Processing composition and structure of the hottes

2022-09-19
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Machining composition and structure of flexible manufacturing system

machining system of flexible manufacturing system

typical FMS is generally composed of three subsystems. They are processing system, logistics system and control and management system. The composition block diagram and functional characteristics of each subsystem are shown in Figure 1. The organic combination of the three subsystems constitutes the energy flow (changing the shape and size of the workpiece through the manufacturing process), material flow (mainly referring to workpiece flow and tool flow) and information flow (information and data processing in the manufacturing process) of a manufacturing system

the processing system in FMS is like human hands and feet. It is an executive system that actually completes the task of changing physical properties. The processing system is mainly composed of CNC machine tools, machining centers and other processing equipment (some with workpiece cleaning, detection and other auxiliary and detection equipment). The processing equipment in the system has standard interfaces that can be connected with other subsystems in three aspects: workpiece, tool and control. From the flexible meanings of flexible manufacturing system, it can be seen that the performance of machining system directly affects the performance of FMS, and machining system is the most expensive part in FMS. Therefore, proper selection of machining system is the key to the success of FMS. The main equipment in the processing system is the machine tool that actually performs machining, such as cutting, and transforms the workpiece from raw materials to products

1. configuration and requirements of machining system

at present, the machining objects of metal cutting FMS mainly include two types of workpieces: prisms (including box shape and plate shape) and rotating bodies (long axis shape and disk sleeve shape). For machining systems, FMS, which is usually used to process prismatic workpieces, consists of vertical and horizontal machining centers, CNC modular machine tools (CNC special machine tools, interchangeable headstock machine tools, modular multi power head CNC machine tools, etc.) and pallet exchangers; FMS for machining rotary workpiece is composed of CNC lathe, turning center, CNC modular machine tool, loading and unloading manipulator or robot, bar conveyor, etc

because the processing time of prismatic workpiece is long and the process is complex, FMS for processing prismatic workpiece was first developed to realize unattended automatic processing at night. The processing system of small FMS is mostly composed of 4 ~ 6 machine tools. These NC processing equipment are configured in FMS in three forms: alternative form (parallel), complementary form (Series) and mixed form (parallel series). See Table 1. It should be noted that these configurations mainly depend on the function of the machine tool, the material flow and information flow of the FMS, rather than the physical layout of the processing equipment

Table 1 Comparison of machine tool configuration forms and characteristics

in principle, the machining system of FMS should be reliable, automatic, efficient and easy to control, with good practicality, matching and processability, and can meet the size range and accuracy of machining objects. Material and other requirements. Therefore, it should be considered when selecting:

1) process concentration. For example, multi-functional machine tools and machining centers are selected to reduce the number of jobs and logistics burden and ensure the processing quality

2) strong control function and good expansibility. If the modular structure is selected, the external communication function and internal management function are strong. There is a CNC system with built-in programmable controller and user macro program, so that it is easy to connect with auxiliary devices such as loading and unloading and detection, and add various auxiliary functions, so as to facilitate system adjustment and expansion, and reduce the load of communication network and superior controller

3) high rigidity, high precision and high speed. Select machine tools with strong cutting function, stable processing quality and high production efficiency

4) good economy. For example, the guide oil can be recycled, and the broken and chip removal can be handled quickly and thoroughly, so as to prolong the service life of the tool. Save the operation cost of the system and ensure that the system can operate safely, stably and automatically without being on duty for a long time

5) good operability, reliability and maintainability. The operation, maintenance and repair of the machine tool are convenient and the service life is long

6) good self protection and self maintenance. Such as cutting force overload protection, power overload protection, travel and working area restrictions, etc. The guide rail and relative moving parts do not need lubrication or can be lubricated automatically, and have fault diagnosis and early warning functions

7) good adaptability and protection to the environment. The requirements for the temperature, humidity, noise, dust, etc. of the working environment are not high. All kinds of seals have reliable performance, no leakage, and the coolant does not splash. It can eliminate smoke and odor in time, and the noise and vibration are small, which can protect a good production environment

8) others. For example, the technical data are complete, the various displays and marks on the machine tool are clear, and the machine tool shape and color are beautiful and coordinated with the system

2. Introduction to common processing equipment in processing system

machining center is a high-efficiency CNC machine tool with a tool library and can automatically change the tool according to the predetermined program to process the workpiece in multiple processes. Its biggest feature is that the process is centralized and highly automated, which can reduce the number of workpiece clamping, avoid the cumulative error caused by multiple positioning of the workpiece, save auxiliary time, and realize high-quality and efficient processing

common machining centers can be divided into boring and milling machining centers, turning machining centers, drilling machining centers, threading machining centers and grinding machining centers according to their process uses. Machining centers can be divided into vertical machining centers, horizontal machining centers, and vertical and horizontal (also known as universal, pentahedral, composite) machining centers according to the spatial position of the spindle during machining

in practical applications, boring and milling machining centers that mainly process prismatic workpieces and turning machining centers that mainly process revolving workpieces are the most common. Because the boring and milling machining center (which was added to the NC milling machine by American km company in 1958)

first appeared and is called machining center, it is customary to call the "key milling machining center" as "machining center". We might as well follow this habit

(1) machining center the machining center can complete boring, milling, drilling, tapping and other work. The main difference between it and ordinary CNC boring machines and CNC milling machines is that it is equipped with a tool magazine and an automatic tool change device, as shown in Figure 2. The indicators to measure the tool magazine and automatic tool change device of the machining center include the storage capacity of tools, the maximum size and weight of tools (including tool handle and tool bar), the repeated positioning accuracy of tool change, safety, reliability, scalability, tool selection method and tool change time, etc

the tool magazine of the machining center has basic types such as chain type, disc type and turret type, as shown in Figure 3. Chain tool magazine is characterized by large tool storage, good expansibility, flexible configuration position on the machining center, but complex structure. The disc and turret type tool magazine is characterized by simple structure, proper selection of the position of the tool magazine, and the omission of the tool changing manipulator, but the capacity of the tool magazine is limited. According to the purpose, the storage capacity of the tool magazine of the machining center can range from several to hundreds, and the most common is 20 ~ 80

the automatic tool change device of machining center often adopts the public tool change manipulator. Public tool changing manipulators include single arm, double arm, rotary and track type. When changing the tool of the double arm manipulator, one arm can take the tool from the tool magazine while the other arm pulls the used tool from the spindle of the machine tool, which can not only shorten the tool changing time, but also help to keep the manipulator balanced, so it is widely used. The gripper structures of commonly used double arm manipulators include hook hand, holding hand, telescopic hand and fork hand, as shown in Figure 4. In addition to the above public manipulator tool change mode, there are multiple manipulator tool change modes, that is, each knife in the tool magazine has a manipulator, in addition, there is a direct tool change mode without manipulator

when the machining center changes the tool, it is necessary to select the specified tool from the tool magazine, and the spindle head must also return to the tool change position. The methods of selecting the required tools from the tool library include sequential selection method, tool holder coding method, tool coding method and tool holder tracking memory method. Among them, the tool holder tracking memory method is the most convenient to use in the processing equipment, and the tool coding method is suitable for the centralized management of FMS tools, so the two methods are often mixed in FMS

there are two quantitative methods for tool change time of machining center: tool to tool change time (the time required to exchange tools after the spindle and the tool base of the tool magazine return to the tool change point) and tool change time of machining to machining (the time required from the end of the previous tool processing to the entry of the next tool after the tool exchange). Usually, the tool change time given in the technical parameters of the machining center is the tool to tool change time (or net tool change time). At present, the fastest time is 0.45s, generally about 5S. The tool change time depends on the tool change mechanism (such as the mechanical type is faster than the machine hydraulic (pneumatic) type), the tool handle specification (such as the tool change speed of the small-size tool handle), the tool weight (such as the tool light tool change speed), the machine tool specification, the size and inertia of the manipulator, etc. Therefore, generally, the larger the handle number, the lower the tool change speed

the most common refueling device in the machining center is the automatic pallet exchanger (APC), which is not only the workpiece conveying interface between the processing system and the logistics system, but also the workpiece buffer station of the logistics system. The tray exchanger can be divided into rotary and reciprocating according to its movement mode, as shown in Figure 5. The pallet exchanger is an auxiliary part of the machining center when the machine tool is running alone, but in the overall function analysis of FMS, it completes or assists in the loading, unloading and exchange of materials (workpieces), and plays a buffer role. Therefore, from the perspective of system analysis, it can also be classified as a logistics system

generally, the pallet exchanger, tool magazine and tool changing manipulator are controlled by the programmable controller of the NC system of the processing equipment, and the driving sources include hydraulic pressure, air pressure and electric energy. Manual operation shall be allowed for pallet exchange, tool selection and tool change to adapt to maintenance and adjustment

(2) turning center turning center is called turning center for short. It is gradually developed on the basis of numerical control lathe to expand its process range. At present, there is no authoritative and clear definition of turning center, but it is generally believed that turning center should have the following characteristics:

with tool magazine and automatic tool change device; Rotary tool with power; The number of linkage axes is greater than 2. Because of these characteristics, the turning center can not only complete turning processing, but also complete drilling, tapping, milling and other processing under one clamping. The workpiece exchange device with one exciting force center generated by the electromagnetic exciter in turning mostly adopts manipulator or walking robot. With the expansion of machine tool functions, multi axis, multi tool rest and turning centers with workpiece exchanger in the machine and automatic bar conveying device have developed rapidly in FMS. The second national nonferrous metal structural material preparation/processing and utilization technology exchange conference hosted by China Nonferrous Metals Society and Henan University of science and technology was held in Luoyang, Henan Province. Such turning centers are also called turning FMM (see Figure 6). For example, the turning center with opposed double headstock and double tool rest can turn the workpiece automatically and complete the whole processing of the rotating workpiece under one clamping

(3) CNC modular machine tools CNC modular machine tools (see Figure 7) refer to processing equipment such as CNC special machine tools, interchangeable headstock CNC machine tools, modular multi power head CNC machine tools, etc. This kind of machine tool is an intermediate model between machining center and modular machine tool, which has the characteristics of flexibility of machining center and high productivity of modular machine tool, and is suitable for flexible production line (FML or FTL) of medium and large batch manufacturing. This kind of machine tool can be installed in the spindle drive automatically or manually according to the needs of workpiece processing

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