5. Multi-tasking machine tools
It is a multi-tasking machine tool with the functions of a machining center and a turning center. It can control 3 straight axes and 2 rotary axes at the same time, and can process parts with complex shapes. Here are examples of each structural form, but there are two types: machining center type and CNC lathe type.
In recent years, multitasking machine tools have become capable of not only performing turning and milling operations, but also performing grinding, laser processing and additive manufacturing operations.
(1) 5-axis control machining center
A 3-axis linear control machining center that adds 2 axes of rotation is called a 5-axis control machining center. The C axis of the turntable has a high-speed rotation function and is a machining center type multi-tasking machine tool.
Figure 48: 5-axis controlled machining center
(2) Multi-tasking CNC lathe type machine tools
It is a machine tool with the same milling capabilities as a machining center on a turning center. There are also structures with tool magazines and automatic tool changers.
Figure 49: Multi-tasking CNC lathe type machine tool
Generally speaking, multitasking machines have the following advantages:
(1) Process integration to reduce labor costs
Compared to using multiple machines to create finished products from materials, multitasking machine tools do not require changeovers, nor the need to install and disassemble parts for the next process, nor the need to move parts between machines, thereby reducing the burden on workers. Here, conversion refers to a series of operations, such as fine-tuning the set direction and fixing the workpiece using measuring tools, as well as preparing the NC program for machining in order to to process the following process.
This figure shows a comparison of the same part machined using a 3-axis controlled machine and a 5-axis controlled multitasking machine (Figure 48). Using the 5-axis control of the machine tool can save two conversions.
Figure 50: Comparison of machining processes between 3-axis and 5-axis controllers
(2) High quality
As shown in Figure 50, the 5-axis control machine can do all processing after the material is fixed. So when installing and disassembling the part for each process, there will be no slight misalignment of the installation or chip biting, which is the case. A case when using a 3-axis control machine often occurs, and the accuracy of the finished product can be maintained evenly.
(3) Save space
Since multiple machine tools are not required to match the process, space in the factory can be used efficiently.
(4) Short overhang of cutting tool
In three-axis controlled machining, the tool protrusion should be taken to avoid interference between the tool holder and the workpiece. However, the longer the protrusion, the greater the tool deflection (the lower the rigidity), and the greater the tool protrusion. it is difficult to maintain accuracy. Additionally, the tip of the cutting tool may not reach the workpiece, ultimately requiring secondary machining via EDM.
Figure 51: Comparison of tool thrust volume between 3-axis and 5-axis controlled machines
On the other hand, in 5-axis controlled machining, the cutting tool or workpiece can be tilted to machine the cutting tool with a short protrusion, thus achieving high precision machining without requiring processing secondary.
(5) The processing position of the tool can be selected.
In a 3-axis machine tool, the cutting tool is always oriented in the vertical direction (Z axis), as shown in the figure. When using a ball nose end mill, the distance traveled in one revolution is different between (1) and (2). Especially at the tip, the blade does not turn. (Zero point of peripheral speed)
Even if the ball milling cutter rotates in this state, the blade is in the same state as when it stops at a certain point, and is pushed to where there is no blade without cutting, and the processed parts at the tip are easy to get dirty.
However, since the inclination angle of the cutting tool can be freely changed in a 5-axis machining machine, as shown in Figure 52, in spherical milling, processing can be carried out at the level of the part where the insert can be cut by escaping the 0. -peripheral speed point.
Figure 52: Comparison of ball mills between 3-axis and 5-axis controlled machines
6. Electroerosion machining machine “Reference to question 19”
(1) EDM machine
In EDM, soft and easily conductive materials (easy-to-process materials) such as graphite and tungsten are transformed into electrodes and parts of the desired shape, which are connected to the positive pole (positive pole) and the negative pole of a power of impulse. power supply that produces instantaneous power in a short time (negative electrode), placed in a machining fluid (insulator) that does not allow the passage of electricity or heat.
Then, when the electrode approaches tens of microns (micron = 0.001 mm) from the workpiece, the insulation state is destroyed and sparks (discharge) are generated (this gap is called “discharge gap “). ).
The discharge is generated continuously by the pulsed power supply and ends, after which if the electrode is moved a little closer to the material, the discharge occurs continuously again. The molten material from the metal part of the workpiece is exploded by the bubbles created by the heat of the electrical discharge of the machining fluid, leaving a small crater-like depression in the workpiece.
By repeating such a pulsed discharge, the metal is melted, cooled and dispersed several times, unnecessary parts of the workpiece are removed and the concave shape (circle of large diameter) carved at the tip of the electrode appears on the workpiece as a convex part, as shown. in Figure 53 shown. The advantage of this process is the possibility of processing materials that are difficult to cut.
Figure 53: EDM machine tools and their processing (part: solar discharge industry)
(2) Wire EDM machine
Wire EDM is a processing method in which wires made of conductive materials such as copper wire are used as electrodes. The wires unwound in sequence are brought closer to the workpiece in the machining fluid and the material is cut by electric discharge.
In the machining example in Figure 54, a wire is passed through a hole drilled in the workpiece, and the workpiece is mounted in a reservoir of machining fluid on a table filled with kerosene-based process oil highly insulating or demineralized water. (In older equipment, there is also a type in which machining fluid is sprayed onto the machined parts.)
Figure 54: Wire EDM machine and its processing
Then the workbench (machining fluid tank) moves at a constant speed to bring the wire closer to the workpiece, and when the gap is about tens of microns or less, discharge occurs. While generating emissions repeatedly in a short period of time, the worktable (processing fluid tank) is sent forward, backward, left and right through the NC control, and the wire is wound while treating Figure 54 as a Contour wire saw. shape.
Some wire cutting machines have a “UV Axis Control” function that allows the upper wire guide to be moved and also to tilt the wire to process inclined surfaces (conical surfaces).
7. Laser processing machine
Sunlight (natural light) is not just a single wave (wavelength), but a mixture of different wavelengths of light. Laser light, on the other hand, consists of a single wave that is a continuous cleaning wave and has precise directionality (a property that does not propagate in a straight line). When this highly directional laser is extruded with a condensing lens, a light source with extremely high energy density (density per unit volume) is obtained, enabling laser processing such as drilling and cutting.
Laser processing can be carried out without contact with the workpiece, so the contact parts will not wear or deteriorate. Depending on the type of processing machine, the table and processing head are controlled by NC.
(1) Carbon dioxide laser processing machine
The carbon dioxide laser processing machine shown in Figure 55 consists of three parts: a laser oscillator, a condenser system and an XY axis drive system. Additionally, the condenser system contains an “auxiliary gas” that removes molten and vaporized metal from the laser beam. This gas oxidizes (burns) the metal which melts with light and quickly cuts the part using oxygen, or nitrogen in other cases, and blows it out at that pressure.
Figure 55: Overview of carbon dioxide laser processing machine
The principle of producing a carbon dioxide laser
In laser media such as carbon dioxide, atoms and molecules (the atoms that come together to form matter) have a certain amount of energy and move freely. If the laser medium (Note) is placed in a glass tube as shown in Figure 57 and external energy is applied to the atoms and molecules with strong discharge light, they will move in an unstable state with high energy higher, as shown in Figure 56. Then, after a while, it releases the excess energy in the form of light and returns to its initial low-energy state.
Figure 56: Energy states of atoms and molecules in laser media
Among the emitted light, light of a specific wavelength parallel to the axis of the glass tube is reflected and amplified by the two opposite mirrors in Figure 57, and when it collides with other atoms and molecules in a low energy state, they also emit light in the same way. The same process is repeated, resulting in a single wavelength of bright light or laser. When the generated laser light leaves the glass tube, it is bent by the mirror, focused by the lens and illuminated onto the workpiece through the nozzle.
Figure 57: Mechanism for generating a carbon dioxide laser
Note: To enhance the effect of carbon dioxide in the laser medium, nitrogen and helium are mixed. Nitrogen becomes unstable when high pressure is applied, similar to the energetic instability of carbon dioxide.
Currently, carbon dioxide lasers and fiber lasers are used for general cutting operations. The principle of fiber laser is the same as that of carbon dioxide laser mentioned above, except that the laser medium is optical fiber, and a semiconductor laser is used as external energy to cause a phenomenon of resonance in optical fiber.
Daguang focuses on providing solutions such as precision CNC machining services (3-axis, 4-axis, 5-axis machining), CNC milling, 3D printing and rapid prototyping services.
