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Overview of Zinc
Zinc is a robust, non-magnetic metallic element commonly alloyed with copper, magnesium, tin, and aluminum. Zinc’s ability to integrate with other metals gives it endless uses in many applications like infrastructure, health, and manufacturing. It is a chemically stable metal with enhanced corrosion resistance, a relatively low melting point of 380°C to 420°C, ductility, and malleability. Zinc is significantly safe and essential for biological systems and forms a protective oxide and carbonate layer when exposed to air, offering additional corrosion resistance.
Common Zinc Alloys for Machining
Every zinc alloy comprises a particular combination of material properties. We will explore some of the widely used zinc alloys:
Zamak 3
The Zamak 3 is a standard zinc alloy grade in the extensive Zamak family of zinc alloys. Its composition includes 96% pure zinc and 4% aluminum. Besides, some variants of Zamak 3 may possess trace amounts of iron, copper, and magnesium.
Zamak 3 provides a unique combination of dimensional stability, strength, ductility, and finishing. This list of characteristics, with its 384°C melting point, makes this zinc grade highly castable. Hence, most industries embrace casting techniques when making zinc parts. Zamak 3 offers excellent electrical conductivity and corrosion resistance, making it an ideal material for intricate electronics and automotive components.
Zamak 5
Zamak 5 is another standard type of zinc alloy within the Zamak family. It comprises 1 % copper, 4% aluminum, and pure zinc. The copper element offers hardness and strength to the Zamak 5 alloy. However, these characteristics are available at the expense of dimensional accuracy and ductility. Nevertheless, this zinc alloy offers other benefits, such as good machinability and castability, allowing manufacturers to achieve complex designs. More importantly, Zamak 5 is ideal for applications like hardware components and consumer products that require wear resistance and durability.
ZA 27
This is a high-aluminum zinc alloy grade with about 2.5% copper and 28% aluminum. It exhibits strength, hardness, low weight, and good creep properties. ZA 27 is one of the ZA alloys with high aluminum content and an ideal option for cold chamber die casting. Industrial machinery and equipment manufacturers commonly use ZA 27 because it can handle high-stress environments.
ZA 8
This is a zinc-aluminum alloy that contains 8.4% aluminum. It is famous for combining unique zinc alloy grade properties, including creep strength, hardness, and high strength-to-weight ratio. Although it is a standard zinc alloy for creating lightweight, durable automotive parts and machinery components, it is suitable for decorative components due to its compatibility with several surface finishes.
ZA 8 is compatible with die-casting techniques, including hot chamber die-casting. Its fluidity is a primary advantage that enables the casting of complex geometries with thin features.
ZA 22
This is another zinc-aluminum alloy known for its machinability, hardness, and strength. Due to its low density, Automotive and aerospace parts manufacturers utilize this zinc alloy for lightweight applications.
ACuZinc
It is a zinc-copper alloy offering good corrosion resistance and machinability. AcuZinc is an ideal option for architectural and marine applications requiring aesthetic appeal and high resistance to saltwater corrosion.
Tombak
Tombak is a brass alloy containing 5 to 20 % zinc element. It is commonly used because of its shiny appearance, malleability, and low cost. However, Tombak is available in different colors/colorations based on the composition of its alloying elements, such as lead, tin, copper, etc. Its gold appearance makes it an ideal choice for creating products of ornamental value, like medals, buttons, and decorative pieces.
EZAC
EZAC is a versatile grade of zinc alloy with copper and aluminum content. It is regarded as one of the best and most widely used zinc alloy grades because it exhibits remarkable strength, creep performance, and hardness. It is compatible with die-casting applications due to its fluidity and low melting point. Moreover, EZAC has increased potential applications in different industries compared to other zinc alloys because of its compatibility with hot chamber die-casting. It allows the creation of complex components with tight tolerances.
How Machinable Are Zinc Alloys?
Machinability is a critical factor in machining Zinc alloys because it can impact the efficiency and quality of the process. Although machinists are less likely to experience pitfalls when machining zinc alloys, understanding the machinability properties of zinc alloys would help achieve optimal machining outcomes. We will explore the core aspects of zinc machinability in this section:
Low Melting Point
Zinc’s low melting point results in temperature-related problems that hinder machinists from employing an aggressive machining approach. Very high feeds, for instance, may be inappropriate since it may result in excessive material shearing and heat buildup. As a result, choose appropriate cutting parameters and CNC tools to mitigate gummy behaviors and ensure smooth machining operation.
Gummy Behavior
Zinc alloys heat up faster during machining, resulting in thermal softening, which could cause complications. When the zinc material becomes gummy, it sticks to the cutting tool’s edges, causing rapid wear and performance deterioration.
Safety Hazards
Grinding or fine-machining zinc alloys can be dangerous even though they produce short, breakable chips. It may produce toxic dust that must not be inhaled. Therefore, machining experts recommend performing such operations in a properly ventilated workshop and using personal protective equipment to reduce exposure to airborne contaminants. More so, proper machining waste handling and disposal would help to ensure workshop safety and prevent environmental contamination.
Brittleness
Brittleness is a prominent factor in zinc machining, irrespective of whether the material exhibits good machinability. The brittleness of high-aluminum zinc alloys can lead to chipping issues regardless of their inherently ductile nature. High machining speeds and feed rates cause zinc alloys to be brittle. Hence, choosing tools with suitable edge geometry and using compatible feed and speed rates would be best to avoid material fracturing and rapid tool wear.
Different Zinc Alloy Machining Techniques
Machine shops adopt various machining processes to cut zinc alloys into different shapes and add desired features. Below are some of the standard zinc machining processes:
Turning
Turning is a standard process for machining cylindrical-shaped zinc workpieces on lathe machines. Modern CNC lathes provide highly precise and accurate multi-axis capabilities, including turn-milling operations.
Milling
This is a widely recognized zinc machining technique with advanced capabilities like 5-axis CNC milling. Milling is an innovative process machinists use to create various zinc parts with irregular, prismatic structures.
Drilling
Drilling is a standard process that uses drill bits of various length-to-radius with helical flutes to create holes of specific depth and diameter in a workpiece. Machinists employ sharpened drill bits and flood cooling when drilling zinc alloys to mitigate heat accumulation in the cutting area.
Electro-Discharge Machining (EDM)
EDM is an advanced process that uses electrical discharges to produce prismatic components with precision. This standard and result-oriented technology is compatible with zinc material due to its good electrical conductivity.
Die Casting
It is a popular and incredibly efficient method for producing zinc items with intricate geometries and tight tolerances. Die casting is unlike conventional machining methods since it utilizes dies or molds to produce zinc parts with desired features.
Industrial Applications of Zinc Parts
Zinc parts apply to different industries due to the unique combination of properties they provide. Below are some of the applications of zinc-machined parts:
- Consumer Goods: Due to their low cost and aesthetic appearance, zinc alloys are widely used to create consumer goods like jewelry, zippers, musical instruments, and hinges.
- Automotive: Manufacturers in the automotive industry use different grades of zinc alloy to make different ornamental fittings, engine blocks, brackets, carburetor bodies, fuel systems, etc.
- Medical Devices and Instruments: Since zinc alloys exhibit exceptional biocompatibility, medical device manufacturers use these materials to create parts like diagnostic device components, equipment housings, and surgical tools.
- Electronics Enclosures: Zinc alloys’ good electrical and thermal conductivity makes them a perfect choice for producing heat sinks and enclosures of electronic devices.
- Hardware: Special combination of zinc properties, such as good corrosion resistance, ample strength, and aesthetic appeal, make zinc alloys an excellent option for fasteners like bolts, screws, and nuts used in low-impact applications like fittings and household appliances.
- Building and Architecture: In this sector, the durability, corrosion resistance, and malleability of zinc alloys make them suitable for door handles, architectural metalwork, and lock fittings.
Compatible Surface Finishes for Machined Zinc Parts
Zinc alloys accept different surface finishing treatments, which improve their functionality and aesthetic appeal. Here are some of the standard surface finish options for zinc parts:
- Anodizing: It develops a thin, protective oxide layer on the zinc part’s surface to make it more appealing and corrosion-resistant.
- Powder Coating: Powder coating creates a protective layer on zinc alloys, making them resistant to abrasions such as scratching and chipping and providing decorative effects with various colors.
- Electroplating: Electroplating enhances the surface of zinc parts by plating them with materials like cobalt and nickel to achieve desired surface roughness properties and improve corrosion resistance.
- Painting: It allows the customization and aesthetic enhancement of different zinc alloy parts with the desired color.
- Chromate Conversion Coating: This surface finish provides a range of colors and enhances zinc components’ corrosion resistance and aesthetic properties.
Best Practices for Successful Zinc Alloy Machining
Zinc alloys exhibit certain behaviors that require meticulous consideration and modifications, as with any materials, to achieve the best outcomes. Here are the machining parameters to consider for effective zinc machining:
Choose Machinable Zinc Alloys
Zinc material selection is one of the critical and first steps to achieving effective machining. It is crucial to choose the specific alloy because it determines the machining behaviors, mechanical properties, and surface finish of the final part.
Although Zamak 3 or Zamak 5 are the typical zinc alloys machinists use, it would be best to choose a material based on the requirements of the intended application, such as thermal/electrical conductivity, corrosion resistance, dimensional accuracy, biocompatibility or castability.
Employ Appropriate Cutting Fluids
Since complications may arise due to heat buildup when machining zinc alloys, it is essential to implement effective cooling and lubrication for seamless machining operations. Generous use of cutting fluid helps to mitigate friction and maintain optimal temperatures during the process, ensuring improved tool life and superior surface finish of machined zinc parts. AT Machining experts recommend using water-based coolants in zinc machining to keep temperatures under control.
Choice of a Surface Finishing
Surface finishing of zinc parts is essential in the early stages of development. There are various surface finishing options, ranging from powder coating to anodizing and electroplating. Choosing a finish that meets the demands of the intended working environment would be best.
Tooling
The choice of a cutting tool is pivotal to achieving smooth machining operations. Experts recommend using carbide, high-speed steel, or coated tools with sharp edges to cut zinc alloys due to their high resistance to wear and ability to achieve a smooth surface. Sharp cutting tools create fine chips and keep the cutting zone clean. You should maintain moderate-to-high cutting speed for higher heat dissipation and chip formation.
Conclusion
Zinc Machining offers a cost advantage and provides precise components for different applications. It offers durable and precise tolerance parts with desired material properties. Familiarize yourself with the various grades of zinc alloys, key considerations, and compatible surface finish to make informed decisions that help elevate your zinc machining project!
AT-Machining is a renowned CNC zinc machining expert with state-of-the-art CNC machining facilities and a team of experienced professionals. We are ISO 900:2015 certified; trust us to deliver quality and precise custom zinc parts with intricate shapes that meet strict specifications and standards. Our certified teams can guide you through the complexities of zinc machining projects; contact us now to achieve the best results!
