Selection features and methods of CNC cutters in machining centers

The choice of cutting tool and the determination of the cutting amount are important contents in the numerical control processing technology. It not only affects the machining efficiency of the numerical control machine tool, but also directly affects the processing quality. The development of CAD/CAM technology makes it possible to directly use CAD design data in CNC machining, especially the connection between microcomputers and CNC machine tools, so that the entire process of design, process planning and programming is completed on the computer, generally do not need output Special process documentation.

Nowadays, many CAD/CAM software packages provide automatic programming functions. These software usually prompt the relevant topics of the process planning in the programming interface, for example, tool selection, processing path planning, cutting amount setting, etc., the programming staff only has to set relevant The parameters can be automatically generated by the NC program and transmitted to the CNC machine to complete the processing.

Therefore, the tool selection and cutting amount determination in CNC machining is completed in the human-machine interaction state, which is in stark contrast with the ordinary machine tool processing. At the same time, the programmer is required to grasp the basic principles of tool selection and cutting amount determination. Take full account of the characteristics of CNC machining when programming. This article discusses the choice of cutting tool and the determination of cutting amount that must be faced in the numerical control programming, gives some principles and recommendations, and discusses the topics that should be paid attention to.

1. Types and Characteristics of Commonly Used Tools for Numerical Control Machining

CNC machining tools must adapt to the characteristics of high-speed, high-efficiency and high-degree of automation of CNC machine tools. Generally, they should include general-purpose tools, universal connection tool holders, and a few special tool holders. The tool holder is connected to the tool and mounted on the power head of the machine, so it has been gradually standardized and serialized. There are several ways to classify CNC tools.

According to the tool structure can be divided into:

(1) Integral;

(2) Inlaid type, using welding or clip-type connection, machine clip type can be divided into two kinds of non-inversion and indexable;

(3) Special types, such as compound tools, shock-absorbing tools, etc.

According to the materials used to make the tool, it can be divided into:

(1) High-speed steel cutters;

(2) Carbide cutting tools;

(3) diamond tools;

(4) Other material tools, such as cubic boron nitride tools, ceramic tools, etc.

From the cutting process can be divided into:

(1) Turning tools, such as outer circle, inner hole, thread, cutting tool, etc.;

(2) Drilling tools, including drills, reamers, taps, etc.;

(3) Boring tools;

(4) Milling tools.

In order to meet the requirements of CNC machine tools for durable, stable, easy adjustment and exchangeable tools, tool-type indexable tools have been widely used in recent years, reaching 30% to 40% of the total number of CNC tools in metal numbers. The amount accounts for 80% to 90% of the total.

Compared with the tools used on ordinary machine tools, CNC tools have many different requirements. The main features are as follows:

(1) Good rigidity (especially rough machining tools), high precision, low vibration and thermal deformation;

(2) Good interchangeability for quick tool change;

(3) high life, stable and reliable cutting performance;

(4) The size of the tool is easy to adjust to reduce the time for tool change adjustment;

(5) The tool should be able to reliably break chips or roll chips in order to facilitate the removal of chips;

(6) Serialization and standardization to facilitate programming and tool management.

2, the choice of CNC machining tools

The selection of the tool is performed in the CNC-programmed human-machine interaction. The tool and shank should be selected correctly based on the machine tool's machining ability, workpiece material's performance, machining process, cutting amount, and other related factors. The general principle of tool selection is: easy installation and adjustment, good rigidity, high durability and high precision. Under conditions that meet the processing requirements, try to choose a shorter tool holder to improve the rigidity of the tool processing.

When selecting a tool, the dimensions of the tool must be adapted to the surface dimensions of the workpiece being machined. In production, the peripheral contours of plane parts are often machined with end mills. When milling planes, hard alloy insert milling cutters are selected. When machining bosses and grooves, high-speed steel end mills are selected; surface roughing or rough machining is performed. In the case of holes, corn milling inserts with carbide inserts can be selected. For the machining of some three-dimensional profiles and variable bevel profiles, ball-end cutters, ring cutters, taper cutters, and disc-type cutters are often used.

When free-form surfaces are machined, the cutting speed of the end of the ball-end tool is zero. Therefore, in order to ensure the machining accuracy, the cutting pitch is generally very close. Therefore, the ball head is often used for surface finishing. The flat-blade cutter is superior to the ball-end cutter in terms of surface machining quality and cutting efficiency. Therefore, as long as the condition of overcutting is not guaranteed, both the rough machining and the finishing machining of the curved surface should be selected preferentially. In addition, the tool's durability and precision have a great relationship with the tool price. It must be noticed that, in most cases, selecting a good tool increases the tool cost, but the resulting process quality and processing efficiency are improved. , you can greatly reduce the cost of the entire process.

In the machining center, various tools are installed on the tool magazine, and the tool selection and tool change actions are performed at any time according to the procedures. Therefore, a standard tool holder must be used so that the standard tool used for drilling, boring, expanding, milling, etc., can be quickly and correctly mounted on the spindle or magazine of the machine tool. The programmer should understand the structural dimensions, adjustment methods, and adjustment range of the tool holder used on the machine tool to determine the radial and axial dimensions of the tool during programming. At present, China's machining center adopts TSG tool system. Its tool holder has two kinds of straight shanks (three types of specifications) and taper shanks (four kinds of specifications), including a total of 16 different types of tool holders.

In the economical numerical control processing, since the sharpening, measurement and replacement of the tool are mostly performed manually, and the occupation time for the tool is longer, therefore, the arrangement order of the tools must be arranged in a fair manner. Generally should follow the following principles:

(1) Minimize the number of tools;

(2) After a tool has been clamped, all the machining positions it can perform should be completed;

(3) Rough-cutting tools should be used separately, even for tools of the same size;

(4) first drill after drilling;

(5) First finish the surface finish and then perform two-dimensional contour finishing.

When possible, the automatic tool change function of the CNC machine tool should be used to improve the production efficiency.

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