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Die Casting: Materials, Designs and Processes

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Introduction

Information regarding die casting and its use with a list of die casting manufacturers

You will learn:

  • What is die casting?
  • The types of metal used in die casting
  • Processes and how die castings are produced
  • Die casting: hot and cold
  • Die casting design geometry
  • And much more.

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Die Cast Parts

Chapter One – What is Die Casting?

Die casting is a high pressure metal casting process that forces molten metal into a mold. It produces dimensionally accurate precision metal parts with a high quality finish. Its ability to produce detailed parts makes it perfect for the mass production of products. Die castings are made from non-ferrous metals such as zinc, copper, aluminum, magnesium, lead, pewter, and tin.

Zinc Die Casting

The two methods of die casting are hot or cold chambers. The process that is used depends on the type of metal and the part. The cold chamber method is used with metals that have a high melting point such as alloys of aluminum, brass, or copper. Hot chamber die casting is limited to metals that won’t dissolve when heated such as zinc, lead, and magnesium alloys.

The die casting process is efficient and cost effective that offers a broad range of shapes and components. Parts produced have a long life and can be produced to be visually appealing giving designers significant advantages and benefits.

The high speed of die casting produces complex shapes with close tolerances requiring no after production processing. There is no need for additional tooling or shaping. Final parts are heat resistant with high tensile strength.

Depending on the feature and its size, tolerances of +/-.002” can be held in aluminum, with tolerances of +/-.0005” in zinc.

Die Castings

Die Casting vs Forging

Die casting and forging are two distinct metal working processes with significant differences.

Die casting involves forcing molten metal into a mold cavity under high pressure, resulting in intricate and detailed shapes with excellent dimensional accuracy. It is ideal for producing complex, thin-walled parts with a smooth surface finish, making it suitable for applications like automotive components and consumer electronics.

Forging involves shaping metal by applying compressive forces through hammering or pressing at high temperatures. This method enhances the material's strength and grain structure, yielding robust and durable parts often used in heavy machinery, aerospace, and construction equipment. While die casting offers precision and complexity, forging excels in strength and structural integrity.

Chapter Two – Metals Used in Die Casting

Choosing the right metal for die casting is a crucial factor that directly impacts the performance, durability, and cost-effectiveness of the final product. The type of metal selected depends on the requirements of an application, weight, corrosion resistance, and necessary mechanical properties.

aluminum die casting is widely used for automotive and truck parts thanks to its excellent strength-to-weight ratio, lightweight characteristics, and natural corrosion resistance. Medical instruments and surgical tools are made of stainless steel for its biocompatibility, hygienic properties, and exceptional resistance to corrosion and oxidation.

Metals and alloys used for die casting must be able to maintain their properties and characteristics during and after the melting process.

  • Aluminum
  • Zinc
  • Brass
  • Bronze
  • Tin
  • Lead
  • Magnesium
  • Silicon tombac
  • Stainless steel
  • Carbon steel

Zinc

Zinc is an adaptable and underutilized die casting metal that has a superior balance of strength, ductility, and finishing options. It is 2.3 times heavier than aluminum and is frequently chosen for small, intricate die-cast parts or medium-volume production where superior surface finish and thin-wall castability are essential. Zinc die casting produces dimensionally accurate complex geometries, making it the go-to material for the electronics, automotive, and hardware industries.

The different variants of Zinc alloys, such as ZAMAK, possess high ductility, remarkable impact strength, and can be easily plated, lending themselves to decorative as well as functional applications. Tight tolerances and excellent repeatability can be achieved in high-volume manufacturing, while zinc’s natural lubricity and strong bearing properties can eliminate the need for bushings or additional wear inserts—adding value and reducing assembly complexity in components such as gears, housings, and connectors. Additionally, the low melting temperature of zinc drastically minimizes die wear, which translates to longer tool life and lower replacement costs, making zinc alloys extremely cost-effective for large production runs.

The outstanding fluidity of zinc alloys enables manufacturers to cast fine details, frictionless moving parts, and thin-walled components (down to 0.025 inches/0.65 mm). This provides significant advantages in miniaturized consumer electronics, medical device housings, and intricate lock or fastening systems. The reduced thermal shock due to lower casting temperatures further preserves die integrity, lowering maintenance intervals and improving productivity for die cast manufacturers.

Disadvantages of Zinc

Zinc has a relatively low melting point, approximately 419°C (786°F), compared to other metals used in die casting, such as aluminum and magnesium. This limitation can restrict the use of zinc die casting in high-temperature applications.

While zinc die castings can achieve good surface finishes, they may not be as corrosion-resistant as other materials like aluminum or stainless steel. Proper post-processing and coatings may be required to enhance corrosion resistance

Zinc

Aluminum

Aluminum die casting is the industry standard for high-volume production components where lightweight, superior strength, corrosion resistance, and outstanding thermal conductivity are required. Aluminum alloys such as A380 and ADC12 are especially valued for their ability to form complex part shapes with thin walls, making them optimal for the automotive, aerospace, and electronics sectors. This leads to significant weight savings—crucial for applications where improving energy efficiency and reducing emissions (such as electric vehicle parts, transmission housings, or consumer electronics enclosures) is key.

The use of Aluminum alloys for die casting is due to its high strength-to-weight ratio, ensuring die castings can withstand demanding loads while minimizing overall component mass. Their excellent thermal and electrical conductivity make aluminum castings ideal for heat sinks, LED housings, chassis, and battery enclosures in power management and telecommunications. Furthermore, aluminum’s natural oxide film provides a layer of corrosion resistance, extending service life for both indoor and outdoor die cast components. The alloy’s malleability and machinability also deliver cost and time advantages in downstream processes.

Disadvantages of Aluminum

Despite its many benefits, aluminum presents some manufacturing challenges. The relatively high shrinkage rate during solidification can cause dimensional variation, necessitating secondary machining or close process control to achieve tight tolerances in complex or multi-cavity molds. On the material side, certain aluminum alloys can be more brittle than zinc or magnesium, which could increase the risk of cracking or fracturing in applications with frequent impact or heavy mechanical loads. Aluminum can also be more prone to porosity if the die casting process does not adequately address gas entrapment or the use of optimal die temperatures and venting.

Aluminum

Brass

Brass is prized in the die casting industry for its robust corrosion resistance, electrical conductivity, and pleasing gold-like appearance, making it a popular choice for decorative hardware, plumbing fittings, and electrical connectors. The alloy’s resistance to rust and tarnishing makes brass ideal for exterior or high-humidity environments where longevity and reliability are critical, such as marine components, valves, and architectural fixtures.

Beyond corrosion protection, brass’s high thermal conductivity is advantageous for manufacturing components requiring rapid heat transfer or dissipation, found frequently in HVAC systems, electrical contacts, and specialty lighting applications. Brass die castings also offer impressive strength and wear resistance, enabling use in lock bodies, mechanical gears, and other high-cycle parts that require both durability and dimensional precision.

Disadvantages

Brass die casting presents unique process challenges. The melting and casting of brass necessitate rigorous temperature control and close monitoring, which can be labor-intensive and increase operational complexity. Improper management of alloys and casting lubricants can result in casting defects such as scaling or burning. Regular issues like porosity (microscopic holes within the metal) and die adhesion demand the expertise of experienced foundry professionals to mitigate. Additionally, brass has a lower melting point than the other alloys, limiting its use for high-temperature or high-stress environments, where deformation or material fatigue would compromise part performance.

For applications with even more demanding properties—such as ultra-high thermal conductivity or special mechanical attributes—alternatives like bronze or specialized steel alloys may be evaluated by engineers and product designers.

Brass

An essential part of a successful die casting process is the selection of the right material for an application. Die casting alloys offer a wide latitude in regard to design and cost factors. Manufacturers work closely with their clients to provide guidance regarding the strength, durability, thermal performance, and corrosion resistance of various alloys. Although cost may be a guiding factor regarding material selection, the requirements of an application may necessitate adjustments. Die casting manufacturers and material experts ensure an optimal balance between performance, endurance, machinability, and the manufacturability of various alloys.

In addition, each type of metal alloy has a processing cost with some requiring secondary finishing while others reduce or eliminate such processing. The size of the final product and the required volume are other cost factors.

Die Cast Parts

Chapter Three – Die Casting – Hot and Cold

The most common types of die casting are hot and cold. The difference between them is that hot chamber die casting heats metals in the casting machine while cold chamber heats metal in a furnace and transfers the molten metal to the casting machine. The process produces complex shapes with close tolerances, heat resistance, and high tensile strength with little need for additional tooling and shaping.

Hot Chamber Die Casting Process

Hot chamber die casting, sometimes referred to as gooseneck die casting, relies on alloys with relatively low melting temperatures. Common materials suitable for this process include zinc, magnesium, and certain lead or tin-based alloys. The die is composed of two primary sections – a stationary (fixed) die half and a movable (ejector) die half. The fixed half is mounted to a stationary platen and is aligned precisely with the gooseneck, which delivers the molten metal into the die cavity. The movable half acts as the ejection system that allows the finished part to be released from the mold after solidification.

Within this process, the molten alloy is maintained in an open holding pot connected to a combustion source or furnace. This setup ensures a constant supply of molten metal to the gooseneck. When the plunger is lifted, the metal flows into the shot chamber. As the plunger moves down, it forces the molten metal up through the gooseneck and into the closed die cavity, filling even the most complex part designs with high accuracy. This delivers rapid production cycles ideal for high-volume manufacturing runs.

Hot Chamber

The two halves of the mold are forced together under great pressure to close the mold. The plunger remains down until the molten metal in the die cools. After solidification, an ejection system pushes the casting out from the two die halves.

Cold Chamber Die Casting Method

The cold chamber die casting process is optimal for high-melting-temperature metals and alloys, such as aluminum, brass, and copper. Unlike the hot chamber process, the cold chamber's temperature is at ambient levels prior to injecting the molten metal. With hot chamber casting, the chamber already contains molten alloy, but in the cold chamber process, the metal is first heated in a separate furnace and then transferred into the shot chamber immediately before casting.

This process begins by ladling or pouring the molten alloy from the separate furnace into the cold shot chamber. Once inside, a hydraulically-operated ram forces the molten metal into the die mold cavity at extremely high pressures, creating dense parts with minimal porosity. The die itself consists of movable and fixed sections similar to hot chamber dies, and the metal is injected into the cavity either horizontally or vertically depending on the machine design. This technique accommodates die cast components with complex forms, fine surface details, and thick or thin wall sections.

Cold Chamber

During injection, the ram maintains pressures from around 2,000 psi (2 ksi) up to 20,000 psi (20 ksi), holding steady until the casting solidifies. High-pressure die casting ensures uniform metal flow, reduces the chance of air entrapment, and increases the structural integrity of the finished component. Once cooled, the casting is ejected and may proceed to post-casting operations, like shot blasting, trimming, or machining, to meet specific application or tolerancing requirements.

Steps in the Die Casting Process

The foundational die casting process follows several key stages designed for efficiency, product quality, and dimensional consistency. High pressure die casting, in particular, optimizes cycle times and delivers reliable, repeatable results for complex mechanical components. Below are the essential steps typically followed in industrial die casting operations, with specific details varying by material and production application.

  • Step one – Preparation of the Die: Prior to casting, the die is treated with a specialized lubricant, which forms a barrier to prevent sticking and ensures an easy release of the cast part. These lubricants are often mixed with water and vaporize quickly when applied to the heated, precision-machined steel die. Detailed die preparation is crucial for repeating high-volume production without quality loss or increased defect rates.

    Aluminum Based Die Casting Lubricant

  • Step two – Clamping the Die: The halves of the die are clamped together under high pressure. The amount of force is determined by the machine.

    Die Casting Mold Halves

  • Step three – Cooling: Following injection, the metal must cool and solidify within the die. The cooling period is carefully controlled based on the alloy type, initial melt temperature, and part geometry, such as wall thickness and complexity. Optimizing cooling ensures minimal distortion and defect-free castings.

    Cooling Design

  • Step four – Ejection: Once adequately solidified, the die halves open and the casting is pushed out using an integrated ejection system. Ejector pins must apply sufficient force to release the part without causing surface marks, dimensional errors, or damage.

    Die Casting Process

  • Step five – Trimming: Unwanted material, such as flash, runners, or gates that occur where the die halves meet, is removed in a process called deflashing or trimming. Automated trim presses or manual finishing tools may be used depending on production requirements and part geometry.

    Trimming Cast Part

Key Die Casting Terms

Understanding the commonly used terminology in die casting provides greater insight into design, production, and quality control considerations. Reliable tooling and carefully engineered die features are essential for producing consistent, high-quality aluminum die castings, zinc cast parts, and other custom metal castings for demanding industries. (Source: www.kineticdiecasting.com)

  • Trim Die – Cuts off excess material from castings after solidification and ejection.
  • Slides – Feature elements in the die that allow for the formation of undercuts, enhancing part complexity.
  • Interchangeable Cores – Allow mold modifications to produce varying hole sizes, supporting product customization and flexibility.
  • Waterlines – Internal channels for water or coolant circulation, significantly increasing production cycles by faster part cooling and reduced thermal distortion.
  • Vents – Microscopically small openings in the die to permit evacuation of trapped gases, minimizing porosity and air pockets in die cast parts.
  • Overflows – Small, strategically placed cavities to manage excess material flow and ensure stable temperature distribution, preventing cold shuts and incomplete filling.
  • Ejector Pins – Mechanical pins that push the die cast part out of the mold upon solidification, facilitating quick production turnaround.
  • Draft – Angles designed perpendicular to the parting plane, providing necessary clearance for smooth ejection and reduced part sticking.
  • Parting line – The interface where the two halves of the die come together, critical to sealing and quality surface finish.

Factors such as part size, wall thickness, production volume, and material characteristics are guidelines regarding the use of hot or cold chamber die casting. The guidance of experienced manufacturers ensures proper die design, process controls, and finishing processes. Suppliers provide value added services, including CNC machining, anodizing, powder coating, and assembly to streamline the supply chain and reduce lead times. Consult a manufacturer or request an engineering consultation for die casting design assistance. For advanced technical guides and in depth industry resources, visit die casting industry associations and standards organizations.

If you are actively evaluating suppliers, consider reviewing case studies, certifications, and capabilities to ensure quality, efficiency, and consistent on-time delivery with your chosen die casting partner.

Leading Manufacturers and Suppliers

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    Frequently Asked Questions

    What is die casting and what metals are used?

    Die casting is a high-pressure process forcing molten metal into a mold to produce precise parts. Common metals include aluminum, zinc, brass, magnesium, lead, tin, bronze, stainless steel, and carbon steel, each chosen for specific performance characteristics.

    How does hot chamber die casting differ from cold chamber die casting?

    Hot chamber die casting heats metals within the casting machine and is used for low-melting alloys like zinc and magnesium. Cold chamber die casting heats metal in a separate furnace, suitable for high-melting metals such as aluminum and brass.

    What are the main steps in the die casting process?

    The die casting process includes die preparation, clamping, injecting molten metal, controlled cooling, ejection, and trimming of excess material. Each stage ensures dimensional accuracy and repeatability for complex, high-volume parts.

    Why is aluminum frequently chosen for automotive die cast components?

    Aluminum die casting offers a superior strength-to-weight ratio, natural corrosion resistance, and excellent thermal conductivity, making it ideal for lightweight automotive parts and helping improve energy efficiency and lower emissions.

    What are the benefits of using zinc in die casting?

    Zinc provides exceptional surface finishing, tight tolerances, high ductility, and excellent repeatability. Its low melting point reduces die wear, making it cost-effective for high-volume production of intricate, small components.

    What factors should be considered when selecting a die casting material?

    Material selection depends on application, weight, corrosion resistance, strength, mechanical properties, cost, volume, and required processing or finishing. Consulting experienced manufacturers ensures optimal performance and manufacturability.

    Chapter Four – Die Casting Design Geometry

    Die casting design geometry determines how parts fill and cool as well as how their geometry affects stress, grain, and porosity. The grain structure and level of stress are determined by the type of metal.

    Different Forms of Die Casting Geometries

    The examples in the above diagram are a sampling of the types of geometric features produced by die casting.

    Geometry Planning

    • Finishing
    • Poor fluid life
    • Part shrinkage
    • Post casting checks
    • Problems with solidification
    • Hot cracking

    Geometric Features

    Draft

    Draft is a draft angle that varies depending on the type of wall and surface, the depth of the surface, and the selected metal. A mathematical formula determines the angle.

    Drafting

    Fillet Radii

    Fillet radii makes a part stronger by redirecting stress concentration at sharp interior corners by distributing it over the broader volume of the fillet to lessen weak points. It prevents cracking during straightening.

    Fillet and Radii

    Parting Line

    The parting line is where the two halves of the die meet, defines the inside and outside surfaces, and which side of the die is the cover and which is the ejector.

    Parting Line

    Bosses

    Bosses are mounting points, stand offs, and are designed to maintain uniform wall thicknesses to eliminate after casting machining.

    Boss with Ribs

    Ribs

    Ribs help the molten metal fill all parts of the die casting. They provide a path for molten metal and simplify and speed up ejection.

    Holes and Windows

    Holes and windows require the highest amount of drafting since they form a connection with the surface of the die making the ejection difficult and may block the flow of the molten metal.

    Plunger Lock Black Die Cast

    Chapter Five – Variations of Die Casting

    There are several variations of die casting, each with its own unique characteristics and advantages. These variations are chosen based on factors such as material selection, part geometry, production volume, and quality requirements. Manufacturers carefully consider these factors when deciding which die casting method to use for a specific application. Variations help overcome flaws, errors, deformities, and other issues found in die casting operations.

    Variants

    Pore Free

    Prior to injecting or pouring the molten metal, the die cavity is filled with oxygen. When the hot metal enters the cavity, the oxygen chemically combines with it to prevent gas bubbles eliminating trapped gas pores. In the diagram below, note the opening for active gas in this cold forging process.

    Pore Free Die Casting

    Acurad

    Acurad is an anagram for accurate, reliable, and dense. It combines stable fill and directional solidification to create fast cycle times. It includes thermal analysis, flow and fill modeling, heat treatable castings, and indirect squeezing. Double pistons increase the pressure when the shot is partially solidified.

    Acurad Process

    Gravity

    Molten metal is poured directly into a permanent die, completely filling, which minimizes turbulence, oxidation, and foaming. The die can be vertical, horizontal, or tilted. Parts have high quality, strength, mechanical characteristics, and stiffness.

    Gravity Die Casting

    Investment

    Investment or lost wax casting, is labor intensive process involving shaping of the mold from a wax prototype dipped in liquid ceramic. When the ceramic hardens, the wax is melted away. Molten metal is poured into the ceramic cavity. After solidification, the ceramic mold is broken away and the metal casting removed.

    Investment Die Casting

    Vacuum Assisted High Pressure

    The die is placed in an airtight housing. Pressure is created in the die cavity drawing in the molten metal where it solidifies and is ejected.

    Vacuum Die Casting

    Semi-Solid

    Semi-solid metal, in a semi-solid or slurry state, is agitated, poured, and directed into a shot sleeve to be forcefully injected into the mold cavity under pressure. This process results in parts with excellent surface finishes, tight dimensional tolerances, and a favorable microstructure.

    Semi-Solid Die Casting

    Low Pressure

    With low pressure die casting, the chamber with the molten metal is below the die. It is forced upward through a riser tube into the die chamber. pressure is constantly applied or increasing increments to completely fill the mold cavity and hold the metal in place until solidification. Once the casting is solidified, the pressure is released and residual molten material flows back into the lower chamber as the casting is removed.

    Low Pressure Die Casting

    Chapter Six – Die Casting Dies

    Die castings are made from steel alloys and have two sections – fixed or cover half and the ejector or removable half. A sprue hole, a round, tapered hole, allows the molten metal to enter the die cavity. The ejection half has a runner or passageway and gate or inlet to route the heated metal in the die cavity. The two halves are locked together with ejector pins.

    The die has an opening for a coolant or lubricant, which helps in releasing the part from and keeping the temperature even. Lubricant improves the finish and prevents the part from sticking to the die cavity. The most common form of lubricant is water mixed with oil.

    A die can last through several thousand parts, which depends on the amount of stress it endure, maintains, and cared. Die casting dies are expensive and can add to the cost of the final part.

    Types of Dies

    There are several types of dies that have been developed. Due to the nature of die casting, dies are ever changing and being introduced.

    Single Cavity

    Produces a single unit and is used with machines that handle one die due to shot height, locking force, and die size. They are useful for low production runs, center gating (the entrance for the molten metal), and complex parts with multidirectional features.

    Single-Cavity Die

    Multiple Cavity

    Multiple cavity dies are capable of producing multiples of the same part during one casting and are specially designed.

    Multiple-Cavity Die

    Combination

    Combination dies are a form of a multiple cavity die. Instead of casting similar parts, combination dies produce different parts that fit together. Known as family dies, the process was designed to increase efficiency and lower metal casting costs.

    Combination

    Unit

    Unit dies are inserted into larger dies. The larger die remains fixed while the unit die can be varied to produce different components. There are limitations regarding the size and weight of a unit die and whether it can be inserted.

    Unit Die

    Chapter Seven – Advantages and Disadvantages of Die Casting

    Die casting is the quickest and most economical of production processes. Hundreds of thousands of parts can be produced from one mold producing dimensionally accurate and precision parts. Listed below are the advantages and disadvantages of die casting.

    Advantages

    Excellent Dimensional Accuracy

    Dimensional accuracy is typically 0.1 mm for the first 2.5 cm and 0.02 mm for each additional centimeter.

    Smooth Surfaces

    Surface finishes of 1 – 25 μm.

    (from website https://firstratemold.com/advantages-and-disadvantages-of-die-casting/).

    Smooth Surface of Die Cast Part

    Production Rate

    The production rate is dependent on cavitation, the number of cavities in a mold. One mold can complete 200 to 300 shots per hour. With smaller parts, it can increase to the thousands.

    Detailed Parts

    Reproduces any design down to the finest details with thin walls and structures.

    Inserts

    Threaded inserts, bearings, and addons can be easily included.

    Steel Insert Casting

    Tensile Strength

    Parts have tensile strengths of 60,000 psi or a 415 MPa.

    Automation

    Hydraulic and pneumatic equipment are commonly used for efficiency and lower cost.

    Hydraulic Die Casting

    Tolerances

    Produces complex parts with extremely close tolerances.

    Die Cast Part

    Disadvantages

    Cost

    Every mold has to be individually precision manufactured, which requires hours of crafting, shaping, and forming.

    Furnaces

    Furnaces have to burn into the 1000’s of degrees consuming costly energy that produces pollutants that have to be air filter controlled.

    Die Casting Furnace

    Equipment

    Molding and shaping equipment is precision designed to withstand the stress of the heating process.

    Die Casting Mold

    Metals

    Only metals with high fluidity can be used, which influences the types of parts to be produced.

    Die Casting Metals

    Labor intensive

    The process has to be closely monitored and managed especially during the cooling phase.

    Dies

    Dies are made of hardened steel and cannot be adjusted or changed. They are very expensive and costly.

    Die Casting Mold or Die

    Defects

    Porosity, shrinkage, flash, and metal pouring are common defects.

    Flash

    Production Time

    Requires very long lead times.

    Chapter Eight – Die Casting vs Permanent Mold Casting

    The choice of a casting process is made in regard to design parameters and cost, which are influenced by volume, the intricacy of a part’s design, and any secondary finishing methods. It is essential to work with a casting specialist who can help determine what casting method is best for a part or design.

    The main methods of casting are permanent mold casting and die casting with sand casting also being used for specific projects. Permanent mold casting and die casting rely on molds that have cavities in the shape of the component being fabricated. Their metal molds are what differentiates permanent mold casting and die casting from sand casting.

    Permanent Mold Casting Process

    The basic difference between die casting and permanent mold casting is how the molten metal is injected into the mold or die. Permanent mold casting has a reservoir that is connected to the mold cavity. During the casting process, a gate regulates the speed of flow into the mold cavity to avoid turbulence that leads to porosity in the final product. As the molten metal from the reservoir flows into the mold cavity, it fills from the bottom up or side to side.

    Advantages of Permanent Mold Casting

    • Permanent mold dies are less complex and less expensive than those for die casting.
    • Surface finishes are in the range of 125 to 300 microinches. Secondary machining is not always necessary.
    • Components have less porosity than die casting.
    • Final molded parts have greater strength.

    Die Casting Process

    The initial phase of die casting involves the injection of molten metal into a die cavity. The difference between permanent mold casting and die casting is regarding this aspect of the process, which involves pressure being applied to the molten metal during injection. The application of pressure to the molten metal during injection is similar to the plastic molding process where melted plastic is forced under pressure into a mold. The popularity of die casting is due to its precision and speed, which enables it to produce high volumes of parts with tight tolerances and smooth even surfaces in a short time frame.

    Advantages of Die Casting

    • Finishes of cast surfaces are better than 125 microinches and require limited secondary machining and finishing.
    • Die casting is able to produce tight geometric tolerances, including thin walls.
    • Die casting is faster part-to-part than permanent mold casting, which lowers per unit costs.
    • Equipment requires less floor space than permanent mold casting, which can further lower overhead costs allocated on the basis of area occupied.

    Die casting is faster but requires expensive tooling. Final products are very accurate and can include thinner walls with smoother surfaces. The tools for permanent mold casting are less expensive but the process is slower and not ideal for high volume production. Produced parts are stronger, more durable with very little porosity.

    In order to make a decision regarding casting, it is best to work with a casting specialist who can provide guidance and knowledge regarding the best process for an application.

    Chapter Nine - Aluminum vs Zinc Die Castings

    The die casting industry uses aluminum and zinc alloys due to their malleability and ease of being cast into a wide range of shapes and configurations. The initial step in the die casting process is to select the correct metal for the component to be cast. This aspect of the process is crucial in regard to choosing the type of material that will meet the purposes, requirements, and design of a component as well as ensuring its optimization and utilization.

    Since aluminum and zinc are the two most widely used metals for die casting, it is important to have an understanding of the differences between them in order to select the right metal for a component or part. Although zinc and aluminum are easy to melt, inject, and mold, they have very different characteristics and properties that determine their viability.

    What are Zinc and Aluminum?

    The unique characteristics of zinc and aluminum have led to their wide use in die casting. They are easy to form and are cost effective. Zinc alloys contain zinc that is alloyed with aluminum, magnesium, copper, cadmium, lead, titanium, and other low temperature alloys. The fluidity of zinc enables it produce very small, minute products with precision and extraordinary details.

    In liquid its form, zinc is 204.4°C (400°F) cooler than aluminum, a factor that impacts the life and use of dies. Unlike aluminum, zinc does not have a chemical reaction with dies, which lengthens the life of dies 3 to 4 times over dies used for casting aluminum.

    Zinc can be cast using the hot chamber process, which increases the speed of die casting. Unlike cold chamber die casting, hot chamber machines have the chamber or gooseneck submerged in a furnace filled with zinc. If the same process were used with aluminum, the gooseneck would melt due to the increased heat.

    • Zinc is ideal for casting. It enables the manufacture of intricate thin-walled parts that have smooth surfaces.
    • The various surface treatments used on zinc parts include electroplating, spraying, painting, polishing, and grinding.
    • The aspects of zinc that make it ideal for die casting is its inability to absorb iron, high resistance to corrosion, and the fact that it does not stick to a mold or react to the metal in the mold.
    • One of the primary mechanical properties of zinc is its resistance to wear at ambient temperatures.
    • The ease of casting zinc is due to its melting point of 385°C (725°F), which enables zinc to be cast and shaped with little effort.

    Aluminum comes in a long list of grades that range from 99% aluminum content up to ones with 95% aluminum content. The variations between the grades are in regard to the types of alloys the aluminum has been alloyed with. Common aluminum alloys are copper, silicon, magnesium, zinc, and magnesium with secondary alloys being nickel, iron, titanium, chromium, and lithium. Although aluminum has lower density than steel, it has an exceptional strength to weight ratio with some aluminum alloys being stronger than steel.

    • One of the main reasons for the use of aluminum alloys in manufacturing is its lightweight, which makes it ideal for automobile manufacturing and the aerospace industry.
    • By modern standards, aluminum is highly regarded for its recyclability and environmentally friendly aspects.
    • The high thermal conductivity, which varies between grades, of aluminum makes it an excellent heat conductor. The thermal conductivity of aluminum varies between 237 W/m-K for pure aluminum and 130 W/m-K for high grades.
    • In low temperature environments, aluminum alloys retain their strength and toughness without becoming brittle.
    • When heat treated, aluminum increases its mechanical properties, physical characteristics, and resistance to corrosion.
    • As with the other factors of aluminum, the strength of aluminum varies in accordance with its alloys. The grades of aluminum begin with the 1000 series, which has the lowest strength. From the 1000 series, the strength of aluminum gradually increases to tensile strengths of 560 MPa.

    Differences

    In their pure forms, zinc and aluminum are quite different. Pure, unalloyed zinc is harder than pure aluminum. This differentiation changes after the metals are alloyed with aluminum becoming much harder and stronger than zinc.

    Hardness

    The hardness of aluminum on the Vicker’s hardness scale is 15 to 30 HV in its pure form, while Zinc’s hardness is 30 to 60 HV in its pure form. On the Brinell and Rockwell C scales zinc and aluminum are very soft when compared to steel.

    Strength

    Aluminum alloys have greater tensile strength and yield strength than pure zinc with some aluminum alloys being vastly stronger than zinc alloys.

    Effects of Temperature

    At -10° to -20°C (14° to -4°F), zinc becomes brittle while aluminum retains its ductility. The strength of both metals changes slightly with the addition of alloys.

    Applications

    Zinc is a preferred metal for die casting, coatings, and the manufacture of bearings. It has a higher as cast hardness than pure aluminum. Various aluminum alloys have very high strength to weight ratios and exceptional fatigue resistance.

    Uses for Die Casting

    The three metals that are commonly used for die casting are magnesium, zinc and aluminum. Each metal has excellent properties and is ideal for the die casting process. There are conditions, situations, and applications where one of the metals is a better choice than the others.

    • Zinc – Zinc is normally die cast for high yield designs that require resistance to stress.
    • Aluminum – Aluminum is normally used for applications that involve high temperatures and require longevity.

    Zinc

    Zinc alloys are used for die casting due to its low cost, strength, and stability. It has exceptional electrical and thermal conductivity and is corrosion resistance, ensuring that components will last long. Zinc is easily castable due to its low melting temperature.

    Aluminum

    Aluminum is economical and versatile. The wide use of aluminum is due to its ability to withstand high operating temperatures. It is more expensive than zinc but has benefits that outweigh its cost. The main characteristics that have made aluminum so popular in modern industry is its lightweight, high strength-to-weight ratio, and long useful life.

    Recyclability

    Zinc and aluminum are very cyclable metals with aluminum saving 95% of energy needed for new production. The recycling of zinc is more challenging due its impurities and the need for complex processes. The recyclability of both metals significantly reduces energy consumption compared to other metals. Recycled aluminum and zinc are used for the manufacture of new products without losing their properties.

    Aluminum

    Aluminum is easily recycled with about 80% of aluminum products being made from it. Compared to primary aluminum, recycled aluminum requires 5% of the necessary energy needed to smelt it, which reduces emissions and production costs. Over 75% of aluminum processed as primary aluminum is still in circulation today thanks to the many concerted recycling efforts.

    Nearly four times more recycled aluminum or secondary aluminum is produced than primary aluminum. Recycled aluminum accounts for 34% of the new supply of aluminum. The key to the success of recycling of aluminum are the many collection efforts that gathers alloy scrap, casting scraps, beverage cans, car parts, and other used aluminum products.

    Prior to recycled or secondary aluminum being used for manufacturing, it undergoes a pre-treatment where the scrap is baled, shredded, crushed, decoated, and demagnetized. Decoating removes paint while demagnetizing removes iron particles that cling to aluminum scraps. In addition, pre-treatment improves the metals density and removes contaminants to make the melting process more efficient and produce cleaner aluminum that does not have dross formations.

    Once the scrap aluminum is prepared, the manufacturing process follows the same steps as those used with primary aluminum. It is melted, treated, and refined before being injected into a mold. The one step in the process that is added is inclusion of chlorine gas to remove any impurities that may remain after the previous treatments.

    The wide use of recycled aluminum is due to its energy and environmental savings. The use of recycled aluminum supports the world’s decarbonization efforts that has the goal of significantly reducing greenhouse emissions.

    Zinc

    About 70% of zinc products are made from mined zinc ore with 30% of products being produced from recycled or secondary zinc. The recycling of zinc is a major part of sustainability efforts that have the aim of minimizing the environmental impact connected with manufacture of zinc. As with aluminum, zinc has a high recycling rate, which is derived from collecting scrap zinc from industrial waste, end of life products, and manufacturing offcuts. Just like aluminum, the collected scrap zinc is shredded and sorted before being melted for reuse.

    Unlike aluminum, the recycling of zinc faces several challenges due to zinc’s impurities and alloying elements. The nature of the recycling concerns is in regard to the effect of the impurities on the quality and properties of the products produced from recycled zinc. The inclusion of impurities in zinc necessitates the use of time consuming and expensive purification methods.

    Although aluminum collection has a vast network, zinc recycling has logistic and processing problems that are complex and resource intensive with a limited infrastructure. Unlike traditional collection methods for recycling, zinc recycling collection does not always produce high quality zinc that is reliable and reuseable. In addition, the ever-changing prices of zinc and its demand impact the economic viability of any recycling efforts, which discourages recycling operators from putting any effort into recycling zinc. Improper handling of the recycling process can cause dangerous emissions and waste creating an environmental impact and contamination.

    Zinc scrap is classified by the Institute of Scrap Recycling Industries (ISRI) into different categories based on composition and source of zinc. The most common and reliable sources of zinc scrap, referred to as new zinc scrap, are sheets, pipes, or stampings. Old zinc scrap includes materials from demolitions, renovations, and end of life products, which include galvanized steel scrap, zinc die-castings, and zinc dross. The new plated zinc die cast scrap category includes clean, plated zinc die cast scrap from manufacturing operations

    The ISRI provides stipulations in regard to the types of recycled zinc alloys that conform to the chemical specifications for zinc that is suitable for reprocessing. Zinc scraps are carefully sorted and processed for recycling, in accordance with ISRI requirements.

    Regardless of the difficulties associated with the recycling of zinc, manufacturers have worked diligently to develop methods to streamline the process. The difficulties with recycling zinc is related to separating it from galvanized steel. The most widely used recycling method is electric arc furnace (EAF) heating, which heats scrap until the zinc content volatizes and separates as a gas. As the gas is treated and collected, the zinc decomposes into a dust that is treated in a Waelz kiln where the dust becomes zinc oxide that is used for the production of zinc metal.

    As of the present, 40% of zinc that is used for manufacturing comes from reclaimed zinc sources. It is the hope of manufacturers that with technological advances that zinc recycling will become more viable increasing the amount of reclaimed zinc and lowering the impact of zinc production on the environment.

    Aluminum and zinc are key elements in the manufacture of 21st century products. Their similarities and differences enable them to be configured and shaped to meet the requirements of different applications. As widely used as aluminum and zinc products are, manufacturers, in an effort to comply with sustainability efforts and reduce environmental impact, are constantly working to find methods for reusing existing sources of these metals without having to return to constantly return to primary sources.

    Conclusion

    • The die casting process is a central part in the production and manufacture of most of the products we use.
    • Society is dependent on die casting and its ability to produce technical devices with high precision.
    • It is very likely that any new innovations will rely on die casting to produce major components economically and efficiently.
    • This short synopsis has provided a brief overview of die casting, its processes, and how it can be implemented and used.
    • In response to what you have read, add your comments below for more information or guidance on how to contact die casting manufacturers.

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      Table of Contents

      What is Die Casting?

      Types of Metals Used in Die Casting

      Die Casting – Hot and Cold

      Die Casting Design Geometry

      Variations of Die Casting

      Die Casting Dies

      Advantages and Disadvantages of Die Casting

      Die Casting vs Permanent Mold Casting

      Aluminum vs Zinc Die Castings

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