1. Get micro-depth by using trigonometric functions. In turning, we often process workpieces with inner and outer circles above the second-level precision. The quality is difficult to guarantee due to cutting heat, tool wear caused by friction between the workpiece and the tool, and repeated positioning accuracy of the square tool rest. In order to solve the problem of precise micro-depth, we use the relationship between the opposite side and the hypotenuse of the triangle in turning, and move the longitudinal tool rest at an angle to accurately achieve the purpose of micro-moving the horizontal depth of the turning tool, saving labor and time, ensuring product quality, and improving work efficiency.
The scale value of the tool rest of a general C620 lathe is 0.05mm per grid. If you want to obtain a transverse depth of 0.005mm, you can check the sine trigonometric function table:
sinα＝0.005/0.05＝0.1 α＝5º44′
Therefore, as long as the tool rest is moved to 5º44′, each time the longitudinal engraving plate on the tool rest is moved one grid, the tool can move a micro amount of 0.005mm in the transverse direction.
2. Three examples of reverse turning technology application Long-term production practice has proved that the reverse cutting technology can achieve good results in specific turning processes. The following examples are given:
(1) Reverse cutting of martensitic stainless steel thread materials
When processing internal and external threaded workpieces with pitches of 1.25 and 1.75mm, because the lathe screw pitch is divided by the workpiece pitch, the resulting value is an indivisible value. If the method of lifting the handle of the matching nut to withdraw the tool is used to process the thread, it often produces random buckles. Ordinary lathes generally do not have random buckle disc devices, and it is quite time-consuming to make a set of random buckle discs by yourself. Therefore, when processing threads of this type of pitch, it is often necessary to use a low-speed forward turning method. Because the high-speed pick-up does not have time to withdraw the tool, the production efficiency is low, and 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 at low speed, the tool gnawing phenomenon is more prominent. The "three-reverse" cutting method created in processing practice, which includes reverse tool loading, reverse cutting, and opposite tool feeding direction, can obtain a good comprehensive cutting effect. Because this method can turn threads at high speed, the movement direction of the tool is from left to right to withdraw the workpiece, so there is no problem that the tool cannot be withdrawn 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); Click to receive the 10G CNC programming tutorial for free. When turning internal threads, grind a reverse internal thread turning tool (Figure 2). Before processing, tighten the reverse friction plate spindle slightly to ensure the speed when starting in reverse. Align the thread cutter, close the opening and closing nut, start the forward rotation at a low speed to the empty cutter groove, and then insert the thread turning tool to the appropriate cutting depth, and then reverse. At this time, the turning tool moves from left to right at high speed. After cutting several times in this way, you can process threads with good surface roughness and high precision. (2) Reverse knurling
In the traditional forward knurling process, iron filings and debris can easily enter between the workpiece and the knurling tool, causing the workpiece to be subjected to excessive force, resulting in chaotic texture, pattern compression or double images, etc.
If the new operation method of reverse knurling with the lathe spindle rotating horizontally is adopted, the disadvantages caused by the forward operation can be effectively prevented and a good overall effect can be obtained.
(3) Reverse turning of internal and external taper pipe threads
When turning various internal and external taper pipe threads with low precision requirements and small batches, you can directly use the new operation method of reverse cutting and reverse tooling without the mold device, and cut while constantly hitting the knife horizontally by hand (when turning external taper pipe threads, it moves from left to right, and it is easy to control the depth of the horizontal tooling from large diameter to small diameter). The reason is that there is pre-pressure when hitting 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.
3. New operation method and tool innovation for drilling small holes In turning, when drilling holes less than 0.6mm, due to the small diameter of the drill bit, poor rigidity, and low cutting speed, and the workpiece material is heat-resistant alloy and stainless steel, the cutting resistance is large. Therefore, when drilling holes, if mechanical transmission feeding is used, the drill bit is very easy to break. The following introduces 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 of the drill bit is a straight shank sliding fit, it can move freely in the pull sleeve. When drilling a small hole, just hold the drill chuck gently with your hand to achieve manual micro-feeding, quickly drill the small hole, ensure quality and quantity, and extend the service life of the small drill bit. 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 pull sleeve and the straight shank) See Figure 3.
4. Shockproof for deep hole processing In deep hole processing, due to the small hole diameter and the slender boring tool bar, it is inevitable to vibrate when turning deep hole parts with a hole diameter of Φ30~50mm and a depth of about 1000mm. To prevent the vibration of the tool bar, the simplest and most effective method is to attach two supports (made of cloth-clamped bakelite and other materials) to the tool bar body, the size of which is exactly the same as the hole diameter. During the cutting process, the cloth-reinforced bakelite block plays a role of positioning support, so the tool bar is not easy to vibrate, and good-quality deep-hole parts can be processed.
5. Small center drill breakage prevention In turning, 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 not lock the tailstock when drilling the center hole, and let the friction between the tailstock's own weight and the machine tool bed surface to drill the center hole. When the cutting resistance is too large, the tailstock will retreat automatically, thus protecting the center drill.
6. Processing technology of "O"-type rubber mold When turning the "O"-type rubber mold, the female mold and the male mold are often misaligned. The shape of the pressed "O"-shaped rubber ring is shown in Figure 4, resulting in a large number of scraps.
After many tests, the following method can basically process the "O"-type mold that meets the technical requirements.
(1) Male mold processing technology
① Fine turn the dimensions of each part and the 45° bevel according to the drawing.
② Install the R forming tool and move the small tool holder to 45°. The tool setting method is shown in Figure 5. Click to receive the 10G CNC programming tutorial for free. According to the figure, when the R tool is in position A, the contact point of the tool contacting the outer circle D is C. Move the large slide plate a distance in the direction of arrow 1, and then move the horizontal tool holder X dimension in the direction of arrow 2. X is calculated as follows: X=(D-d)/2+(R-Rsin45°)=(D-d)/2+(R-0.7071R)=(D-d)/2+0.2929R (i.e. 2X=D-d+0.2929Φ). Then move the large slide plate in the direction of arrow 3 to make the R tool contact the 45° inclined surface. At this time, the tool is in the center position (i.e. the R tool is in position B). ③ Move the small tool holder in the direction of arrow 4 to shape the cavity R, and the feed depth is Φ/2. Note ① When the R tool is in position B:
∵OC=R, OD=Rsin45°=0.7071R
∴CD=OC-OD=R-0.7071R=0.2929R,
②The X dimension can be controlled by a block gauge, and the R dimension can be controlled by a dial indicator.
(2) Female mold processing technology
①Process the dimensions of each part according to the requirements of Figure 6 (the cavity dimensions are not processed).
②Grind the 45° bevel and end face.
③ Install the R forming tool, move the small tool holder to 45° (move once to process the male and female molds), and when the R tool is at position A′ in Figure 6, make the tool contact the outer circle D (the contact point is C), move the large slide in the direction of arrow 1 to make the tool leave the outer circle D, and then move the horizontal tool holder in the direction of arrow 2 by a distance of X, and X is calculated as follows:
X=d+(D-d)/2+CD
=d+(D-d)/2+(R-0.7071R)
=d+(D-d)/2+0.2929R
(i.e. 2X=D+d+0.2929Φ)
Then move the large slide in the direction of arrow 3 until the R tool contacts the 45° slope, and the tool is now in the center position (i.e. position B′ in Figure 6).
④ Move the small tool holder in the direction of arrow 4 to shape the cavity R, and the feed depth is Φ/2.
Note: ①∵DC=R, OD=Rsin45°=0.7071R
∴CD=0.2929R,
②X dimension can be controlled by block gauge, R dimension can be controlled by dial gauge to control depth.
7. Anti-vibration of 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. The following introduces several simplest anti-vibration 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 plugged tightly, and cloth-reinforced bakelite plugs can be plugged at both ends of the workpiece at the same time, and then the support claws on the tool rest can be replaced with support melons made of cloth-reinforced bakelite. After correcting the required arc, the stainless steel hollow slender rod can be turned. This simple method can effectively prevent the vibration and deformation of the hollow slender rod during cutting. (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. If a rubber strip, sponge or other shock-absorbing material is wrapped around the outer circle of the workpiece, the shock-proof effect can be effectively achieved. (3) When turning the outer circle of a heat-resistant alloy thin-walled sleeve workpiece, due to the combined factors of the large cutting resistance of the heat-resistant alloy, vibration and deformation are very likely to occur during cutting. If the workpiece hole is filled with rubber, cotton thread or other debris, and then the two end faces are clamped to clamp, vibration and workpiece deformation during cutting can be effectively prevented, and high-quality thin-walled sleeve workpieces can be processed. 8. Disk-shaped disc clamping tool The disk-shaped part is a thin-walled part with double bevels. When turning the second process, it is necessary to ensure the shape and position tolerance requirements and prevent the workpiece from deforming during clamping and cutting. For this purpose, you can make a set of simple clamping tools by yourself. Its characteristics are that the inclined surface processed in the previous process of the workpiece is used for positioning, and then the disc-shaped part is fastened in this simple tool with the nut on the inclined surface of the outer sleeve, so that the arc R on the end face, hole and outer inclined surface can be turned, as shown in Figure 7.
9. Precision boring large diameter soft jaw limit tool In the turning and clamping of precision workpieces with large diameters, in order to prevent the three jaws from moving due to the gap, a bar with the same diameter as the workpiece must be pre-clamped at the rear of the three jaws before the soft jaws can be repaired. The characteristics of our self-made precision boring large diameter soft jaw limit tool are (see Figure 8). The three screws of the No. 1 part can be adjusted as needed in the fixed plate to adjust the diameter of the expansion, thereby replacing bars of various diameters.
10. Simple precision additional soft jaws are often encountered in the processing of medium and small precision workpieces in turning. Due to the complex internal and external shapes of the workpieces and the strict shape and position tolerance requirements, we add a set of self-made precision soft jaws to the three-jaw chuck of C1616 and other lathes, thereby ensuring the various shape and position tolerance requirements of the workpiece, and the workpiece will not be clamped and deformed during multiple clamping. This precision soft jaw is simple to manufacture. The aluminum alloy bar is turned as required and then bored. A base hole is drilled on the outer circle and tapped M8. After milling the two sides, it can be installed on the hard jaws of the original three-jaw chuck, locked on the three jaws with M8 hexagonal screws, and then the positioning holes are finely bored as required. The workpiece can be clamped in the aluminum soft jaws for cutting. The use of this achievement will produce significant economic benefits, and the production can be shown in Figure 9.
11. Additional anti-vibration tools Due to the poor rigidity of slender shaft workpieces, vibration is easy to occur during multi-slot cutting, resulting in poor surface roughness of the workpiece and damage to the tool. A set of self-made additional anti-vibration tools can effectively solve the vibration problem of slender parts in grooving processing (see Figure 10).
Before work, install the self-made additional anti-vibration tool in a suitable position on the square tool holder. Then install the required groove turning tool on the square tool holder, adjust the distance and the compression of the spring, and then you can operate. When the turning tool cuts into the workpiece, the additional anti-vibration tool is simultaneously pressed against the surface of the workpiece, playing a good anti-vibration role.
12. When turning small shafts of various shapes for fine machining, it is necessary to use a live center to hold the workpiece before cutting. Because the workpiece ends have different shapes and small diameters, and ordinary live centers cannot be used, I made various shapes of additional live pre-point caps by myself in production practice, and installed them on ordinary live pre-points, and they can be used. The structure is shown in Figure 11.
13. Honing finishing of difficult-to-process materials When we are finishing high-temperature alloys, hardened steel and other difficult-to-process materials, the surface roughness of the workpiece is required to be Ra0.20~0.05μm, and the dimensional accuracy is also high. The final finishing is usually performed on a grinder.
Make a set of simple honing tools and honing wheels by yourself, and replace the finishing process with honing on the lathe to achieve better economic results.
Honing wheel Manufacturing of honing wheels
① Ingredients
Binder: 100 grams of epoxy resin
Abrasive: 250~300 grams of corundum (single crystal corundum for difficult-to-process high-temperature nickel-chromium materials). Use No. 80 for Ra0.80μm, No. 120~150 for Ra0.20μm, and No. 200~300 for Ra0.05μm.
Hardener: 7~8 grams of ethylenediamine.
Plasticizer: 10~15 grams of dibutyl phthalate.
Mold material: HT15~33 shape.
② Casting method
Mold release agent: Heat the epoxy resin to 70~80℃, add 5% polystyrene, 95% toluene solution, and dibutyl phthalate and stir evenly, then add corundum (or single crystal corundum) and stir evenly, then heat to 70~80℃, add ethylenediamine when cooled to 30°~38℃, and quickly stir evenly (2~5 minutes), then pour into the mold, and keep it at 40℃ for 24 hours before demolding.
③Linear speed V=V1COSα (V is the relative speed to the workpiece, that is, the grinding speed under the condition that the honing wheel does not make longitudinal feed), thereby producing a grinding effect on the workpiece. During honing, in addition to rotation, the workpiece axis is also given a feed amount S for reciprocating motion.
V1=80～120m/min
t=0.05～0.10mm
Residue<0.1mm
④Cooling: 70% kerosene mixed with 30% No. 20 engine oil, correct the honing wheel before honing (pre-honing).
The structure of the honing tool is shown in Figure 13.
14. Quick loading and unloading spindles are often encountered in turning processing for fine turning of the outer circle and inverted guide taper of various types of bearing kits. Due to the large batch size, loading and unloading during the processing process, the tool change auxiliary time is longer than the cutting time, and the production efficiency is low. The quick loading and unloading spindle and single-blade multi-edge (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 small taper mandrel. The principle is to use the 0.02mm taper at the rear of the mandrel. After the bearing is installed, the part is tightened on the mandrel by friction. Then use a single-blade multi-edge turning tool to turn the outer circle, turn the 15° taper angle, stop the car, and use a wrench to eject the part quickly and well, as shown in Figure 14.
15. 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 broaches (repair after fracture)
② Self-made non-standard thread plug gauge (hardened hardware)
③ Turning of hardened hardware and sprayed parts
④ Turning of hardened hardware smooth plug gauges
⑤ Threads modified with high-speed steel tools
Calendering taps
For the hardened hardware and various difficult-to-process parts encountered in the above production, the selection of appropriate tool materials, cutting parameters, tool geometry angles and operating methods can achieve good comprehensive economic results. For example, if a square broach is regenerated after it breaks, if it is re-produced to manufacture a square broach, not only the manufacturing cycle is long, but also the cost is high. We use carbide YM052 and other blades at the root of the original broach to grind it into a negative rake angle r. =-6°～-8°, the cutting edge can be turned after being carefully ground with an oilstone, the cutting speed V=10～15m/min, after turning the outer circle, cut the empty tool groove, and finally turn the thread (divided into rough and fine turning). After rough turning, the tool must be re-sharpened and ground before fine turning the outer thread, and then prepare a section of the inner thread of the connecting rod, and then trim it after connection. A broken and scrapped square broach is restored to its old and new state after turning and repair.
(2) Selection of tool materials for turning hardened parts
① New carbide blades such as YM052, YM053, and YT05 generally have a cutting speed 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 hardened steels and sprayed parts, with a cutting speed of up to 100m/min and a surface roughness of up to Ra0.80~0.20μm. The composite cubic boron nitride tool DCS-F produced by the State-owned Capital Machinery Factory and Guizhou Sixth 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 cemented carbide, the depth of penetration is small, and the price is more expensive than cemented carbide. In addition, if used improperly, the tool head is easily damaged).
⑨ Ceramic tool, cutting speed is 40~60m/min, and the strength is poor.
The above tools have their own characteristics in turning hardened parts, and should be selected according to the specific conditions of turning different materials and different hardness.
(3) Selection of types of hardened steel parts of different materials and tool performance
The hardened steel parts of different materials have completely different requirements for tool performance at the same hardness, which can be roughly 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 of more than 10%.
② Alloy steel: refers to tool steel and die steel with an alloying element content of 2-9%, such as 9SiCr, CrWMn and high-strength alloy structural steel.
③ Carbon steel: includes various carbon tool steels and carburizing steels such as T8, T10, 15 steel or 20 steel carburizing steel. For carbon steel, the microstructure after quenching is tempered martensite and a small amount of carbide, with a hardness of HV800-1000, which is much lower than the hardness of WC and TiC in cemented carbide and A12D3 in ceramic tools. In addition, its hot hardness is lower than that of martensite without alloying elements, generally not exceeding 200℃. 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 and M3, 2C and other types of carbides. Among them, VC has a high hardness (HV2800), which is 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 multiple alloying elements can be increased to about 600℃. Therefore, the machinability of hardened steel with the same macroscopic hardness is not the same, and the difference is very large. Before turning hardened steel parts, analyze which category it belongs to, master its characteristics, and select appropriate tool materials, cutting parameters and tool geometry angles to successfully complete the turning of hardened steel parts.
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