The unique tool magazine of the CNC machining center can realize the functions of automatic tool change and spindle orientation, and is more suitable for the processing of assembly lines. Therefore, the price is higher than that of general CNC machine tools. The correct selection is the key to making good use of the machining center and making the machining center play a good role. The model of the company choosing the machining center is also very cautious.
Machining center selection Raiders
1, selection process
Correctly and comprehensively understanding the machining center is the basis for selection and ordering. We must have a comprehensive and detailed understanding and mastery of the performance, characteristics, types, main parameters, functions, application scope, and deficiencies of the machining center. On the basis of full understanding, it can be developed as follows:
A, correct choice of processing object
Choose a typical processing object among the numerous parts produced by the company, that is, the part family selection. CNC machining center is suitable for multi-variety, small-batch production. Batch formation is not only determined by the geometry and number of parts, but also the grouping of processes. With group technology, the processing volume of similar parts can be effectively increased to achieve the efficiency and efficiency of large-scale production, and the production of medium and small batches can be realized. The appropriate choice of part family has a very important impact on the full play of investment benefits.
B. Formulate the process plan
Process analysis is performed on the typical parts (main parts) of the identified part family to develop a process plan. Select the machine tools whose specifications, accuracy, and function meet the requirements, and consider the future development of the company to decide whether or not to reserve the functions. At the same time, the machining center’s processing time cost is high. When considering the process load, not only the possibility of machine tool processing, but also the economics of processing must be considered.
2, selection
A, type selection
Consider the factors such as the processing technology, the best processing object of the equipment, the range, and the price, and choose according to the selected part family. For example, the processing of two or more workpieces or radially arranged in the surrounding hole system, surface processing, such as various boxes, should be selected horizontal machining center; single-sided processing of the workpiece, such as various types of board parts The vertical machining center should be selected; when machining complex curved surfaces, such as the wind deflector and the integral impeller on the engine, a five-axis machining center can be selected; the position accuracy of the workpiece is relatively high, and the horizontal machining center is used. When a multi-face machining is required in a fixture, a five-face machining center can be selected; when the workpiece size is large, such as a machine bed, a column, etc., a gantry machining center can be selected. Of course, the above points are not absolute. In particular, CNC machine tools are moving in the direction of compounding. Ultimately, they must make decisions under the conditions of process requirements and financial balance.
B, parameter selection
The most important parameter of the CNC machining center is the size of the table, etc., which is selected based on the typical parts of the determined part family.
C, table size
This is the main parameter of the machining center, which mainly depends on the dimensions of the typical parts and the clamping method. Should choose a slightly larger than the typical part of the work table, in order to allow space for the installation fixture, but also consider the carrying capacity of the table, bearing capacity should be considered when the increase in the size of the table to increase the carrying capacity.
D, coordinate axis travel
The most basic axes are X, Y, Z, and their strokes have a proportional relationship with the size of the table. The size of the table basically determines the size of the processing space. If the size of an individual workpiece is greater than the machine coordinate travel, then the machining area of the workpiece must be within the travel range of the machine.
E. Spindle motor power and torque
It reflects the cutting efficiency of CNC machine tools and reflects the rigidity of the machine tool from one side. With different machine tools of the same specification, the motor power can vary greatly. Should be based on the workpiece blank allowance, the required cutting force, machining accuracy and tools and other comprehensive considerations.
Spindle speed and feed speed When high-speed cutting or ultra-low speed cutting is required, attention should be paid to the spindle speed range. Especially for high-speed cutting, both high spindle speeds and feedrates that match the spindle speed are required.
F, precision selection
The accuracy grade of the machine tool is mainly determined according to the accuracy of key parts of typical parts. Mainly positioning accuracy, repeat positioning accuracy, milling accuracy. CNC precision is usually measured by positioning accuracy and repeatability, especially repeatability. It reflects the positioning stability of the axis and is the basic index to measure whether the axis is stable and reliable. It is particularly worth noting that a full analysis must be performed when selecting and ordering, and the precision values listed in the product samples cannot simply be considered. Because the standards are different, the specified values are different, and the detection methods are different, the meaning of the values is different. The permissible values (eg ±0.01/300) per unit length listed in publications, samples, and certificates are often unclear. When ordering, special attention must be paid. It must be clarified that ISO standards, VDI/DGQ344182 (Germany Standard), JIS (Japanese Standard) or NMTBA (American Standard). Further analysis of the detection and calculation methods and testing environmental conditions stipulated by various standards will not lead to misunderstandings.
The milling accuracy is one of the main indexes for evaluating the servo following motion characteristics of numerical control machine tools and the interpolation function of the numerical control system. Some large holes and large arcs can be circularly milled using end mills. Regardless of the need for typical workpieces, this indicator must be taken into account for possible future needs and better control of accuracy.
CNC precision has a decisive influence on the quality of processing. At the same time, it is necessary to pay attention to the two different concepts of machining accuracy and machine tool accuracy. It is wrong to regard the positional accuracy on the production plant sample or on the product certificate as the machining accuracy of the machine tool. The accuracy of the position marked on the sample or certificate is the accuracy of the machine tool itself, and the machining accuracy is the sum of the errors generated by various factors of the entire process system, including the error allowed by the machine tool itself. The reason for the error of the entire process system is that it is very complicated and it is difficult to quantitatively express it with a linear relationship. In the selection process, the evaluation method of the process capability kp can be used as the selection basis for accuracy. In general, the calculation should be greater than 1.33.
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