Aluminium is coined as the ‘wonder metal’ of 21st century. It is a metal that lends itself to a variety of metal working processes. It can be cast, forged, rolled, machined, heat treated, polished, painted or plated, It is the world’s most abundant metal - at 8% of earth’s crust. Surprisingly, it was not until 1820 that aluminium was for the first time produced in pure metallic form. Curiously, while the human body contains a host of other metals in some form or the other (sodium, potassium, magnesium, iron etc), aluminium does not feature in the list.
The chief source of aluminium is bauxite ore. Pure aluminium (99.5 - 99.8%) is extracted by the Hall- Heroult electrolytic process. Secondary or recycled metal is produced from scrap of various kinds, and usually alloyed to specification. By utilising various combinations of its advantageous properties, such as strength, lightness, corrosion resistance, recyclability and formability, aluminium is being employed in ever-increasing number of applications.
World-wide demand for aluminium is 60 mmt (million metric tonnes)/year; about 45 mmt/year of fresh metal and 15 mmt/year of recycled scrap. The use of recycled Al is economically and environmentally compelling, as it takes only 5% of the energy required to produce one tonne of pure aluminium, with corresponding reduction in emission.
What is needed?
Aluminium castings form a large part of requirements of the aviation, automotive and other prime mover industries. The automobile industry in particular is by far the largest single customer. In recent past, the emphasis on lighter weight in order to achieve better fuel efficiency and lower emission has been relentless. Aluminium castings are replacing cast iron castings in almost every application.
Compared to cast iron, production processes of aluminium castings are of recent origin. Sand casting, gravity die casting, pressure die casting and low pressure die casting are the major categories of aluminium castings. Die casting has seen revolutionary changes in development & application of computer software for simulation of die design & casting process and die casting machines. This has allowed automation of the process to a great extent, resulting in consistently high levels of quality and output.
The solution: Aluminium die casting
Aluminium is basically a lightweight alloy with high dimensional stability and if some aluminium parts are being designed considering the manufacturing process, aluminium die casting is the go-to-solution. Aluminium die casting is a popular manufacturing process to create complex shapes and designs that produces smooth, defined and textured surface metal parts.
Die casting is no longer a ‘Black Art’ of medieval ages. It has developed into a highly advanced technology-based mass manufacturing activity. Fully automated cellular units make extensive use of computerised programming, monitoring, analysis and control. Computer-aided design and manufacture of dies and casting simulation techniques are the order of the day. The growing sophistication of plant and machinery calls for a corresponding higher level of competence, knowledge and skill among the operating personnel, particularly those responsible for maintenance and upkeep.
How is the desired output achieved?
Aluminium die casting is a manufacturing method to create metal parts. Casting is a general term for products at or near net shape, formed by solidification. The method in which the molten metal is introduced into the die and the pressure applied on the metal while it is cooling and solidifying defines the category of casting : Gravity die cast(GDC) Low Pressure die cast (LPDC) or High Pressure die cast. (HPDC).
To begin with, an aluminium bar should be heated and melted entirely at a high temperature and then force it into a pre-shaped mould cavity to create desired metal parts. This process uses the casting machine’s cold chamber, as the high molten aluminium temperature would damage the machine if the injection mechanism is submerged like the hot chamber process. In the cold chamber machine, the melting pot is separated and the molten aluminium alloys then are ladled from the pot into the die under high pressure. After injecting the molten aluminium, it takes a while to solidify. Then, one need to separate the two halves of the mould to reveal the aluminium cast part. The pressure requirements for cold chamber castings are typically higher than those of hot chamber die castings.
The die casting process devices a steel mould often capable of producing thousands of castings in rapid succession. This process can be either simple or complex depending upon the complexity of the casting. Most of the machines use mechanisms actuated by hydraulic cylinders to achieve locking. Others use direct acting hydraulic pressure. Die casting machines - large or small - are highly fundamentally only in the method used to inject molten metal into the die.
The end product comes out with a smooth surface. Most of the time, the finished products don’t need minimal machining and move into the delivery stage quickly. Moreover, the die cast mould is recycled to manufacture the same parts before it deteriorates. Therefore, aluminium die casting is an ideal manufacturing process for large-scale production. And that is why manufacturers prefer to die casting this and it is popular in various industries.
Versatile in use
One of the impressive ability of aluminium die casting is that, being a non-ferrous metal in the world, it has the ability to produce lightweight and complex parts without sacrificing its strength while having extensive surface finish options that neither extrusion nor machining can effectively create. Its dimensional stability is another big advantage of the aluminium die casting process. Moreover, they are versatile, and one can use them for nearly any industry.
The aluminium die cast parts can withstand high-operating temperatures than other non-ferrous materials. These die cast parts are corrosion resistant, highly conductive, have a good stiffness and strength-to-weight ratio. Since, this casting process is based on rapid production that allows a high volume of die casting parts to be produced very quickly and more costeffectively than alternative casting processes.
Considering the fact that aluminium alloy comes with various advanced chemical and mechanical properties; they are highly corrosion-resistant and have high heat dissipation properties. Moreover, strength-to-weight ratio is also a significant advantage.
Application areas of aluminium
Aluminium alloy being lightweight in its natural form, large structures such as bridges and commercial buildings use die cast aluminium parts in the construction process. The die cast parts are also considered essential in most of the vehicles. Therefore, one can see these alloys in a wide range of applications in the automotive industry – from engine to body parts, they are everywhere.
Aluminium has been playing a major role in the electronic industry. The uses of die cast aluminium alloy in this specific industry have risen over the past two decades. From smartphones to 5G network housing, die cast aluminium alloy plays a significant role in this development.
The furniture industry has also adopted the aluminium die casting owing to its high strength, corrosion-resistance and reasonable price point. As a result, the furniture industry uses an aluminium alloy to manufacture various home & office furniture, such as door locks, hinges, knobs and other aluminium fittings.
This process also plays an important role in the aerospace industry as some of its parts are made of die cast aluminium, like airplane engine piston heads, cargo loading housings, fuel system parts, airplane distributor cap housings, as well as lighting fixture parts and electronic enclosures detention ring parts. To give a perfect example of this process is the production of complex automotive parts, like transmissions and engine blocks. Other processes cannot consistently achieve the complexity and tight tolerances required for these products.
Acknowledging the mastery of aluminium die casting used in applications around the world driving competitive markets, the transportation sector is the largest end-use segment for this industry. The increasing emission laws by the government regulatory authorities, along with consumer demand for a higher fuel-efficient vehicle is developing a necessity for aluminium casting. The increased operations for the industry include the replacement of iron and steel components in a vehicle with lightweight high-quality aluminium in order to increase the fuel efficiency.
Another sector demanding this process includes building and construction in developing economies. Aluminium die casting is associated with the creation of products including windows, cladding, curtain walling, pre-fabricated buildings, shop partitions and fittings.