In this paper, the titanium alloy actuator parts on the engine tail nozzle are important parts. The shape accuracy and surface roughness of the cylinder inner hole are one of the most important factors that affect the engine work, so the machining method of the cylinder inner hole is selected. Very important. Because the titanium alloy material is not easy to grind, it is necessary to adopt the honing process to solve the problem of the accuracy of the inner hole. According to the working principle of honing and the characteristics of honing, the honing stone suitable for processing titanium alloy materials as the moving cylinder is selected. Combined with the actual production, the honing process method and practice of the inner bore of the cylinder were discussed.
Keywords Titanium alloy; Actuating cylinder; Inner hole; Honing; Whetstone
The surface quality of the inner hole of the cylinder directly affects the stability and reliability of the engine’s tail nozzle during operation. The surface roughness and machining accuracy of the inner hole of the actuating cylinder have a significant impact on the engine operation. The main process that determines the accuracy of the inner bore of the actuator is the quilting process. Quilting is an effective method to improve hole precision and reduce roughness. The surface roughness of the workpiece after quilting can reach RA0.8-0.2.
At present, the honing of the inner hole of the titanium alloy actuator is still in its infancy. The previous process methods used are precision turning and grinding. The dimensional accuracy, cylindricity and surface roughness of the inner hole after processing are all lower. The surface after grinding is easy to burn. It is necessary to find the inner hole during processing. The coaxiality of the two ends of the hole is difficult to ensure. The production efficiency is low and a more advanced process method-honing is required. However, there are few honing equipments, and it is difficult to determine the honing stone parameters and honing allowances. To repeatedly explore the parameters of whetstones and honing allowances, then to achieve the honing of the inner hole of the titanium alloy actuator, it is necessary to find out the suitable parts in combination with the actual parts. The honing allowance, grinding parameters and related parameters of the honing oilstone required for honing the inner hole, the following will explain how to solve the problem of honing the inner hole of the titanium alloy cylinder.
1 The problems faced by the machining of inner holes of typical titanium alloy actuator parts
The size, geometric accuracy and surface roughness of the inner hole of the actuator are one of the most important factors that affect the operation of the engine. The process of forming the final accuracy of the inner hole of the actuator-the honing process has also become the processing of the actuator The most important process.
Analysis of typical actuating cylinder structure: main dimensions, technical conditions and surface roughness
1) The coaxiality of the holes at both ends is 0.03mm and the cylindricity is 0.01mm over the length of 160mm, which is the technical key to ensure the stability of the actuator;
2) The size tolerance of the large and small holes is 0.02mm, 0.021mm, and the surface roughness is 0.2;
3) The wall thickness of the part is 3.0mm;
4) The material of the parts is TC6.
1.1 Actuating cylinder process route
Original process route: die forgings-outer circle of rough car, drilling-outer circle of the other end of rough car, boring-inner hole of semi-finished car and-inner hole and groove of the other end of semi-finished car-car spout ——External round ribs and threads for fine turning——Grinding large and small holes——Polishing inner holes——Correcting threads at both ends——Cleaning——Fluorescence inspection——Inspection.
The role of the above main processing steps:
1) Inner holes at both ends of semi-precision turning; as a reference for turning nozzles and external ribs;
2) Large hole for fine turning; to ensure the dimensional allowance and surface roughness before grinding;
3) Finishing small holes; to ensure the dimensional allowance and surface roughness before grinding;
4) Grinding large holes; to ensure the dimensional accuracy and cylindricity and surface roughness of inner holes;
5) Grinding small holes: to ensure the dimensional accuracy, coaxiality and surface roughness of small holes.
1.2 Analysis of the problem
Problems in the original process route:
1) Because the actuator is a titanium alloy, the grinding performance is poor, and the inner hole is easy to burn. The parts are long and thin, the dimensional accuracy and cylindricity are super poor after processing, and the surface roughness value of the inner hole is high;
2) The coaxiality of 0.03 is guaranteed by the positioning processing with large holes. Due to the poor precision of large holes, the coaxiality of large holes to small holes is easily out of tolerance;
3) The processing procedures are scattered, requiring more special fixtures, the cost of tooling increases, and the production efficiency is low;
4) Most of the procedures are processed on ordinary equipment, and the clamping is repeated many times, the positioning error is large, and the dimensional accuracy is low.
1.3 Measures taken
1) Concentrate the parts process, according to the structural characteristics of the parts, the processing of the inner hole and the outer nozzle are arranged on the turning and milling machining center, which improves the processing efficiency and size and geometric accuracy of the parts, reduces the number of special fixtures and reduces the cost of tooling ; 2) Due to the high precision of the machining center equipment, large and small holes can be processed at one time, which not only guarantees the dimensional accuracy but also ensures the coaxiality of the two holes, and lays the foundation for honing holes; 3) For convenient honing, large holes can be used Machining up and down, and strictly controlling the remaining hole and geometric accuracy of the inner hole before honing, laid a good foundation for the honing process; 4) Change the grinding process of large and small holes to honing processing to improve the dimensional accuracy of the inner hole, surface roughness and Cylindricity.
Improved process route: die forgings-rough turning outer circle, drilling-rough turning at the other end of the outer circle, boring-turning the inner and outer surfaces and threads, milling threaded nozzles-honing large holes-honing small holes ——Correction of threads at both ends——Cleaning——Fluorescence inspection——Inspection.
1.4 Selection of processing parameters for honing process
How honing works
Quilting is through the oil stone installed on the quilting head, which is pressed against the wall of the workpiece hole by the opening mechanism, and the hole can be ground or broken at a low speed by rotating or reciprocating linearly.
Honing processing has the following characteristics compared with general cutting processing:
- 1) High processing accuracy can be obtained; when processing medium holes with a diameter of 50mm ~ 200mm, the roundness tolerance can reach 3um ~ 5um, and the cylindricality tolerance can reach 10um;
- 2) High surface quality can be obtained, the surface roughness Ra value can usually reach 0.8um ~ 0.1um, the highest can reach below 0.1um.
- 1) Abrasives for honing oilstone
The abrasive material of honing stone is an important performance of whetstone, which directly affects the surface quality and productivity of honing process. The honing oil stones used in production mainly include white corundum, brown corundum, black silicon carbide, green silicon carbide, artificial diamond, cubic boron nitride, etc.
- 2) The particle size of the honing stone
Honing whetstone particle size directly affects the surface roughness of the processed surface. Under the premise that the surface roughness allows, selecting a coarser particle size can achieve high productivity. For fine honing, the specifications above W40 should be used, for semi-precision honing, the specifications for 180 # -280 # should be used, and for general coarse honing, the specifications for 80 # -180 # should be used.
- 3) Hardness of honing stone
The hardness of the quilted whetstone should be selected according to the hardness of the quilted metal. Under normal circumstances, soft kerosene should be selected for hard quilted entry, while harder kerosene should be used for quilted soft metal. The hardness of the oil stone mentioned here has nothing to do with the hardness of the abrasive particles, and refers to the strength of the bonding agent to the abrasive particles. The hardness of the quilted whetstone is too low, the whetstone is consumed quickly, and it is not easy to control the size. Abrasive particles falling off can also easily scratch the workpiece. The effect of quilting is slightly worse. However, if the hardness of the quilted whetstone is too high, the abrasive grains after wear are not easy to fall off, causing the surface of the whetstone to block, the machinability is reduced or even disappeared, and the workpiece surface is easily burned. Therefore, the choice of hardness of quilted whetstone is very important. 4) Binder and organization of honing oilstone
There are generally two types of quilted whetstones:. Ceramic binder (code V) and resin binder (code B). The main characteristics of ceramic bonding agent are uneven hardness, relatively brittle oilstone, and easy to peel off during honing. The resin stone has high strength, elasticity and anti-vibration. Whetstone wears evenly and is not easily broken. Honed workpieces are smoother than ceramic binders.
Amount of honing
Honing dosage includes: cutting speed, reticulation cross angle, whetstone working pressure, micro feed rate, machining allowance and overtravel, etc.
- 1) Cutting speed and cross angle
Honing processing efficiency and processing quality are related to honing cutting speed, cutting cross angle, circumferential speed, and reciprocating speed. The grinding performance of the processed material determines the peripheral speed and reciprocating speed. For tough materials, the two speeds should be smaller; for brittle materials, the two speeds should be larger. The honing speed also varies depending on the equipment and honing process, which depends to a large extent on the quality of the honing stone and the adaptation to the workpiece material.
- 2) Honing whetstone working pressure
The working pressure of oilstone generally refers to the average pressure acting vertically on the unit area of oilstone. The determination of the size of the pressure should take into account factors such as the material, shape, size, rigidity of the head and so on.
- 3) Micro feed rate
Honing whet micro-feed rate (ie radial feed) has a great influence on processing efficiency, processing accuracy, processing surface roughness and whetstone wear. The selection of the micro feed rate should be considered according to factors such as the material of the workpiece, the type of oil stone, the performance, the machining accuracy, and the shape tolerance of the workpiece hole.
- 4) Processing allowance for honing
Honing process margin has a great influence on honing quality and productivity. The honing process margin is generally 2 to 3 times the shape error of the previous process and the comprehensive error of the surface deformation layer.
1.4.5 Cutting fluid
Must use cutting fluid in quilting. It plays a cooling role in quilting, which can wash away the abrasive particles and debris from the quilting in time to avoid blockage of oil stones. A layer of oil film can be formed on the contact surface of the oil stone and the workpiece to improve the working condition.
Type of cutting fluid:
There are two kinds of oil agent and water agent, the water agent cutting fluid has better cooling and rinsing properties, and is suitable for coarse honing. The oil cutting fluid is usually added with an appropriate amount of sulfide. The sulfur and iron elements combine to form an anti-bonding welding and clogged iron sulfide, which is beneficial to improve the honing process.
5 Test the honing process according to the actual situation
According to the material of the actuating cylinder, the parameters of oil stone, the amount of honing and the cutting fluid of oil were selected for trial processing.
- 1) Install the selected honing stones and fine honing stones on the general honing head respectively, and trim the honing stones according to the required honing size;
- 2) Check whether the dimensional accuracy of the inner bore of the actuating cylinder (including inverted dimension, geometric shape accuracy, coaxiality and surface roughness) meets the dimensional accuracy before honing. Fix the outer circle of the parts on the special fixture on the American Shanneng vertical honing machine equipment, locate with small holes, divide the coarse and fine honing large holes, and then use the large holes as the positioning, divide the coarse fine honing small holes, select coarse and fine Honing allowance requires cooling with oil cutting fluid to ensure dimensional accuracy.
Among them: the coaxiality of the inner holes at both ends is guaranteed by the one-time machining process before honing. The honing allowance is the dimensional accuracy, geometric accuracy and surface roughness controlled when turning the inner hole.
In the experiment, through trial and error of the titanium alloy actuating cylinder honing parameters, the suitable honing stone and honing parameters were determined.
6 Selection of honing stone and honing allowance
According to the working principle of honing, characteristics of honing whetstones, and honing cutting parameters, the honing whetstones and honing parameters suitable for processing titanium alloy inner cylinder bores were selected.
Specific parameters of oil stone:
- (1) Abrasives for honing oilstone; white corundum abrasives;
- (2) The particle size of the honing oilstone; use 80 # -180 # for coarse honing, and then select W40 for fine honing;
- (3) Hardness of honing stone; L-Q for coarse honing, M-R for fine honing;
- (4) The binding agent and structure of honing oilstone; resin binding agent.
2) Amount of honing:
- (1) In rough honing, the peripheral speed is 18m.min ～ 25m.min, the reciprocating speed is 10m.min ～ 25m.min, and the crossing angle is 45 °. In fine honing, the peripheral speed is 25m.min ～ 30m.min, the reciprocating speed is 10m.min ～ 25m.min, and the crossing angle is 30 °;
- (2) Whetstone working pressure during rough honing processing 0.8MPa ～ 2.0MPa, whetstone working pressure during fine honing processing 0.8MPa ～ 2.0MPa;
- (3) The honing allowance of coarse honing is 0.08mm ～ 0.15mm. The honing allowance of fine honing is 0.02mm ～ 0.06mm.
7 Test results
Processing through an improved process route, using selected honing whetstone parameters and honing margins for trial processing on a batch of actuating cylinders, the test results: through the combination of processes, the production efficiency has increased by more than 60%, and the cost of tooling has been reduced. The honing process replaces the grinding process to process the inner hole. The quality of the inner hole meets the requirements of the drawings and the pass rate reaches 100%. The running cylinder has passed the running-in test to eliminate the stagnation phenomenon and ensure the smooth operation of the working cylinder. The honing whetstone parameters and honing margin of the honing titanium alloy material are explored, which lays a good foundation for honing similar parts in the future. The purpose of this research.
8 Safety technical requirements for operating honing equipment
- 1) Workpieces are clamped firmly, pay attention to possible collision when adjusting the stroke, the first stroke should be slow feed test, lubricate the parts before use, and run for 2min ~ 3min;
- 2) The processed parts should be placed stably and the ground oil stains can be removed at any time;
- 3) If the honing head is equipped with a universal joint, the front end of the honing head must be inserted into the workpiece before driving to prevent the honing head from flying out and hurting people.
- 4) Before working, check whether the ground wire is safe and reliable. Prevent electrical equipment from getting lubricating fluid and cooling fluid during work, and prevent electric leakage accidents due to wear of electric wires and moving parts.