1. Die Cast Machines

2. Die Casting Process Explained

3. Advantages of Die Casting

4. Die Casting vs. Other Processes

5. Choosing the Proper Alloy

6. Die Construction

7. Future of Die Casting

Glossary

Introduction

Die casting is a manufacturing process for producing engineered metal parts by injecting molten metal under high pressure into reusable hardened steel molds called dies. Each mold or die can be designed to produce simple or complex shaped parts with smooth or textured surfaces and with a high degree of accuracy and repeatability. Close tolerances, hardness, machinability and plateablity are only a few of the advantages of die cast parts.

The high-pressure die casting process is the fastest and most cost-effective manufacturing process available for producing precise, high-integrity, near net-shape non-ferrous metal parts with excellent surface finishes.

Die castings are important products that range from very small cell phone parts, computer parts and miniature die cast car parts to large and complex aircraft engine fuel valves, marine boat propellors, gas regulator valves and automotive parts such as transmission housings and wheel rims. 

Die castings are among the largest volume, mass-produced items manufactured in the metalworking industry and can be found in thousands of consumer products and industries such as aerospace, automotive, commercial, electronics, industrial, irrigation, lawn and garden, lighting marine, medical, military, mining, railroad, transportation, etc.

Die cast parts are commonly found in many places around the home and office and are used for all types of parts such as bathroom fixtures, carburators, casings, covers, decorative hardward, die cast toys, door handles, faucets, flanges, grips, handles, heat sinks, housing, kitchen hardware, knobs, power tools, pumps, rotors, valves, plus many more. 

1. Die Cast Machines

Die casting machines are typically rated in clamping tons equal to the amount of pressure they can exert on the die. Machine sizes range from 400 tons to 4000 tons. Regardless of their size, the only fundamental difference in die casting machines is the method used to inject molten metal into a die. The two methods are hot chamber for Zinc alloys and cold chamber for Aluminum alloys.


2. Die Casting Process Explained

In the Aluminum die casting process, solid ingots of aluminum are melted in furnaces at approximately 1200-1300 Degrees Fahrenheit. Once liquified, the aluminum metal is picked up using a ladle and poured by hand or robotically into a steel shot sleeve. The two halves of the die or mold are mounted on the machine and the machine closed and holds the two die halves together. The molten aluminum metal is then injected with hydraulic pressure into the two halves of the die. The molten aluminum metal is then held under high pressure until the metal solidifies, usualy within only a matter of 2-15 seconds depending on the size of the parts. The die halves are then opened and the part(s) ejected and removed by hand or robotically. Finishing operations follow such as trimming, tumble deburring, precision machining, painting, anodizing, chrome plating and assembly.

In the Zinc die casting process, ingots of zinc are melted in a furnace at approximately 700-800 Degrees Fahrenheit. Once liquified, the zinc metal remains in the furnace. The shot sleeve (called a gooseneck for its shape like a goose's neck) is immersed in the furnace and the zinc metal is injected directly from the furnace into the two die halves held together by the machine. The remaining process is identical to that of casting aluminum parts.

A complete die casting cycle can vary from seconds for small components weighing less than an ounce to three minutes for a casting weighing several pounds.

3. Advantages of Die Casting

Die casting is an efficient and very cost-effective manufacturing process that offers a broader range of shapes, sizes and dimensionally precise die castings than any other manufacturing process. Parts have a long lifespan and designers can gain a number of advantages and benefits by specifying die cast parts.

High-speed production - Die casting provides complex shapes within closer tolerances than many other mass production processes. Little or no machining is required and thousands of identical castings can be produced before additional tooling is required.

Dimensional accuracy and stability - Die casting produces parts that are durable and dimensionally stable, while maintaining close tolerances. They are also heat resistant.

Strength and weight - Die cast parts are stronger than plastic injection moldings having the same dimensions. Thin wall castings are stronger and lighter than those possible with other casting methods. Plus, because die castings do not consist of separate parts welded or fastened together, the strength is that of the alloy rather than the joining process.

Multiple finishing techniques - Die cast parts can be produced with smooth or textured surfaces, and they are easily plated or finished with a minimum of surface preparation.

Simplified Assembly - Die castings provide integral fastening elements, such as bosses and studs. Holes can be cored and made to tap drill sizes, or external threads can be cast.

4. Die Casting vs. Other Processes

Die Casting vs. Plastic Injection Molding - Die casting produces stronger parts with closer tolerances that have greater stability and durability. Die cast parts are more heat resistant, have greater resistance to temperature extremes and superior electrical properties. Die castings are far superior to plastics for applications such as anodizing or chrome plating. Die castings  Die castings are much better for permanence under loads and resistance to chemicals and ultra-violent rays.

Die Casting vs. Sand Casting - Die casting is faster and produces parts that cost much less, have closer dimensional limits, thinner casting walls and much smoother surfaces. Die cast parts require much less machining, finishing costs are less and tooling can last for 20 years or more and make thousands and even millions of parts with proper maintenance.

Die Casting vs. Permanent Mold - Die casting offers many of the same advantages as compared with sand casting. Faster production, much lower costs, closer dimensional limits, thinner casting wall sections, holes cored to near net shape, lower machining and finishing costs and extended tooling life.

Die Casting vs. Forging - Die casting produces complex shapes, cast-in cored holes, closer tolerances, thinner walls and lower finishing costs. Complex shapes and cast-in cored holes are not available with forging.

Die Casting vs. Stamping - Die casting produces more complex shapes with variations in section thicknesses, closer dimensional tolerances and fewer assembly operations. One casting may replace several stampings and reduce assembly time.

Die Casting vs. Screw Machine Products - Die casting produces shapes that are difficult or impossible to produce from bar or tubular stock, while maintaining tolerances without tooling adjustments. Die casting requires fewer operations and reduced waste and scrap.

5. Choosing the Proper Alloy

Aluminum and Zinc metal alloys available for die casting offer distinct advantages depending upon the end use of the product:

Aluminum - This alloy is lightweight and possesses high dimensional stability for complex shapes and thin walls. Aluminum has good corrosion resistance and mechanical properties, high thermal and electrical conductivity, as well as strength at high temperatures. Aluminum is the most common die cast alloy because of it's many beneficial properties.

Zinc - The easiest alloy to cast, it offers high ductility, high impact strength and is easily plated. Zinc is economical for small parts, has a low melting point and promotes long die life.

Magnesium - The easiest alloy to machine, magnesium has an excellent strength-to-weight ratio and is the lightest alloy commonly die cast. However, magnesium is highly flammable and extremely hazardous to manufacture.

Copper - This alloy possesses high hardness, corrosion resistance and mechanical properties. It offers excellent wear resistance and dimensional stability with strength approaching that of steel parts. However, high metal temperatures lead to rapid die degradation and the added costs of new tooling.

Lead and Tin - These alloys offer high density and close dimensions and are also used for special forms of corrosion resistance. However, the toxicity of Lead based alloys makes Lead dangerous, unhealthy and costly.

6. Die Construction

Dies, or die casting tooling, are made of alloy tool steels in at least two sections, the fixed die half, or cover half, and the ejector die half, to permit removal of castings. Modern dies also may have moveable slides, cores or other sections to produce holes, threads and other desired shapes in the casting. Sprue holes in the fixed die half allow molten metal to enter the die and fill the cavity. The ejector half usually contains the runners (passageways) and gates (inlets) that route molten metal to the cavity. Dies also include locking pins to secure the two halves, ejector pins to help remove the cast part, and openings for coolant and lubricant.

When the die casting machine closes, the two die halves are locked and held together by the machine’s hydraulic pressure. The surface where the ejector and fixed halves of the die meet and lock is referred to as the "die parting line." The total projected surface area of the part being cast, measured at the die parting line, and the pressure required of the machine to inject metal into the die cavity governs the clamping force of the machine.


7. The Future of Die Casting

Improvements continue to be made in both the casting process and the alloys used in die casting that continue to expand die casting applications into almost every known market in the world. Today’s die casters can efficiently and economically produce strong, durable and dimensionally precise castings in a wide variety of shapes, sizes and wall thicknesses.