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Processing techniques for metal finishing
In this post we are going to list some of the most common processing techniques for metal finishing and their effect on the surfaces.
Surface finishing are among the last processes that a die-cast product needs to undergo before assembly: they can be divided in coating treatments and post-casting treatments. Coating treatments include painting, plating and chroming, and define the final look of a component. Post-casting treatments on the other hand can serve two functions: the first one is to improve function of the component, the second one is to improve its surface qualities and aesthetics.
Post-casting treatments are often used to prepare the surface to receive the final coating treatments, but they can also be used to determine the final finish of a metal component.
Processing techniques: surfaces preparation or final act?
“Processing techniques” is a very general term that identifies industrial processes aimed at modifying a manufactured product, component or surface in order to improve their properties or features.
When considering metal finishing, these techniques can be both mechanical or chemical and they comprehend a wide range of treatments and effects: from improvements in grip of a component, as in knurling, up to smooth of sharp edges, as in sandblasting. However, most of these techniques improve not only mechanical qualities of the component, but also their final appearance.
This means that processing techniques can be used as last process of a component before assembly or shipping: most processing techniques leave a distinctive texture to product surface, giving them a pleasing overall look even without coatings.
However, the most common use of post-casting treatments is to prepare components surface for coating: having a clean surface is fundamental to prevent coating defects. Hereunder you can find a list of the most commonly used techniques for zinc die casting finishing:
- Abrasive Blasting
- Chemical-mechanical planarization (CMP)
- Electro polishing
- Industrial etching
- Vibratory finishing
- Polishing & Buffing
- Thermal Deburring
Abrasive blasting is the process of driving a high pressure stream of abrasive material against a surface. It can be used to make it less rough or rougher, but also to shape it or to remove contaminants.
Among the different kinds of abrasive blasting, one of the heaviest is sandblasting, done with sand: the resulting effect is similar to the one achieved through the use of sandpaper.
Burnishing is a plastic deformation usually obtained by the action of steel balls in a vibrating machine: their action makes the zinc surface smoother and brighter.
Chemical-mechanical planarization (CMP)
Chemical-mechanical planarization (CMP) is a process which combines chemical and mechanical forces: it is implemented by using a rotational brushing movement to uniformly apply a polishing slurry, resulting in smoother zinc surfaces.
With electropolishing it is possible to remove any material from metallic workpieces. The process is similar to electroplating, but it acts in reverse: a metal component is deepen in an electrolytic bath and it serves as an anode, having particles drifted away towards the cathodes and resulting in a smoother surface. Electropolishing has many applications in the metal finishing industry because it can be effectively used on irregularly-shaped objects. It is normally used to polish and passivate, but it can also be used to deburr metal parts: anodic dissolution under electropolishing conditions deburrs metal objects due to increased current density on corners and burrs.
Grinding can be defined as an abrasive process and it is used to produce a smooth finish on flat surfaces. It is also a very precise technique, since it can be used to produce shallow cuts of just a few micrometers in metals surfaces.
Industrial etching is also known as chemical milling: it is an technique used to both to clean and to carve metal surfaces. In industrial etching baths of temperature-regulated etching chemicals are used to remove material and give the desired shape to a product.
Linishing is the use of grinding techniques to improve the flatness of a zinc surface finish or to polish it.
Barreling, also known as tumbling, is a procedure applied to small metal parts to make rough surfaces smoother. It is a very common metal finishing since it can also be used to remove burrs and rust in addition to making the whole surface shiner.
Vibratory finishing is a particular technique that enables to deburr, burnish, clean, and brighten small workpieces or components. During the process parts are placed into a vibratory tumbler tub in order to obtain the desired effect: the tub of the vibratory tumbler and all of its contents are then vibrated. This process differs from barreling, since it can finish internal features, such as holes, and it is also quicker and less loud.
Polishing & Buffing
Polishing and Buffing both require the use of abrasive tools to smooth a product surface. Polishing is usually done by abrasive belts or discs and used to level surfaces, remove scratches and pits, and polish the surface leaving a brushed or lined finish.
Buffing is often used to remove the polishing lines: it consists of a rotating cloth wheel that is impregnated with fine abrasive compounds that produces a shining finish on metal.
During Thermal Deburring the combustion of methane gas within a pressurized chamber is used to remove burrs, flashings or hidden contaminants through an oxidation reaction. The process is especially efficient for internal holes and shafts that would be difficult to reach and deburr with other techniques.
These are just some of the many kinds of metal finishing existent, and the most commonly used with zinc die casting products. Depending on the product and its material, there can be different finishing processes to choose from: in order to be sure of choosing the most suited to your needs, it would be advisable to contact your supplier for advices.
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