Zinc (symbol: Zn) is a utility metal in the manufacturing industry due to its favorable material properties such as good corrosion resistance, electrochemical performance and biocompatibility.
In this article, we discuss the properties of zinc and its alloys as CNC machining materials. It also covers the properties of zinc, different types of zinc alloys, various zinc machining processes, and an in-depth analysis of the machinability of zinc alloys.
Properties and characteristics of zinc
In its pure form, zinc metal is a shiny, brittle gray chemical element with limited industrial applications. As it is a pure metal, it is useful for galvanizing other metals such as iron to improve corrosion resistance.
However, zinc alloys are incredibly useful and have a number of desirable properties that put them at the top of the list of most common machining materials. Zinc alloys have good tensile strength, corrosion resistance and high ductility. Furthermore, they are environmentally friendly due to their recyclability. Furthermore, zinc is a cheap metal with abundant deposits.
Types of zinc alloys for machining
Each zinc alloy offers a specific combination of material properties. In this section we will discuss some popular zinc alloys. Some of zinc's most important alloying elements are copper, tin, magnesium and aluminum.
Zamac 3
The Zamak family of zinc alloys includes the most common zinc alloy types, with Zamak 3 being the standard alloy. Zamak 3 contains 96% high purity zinc and 4% aluminum. Additionally, certain variants of Zamak 3 may also contain traces of copper, magnesium and iron.
It offers a combination of ductility, strength, finish and dimensional stability. These properties, complemented by its melting point of 384°C, make it very easy to pour. Therefore, casting is probably its most popular industrial use.
In addition, Zamak 3 also has the corrosion resistance and electrical conductivity characteristic of zinc alloys.
Zamac 5
Zamak 5 is another zinc alloy from the Zamak group. Its composition contains ~1% copper, in addition to the 4% aluminum that is common in all zamak varieties.
This copper additive gives strength and hardness to the zinc alloy. However, these properties come at the expense of reduced ductility and dimensional accuracy. Overall, however, Zamak 5 is an excellent zinc alloy with good castability and machinability.
ZA8
ZA 8 is a zinc-aluminum alloy with 8.4% aluminum content. Its main properties include high strength and hardness, as well as creep resistance, a unique property among zinc alloys. It also supports various surface finishing processes, being a common choice in the manufacture of pieces for decorative purposes.
One of its main advantages is its compatibility with pressure casting processes, including hot chamber pressure casting. Its fluidity allows you to merge complex geometries with fine structures.
EZAC
EZAC is an innovative zinc alloy with aluminum and copper content. It has remarkable strength, hardness and creep resistance and is often referred to as the best among common zinc alloys.
Its melting point and fluidity make it particularly suitable for pressure casting applications. Due to its low melting point, it is compatible with hot chamber pressure casting, expanding its application potential in various sectors.
ZA 27
ZA 27 is another high aluminum zinc alloy, with approximately 28% aluminum and 2.5% copper. It is light, strong, hard and has good creep properties. Furthermore, it has a relatively high melting point among zinc alloys, making it suitable for cold chamber pressure casting.
Tombac
Tombak is mainly a brass alloy with a zinc content of around 5-20%. It is known for its low cost, malleability and shiny appearance. Depending on the composition of other alloying elements (tin, copper, lead, etc.), it can take on different colors.
Due to its golden appearance, it is a popular choice for making products with decorative value such as medals, decorative pieces and buttons.
Machinability of zinc alloys
Zinc alloys are generally easy to machine and do not cause many problems. However, as with any material, they have specific behaviors that require specific considerations and adjustments on the part of the machine operator to achieve optimal results. Some important aspects of zinc machinability are explained below.
Rubbery behavior
Zinc heats up quickly during machining. Thermal softening associated with increased temperature can lead to a “rubbery” of the material. This means that the zinc alloy tends to stick to the cutting edge of the tool, increasing tool wear and degrading cutting performance.
Low melting point
A similar temperature-related issue is that thermal softening can sometimes prevent the machine operator from adopting an aggressive machining approach. For example, very high feeds may not be possible due to excessive shear in the material.
fragility
Although ductile in nature, the brittle behavior of some aluminum alloys can cause chipping problems.
Security risks
Although zinc processing produces short, manageable chips, fine machining or grinding processes can produce dust that should not be inhaled. Therefore, it is recommended to ensure adequate ventilation when carrying out such operations.
Various Processing Methods for Zinc Alloys
Zinc alloys are a common material in machine shops. They support a variety of editing methods, some of which are briefly explained below.
Grind
Milling is the most widely used machining process for machining zinc. With advanced features such as 5-axis CNC machining, it is a world-class process for producing irregular prismatic shapes.
Turn
Turning is useful when machining cylindrical objects on lathes. Modern lathes offer high-precision multi-axis capabilities, including turning-milling operations. Zinc turning, like milling, is simple, but can present some problems with the softening (rubbery) of the material.
Stick
Drilling is the standard machining method for making holes. Drills with different length-radius ratios and spiral-shaped grooves are used. Drilling in zinc alloy is best performed using flood cooling and sharp bits to minimize heat build-up in the cutting zone. Otherwise, zinc alloys can be machined with generous cutting parameters, allowing high material removal rates.
cast
Die casting is a highly efficient and popular manufacturing process for producing zinc components with complicated shapes and tight tolerances. Unlike traditional machining processes, pressure casting uses molds or dies to produce the desired part.
Electrical erosion (EDM)
EDM is not a classic machining process, but it is still a very useful and common method for producing prismatic parts in machine shops. Zinc's good electrical conductivity makes it a suitable material for erosion.
Surface finishing options for zinc parts
Zinc alloys are compatible with a variety of surface finishing processes, including:
- Electroplating : Zinc alloys support electroplating with materials such as nickel and cobalt to achieve specific surface finishes, properties and improved corrosion resistance.
- Chromate Conversion Coating : Chrome plating improves the appearance and corrosion resistance of zinc alloys. Furthermore, it is available in different colors.
- Powder Coating : Powder coating gives the surface a rougher appearance and makes it more resistant to abrasive influences such as chips and scratches.
- Anodizing : Anodizing creates a thin protective oxide layer on the surface of the zinc alloy, which improves corrosion resistance.
- Painting : Zinc alloys are color compatible, allowing users to get any color they want.
Tips and tricks for processing zinc alloys
In the previous sections, we found that the machinability of zinc alloys is high. They are not as difficult to work with as other materials, such as titanium machining. However, there are also some specialized solutions to optimize zinc alloy machining processes.
Choose machinable zinc alloys
This is evident, but it is also easily forgotten. If you have a choice between several zinc alloys, choose the one that is easiest for your machinists to handle, such as Zamak 3 or Zamak 5. This will pay off in terms of dimensional accuracy and time savings.
Sharp cutting tools
To combat the rubberiness of zinc alloys and minimize tool wear, sharper cutting tools are preferred. They apply concentrated cutting forces and minimize the plowing effect. This creates short chips that fly away instead of sticking to the tool.
Be generous with the soda
Thermal softening is a major problem in zinc processing. Therefore, adequate coolant supply helps minimize friction and keep temperatures under control, which in turn improves surface finish and chip production. Also, you should prefer water-based soft drinks.
Medium to high cutting speeds
If the zinc alloy heats up quickly, increase the cutting speed slightly to reduce cutting temperatures. This shortens the contact time between the tool and the material and leads to greater heat dissipation through the chips.
Carbide/HSS Tools
Zinc alloys may cause excessive tool wear or thermal distortion. Therefore, carbide is a good choice because of its good wear resistance and thermal stability. For lighter work, HSS also works great with zinc alloys.
Zinc Parts Applications
Now that we understand the machinability aspects of zinc alloys, it is time to discuss some of the applications of zinc machined parts. Below is a short list of zinc alloy parts.
- Automotive components : Automakers use zinc alloys to produce components for engine blocks, supports, decorative items, etc.
- Electronic housing : Due to their good electrical and thermal conductivity, zinc alloys are ideal for producing housings and heat sinks for electronic devices.
- Medical instruments : The biocompatibility of zinc alloys makes them a favorable material for some medical instruments.
- Hardware : Zinc alloys are a popular choice for fasteners such as screws, nuts and bolts for low voltage applications such as appliances and fixtures. They provide sufficient strength, corrosion resistance and aesthetic surface options for such applications.
- Consumer Goods : Zinc alloys are also a popular choice for consumer products such as zippers, hinges and jewelry due to their low cost and decorative appearance.
Start of zinc processing at WayKen
Conclusions
Zinc alloys are undoubtedly one of the most important groups of materials in the machining industry and are available in different grades, processes and applications. Their advantageous properties and high machinability make them perfect for use in machine shops.
