Grinding and Polish
Grinding and polishing are common finishing processes that enhance the quality of the surface features of a workpiece. While machining can achieve the desired dimensional accuracy and tolerance, grinding and polishing can improve the surface roughness, flatness, and reflectivity.
Grinding machines use abrasive wheels that rotate at high speed to remove material from the workpiece by abrasion. The abrasive grains on the wheel act as cutting tools that create small chips on the workpiece surface. There are different types of grinding machines, such as cylindrical, surface, centerless, and internal grinding machines, depending on the shape and size of the workpiece and the desired finish.
The abrasion process can be classified into two types: ductile-mode and brittle-mode. In ductile-mode abrasion, the material is plastically deformed and removed by shear. In brittle-mode abrasion, the material is fractured and removed by tensile stress. The type of abrasion depends on the properties of the workpiece material, the abrasive grains, and the grinding conditions.
One of the main concerns in grinding is the wheel wear, which affects the performance and efficiency of the process. The wheel wear can be caused by three mechanisms: attritious wear, grain fracture, and bond fracture. Attritious wear occurs when the abrasive grains lose their sharpness due to rubbing against the workpiece. Grain fracture occurs when the abrasive grains break into smaller pieces due to excessive force or temperature. Bond fracture occurs when the bond material that holds the grains together breaks due to fatigue or thermal stress.
The material removal rate (MRR) in grinding is a measure of how much material is removed from the workpiece per unit time. The MRR depends on several factors, such as the force applied on the wheel, the wheel speed, the workpiece speed, the depth of cut, and the grinding ratio. The grinding ratio is defined as the ratio of the volume of material removed from the workpiece to the volume of material removed from the wheel. A high grinding ratio means that the wheel wears less and lasts longer.
Polishing is a process that uses finer abrasives or polishing compounds to create a smooth and shiny surface on a workpiece. Polishing can reduce or eliminate surface defects such as scratches, pits, and marks that are left by previous machining or grinding operations. Polishing can also improve the corrosion resistance, wear resistance, and aesthetic appeal of a workpiece.
There are different methods of metal polishing, such as mechanical polishing, electrochemical polishing, and chemical polishing. Mechanical polishing uses abrasive tools or media that rub against the workpiece surface to remove a thin layer of material. Electrochemical polishing uses an electric current to dissolve the surface irregularities of a workpiece immersed in an electrolytic solution. Chemical polishing uses a chemical solution to etch away the surface roughness of a workpiece.
