CNC engraving and CNC milling, along with machining centers, each have their own advantages in machining. Combining CNC engraving and CNC milling to fully leverage their respective strengths and compensate for each other's weaknesses is undoubtedly a wise choice. Based on a comparison of advantages and disadvantages, this paper discusses a combined machining strategy that integrates CNC engraving and CNC milling. 1 Introduction CNC engraving machines have seen significant development in China in recent years, while CNC engraving and milling machines have existed abroad for a long time. To be precise, engraving is a part of milling. Traditional CNC milling machines and CNC machining centers have high power, high processing efficiency, and good machine stability, but they suffer from low surface finish and low processing efficiency when machining soft materials such as copper and aluminum. While high-speed CNC machining centers can overcome these shortcomings, they are expensive and unaffordable for most manufacturers. Compared with traditional CNC equipment, CNC engraving machines have advantages such as high speed, high efficiency in processing soft materials, high surface finish, and high cost-effectiveness. Engraving is a craft-type labor that embodies high intelligence and skill, and contemporary engraving manufacturing technology is undergoing a transformation from manual engraving to CNC engraving. Combining CNC engraving and CNC milling, giving full play to their respective advantages and complementing each other's strengths, is undoubtedly a wise choice. This is the joint processing strategy of CNC engraving and CNC milling machines. The following is a brief discussion of the key related technologies. 2 Comparison of CNC Engraving and CNC Milling with Machining Centers 2.1 Mechanical Parts The machine tool's mechanics consist of two parts: the worktable, spindle slide, etc., are moving parts; the bed, base, column, etc., are non-moving parts. 2.1.1 CNC Milling and CNC Machining Centers have high rigidity requirements for both the non-moving and moving parts of CNC milling and CNC machining centers, thus enabling heavy cutting. However, due to the equally large moving parts, the flexibility of the machine tool is sacrificed, making it inadequate for fine cutting and rapid feed. 2.1.2 CNC Milling Machine The rigidity of the non-moving parts of the milling machine should be as good as possible, while the rigidity of the moving parts should be flexible and designed to be as lightweight as possible while maintaining a certain rigidity. A CNC engraving machine designed in this way can perform fine machining with high precision and can perform high-speed machining on soft metals. However, due to the poor rigidity of the moving parts, it is impossible to perform heavy cutting. How to solve the contradiction between light weight and good rigidity of the moving parts from the perspective of mechanical structure? The key lies in the mechanical structure design. The following technical measures can be adopted: (1) Use 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 bed has higher rigidity, more even force, and the workpiece only moves in one axis. The motion axes and relative inertia are low. The design is compact and precise, which can ensure high rigidity, high precision and high dynamic characteristics. The crossbeam of the machine tool can adopt a 30-degree inclined structure, so that the center of gravity of the spindle saddle moves backward and the guide rail spacing of the crossbeam is maximized, which can greatly improve the stability and rigidity of the spindle. Since the mass of the column is much greater than the mass 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 made of cast iron integral casting, and adopts a mesh box structure with high and low ribs, or directly adopts a honeycomb-connected internal hexagonal mesh structure to ensure that the base has enough weight to increase the stability of the machine tool. Such a high rigidity base design can ensure the rigid support of the fixed worktable and column, as well as the moving parts such as the saddle and spindle, so that the stability of the machine tool dynamic processing is the best, and the column is fully supported throughout the entire stroke range, so that the deformation generated during processing is minimized. (3) Its moving part is significantly different from that of CNC milling in that the distance between the guide rails is widened to overcome the influence of adverse torque. (4) Since the rigidity of the machine tool is mainly used to overcome the strong impact of the moving parts on the non-moving parts when the moving parts move at high speed, the guide rails and lead screws are required to be thicker, and the rigidity of the connecting parts is strengthened. Finally, in order to meet the dual requirements of high speed and heavy-duty cutting, the X/Y/Z axes all use servo motors with high-precision elastic couplings to connect high-precision ball screw pairs. All guide rails and lead screws are made of high-grade, low-friction coefficient, high-hardening layer high-quality products. This ensures both the rigidity of the machine tool under heavy load and the accuracy of high-speed movement, ensuring low wear and accuracy retention of the machine tool under long-term continuous high-speed machining, which can save users' maintenance costs. (5) For CNC milling and CNC machining centers, because low speed and high torque are required to output, the reduction ratio of the spindle gearbox is required to increase torque. Therefore, low speed is unavoidable. The maximum speed of CNC milling and CNC machining centers is generally 6000 r/min, and it is unlikely to use tools with very small radius. However, for CNC engraving machines, the spindle typically operates at 20,000–30,000 rpm, with a rotational accuracy of around 2 μm. Otherwise, tool breakage will be severe. Therefore, an electric or pneumatic spindle must be used, where the motor and spindle are integrated. The spindle mounting plate is generally made of lightweight materials such as aluminum alloy. High-speed cutting equipment requires a built-in electric spindle and a certain torque even at low speeds. An oil-water cooler is needed to maintain a constant spindle operating temperature. The spindle power should be above 7.5–8 kW, and the speed should exceed 25,000 rpm. 2.2 CNC System CNC milling and CNC machining centers generally require high-speed CNC systems, with spindle speeds around 0–6000 rpm. Engraving and milling machines, on the other hand, require high-speed CNC systems and excellent servo motor characteristics, with spindle speeds around 3000–40000 rpm. They should directly support G-code generated by various CAD/CAM software such as MasterCAM. The CNC system also has the following functions: (1) Automatic tool setting function: Automatically finds the center, corners, and depth with extremely high precision, solving the problem of mold alignment; (2) Automatic/manual machining: Supports ISO standard G commands; (3) Incremental feed and feed rate online adjustment function: This operation can accurately set the feed speed; (4) User data input (MDI) function: Users can input AG commands online and execute them immediately; (5) Single-step mode: Users can set the machining task to be executed to single-step mode; (6) High-speed smooth speed connection characteristic: Adaptively determines the connection speed between the current command and the next command. It not only greatly improves machining efficiency, but also improves machining performance and can eliminate speed connection tool marks left on the machining surface; (7) Three-dimensional simulation display function: Through simple operation, the three-dimensional machining results can be observed from various angles; (8) Simulation function: The machining program can be quickly simulated and completed in a very short time. At the same time, it can check whether the machining program is wrong, whether the machining result is satisfactory, and can accurately calculate the actual machining time required. 2.3 Programming Software (1) Diverse 2D Design Many carving software programs currently offer powerful graphic creation, editing, and layout functions, precise drawing and artistic drawing functions, and powerful text processing functions. They have various artistic text arrangement effects with arbitrary curves, and the font and size can be adjusted and edited at will; powerful node editing functions can quickly and freely modify the local shape of the outline. (2) Flexible 3D Design Relief carving software provides a powerful function to easily and quickly generate 3D models from 2D graphics, construct artistic reliefs and complex curved surfaces with strong artistic effects from 2D curves, and perfectly combine artistic reliefs with curved surface modeling to produce carving products with complex shapes. It can also directly output 2D and 3D toolpaths, and the toolpaths provide functions such as roughing, semi-finishing, finishing and toolpath simulation. (3) Powerful CAD modeling design: CAD/CAM mold design and manufacturing software is currently widely used and quite successful in the machining industry. It not only has the function of accurately drawing two-dimensional and three-dimensional graphics, but also has powerful functions such as generating curved surfaces and solid models. Moreover, it has the powerful function of directly compiling toolpaths for graphics, curved surfaces, and solid models, verifying NC programs through simulated toolpaths, and inputting the computer into CNC engraving machines and CNC machine tools to complete workpiece processing. (4) Convenient data exchange function: Two-dimensional and three-dimensional data can be directly converted between software. Like CNC milling machines, CNC engraving machines, CNC machining centers, and CNC milling machines, their processing basis is computer-aided design data, which is the key to the engraving CAD function. At present, the functions of advanced computer engraving software at home and abroad are different. From the software perspective, CNC milling machines, CNC machining centers, and CNC engraving machines can all use standard CAD/CAM software. CAD/CAM software first performs 3D graphic design of the product, then designs and formulates CNC machining process according to the characteristics of the product, inputs machining parameters, generates toolpaths, generates machining programs, and sends them to the control system of CNC machine tools for automated processing. A CNC four-axis computer engraving machine is shown in Figure 1. 2.4 Automatic tool changer and fully automatic tool setting machining centers are CNC equipment designed to automate multiple processes, primarily used for fixed, high-volume production operations. However, for the mold industry and small-batch production units, it's crucial to avoid indiscriminately using machining centers. Many manufacturers purchase machining centers for CNC milling. While using a tool magazine is simple for the CNC system, the spindle, tool magazine, air compressor, and various tool holders increase costs, and programming and adjusting the tool magazine also require time. Therefore, for machining operations producing a small quantity of the same type of workpiece, avoid using machining centers due to their high cost and low efficiency. A fully automatic tool setting system can be used instead. Simply load the tool, press a button, and the machine automatically sets the tool and begins machining. The error is within 0.001–0.0003 mm, which is not significantly slower than automatic tool changers. In practice, a machining center without an automatic tool setting device is far more efficient than one without a tool magazine but with an automatic tool setting device. For domestic manufacturing industries, especially mold manufacturing enterprises, production is generally done on a single-piece basis, and labor resources are abundant. Therefore, for the processing of small batches of industrial parts, the utilization value of funds should be fully considered, and machining center equipment should not be used indiscriminately. Moreover, the tool magazine system of domestic manufacturers still has many problems. Figure 2 is a view of a machining center. [IMG=Figure 1 CNC Four-Axis Computer Engraving Machine]/uploadpic/THESIS/2007/11/20071114100651814665.jpg[/IMG] Figure 1 CNC Four-Axis Computer Engraving Machine [IMG=Figure 2 Machining Center]/uploadpic/THESIS/2007/11/2007111410105423432P.jpg[/IMG] Figure 2 Machining Center 3 Application of Combined Machining Strategy With the continuous improvement of production levels, CNC high-speed machine tools have also gained favor among mold manufacturers. The essence of high-speed cutting is to complete the tool travel length in a short time. Due to its excellent characteristics, it can significantly improve machining efficiency, thereby reducing production costs. High-speed CNC machining centers can reach speeds of up to 40,000 rpm, but their use currently faces many challenges. Firstly, there's the issue of experience in high-speed machining. Many programmers are unsure how to use cutting parameters on high-speed machines, relying primarily on experience and intuition accumulated from low-speed CNC machine tools. Therefore, they lack the necessary feel for high-speed machining. Secondly, the material and hardness of the workpiece must be considered; harder materials require smaller cutting parameters. The performance of the cutting tools is also crucial, as the chosen tool determines the usable spindle speed and whether the machining is conventional or high-speed. Only by selecting high-speed tools can the appropriate high speed be achieved for high-speed machining. Furthermore, tool parameters vary significantly between companies, requiring programmers to access relevant technical data on the tools. Compared to ordinary low-speed CNC machine tools, since the machine's power is fixed, a higher spindle speed means a lower cutting force, necessitating a smaller depth of cut during high-speed machining. Only by combining machine tools, cutting tools, machining materials, and machining characteristics can the optimal cutting parameters be determined to achieve the best production efficiency. In this situation, after weighing the pros and cons, the following machining process can be adopted: Currently, there are many machine tools suitable for heavy cutting in China, and the machining costs and cutting tools are also inexpensive. For general workpieces, the machining volume is large, and the precision requirements are not high. Given this situation, most of the cutting volume (heavy cutting) can be completed using profile milling or CNC milling, leaving a 2-3mm machining allowance. The remaining cutting volume can be quickly completed on a high-speed CNC engraving machine. After switching to high-speed cutting, because the workpiece is almost formed, the cutting volume of the first cut is very uniform. Imported cutting tools can be used; although the tools are expensive, the machining time is short and the cutting volume is small, so the performance-price ratio is very good. For small molds with small machining allowances, all machining tasks can be completed on a CNC engraving machine. 4. Conclusion Currently, the rapid development of CNC technology, coupled with the far faster development of CAD/CAM software compared to CNC machine tools, allows for the organic integration of CNC engraving and CNC machining. This is achieved by utilizing advanced software such as Pro/ENGINEER and MasterCAM for CAD/CAM design and manufacturing, leveraging the strengths of each, and then transmitting the final CAM program to a CNC engraving machine for execution. CNC milling and CNC machining centers are primarily used for machining workpieces with large milling volumes; while CNC engraving machines are mainly used for machining workpieces with smaller milling volumes and high surface finishes or soft metals. The application of this combined machining strategy will make CNC engraving an indispensable processing method in mold making, with broad application prospects. (Proceedings of the 2nd Servo and Motion Control Forum; Proceedings of the 3rd Servo and Motion Control Forum)