CNC manufacturing has good flexibility and high degree of automation. It is especially suitable for manufacturing curves and curved parts with complex contour shapes, as well as complex box and prism parts with a large number of holes and grooves. In the case of multiple varieties and small batch production, CNC machine tools are used. Manufacturing can obtain higher economic benefits.
The manufacturing of CNC manufacturing technology is basically the same as that of ordinary manufacturing, but it has its own characteristics. Therefore, when designing the CNC manufacturing process of parts, it is necessary to follow the CNC manufacturing with good flexibility and high degree of automation, especially suitable for manufacturing curves and curved parts with complex contour shapes, as well as complex box and prism parts with a large number of holes and grooves. In the case of multi-variety and small-batch production, the use of CNC machine tools can obtain higher economic benefits.
The manufacturing of CNC manufacturing technology is basically the same as that of ordinary manufacturing, but it has its own characteristics. Therefore, when designing the CNC manufacturing process of parts, we must not only follow the basic principles and methods of ordinary manufacturing processes, but also consider the characteristics of CNC manufacturing itself and the requirements of part programming.

(1) The part clamping method is indeed the same as the fixture selection.

The clamping method of the machined parts on the CNC machine tool is the same as that on the general machine tool, and the positioning reference and clamping scheme must also be selected reasonably. When choosing a fine benchmark, the principles of “unified benchmarks” and “coincident benchmarks” must also be followed. In addition to this, a few points should also be considered:

1) Try to complete the manufacturing of all the surfaces that can be processed in one positioning clamp.

To this end, choose a positioning method that facilitates the manufacturing of each surface. For the box parts, the positioning method with two pins on one side should be adopted, or the positioning method with a certain side as the guide datum and removing the guide element after clamping the workpiece can also be used.
2) For one-time clamping of the workpiece, the manufacturing of each surface on the workpiece can be completed

The rough surface can also be directly used as the positioning reference. However, at this time, the manufacturing accuracy of the blank is higher.

3) For the manufacturing center, the placement of the workpiece on the work table should be determined in consideration of the manufacturing of each station

The influence of the tool length and its rigidity on the manufacturing quality must be considered. For single-station single-sided manufacturing, the workpiece should be placed on the side of the table in the middle of the table. This can reduce the extension length of the cutter bar and improve the rigidity.

4) Most of the fixtures used in CNC manufacturing are relatively simple in structure

The combined adjustable fixtures assembled by general components should be selected as much as possible to shorten the production preparation cycle. In order to simplify positioning, programming and tool setting, and to ensure that the workpiece can be processed in the correct position according to the program, the dimensional relationship between the workpiece, fixture and machine coordinate system must be coordinated.

(2) The arrangement of the manufacturing order

in addition to arranging the manufacturing order according to the basic principles of “face first, then hole”, “coarse first, then fine”, should also pay attention to the following principles:

1) In order to reduce the number and time of tool change, usually the process should be concentrated according to the tool.

That is, in one clamping, after using the same tool to process all the parts on the workpiece that need to be pressed by the tool, change a tool for manufacturing. For the manufacturing center, if the tool change time is longer than the table indexing time, all the machinable surfaces to be machined should be processed in the same station, and then the other surface can be processed on the rotating table.

2) For the hole system with high coaxiality requirements, after one-time positioning (under the same station)

The tools should be changed continuously in sequence, after all the holes of the hole system are processed sequentially, then the holes at other coordinate positions , In order to eliminate the influence of repeated positioning errors and improve the coaxiality of the hole system.

(3) Determination of tool setting point and tool change point. Tool setting point is the starting point of tool movement relative to the workpiece during CNC manufacturing.

Since the program is also executed from this point, the tool setting point is also called the starting point or starting point of the program. When programming, you should first consider the choice of tool setting point.
When the manufacturing accuracy is not high, some surfaces on the workpiece or fixture can be used as the tool setting surface; when the manufacturing accuracy is high, the tool setting point should be selected as much as possible on the design basis or process basis of the part, such as positioning with holes Parts, it is more appropriate to take the axis of the hole as the tool setting point.
The tool setting point must have a certain coordinate relationship with the positioning reference of the workpiece, so as to determine the relationship between the machine tool standard system and the workpiece coordinate system. The selection of tool setting point should facilitate the calculation of coordinate values and make tool setting convenient.
When setting the tool, the tool setting point and the tool position point should coincide. The so-called tool point refers to the intersection of the tool axis and the bottom of the tool for flat-bottom end mills; for the ball-end milling cutter, it refers to the center of the ball head; for turning tools, it refers to the tip; for drill bits, it refers to the drill tip; The wire electrode cutting machine refers to the focus of the wire electrode axis and the part surface.
When the tool needs to be changed during the process, the tool change point should be specified, and the position of the tool change point should be set according to the principle that the workpiece, fixture and machine tool should not be injured during the tool change.
(4) The planning of the tool feed route. The feed route is the tool (tool point) in the process of exponential control. For the movement path of the machined part, the principles that should be followed when planning the feed route are:

• 1) Ensure that the processed parts get good manufacturing accuracy and surface quality.
• 2) Make numerical calculation work simple.
• 3) Make the feed route the shortest.

When milling the outline of a flat part, the side edge of the end mill is generally used for cutting. In order to ensure the smooth shape of the workpiece, the cut-in and cut-out points of the mill should be extended along the periphery of the part. Will leave obvious knife marks on the shape of the part.
When milling the closed contour of the internal groove of a planar part, there should be no extensions when cutting in and out. At this time, you can cut in or cut out along the normal of the part contour, and when possible, its cut-in and cut-out points should be selected at the intersection of the two geometric elements of the part contour.