CNC lathe machining process skills

CNC lathe is a kind of high-precision and high-efficiency automatic machine tool. The use of CNC lathe can improve machining efficiency and create more value. The emergence of CNC lathe has made enterprises get rid of the backward processing technology. The technology of CNC lathe processing is compared with ordinary lathes. The machining process is similar, but because the CNC lathe is one-time clamping and continuous automatic machining to complete all turning procedures, the following aspects should be paid attention to.

Reasonable choice of cutting amount

For high-efficiency metal cutting processing, the material to be processed, cutting tools, and cutting conditions are the three major elements. These determine the processing time, tool life and processing quality. The economical and effective machining method must be a reasonable choice of cutting conditions.

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

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

The user should select the cutting speed to be used according to the processed material, hardness, cutting state, material type, feed rate, depth of cut, etc.

The selection of the most suitable processing conditions is selected on the basis of these factors. Regular, stable wear and longevity are the ideal conditions.

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

How to determine the three elements of cutting

How to choose these three elements correctly is a main content of the metal cutting principle course. The metal processing WeChat extracts some of the main points. The basic principles for selecting these three elements are:

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

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

Tool material:

For cemented carbide, V can be higher, generally more than 100m/min. Generally, the technical parameters are provided when purchasing the blade:

How many linear speeds can be selected when processing what material. High-speed steel: V can only be low, generally not more than 70 m/min, and in most cases, it is less than 20-30 m/min.

Workpiece material:

For high hardness, the value of V is low; for cast iron, the value of V is low. When the tool material is cemented carbide, it can be 70~80 m/min; for low-carbon steel, V can be more than 100 m/min. For non-ferrous metals, V can be higher (100 ~200m/min). For hardened steel and stainless steel, V should be lower.

Processing conditions:

For rough machining, V should be lower; for finishing, V should be higher. The rigid system of the machine tool, workpiece, and tool is poor, and V is set to be low. If the S used by the CNC program is the number of spindle revolutions per minute, then S should be calculated according to the workpiece diameter and the cutting linear speed V: S (spindle revolutions per minute) = V (cutting linear speed) * 1000/ (3.1416 * workpiece Diameter) If the CNC program uses a constant linear speed, then S can directly use the cutting linear speed V (m/min)

(2) Feed amount (cutting amount)

F mainly depends on the surface roughness requirements of the workpiece. When finishing, the surface requirements are high, and the cutting amount is small: 0.06~0.12mm/spindle rotation. When roughing, it is better to be larger. It is mainly determined by the strength of the tool. Generally, it can be more than 0.3. When the main clearance angle of the tool is large, the tool strength is poor, and the feed amount cannot be too large. In addition, the power of the machine tool, the rigidity of the workpiece and the tool should also be considered. The CNC program uses two units of feed rate: mm/min, mm/spindle per revolution, the unit used above is mm/spindle per revolution, if you use mm/min, you can use the formula to convert: feed per minute=per The amount of turning into the tool * spindle revolutions per minute

(3) Cutting depth (cutting depth)

When finishing, generally it can be less than 0.5 (radius value). When roughing, it is determined according to the situation of the workpiece, tool and machine tool. Generally, a small lathe (maximum processing diameter is below 400mm) is used for turning No. 45 steel in the normalized state, and the cutting depth in the radius direction generally does not exceed 5mm. Also note that if the spindle speed of the lathe adopts ordinary frequency conversion speed regulation, when the spindle speed per minute is very low (less than 100~200 rpm), the output power of the motor will be significantly reduced. The depth and feed rate can only be achieved very small.

Choose a tool reasonably

1. When rough turning, choose a tool with high strength and good durability to meet the requirements of large back-grabbing and large feed when rough turning.

2. When finishing turning, choose high-precision and durable tools to ensure the requirements of machining accuracy.

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

Reasonable selection of fixtures

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

2. The part positioning datum coincides to reduce the positioning error.

Determine the processing route

The processing route is the movement track and direction of the tool relative to the part during the processing of the index-controlled machine tool.

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 relationship between processing route and processing allowance

At present, under the condition that the CNC lathe has not reached the popular use, the excess margin on the blank, especially the margin containing the forging and casting hard skin layer, should be arranged on the ordinary lathe for processing. If you must use a CNC lathe to process, you need to pay attention to the flexible arrangement of the program.

Main points of fixture installation

At present, the connection between the hydraulic chuck and the hydraulic clamping cylinder is realized by a tie rod. The main points of hydraulic chuck clamping are as follows: First, use a moving hand to remove the nut on the hydraulic cylinder, remove the pull tube, and pull it out from the back end of the spindle. Use a moving hand to remove the chuck fixing screw to remove the chuck.

Post time: Jun-24-2021