Process analysis of finishing titanium alloy in machining center!

Release time：2022-09-15 16:53:50 丨 Number of visits：

       Titanium alloy materials are widely used due to their low density, high specific strength, high temperature resistance, and good oxidation resistance. However, the poor machinability of titanium alloys affects the widespread use of this material.

       Titanium alloys add alloying elements to industrial pure titanium to improve the strength of titanium. Titanium alloys can be divided into three types: a titanium alloy, b titanium alloy and a+b titanium alloy. a b titanium alloy is composed of a and b dual phases. This kind of alloy has stable structure, good high temperature deformation performance, toughness and plasticity, and can be quenched and aged to strengthen the alloy. The performance characteristics of titanium alloys are mainly reflected in:

       1) High specific strength. Titanium alloy has low density (4.4kg/dm3) and light weight, but its specific strength is greater than that of ultra-high strength steel.

       2) High thermal strength. Titanium alloy has good thermal stability, and its strength is about 10 times higher than that of aluminum alloy at 300-500 °C.

       3) High chemical activity. Titanium can have a strong chemical reaction with oxygen, nitrogen, carbon monoxide, water vapor and other substances in the air, forming a hardened layer of TiC and TiN on the surface.

       4) Poor thermal conductivity. The thermal conductivity of titanium alloy is poor. The thermal conductivity of titanium alloy TC4 at 200 °C is l=16.8W/m·°C, and the thermal conductivity is 0.036 cal/cm·second·°C.

Analysis of machining characteristics of titanium alloy

       First of all, the thermal conductivity of titanium alloy is low, only 1/4 of steel, 1/13 of aluminum, and 1/25 of copper. Due to the slow heat dissipation in the cutting area, it is not conducive to thermal balance. During the cutting process, the heat dissipation and cooling effects are very poor, and it is easy to form a high temperature in the cutting area. Durability decreased. Secondly, the thermal conductivity of titanium alloy is low, so that the cutting heat is not easily dissipated in a small area near the cutting tool, the friction of the rake face increases, it is not easy to remove chips, and the cutting heat is not easy to dissipate, which accelerates tool wear. Titanium alloy has high chemical activity, and it is easy to react with the tool material when processed at high temperature, forming deposition and diffusion, resulting in the phenomenon of sticking, burning and breaking of the knife.

       Tests on commonly used tool materials in China and foreign tool materials show that the use of high-cobalt tools is ideal. The main role of cobalt can strengthen the secondary hardening effect, improve the red hardness and the hardness after heat treatment, and has high toughness, wear resistance and wear resistance. properties, good heat dissipation.

Geometry of the milling cutter

       The machining characteristics of titanium alloys determine that the geometric parameters of the tool are quite different from those of ordinary tools.

       ·The helix angle β selects a smaller helix angle, the chip flute increases, the chip removal is easy, the heat dissipation is fast, and the cutting resistance during the cutting process is also reduced.

       ·The cutting edge of rake angle γ is sharp, and the cutting is light and fast, so as to avoid excessive cutting heat generated by titanium alloy, thereby avoiding secondary hardening.

       ·Relief angle α reduces the wear rate of the blade, which is beneficial to heat dissipation, and the durability is also greatly improved.

Cutting parameter selection

       Titanium alloy machining should choose a lower cutting speed, an appropriately large feed, a reasonable depth of cut and finishing, and sufficient cooling.

       ·Cutting speed Vc Vc=30～50m/min

       ·Feed amount f Take larger feed amount for rough machining, and moderate feed amount for finishing and semi-finishing.

       ·The cutting depth ap ap=1/3d is suitable, the titanium alloy has good affinity, and chip removal is difficult.

       ·The finishing allowance αc is moderate. The surface hardened layer of titanium alloy is about 0.1~0.15mm. The allowance is too small. The cutting edge cuts on the hardened layer, and the tool is easy to wear. The processing of the hardened layer should be avoided, but the cutting allowance should not be too large.

Coolant

       Chlorine-containing coolant is not used for titanium alloy processing, which avoids the production of toxic substances and causes hydrogen embrittlement, and can also prevent high-temperature stress corrosion cracking of titanium alloys.

       Synthetic water-soluble emulsion is selected, and cooling liquid can also be used.

       When cutting, the coolant should be sufficient, the coolant circulation speed should be fast, and the flow rate and pressure of the cutting fluid should be large.

       Through the analysis of the characteristics of titanium alloys, the problems existing in the cutting process of titanium alloys are solved; by compiling correct and scientific processing technology, the cost can be reduced and the production efficiency can be improved. The following conclusions are drawn:

       ·Using the machining center to finish machining the titanium alloy can meet the requirements of complex shape and high precision of the parts, and can process multiple pieces at the same time to improve the production efficiency.

       ·High cobalt tool material is an ideal tool for processing titanium alloys.

       ·Choose reasonable tool geometry parameters, cutting parameters and coolant, which can prolong the life of cutting tools and improve production efficiency.

       · Arranging reasonable and scientific process procedures is a method to improve efficiency and save costs.