Mechanical Knowledge

9 practical tips of lathe processing

1. Defect elimination method when turning slender shaft when doing lathe processing

1) Drum-shaped.That is, after turning, the diameter of both ends of the workpiece is small, and the middle diameter is large. The reason for this defect is due to the poor rigidity of the slender shaft, the contact between the support claw of the tool holder and the surface of the workpiece is not real, and the wear produces a gap. When turning to the middle part, due to the radial force, the turning tool will The center of rotation of the workpiece is pressed to the right of the center of rotation of the spindle, which reduces the cutting depth, while the rigidity of the two ends of the workpiece is better, and the cutting depth is basically unchanged. The slender shaft is bulged due to the "make knife" in the middle.

Elimination method. When you follow the claw of the tool holder, you must be careful so that the claw surface is in contact with the surface of the workpiece without gaps. The main declination of the turning tool should be selected from 75° to 90° to reduce the radial force. With the claw of the tool holder, cast iron with better wear resistance should be selected.

2) Slub shape. It is shaped like a bamboo, and its pitch is approximately equal to the distance between the supporting claw of the tool rest and the tip of the turning tool, and it appears cyclically. The reason for this defect is that the gap between the large carriage and the middle carriage of the lathe is too large, and the centrifugal force is caused when the blank is bent and rotated, and the "knife" when the tool is connected is generated at the position where the tool is supported by the reference tool. The diameter of the turning section is slightly larger than the reference section, and the tool continues to be turned, and the tool holder support claw contacts the section with the larger diameter of the workpiece, so that the center of rotation of the workpiece is pressed to the side of the turning tool, and the diameter of the turned workpiece is reduced. In this way, the tool post is cyclically supported at different diameters of the workpiece, so that the workpiece leaves and approaches the turning tool, forming a regular slub shape. There is also too much force in the follower and the heel of the tool holder, so that the center of rotation of the workpiece is pressed against the turning tool side, which causes the diameter of the turning tool to become smaller, and the tool is continued to move. This cycle also forms a slub.

Elimination method. Adjust the gap of each part of the machine to enhance the rigidity of the machine. When contacting the tool holder claw, make sure that the surface of the claw is in contact with the work piece without excessive force. More cutting depth (0.050.1) mm at the tool joint to eliminate the "make knife" phenomenon when the tool is being moved. The size of the cutting depth should be mastered by the rules of the machine tool and flexibly mastered.

lathe processing

2. Reverse knurling when doing lathe processing

In the traditional forward knurling process, chips easily enter between the workpiece and the knurling during the rolling process, resulting in excessive stress on the workpiece, resulting in pattern buckling and ghosting. If the spindle is reversed, the above-mentioned defects can be effectively prevented, and a pattern with clear lines can be rolled out.

3. When doing lathe processing, how to prevent the center drill from breaking when drilling a small center hole

When drilling a center hole with a diameter of less than 1.5 mm on a lathe, the center drill is easily broken. Except for careful and diligent chip removal when drilling, when drilling, do not lock the tailstock, and allow the friction between the weight of the tailstock and the machine tool guide rail to drill. When the drilling resistance is too large, the tailstock will retreat on its own, protecting the center drill.

4. Set of small eccentric workpieces when doing lathe processing

Using a sleeve to clamp the work car is eccentric, and its clamping efficiency is 6 to 8 times higher than that with a four-jaw chuck.

Knowing the eccentricity e and the outer diameter of the workpiece Φ2, the inner diameter Φ1 of the fixture sleeve can be obtained, Φ1=2e+Φ2. When processing the inner diameter of the fixture sleeve Φ1, we must pay attention to the accuracy of the inner hole to avoid affecting the dimensional accuracy of the eccentricity of the workpiece.

5. The method of rotating shaft when doing lathe processing

The screw conveyor mechanism is widely used in factories that transport granular materials. When the spiral shaft in this mechanism is manufactured, its spiral pieces are welded with steel plates. This spiral plate has a high tooth shape, a small bottom diameter, and an outer diameter that must be coaxial with the journal. To meet this requirement, the outer diameter of the screw shaft must be turned with a lathe.

This type of shaft is generally long. When machining the outer diameter, due to the large pitch, deep tooth, thin tooth, poor rigidity, and intermittent cutting, the tooth part is vibrated by the cutting impact, making it unable to cut normally, but also damaged Cutter. In order to solve this problem, the cutting speed, cutting depth and feed have to be reduced, which greatly reduces the work efficiency.

In order to improve work efficiency and quality, a simple and easy method of turning threads is adopted, the hanging wheel is hung according to the pitch of the spiral shaft, and the large screw is used to drive the large carriage to carry the tool for turning. After turning the first knife, remember the scale of the middle carriage. After the big carriage returns, move forward (0.5-0.7) mm with the small carriage, and then start to walk the second cutter, until the outer circle is turned.

Using this method to turn the spiral shaft tooth tip is smooth, basically eliminating intermittent cutting, processing efficiency increased by nearly 10 times compared with the original.

lathe processing

6. Processing of threads other than the nameplate of the lathe when doing lathe processing

In many mechanical transmissions, the pitch and lead of the multi-head worm, multi-head screw, multi-head spiral spline, variable lead worm, double lead variable thickness tooth worm, helical gear meshing worm, etc. are not found on the nameplate of the lathe. Processing brings difficulties. Now we introduce a solution to find the required pitch (or lead) on the lathe nameplate, which can save the trouble of hanging wheels.

For example, on a imported milling machine, a worm that meshes with a helical gear has a normal modulus of 3.175 and a circumferential modulus of 3.184. The 3.184 module cannot be found on a lathe. If you want to process it, you need to calculate and make a hanging wheel. After calculation and analysis, the module pitch is converted into metric pitch, that is 3.184×3.1416=10.003mm, so that it can be processed according to the pitch of 10mm.

In the overhaul and maintenance of equipment, most of them measure the pitch of the thread in metric system, so that non-standard pitch will appear. In fact, the thread is divided into ordinary, inch system, modulus, diameter joint and non-standard thread, and their pitch can be converted between each other. For example, 9.4248mm, 12.5664mm, 12.7mm, 25.4mm and 7.9756mm can be processed according to other types of threads. The result is P=9.4248mm and P=12.5664mm, which are module 3 and module 4, respectively.

Another example is 12.7mm and 25.4mm, which are 2 threads/inch and 1 thread/inch inch thread. P=7.9756mm is DP=10 pitch thread.

7. Tooling for boring large inner cone holes when doing lathe processing

When machining a large diameter and long internal cone hole on a lathe, if the general turning method is adopted, due to the poor rigidity of the cutter bar, the vibration during turning, the cutting amount is small, and even the cutting is impossible. For this reason, tooling was adopted, and many large-scale inner holes or inner cone holes were successfully processed on many occasions.

During processing, one end of the workpiece is clamped by a chuck and the other end is supported by a center frame. Put an anti-center in the spindle hole of the lathe, position one end of the cutter bar with a steel ball, and fix the cutter bar on the sleeve of the lathe tailstock with a connecting sleeve and a fastening screw at the other end, so that when the workpiece rotates, the cutter bar does not Turn. Due to the key, the cutter head can only slide axially on the cutter bar. One end of the iron wire is fixed on the cutter head, and the other end is fixed on the large pallet of the lathe. When the large pallet moves the cutter longitudinally, the cutter head is pulled to move axially to complete the feed movement and perform cutting.

Before the cutter bar is installed, the rear seat of the lathe must be placed in front of the large carriage to facilitate the large carriage to pull the iron ribbon to move the cutter head. The amount of feed can be obtained by adjusting the handle of the knife box. When machining taper holes, the tailstock can be offset so that the axis of the arbor and the axis of the workpiece are offset by an oblique angle in the horizontal direction. When the cutter head returns, push the cutter head by hand.

This tooling is used to process large internal holes on a lathe. The operation is very convenient, and the structure is simple. The rigidity of the cutter bar is good.

8. Change the number of teeth of the driving wheel of the hanging wheel box and increase the range of the worm thread of the car

Increase the number of teeth of the main wheel of the C620-1 lathe hanger box 32 to 48 teeth, then the modular threads that are not on the nameplate can also be processed. If the 32 teeth of the driving wheel are changed to 64 teeth, then the worm can be independent of the speed ratio of the main shaft, and the low-speed precision turning is used to help improve the surface roughness of the thread.

9. Method to reduce surface roughness of slender shaft (rod) when doing lathe processing

The process method of reducing the surface roughness of the slender shaft (rod) on the lathe is one using the single-wheel honing method; the other is the rolling method. This is an effective measure that uses simple tools and processes on the lathe to solve the low roughness requirements and the problem of grinding without a grinder.

After finishing the slender shaft (rod) on the lathe, if the roughness has not reached the requirements of the drawings, the single-wheel honing method can be used to rework the surface of the workpiece, which can reduce the roughness of the workpiece surface from Ra6.3μm to masonry (1.60.2)μm. The angle between the axis of the honing wheel and the axis of the main axis of the lathe is generally 28°-30°. Large angle, high efficiency, high roughness, small angle, low efficiency, low roughness. The speed of the honing wheel is generally (3060)m/min, the feed amount is (0.52)mm/r, and the larger value is selected for coarse honing. The pressure of the honing wheel on the workpiece is (150200)N. For workpieces with poor rigidity, a follower holder should be used. The particle size of the honing wheel is generally 100#180#. If the roughness is to reach Ra0.2, the particle size of the honing wheel should be W40W280. The lubricating fluid used for honing should be kerosene or diesel oil with 5%-10% oleic acid added. . When there are no conditions, ordinary emulsion can also be used to clean and lubricate the honing process.

The rolling processing of the slender shaft (rod) can efficiently reduce the surface roughness while improving the surface hardness and wear resistance. Due to the poor rigidity of the workpiece, the follow tool holder must be used when rolling. The method is the same as the slender shaft of the rough turning, that is, the follow tool holder is placed in front of the rolling tool, so as to avoid the claw of the follow tool holder from scratching the workpiece surface. Both rigid and elastic rolling tools can roll the elongated shaft (rod). The rolling times are generally not more than twice. The rolling speed is (20 ~ 30) m/min, and the feed rate is (0.1 ~ 0.2) mm/r. It is lubricated by engine oil and can also be lubricated by emulsion.

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