The turning of titanium alloy sheet product is easy to obtain better surface roughness, the machining hardening is not serious, but the cutting temperature is high, the tool wear is fast. In view of these characteristics, mainly in the tool, cutting parameters to take the following measures:
Tool materials: YG6, YG8, YG10HT are selected according to the existing conditions of the factory.
Tool geometric parameters: the appropriate tool front and rear Angle, tool tip grinding round.
Low cutting speed, moderate feed, deep cutting depth, full cooling, the tool tip should not be higher than the center of the workpiece when the outer circle, otherwise it is easy to punch the knife, fine turning and turning thin wall parts, the main Angle of the tool should be large, generally 75 ~ 90°.
Milling of titanium alloy products is more difficult than turning, because milling is intermittent cutting, and the chip is easy to bond with the blade, when the chip of the cutter teeth again cut into the workpiece, the chip was knocked off and take away a small piece of tool material, the formation of a broken edge, greatly reduce the durability of the tool. Metal processing WeChat, good content, worthy of attention. Therefore, three measures are taken for milling titanium alloy:
Milling method: generally adopts the following milling. Tool material: high speed steel M42. Improve the rigidity of the process system from the aspects of workpiece clamping and equipment.
Here needs to point out in particular is: general alloy steel processing are not using the following milling, because of the influence of the machine tool screw, nut clearance, when the following milling, milling cutter on the workpiece, in the direction of the feed component and the same direction of the feed, easy to make the workpiece table clearance channeling, resulting in a tool. For downmilling, the teeth of the cutter are hard to cut at the beginning and lead to tool damage. But because the reverse milling chip is from thin to thick, at the beginning of the cutting tool and workpiece easy to dry friction, increase the tool chip and chip, in titanium alloy, the latter contradiction is more prominent.
In addition, in order to make the smooth milling of titanium alloy, we should pay attention to the following points: relative to the general standard milling cutter, the front Angle should be reduced, the back Angle should be increased. ; Milling speed should be low. ; Adopt sharp tooth milling cutter as far as possible, avoid using gear cutter; The tip should be smoothly transferred; Heavy use of cutting fluid. ; In order to improve production efficiency, the milling depth and width can be appropriately increased. Generally, the milling depth is 1.5-3.0mm for rough machining and 0.2-0.5mm for finishing machining.
The common problems in grinding titanium alloy parts are blockage of grinding wheel and surface burn caused by debris. The reason is that the thermal conductivity of titanium alloy is poor, so that the grinding area produces high temperature, so that the titanium alloy and the abrasive bond, diffusion and strong chemical reaction. Adhesion and blockage of grinding wheel lead to significant reduction in grinding ratio, diffusion and chemical reaction result in the workpiece being burned on the grinding surface, resulting in reduced fatigue strength of parts, which is more obvious when grinding titanium alloy castings.
In order to solve this problem, the following measures are adopted: select suitable grinding wheel material: green silicon carbide TL. Slightly lower grinding wheel hardness: ZR1. Coarse grinding wheel size: 60. Slightly lower grinding wheel speed: 10 ~ 20m/s. Slightly smaller feed, fully cooled with emulsion.
Titanium alloy drilling is more difficult, often in the process of cutting the phenomenon of burning and cutting. This is mainly due to bad bit grinding, chip not timely, poor cooling and process system rigidity. Therefore, in the titanium alloy drilling processing must pay attention to the following: tool materials: high speed steel M42, B201 or cemented carbide. Reasonable bit sharpening: increase the top Angle, reduce the front Angle of the outer edge, increase the back Angle of the outer edge, add the inverted cone to 2 ~ 3 times of the standard bit. Return the knife frequently and remove the chip timely, pay attention to the shape and color of chip. If the chip appears pinnate or color changes in the drilling process, it indicates that the bit is blunt and should be sharpened by changing the blade in time.
Add enough cutting fluid: generally use soybean oil, when necessary, can add French OLTIP drilling tapping special oil. Improve process system rigidity: drill die should be fixed on the working table, drill die guide should be close to the processing surface, try to use short bit. It is also worth noting that when manual feed is adopted, the drill bit must not be in the hole, or the friction of the drill edge machining surface, resulting in machining hardening, making the bit blunt.
When titanium alloy is hinged, the tool wear is not serious, the use of carbide and high speed steel reamer can be. Commonly used in factories are W18Cr4V, M42, YW1, YG8, YG10HT, etc. When using carbide reamer, the rigidity of the process system similar to drilling should be adopted to prevent the reamer from collapsing. Metal processing WeChat, good content, worthy of attention. The main problem of reaming in titanium alloy is not only reaming, the following measures can be taken to solve: narrow reaming edge width in oil stone, to avoid the bond between the edge and the hole wall, but to ensure sufficient strength, generally in 0.1 ~ 0.15mm edge width is better.
The connection between the cutting edge and the calibration part should be a smooth arc, which should be repaired in time after wear, and the size of each tooth arc should be the same. If necessary, the calibration part of the inverted cone can be increased; Two hinges. The coarse hinge allowance is 0.1mm and the fine hinge allowance is generally less than 0.05mm. Spindle speed: 60r/min; When the reamer is finished, the hand reamer should not be reversed and the reamer should be withdrawn without stopping.
Tapping of titanium alloy products, especially the holes below M6mm, is very difficult. Mainly because the chip is small, easy to bond with the blade and workpiece, resulting in a large surface roughness value, torque. Improper tap selection and operation during tapping can easily lead to machining hardening, and the machining efficiency is very low and the tap breaks sometimes. The solution is as follows:
Priority to choose a thread in place of the tap, the number of teeth should be less than the standard tap, generally 2 ~ 3 teeth. Taper Angle should be large, taper part is generally 3 ~ 4 thread length. In order to facilitate chip removal, the cutting cone can also be worn out a negative Angle. Try to use short tap to increase tap rigidity. In order to reduce the friction between the tap and the workpiece, the inverted taper part of the tap should be increased appropriately compared with the standard.
When machining the bottom hole of thread, rough drilling and then reaming drilling are used to enlarge the hole, so as to reduce the working hardening of the bottom hole. For the thread whose pitch is 0.7 ~ 1.5mm, the size of the bottom hole can be processed to the upper difference of the standard thread bottom hole stipulated by the national standard and is allowed to be increased by 0.1mm.
If not limited by the position of screw hole and workpiece shape, try to use machine tapping, to avoid manual tapping feed uneven, stop and caused by hardening.