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Attention Points for Turning in Machining

1. What is turning process?

Turning is a process in which the shape and size of blanks, which are fixed on lathes, are changed by using the rotation of the workpiece and the linear or curved motion of the cutting tool to meet the requirements of the drawing. It is different with custom precision machining.

Turning process is a method of cutting the workpiece on the lathe by the rotation of the workpiece relative to the tool. The cutting energy of turning is mainly provided by the workpiece rather than the cutting tool. Turning is the most basic and common cutting processing method, and it occupies a very important position in the production. Turning in machining is suitable for processing the rotary surfaces. Thus, most workpieces with rotary surfaces can be processed by turning methods, such as inner and outer cylindrical surfaces, inner and outer conical surfaces, end faces, grooves, threads, and rotary forming surfaces, etc., and the main tools used are turning tools.

Among all types of metal cutting machine tools, lathe, accounting for about 50% of the total number of machine tools, belongs to the most widely kind. The lathe can be used not only for turning the workpiece, but also for drilling, reaming, tapping and knurling operations such as drill, reamer, tap and knurling knife. According to different processing characteristics, layout forms and structural characteristics, lathes can be divided into horizontal lathes, floor lathes, vertical lathes, turret lathes, and copying lathes, etc., most of which are horizontal lathes.

2. Matters needing attention in turning process

The processing technology of CNC lathes is similar to that of common lathes, but because CNC lathes require one-time clamping and then they will automatically complete all turning processes. Large machining companies always apply this kind of lathes. Thus special attention should be paid to the following aspects, which is a part of machining. Lathe process mainly uses the turning tool to turn rotating workpieces. And lathes are mainly used for processing shafts, discs, sleeves and other workpieces with rotating surfaces, which are the most widely used type of machine tool processing in machinery manufacturing and repair factories.

1. Make reasonable choice for cutting amount:

For high-efficient metal cutting processing, the material to be processed, cutting tools, and cutting conditions are the three main factors. The three determine the processing time, tool life and processing quality. The economical and effective processing method must be owed to a reasonable choice of cutting conditions. And the three elements of cutting conditions are cutting speed, feed rate and depth-of-cut, which are directly related to the damage to the tool .

With the increase of cutting speed, the temperature of the tool tip will rise, causing mechanical, chemical, and thermal wear to happen. Cutting speed increased by 20% will lead a reduction of tool life by 50%. The relationship between the feed conditions and the wear on the back of the tool occurs in a very small range. However, if the feed rate increases, the cutting temperature will rises, and more wear will occur. It has less influence on the tool than cutting speed. Although the influence of depth-of-cut on the tool is not as large as the cutting speed and feed,  when it comes to small depth of cut, the material being cut will produce a hardened layer, which will also reduce the the tool life.

The user should choose the cutting speed according to the processed material, its hardness, cutting state, material type, feed, depth-of-cut, etc.. Best choice of the most suitable processing conditions is based on these factors. The Longevity of tool life achieved by regular and stable wear is the ideal conditions.

However, in practical operations, the choice of tool life is related to tool wear, size changes of the processed material, surface quality, cutting noise, and processing heat and so on. When determining the processing conditions, it is necessary to conduct research according to the actual situation. For difficult-to-cut material such as stainless steel and heat-resistant alloys, coolants or blades with good rigidity can be used.

2. Make reasonable choice for cutting tools:

(1) During rough turning in machining, choose durable tools with high-strength to meet the requirements of large back-grabbing and large feed in rough turning process.

(2) During fine turning in machining, finishing turning in machining, choose the durable tools of high-precision to ensure the requirements of processing accuracy.

(3) In order to reduce the time for tool change and facilitate tool setting, machine-clamped knives and machine-clamped blades should be used as much as possible.

3. Make reasonable choice for fixtures:

(1) Try to use general fixtures to clamp the workpiece, avoid using special fixtures.

(2) The positioning datum of the parts should be overlapped to reduce positioning errors.

4. Determine the processing route:

The processing route is the movement track and direction of the tool relative to the parts in the CNC lathes turning processing.

(1) Processing accuracy and surface roughness requirements should be met;

(2) The processing route should be shortened as much as possible to reduce the idle travel of the tool.

5. Connection between processing route and processing allowance:

At present, under the condition that the CNC lathe has not reached the universal use, the excess margin on the blank, especially the margin containing the forged and cast hard skin layer, should be arranged on the ordinary lathe for processing. If CNC lathe for processing is required, attention should be paid to the flexible arrangement of the program.

6. Main points of fixture installation:

At present, the connection of hydraulic chuck and hydraulic clamping cylinder is realized by pulling rod. The main points of hydraulic chuck clamping are as follows: First, use a wrench to remove the nut on the hydraulic cylinder, remove the pull tube, and pull it out from the rear end of the spindle. Then use the wrench to remove the chuck fixing screw to remove the chuck.

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