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Die Casting - An Efficient Manufacturing Process for Metal Products
Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarly to an injection mold during the process. Die casting is especially suitable for producing geometrically complex metal parts in high volumes. It allows for the production of components with smooth surfaces, tight dimensional tolerances and thinner walls than many other casting processes.
The History and Development of Die Casting
The die casting process was first developed in the early 1850s. The first die casting machines were primitive compared to modern equipment, but established the basic principles that are still utilized today. Originally die casting was done at low pressures using metals with relatively low melting points like tin, zinc and lead. Eventually the process evolved to apply much higher pressures and cast higher melting point metals like aluminum and brass alloys.
The introduction of hydraulic presses in the early 20th century greatly increased the amount of clamping force that could be applied during the casting process. This allowed for high pressure die casting, permitting the casting of alloys with higher melting temperatures. More complex shapes could be formed as thinner walls were made possible by high pressure casting. Aluminum especially began to see widespread use in die casting.
Modern computerized control systems now allow for precisely managed timing of the stages of the die casting process. State of the art die casting facilities employ advanced temperature controlled equipment, high performance alloys and sophisticated dies to achieve extremely high levels of productivity and component precision.
Benefits of Die Casting
There are many reasons why die casting has become one of the most popular manufacturing processes for metal components across a vast array of industries.
- High Productivity: Die casting is highly efficient at producing a high volume of metal parts in a streamlined automated process. Large numbers of complex parts can be created with minimal scrap loss.
- Dimensional Precision: The pressures used allow for metal to flow into very fine detail in the die. Parts can be created with tight tolerances and smooth surfaces that need little finishing work.
- Material Versatility: Most alloys can be die cast, including aluminum, zinc, copper, steel, magnesium and tin alloys. This allows material properties to be optimized for the application.
- Complex Shapes: Nearly any shape that can be machined into a steel die is possible to cast. Intricate shapes and thin walls are no problem.
- Reduced Finishing: Die cast parts have smooth surfaces and an excellent finish straight from the die, minimizing any secondary machining operations.
- Fast Production: Die casting is a quick process allowing very rapid production once the initial dies are made. Large volumes can be produced in short timeframes.
Key Die Casting Terminology
There are some key terms used in the die casting industry to describe components of the process that are important to understand.
- Die: The mold into which molten metal is injected under high pressure. Usually made of tool steel.
- Cavity: The impressions within the die that give the molded shape. A die may have multiple cavities to increase output.
- Core: Used to form internal cavities and undercut surfaces. Inserted into die prior to casting.
- Alloy: Metal material to be cast, usually non-ferrous alloys like aluminum, zinc, magnesium.
- Furnace: Pot of molten metal, kept liquid for pouring into dies.
- Shot: Amount of metal poured into die for each casting cycle.
- Clamping: Applying high force to close and lock the two die halves.
- Ejector pins: Pins used to push cast products out of die cavity after clamping force is removed.
The Die Casting Process Step-by-Step
While there are variations, the basic high pressure die casting process consists of the following steps:
1. Die Lubrication - The surfaces of the opened die are sprayed with lubricant to facilitate smooth release of the casting.
2. Closing and Locking - The two die halves are brought together with tremendous hydraulic force, 20,000 tons or more.
3. Injection - Molten metal is injected into the die under high pressure, completely filling the cavity.
4. Solidification - The metal rapidly cools and solidifies in the water-cooled die into the cast shape.
5. Opening - The die halves separate and the casting is mechanically pushed out of the movable die half.
6. Ejection - Ejector pins push the casting completely out of the opened die in preparation for the next cycle.
7. Trimming - Excess metal flash left attached to the casting is trimmed in a separate die or by another method.
8. Post-Finishing - Additional finishing operations like grinding or drilling may be done to achieve final dimensions.
Die Casting Metals
The most popular metals used in die casting include:
- Aluminum: Best all-around choice. Low melting point, lightweight, good strength and surface finish. Used for housings, automotive parts, etc.
- Zinc: Lowest melting point. Used for hardware components and children's toys.
- Magnesium: Very lightweight. Used for electronic gear boxes and aircraft components.
- Copper: Good thermal & electrical conductivity. Used in electrical parts like motor rotors.
- Tin: Dense but softer. Used for some bearing surfaces or as an alloy addition.
- Lead: Lowest hardness. Used for acid battery grids. Being phased out due to toxicity.
Aluminum Die Casting Companies
There are many companies that specialize in aluminum die casting due to its ideal properties for most applications. Some of the major aluminum die casting companies include:
- Shiloh Industries (US) - massive capacity, complex high-pressure castings. Major automotive supplier.
- GF Casting Solutions (Switzerland) - innovator, aerospace and electronics casting.
- Ryobi Die Casting (US) - focus on safety-critical automotive components.
- Consolidated Metco (US) - low cost, quick turnaround on high-volume parts.
- Alcoa (US) - invented aluminum die casting in 1910. Major castings producer.
- Walbro (US) - specialized in fuel system, engine and outdoor power equipment castings.
- Llumar (Mexico) - high-quality aluminum castings at competitive prices.
- Endurance (US) - robotically molded castings for volume production.
- Rockman Industries (India) - innovative lightweight aluminum castings.
- Mingtai Al. (China) - rapid prototyping and high volume production.
Die casting has proven to be one of the most versatile and cost-effective manufacturing methods for quality metal components. Continuous advancements in casting alloys, die materials and automation ensure die casting will remain an essential fabrication process across many industries for years to come. CNC Milling