CNC machining process design

The design of the numerical control processing route must be fully considered. Attention should be paid to the correct division of the process, the rational arrangement of the sequence, and the convergence of the numerical control machining process and the ordinary process.

1. Division of processes

Compared with the processing of CNC machine tools and ordinary machine tools, the machining process is more concentrated. According to the processing characteristics of CNC machine tools, the division of machining processes can be done in the following ways:

1) According to the clamping positioning division process

This method is generally adapted to the processing of a small number of parts, mainly the processing site is divided into several parts, each process processing part of it. For example, when machining the shape, the inner cavity is used for clamping; when the inner cavity is machined, the outer shape is clamped.

2) Divide the process by the tool used

In order to reduce the number of tool changes and idle time, you can use the principle of tool concentration to divide the process, use a knife in a fixture to complete all processing parts that can be processed, and then change the second knife to process other parts. This method is mostly used on special CNC machine tools or machining centers.

3) Dividing processes by rough and fine processing

For parts that are prone to machining deformation, taking into account the machining accuracy, deformation and other factors of the workpiece, the process can be divided according to the principle of rough and fine processing separation, that is, after the first rough finish.

In the process division, it is necessary to be flexible in accordance with the structural requirements of the workpiece, the installation method of the workpiece, the processing technology of the workpiece, the performance of the CNC machine tool, and the factory production organization and management, and strive to be reasonable.

2. Arrangement of processing sequence

The arrangement of the processing sequence shall be based on the structure of the workpiece and the condition of the blank, and the positioning and installation of the workpiece shall be selected to ensure that the rigidity of the workpiece is not destroyed and the deformation is minimized. Therefore, the arrangement of the processing sequence shall follow the following principles:

1) The processing of the previous process cannot affect the positioning and clamping of the next process

2) Processing the outer contour of the workpiece after machining the inner cavity of the workpiece first

3) Minimize repeat positioning and tool change times

4) In a multi-step process of installation and processing, the process of rigidly destroying the workpiece is arranged first.

3. The connection between CNC machining process and common process

As the NC machining process is interspersed throughout the entire process of the workpiece processing, each process needs to establish state requirements, such as the allowance of the machining allowance, the precision and tolerance of the positioning surface and hole, and the technical requirements of the orthopedic process. For heat treatment of blanks, various processes must be considered before and after.

4. Design of CNC machining process and processing route

The main task of CNC machining process design: determine the specific processing content, cutting amount, process equipment, positioning and installation methods and tool movement trajectory of the process, in order to prepare the program. Among them, the setting of the processing route is a very important link. The processing route is the movement path of the tool location relative to the workpiece during the cutting process of the tool. It not only includes the contents of the machining process, but also reflects the arrangement of the processing sequence. Therefore, the processing route is The important basis for the preparation of processing procedures.

1) The principle of determining the processing route

1 The processing route should ensure the accuracy and surface roughness of the workpiece being machined.

2 Design and processing routes should reduce idle travel time and improve processing efficiency.

3 Simplify numerical calculations and reduce program sections, reducing programming workload.

4 According to the shape of the workpiece, stiffness, allowance, machine tool system stiffness, etc., determine the number of cycles of processing.

5 Reasonably design the cutting and cutting direction of the tool. Unidirectional approach to positioning is used to avoid positioning errors caused by the backlash of the transmission system.

6 Reasonably choose milling milling or milling in the milling process. In general, CNC machine tools use ball screw, the movement clearance is very small, so the advantage of milling is more than the milling.

2) CNC machining process

1 CNC lathe processing route

CNC lathe turning processing line shown in Figure 1 AB-0p-D, where A is the tool change point, B is the entry point, C-0p is the tool cutting path, 0p is the cut-out point, D is the retract point.

Figure 1 CNC lathe turning face processing route

The processing line of the CNC turning lathe turning circle is shown in Figure 2 ABCDEF, where A is the tool change point, B is the entry point, CDE is the tool cutting path, E is the cut-out point, and F is the retraction point.

Figure 2 CNC lathe turning machining line

2 CNC milling machine processing route

Milling cutters side milling To avoid the normal cutting and cutting out of the outer contour of a part when milling the outer contour of a plane part, as shown in Fig. 3, it should be cut or cut along the tangential extension of the outer contour curve, so as to avoid the tool Blade cuts produced when cutting in or out to ensure a smooth transition of the part's surface. When milling closes the inner contour surface, the tool also feeds and retracts along the tangential direction of the contour line. As shown in Figure 4, ABC cuts the contour path for the tool tangentially, and CDC closes the inner contour path for the tool cutting workpiece. CEA Cut the contour trajectory for the tool tangentially.

Figure 3 Processing route of the outer contour milling

Figure 4 Processing route of inner contour milling

3-hole machining positioning route

Reasonably arranging the hole machining positioning path can improve the position accuracy of the hole. As shown in FIG. 5, four holes A, B, C, and D are processed in the XY plane. When the hole processing route is arranged, attention must be paid to the consistency of the positioning directions of the holes. That is to say, the unidirectional approach positioning method is used to move the C-hole to the left after moving a certain distance, and then return to the machining D-hole. This positioning method avoids the positioning error caused by the backlash of the transmission system and improves the D-hole and others. Positional accuracy between holes.

Figure 5 hole processing positioning route

5. Workpiece installation and fixture selection

1) Installation of the workpiece

1 It strives to meet the basic unity principle of design basis, process standard, installation datum, and workpiece coordinate system.

2 Decrease the number of mountings, and make it possible to machine all surfaces to be machined after one set-up.

3 Use special fixtures as much as possible to reduce the time taken to install and adjust the machine.

2) Selection of fixtures

According to the processing characteristics of CNC machine tools, coordinate the three relationships between the fixture coordinate system, the machine coordinate system and the workpiece coordinate system, in addition to the following points:

1 Process parts in small batches and use combination fixtures, adjustable fixtures, and other universal fixtures as much as possible.

2 Batch production considers the use of special fixtures for easy loading and unloading.

3 The positioning of the fixture and the components of the clamping mechanism do not affect the movement of the tool.

4 The loading and unloading of parts should be convenient and reliable. Batch production can use pneumatic clamps, hydraulic clamps and multi-station clamps.