Ingenious use of trigonometric functions to achieve micro-intensity
In turning processing, workpieces whose inner and outer circles have a level of accuracy above second level are often processed. Due to various reasons such as cutting heat, friction between the workpiece and the tool causing tool wear and repeated positioning accuracy of the square tool holder, the quality is difficult to guarantee. In order to solve the precise micro-intake depth, during turning processing, we use the relationship between the opposite sides and the hypotenuse of the triangle as needed to move the longitudinal small tool holder to an angle, so that the transverse depth-in-depth value of the micro-moving turning tool can be accurately achieved. The purpose is to save labor and time, ensure product quality and improve work efficiency.
The scale value of the general C620 lathe tool holder is 0.05mm per division. If you want to obtain the lateral depth value of 0.005mm, check the sine trigonometric function table:
sinα＝0.005/0.05＝0.1 α＝5º44′
Therefore, as long as the tool holder is moved to 5º44′, every time the tool holder is moved one frame longitudinally, the turning tool can be moved to a minimum depth of 0.005mm in the transverse direction.
02
Three examples of application of reverse turning technology
Long-term production practice has proven that in specific turning processes, the use of reverse cutting technology can achieve good results. Current examples are as follows:
(1) The reverse cutting thread material is martensitic stainless steel parts
When processing internal and external threaded workpieces with pitches 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 inexhaustible value. If you use the method of lifting the coupling nut handle and retracting the tool to process threads, random buckling will often occur. Ordinary lathes generally do not have a buckling disk device, and a self-made set of buckling disks is quite time-consuming. Therefore, when processing this type of thread pitch, Thread time, often. The method used is low-speed turning. Because it is too late to withdraw the tool with high-speed picking, the production efficiency is low. It is easy to produce tool gnawing during turning, and the surface roughness is poor, especially when processing martensitic stainless steel materials such as 1Crl3 and 2 Crl3. When cutting at low speed, the phenomenon of tool biting is more prominent. The "three reverses" cutting method of reverse tool loading, reverse cutting, and opposite cutting directions created in machining practice can achieve good comprehensive cutting effects, because this method can cut threads at high speed, and the movement direction of the tool is The tool exits the workpiece from left to right, so there is no problem that the tool cannot exit when cutting threads at high speed. 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).
Before processing, tighten the counter-rotating friction disc spindle slightly to ensure the rotation speed when starting the counter-rotation.
Align the thread cutter, close the opening and closing nut, start forward rotation at low speed, walk to the empty slot, then enter the thread turning tool to the appropriate cutting depth, and then reverse rotation. At this time, the turning tool rotates from left to right at high speed. Move the tool to the right, and after several cuts in this way, you can process a thread with good surface roughness and high precision.
(2)Reverse knurling
During the traditional forward-turn knurling process, iron filings and debris can easily get into the space between the workpiece and the knurling cutter, causing the workpiece to be overstressed, resulting in random bundles of patterns, crushed patterns, or ghosting.
If the new operation method of lathe spindle horizontal rotation and reverse knurling is adopted, the disadvantages caused in the parallel turning operation can be effectively prevented and a good comprehensive effect can be obtained.
(3) Reverse turning of internal and external tapered pipe threads
When turning internal and external tapered pipe threads that require low precision and small batches, you can directly use the new operating method of reverse cutting and reverse tool installation without using the template device, and keep cutting while cutting. The reason why the manual lateral swiping knife (when turning the external taper pipe thread is from left to right, and the lateral slapping knife is easy to control the depth of the slicing knife from the large diameter to the small diameter) is that there is pre-pressure when slicing the knife.
The scope of application of this new reverse operation technology in turning technology is becoming more and more extensive, and it can be flexibly applied according to various specific situations.
03
New operating methods and tool innovation for drilling small holes
In turning processing, when drilling holes smaller than 0.6mm, due to the small diameter of the drill bit and poor rigidity, the cutting speed cannot be increased. The workpiece material is heat-resistant alloy and stainless steel, which has high cutting resistance. Therefore, when drilling, if In the mechanical transmission feeding method, the drill bit is easily broken. Here is a simple and effective tool and manual feeding method.
First, the original drill chuck is modified into a straight-shank floating type. When working, just clamp the small drill bit on the floating drill chuck to drill smoothly. Because the rear part of the drill bit has a straight handle and a sliding fit, it can move freely in the puller. When drilling a small hole, gently hold the drill chuck with your hand to achieve manual micro-feeding and quickly drill the small hole. Maintain quality and quantity and extend 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 you drill a larger hole, you can insert a limit pin between the puller sleeve and the straight handle.) See Figure 3.
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04
Shockproof for deep hole processing
In deep hole processing, due to the small hole diameter and slender boring tool shank, vibration will inevitably occur when turning deep hole parts with a hole diameter of Φ30~50mm and a depth of about 1000mm. In order to prevent the tool shank from vibrating, the simplest and most effective method is to Two supports (made of materials such as cloth and bakelite) are attached to the rod body, and their sizes are exactly the same as the hole diameter. During the cutting process, since the bakelite block sandwiched with cloth serves as a positioning support, the tool bar is less likely to vibrate, and high-quality deep hole parts can be processed.
05
Breakage prevention for small center drills
In turning processing, when drilling a center hole smaller than Φ1.5mm, the center drill is very easy to break. A simple and effective way to prevent breakage is to do not lock the tailstock when drilling the center hole, so that the dead weight of the tailstock and the machine tool bed The friction force generated between them is used to drill the center hole. When the cutting resistance is too large, the tailstock will retreat on its own, thus protecting the center drill.
06
Shock protection for turning thin-walled workpieces
During the turning process of thin-walled workpieces, vibration often occurs due to the poor rigidity of the workpiece; especially when turning stainless steel and heat-resistant alloys, the vibration is more prominent, the surface roughness of the workpiece is extremely poor, and the service life of the tool is shortened. Here are some of the simplest anti-shock methods in production.
(1) When turning the outer circle of a stainless steel hollow slender tube workpiece, the hole can be filled with sawdust and tightly plugged. At both ends of the workpiece, put cloth-coated bakelite plugs at the same time, and then replace the support claws on the tool holder with Use the support melon covered with bakelite material and correct the required arc before turning the stainless steel hollow slender rod. This simple method can effectively prevent the vibration and deformation of the hollow slender rod during the cutting process.
(2) When turning the inner hole of a heat-resistant (high nickel-chromium) alloy thin-walled workpiece, due to the poor rigidity of the workpiece and the slender tool bar, severe resonance occurs during the cutting process, which can easily damage the tool and produce waste products. If the outer circle of the workpiece is wrapped with rubber strips, sponges and other shock-absorbing materials, the shock-proof effect can be effectively achieved.
(3) When turning the outer circumference of a heat-resistant alloy thin-walled sleeve workpiece, due to comprehensive factors such as the high cutting resistance of the heat-resistant alloy, vibration and deformation are easily generated during cutting. If rubber or cotton is inserted into the workpiece hole, etc., and then use the clamping method of clamping with both ends to effectively prevent vibration and workpiece deformation during cutting, and can process high-quality thin-walled sleeve workpieces.
07
Additional anti-shock tools
Due to the poor rigidity of slender shaft workpieces, vibrations are easily generated during multi-groove cutting, resulting in poor surface roughness of the workpiece and damage to the tool. A self-made set of additional anti-vibration tools can effectively solve the vibration problem of slender parts during grooving (see Figure 10).
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Before working, install the homemade additional anti-shock tool in a suitable position on the square tool holder. Then install the required grooved turning tool on the square tool holder, adjust the distance and the compression amount of the spring, and you can start the operation. When the turning tool cuts into the workpiece, an additional anti-shock tool is pressed against the surface of the workpiece at the same time to provide good anti-shock. effect.
08
Honing finishing of difficult-to-machine materials
When we finish turning high-temperature alloys, quenched 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 operations are usually performed on a grinding machine.
Make a set of simple honing tools and honing wheels by yourself, and replace the fine grinding process with honing on the lathe to achieve better economic results.
09
Quick loading and unloading spindle
In turning processing, we often encounter various types of bearing kits with finely turned outer circles and inverted guide taper angles. Due to the large batch size, they need to be loaded and unloaded during the processing. The auxiliary time for tool change is longer than the cutting time, which affects the production efficiency. Low. The quick loading and unloading mandrel and single-blade multi-blade (tungsten carbide) turning tool introduced below can save auxiliary time and ensure product quality when processing various bearing sleeve parts. The production method is as follows.
The principle of making a simple small-taper mandrel is to use a slight taper of 0.02mm at the rear of the mandrel. After the bearing is installed, the parts are tightened on the mandrel by friction, and then a single-blade multi-edged turning tool is used to turn the surface. After rounding, invert the cone angle to 15°, then stop and use a wrench to eject the parts quickly and efficiently, see Figure 14.
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10
Turning of hardened steel parts
(1) One of the key examples of turning quenched steel parts
①Reconstruction and regeneration of high-speed steel W18Cr4V hardened broaches (repair after fracture)
② Homemade non-standard thread plug gauge (hardened hardware)
③ Turning of quenched hardware and spray-coated parts
④ Turning of hardened smooth plug gauges
⑤ Thread calendering tap modified with high-speed steel cutting tool
For the hardened hardware and various difficult-to-machine material parts encountered in the above production, the selection of appropriate tool materials and cutting quantities, tool geometric angles and operating methods can achieve good comprehensive economic effects. For example, if a square-mouth broach is regenerated after it is broken, if it is put into production again to manufacture a square-mouth broach, not only the manufacturing cycle will be long, but also the cost will be high. We use carbide YM052 and other blades to sharpen the blade tip at the fractured root of the original broach into a negative Front angle r. =-6°~-8°, the cutting edge can be turned after being carefully ground with a whetstone. The cutting speed is V=10~15m/min. After turning the outer circle, an empty groove is cut, and finally the thread is turned (divided into rough and fine turning) ), after rough turning, the tool must be re-sharpened and ground before finishing the external thread, and then prepare a section of internal thread to connect the tie rod, and then trim it after the connection. A broken and scrapped square broach was repaired by turning and made as good as new.
(2) Selection of tool materials used for turning hardened hardware
①The general cutting speed of new grades of carbide inserts such as YM052, YM053, and YT05 is below 18m/min, and the surface roughness of the workpiece can reach Ra1.6~0.80μm.
② Cubic boron nitride tool FD can process various quenched steel and spray-coated parts, the cutting speed can reach 100m/min, and the surface roughness can reach Ra0.80~0.20μm. The composite cubic boron nitride tool DCS-F produced by the state-owned Capital Machinery Factory and Guizhou No. 6 Grinding Wheel Factory also has this performance. The processing effect is worse than that of cemented carbide (but the strength is not as good as that of cemented carbide, the depth of penetration is smaller, and the price is more expensive than cemented carbide, and the cutter head is easily damaged if used improperly).
⑨Ceramic cutting tools have a cutting speed of 40-60m/min and poor strength.
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 hardnesses.
(3) Selection of types of quenched steel parts of different materials and tool performance
Quenched steel parts of different materials have completely different requirements for 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) with a total alloying element content exceeding 10%.
②Alloy steel: refers to tool steel and die steel with an 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 carburized steels such as T8, T10, No. 15 steel or No. 20 steel carburized steel, etc.
For carbon steel, the microstructure during processing after quenching is tempered martensite and a small amount of carbides. The hardness is HV800~1000, which is harder than WC and TiC in cemented carbide and A12D3 in ceramic tools. Much lower, in addition, its hot hardness is lower than that of martensite without alloy elements, generally not exceeding 200°C.
As the content of alloying elements in steel increases, the carbide content of steel after quenching and tempering also increases, and the types of carbides become quite complex. Taking high-speed steel as an example, the carbide content in the microstructure after quenching and tempering can reach 10-15% (volume ratio) and contains MC, M2C, M6, M3, 2C and other types of carbides, among which VC High hardness (HV2800), much higher than the hardness of the hard point phase in general tool materials. In addition, due to the presence of a large number of alloying elements, the hot hardness of martensite containing a variety of alloying elements can be increased to about 600°C, so The machinability of quenched steel with the same macro hardness is not the same, and the difference is very big. Before turning the quenched steel part, first analyze which category it belongs to, master its characteristics, and select appropriate tool materials, cutting quantities, and tool geometry. The turning of hardened steel parts can be successfully completed at any angle.
