What is Die Casting?
Die casting is a century old process of injecting molten metal into a steel die under high pressure. The metal, either aluminum, zinc, magnesium and sometimes copper, is held under pressure until it solidifies into a net shape metal part. In modern applications, using computerized controls, Pacific Die Casting can produce precision and high-strength products at a rapid production rate. No other metal casting process allows for a greater variety of shapes, intricacy of design, or closer dimensional tolerance.
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 machineís 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.
There are four types of dies:
1. Single cavity to produce one component
2. Multiple cavities to produce a number of identical parts
3. Unit die to produce different parts at one time
4. Combination die to produce several different parts for an assembly.
What Is Die Casting and Why Use It?
Die casting is an efficient, economical process offering a broader range of shapes and components than any other manufacturing technique. Parts have long service life and may be designed to complement the visual appeal of the surrounding part. 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.
The Recycle Value Of Die Casting
Die casting alloys offer the designer concerned with post-consumer recyclability one of the most advantageous material options. Die castings and the die casting process provide the product engineer who is designing for the environment:
(1) Components that can maintain their integrity through disassembly, repair, remanufacturing and reassembly;
(2) Product recyclability, at the end of useful life, with the potential for return to high-performance applications;
(3) Knowledge that a proven recycling infrastructure is in place to reclaim recycled die cast parts.
This effort has been driven by the world-wide emphasis on "green" product design. Designers for world use products are being urged, and mandated, to specify engineering materials in functional and decorative products which are easily recyclable during manufacturing and that can be readily reclaimed, recycled and utilized in new products, to form a continuous circle of environmental recycling.
Recyclability and the real-world recycling infrastructure for metal have created more reasons for engineering decisions in favor of die cast products. Kodak engineers, for example, stated that recyclability of the die cast Mg case for their new Professional DCS 620 digital camera (built around Nikon F-5 optics) was an additional reason for their final engineering material selection.
This basic recycling pattern, with variations based on the amount of reclaimed alloy going to secondary and primary producers, applies to the majority of die castings currently being manufactured.
Die Casting's Unique Environmental Position
The die casting industry has long been built on recycling. The metal alloys used by the die casters are produced from recycled raw materials, created with far less energy than is required for virgin alloys. Over 95% of the aluminum die castings produced in North America are made of post-consumer recycled aluminum, helping to keep the aluminum content of municipal solid waste to less than 1%.
Die castings are not hazardous waste and pose no problems in handling or reprocessing. At the end of a castingís life cycle, a metal reclamation infrastructure exists to reclaim, re-alloy and recycle these parts back into high performance manufactured components and ensure the availability of yet unimagined die castings for tomorrow.
Most engineers, as concerned citizens, know that the problems of waste disposal in the U.S. are serious. Minimum-content laws have been passed by many U.S. states, mandating the use of recycled materials in new products. Disappearing waste disposal sites are of even more concern in Europe. Legislation in several countries now bans incineration. It is clear that the product designer is not only responsible for optimum function and easy fabrication of a product, but also is now required to account for the product's ultimate destiny at the end of its service life.
Other considerations being equal, what the designer of todayís products must distinguish between are theoretical or future possibilities of reprocessing a material, on the one hand, and in-place recycling, on the other. The fact is that metals can claim the support of an existing world-wide infrastructure that economically collects, reprocesses and channels reprocessed materials back into manufacturingóand allows reuse at costs significantly less than that of virgin materials. Supporting the automotive industry, a network of automotive dismantlers daily salvages metal auto parts and then places the remainder of the vehicle in the hands of "shredders." The shredding process, which has proven its economic viability, results in the recycling of almost 75% of the weight of a typical caró nearly all of this as ferrous and nonferrous metal. Over 85% of the aluminum in a car is currently reclaimed and recycled.
The nonmetallic portion of a product is generally regarded by recyclers as "fluff," consisting mostly of plastic. Nearly one-quarter of all solid waste is estimated to be plastics and less than 3% of this plastic is being recycled. Problems with plastic product recyclability were pointed up by a national task force which requested that plastics marketers refrain from use of the universal symbol for recycling in advertisements. The implication of recyclability was regarded as misleading.
Nearly all metals, and die castings in particular, have always been readily recyclable. Die castings are not hazardous waste and pose no problems in handling or reprocessing, as do some toxic nonmetallics. Die castings are recyclable components with engineering advantages not available in other metal forming processes. The major cost and performance benefits of parts consolidation that are possible with plastic components are available in die casting designs but with additional advantages Net-shape die castings can be produced with thinner walls than comparable plastic parts, and can provide greater strength and product durability over a longer life cycleówith added serviceability.
How Is Die Casting Different From OtherCastings?
Aluminum die casting alloy recycling has been in place almost from the beginning of custom die casting production. Specifications for aluminum alloys have been developed that provide for a full range of compositions that can utilize various types of recycled metal. Carefully engineered and spectrographically controlled formulas result in precise specification ingot for each of the commonly used die casting alloys. Over 95% of the aluminum die castings produced in North America are made of post-consumer recycled aluminum. Since the production of recycled aluminum alloy requires approximately 5% as much energy as primary aluminum production, this results in a dramatic conservation of nonrenewable energy resources. Die castings, as opposed to forgings or extrusions, for example, can make far greater use of recycled material. In selecting materials and manufacturing processes to meet consumer concerns, the product designer should ask these questions:
1) Does the material allow for efficient and economical maintenance, repair, refurbishing or remanufacturing of the product to extend its life, where this is a design benefit?
2) Is the material non-toxic and readily recyclable at the end of its useful life?
3) Can the material be recovered and reused in high performance applications?
4) Is the necessary infrastructure in place to make recycling of the reclaimed material a practical reality?