Surface Finishes & Plating

The anodization process ensures corrosion resistance, while the subsequent painting serves both functional and aesthetic purposes, depending on the specific type of treatment required for high-performance components, such as drag reduction system (DRS) parts. This combination aims to enhance durability, aerodynamic efficiency, and overall visual appeal.

The term “as-cast surface finish” in investment casting refers to the quality of the surface as it comes directly from the mold without undergoing any further machining or finishing. It is largely determined by the characteristics of the wax pattern and the ceramic shell mold. As-cast moldings can achieve a 125 to 150 μin (Ra) surface finish.

This chemical conversion coating process involves transforming the surface of a part into black oxide, primarily aimed at providing corrosion and wear resistance. While its primary function is not centered around aesthetics, this method can produce a visually appealing black matte appearance.

Cerakote, a ceramic-based thin-film coating applied through a distinctive solvent-based curing process, has found prominence in the firearms industry due to its exceptional wear resistance, corrosion resistance, and heat resistance. Particularly effective in resisting abrasion and friction, Cerakote stands out for its suitability in parts subjected to high contact stress or wear. It provides superior protection against rust, chemicals, and harsh environments. Despite its durability, Cerakote adds minimal weight, setting itself apart from thicker coatings and ensuring practical versatility in various applications.

Chrome finishes are widely employed to improve aesthetics and functionality in various applications. Recognized for its durability, chrome is especially suitable for components exposed to friction, offering both visual appeal and long-lasting resilience. 

E-coat guarantees a uniform and consistent finish, even on intricate geometries, unlike certain liquid paints. Despite its thin application, typically ranging between 20-30 microns, this coating provides effective protection against corrosion, scratches, and chemicals. The thin yet robust nature of e-coat makes it a reliable choice for achieving both an even surface finish and durable protection on complex structures. 

Electroless nickel (EN) plating a chemical deposition process, creates a thin and even layer of nickel alloy on the casting’s surface. This method offers exceptional corrosion resistance, surpassing the base material’s inherent resistance in diverse chemical environments. The deposited nickel layer enhances wear resistance, reducing friction and abrasion, especially vital for parts under high contact stress. Overall, EN plating improves casting durability and ensures reliable performance in challenging conditions. 

Extrude hone is a post-casting process that significantly improves both surface topography and internal properties, indirectly enhancing the final surface quality. This method reduces surface roughness, creating a smoother finish, while also removing burrs and sharp edges to diminish stress concentrations and potential failure points. The refined surface achieved through extrude hone not only enhances aesthetics but also improves functional aspects such as fluid flow and heat transfer, making it a valuable step in optimizing both visual and operational characteristics of cast components.

This conversion coating process involves the transformation of the part’s surface into an iron nitride compound, resulting in an exceptionally hard surface finish. Key characteristics of this coated surface involve outstanding wear resistance, enhanced fatigue resistance, corrosion resistance, and other valuable attributes.

Widely respected for enhancing cast metal surfaces, hard coat anodizing excels in resisting abrasion and friction, making it ideal for high-stress components. This treatment significantly enhances protection against rust, chemicals, and harsh environments compared to the base metal. The resulting oxide layer also provides effective electrical insulation, making hard coat anodizing a preferred solution for durable and functional cast metal parts. 

Hot Isostatic Pressing (HIP) is a post-casting treatment designed to enhance the internal structure and mechanical properties of castings, which can indirectly influence surface quality in certain cases. In the HIP process, the casting undergoes simultaneous high pressure and elevated temperature within a specialized chamber. The pressure aids in closing internal microscopic voids or porosity, resulting in increased strength, fatigue resistance, and ductility due to a denser and more uniform internal structure. HIPing can further assist in stabilizing casting dimensions and reducing distortion, ensuring greater precision in the final product. 

Renowned for its flexibility, liquid paints offer the broadest spectrum of colors, metallic finishes, and textures, enabling unparalleled customization and visual appeal. This versatility makes liquid paint a favored option, allowing for the creation of diverse and aesthetically pleasing finishes across a wide range of applications. 

Media blasted finishes include a range of techniques involving shot, girt, sand, and/or glass bead to enhance the surface quality of castings. This post-casting surface finish technique uses a pressurized stream of abrasive media to meticulously clean, modify, and elevate the overall surface characteristics of the casting. The use of various media blasting materials allows for customization, providing flexibility in achieving desired texture and appearance. The process is applied for surface improvement beyond 125 μin (Ra) to ensure a refined and polished outcome.

Nickel plating, achieved through electroplating, involves depositing a thin layer of nickel onto the casting’s surface using an electric current. This provides exceptional corrosion resistance surpassing the inherent resistance of the base material. The nickel layer further showcases superior wear resistance, effectively minimizing friction and abrasion. 

In automotive applications, the term commonly refers to the mold material rather than the final finish of the cast metal part. Recognized for its strength, flexibility, and chemical resistance, this material ensures good dimensional stability during the casting process.

This finish is a form of conversion coating that interacts with the base alloy, revealing distinctive features such as corrosion resistance, lubricity, adhesion, and more. 

These two pre-treatment processes are typically used simultaneously to prepare the surface of investment castings for additional finishes to improve corrosion resistance. Pickling effectively eliminates contaminants, oxides, and weld scale from the casting surface to improve adhesion for any subsequent finishes. Passivation is utilized to increase the natural protective oxide layer on the metal’s surface, bolstering the metal’s resistance to corrosion and pitting. These pre-treatment steps collectively contribute to the overall quality and longevity of the castings,

Powder coating stands as a widely used and adaptable surface treatment, delivering a robust, protective, and visually appealing finish to castings. Offering notable resistance against corrosion, scratches, chemicals, and UV rays, powder coating is well-suited for parts subjected to harsh environmental conditions or frequent wear and tear. It’s wide range of colors and textures further enables diverse customization, catering to both functional requirements and aesthetic preferences. 

For additional surface improvement, a tumbling machine with a vibrating bowl filled with media and compound is used to deburr, polish, clean, and refine the surface of the casting. The vibrating bowl facilitates a thorough treatment, ensuring an even and consistent improvement to the surface quality while contributing to the overall aesthetic appeal and function of the cast component.