The article mainly researches and tests titanium alloy parts on the problem of grinding burns, and summarizes the parameters that inhibit grinding burns, grinding wheels, cooling fluid and other influencing factors to prevent the occurrence of titanium alloy grinding burns.
Keywords: titanium alloy parts; grinding burn; grinding wheel; coolant
The research of titanium alloy grinding has a history of decades abroad. Both the titanium alloy grinding mechanism and the performance of titanium alloy grinding have been thoroughly researched, and applicable specifications and standards have been formed. , Cooling fluid, processing methods, grinding process parameters are clearly defined. At present, it is already a very mature technology abroad, and it has been widely used in the field of aviation. The accuracy of products has been greatly improved, making aerospace manufacturing technology ahead of China for decades.
Through the titanium alloy grinding test, in-depth study of titanium alloy grinding, to find out the grinding parameters to suppress grinding burns and grinding cracks.
2 Factors affecting titanium alloy grinding burn
2.1 Titanium alloy material characteristics
- (1) High specific strength;
- (2) Good heat resistance;
- (3) Good corrosion resistance;
- (4) Small thermal conductivity;
- (5) The elastic modulus is small.
Grinding characteristics caused by titanium alloy material characteristics:
- (1) Large grinding force and high grinding temperature;
- (2) The deformation is complicated during grinding;
- (3) The grinding wheel adheres badly, and the falling off of the adherend can cause the grinding wheel abrasive particles to break and fall off.
2.2 Grinding principle
The heat release phenomenon in the grinding area is the main cause of burns. The heat release result changes the metallographic structure of the surface layer of the workpiece, greatly changing its mechanical properties and performance.
2.3 Machine tool
In order to ensure the dimensional accuracy of parts and the stability of various processing parameters, and can achieve contour grinding, vibration grinding and other functions. The machine tool has a vibration grinding function, an operation panel, a portable operation unit, which can set the speed of the dressing tool, and also has the function of correcting the entire workpiece and dressing the shape of the special grinding wheel.
2.4 Grinding wheel
According to the general principles of material, particle size and hardness selection of titanium alloy grinding wheels, the grade of grinding wheels suitable for titanium alloy grinding was determined. The structure of the grinding wheel is loose and has certain pores. When grinding titanium alloy, the efficiency is higher, the grinding temperature is lower, and the grinding wheel is not blocked; the diamond dressing roller is used to complete the grinding wheel. The hardness of the grinding wheel is medium to soft, and the abrasive grain size is 60-120.
Norton GC60-J10 V02P 35M / S produced by Saint-Gobain Abrasives
Wheel size: 60
Abrasive material: silicon carbide (GC)
Grinding wheel hardness: soft (J)
Wheel structure: loose (10)
Wheel bond: ceramic bond (V02)
Available minimum diameter of grinding wheel: 350mm
The shape of the grinding wheel for grinding the end teeth of the arc is shown in Figure 1, which is a cup-shaped grinding wheel, and the length of the grinding wheel is H
According to the selection principle of the coolant composition and the recommendation of the machine tool manufacturer, we selected Castrol semi-synthetic cutting fluid commonly used in the world as the cooling fluid for titanium alloy grinding, and ensure that the direction of the nozzle can be directly poured into the parts and grinding wheel At the same time, the maximum flow is used on the contact surface, so as to achieve the purpose of sufficient cooling. The grinding fluid not only has good cooling performance, but also its lubricating performance inhibits the adhesion of the grinding wheel to the titanium alloy and reduces the grinding temperature. The grinding fluid does not contain chlorides or sulfides that pollute the titanium alloy. When grinding titanium alloy, the flow rate of grinding fluid is not less than 15 ～ 20ml / min.
Castrol semi-synthetic cutting fluid HYSOL X related information: is a high-tech, multi-purpose, bio-stable solvent semi-synthetic cutting fluid, has good lubrication and extreme pressure characteristics, the product has a wide range of use, ferrous metals and non-ferrous metals A variety of metal processing has excellent performance. The adaptability of water quality is strong, but its low foam characteristics are more prominent in soft water. It can be widely used in aviation industry. This product does not contain chlorine.
- (1) Coolant application: It is suitable for processing many different metals on high-speed machining centers and flexible machining systems using the latest technology. In processing steel, titanium alloy, cast iron and even various difficult-to-machine metals such as stainless steel, nickel silicon aluminum steel.
- (2) The role of the cooling fluid: This product is designed for most metal processing, and is also suitable for large central cooling systems and small cooling devices. Suitable for milling, drilling, boring, reaming, broaching and low-feed grinding.
- (3) The advantages of the coolant: a. The processing brightness is good and the tool life can be extended, even for materials that are difficult to process. b. Wide range of applicable materials and processing methods. c. Even under extreme pressures above 70 bar, foaming is still rare. d. Does not corrode and pollute aluminum. e. Strong adaptability to water quality and long service life. f. Good lubricating properties can reduce the residue of lubricating fluid and ensure that the machine tool and parts are clean. g. The operator and the environment are not at risk of contaminating free chlorine, nitrite and phenol. h. Will not destroy the paint marks and other marks usually hit on the parts.
2.6 Grinding parameters
According to the machine manual of the equipment and the relevant foreign standards, determine the grinding wheel speed of 35m / s and the workpiece speed of 100r / min. Because the titanium alloy material is easy to adhere to the grinding wheel, it is not easy to dissipate heat. In order to ensure the permeability of the grinding wheel, the grinding wheel is trimmed before semi-finishing and finishing. After solidifying the basic factors affecting grinding burns, the machine tool, grinding wheel, coolant, and grinding parameters will focus on optimizing the contact area, grinding depth, and feed between the grinding wheel and the workpiece.
3 Titanium alloy grinding burn acid etching inspection
- (1) The acid, alkali and water tank used for acid etching inspection should have enough volume to ensure that the parts can move freely and be completely submerged.
- (2) The container material and the solution in the container must not react, nor damage the inspected parts. The material used to make the container is PVC or austenitic stainless steel.
- (3) All containers should be labeled with the solution contained, and covered with a lid when not in use.
- (4) There should be a good ventilation device in the acid erosion work site.
Nitric acid, hydrofluoric acid, alcohol, deionized water
3.3 Etching procedure
- (1) Check before acid etching. Before the acid corrosion inspection, there should be no scratches, scratches, rust, etc. on the surface of the parts that may affect the inspection results.
- (2) Degrease. Immerse the parts in gasoline for washing. If necessary, use a nylon brush to dip in gasoline until the oil is completely removed.
- (3) Cleaning. Clean the degreased parts with alcohol for 2 minutes. Ensure that the parts get a moist, stain-free, uniform gloss and clean surface.
- (4) Etching. Immerse the cleaned parts in the prepared acid etching solution and shake the parts. The residence time is about 90s at room temperature, and then a macro inspection is performed. If the macroscopic examination finds that the corrosion is insufficient, it is corroded in the original solution for another 30 seconds.
- (5) Rinse. Immerse it in flowing water at room temperature and rinse for 3 minutes.
- (6) Blow dry. Dry the parts with clean, dry compressed air.
3.4.1 Inspection method
Use Olympus SZX16 solid microscope to inspect all the parts to be inspected surface under the magnification of 10X ～ 30X.
3.4.2 Acceptance criteria
Typical grinding burn determination photos are shown in Figure 3 to Figure 5.
Through the analysis of the relevant factors in the grinding of titanium alloy grinding parts and the modulus in actual processing, it summarizes the processing parameters, coolant, grinding wheel, machine tool related parameters suitable for preventing grinding burns.