Joint machining strategy of the most popular CNC e

2022-07-24
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Combined machining strategy of CNC engraving and CNC milling machine Abstract: CNC computer engraving, CNC milling and machining center have their own advantages in machining. It is undoubtedly a wise choice to combine CNC engraving and CNC milling to give full play to their respective advantages and learn from each other. Based on the comparison of advantages and disadvantages, this paper discusses a combined machining strategy of CNC engraving and CNC milling machine

key words: Joint machining strategy of CNC engraving and milling machine

1 contracting introduction

cnc engraving machine has made great development in China in recent years, and there has been a cncengravingandmillingmachine abroad. To be exact, carving is a part of milling. Traditional CNC milling machines and CNC machining centers have high power, high processing efficiency and good machine tool stability. However, when processing soft materials such as copper and aluminum, there are some shortcomings such as low surface finish and low processing efficiency. Although high-speed CNC machining centers can overcome the above shortcomings, they are expensive, which is difficult for ordinary manufacturers to bear. Compared with traditional CNC numerical control equipment, CNC computer engraving machine has the advantages of high speed, high efficiency in processing soft materials, high surface finish, high cost performance, etc. engraving processing is a highly intelligent and skilled craftsman labor full of human beings. Contemporary engraving manufacturing technology is undergoing the transformation from manual engraving to CNC engraving. It is undoubtedly a wise choice to combine CNC engraving and CNC milling to give full play to their respective advantages and learn from each other. This is the joint processing strategy of CNC engraving and CNC milling machine. The key technologies are briefly discussed below

2 comparison between CNC computer engraving and CNC milling and machining center

2.1 mechanical part

the machine tool machinery is composed of two parts: the workbench and the spindle slide plate are the moving parts; The bed, base and column are non moving parts

(1) NC milling and CNC machining center

have high requirements on the rigidity of non moving parts and moving parts of NC milling and CNC machining center, so they can be re cut. However, because the moving part is also huge, the flexibility of the machine tool is sacrificed, and it is unable to cope with small cutting and rapid feed

(2) CNC engraving and milling machine

the rigidity of the non moving part of the engraving and milling machine should also be as good as possible, while the rigidity of the moving part should be based on flexibility. It should be designed as light as possible while maintaining a certain rigidity. The CNC engraving machine designed in this way can carry out fine finishing with high machining accuracy. It can carry out high-speed machining for soft metals, but due to the poor rigidity of the moving part, it is impossible to carry out heavy cutting. How to solve the contradiction between light weight and good rigidity of the moving part from the mechanical structure, the key lies in the mechanical structure design, and the following technical measures can be adopted:

1) adopt ultra wide columns and beams, because the gantry structure has excellent symmetry and excellent rigidity, it is the preferred structure for high-speed cutting equipment. Compared with the traditional C-type bed structure, the gantry type bed has higher rigidity, average stress, the workpiece moves only in one axis, each moving axis and relative inertia are low, and the design is compact and precise, which can ensure high rigidity, high precision and high dynamic characteristics. The beam of the machine tool can be inclined by 30 degrees, so that the center of gravity of the spindle saddle moves backward, and the guide rail spacing of the beam is maximized, which can greatly improve the stability and rigidity of the spindle. Since the quality of the column is far greater than that of the moving parts such as the spindle, it provides a solid guarantee for the high-speed movement of the machine tool and the high-speed operation and load cutting of the spindle

2) the base is integrally cast with cast iron, and the box structure with high and low reinforcement is adopted, or the plastic structure with honeycomb connected inner hexagonal structure is directly adopted to ensure that the base has enough weight to increase the stability of the machine tool. Such a highly rigid base design can ensure the rigid support for the fixed worktable, column, saddle, spindle and other moving parts, so that the dynamic processing stability of the machine tool is the best, and the column is fully supported within the full range of travel, Minimize the deformation caused by machining

3) the significant difference between the moving part and NC milling is that the distance between the guide rail and the guide rail is widened to overcome the influence of bad torque

4) since the rigidity of the machine tool is mainly used to overcome the strong impact of the moving part on the non moving part when moving at high speed, the guide rail and screw rod shall be thicker and the rigidity of the connecting part shall be strengthened. Finally, in order to meet the dual requirements of high-speed and load cutting, the x/y/z three axes are connected with high-precision ball screw pairs by servo motors and high-precision elastic couplings. All guide rails and lead screws are made of high-grade high-quality products with low friction coefficient and high hardening layer, which not only ensures the rigidity of the machine tool under heavy load, but also ensures the accuracy of high-speed movement, and ensures the low wear and accuracy retention of the machine tool under long-term continuous high-speed machining, It can save users' maintenance costs

5) for NC milling and CNC machining centers, it is necessary to use the reduction ratio of the spindle gearbox to increase the torque because it is required to output large torque at low speed. Therefore, low speed is inevitable. Generally, the maximum speed of NC milling and CNC machining centers is 6000r/min, and it is unlikely to use tools with very small radius. However, for CNC engraving machines, the spindle usually works at 20000 ~ 30000r/min, and the rotation accuracy is generally 2 μ Left and right, otherwise the knife breaking phenomenon will be very serious, so the electric spindle or pneumatic spindle must be used, that is, the motor and the spindle are integrated, and the fixing plate of the spindle is generally made of light materials such as alloy aluminum. For high-speed cutting equipment, the built-in electric spindle is required, and a certain torque should be used at low speed. There should be an oil-water cooler to keep the working temperature of the spindle constant. The power of the spindle should be above 7.5 ~ 8kw, and the speed should exceed 25000r/min

2.2 CNC system

CNC milling and CNC machining centers require general speed for the CNC system, and the spindle speed is about 0 ~ 6000r/min. The engraving and milling machine requires a high-speed CNC system and excellent servo motor characteristics. The spindle speed is about 3000 ~ 40000 R/min. Directly support g codes generated by various cad/cam software such as MasterCAM. The CNC system also has the following functions:

(1) automatic tool setting function: automatic center finding, edge angle, depth, high precision, solving the problem of mold alignment

(2) automatic/manual machining: support G instruction of ISO standard

(3) incremental feed and feed rate adjustment function: this operation can accurately set the feed speed

(4) user data input (MDI) function: the user can input Ag instructions and execute them immediately

(5) single step mode: the user can set the processing task to be executed as single step mode

(6) high speed smooth speed connection feature: adaptively determines the connection speed between the current instruction and the next instruction. Not only the machining efficiency is greatly improved, but also the machining performance is improved, and the speed tool contact marks left on the machined surface can be eliminated

(7) 3D simulation display function: 3D machining results can be observed from all angles through simple operation

(8) simulation function: it can quickly simulate the processing of the processing program, complete it in a very short time, check whether the processing program is wrong, whether the processing results are satisfactory, and accurately calculate the time required for actual processing

2.3 programming software

(1) various two-dimensional designs

at present, many carving software provide powerful graphic creation, layout, accurate drawing and artistic drawing functions, and powerful word processing functions. It has a variety of artistic character arrangement effects with arbitrary curves, and the font and size can be adjusted at will; The powerful node editing function can quickly and arbitrarily trim the local shape of the contour

(2) flexible three-dimensional design

relief carving software provides a powerful function to easily and quickly generate three-dimensional models from two-dimensional graphics, construct artistic relief and complex surfaces with strong artistic effects from two-dimensional curves, and perfectly combine artistic relief and surface modeling to produce carving products with complex shapes. It can also directly output 2D and 3D tool paths. Rough machining, semi finishing, finishing and tool path simulation are provided in the tool path

(3) powerful CAD modeling design

cad/cam mold design and manufacturing software is widely used and quite successful software in the machining industry at present. It not only has the function of accurately drawing two-dimensional and three-dimensional graphics, but also has powerful functions such as surfaces and solid models. It also has the ability to directly compile tool paths for graphics, surfaces and solid models, and verify NC programs by simulating tool paths, Computer input CNC engraving machine and CNC machine tool to complete the powerful function of workpiece processing

(4) convenient data exchange function

the software can directly convert the two-dimensional and three-dimensional data. Like CNC machining center and NC milling, CNC engraving machine is based on computer-aided design data, which is the key to the function of engraving CAD. At present, the more advanced computer engraving software at home and abroad has their own advantages. From the perspective of software, standard cad/cam software can be used for NC milling, CNC machining center and CNC engraving machine. Cad/cam software first carries out the 3D graphic design of the product, and then drafts the NC machining process according to the product's characteristics, inputs the machining parameters, and generates the tool path, Then the machining program is generated and transmitted to the control system of the NC machine tool for automatic machining. CNC four axis computer engraving machine is shown in Figure 1

figure 1cnc four axis computer engraving machine

2.4 automatic tool change and full-automatic tool setting of tool magazine

machining center is a numerical control equipment to complete a variety of processes in automatic state, which is mainly used for some fixed mass production operations. However, for the mold industry and small batch production units, do not go to the machining center at any time. Many manufacturers buy the machining center to be used as CNC milling. Using the tool magazine is very simple for the CNC system, but the cost of spindle, tool magazine, air compressor and various tool handles will increase, and it will take corresponding time to program and adjust the tool magazine. Therefore, do not use a machining center for the processing of the same variety with a small number of workpieces, because the cost is high and the efficiency is low. The fully automatic tool setting system can be used. When the tool is installed upward and a button is pressed, the machine tool automatically sets the tool for direct processing. The error is within 0.001 ~ 0.0003mm. Compared with the automatic change time, it is not much slower. If it is a machining center, the efficiency of the machine tool without automatic tool setting device is much higher than that of the machine tool without tool magazine but with automatic tool setting device in practice. For the domestic manufacturing industry, especially the mold manufacturing enterprises, it is generally single piece production, and the labor resources are sufficient. Therefore, for the processing of small batch industrial parts, we should fully consider the utilization value of funds, and do not readily use the machining center equipment. Moreover, there are still many problems in the tool magazine system of domestic manufacturers. Figure 2 shows the view of a machining center

Figure 2 Application of machining center

3 combined machining strategy

with the continuous improvement of production level, CNC high-speed machine tools have also been favored by mold manufacturers. The essence of high-speed cutting is to complete the walking length of the cutting tool in a short time. Due to its excellent characteristics, it can greatly improve the machining efficiency and reduce the production cost. The speed of high-speed CNC machining center can reach 40000r/min, but the use of high-speed machine

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