As everyone knows, Titanium and its alloys are difficult to machine and process due to their high strength, low thermal conductivity and chemical reactivity with tool materials (at elevated temperatures), pose a hazard to the tool and significantly reduce the tool life. In addition, a relatively low Young’s modulus leads to spring-back and chatter leading to poor surface quality of the finished product. During turning and drilling, long continuous chips are produced; causing their entanglement with the cutting tool and making automated machining near impossible. In the last article, we explained what-makes-alloyed-titanium-grade5-so-difficult-to-machine in details. Today I will discuss what should I do to makes Titanium easy to machine and supplied several tips about the processing of most commonly used alloy Titanium grade 5 alloy ( 6Al-4V) :
- Using carbide cutting tools. Tungsten-cobalt cemented carbides are characterized by high strength and good thermal conductivity and are not easy to react with titanium at high temperature. They are suitable for processing titanium alloys.
- Select reasonable geometry parameters of tools. In order to reduce the cutting temperature and tool bonding, the front Angle of the tool can be appropriately reduced and the contact area between the chip and the front cutter surface can be increased to dissipate heat. At the same time, the rear angle of the cutter is increased to reduce the phenomenon of tool bonding and the precision of the machined surface is reduced due to the rebound of the machined surface and the friction contact between the machined surface and the machined surface. The tip should use arc transition to enhance tool strength. It is necessary to maintain the sharpness of the sharpener frequently to ensure that as little cutting heat as possible is generated during the processing.
- Appropriate cutting parameters. Lower cutting speed – high cutting speed will lead to a sharp increase in cutting temperature; Moderate feed — large feed leads to high cutting temperature, while small feed leads to accelerated wear of the blade due to long cutting time in the hardened layer; Greater cutting depth — cutting beyond the hardened layer on the titanium alloy surface of the tip improves tool life.
- Maintain a high cutting fluid flow and pressure. Sufficient continuous cooling of the machining area is required to reduce the cutting temperature.
- Avoid machine tool vibration. Vibration can cause blade breakage and blade damage. Choose a larger cutting depth, but the titanium alloy machining rebound, the larger clamping force will aggravate the workpiece deformation, finishing can consider the use of jigs and other auxiliary tools to meet the stiffness requirements of the processing system.
- The climbing milling methods by which milling is carried out. In titanium alloy processing, the milling cutter caused by reverse milling is much more damaged than the milling cutter caused by climbing milling.
- Grinding with a green silicon carbide grinding wheel. The sticky chips will cause the blockage of grinding wheel and the surface burns of parts. Therefore, it is appropriate to use the green silicon carbide grinding wheel with sharp grinding particles, high hardness and good thermal conductivity. The grinding wheel size can be F36 ~ F80 that depending on the surface finish. The hardness of the grinding wheel should be soft so as to reduce the adhesion between grinding particles and grinding chips and the grinding heat. At the same time to ensure a small grinding and low speed, sufficient emulsion.
- Drilling. Standard drill bits need to be polished during drilling to reduce burners and broken bits. Grinding method: increase the top Angle and decrease the front angle of cutting part, increase the back Angle of cutting part, double the number of taper of cylindrical edge. During processing, the cutting times should be increased and the drill bit should not stay in the hole, sufficient emulsion cooling, timely removal of chips and observe whether the drill bit becomes blunt.
- Titanium alloy reaming needs to be calibrated. The width of the blade belt should be less than 0.15mm. Multiple reamer sets can be used for multiple reamers. The diameter of each reamer increase shall be less than 0.1mm. Reaming with this method can meet the requirement of a high finish. Handle cleaned titanium alloy parts should wear clean gloves, to avoid sodium chloride stress corrosion.
- Tapping is the most difficult process in titanium alloy processing. Excessive torque causes rapid wear of the tap cutter teeth, and the rebound of the processed part can even break the tap in the hole. Ordinary tap processing should be according to the diameter size appropriate to reduce the number of the chip to increase the space, set aside on the calibration of tooth belt should be after 0.15 mm width of blade Angle increases to about 30 °, remove tooth back 1/2 ~ 1/3, calibration tooth number 3 after increases taper pouring. If you want to achieve better processing results, jumping wire is a good choice, which can effectively reduce the cutting tool and the workpiece contact area.
It is worth noting that: It is important to use non-combustible or non-combustible tools to transfer titanium chips and ensure that the cutting area has fire protection facilities. Trace cutting of titanium chips once a fire can be dry powder extinguishing agent or dry soil, dry sand extinguishing.