Selection and ordering of the hottest machining ce

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Selection and ordering of machining centers

in the technological transformation of enterprises, in order to improve competitiveness, machining centers are given priority. Manufacturing enterprises are urgently required to make full use of various new digital platforms to better integrate into the global industrial chain and innovation chain. They all hope to obtain machine tools with high precision, strong functions and reliable operation with the least investment. Due to the large one-time investment and complex technology of the machining center, it is inconvenient for users to select and order; At the same time, price, function and precision are a unity of opposites. Therefore, it is very important for users to choose a suitable machine tool. Machine tool selection is not only a practical comprehensive application technology based on machine tool technology and processing technology, but also an application technology constrained by its own economic strength. The model selection of machining center is more restricted because the price is much more expensive than ordinary machine tools, and the choice of machine tools is more prominent. Correct model selection is the key to make good use of the machining center and bring the machining center into full play

1 model selection procedure

a correct and comprehensive understanding of the machining center is the basis for model selection and ordering. It is necessary to have a comprehensive and detailed understanding and mastery of the performance, characteristics, types, main parameters, functions, scope of application, deficiencies, etc. of the machining center. On the basis of full understanding, the following procedures can be followed

(1) correctly select the machining object and select the typical machining object among the numerous parts produced by the enterprise, that is, part family selection. The machining center is suitable for multi variety and small batch production. The formation of batch is not only determined by the geometric size and quantity of parts, but also by the grouping of processes. Using group technology, the processing batch of similar parts can be effectively increased to approach the efficiency and benefit of mass production, and realize medium and small batch production. Whether the selection of part family is appropriate or not has a very important impact on giving full play to the investment benefits

(2) develop a process plan, analyze the process of the typical parts (main samples) of the determined part family, and develop a process plan. Select machine tools with specifications, accuracy and functions that meet the requirements, and decide whether to reserve functions in consideration of the future development of the enterprise. At the same time, the processing man hour cost of the machining center is high. When considering the process load, we should not only consider the possibility of machine tool processing, but also consider the economy of processing

2 type selection

(1) type selection

considering the processing technology, the best processing object, range, price and other factors of the equipment, select according to the selected part family. For example, horizontal machining center shall be selected for machining workpieces with more than two sides or holes and surfaces arranged radially around, such as various boxes; For single-sided workpiece, such as various plate parts, vertical machining center should be selected; Five axis machining center can be selected for machining complex curved surface, such as air guide wheel, integral impeller on engine, etc; The position accuracy of the workpiece is required to be high, and the horizontal machining center is adopted. Five side machining center can be selected when multi side machining is required in one-time clamping; When the workpiece size is large, such as machine bed, column, etc., gantry machining center can be selected. Of course, the above points are not absolute. In particular, CNC machine tools are developing in the direction of compounding. Ultimately, decisions should be made under the conditions of process requirements and capital balance

(2) parameter selection

the main parameters of the machining center are the workbench size, etc., which are selected according to the typical parts of the determined part family

table dimension is the main parameter of machining center, which mainly depends on the outline dimension and clamping mode of typical parts. The workbench slightly larger than the typical parts shall be selected to reserve the space required for installing the fixture. The bearing capacity of the workbench shall also be considered. If the bearing capacity is insufficient, the workbench size shall be increased to improve the bearing capacity

The most basic coordinate axes of the travel of the

coordinate axis are x, y and Z, and their travel is proportional to the size of the workbench. The size of the worktable basically determines the size of the machining space. If the size of individual workpiece is larger than the coordinate travel of the machine tool, the processing area of the workpiece must be within the travel range of the machine tool

spindle motor power and torque reflect the cutting efficiency of CNC machine tools, and also reflect the rigidity of machine tools from one side. The motor power of different machine tools of the same specification can vary greatly. It shall be comprehensively considered according to workpiece blank allowance, required cutting force, machining accuracy and cutting tools

when the spindle speed and feed speed need high-speed cutting or ultra-low speed cutting, the spindle speed range should be paid attention to. Especially in high-speed cutting, both high spindle speed and feed speed matching with spindle speed are required

(3) accuracy selection

the accuracy grade of the machine tool is mainly determined according to the accuracy of key parts of typical parts. It mainly includes positioning accuracy, repeated positioning accuracy and milling accuracy. NC accuracy is usually measured by positioning accuracy and repeated positioning accuracy, especially the repeated positioning accuracy, which reflects the positioning stability of the coordinate axis. It is the basic indicator to measure whether the axis is stable and reliable. It is particularly noteworthy that a comprehensive analysis must be carried out during model selection and ordering, and the precision values listed in the product samples cannot be simply looked at, because different standards, different specified values and different detection methods lead to different meanings of values. The allowable ± value (e.g. ± 0.01/300) of unit length listed in publications, samples and certificates of conformity is often unclear. Special attention should be paid to when ordering. It must be made clear whether it is ISO standard, vdi/dgq344182 (German standard), JIS (Japanese standard) or nmtba (American Standard). Then, the test calculation methods and test environmental conditions specified in various standards are analyzed, so as to avoid misunderstanding

circle milling accuracy is one of the main indexes to comprehensively evaluate the servo following motion characteristics of CNC axis and the interpolation function of CNC system. Some large holes and large arcs can be milled with end mills for arc interpolation. No matter whether the typical workpiece has this need or not, this index must be paid attention to in order to meet the possible needs in the future and better control the accuracy

NC accuracy has a decisive impact on machining quality. At the same time, it should be noted that machining accuracy and machine tool accuracy are two different concepts. It is wrong to regard the position accuracy on the manufacturer's sample or product certificate as the machining accuracy of the machine tool. The position accuracy indicated on the sample or certificate is the accuracy of the machine tool itself, while the machining accuracy is the sum of errors generated by various factors of the whole process system, including the allowable error of the machine tool itself. The reason for the error of the whole process system is very complex, and it is difficult to express it quantitatively by linear relationship. During model selection, the evaluation method of process capability KP can be used as the basis for precision model selection. Generally speaking, the calculation result should be greater than 1.33

(4) rigidity of machine tool

rigidity directly affects productivity and machining accuracy. The machining speed of the machining center is much higher than that of ordinary machine tools, and the motor power is also higher than that of ordinary machine tools of the same specification. Therefore, the rigidity of its structural design is much higher than that of ordinary machine tools. Rigidity is an important feature of machine tool quality. However, there is no reference standard for the evaluation of the output recording paper of the plotter driven by the rigidity of the selected machine tool. In fact, when selecting the type, the user integrates his own use requirements, and the choice of the main parameters and accuracy of the machine tool includes the meaning of the rigidity requirements of the machine tool. When ordering, it can be checked according to the process requirements, the maximum allowable torque, power, axial force and feed force, and the values provided by the manufacturer. Special attention should be paid to rigidity of machine tools used for machining difficult cutting materials. At this time, in order to obtain the high rigidity of the machine tool, it is often not limited to the size of the parts, but select the machine tool with 1 to 2 specifications larger than the size of the parts

(5) CNC system selection

CNC functions are divided into basic functions and selection functions, which can be measured from the aspects of control mode, driving mode, feedback mode, detection and measurement, user function, operation mode, interface mode and diagnosis. Basic functions must be provided. However, the manufacturer will only provide the selection function after the user selects these functions. Additional price is required, and the price is generally high. The functions of the CNC system must be selected according to the performance needs of the machine tool. When ordering, the required functions must be fully ordered without omission. At the same time, the waste caused by low utilization rate should be avoided. Attention should also be paid to the correlation between various functions. In the optional CNC system, the performance varies greatly, and the price can vary several times. It should be selected according to needs, and should not pursue high indicators unilaterally to avoid waste. When selecting multiple machine tools, the CNC system of the same manufacturer shall be selected as far as possible, so that the operation, programming and maintenance are more convenient. At the same time, it should be noted that no matter how good the system is, it must be supported by the reliable part quality and assembly quality of the machine tool in order to give full play to its efficiency

(6) the number of coordinate axes and linkage axes

the number of coordinate axes and linkage axes shall meet the processing requirements of typical workpieces. The number of general coordinate axes is also a sign of the grade of the machine tool. Generally, for machine tools of the same manufacturer, specification and accuracy, if a standard coordinate axis is added, the price will increase by about 35%. Although increasing the number of axles can strengthen the function of the machine tool, we should finally pay attention to the process requirements and capital balance

(7) workbench function selection

the horizontal machining center has a rotary workbench. There are two types of rotary worktable, rotary worktable for indexing and CNC rotary worktable. The indexing and positioning distance of the rotary worktable used for indexing is limited to a certain extent, and the worktable only plays the role of indexing and positioning, and cannot participate in cutting during the rotation process. Graduation angle: 0.5 ° times; 720、5°times; 72、3°times; 120 and 1 ° times; 360, etc., which must be selected according to the processing requirements of the specific workpiece. The NC turntable can achieve arbitrary indexing, which is used as the linkage control of b axis and other axes. Vertical machining centers can also be equipped with CNC dividing heads. However, it must be determined according to actual needs for the purpose of economy and practicality

(8) automatic tool change device (ATC) and magazine capacity

atc work quality and magazine capacity directly affect the service performance, quality and price of machine tools

the capacity of tool magazine shall be based on the principle of meeting the tool needs of a complex machined part. The tool magazine capacity shall be selected by calculating the total number of tools required for machining parts according to the process analysis of typical workpieces. When the required quantity is too large, the process can be properly decomposed, and a workpiece can be decomposed into two or three processes to reduce the capacity of the tool magazine. At the same time, pay attention to the maximum tool size and maximum tool weight

atc selection mainly considers tool change time and reliability. Short tool change time can improve productivity, but the tool change time is short. Generally, the tool change device has complex structure, high failure rate and high cost. Overemphasizing the tool change time will greatly increase the price and the failure rate. According to statistics, about 50% of the failures of the machining center are related to ATC. Therefore, on the premise of meeting the use requirements, ATC with high reliability shall be selected as far as possible to reduce the failure rate and the cost of the whole machine

(9) cooling methods

there are many types of cooling devices. Some machining centers with full protective covers are equipped with large flow shower cooling devices, and some are equipped with tool internal cooling devices (through the tool internal cooling mode of the spindle or the external tool internal cooling mode)

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