Pressure Die Casting Aluminum Lighting Parts vs Gravity Casting. There are many processes used to create parts for different things. Let’s take lighting fixtures for example. Everywhere you go, whether it is a room in your house or a mall, you’ll find all kinds of lighting fixtures inside and outside of the building. Now, knowing that nothing in this world is perfect, lighting fixtures can get damaged and may be in need of new parts to keep it functioning. To be able to do this, parts are made through certain processes known as die casting. Die casting basically refers to the process of creating parts, housings, and the like by forcing molten metal through high pressure to be able to create molds. These molds help shape and create the parts needed.
What sets things apart in die casting is the material or alloy being used. The die casting process that is also adopted makes a difference. For lighting fixtures, for example, gravity casting is one of the casting processes used to make the parts needed to keep it stable and in place. But because of the many advantages manufacturers and consumers get from aluminum die casting, such as the end-product being lightweight, cost-efficient, strong, sturdy, and shapely to fit it in closer dimensional limitations, many prefer aluminum die casting over gravity casting. What’s more, it’s quicker to produce.
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Die Casting Process
Die casting is a process of casting Aluminum, Zinc and Copper alloy under pressure, which can produce precision parts in high volume at low costs. There are two processes of aluminum die casting namely hot chamber die casting and cold chamber die casting. Die casting machines are typically rated in amount of pressure they can exert on the die. Regardless of their size, the only fundamental difference in die casting machines is the method used to inject molten metal into a die. A complete die casting cycle can vary from one second for small components to minutes for a casting of large part, making die casting the fastest technique available for producing precise metal parts.
Advantages of Die Casting
– Die casting is economical process offering a wide range of shapes of components than any other manufacturing technique.
– Die casted parts have long service life and can be manufactured to complement the visual appeal of the final product. Designs can benefit by utilizing die cast parts.
– Die casting deliver complex shapes and high dimensional accuracy and stability than many other mass production processes. Some machining may be required depending on the design
– 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.
– Die cast parts can be produced with smooth or textured surfaces, and they can be easily finished with a minimum of surface preparation.
– Die castings can provide integral fastening elements as part of the design. For many parts, post-machining can be totally eliminated, or very light machining may be required to bring dimensions to size
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Cold chamber hot chamber process explained:
In a cold chamber process, the molten metal is ladled into the cold chamber for each shot. There is less time exposure of the melt to the plunger walls or the plunger. This is particularly useful for metals such as Aluminum, and Copper (and its alloys) that alloy easily with Iron at the higher temperatures.
In a hot chamber process the pressure chamber is connected to the die cavity is immersed permanently in the molten metal. The inlet port of the pressurizing cylinder is uncovered as the plunger moves to the open (unpressurized) position. This allows a new charge of molten metal to fill the cavity and thus can fill the cavity faster than the cold chamber process. The hot chamber process is used for metals of low melting point and high fluidity such as tin, zinc, and lead that tend not to alloy easily with steel at their melt temperatures.
Extrusions
Extrusion is the process by which long straight metal parts can be produced. The cross-sections that can be produced vary from solid round, rectangular, to L shapes, T shapes. Tubes and many other different types. Extrusion is done by squeezing metal in a closed cavity through a tool, known as a die using either a mechanical or hydraulic press.
Extrusion produces compressive and shear forces in the stock. No tensile is produced, which makes high deformation possible without tearing the metal. The cavity in which the raw material is contained is lined with a wear resistant material. This can withstand the high radial loads that are created when the material is pushed the die. Extrusions, often minimize the need for secondary machining, but are not of the same dimensional accuracy or surface finish as machined parts.
Cold Extrusion: Cold extrusion is the process done at room temperature or slightly elevated temperatures. This process can be used for most materials-subject to designing robust enough tooling that can withstand the stresses created by extrusion. Examples of the metals that can be extruded are lead, tin, aluminum alloys, copper, titanium, molybdenum, vanadium, steel. Examples of parts that are cold extruded are collapsible tubes, aluminum cans, cylinders, gear blanks. The advantages of cold extrusion are:
– No oxidation takes place.
– Good mechanical properties as long as the temperatures created are below the re-crystallization temperature.
– Good surface finish with the use of proper lubricants.
Hot Extrusion: Hot extrusion is done at fairly high temperatures, approximately 50 to 75 % of the melting point of the metal. The pressures can range from 35-700 MPa (5076 – 101,525 psi). Due to the high temperatures and pressures and its detrimental effect on the die life as well as other components, good lubrication is necessary. Oil and graphite work at lower temperatures, whereas at higher temperatures glass powder is used.
Typical parts produced by extrusions are trim parts used in automotive and construction applications, window frame members, railings, aircraft structural parts.
Choosing the Proper Alloy
Each of the metal alloys available for die casting offer particular advantages for the completed part.
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.
Aluminum – This alloy is lightweight, while possessing 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.
Magnesium – The easiest alloy to machine, magnesium has an excellent strength-to-weight ratio and is the lightest alloy commonly die cast.
Copper – This alloy possesses high hardness, high corrosion resistance and the highest mechanical properties of alloys cast. It offers excellent wear resistance and dimensional stability, with strength approaching that of steel parts.
Lead and Tin – These alloys offer high density and are capable of producing parts with extremely close dimensions. They are also used for special forms of corrosion resistance.
Die design
Die casting is one of the fastest and most cost-effective methods for producing a wide range of components. However, to achieve maximum benefits from this process, it is critical that designers collaborate with the die caster at an early stage of the product design and development. Consulting with the die caster during the design phase will help resolve issues affecting tooling and production, while identifying the various trade-offs that could affect overall costs.
For instance, parts having external undercuts or projections on sidewalls often require dies with slides. Slides increase the cost of the tooling, but may result in reduced metal use, uniform casting wall thickness or other advantages. These savings may offset the cost of tooling, depending upon the production quantities, providing overall economies.
Comment by Tod — June 25, 2011 @ 12:02 pm