After CNC machining of copper products, surface defects are often closely related to factors such as tool wear, unreasonable cutting parameters, insufficient cooling and lubrication, or improper machining processes. Common surface defects include scratches, burrs, oxidation discoloration, uneven texture, and dimensional deviations. These defects not only affect the appearance quality of copper products but may also reduce their corrosion resistance and mechanical properties. Therefore, targeted treatment measures must be taken for different types of surface defects, and the process flow should be optimized in combination with the characteristics of CNC machining to achieve efficient and high-quality surface treatment.
Scratches are one of the common surface defects in CNC-machined copper products, usually caused by tool wear, excessive cutting force, or unstable workpiece clamping. After prolonged use, the cutting edge of the tool gradually dulls, increasing friction with the copper material during cutting, easily leaving fine scratches on the surface. In addition, unreasonable cutting parameter settings, such as excessively fast feed rate or excessive depth of cut, will also exacerbate friction between the tool and the workpiece, leading to scratches. Scratches can be treated by manual grinding or mechanical polishing. Hand polishing is suitable for small, localized scratches. By selecting sandpaper of appropriate grit or polishing paste, and polishing evenly along the grain of the copper, scratches can be gradually eliminated and the surface gloss restored. Mechanical polishing is suitable for large-area scratches. Using a polishing machine with polishing wheels and polishing fluid, the surface can be quickly smoothed. However, it is important to control the polishing pressure and time to avoid over-polishing, which can cause surface roughness to rebound.
Burnt burrs are an unavoidable byproduct of CNC machining, especially in drilling and milling processes, where tiny burrs are easily generated when the cutting edge of the tool separates from the copper. Burrs not only affect the appearance of copper products but may also scratch other parts during assembly or use, therefore they must be thoroughly removed. Burr removal methods include manual deburring, mechanical deburring, and chemical deburring. Manual deburring is suitable for simple structural parts. Using files, sandpaper, or specialized deburring tools, burrs can be precisely removed, but the efficiency is relatively low. Mechanical deburring is suitable for mass production. Using equipment such as vibratory grinders and tumble polishers, it removes burrs through the friction between abrasives and the copper material, offering high efficiency and good consistency. Chemical deburring utilizes the micro-corrosion effect of chemical solutions on the copper material, dissolving and removing burrs. It is suitable for complex structural parts, but requires strict control of solution concentration and processing time to avoid excessive corrosion affecting workpiece dimensional accuracy.
Oxidation discoloration is a common problem in copper processing, especially during high-temperature cutting or insufficient cooling and lubrication. The copper surface easily reacts with oxygen in the air, forming copper oxide or cuprous oxide, resulting in black or brown patches on the surface. Oxidation discoloration not only affects the appearance of copper products but may also reduce their corrosion resistance. To treat oxidation discoloration, acid pickling or electrolytic polishing methods can be used. Acid pickling involves immersing the copper products in a dilute sulfuric acid or dilute hydrochloric acid solution, using the corrosive effect of the acid to remove the oxide layer and restore the copper's original color. However, it is crucial to control the acid concentration and immersion time to avoid excessive corrosion. Electrolytic polishing utilizes the principle of electrolysis to form a passivation film on the surface of copper products, preventing further oxidation and simultaneously achieving surface brightening. It is suitable for copper products with high surface quality requirements.
Uneven texture is a surface defect in CNC machining caused by unreasonable toolpath planning or fluctuations in cutting parameters. It manifests as cutting marks or ripples of varying depths on the surface. To address uneven texture, toolpath planning needs to be optimized to ensure consistent cutting direction. Cutting parameters should also be adjusted, such as reducing feed rate and depth of cut, to reduce cutting force fluctuations. Furthermore, high-speed machining technology, by increasing spindle speed and feed rate, can significantly improve surface texture and achieve a mirror finish.
Dimensional deviation is a strictly controlled indicator in CNC machining. However, due to factors such as machine tool precision, tool wear, or clamping errors, dimensional deviations may still occur. To address dimensional deviations, the deviation value must first be accurately measured using precision measuring equipment such as a coordinate measuring machine (CMM). Then, tool compensation or machine tool parameters are adjusted according to the direction of the deviation, and the material is re-machined to the acceptable dimensions. To address dimensional deviations in mass production, it is necessary to analyze the root causes of the deviations and optimize the processing technology, such as by employing online measurement and compensation techniques to achieve real-time closed-loop control of the processing and ensure dimensional stability.
