The machine tool spindle is the core component of a machine tool, its function being to drive the rotation of the cutting tool (grinding wheel) or workpiece to achieve machining. The quality of the machine tool spindle in CNC lathe machining directly affects the surface quality, machining accuracy, and production efficiency of the machined parts. Therefore, to improve the machining performance of machine tools, thereby enhancing machining quality, accuracy, and production efficiency, and to enable machine tools to produce higher-quality products that meet our growing production and living needs, the rationality of the process flow in CNC lathe spindle machining directly has a significant impact on the precision and quality of the manufactured machine tool. This paper analyzes and summarizes several important steps in CNC lathe machining, and takes the machining of the spindle component of an ultra-precision machine tool on a CNC lathe as an example. Through extensive actual machining and research analysis, the process is optimized, process defects and improvement measures are proposed, the causes affecting machining accuracy and quality are identified, production efficiency is improved, and economic benefits are created for enterprises.
The performance of machine tool spindles must meet the requirements of machining accuracy and efficiency. Some traditional spindle concepts can no longer meet the needs of modern machine tool spindles. They must have good speed, accuracy, and a good match between rigidity and power, thus necessitating quality considerations. When machining parts on a CNC lathe, the turning parameters and toolpaths are set and then executed by a computer control system. Therefore, the machining process of the CNC lathe is a crucial factor affecting the machining quality and efficiency of the parts. While machining quality is improving with the development of CNC technology, there is still a lack of standardized guidance on CNC machining processes, resulting in inconsistent and stable product quality. This factor, to some extent, restricts the technological development of CNC lathes. The following analysis examines effective ways to modify the machining process of parts from several important steps, including machining methods and process selection, path planning, and tool installation.
I. Accurate processability analysis of machined parts is required.
1. The manufacturability of the parts to be machined must conform to the characteristics of CNC machining.
When designing drawings for lathe-machined parts, the dimensions should be marked with ease of machining in mind. A unified datum and coordinate dimensions should be directly used on the drawings. This facilitates programming and coordination of various dimensions, ensuring consistency between process datums, design datums, inspection datums, and programming origins. This alleviates designers' concerns about the product's usability. In manual programming, the coordinates of the base points and calculation points must be calculated, ensuring that the conditions of the workpiece's contour geometry are fully permitted. In automatic programming, all geometric elements must be defined, and the process analysis must fully consider the reasonable characteristics of each geometric element.
2. The parts to be machined are suitable for CNC lathe machining.
First, it's crucial to ensure that the shape and internal holes of the parts are processed using tools of uniform size and geometry, minimizing tool changes. The quality of the machined parts is directly related to their contour shape and radius of curvature. Therefore, the fillet radius within the slot should not be too small, as there may not be a suitable tool available. It's also necessary to prevent stress concentration on the edges caused by poor part structure, which can affect part lifespan. To prevent repeated clamping of the workpiece, which can lead to asymmetry in the dimensions and contour positions of the two machined surfaces, we strive to unify the positioning datum in the process planning. This can be achieved by using process holes for the corresponding datum holes, and the workpiece should also have positioning datum holes. If neither of these methods is feasible, a uniform positioning standard can be achieved by using a finished surface, which can reduce the error between two clamping operations.
II. Appropriate processing methods and procedures should be adopted.
1. Select an appropriate processing method
The appropriate machining method should ensure that the machining accuracy and surface roughness of the workpiece meet the design requirements and standards. When selecting a machining method, the shape, size, and heat treatment requirements of the part must be considered. Among machining methods that can achieve the same level of performance, the most efficient and suitable method should be chosen. Based on the actual conditions of the production equipment, reaming is chosen for holes on the surface of some boxes. Larger holes on the box surface are generally bored, while smaller holes are generally reamed. At the same time, we must also consider factors such as minimizing production costs and maximizing production efficiency based on the actual situation.
2. Select appropriate processing procedures
When machining on a CNC lathe, it's crucial to consider whether all or most of the machining operations can be completed in a single setup. The operations should be as concentrated as possible. This requires analyzing whether the entire part in the drawing can be machined in one setup. If not, the number of setups and tool changes should be reduced. Furthermore, when dividing the machining steps, machining accuracy and efficiency should be given priority. The machining sequence on the same workpiece surface can be roughing, semi-finishing, and finishing, or roughing and finishing can be performed separately for all surfaces.
III. Developing the Optimal Processing Route
The principles for formulating machining paths should follow: reduce tool idle time and ensure the shortest machining path, and reduce invalid program segments; ensure the surface accuracy and surface roughness of the parts; simplify numerical calculations to reduce programming workload; in some CNC lathes, point control only requires high positioning accuracy, and the tool path is not very important. Therefore, for lathes like these, the shortest idle travel is used as the tool path, and the distance of the tool in the axial direction must be determined, which is affected by the length of the workpiece.
IV. Develop installation design and process cards for cutting tools on CNC lathes.
1. Tool installation design
The most basic principles we should consider when installing tools are: to standardize the process and set the programming references for each step; to minimize the number of clamping operations, and to complete all machining surfaces in a single clamping operation; thereby maximizing the efficiency of the CNC lathe and avoiding manual adjustments during machine operation. When machining on a CNC lathe, it is also important to note that when the number of parts being machined is not large, the following basic requirements apply to the fixture: firstly, the coordinate directions of the machine tool and the fixture should be relatively fixed; secondly, the relationship between the dimensions of the machine tool's coordinate system and the parts should be considered. This will save production costs and reduce production preparation time.
2. Regarding the development of CNC lathe process cards
CNC lathes are expensive and perform well. Due to their characteristics, they are suitable for complex machining processes, enabling them to complete intricate tasks. Improving machining steps in CNC lathe programming is a key factor in increasing efficiency. Therefore, it is essential to carefully consider the main elements of the CNC machining process, including the machining path, tool setting point, tool change point, origin, turning parameters, and programming instructions.
3. Regarding the effects of the improved shaft type
We conducted an improvement experiment on the CNC turning process of the machine tool spindle. After optimizing the turning process, we performed various tests and analyses on the surface roughness and dimensional accuracy of 100 finished parts. The results showed that all dimensional tolerances were controlled within the tolerance range, and the product quality was very good. In addition, the runout tolerance and coaxiality tolerance were controlled within the qualified range of 0.01mm and φ0.005mm respectively, which is sufficient for subsequent processes. The roughness of the end face and outer circle met the drawing requirements. The length dimension was controlled within the tolerance range, which fully met the company's requirements. The production efficiency was also greatly improved, from 50 minutes per piece to 35 minutes per piece.
V. Conclusion
Based on the above research and analysis, in the practical application of CNC lathes for machine tool spindle machining, the use of CNC machine tools should be rationally arranged according to actual production needs. In particular, CNC machine tools should not be used arbitrarily. In actual production, to maximize the performance of the enterprise's CNC machine tools and thus achieve the greatest return on investment, years of practice have shown that process optimization in CNC machining is not theoretical or based on mere imagination. It stems from recording, organizing, summarizing, analyzing, and researching shortcomings in practical work, thereby obtaining optimized and improved process flows that are applied in practice. This improves part quality and production efficiency, significantly enhancing the enterprise's economic benefits.
