Features, types, functions and main technical para

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Characteristics, types, functions and main technical parameters of machining centers

this project mainly summarizes the characteristics, types, functions and main technical parameters of machining centers, so that beginners have a basic understanding of machining centers

basic composition of project I machining center

the structural layout of the same type of machining center is similar to that of the NC milling machine, and there are differences in the structure and position of the tool magazine, which is generally composed of the bed, headstock, workbench, base, column, beam, feed mechanism, automatic tool change device, auxiliary system (gas-liquid, lubrication, cooling), control system, etc., as shown in the figure

Project II Classification of machining centers

there are many varieties and specifications of machining centers. Here, only one classification is made from the structure

I. vertical machining center

refers to the machining center whose spindle axis is set in a vertical state. Its structural form is mostly fixed column type. The workbench is rectangular and has no indexing and rotation function. It is suitable for processing disc, sleeve and plate parts. Generally, there are three linear motion coordinates, and a horizontal axis CNC rotary table can be installed on the workbench to process spiral parts

the vertical machining center is convenient for clamping workpieces, easy to operate, and easy to observe the processing conditions, but it is not easy to eliminate the chips during processing, and due to the limitation of the height of the column and the tool change device, it cannot process too high parts

the vertical machining center has simple structure, small floor area, relatively low price and wide application

II. Horizontal machining center

refers to the machining center whose spindle axis is set in horizontal state. Generally, there is a workbench that can carry out indexing and rotary movement. Horizontal machining centers generally have three to five motion coordinates. The common one is three linear motion coordinates plus one rotary motion coordinate. It can make the workpiece complete the processing of the other four surfaces except the mounting surface and top surface after one clamping, which is most suitable for processing box parts

it is inconvenient to observe and monitor the debugging program and trial cutting of horizontal machining center, and it is inconvenient to clamp and measure parts, but it is easy to remove chips during processing, which is beneficial to processing

compared with the vertical machining center, the horizontal machining center has complex structure, large floor area and high price

III. gantry machining center

the shape of gantry machining center is similar to that of gantry milling machine, main 2 The working environment for placing the instrument should be kept clean. Most of the axes are set vertically. In addition to the automatic tool change device, there are also replaceable spindle accessories. The functions of the numerical control device are also relatively complete, which can be used for multiple purposes. It is especially suitable for processing large or complex parts, such as beams, frames, wallboards, etc. on aircraft

the main processing objects of the third machining center of the project

the machining center is suitable for parts with appropriate batches that are complex, have many processes, have high accuracy requirements, need many types of ordinary machine tools and a variety of cutting tools and tooling, and can be processed after many clamping and adjustment. Its main processing objects include the following four categories:

first, box parts

box parts refer to parts with more than one hole system and more cavities. These parts are widely used in machinery, automobile, aircraft and other industries, such as automobile engine block, gearbox, machine tool headstock, headstock, diesel engine block, gear pump shell, etc

box parts are processed on the machining center, and one-time clamping can complete 60% - 95% of the process content of ordinary machine tools. Many polluting enterprises of parts are ordered to rectify, with good accuracy consistency and stable quality. At the same time, it can shorten the production cycle and reduce costs. Horizontal machining centers are generally used for parts with many machining stations and worktables that need multiple rotation angles to complete; When there are few processing stations and the span is not large, the vertical machining center can be selected to process from one end

II. Complex surfaces

among products in aerospace, automotive, marine, national defense and other fields, complex surfaces account for a large proportion, such as impellers, propellers, various surface forming molds, etc

in terms of the possibility of machining, when there is no machining interference area or machining blind area, the ball end milling cutter can generally be used for three-dimensional linkage machining of complex surfaces, with high machining accuracy but low efficiency. If the workpiece has processing interference area or processing blind area, we must consider using four coordinate or five coordinate linkage machine tools

III. special shaped parts

special shaped parts are parts with irregular shape, and most of them require multi station mixed processing of points, lines and surfaces, such as brackets, bases, templates, profiling, etc. The rigidity of special-shaped parts is generally poor, the clamping and cutting deformation are difficult to control, and the machining accuracy is also difficult to ensure. At this time, we can give full play to the centralized process characteristics of the machining center, and adopt reasonable process measures to clamp once or twice to complete multiple processes or all the processing content

IV. disc, sleeve and plate parts

disc sleeve or shaft parts with keyway, radial hole or distributed hole system on the end face and curved surface, as well as plate parts with more holes, are suitable for machining with machining center. Vertical machining center should be selected for parts with distributed hole system and curved surface on the end face, and horizontal machining center can be selected for parts with radial holes

main technical parameters of project 4 machining center

the main technical parameters of the machining center include workbench area, travel of each coordinate axis, swing angle range, spindle speed range, cutting feed speed range, tool magazine capacity, tool change time, positioning accuracy, repeated positioning accuracy, etc. see Table 5-1 for the specific contents and functions

item 5 automatic tool change device

the automatic tool change device on the machining center is composed of a tool magazine and a tool driving industrial structure optimization tool exchange device, which is used to exchange tools or tools in the spindle and the tool magazine

I. requirements for automatic tool change device

the machining center has the following specific requirements for automatic tool change device:

1. The capacity of the tool magazine is appropriate

2. The tool change time is short

3. The tool change space is small

4. The action is reliable. PCU is more antioxidant than UHMWPE, and the use is stable

5. The tool repeated positioning accuracy is high

6. The tool recognition is accurate

II. The tool magazine

is on the machining center.There are mainly two kinds of tool magazine used, One is disc magazine and the other is chain magazine. The loading capacity of disc tool magazine is relatively small, generally 1 ~ 24 tools, which is mainly suitable for small machining centers; The chain tool magazine has a large tool loading capacity, generally 1 ~ 100 tools, which is mainly suitable for large and medium-sized machining centers

III. tool change mode

there are generally two tool change modes in machining centers: manipulator tool change and spindle tool change

1. Manipulator tool change

the tool is selected by the tool magazine, and then the manipulator completes the tool change action, which is a commonly used form in machining centers. The form and action of the manipulator are different with the structure of the machine tool

2. Spindle tool change

tool change is completed through the cooperative action of the tool magazine and the spindle box, which is applicable to the situation that the tool position in the tool magazine is consistent with the tool position on the spindle. Generally, the disc tool magazine is set at the position where the spindle box can move, or the whole tool magazine can move to the position where the spindle box can reach. During tool change, the spindle moves to the tool change position on the tool magazine, and the spindle directly takes or puts back the tool. It is mostly used in small and medium-sized machining centers with tool shanks below 40

IV. tool identification methods

there are many tools in the tool library of the machining center. How to call out the required tools from the tool library, you must identify the tools. There are two methods of tool identification

1. The tool holder code

is numbered on the tool holder of the tool magazine. Before loading the tool, the tool magazine is first reorganized and set. After setting, it becomes the case that the tool number is consistent with the tool holder number. At this time, the No. 1 tool holder corresponds to the No. 1 tool. After changing the tool, the No. 1 tool is not necessarily placed in the No. 1 tool holder (the tool magazine adopts the principle of placing the tool nearby), At this time, the numerical control system automatically remembers the number one tool placed in the number of tool holders, and the numerical control system adopts the circular memory mode

2. Tool handle code

the identification sensor is coded with a number on the tool handle. First, the tool number is corresponding to the tool handle number. Install the tool on the tool handle, and then install it into the tool magazine. There is a tool handle sensor on the tool magazine. When the required tool is transferred from the tool magazine to the position equipped with the sensor, it is sensed, and then transferred out of the tool magazine to the spindle

item 6 workbench automatic exchange device

according to the needs, the machining center can be equipped with the workbench automatic exchange device, so that it can carry the workpiece to convert between the station and the machine tool, so as to effectively reduce the positioning error, reduce the clamping time, and achieve the purpose of improving the machining accuracy and production efficiency, which is also the basic means of FMS

I. requirements for the automatic tool change device of the worktable

the machining center has the following specific requirements for the automatic tool change device:

1. The number of worktables is appropriate

generally, two worktables are used for single machine operation, and multiple worktables are used for multi machine joint operation

2. Short exchange time

manipulator and robot can be used for the exchange of multiple worktables to shorten the time

3. Small exchange space

4. Reliable action and stable use

5. High accuracy of repeated positioning of the workbench

2. The type of automatic exchange device of the workbench

1. The rotary exchange type

exchange space is small, which is mostly used when a single machine is used.

2. The mobile exchange type

the workbench moves to the working position along the guide (sliding) rail for exchange, which is mostly used in the situation of many stations and contents in processing (end)

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