October 2020 – Page 9 – CNC Machining & Turning, Milling, Metal parts

Positioning datum of computer gong processing

When there is a large plane on the part that can be used as the positioning reference, the plane is always processed first, and then the hole is positioned by the plane to ensure the position accuracy between the hole and the plane. In this way, the positioning is relatively stable, the clamping is convenient, and the deflection caused by the drilling on the rough surface can be avoided.

c) The principle of “first primary and then secondary” is to process the main surface (datum plane and working surface with high position accuracy requirements) before processing the secondary surface (such as keyway, screw hole, fastening hole, etc.). The secondary surface is generally after the main surface reaches a certain precision and before the final finishing.

d) According to the principle of “first rough and then fine”, for parts with high precision requirements, it is carried out in order from coarse to fine, so as to gradually improve the machining accuracy. High speed computer gongs processing this point for poor rigidity parts, especially can not be ignored. In order to solve such problems, the characteristics of titanium alloy materials, machining characteristics, tool data selection, milling processing characteristics, coolant and other aspects are analyzed to improve the one-time acceptance rate of titanium alloy parts, so as to control the product quality of the parts. In order to better control the product quality, it is necessary to control the cutting parameters of non-standard equipment parts and understand and master the processing characteristics of materials.

Mechanical processing technology is to change the shape, size, relative position and nature of the production object on the basis of the process. CNC processing makes it a finished product or semi-finished product. It is a detailed description of each process. For example, as mentioned above, rough machining may include blank manufacturing, grinding, etc., and finishing may be divided into turning, fitter, milling machine, etc., and each step is just like this There must be detailed data, such as how much roughness and tolerance should be achieved.

The classification of machining is as follows:

Design datum: the datum used to determine the position of other points, lines and planes on the part drawing, which is called design datum.

Process datum: the datum used in the process of machining and assembling parts, which is called process datum. According to different uses, the process datum of die and mould can be divided into assembly datum, measuring datum and locating datum.

(1) Assembly datum: the datum used to determine the position of parts in parts or products during assembly, which is called assembly datum.

(2) Measurement datum: the datum used to check the size and position of machined surface, which is called measuring datum.

(3) Positioning datum: the datum used for workpiece positioning during machining, which is called positioning datum. For the surface (or line, point) as positioning reference, only the rough surface can be selected in the first working procedure. This positioning surface is called rough datum. The machined surface can be used as the positioning datum in the following processes, and the positioning surface is called the precise datum.

The correct use and maintenance of equipment parts processing mold is also a major factor to improve the quality of mold. Mechanical parts processing, such as: large CNC processing mold device debugging mode should be appropriate, in the case of hot runner, the power wiring should be correct, the cooling water circuit should meet the design requirements, and the parameters of injection molding machine, die-casting machine and press machine should be consistent with the design requirements. In order to improve the surface wear resistance of the die parts and improve the quality of the die, the surface strengthening of the main parts of the die is carried out in the precision parts processing. For the surface strengthening, different strengthening methods should be selected according to the mold for different purposes.

Fire prevention in mechanical parts processing plant

(1) The large-scale machining workshop shall be of grade I and II fire-resistant rating, and other simple buildings shall not be built in the workshop.

(2) For used oil rags, oil cotton yarn and oil sawdust. CNC processing should be concentrated in the metal cylinder (box) with cover and processed every day.

(3) It is forbidden to use gasoline, alcohol and other wiping machine tools in the workshop. The residual oil after washing parts shall not be poured into the sewer or trench at will, but shall be poured into the container at the designated place for unified treatment.

(4) Gasoline shall not be stored in the workshop. The storage capacity of machine oil and kerosene should not exceed one day’s consumption. CNC processing and storage in covered iron drums. If the storage capacity is large, a special oil storage room should be set up. No other combustible materials shall be stored in the oil storage room, and the indoor ventilation shall be maintained. The electrical switch shall be installed in the outdoor distribution box.

(5) In the workshop, due to careless use of the stove for heating, using waste oil cotton yarn to light a fire, throwing cigarette butts, match sticks and so on, fires are often caused. Therefore, strict management should be carried out on site smoking and stove heating.

(6) If it is necessary to carry out open flame welding and cutting in the workshop, the surrounding environment should be checked first, combustible materials should be removed, and the nearby machine tools should be covered with refractory materials. At the same time. Special person must be assigned to be responsible for monitoring, and residual fire should be checked and eliminated after operation.

(7) The electrical equipment of the machine tool must be checked frequently, and the hidden danger should be eliminated in time. It is not allowed to run with a fault. CNC processing, installation, removal, maintenance, debugging must be operated by professional electricians according to the regulations. The metal shell of all electrical equipment shall be reliably grounded, and its grounding resistance shall not be greater than 4 Ω.

CNC cutting mode

The influence of vibration of cutter teeth on the surface roughness and tool life. In order to prevent the decline of machining accuracy and tool life, the selected machining center must be equipped with a spindle with excellent dynamic balance performance, and the selected boring tool must also have high dynamic balance characteristics. Especially for the cutter tooth part of boring tools, the geometry, tool material and clamping mode suitable for high-speed cutting should be selected. In order to improve the machining efficiency, the feed rate should be increased on the premise of obtaining the same surface roughness. However, the increase of feed rate should be enough, otherwise it will increase the cutting resistance, which is not conducive to improving the processing efficiency. The cutting edge should be set with negative chamfering less than 0.1 mm, which can effectively maintain the stability of tool life.

In addition to CNC cutting method for precision machining of holes, boring and reaming can also be used for high-precision machining of holes. With the high-speed spindle of machining center, boring tools can be used for high-speed and precision machining of holes. It is reported that the cutting speed can be increased to more than 1500m / min when the diameter of boring is about 40mm on aluminum alloy. This cutting speed can also be used when using CBN sintered body as cutting edge to process steel, cast iron and high hardness steel. It is predicted that the high speed of boring will be popularized rapidly in the future.

As for the tool material, it depends on the nature of the material being processed. For example, when machining steel below 40HRC, cermet tool can be selected. Under the high-speed cutting condition of V = 300m / min, good surface roughness and long tool life can be obtained. Coated cemented carbide tools are suitable for high-speed cutting of steels below 60HRC. The tool life is very stable, but the cutting speed is slightly lower than cermet tools.

Sintered tool is suitable for machining high hardness steel, cast iron and other materials. The cutting speed can reach more than 1000m / min, and the tool life is very stable. Proper chamfering should be carried out on the cutting edge of CBN cutter teeth in CNC machining, which is very beneficial to stable high-speed cutting and prolonging tool life. In ultra-high speed cutting of nonferrous metals and non-metallic materials such as aluminum alloy, diamond sintered body tool can be selected. This kind of cutting tool is stable and has a long service life. It should be noted that when using diamond tools, the blade belt must be chamfered, which is an important condition to ensure the stability of cutting.

Computer gong processing inverter

The power control equipment of AC motor is controlled by the frequency mode of motor power supply. In CNC machine tools, the frequency converter is mainly used to control the action of the spindle.

The blade of end mounted structure milling cutter (as shown in FIG. 10) is fixed on the cutter groove with only one screw, which is simple in structure and convenient in rotation. Although there are few tool parts in mechanical parts processing plant, it is difficult to process the cutter body. Generally, it needs five coordinate machining center for machining. Since the blade is clamped by cutting force, the clamping force increases with the increase of cutting force, so the clamping element can be omitted and the chip holding space is increased. Because the blade is installed in tangential direction, the section of cemented carbide in the direction of cutting force is large, so it can be used for large cutting depth and large cutting distance. This kind of milling cutter is suitable for heavy and medium milling.

The angle of milling cutter includes front angle, back angle, main deflection angle, auxiliary deflection angle, edge inclination angle, etc. In order to meet the different processing needs, there are a variety of angle combination types. Among the various angles, the main deflection angle and rake angle are the main ones (the main deflection angle and rake angle of the cutter are generally clearly stated in the product samples of the manufacturer).

Main deflection angle KR

The main deflection angle is the angle between the cutting edge and the cutting plane, as shown in FIG. 11. The main deflection angles of milling cutter are 90 °, 88 °, 75 °, 70 °, 60 ° and 45 ° etc.

Principal deflection angle

The main deflection angle has a great influence on the radial cutting force and cutting depth. The size of radial cutting force directly affects the cutting power and anti vibration performance of cutting tools. The smaller the main deflection angle of the milling cutter is, the smaller the radial cutting force is, the better the vibration resistance is, but the cutting depth is also reduced.

The main deflection angle of 90 ° is selected when milling the plane with shoulder, and CNC machining is not generally used for pure plane machining. This kind of tool has good versatility (not only can process step surface, but also can process plane), so it can be selected in single piece and small batch processing. Because the radial cutting force of this kind of cutting tool is equal to the cutting force, the feed resistance is large, and it is easy to vibrate. When machining the plane with shoulder, the milling cutter with 88 ° main deflection angle can also be selected. Compared with the milling cutter with 90 ° main deflection angle, its cutting performance is improved to some extent.

The main deflection angle of 60 ° to 75 ° is suitable for rough machining of plane milling. Due to the obvious reduction of radial cutting force (especially at 60 degrees), its vibration resistance is greatly improved, and the cutting is smooth and light. Therefore, it should be preferred in plane machining. 75 ° main deflection angle milling cutter is a general-purpose tool with wide application range; 60 ° main deflection angle milling cutter is mainly used for rough milling and semi finishing milling on boring and milling machines and machining centers.

The radial cutting force of this kind of milling cutter with 45 ° main deflection angle is greatly reduced, which is approximately equal to the axial cutting force. The cutting load is distributed on the longer cutting edge, and has good vibration resistance. It is suitable for the machining occasions with longer spindle overhang of boring and milling machine. When machining plane with this kind of cutting tool, the damage rate of blade is low and the durability is high; when machining iron castings, the edge of the workpiece is not easy to break.

Anterior angle γ

The rake angle of milling cutter can be divided into radial rake angle γ F and axial rake angle γ P. the radial rake angle γ f mainly affects the cutting power; the axial rake angle γ P affects the chip formation and the direction of axial force. When γ P is positive, the chip will fly away from the machining surface.

Anterior horn

The common combination forms of front angle are as follows:

The milling cutter with double negative rake angle and double negative rake angle usually adopts square (or rectangular) blade without back angle. The cutter has many cutting edges (generally 8), high strength and good impact resistance, which is suitable for rough machining of cast steel and cast iron. Because the chip shrinkage ratio is large, it needs a large cutting force, so the machine tool has higher power and higher rigidity. Because the forward angle of the shaft is negative, the chip can not flow out automatically. When cutting ductile materials, chip accretion and tool vibration are easy to occur.

It is suggested to use double cutting tool with negative rake angle when machining. When double positive rake angle milling cutter is used to produce chipping edge (i.e. large impact load), the double negative rake angle milling cutter should also be preferred when the machine tool allows.

The milling cutter with double positive rake angle and double positive rake angle adopts the blade with back angle, which has small wedge angle and sharp cutting edge. Because of the small shrinkage ratio of the chip, the cutting power consumed is small, and the chip is discharged in a spiral shape, which is not easy to form a chip accumulation lump. This kind of milling cutter is most suitable for cutting soft materials, stainless steel, heat-resistant steel and other materials. For the machine tools with poor rigidity (such as boring and milling machines with long spindle overhanging), low power and machining welded structural parts, double positive rake angle milling cutters should also be preferred.

Positive and negative rake angle (axial positive rake angle, radial negative rake angle) this kind of milling cutter combines the advantages of double positive rake angle and double negative rake angle milling cutter. The axial positive rake angle is conducive to the formation and discharge of chips; the radial negative rake angle can improve the edge strength and impact resistance. This kind of milling cutter has the advantages of smooth cutting, smooth chip removal and high metal removal rate, which is suitable for large allowance milling. Computer gong processing, Dongguan computer gong processing, high speed computer gong processing, mechanical parts processing, computer gong processing, Walter’s tangential tooth distribution heavy cutting milling cutter f2265 is a milling cutter with axial positive rake angle and radial negative rake angle structure.

The number of milling cutter teeth is large, which can improve the production efficiency. However, due to the limitation of chip holding space, cutter tooth strength, machine tool power and rigidity, the number of teeth of milling cutter with different diameters has corresponding regulations. In order to meet the needs of different users, there are three types of milling cutters with the same diameter: coarse teeth, medium teeth and dense teeth.

Rough tooth milling cutter is suitable for large allowance rough machining of ordinary machine tools and milling of soft materials or large cutting width; when the power of machine tool is small, in order to make cutting stable, coarse tooth milling cutter is often used.

The middle gear milling cutter is a universal series, which makes

Shaft processing technology of computer gongs

Input shaft: forging and blank making → normalizing → finishing turning → gear rubbing → drilling → gear shaping → undercut angle → hobbing → shaving → heat treatment → grinding → meshing and finishing.

Output shaft: forging billet → normalizing → finishing turning → rolling gear → shaving → heat treatment → grinding → meshing and finishing.

Specific process flow

(1) Forging billet

Hot die forging is a widely used blank forging process for automobile gear parts. Computer gong processing, Dongguan computer gong processing, high speed computer gong processing, mechanical parts processing, computer gong processing

Hot forging and cold extrusion are widely used in the past. In recent years, cross wedge rolling technology has been widely used in shaft machining. This technology is especially suitable for the production of complex stepped shafts. It not only has high precision, small machining allowance, but also has high production efficiency.

(2) Normalizing

The purpose of this process is to obtain the hardness suitable for subsequent gear cutting and to prepare the microstructure for the final heat treatment, so as to effectively reduce the heat treatment deformation. Due to the influence of personnel, equipment and environment, the normal normalizing can not control the cooling rate and cooling uniformity of workpiece, resulting in large hardness dispersion and uneven microstructure, which directly affects machining and final heat treatment.

(3) Finish turning

In order to meet the positioning requirements of high-precision gear machining, CNC lathe is used for the finish turning of gear blank. First, the inner hole and locating end face of the gear are machined, and then the machining of the other end face and outer diameter is completed synchronously. It not only ensures the perpendicularity requirement between the inner hole and the locating end face, but also ensures the small size dispersion in the mass production of gear blanks. Thus, the accuracy of gear blank is improved and the machining quality of subsequent gear is ensured.

There are mainly three ways of positioning datum and clamping for shaft parts processing

Positioning by the center hole of the workpiece: in the machining of the shaft, the coaxiality of the outer circle surface and end face of the part, and the perpendicularity of the end face to the rotating axis are the main items of their mutual position accuracy. The design basis of these surfaces is generally the center line of the shaft. If two center holes are used for positioning, it is in line with the principle of datum coincidence.

Outer circle and central hole as the positioning reference (one clip and one top): Although the centering accuracy is high, the rigidity is poor, especially when machining heavy workpieces, and the cutting parameters cannot be too large.

In rough machining, in order to improve the rigidity of the parts, the cylindrical surface of the shaft and a central hole can be used as the positioning reference. This positioning method can bear large cutting torque and is the most common positioning method for shaft parts.

Take two cylindrical surfaces as positioning datum: when machining the inner hole of hollow shaft (for example: machining the inner hole of Morse taper on the machine tool), the central hole cannot be used as the positioning reference, and the two outer cylindrical surfaces of the shaft can be used as the positioning reference. When the workpiece is the spindle of machine tool, the two supporting Journal (assembly reference) is often used as the positioning reference, which can ensure the coaxiality requirement of the taper hole relative to the supporting journal, and eliminate the error caused by the non coincidence of the reference.