During CNC machining of metal mobile phone protective cases, the formation of surface burrs is often closely related to the cutting conditions between the tool and the workpiece. Properly matching tool speed and feed rate is the key to controlling this cutting condition. Burrs are essentially excess metal remaining after plastic deformation or tearing of the material under cutting forces. Their formation is directly related to the degree of shearing and compression of the material by the tool during cutting. When the speed and feed rate are out of balance, the stress distribution in the cutting area becomes uneven, preventing the tool from neatly cutting the material, resulting in irregular burrs on the workpiece edge or surface. Therefore, finding the optimal balance between the two can fundamentally reduce the occurrence of this undesirable phenomenon.
The choice of tool speed significantly affects the energy input and material conditions during cutting. When the speed is too low, the contact time between the tool and the workpiece is prolonged, and cutting forces accumulate in a localized area, easily leading to excessive compression of the material rather than smooth shearing. This is especially true for materials with a certain degree of plasticity, such as aluminum alloys, which are more likely to leave burrs caused by pulling where the tool passes. While excessively high rotational speeds increase cutting speed, lacking an appropriate feed rate can cause tool vibration, leading to unstable contact between the blade and the workpiece. This prevents the blade from consistently cutting the material evenly. Instead, high-frequency vibrations can cause localized material tearing, resulting in fine burrs. Therefore, the rotational speed must be set to ensure cutting stability, allowing the tool to form a continuous and uniform cutting path at an appropriate linear speed.
The feed rate determines the distance the tool travels per revolution, directly impacting the cutting load applied to each cut. Excessive feed increases the amount of material removed per tooth, increasing the cutting force. When the feed rate exceeds the material's shear strength, the material is not only severed but also deformed behind the blade, forming burrs extending along the cutting direction. However, excessively low feed rates prolong friction between the tool and the workpiece surface, preventing the heat generated by cutting from dissipating easily. This can lead to localized softening of the material, making it more likely that the blade will stick to the softened workpiece, resulting in fine burrs adhering to the surface. As can be seen, the feed rate setting must be adapted to the material's cutting properties. It neither overloads the tool nor causes unnecessary friction due to insufficient cutting depth.
The matching logic between tool speed and feed rate is essentially a balance between cutting efficiency and quality. For aluminum alloys, commonly used in metal mobile phone protective cases, its cutting characteristics require the tool to maintain sufficient cutting energy at a certain speed. At the same time, the feed rate controls the depth of cut with each cut, allowing the material to be precisely separated by the shearing action of the blade. When the speed and feed rate form a reasonable ratio, the blade can obtain sufficient kinetic energy to separate the material each time it contacts the workpiece. At the same time, the feed rate matches the blade's cutting rhythm, preventing excessive material accumulation or uneven force in the cutting area. This balanced state ensures even cutting force distribution, resulting in a clean fracture surface and naturally reducing burr formation.
The matching requirements for speed and feed rate vary depending on the machining stage. In the roughing stage, while the primary goal is to quickly remove excess material, it is also important to avoid excessive burrs caused by an imbalance between speed and feed rate, as this increases the burden on subsequent finishing. During this phase, the matching should focus on ensuring stable cutting forces. By combining a moderate speed with a slightly higher feed rate, efficient cutting is achieved while minimizing excessive material deformation. During the finishing stage, to maintain surface accuracy and edge quality for the phone case, the speed is typically increased to enhance the tool's cutting sharpness. At the same time, the feed rate must be precisely controlled to ensure the blade can meticulously refine the surface and completely remove minor burrs left over from rough machining.
In actual machining, the matching relationship between speed and feed rate must be dynamically adjusted based on the structural characteristics of the phone case. For complex areas like corners and curved surfaces, the tool's cutting path changes more frequently. Using a single speed and feed rate can easily cause burrs at turning points due to sudden changes in cutting forces. In these areas, the feed rate should be appropriately reduced, and the speed should be increased accordingly. This ensures stable cutting during the turning motion and avoids tearing caused by sudden load changes. Furthermore, tool wear can affect the matching effect. As the tool edge becomes blunt, fine-tuning of the speed and feed rate is necessary to compensate for the decrease in cutting capacity and maintain stable cutting conditions.
The key to reducing burrs by matching tool speed and feed rate is achieving a smooth cutting process. Whether it's speed or feed rate, both ultimately serve the goal of ensuring the tool cuts the material with the least effort and most uniformity. When these two factors are combined to maintain optimal cutting forces and temperatures, allowing the material to separate cleanly without being torn or crushed by the blade, the surface of the metal mobile phone protective case remains smooth and flat, significantly reducing burrs and paving the way for subsequent surface treatment and assembly.
