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Zinc is one of the most versatile metals in the manufacturing industry. You’ll often find it serving as a protective coating on steel and other metals, thanks to its natural ability to combat rust.
Generally, zinc alloys are shaped using die casting to create parts. However, machining is still essential for precision parts and for creating intricate geometries that casting alone cannot provide.
This article will walk you through zinc’s properties, how it performs during machining, the best alloys for the job, and best practices in zinc machining.
An Overview of Zinc Properties
Zinc is a transition metal with the atomic number 30. It has a bluish-white color and a moderate density (7.14 g/cm³) that puts it between metals like aluminum and steel.
Pure zinc is brittle at room temperature, but becomes ductile at slightly higher temperatures, at about 120°C. It also has a low melting point (419.5°C), which makes it easy to cast.
Some properties that make zinc an industrial choice:
Corrosion resistance
Zinc forms a protective oxide layer (called patina) that shields the underlying metal from rust. This is also a reason why it’s used for galvanizing ferrous metals like steel, which are more susceptible to corrosion.
Affordability
Zinc is cheaper than many other common metals such as aluminum, steel, and copper. This lower cost makes it an attractive choice for product applications.
Alloying Properties
Zinc naturally brings great properties to the table, which is why it’s a common alloying element. For instance, adding zinc to aluminum alloys helps improve strength and grain size. In some cases, it also improves the heat resistance of the alloy.
Machining Zinc: Processes and Application
Zinc, due to its low melting point and fluidity, mostly undergoes die-casting to make parts. However, machining is often required to achieve tighter tolerances in casted products, refine features, or create intricate geometries out of zinc ingot.
Zinc Milling
Milling is a versatile machining process that removes material from zinc workpieces by feeding a block of metal into a rotating cutter.
Zinc milling is used to produce brackets, enclosures, and housings that require flat surfaces or precise grooves. It is also used to prepare parts for surface finishing or assembly.
Zinc Turning
Turning involves rotating a zinc workpiece on a lathe while a cutting tool removes material to shape the part. This method is used for creating cylindrical or conical components (bushings, spacers, shafts) and refining diameters.
Best Alloys of Zinc for Machining
Pure zinc is primarily used in galvanizing and applications requiring high conductivity and is less common for machining. However, zinc alloys offer a balance of strength, corrosion resistance, and machinability, which makes them ideal for precision manufacturing.
Some commercially known zinc alloys are:
Zamak Series
Zamak family is one of the commercially known families of zinc alloys. Among them, two grades are very common:
- Zamak 3 is the standard grade, with 96% pure zinc and 4% aluminum, having excellent dimensional stability and corrosion resistance. It is highly castable, considering the low melting temperature; so a common choice in industrial settings.
- Zamak 5 has a similar composition, with an added 1% copper. That adds more strength and hardness, but the ductility is compromised. Still, it offers great machinability and castability.
Tombak
Tombak is a brass-like alloy with 5–20% zinc content. It is valued for its malleability, corrosion resistance, and shiny appearance (the color is subject to alloying elements). It’s common for aesthetic applications including medals, buttons, and ornamental pieces.
EZAC
EZAC is a high-performance zinc alloy with aluminum and copper. It provides exceptional strength, hardness, and creep resistance. It’s best suited for die casting in industrial components subjected to high stress.
ZA27
It’s one of the strongest zinc alloys, thanks to a higher aluminum content (28%). Due to its lightweight nature and good creep properties, it’s suitable for heavy-duty applications like automotive components and structural parts.
Machining Challenges with Zinc
Zinc’s softness may suggest it’s easy to machine. That’s true to some extent but there’s another set of unique challenges that come with zinc machining.
Gummy Nature
Zinc’s low melting point (419.5°C) is one of the biggest machining challenges. During cutting, the heat generated can soften the material, causing it to become gummy and stick to the cutting tool. This leads to tool wear, reduced precision, and surface finish issues.
Brittleness
Pure zinc is brittle but most of its alloys are known to have a ductile nature. In alloys with higher aluminum content, brittleness can re-emerge, especially in cast forms, leading to chipping or cracking during machining.
Safety Challenges
Zinc dust produced during machining is flammable and can lead to respiratory irritation if inhaled. Moreover, when zinc overheats, it can oxidize, forming zinc oxide. Inhalation of zinc oxide fumes can cause a condition known as metal fume fever.
Best Practices for Best Practices for Zinc Machining
Considering the properties and challenges associated with machining zinc, we have compiled a list of practices to help you navigate this process efficiently.
Grade Choices
The right choice of the alloy is the key. Experts favor Zamak 3 and Zamak 5 for casting and machining due to their ease of handling and excellent dimensional stability.
Cutting Tools and Parameters
Zinc is often compared to aluminum 6061 as a reference for machining parameters. For milling zinc, peripheral milling with a standard HSS end mill is effective. Recommended cutting speeds are about 50% of those for aluminum, with feed rates at 93% of aluminum’s typical rates.
When slotting with an HSS end mill, reduce speeds to 68% of aluminum’s rates and use feed rates at 34% of aluminum’s typical rates.
Choice of Coolants
Zinc’s low melting point requires effective cooling to avoid overheating and deformation. Both soluble and water-based coolants can be used. Water-based coolants are particularly effective, as they provide excellent thermal management.
Safety Gear
Due to zinc dust and fumes, proper personal protective equipment (PPE) – including gloves, goggles, and respiratory masks – is necessary. The workshop needs to have adequate ventilation to prevent the inhalation of zinc oxide fumes.
Surface Finishing Choices for Zinc
Zinc may be corrosion-resistant, but additional surface finishing is often necessary to enhance its appearance, improve durability, or prepare it for specific applications.
Painting
Painting is colorizing the surface. It provides additional corrosion protection and allows for aesthetic customization. The practice is used for architectural elements, consumer goods, and automotive parts.
Electroplating
Electroplating deposits a thin layer of another metal (like nickel, chromium, or gold) onto the zinc surface using an electric current. The zinc component is immersed in a solution containing metal ions, which bond to the zinc during the process.
Electroplating proves surface hardness, wear resistance, and electrical conductivity. Like other finishing options, it’s used for decorative finishes in electronics, automotive, and industrial components.
Chromate Conversion Coating
Chromate conversion (alodine) coating is done by immersing zinc components into a chemical bath that forms a conversion layer on the surface. The coating serves two purposes: inhibits corrosion and serves as a primer for the adhesion of paints.
Choose Richconn for CNC Zinc Machining Needs
If you need assistance with machining zinc or other metals, Rich Conn is here to help. We offer a comprehensive range of Metal CNC Machining services, including milling, turning, and wire EDM, to meet your precision manufacturing needs.
Whether you’re in the concept phase or exploring the best materials for your product or prototype, our expert engineering team can guide you in selecting the right materials.Turn your ideas into market-ready products with Richconn. Contact us today to learn more about our services or to get a quote for your project!
