Cast iron material offers high rigidity and heat dissipation, it is the most stable material for manufacturing machine tool structure parts. Not only does it reduce the amount of work involved, but it can also cut complex workpieces such as bumpers, dashboards, and headlamp lenses. For any machine tool used for milling large parts, the first requirement is to have a very strong cast-iron structure and be equipped with a spindle with a heat dissipation function. Here we will discuss several problems you should pay attention to mold processing of cast iron machine tool.
- Proper machine and cutting tools
The spindle of the machine must adopt the built-in cooling technology to cool the spindle from the outside of the bearing, so as to ensure that the spindle itself will not be burnt out or cause a precision loss due to thermal expansion during the long processing. These factors are important because processing large molds takes a long time, and in heavy cutting conditions, this increases the heat and stress in the molds. Therefore, the structural parts of the machine tool must have good rigidity and heat dissipation characteristics, which is the premise of processing a large quality mold. So it is necessary to limit the vibration of machine tools in the process of machining to the greatest extent, and quickly spread the heat generated in the process of machining. Choosing the right machine tools and tools can reduce costs and production cycles.
- Thermal stabilization technology
In the case of long-time processing, the influence of environmental temperature must also be considered. Large mold on the machine in normal, for example, that the environment temperature change about 10 ℃ will cause a 6 ℃ change of the machine tool column, leading to the main shaft Angle plate parallel degree change of 0.07 mm. Therefore, the design of machine tools must take into account the effect of environmental temperature to avoid the impact of environmental temperature on the precision of parts.
For a large mold machining center whose stroke can be moved rapidly, the spindle speed of the large mold machining machine should reach at least 20000r/min and the cutting speed of the metal should meet 762 ~ 20000mm/min.
Precision control is always the key in each stage of mold processing. If coarse machining and fine machining of large molds need to be realized on a machining center, then the positioning accuracy and repeated positioning accuracy of the machine must be strictly controlled. For large molds, the positioning accuracy can be up to 1.5 m, and repeat positioning accuracy should be up to 1 m. At the same time, the pitch accuracy should be kept within 5μm.
For high precision surface machining, the feedback resolution of the machine tool itself is very important for detecting the precision of machining parts. The standard 1 m feedback resolution is not ideal. If the resolution can reach 0.05 m, the finish is almost ideal. In addition, the machining quality of parts can be further improved by controlling the resolution of the machine tool, ruler feedback, and bar pitch ball screw.
The spindle on the large die machining center must meet the requirements for rough machining, semi-finishing, and high-quality finishing, and as a reference standard, the surface machining quality should be controlled within 2 m. It is usually very important to finish the closed surface and parting line of the die, but under the traditional technology, many die manufacturers have to use manual polishing to make up for the problem of insufficient machining precision. Because of the high cost of large processing machine tools, it’s obviously not unrealizable if the purchase of multi-function machine tools for this process.
In addition, the reasonable spindle design must be able to maximize the service life of the tool so that it can be in the processing cycle to low vibration, low-temperature rise in the state of continuous work. For example, when processing automobile instrument panel molds in a large-scale mold processing center, such as the use of 16mmCBN insert blade finishing tool, the processing speed can reach 8m/min, service life more than 30h, can be processed surface quality control in 0.336 ~ 3.2 m. It can be seen that considering the increase of tool cost when processing large molds, the use of specially designed large mold processing machine tool, not only extends the service life of the tool but also save a large number of machining tool cost per mold.
- The movable multi-axis machining head
Due to the limitation of mold size and weight, it usually takes a long time to install and clamp the workpiece. The 3-axis machining center not only reduces the number of debugging and clamping of the workpiece but also does not affect the machining accuracy of the machine tool so as greatly improving the production capacity of the workshop for processing large molds. The movable multi-axis machining head can be used for machining large molds with, particularly complex structures. The head designed according to the variable geometry allows for 3-axis combined machining. With only one clamping of the workpiece, it can be used for milling deep cavity molds and cooling holes, as well as cutting many other parts with complex geometry. For example, when the spindle is tilted at the best Angle, the proximity of the machining head to the milling point can be improved, so that the processing of the inclined hole can be completed by using the multi-axis machining head. In addition, when machining the surface of the workpiece with a multi-axis machining head, the radius of the tool rather than the blade of the tool is used to improve the surface roughness.
A large number of chips are generated during metal cutting. If these chips cannot be removed in time, the temperature of the machine tool structure parts or the workpiece surface will increase. The large mold processing center under the table usually has 18 chip holes, no matter what position the table moved to, it can be reliably removed from the chip. The machine has four internal hinged chip conveyors that deliver the chip to the front of the machine at a high speed.
High-pressure coolant plays an important role in large mold processing. For example, when drilling inclined holes using the 2+3 axis machining method, a coolant with a pressure of 1,000 psi (1psi=6890Pa) is required to effectively remove the chips and achieve higher precision of cutting. If there is no such high-pressure coolant, additional machine tools are needed to process inclined holes, and the secondary clamping reduces the processing accuracy and increases the cycle cost. According to the above analysis, it can be seen that the simple processing of large mold requires more and better functions of machine tools.
According to the problems above, the choice of machine tools to meet the processing requirements as far as possible, such as strong CNC system function, machine tool accuracy to be high, good rigidity, good thermal stability, and profiling function.