Buffing and polishing
In the sheet metal fabrication process, buffing and polishing is a common parts processing process. It is the process of pre-processing such as cutting or grinding to provide a smooth surface. The accuracy of geometric shapes such as surface texture (surface roughness), dimensional accuracy, flatness, and roundness can be improved.
Buffing and polishing are the last procedures when preparing sheet metal for finishing. Polishing is a relatively simple process involving removing imperfections through sanding. It gives sheet metal the ultimate perfection and a good look.
During polishing, an abrasive glued on the wheel is used to remove imperfections on the metal. After polishing, a loose abrasive is used in a process known as buffing. The primary purpose of buffing is to create a defect-free and reflective surface.
Two METHODS of buffing and polishing
- One is the “fixed abrasive processing method” by fixing a hard and fine grinding wheel to the metal,
- The other is the “free abrasive processing method” in which grit is mixed with a liquid.
Fixed abrasive processing method
The fixed grinding process uses abrasive particles that are bonded to the metal to polish the protrusions on the surface of the component. There are machining methods such as honing and superfinishing, which are characterized by a shorter polishing time than free-grinding machining methods.
Free abrasive grain processing method
In the free abrasive processing method, abrasive grains are mixed with a liquid and used for grinding and polishing. Scratch the surface by securing the part from the top and bottom and rolling the slurry (a liquid containing abrasive particles) over the surface. There are processing methods such as grinding and polishing, and its surface finish is better than that of fixed abrasive processing methods.
7 types of buffing and polishing
Honing is the polishing of the inner diameter of a part, and it is usually used to polish the inner diameter of parts such as engine blocks. Several whetstones (whetstones) are attached to the side of the cylindrical rotary tool.
Polishing is done by rotating and reciprocating, while being pressed against the inner surface by the force of the spring, thus achieving a glossy mirror effect. Because polishing is performed through rotational and reciprocating motions, a mesh of lines called cross-hatching is formed on the machined surface. In parts that slide like the relationship between an engine’s cylinder and piston, these mesh streaks act as lubrication grooves for low friction.
Electropolishing is a polishing method in which the object (metal) to be polished is immersed in an electrolyte and an electric current is applied to chemically melt the protrusions to mirror-polish the surface. Connect the object to be polished to the anode (+) and generally the lead plate to the cathode (-). Then, a current is passed through the electrolyte to smooth the metal protrusions.
The metal is dissolved into the electrolyte through the mucus layer. Since the mucus layer is thinner at the bulge, the bulge on the metal surface is easy to flow with electric current, which is first dissolved and becomes smooth.
In recent years, the precision of mechanical equipment has increased, and high-precision parts that require polishing, such as polishing, are required. Superfinishing is similar to grinding finishing, but it can improve the accuracy of surface texture and geometry than grinding finishing. It is mainly used for finishing the inner and outer rings of shafts and bearings, as well as the outer rings of engine camshafts. Machines that perform superfinishing are called “superfinishing machines”, and there are special machines for bearings and shafts.
For example, when finishing a cylindrical surface such as a bearing, a vibration (vibration) of about 1040 Hz is applied while pressing the grinding wheel against the workpiece at a low pressure, and smoothing is performed.
To grind, place the object to be processed on the grinder and pressurize it from above. Then, the slurry (abrasive grains) is sprayed between the workpiece and the grinder, and grinding is performed while polishing, and the abrasive grains are injected while rotating. Surface quality (surface roughness) and thickness can be controlled for precision. Grinders can generally polish both sides at the same time, or one of the top or bottom.
Fluid polishing is driven by hydraulic pressure, and the abrasive particles reciprocate through the surface of the workpiece with the liquid at high speed to process the contact surface of the workpiece to achieve the polishing effect. Commonly used fluid polishing methods are: abrasive jet machining, liquid jet machining, hydrodynamic grinding, etc.
There are many types of vibration polishing, the first of which is barrel polishing. The “abrasive” and “object to be processed” are placed into the drum, which rotates and moves up and down to polish the processed object. Mainly used for many very small objects to be processed, such as steel balls, and suitable for polishing multiple objects at once. It can also be used to remove burrs and sharp edges that appear on parts during the cutting process.
Similar to vibration polishing, there is also ultrasonic polishing, the principle of which is similar to that of drum polishing. The workpiece is put into the abrasive suspension and placed in the ultrasonic field together, and the abrasive is ground and polished on the surface of the workpiece by the oscillation of the ultrasonic wave. The ultrasonic processing force is small and will not cause deformation of the workpiece, and it can also be combined with chemical methods.