Cleaning of die castings
Cleaning die-cast parts is the first step in post-processing. It primarily removes impurities and defects from the surface and interior of the die-cast parts, laying a solid foundation for subsequent processing and treatment. The quality of this cleaning effort directly impacts the subsequent processing and final quality of the die-cast parts. Incomplete cleaning can lead to more serious quality issues in subsequent processes. Die-cast cleaning primarily involves removing burrs, degreasing surfaces, removing scale, and cleaning internal channels and cavities. Different cleaning methods and equipment are required for different cleaning tasks.
Removing flash and burrs is a primary task in die-casting cleaning. Flash refers to excess metal at the parting surface of a die-casting, while burrs are small metal protrusions on the surface or edges of a die-casting. These defects are primarily caused by factors such as excessive mold clearance and improper die-casting parameters. Methods for removing flash and burrs include manual cleaning, mechanical cleaning, and chemical cleaning. Manual cleaning is suitable for small, complex die-castings. Using tools such as files, sandpaper, and scrapers, manual removal of flash and burrs offers high flexibility but is inefficient, labor-intensive, and suffers from poor quality consistency. Mechanical cleaning is suitable for mass-produced die-castings. Commonly used equipment includes vibratory grinders, drum grinders, belt grinders, and ultrasonic deburring machines. Vibratory grinders place the die-casting and abrasive media (such as ceramic or plastic abrasives) in a vibrating tank. The vibration creates friction between the die-casting and the abrasive, removing flash and burrs. This method is highly efficient and offers consistent quality, making it suitable for cleaning small and medium-sized die-castings.
Removing surface oil and impurities is a crucial step in cleaning die-cast parts. During the die-casting process, die-cast parts become contaminated with release agents, lubricants, metal debris, and other contaminants. Failure to remove these substances can impair subsequent surface treatments (such as electroplating and painting), leading to defects such as poor coating adhesion, blistering, and shedding. Methods for removing surface oil and impurities include solvent cleaning, alkaline cleaning, acid cleaning, and ultrasonic cleaning. Solvent cleaning utilizes the dissolving action of organic solvents (such as gasoline, kerosene, alcohol, and trichloroethylene) to remove oil. While suitable for light oil removal, solvent cleaning is simple to perform, but the cost is high, and organic solvents are volatile, potentially polluting the environment. Alkaline cleaning utilizes alkaline solutions (such as sodium hydroxide, sodium carbonate, and sodium silicate) to chemically react with oil, emulsifying and removing it. It is suitable for removing heavier oil stains, offering low cost and excellent results, making it one of the most widely used cleaning methods. Ultrasonic cleaning uses the high-frequency vibrations generated by ultrasound in the liquid to produce a large number of tiny bubbles in the liquid. The impact force generated when the bubbles burst can remove oil and impurities on the surface and gaps of the die-casting. It is suitable for die-castings with complex shapes, deep holes and gaps, with good cleaning effect and high efficiency.
Removing scale and rust is a cleaning process for die-castings stored for long periods of time or produced in humid environments. Die-castings (especially aluminum and magnesium alloy die-castings) are easily oxidized in air, forming scale. Humid storage environments can also cause rust, which can affect the appearance and performance of the die-castings. The main methods for removing scale and rust include mechanical cleaning (such as sandblasting and shot blasting) and chemical cleaning (such as pickling). Sandblasting uses compressed air to spray abrasives (such as quartz sand and corundum sand) at high speed onto the surface of the die-casting. The impact and grinding action of the abrasive removes scale and rust, while also creating a certain surface roughness that facilitates subsequent surface treatment. Shot blasting uses a high-speed rotating impeller to project steel or glass shot onto the surface of the die-casting to achieve cleaning results. It is suitable for cleaning large die-castings. Pickling uses an acid solution (such as hydrochloric acid, sulfuric acid, or nitric acid) to chemically react with scale and rust, dissolving and removing them. Neutralization is required after pickling to prevent residual acid from corroding the die-casting.
Post-cleaning inspection and quality control are crucial steps to ensure the effectiveness of cleaning. Cleaned die-castings require a comprehensive inspection to ensure that the surface is free of defects such as burrs, oil stains, scale, and rust, and that the surface roughness meets the required level. Inspection methods primarily include visual inspection, tactile inspection, and gaging inspection. Visual inspection primarily observes the die-casting surface for obvious defects and impurities; tactile inspection primarily involves feeling the surface for smoothness and the presence of burrs; and gaging inspection uses tools such as roughness gauges and calipers to measure the surface roughness and dimensional accuracy of the die-casting. Die-castings that fail cleaning must be reworked until they meet quality requirements. Cleaned die-castings must also be properly stored to prevent further contamination and damage, typically in a dry, clean environment and packaged for protection when necessary. Rigorous cleaning and quality control provide a sound foundation for subsequent processing and use of die-castings, ensuring the quality of the final product.
