Monday, June 3, 2024

 CNC turning is a high-precision, high-efficiency automated machine tool. The use of CNC lathes can improve processing efficiency and create more value. The emergence of CNC lathes has enabled enterprises to get rid of backward processing technology. The processing technology of CNC lathes is similar to that of ordinary lathes, but because CNC lathes are clamped once and continuously and automatically complete all turning processes, attention should be paid to the following aspects.

Reasonable selection of cutting parameters

For efficient metal cutting, the material to be processed, cutting tools and cutting conditions are the three major factors. These determine the processing time, tool life and processing quality. An economical and effective processing method must be a reasonable selection of cutting conditions.

The three elements of cutting conditions: cutting speed, feed rate and cutting depth directly cause tool damage. With the increase of cutting speed, the temperature of the tool tip will rise, which will cause mechanical, chemical and thermal wear. If the cutting speed is increased by 20%, the tool life will be reduced by 1/2.

The relationship between feed conditions and tool back wear occurs within a very small range. However, when the feed rate is large, the cutting temperature rises and the back wear is large. It has less impact on the tool than the cutting speed. Although the impact of cutting depth on the tool is not as great as cutting speed and feed rate, when cutting at a small cutting depth, the cut material produces a hardened layer, which will also affect the tool life.

Users should choose the cutting speed to be used according to the material to be processed, hardness, cutting state, material type, feed rate, cutting depth, etc.

The selection of the most suitable processing conditions is based on these factors. Regular and stable wear to reach the life is the ideal condition.

However, in actual operation, the choice of tool life is related to tool wear, change in the size of the machined part, surface quality, cutting noise, processing heat, etc. When determining the processing conditions, it is necessary to study according to the actual situation. For difficult-to-process materials such as stainless steel and heat-resistant alloys, coolants can be used or blades with good rigidity can be selected.

How to determine the three elements of cutting processing

How to correctly select these three elements is a major content of the metal cutting principle course. Metal processing WeChat has excerpted some key points. The basic principles for selecting these three elements:

1) Cutting speed (linear speed, circumferential speed) V (m/min)

To select the number of revolutions per minute of the spindle, you must first know how much the cutting linear speed V should be. The choice of V: ​​depends on the tool material, workpiece material, processing conditions, etc.

Tool material:

For carbide, V can be higher, generally more than 100 m/min, and technical parameters are generally provided when purchasing blades:

What material can be selected when processing how much linear speed. High-speed steel: V can only be lower, generally not more than 70 m/min, and in most cases less than 20~30 m/min.

Workpiece material:

High hardness, low V; cast iron, low V, when the tool material is carbide, it can be 70~80 m/min; low carbon steel, V can be more than 100 m/min, non-ferrous metal, V can be higher (100~200 m/min). Hardened steel, stainless steel, V should be lower.

Processing conditions:

Roughing, low V; finishing, high V. Poor rigidity system of machine tools, workpieces, and tools, low V. If the S used in the CNC program is the spindle revolutions per minute, then S should be calculated based on the workpiece diameter and cutting line speed V: S (spindle revolutions per minute) = V (cutting line speed) * 1000 / (3.1416 * workpiece diameter) If the CNC program uses a constant line speed, then S can directly use the cutting line speed V (m/min)

II) Feed (cutting amount)

F mainly depends on the surface roughness requirements of the workpiece. During fine machining, the surface requirements are high, and the feed rate is small: 0.06~0.12mm/spindle revolution. During rough machining, it can be larger. It is mainly determined by the tool strength, generally it can be more than 0.3. When the tool main clearance angle is large, the tool strength is poor, and the feed rate cannot be too large. In addition, the power of the machine tool and the rigidity of the workpiece and the tool should also be considered. The CNC program uses two units of feed rate: mm/min and mm/spindle revolution. The units used above are mm/spindle revolution. If mm/min is used, the formula can be used for conversion: feed rate per minute = feed rate per revolution * spindle revolutions per minute

3) Cutting depth (cutting depth)

During fine machining, it can generally be less than 0.5 (radius value). During rough machining, it is determined according to the workpiece, tool, and machine tool. Generally, a small lathe (maximum machining diameter is less than 400mm) turns 45 steel in the normalized state, and the radial cutting depth generally does not exceed 5mm. In addition, it should be noted that if the lathe spindle speed change adopts ordinary frequency conversion speed regulation, then when the spindle speed is very low (lower than 100~200 rpm), the motor output power will be significantly reduced, and the cutting depth and feed amount can only be very small.

Reasonable selection of tools

1. When rough turning, choose tools with high strength and good durability to meet the requirements of large back cutting amount and large feed rate during rough turning.

2. When fine turning, choose tools with high precision and good durability to ensure the requirements of processing accuracy.

3. In order to reduce tool change time and facilitate tool alignment, machine clamping tools and machine clamping blades should be used as much as possible.

Reasonable selection of fixtures

1. Try to use general fixtures to clamp workpieces and avoid using special fixtures;

2. The positioning reference of parts overlap to reduce positioning errors.

Determine the processing route

The processing route refers to the movement trajectory and direction of the tool relative to the part during the CNC machine tool processing.

1. It should be able to ensure the processing accuracy and surface roughness requirements;

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

The connection between the processing route and the processing allowance

At present, under the condition that CNC lathes have not yet been widely used, the excess allowance on the blank, especially the allowance containing forging and casting hard skin layers, should generally be arranged on ordinary lathes for processing. If CNC lathes must be used for processing, attention should be paid to the flexible arrangement of the program.

Key points for fixture installation

Currently, the connection between the hydraulic chuck and the hydraulic clamping cylinder is achieved by a pull rod. The key points for clamping the hydraulic chuck 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 a wrench to remove the chuck fixing screws to remove the chuck.


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