the back angle is too large, the cutter will be weakened and the blade will easily break. Therefore, most tools for cutting titanium alloys use a 15° relief angle. From the perspective of tool durability, α0 is less than or greater than 15°, which will reduce the durability of turning tools. In addition, the cutting edge of the tool with α0 of 15° is sharper and can reduce the cutting temperature.
Because the titanium alloy will form hard and brittle compounds with oxygen, hydrogen, nitrogen, etc. in the air during the cutting process, causing tool wear (mainly occurring on the rake face of the tool), a small rake angle should be used; in addition, the titanium alloy The plasticity of the chip is low, and the contact area between the chip and the rake face is small. Therefore, a small rake angle should also be selected. Nearby, it is not only conducive to heat dissipation, but also strengthens the cutting edge to avoid chipping due to concentrated cutting force. Therefore, when machining a titanium alloy with a cemented carbide tool, take a rake angle γ0=5° and grind a chamfer f (width is 0.05～0.1mm), γf=0°～10°, the blade tip is grinded to r=0.5 Arc with small value of mm, blade inclination angle λ=+3°.
3. Conclusion
The processing of titanium alloy parts occupies a very important position in the machinery manufacturing industry. The cutting of titanium alloy materials has always been the difficulty of current processing technology. In order to meet the growing demand for titanium alloy workpieces in aerospace, my country's titanium alloy cutting process must make great progress. On the basis of domestic materials, machine tools, management and other conditions, further strengthening the optimization of titanium alloy material processing route, optimization of processing parameters, improving processing efficiency and product quality are important to promote the development of domestic titanium alloy industry and aerospace industry factor. The internal cavity cylindrical surface finishing boring cutter designed in this article has a simple structure and is very convenient to manufacture and use. It solves the problem of processing technology of spherical ring frame parts.