CNC milling machine is an automatic processing equipment developed on the basis of general milling machine.
The processing techniques of the two are basically the same, and the structure is somewhat similar.
CNC milling machines are divided into two categories: without a tool magazine and with a tool magazine.
The CNC milling machine with a tool magazine is also called a machining center.
In addition to the characteristics of ordinary milling machines, CNC milling has the following features:
- The parts are highly adaptable and flexible, and can process parts with particularly complicated contour shapes or difficult to control dimensions, such as mold parts and shell parts;
- It can process parts that cannot be processed or difficult to machine with ordinary machine tools, such as complex curve parts and three-dimensional space surface parts described by mathematical models;
- Parts that can be processed in multiple processes after being able to process a single clamping position;
- The processing precision is high, the processing quality is stable and reliable, the pulse equivalent of the numerical control device is generally 0.001mm, and the high-precision numerical control system can reach 0.1μm. In addition, the numerical control processing also avoids the operator’s operation error;
- High degree of production automation, can reduce the labor intensity of the operator. Conducive to the automation of production management;
- High production efficiency. CNC milling machines generally do not need special process equipment such as special fixtures. When replacing workpieces, it is only necessary to call the machining program, clamping tool and tool data stored in the numerical control device, thus greatly shortening the production. cycle.
Secondly, the CNC milling machine has the functions of milling machine, boring machine and drilling machine, which makes the process highly concentrated and greatly improves the production efficiency.
In addition, the spindle speed and feed speed of the CNC milling machine are infinitely variable, so it is beneficial to choose the best cutting amount.
Structure and composition
(1) Basic structure
There are many different types of CNC milling machines. Although there are differences in the composition of different types of CNC milling machines, there are many similarities.
The XK5040A CNC vertical lifting table milling machine is taken as an example to introduce its composition.
XI Saw 040A CNC vertical lifting table milling machine is equipped with IV3MA numerical control system and adopts full digital AC servo drive.
The machine consists of six main parts. That is, the bed part, the milling head part, the worktable part, the cross feed part, the lift part, the cooling and lubrication part.
The interior of the bed is well laid out and has good rigidity.
There are 4 adjusting bolts on the base to facilitate the horizontal adjustment of the machine.
The cutting fluid reservoir is located inside the machine base.
(2) System classification
① Cooling system
The cooling system of the machine tool is composed of a cooling pump, an outlet pipe, a return pipe, a switch and a nozzle.
The cooling pump is installed in the inner cavity of the machine base. The cooling pump pumps the cutting fluid from the reservoir in the base to the outlet pipe, and then sprays it through the nozzle to cool the cutting zone.
② Lubrication system and method
The lubrication system is composed of a manual oil pump, oil separator, throttle valve, oil pipe.
The machine tool adopts the periodic lubrication method, and uses the manual lubricating oil pump to lubricate the main shaft sleeve, the vertical and horizontal guide rails and the three-way ball screw through the oil separator to improve the service life of the machine tool.
In the sight of digital control technology features
Since the CNC machine tool adopts the servo motor, the digital technology realizes the direct control of the working sequence and the motion displacement of the machine tool. The gearbox structure of the traditional machine tool is cancelled or partially canceled, and the mechanical structure is also greatly simplified.
Digital control also requires mechanical systems with high transmission stiffness and no drive clearance to ensure control command execution and control quality.
At the same time, due to the continuous improvement of computer level and control capability, it has become possible to allow more functional components to perform various auxiliary functions at the same time on the same machine tool, so the mechanical structure of the CNC machine tool has higher integration function requirement than the traditional machine tool.
In the sight of manufacturing technology development requirements
With the advent of new materials and new processes, and the demand for low cost in the market, metal cutting is moving toward higher cutting speeds and precision, higher production efficiency and more reliable systems.
This requires the CNC machine tools developed on the basis of traditional machine tools to have higher precision and drive power. The mechanical mechanism is quieter and hotter, the thermal stiffness is better, the work is more reliable, and the long-term continuous operation and the minimum downtime can be realized.
(3) Milling head
The milling head section consists of a stepped (or stepless) gearbox and a milling head.
The milling head spindle is supported on a high precision bearing.
The spindle has high rotation precision and good rigidity; the spindle is equipped with a quick tool changer, the front cone adopts 1$0505 taper; the spindle adopts mechanical stepless speed change, the adjustment range is wide, the transmission is stable, and the operation is convenient.
The brake mechanism enables the spindle to brake quickly, saving auxiliary time.
When braking, the brake ring is used to open the stop ring to brake the spindle immediately.
When starting the main motor, be careful to loosen the spindle brake handle.
The milling head assembly is also equipped with a servo motor, an internal toothed pulley, a ball screw pair and a spindle sleeve, which form a vertical direction (z-direction) feed drive chain to make the spindle move vertically.
The table and the saddle are supported on a wide horizontal rail of the lifting platform, and the longitudinal feed of the table is driven by a servo motor mounted at the right end of the table.
The precision ball screw is driven by the internal toothed pulley to obtain longitudinal feed of the table.
Handwheels and dials are mounted on the left end of the table for manual operation.
The vertical and horizontal guide surfaces of the saddle are made of TuRcllE B plastic surface, which improves the wear resistance, smoothness and precision of the guide rail, eliminating the phenomenon of low speed creep.
(4) Basic parts
The basic components of CNC milling machines usually refer to structural parts such as bed, column, beam, workbench, base, etc., which are large in size (commonly known as large pieces) and constitute the basic framework of the machine tool.
Other components are attached to the base member, and some components also need to be moved along the base member.
Since the base member functions as a support and guide, the requirement for the base member is that the rigidity is good.
Variable frequency (VFD) is the application of frequency conversion technology and microelectronic technology.
The power control device of the AC motor is controlled by changing the frequency of the motor operating power source.
In CNC machine tools, the frequency converter is mainly used to control the motion of the spindle.