1. Cleverly obtain trace food depth, clever use of trigonometric functions
In turning processing, some workpieces whose inner and outer circles are above the secondary precision are often processed. Due to various reasons such as cutting heat, friction between the workpiece and the tool, tool wear, and repeated positioning accuracy of the square tool holder, the quality is difficult to guarantee. In order to solve the precise micro-cutting depth, we use the relationship between the opposite side and the hypotenuse of the triangle according to the needs in the turning process, and move the small vertical tool holder to an angle, so as to accurately achieve the horizontal cutting depth value of the micro-moving turning tool. Purpose, saving labor and time, ensuring product quality and improving work efficiency.
The scale value of the general C620 lathe small tool post is 0.05mm per division. If you want to obtain the horizontal depth of penetration of 0.005mm, you can check the sine trigonometric function table:
sinα＝0.005/0.05＝0.1α＝5º44′
Therefore, as long as the small knife rest is moved to 5º44', every time the small knife rest is moved vertically to carve a grid, the micro movement of the turning tool in the transverse direction with a cutting depth of 0.005mm can be achieved.
2. Three examples of application of reverse turning technology
The long-term production practice has proved that in the specific turning process, the use of reverse cutting technology can obtain good results. Examples are as follows:
(1) The reverse cutting thread material is martensitic stainless steel
When processing internal and external thread workpieces with a pitch of 1.25 and 1.75mm, because the pitch of the lathe screw is removed by the pitch of the workpiece, the resulting value is an indivisible value. If the thread is processed by lifting the handle of the coupling nut and withdrawing the tool, random buckling often occurs. Generally, ordinary lathes do not have a random buckling disc device, and a self-made set of random buckling discs is quite time-consuming. Therefore, when processing this type of pitch When threaded, often. The method adopted is the low-speed parallel turning method, because it is too late to retract the tool with high-speed buckle, so the production efficiency is low. Add WeChat: Yuki7557 to send a copy of the macro program tutorial. It is easy to gnaw the tool during turning, and the surface roughness is poor, especially in the When processing 1Crl3, 2Crl3 and other martensitic stainless steel materials such as low-speed cutting, the phenomenon of biting the knife is more prominent. The "three-reverse" cutting method created in machining practice, which is reverse loading, reverse cutting, and opposite direction of cutting, can obtain good comprehensive cutting effects, because this method can turn threads at high speed, and the moving direction of the tool is The tool exits the workpiece from left to right, so there is no disadvantage that the tool cannot be withdrawn during high-speed thread cutting. The specific method is as follows:
When turning external threads, grind a similar internal thread turning tool (Figure 1);
When turning internal threads, grind a reverse internal thread turning tool (Figure 2).
Tighten the main shaft of the reverse friction plate slightly before processing to ensure the rotation speed at reverse start.
Align the thread cutter, close the split nut, turn forward at low speed and go to the empty tool groove, then enter the thread turning tool into the appropriate cutting depth, and then turn it reversely. At this time, the turning tool rotates from left to right at high speed. Move the tool to the right, and after cutting several times in this way, the thread with good surface roughness and high precision can be processed.
(2) Reverse car knurling
Iron filings and sundries can easily enter between the workpiece and the knurling cutter during the traditional forward knurling process, resulting in excessive stress on the workpiece, resulting in random bundles of lines, crushed patterns or double images.
If the new operation method of turning the main shaft of the lathe horizontally and reversely turning the knurling is adopted, it can effectively prevent the disadvantages caused by the parallel operation and obtain a good comprehensive effect.
(3) Reverse turning inner and outer tapered pipe threads
When turning various internal and external tapered pipe threads with low precision requirements and small batches, you can directly use the new operation method of reverse cutting and reverse tool loading without using the profiling device, and use it continuously while cutting. The hand strikes the knife horizontally (the external tapered pipe thread moves from left to right, and the horizontal knife is easy to control the depth of the knife from the large diameter to the small diameter) because there is pre-pressure when the knife is opened.
The range of application of this new type of reverse operation technology in turning technology is more and more extensive, and it can be flexibly applied according to various specific situations.
3. New operation method and tool innovation for drilling small holes
In turning processing, when drilling a hole smaller than 0.6mm, due to the small diameter of the drill bit, the rigidity is poor, and the cutting speed cannot be increased. The workpiece material is heat-resistant alloy and stainless steel, and the cutting resistance is large. Therefore, when drilling, if using In the way of mechanical transmission feeding, the drill bit is very easy to break. The following introduces a simple and effective tool and manual feeding method.
Firstly, the original drill chuck is changed into a straight shank floating type, and the drilling can be smoothly carried out as long as the small drill bit is clamped on the floating drill chuck during work. Because the back of the drill bit is a straight shank sliding fit, it can move freely in the puller sleeve. When drilling small holes, gently hold the drill chuck with your hand, add WeChat: Yuki7557 to send a copy of the macro program tutorial, and you can realize manual micro-quantity Feed, drill small holes quickly, maintain quality and quantity and prolong the service life of small drill bits. The modified multi-purpose drill chuck can also be used for small-diameter internal thread tapping, reaming, etc. (if drilling a larger hole, a limit pin can be inserted between the puller sleeve and the straight shank). See Figure 3.
4. Shockproof for deep hole processing
In deep hole processing, due to the small aperture and slender boring tool bar, vibration will inevitably occur when turning deep hole parts with a diameter of Φ30-50mm and a depth of about 1000mm. To prevent the tool bar from vibrating, the easiest and most effective way is Add two supports (with materials such as cloth bakelite) on the rod body, and its size is just in time consistent with the aperture size. During the cutting process, because the bakelite block acts as a positioning support, the tool rod is not easy to vibrate, and it can process deep hole parts with good quality.
5. Anti-breakage of small center drill
In turning processing, when drilling a center hole smaller than Φ1.5mm, the center drill is easily broken. The simple and effective method of preventing breakage is not to lock the tailstock when drilling the center hole, so that the weight of the tailstock and the machine bed surface The friction generated between them is used to drill the center hole. When the cutting resistance is too large, the tailstock will retreat by itself, thus protecting the center drill.
6. Difficult-to-machine materials should be honed and finished
When we finish turning high-temperature alloys, hardened steel and other difficult-to-machine materials, the surface roughness of the workpiece is required to be Ra0.20-0.05μm, and the dimensional accuracy is also high. Final finishing is usually performed on a grinding machine.
7. Quick loading and unloading mandrel
In the turning process, various types of bearing kits are often encountered in the finishing turning of the outer circle and the reverse guide cone angle. Due to the large batch size, the auxiliary tool change time is longer than the cutting time during the process of loading and unloading, and the production efficiency Low. The quick loading and unloading mandrel and single-knife multi-edged (tungsten carbide) turning tool introduced below can save auxiliary time and ensure product quality in the processing of various bearing sleeve parts. The production method is as follows.
Make a simple mandrel with small taper. The principle is to use the 0.02mm taper at the back of the mandrel. After the bearing set is installed, the parts will be tightened on the mandrel by friction. After the circle is reversed and the cone angle is 15°, the parking wrench is used to eject the parts quickly and well.
8. Turning of hardened steel parts
(1) One of the key examples of turning hardened steel parts
① Remanufacturing and regeneration of high-speed steel W18Cr4V hardened broach (repair after fracture)
② Self-made non-standard threaded plug gauge (hardened hardware)
③Turning of quenched hardware and sprayed parts
④ Turning of quenched hardware smooth plug gauge
⑤Thread calendered taps modified with high-speed steel tools
For the hardened hardware and various difficult-to-machine material parts encountered in the above production, choosing the appropriate tool material and cutting amount, as well as the geometric angle and operation method of the tool can receive good comprehensive economic results. For example, the regeneration of a square broach after it is broken, if it is put into production again to manufacture a square broach, not only the manufacturing cycle will be long, but also the cost will be high. At the root of the original broach fracture, we use hard alloy YM052 and other blades to sharpen into negative front angle r. =-6°～-8°, the cutting edge can be turned after being carefully ground with oilstone, the cutting speed V=10～15m/min, after the outer circle is turned, the slit is cut, and finally the thread is turned (rough and fine turning) ), after rough turning, the tool must be re-sharpened and ground before fine-turning the external thread, and then prepare a section of internal thread connecting the tie rod, and then trim it after connecting. A broken and discarded square broach is as good as new after being turned and repaired.
(2) Selection of cutting tool materials for turning and quenching hardware
①The cutting speed of cemented carbide YM052, YM053, YT05 and other new brands of inserts is generally below 18m/min, and the surface roughness of the workpiece can reach Ra1.6-0.80μm.
②Cubic boron nitride tool FD can process various hardened steel and sprayed parts, the cutting speed can reach 100m/min, and the surface roughness can reach Ra0.80～0.20μm. The compound cubic boron nitride cutting tool DCS-F produced by the state-run Capital Machinery Factory and Guizhou No. 6 Grinding Wheel Factory also has this performance. The processing effect is worse than cemented carbide (but the strength is not as good as cemented carbide, the depth is smaller, and the price is more expensive than cemented carbide, and the cutter head is easily damaged if used improperly).
⑨Ceramic tools, the cutting speed is 40-60m/min, and the strength is poor.
The above various tools have their own characteristics in turning quenched parts, and should be selected according to specific conditions such as turning different materials and different hardness.
(3) Selection of types of quenched steel parts of different materials and tool performance
Quenched steel parts of different materials have completely different requirements on tool performance under the same hardness, which can be divided into the following three categories;
① High-alloy steel: refers to tool steel and die steel (mainly various high-speed steels) whose total alloying elements exceed 10%.
②Alloy steel: refers to tool steel and die steel with alloy element content of 2 to 9%, such as 9SiCr, CrWMn and high-strength alloy structural steel.
③Carbon steel: including various carbon tool steels and carburizing steels such as T8, T10, No. 15 steel or carburizing steel of No. 20 steel.
For carbon steel, the microstructure during processing after quenching is tempered martensite and a small amount of carbide, and the hardness is HV800-1000, which is harder than WC and TiC in cemented carbide and A12D3 in ceramic tools. It is much lower, and it is lower than the hot hardness of martensite without alloying elements, and generally does not exceed 200 °C.
As the content of alloying elements in steel increases, the content of carbides in steel after quenching and tempering also increases, and the types of carbides become quite complex. Taking high-speed steel as an example, the content of carbides in the microstructure after quenching and tempering can reach 10-15% (volume ratio) and contains types of carbides such as MC, M2C, M6, M3, and 2C, among which VC The hardness is high (HV2800), which is much higher than the hardness of the hard point phase in general tool materials. In addition, due to the existence of a large number of alloying elements, the thermohardness of martensite containing various alloying elements can be increased to about 600 ° C, so The machinability of hardened steel with the same macroscopic hardness is not the same, and the difference is very large. Before turning the hardened steel, analyze which type it belongs to, grasp its characteristics, and select the appropriate tool material, cutting amount and tool geometry. The turning process of hardened steel parts can be completed smoothly.
