CNC Engraving Machining
Figure 6-2 shows a cavity insert for a soap box injection mold, including the inverse text "Shaanxi University of Science and Technology" in Chinese and the inverse pattern of the English letters "SHAANXI UNIVERSITY OF SCIENCE & TECHNOLOGY". All text patterns are 0.2 mm deep, and the stroke width of the English letters is 1 mm. The machining of this text can use CNC engraving, laser engraving, or chemical etching. Since CNC engraving is affected by the tool, some details are difficult to machine precisely. Laser engraving can solve this problem, but the machining equipment is more expensive. The application of laser engraving for processing text and patterns in modern mold manufacturing is becoming increasingly wide. Chemical etching has a relatively small machining depth and lower machining cost, and it is still widely used in mold manufacturing today. Here, we will first introduce the basics of CNC engraving.
For the CNC engraving of text, rough machining is generally performed first with a coarser scraping tool according to the CNC program, and then a finer scraping tool is used for finishing. Therefore, for the engraving of this part, a diameter 1 mm round tool is first used for rough machining, and then a diameter 0.1 mm ball-end mill is used for the final finishing.
Computer Numerical Control Engraving Machining Technology (CNC Engraving Machining Technology) is a product of the combination of traditional engraving technology and modern numerical control technology. It inherits the fine, nimble, and flexible operating characteristics of traditional engraving, while utilizing the automation technology in traditional numerical control machining. The CNC engraving machine is an advanced numerical control machining equipment that integrates Computer-Aided Design (CAD) technology, Computer-Aided Manufacturing (CAM) technology, Numerical Control (NC) technology, and precision manufacturing technology. The working principle of the CNC engraving machine is the same as that of CNC milling machines and machining centers, where the numerical program controls the operation of each component of the machine tool. In contrast, the CNC engraving machine has the following characteristics:
① The processed objects are small in size, complex in shape, and require high finishing quality;
② The process feature is the use of small tools for machining;
③ The products have high dimensional accuracy and good product consistency;
④ A high-speed, small-feed, and quick-setting tool removal milling method is adopted.
On the surface, the differences between the three, and the differences in machine tool configuration, are as follows: the machining center has a tool magazine, and after clamping a workpiece, multiple tools can complete the machining at one time; the CNC engraving machine and CNC milling machine do not have a tool magazine, and the tool must be manually stopped and replaced after each tool completes machining.
The differences in machine tool control systems: their control system functions are similar, but because they are developed by different manufacturers, there will be certain differences in the operation methods and specific functions of the control systems. These differences do not play a decisive role in the difference in machine tool performance.
The key to determining the difference in machine tool performance lies in specific details: the spindles of CNC milling machines and machining centers are relatively large, and the speed is relatively low. Generally, the maximum speed of CNC milling machines is below 20000 r/min, but the power is relatively high, and the spindle output torque is relatively large, which is suitable for larger diameter tools.
In addition, the spindle power of CNC milling machines is large, generally 10 to 100 kW; the spindle power of CNC engraving machines is small (below 4 kW), and the maximum speed is high, generally 15000 to 40000 r/min, up to 100000 r/min. The feed rate is high, generally 400 m/min, and it can machine hardened steel around 60 HRC; it is suitable for the fine machining of small and medium-sized parts.
The CNC engraving machine has a relatively high speed, and the spindle output torque is relatively small, which is suitable for tools with a diameter of 0.05 to 10 mm. Because of the high spindle speed and small tool size, the machined parts are relatively delicate, and the surface finish is high. In addition, the bed of the CNC milling machine and machining center is relatively large, and the moving parts are correspondingly large and heavy. The acceleration is relatively slow after movement, which is more suitable for machining large workpieces. The bed of the CNC engraving machine is relatively small, and the moving parts are small and light, which is conducive to rapid turning and head changes, and the average machining speed is relatively high when machining small workpieces.
Therefore, the CNC engraving machine is suitable for using small and medium-sized tools, machining small and medium-sized workpieces, fine machining of detailed parts, and high surface finish; the CNC milling machine and machining center are suitable for using larger tools, machining large workpieces. Due to their lower spindle speed and larger tools, the surface finish is relatively low compared to the CNC engraving machine, and small details are not machined precisely. These situations where machining is not precise and the finish is relatively poor can also be assisted by the CNC engraving machine to reduce the amount of post-processing. The CNC engraving machine, CNC milling machine, and machining center each have their strengths and weaknesses. For workpiece machining, especially mold machining, they are indispensable machining tools.
The use of the CNC engraving machine is similar to that of CNC machine tools, and no detailed introduction will be given here. You can watch the China University MOOC "Mold Manufacturing Technology" (Course Number: 0802SUST006) resource library video "Mold Engraving.mp4" under the "Case Videos" folder to understand CNC engraving machining.