Figure 1 Milling
Figure 2 Drilling
Figure 3 thread processing
Fig. 4 Boring processing
1. Process analysis
Generally consider the following aspects:
(1) Select the processing content The machining center is most suitable for machining complicated shapes, more processes and higher requirements. It is necessary to use a variety of types of general-purpose machine tools, tools and fixtures, and parts that can be processed after many times of clamping and adjustment.
(2) Check the part pattern
Parts drawings should be correctly expressed and marked. At the same time, special attention should be paid to the fact that a uniform design reference should be used as far as possible to simplify the programming and ensure the accuracy of the parts.
Figure 5 Standards for Parts Machining
For example, the part pattern shown in FIG. In Fig. 5a, both sides A and B have been processed in the previous step, and only the processing of all the holes is performed on the machining center. When positioning on both sides of A and B, the dimensions of the ф48H7 hole and the two upper ф25H7 holes and the B surface are indirectly ensured due to the lack of a uniform design reference in the height direction. To ensure the dimensions of 32.5±0.1 and 52.5±0.04, it must be on the road. The 105±0.1 dimensional tolerances are compressed in the process. If the dimension shown in Fig. 5b is changed, the dimensions of each hole are based on the A surface. The reference is unified, and the process reference coincides with the design reference. The dimensions are easily guaranteed.
(3) Analyze the technical requirements of parts According to the function of the parts in the product, analyze whether the geometric accuracy and technical requirements are reasonable; consider whether processing in the processing center can ensure its accuracy and technical requirements; which kind of machining center is the most reasonable .
(4) Examine the structure of parts. Craft analysis of whether the structural rigidity of the parts is sufficient or not, and whether the structure of each processing part is reasonable or not.
2. Process design
When designing a process, it mainly considers both precision and efficiency, and generally follows the principles of first face back hole, first reference after other, and first rough after finish. The machining center completes machining of all surfaces that can be machined in one setup. For the hole machining with higher requirements for position accuracy, special attention must be paid to the arrangement of the holes in the machining sequence. If improperly arranged, it is possible to bring back the backlash of the transmission pair and directly affect the position accuracy. For example, when arranging the hole machining sequence of the parts shown in FIG. 6a, if the machining is performed according to the route of FIG. 6b, the y-direction backlash increases the error because the 5.6% hole and the 1.2.3.4 hole are oriented in the Y direction. , thereby affecting the positional accuracy of 5.6 holes and other holes. According to the route shown in Figure 6c, the introduction of backlash can be avoided.
Figure 6 Boring process
During the machining process, in order to reduce the number of tool changes, the tool centering process can be used. That is, the same tool can be used to process the corresponding parts of the parts, and the second tool can be used for further processing. However, for the hole system with high accuracy, if the part is determined by the rotation of the table to determine the corresponding machining position, this method cannot be adopted due to the presence of repeated positioning errors.
3. The installation of parts
(1) Selection of positioning reference When machining in a machining center, the positioning of parts should still follow the six-point positioning principle. At the same time, special attention should also be given to the following points:
1) When performing multi-station machining, the selection of the positioning reference should consider the ability to complete as much processing as possible, even if the positioning method can be processed on each surface. For example, for a box part, a combined positioning method with one side and two pins is used as much as possible.
2) When the positioning reference of the part is difficult to coincide with the design reference, the assembly drawing shall be carefully analyzed to specify the design function of the design reference of the part. Through the calculation of the dimensional chain, the dimensional and positional accuracy between the positioning reference and the design reference shall be strictly specified to ensure that Precision.
3) The programming origin and the part positioning reference may not coincide, but there must be a certain geometric relationship between the two. The choice of programming origin is mainly considered for ease of programming and measurement. For example, the parts in Fig. 7 are machined with Φ80H7 and 4-Φ25H7 holes on the machining center, where 4-ф25H7 is based on the ф80H7 hole and the programming origin should be selected on the centerline of the ф80H7 hole. When the part positioning reference is A, B on both sides, the positioning reference and the programming origin do not coincide, but the same processing accuracy can be guaranteed.
Figure 7 Programming Origin and Positioning Reference
(2) Clamping of parts When considering the clamping scheme, it is necessary to ensure reliable clamping and minimize clamping deformation.
(3) Selection of fixtures On the machining center, the task of the fixture is not only to set up the parts, but also to use the positioning reference as a reference to determine the processing origin of the parts. Therefore, the positioning reference must be accurate and reliable.
4 tool selection
The basic requirements for machining tools in machining centers are:
1) Good cutting performance: Can withstand high-speed cutting and strong cutting and stable performance;
2) Higher accuracy: The accuracy of the tool refers to the shape accuracy of the tool and the positional accuracy of the tool and the chucking device;
3) Equipped with a complete tool system: to meet the requirements of multi-knife continuous processing.
The head part of the tool used in the machining center is basically the same as the tool used in the CNC milling machine. The selection of the CNC milling tool is used. The shank portion of the tool used in the machining center is different from the shank portion of the general CNC milling machine. The shank of the machining center is provided with a clamping groove for the robot hand to hold.