- Fettling and Linishing
- Polishing
- Shot Blasting & Shot Peening
- Heat Treatment
- Powder Coating & Painting
- Anodizing
- Plating
- Impregnation
- Pre-assembly
Fettling and Linishing
Fettling is utilizing cutting machine to remove risers and any unwanted material from the casting blanks, and it’s the first step of finishing process for any casting process. Typically, linishing is utilizing abrasive belts or grinding wheels to grind castings surfaces, through which to remove burrs and improve the surface flatness.
Fettling and linishing are the basic finishing processes for any further processing. We do both of fettling and linishing in-house.
Polishing
Polishing is removal surface irregularities to reduce surface roughness, thus improve surface flatness and get bright, mirror-like surfaces. Polishing can be carried out via mechanical, chemical or electrochemical method.
Mechanical polishing is carried out by utilizing abrasive tools to grind the casting surfaces. Chemical polishing is carried out by sinking castings in chemical corrosion solution to corrode the casting surfaces. Electrochemical polishing is carried out by sinking castings in electrolyte, setting castings as positive pole and setting lead plate as negative pole to electrolyze the castings surfaces.
Dolin provides these three polishing processes. We do mechanical polishing in-house, while chemical and electrochemical polishing are done by our qualified subcontractors.
Shot Blasting & Shot Peening
Shot blasting and shot peening are both coarsening processes sharing the same theory, which utilizing high speed shot flow propelled by compressed air to impact the castings surfaces. The end result of these two processing is that the surface area of castings is extended. Bigger surface area means better surface adhesion, so both shot blasting and peening are the must pretreatment processes for surface treatment as powder coating, painting, anodizing and plating.
Shot peening is carried out by spraying spherical shots made of glass, stainless steel, or casting steel. In this process, there is almost no material removed from castings surface. The main purpose of shot peening is to improve the mechanical properties of castings. While shots utilized in shot blasting is made of hard and sharp sand including quartz sand, corundum etc. The main purpose of shot blasting is to improve surface quality, such as removal of burrs, oil stain and oxide scale etc. Dolin can do both of shot blasting and shot peening processes in-house.
Heat Treatment
Heat treatment of aluminum castings, carried out by control of heating rate, holding time and cooling rate to change the microstructure of castings, is a process to improve castings’ mechanical properties, corrosion resistance and processability. There are four basic types of heat treatment for aluminum castings, including annealing treatment, solution process, aging treatment and thermal-cold cycling treatment.
Annealing treatment is a process carried out by heating aluminum castings up to about 300 degrees Celsius, holding temperature for a certain time, and cooling with the furnace temperature to room temperature. The aim of annealing treatment is to reduce the internal stresses and deformation of castings, as well as to improve the plasticity of castings.
Solution process is a process carried out by heating aluminum castings close to the melting point of eutectic, holding temperature for time long enough, and cooling instantly by sinking castings in a liquid media. The aim of solution process is to improve strength, plasticity and corrosion resistance of castings.
Aging treatment is a process by heating aluminum castings processed by solution process up to a certain temperature, holding temperature for a certain time, and cooling slowly in room temperature. Aging treatment includes natural aging and artificial aging. As well, artificial aging include under-aging, full-aging and over-aging. The ultimate aims of different aging treatments are to get different mechanical properties of castings, and improve corrosion resistance of castings.
Thermal-cold cycling treatment is a process carried out by cyclically heating and cooling aluminum castings. The aim of thermal-cold cycling treatment is to improve mechanical properties and reduce internal stresses of castings.
Dolin is able to do full range of heat treatment for aluminum castings in-house, including T1(artificial aging), T2(annealing), T4(solution treatment plus natural aging), T5(solution treatment plus under-aging), T6(solution treatment plus full-aging), T7(solution treatment plus stabilization treatment), T8(solution treatment plus softening treatment), T9(thermal-cold cycling treatment).
Powder Coating & Painting
Electrostatic powder spraying is the most popular powder coating process. In this process, resin powders carrying negative charges are spayed out from spray gun, and adsorbed on the surfaces of castings carrying positive charges. When adsorption layer of powder is thick enough, powders on the castings surfaces will reach to saturation, meanwhile the castings will stop adsorbing any excess powders. After heating, melting, leveling and solidification in oven, resin powders will form a uniform and dense film on castings surfaces. The colors and thicknesses of powder coating can be customed according to different specifications. Mostly, the aim of powder coating for aluminum castings is to beautify the appearance, and enhance the corrosion resistance.
Painting includes primer and topcoat. Generally, primer is for corrosion resistance consideration, while topcoat is for both appearance and corrosion resistance. In this process, lacquer suspended in solvent is forced by compressed air to spray out from spray gun, and is atomized in air. Meanwhile, atomized lacquer is adsorbed on the castings surfaces uniformly. After oven-drying or open-air drying, lacquer will form a solid, uniform and dense film on the casting surfaces. Painting can be done with different colors and surface finish such as light, half-matt and matt.
Dolin is able to provide both powder coating and painting services according to customers’ specification.
Anodizing
Anodizing is a surface treatment process utilizing electrolysis method to produce an oxide film on aluminum castings surface. In this process, alumnium castings work as the anode, while lead plate works as the cathode, and acid solution (such as sulphuric acid solution, chromic acid solution, oxalic acid solution or phosphoric acid solution) works as the electrolyte. Generally, the aim of anodizing is to improve corrosion resistance and enhance the appearance of castings.
Anodizing covers sulphuric acid anodizing, chromic acid anodizing, oxalic acid anodizing, hard anodizing and phosphoric acid anodizing. Sulphuric acid anodizing is the most popular anodizing process, in which the film can be dyed with different colors.
Dolin is able to provide the full range of anodizing services according to customers’ specifications.
Plating
Plating is a surface treatment process utilizing electrolysis method to form a coating made of plating metal on the aluminum castings surfaces. The aims of plating are to improve corrosion resistance, welding property, wear resistance, and enhance appearance of aluminum castings.
Plating of aluminum castings includes chrome plating, nickel plating, copper plating etc. Chroming plating is to improve the wear resistance, corrosion resistance, as well as enhance the appearance of castings. Nickel plating is to improve the welding property and corrosion resistance. Copper plating is to improve the conductivity.
Dolin is able to provide the full range of plating services according to customers’ specifications.
Impregnation
Impregnation is a micropore sealing process. In this process, penetrating agents permeate into micropores by the way of self-absorption, vacuuming and pressurizing. After cooling or heating process, penetrating agent is solidified, thus seal the micropores in aluminum castings. The aim of impregnation is to improve the compactness, airtightness and corrosion resistance of aluminum castings.
Impregnation includes vacuum impregnation, pressurized impregnation, vacuum pressurized impregnation, ultrasound impregnation etc. Dolin is able to provide the full range of impregnation services.
Pre-assembly
Assembly, including pre-assembly and final-assembly, is a process of putting together the parts or modules of a machine. Generally, pre-assembly is the preceding process of final-assembly and carried out in different sites with final-assembly. Like the process of aircraft assembly, different modules (such as wings, engines, landing gears, fuselage etc.) are pre-assembled in different plants and shipped to aircraft plant for final-assembly.
Pre-assembly helps achieve rational allocation and optimization of resources, thus reduce the production cost eventually. Taking advantage of rich resources in China, Dolin provides cost-saving pre-assembly service according to our customers’ specifications. Supplied parts assembly and turn-key assembly services are both available.