What is a CNC milling machine?
Numerical control milling machine, referred to as CNC milling machine, is a control technology that applies digital computing technology to milling machines. It represents various control information in the mechanical processing process with coded numbers and inputs it into the CNC device through the information carrier. After calculation and processing, the CNC device sends out various control signals to control the movement of the milling machine, and automatically processes the parts according to the shape and size required by the drawing. CNC milling machine can better solve the problem of complex, precise, small batch and multi-variety parts processing. It is a flexible and high-performance automated milling machine. It represents the development direction of modern milling machine control technology and is a typical electromechanical integration. chemical products.
What are the types of CNC milling machining centers?
According to the structure of the machining center, there are three types of machining center machine tools: vertical machining center, horizontal machining center, and gantry machining center.
Vertical Machining Center
It refers to a machining center with the spindle axis set perpendicularly to the workbench. The main vertical machining center is suitable for processing complex parts such as plates, disks, molds and small shells. Vertical machining centers can complete processes such as milling, boring, drilling, tapping and cutting threads. The vertical machining center has at least three axes and two linkages, and generally can achieve three axes and three linkages. Some can perform five-axis or six-axis control. The height of the vertical machining center column is limited, and the processing range of box-type workpieces needs to be reduced. This is a shortcoming of the vertical machining center.
Horizontal machining center
Horizontal machining center refers to a machining center with the spindle axis set parallel to the workbench. It is mainly suitable for processing box-type parts. Its working principle is that after the workpiece is clamped once on the machining center, the computer can automatically select different tools, automatically change the machine tool spindle speed, and sequentially complete multiple processes on multiple surfaces of the workpiece. Its advantage is that it can greatly improve production efficiency, but it occupies a large area and is costly.
Gantry machining center
The gantry machining center refers to a machining center in which the spindle axis is set perpendicularly to the workbench. The workbench is basically rectangular. Large castings such as the worktable, bed, columns, beams and rams of the gantry machining center are made of Meehanite cast iron or welded parts. The inner cavity of the castings is a honeycomb composite arrangement structure with advanced design. They have been aged and secondary tempered to eliminate The residual internal stress stabilizes the material, ensuring the stability of the workpiece processing accuracy and the life of the machine tool.
What is the difference between a vertical machining center and a horizontal machining center?
Vertical Machining Center:
The vertical machining center has a vertical machining center with a spindle center line. It has two structural modes: fixed column type and movable column type. Generally, most of them use fixed column structure. The advantages of the vertical machining center are: small footprint, simple structure, relatively low price, convenient clamping operations, simple debugging procedures, and a wide range of applications.
The disadvantage is that it cannot process parts that are too high, and the chips are not easily removed when processing the cavity or concave profile. In severe cases, the tool may be damaged, the machined surface may be damaged, and the smooth progress of the processing may be affected. Application: It is more suitable for processing workpieces with relatively small height dimensions.
Horizontal machining center:
Horizontal machining centers have a horizontal spindle centerline. They generally use a movable column structure. They usually have a square indexing workbench capable of reverse movement. They generally have 3-5 motion coordinates. The most common ones are Three linear motion coordinates plus one reversal motion coordinate, that is, the reversal workbench. The advantage of the horizontal machining center: easy chip removal when processing parts.
Its disadvantages: compared with vertical machining centers, horizontal machining centers are not suitable for observation during height procedures and trial cutting, are not convenient for supervision during processing, and are not convenient for clamping and measuring parts.
What are the advantages of CNC milling machines in processing?
CNC milling machines have incomparable advantages in processing that ordinary machine tools cannot match. Let’s learn about them with CNC milling machine manufacturers today.
- Productivity can be greatly improved. After the workpiece is clamped, enter the prepared processing program, and the machine tool will automatically complete the processing process. When the parts to be processed are changed, usually only the CNC program needs to be changed, thus greatly shortening the processing time, and thus improving productivity several times more than that of ordinary machine tools.
- It has high processing precision and the product quality is very stable. Because it is automatically processed according to the program, the processing accuracy can also be corrected and compensated using software, so extremely high processing accuracy can be obtained. Nowadays, almost all high-precision and cutting-edge products in various enterprises are processed using CNC milling machines.
- The high degree of automation greatly reduces labor intensity and dilutes the difference between physical labor and mental labor to a large extent. The working process of CNC milling machine operators has a high technological content, which places higher quality requirements on operators and higher technical requirements on maintenance personnel. They are no longer “blue-collar workers” in the previous sense. People who can operate CNC milling machines are called “grey collars”; people who know how to repair CNC milling machines are called “silver collars”; CNC generalists who can both operate and repair are called “gold collars”.
What are the characteristics of CNC milling machines?
- Processing
If the processing part is a frame-shaped plane or steps of different heights, then a CNC milling machine with a point-line system can be used. If the processing part is a curved surface contour, the choice of two-coordinate linkage or three-coordinate linkage system should be determined based on the geometry of the surface. According to the parts processing requirements, a CNC dividing head or CNC rotary table can be added to the general CNC milling machine. At this time, the system of the machine tool is a four-coordinate CNC system, which can process spiral grooves, blade parts, etc.
- Size
The worktable width of the smaller lifting table CNC milling machine is usually less than 400mm. It is most suitable for the processing of small and medium-sized parts and the contour milling tasks of complex surfaces. Larger specifications such as gantry milling machines, with worktables above 500-600mm, are used to solve the processing needs of large-sized and complex parts.
- Accuracy
Our country has formulated accuracy standards for CNC milling machines, including professional standards for CNC vertical milling machines and lifting table milling machines. The standard stipulates that the positioning accuracy of its linear motion coordinates is 0.04/300mm, the repeatability accuracy is 0.025mm, and the milling accuracy is 0.035mm. In fact, the factory accuracy of machine tools has considerable reserves, which is about 20% smaller than the national standard tolerance value. Therefore, from the perspective of accuracy selection, a general CNC milling machine can meet the processing needs of most parts. For parts that require relatively high precision, you should consider choosing a precision CNC milling machine.
- Batch
For large quantities of items, special milling machines can be used. If it is a small or medium-sized batch that is often repeated periodically, then using a CNC milling machine is very suitable, because the multi-tool fixtures, programs, etc. prepared in the first batch can be stored and reused. In the long run, it is inevitable that milling machines with a high degree of automation will replace ordinary milling machines to reduce labor workload and increase productivity.
What are the characteristics of down milling and reverse milling of CNC milling machines?
If the rotation direction of the contact part between the milling cutter and the workpiece is the same as the feed direction of the workpiece, it is called down milling, and vice versa. There is always a large or small gap between the nut and the screw of a milling machine. During down milling, as the horizontal milling component changes, the workbench and the screw will move left and right. This periodic movement makes the work The movement of the table is very unstable, which can easily cause damage to the cutter teeth. However, the vertical milling component of down milling presses the workpiece towards the worktable. The cutter teeth slide against the machined surface and the friction is small, which is helpful for reducing cutter tooth wear, work hardening and work hardening. Reducing surface roughness is beneficial. Therefore, when the gap between the workbench screw and nut is adjusted to less than 0.03mm or when milling thin and long workpieces, it is appropriate to use down milling. During up milling, the vertical component of the milling force lifts the workpiece up, and the friction between the cutter teeth and the machined surface increases. However, the horizontal component of milling force helps the screw and nut to be in close contact, making the table movement relatively smooth, and the wear of the cutter teeth caused by milling castings and forgings is also small. Therefore, reverse milling is generally used for milling.
Features of down milling:
During down milling, the cutting thickness of each tool gradually changes from small to large. When the cutter tooth first contacts the workpiece, the cutting thickness is zero. Only when the cutter tooth slides a certain distance on the cutting surface left by the previous cutter tooth and the cutting thickness reaches a certain value, the cutter tooth actually starts cutting. Up milling causes the cutting thickness to gradually change from large to small, and the sliding distance of the cutter teeth on the cutting surface is also very small. Moreover, during down milling, the distance traveled by the cutter teeth on the workpiece is also shorter than that during up milling. Therefore, under the same cutting conditions, the tool is prone to wear when up milling is used. During down milling, the cutter teeth start cutting from the surface of the workpiece every time, so it is not suitable for processing workpieces with hard skin. .The average cutting thickness during down milling is large, the cutting deformation is small, and the power consumption is less compared with uphill milling.
Features of up milling:
,Since the direction of the horizontal cutting force exerted by the milling cutter on the workpiece is opposite to the direction of the feed movement of the workpiece, the table screw and the nut can always keep one side of the thread in close contact. This is not the case in down milling. Since the direction of the horizontal milling force is consistent with the feed movement direction of the workpiece, when the force of the cutter teeth on the workpiece is large, the worktable will shift due to the gap between the worktable screw and the nut. This not only destroys the stability of the cutting process, affects the processing quality of the workpiece, but also damages the tool in severe cases. Due to the large friction between the cutter teeth and the workpiece, the cooling and hardening of the machined surface is serious.
Four conditions for using CNC machining center
- Environmental requirements for the location of the machining center
The machining center should be located away from the source of vibration, away from direct sunlight and thermal radiation, and away from moisture and airflow. If there is a vibration source near the CNC machine tool, anti-vibration grooves should be installed around the machining center. Otherwise, it will directly affect the processing accuracy and stability of the CNC machining center, cause poor contact of electronic components, cause malfunctions, and affect the reliability of the machining center.
- Power requirements
Generally, the machining center is installed in the machine processing workshop. Not only does the ambient temperature change greatly and the usage conditions are poor, but there are also many kinds of mechanical and electrical equipment, causing the power grid to fluctuate greatly. Therefore, the location where the machining center is installed requires strict control of the power supply voltage. The power supply voltage fluctuation must be within the allowable range and remain relatively stable. Otherwise, it will affect the normal operation of the CNC system of the machining center.
- Temperature conditions
The ambient temperature of the CNC machining center is lower than 30 degrees Celsius, and the relative temperature is less than 80%. Generally speaking, there is an exhaust fan or air cooler inside the CNC electric control box to keep the operating temperature of electronic components, especially the central processor, constant or the temperature difference changes very little. Excessive temperature and humidity will reduce the life of control system components and lead to an increase in failures. The increase in temperature and humidity and the increase in dust will cause adhesion on the integrated circuit board and lead to short circuits.
- Use the machining center according to the instructions.
When using the machining center, users are not allowed to arbitrarily change the parameters set by the manufacturer in the control system. The settings of these machining center parameters are directly related to the dynamic characteristics of each component of the machining center. Only the gap compensation parameter value can be adjusted according to the actual situation.