Technological Analysis of CNC Machining Parts

According to the material, contour shape, machining accuracy, etc. of the workpiece to be machined, the appropriate machine tool is selected, the machining plan is formulated, the machining sequence of the parts, the tools, fixtures and cutting quantities used in each process are determined.

1. Reasonable selection of machine tools

When machining parts on CNC machine tools, there are generally two situations.

The first case: there are part drawings and blanks, and a CNC machine tool suitable for processing the part should be selected.

The second case: there is already a CNC machine tool, and parts suitable for processing on the machine must be selected. In either case, the main factors to be considered are the material and class of the blank, the complexity of the contour shape of the part, the size, the machining accuracy, the number of parts, and the heat treatment requirements.

To sum up, there are three points:

①It is necessary to ensure the technical requirements of the processed parts and process qualified products.

②Conducive to improving productivity.

2. Technological analysis of CNC machining parts

The technological analysis of CNC machining involves a wide range of aspects, and here we only analyze the possibility and convenience of CNC machining.

(1) The size data given on the part drawing should conform to the principle of programming convenience

1. The dimensioning method on the part drawing should be adapted to the characteristics of CNC machining. On the CNC machining part drawing, the dimensions should be quoted on the same datum or the coordinate dimensions should be given directly. This labeling method is not only convenient for programming, but also facilitates the coordination between dimensions, which brings great convenience in maintaining the consistency of design benchmarks, process benchmarks, detection benchmarks and programming origin settings. Because part designers generally consider assembly and other use characteristics in dimensioning, they have to adopt locally scattered labeling methods, which will bring a lot of inconvenience to process arrangement and CNC machining.

2. The conditions of the geometric elements constituting the outline of the part should be sufficient

The base point or node coordinates are calculated during manual programming. During automatic programming, all the geometric elements that make up the part outline are defined. Therefore, when analyzing the part drawing, it is necessary to analyze whether the given conditions of the geometric elements are sufficient. For example, arc and straight line, arc and arc are tangent on the drawing, but according to the size given in the figure, when calculating the tangent condition, it becomes the state of intersection or separation.

(2) The structural manufacturability of each processing part of the part should conform to the characteristics of CNC machining

1) The inner cavity and shape of the part should preferably adopt a unified geometric type and size. In this way, the tool specification and the number of tool changes can be reduced, the programming is convenient, and the production efficiency is improved.

2) The size of the inner groove fillet determines the size of the tool diameter, so the radius of the inner groove fillet should not be too small. The quality of the part's manufacturability is related to the height of the contour to be processed, the size of the radius of the transfer arc, etc.

3) When milling the bottom plane of the part, the fillet radius r of the groove bottom should not be too large.

4) A unified datum positioning should be used. In CNC machining, if there is no unified datum positioning, the position and size of the contours on the two surfaces after machining will be uncoordinated due to the re-installation of the workpiece.

It is best to have a suitable hole on the part as a positioning reference hole. If not, set a process hole as a positioning reference hole (such as adding a process lug to the blank or setting a process hole on the allowance to be milled in the subsequent process).

3. Selection of processing method and determination of processing plan

(1) Selection of processing methods

The selection principle of the machining method is to ensure the machining accuracy and surface roughness of the machined surface. Since there are generally many processing methods to obtain the same level of precision and surface roughness, in the actual selection, it is necessary to comprehensively consider the shape, size and heat treatment requirements of the parts.

(2) Principles for determining the processing plan

The machining of relatively precise surfaces on parts is often achieved gradually through roughing, semi-finishing and finishing. For these surfaces, it is not enough to select the corresponding final processing method only according to the quality requirements, but also to correctly determine the processing plan from the blank to the final forming.

When determining the processing plan, the processing method required to meet these requirements should be preliminarily determined according to the requirements of the accuracy and surface roughness of the main surface. For example, for a hole with a small diameter of IT7 precision, when the final processing method is fine reaming, drilling, reaming and rough reaming are usually processed before fine reaming.

Fourth, the division of processes and steps

(1) Division of processes

When machining parts on CNC machine tools, the process can be relatively concentrated, and most or all of the processes can be completed in one clamping as much as possible. First of all, according to the part drawing, consider whether the processed part can be processed on a CNC machine tool. If not, it should be decided which part is processed on the CNC machine tool and which part is processed on other machine tools. The processing steps are divided. There are several ways to divide the general process: (2) Division of work steps The division of work steps is mainly considered from the two aspects of machining accuracy and efficiency. In a process, different tools and cutting amounts are often used to process different surfaces.

1) The same surface is completed by roughing, semi-finishing and finishing in sequence, or all the machined surfaces are separately processed according to roughing and finishing.

2) For parts with both milling surfaces and boring holes, the surfaces can be milled first and then the holes can be boring. Dividing the steps according to this method can improve the accuracy of the hole. Because of the large cutting force during milling, the workpiece is prone to deformation.

In short, the division of processes and steps should be comprehensively considered according to the structural characteristics and technical requirements of specific parts.