Who uses foundry services? What does the casting process look like?
We will try to answer these questions in this article. Firstly, let us learn what an aluminium foundry is and who needs aluminium castings.
Casting, or metalcasting, is a process which is aimed at producing aluminium (or other) components of a given shape. After the component is cast, machining is performed. As a result, we obtain a beautiful, dimensionally accurate part. Casting is a popular process known for ages. It utilizes many different materials, but let us focus on aluminium alloy casting.
Metalcasting is a large industry, which is also important for art. It is vital for making sure the cost of manufacturing is low.
Aluminium foundries make both simple components and very complex ones. Machining of castings guarantees high accuracy, so the results are highly satisfying.
Who uses aluminium foundry services?
The reality is that we all do… We all have products with aluminium components around us. From cars, smartphones, white goods, window and door systems, cladding, art castings, to products so peculiar we are unaware of their existence at all. These are, e.g., components for Energy, Medical, Aerospace, Rail and many other industries. Aluminium castings are literally everywhere!
However, industry remains the main recipient of castings.
What does the casting process look like?
Firstly, the design needs to be made. These days, it is done on computers. Modern foundries have highly advanced equipment and software.
After the design is finished, the casting pattern is made, e.g., with the use of 3D printers. Next, the top and the bottom halves of the mould are made. They are called cope and drag. Then, cores are produced, which shape the inner surfaces of the cast part. The above actions require a lot of care and knowledge. Any rush at this stage is completely out of the question.
The next stage is mould assembly and subsequent pouring of molten aluminium. After the casting is removed from the mould, it is cleaned. Next, it undergoes a whole cycle of different machining processes. However, this is a whole new stage with a degree of variability.
We have a finished casting
What should a professional aluminium foundry provide to its clients?
The answer is the design, pattern, mould and cores, non-destructive testing, machining, assembly into the complete component, optional delivery and, on top of that, all of the above together should be documented with applicable certificates. A hugely important fact is that the foundation of a professional aluminium foundry is its employees. Every customer is assigned a consultant. That is important, because castings are very often “top secret” products. Unfortunately, there are very few foundries in the European and global markets which operate like that.
What are the different kinds of aluminium (and other) foundries
No-bake (Air-set) Sand Foundry
Sand casting is the most popular aluminium casting process, because it is versatile and low-cost.
No-bake (air-set) sand foundries are used for low to medium volume production. The casting process there starts with making individual moulds from a mixture of silica sand, selected as per the product type, and binder. Next, the mould is filled with molten aluminium with correct physical and chemical properties. If we consider mould design, cores are its inherent part. They shape the internal surfaces of the cast product.
Sand castings undergo further machining to get their final shape.
Die Casting Foundry
Die casting foundries are used for high volume production – bigger lots.
Die casting guarantees high quality of castings and dimensional consistency.
Depending on the type and production of an aluminium foundry, die castings are made in different sizes, which are determined by the size of the die (also called “permanent mould” when it is gravity-fed).
Everything depends on the size of the foundry. In high volume production, dies are filled automatically. Low volume production dies can be filled manually. Since die casting requires high precision, die temperature needs to be measured every time. Pouring speed is also a vital factor.
Yes, the process is by no means easy…
Professional casters need experience and awareness to control the process. That is why so many people involved in this industry are so passionate. Everyone who has spent at least a few days on the foundry floor knows this! 😀
Low Pressure Die Casting Foundry – Large Lots
Low Pressure Die Casting (LPDC) makes high volume production parts for, e.g., for automotive. LPDC machines are also used in making castings with complex sand cores (semi-permanent mould) or metal cores. This casting method requires many modern and very, VERY efficient equipment. State-of-the-art foundries around the world have LPDC facilities with unique pouring parameters and die sizes.
Casting moulds – an absolute must for casting
The key process for every foundry is the preparation of the casting mould. In a good aluminium foundry, the mould is prepared from scratch. A dedicated department, sometimes called a design department, designs the mould using advanced software. Next, the mould is manufactured (e.g. using CNC machining) by the machine shop.
The moulds are made from cast iron or structural steel for every casting batch. Both metal cores integrated with the mould or hardened cores can be used. Die casting allows for good surface finish and it is a more efficient and a faster process than sand casting.
Aluminium used for casting
Aluminium foundries melt and use certified aluminium which is bought from around the world from aluminium smelters in the form of so called ingots. There a few “big players” in this field. The aluminium market is like a stock market, where the price goes up and down. In big foundries, there are sales departments which check the price constantly. Selecting the aluminium alloy for a customer order is based on measurements and process tests. The chemical composition of the melt which is poured into moulds has to conform to customer requirements. To achieve that, alloying elements are added to the molten aluminium alloy. Melt quality is also improved by refinement.
What about aluminium scrap?
Exactly! What about it? Foundries sometimes melt aluminium scrap, but there’s a catch: That isn’t common practice. Predominantly, to maintain quality, foundry scrap is used (to top up or to have enough melt for the gating system). The scrap must be very carefully selected, so that it does not differ from the primary metal needed to make the casting.
Before casting, primary aluminium needs to be melted. Melting primary aluminium, which is bought from smelters, is a distinct process. Aluminium ingots (similar to gold bars 😀 ) are melted in either induction furnaces or gas-powered furnaces. In big foundries, holding furnaces are used to ensure continuity of the pouring process. Melting takes place at 800°C and takes a few hours depending on the size of the furnace.
The melting process is continuously monitored to obtain the right temperature, composition and desired quality of aluminium. Quality of finished castings depends on how good the melt is.
Casting pattern and prototype
Design and manufacturing of dies
Aluminium foundries design and make moulds for die casting (small foundries outsource dies). Based on a Request For Quotation (RFQ), drawing or a similar casting, designers come up with a concept and draft the shape of the mould, which is discussed, approved and later made. Next, production can be started by fitting the mould in the casting machine. The mould is made using CNC machines, where precision is key.
Modern foundries have replaced traditional patternmaking with cutting-edge CAD/CAM technologies and state-of-the-art numerically controlled 5-axis machining. 3D printers are already commonly used for patternmaking and prototyping. 3D printing allows for accurate shapes and material structures.
Pattern and moulds for aluminium sand castings
It is absolutely clear and obvious to everyone that pattern quality has an impact on casting accuracy ? Sand foundries make casting patterns from various materials. Those include, e.g., steel, wood and resin. Choosing a pattern materials depends on the lot size. In addition, tooling is manufactured, which allows for giving the mould cavity its desired shape, making cores and the correct assembly of mould components.
Machining of aluminium castings
A good aluminium foundry has its own CNC department, where castings are machined. Machining could mean, e.g., drilling, milling, grinding, turning, broaching or cutting. Most of the processes are performed on CNC machines. The biggest, cutting-edge foundries provide an additional service—they assemble cast parts into ready-to-mount components. Many big companies, e.g., in rail, energy or automotive industries order this service very often. It shortens their lead times and lowers their costs. But we have to highlight the fact that there are very few foundries which offer a full service package like this…
Quality Control and Heat Treatment in aluminium foundries
Let us imagine an airborne passenger plane, 200 people on board and tens or hundreds of aluminium castings within the plane structure. Will they break? Will they bend? Will it go “bang”? Be it a plane, a train or a car going 100 (or 200 ?) km/h, it better be OK!
In order to make sure it is, foundries do thorough tests at different production stages. These tests check, e.g., chemical composition, hardness, leaks, mechanical strength or tests for discontinuities in internal and external structures. Those quality inspections are very thorough and performed by qualified personnel. The standards used, e.g., for aerospace, rail or energy are usually international standards, so very high!
Fettling and post processing
Right after casting, degating needs to be performed. The process consists in cutting off the gating system components, such as the sprue, through which the metal was poured, and risers, which are filled during pouring. Even though degating is a rough process, the employee performing the process must be careful, because it is easy to damage the part.
The next stage is usually cleaning which consists of manual or automatic grinding. Manual grinding requires a lot of experience from employees. They have to know what tools to use to obtain the desired quality and efficiency. It is worth pointing out that manual labour in the foundries is not going to become obsolete anytime soon. However, automatic grinding often takes place together with finishing and it is often performed by advanced machines, often robots. You read this right, robots often work in fettling departments in modern foundries!
Post processing involves a lot of different activities. Many of them are additional services which may or may not be needed for a particular customer. Such services are, e.g., copper-plating or welding.
Since any aluminium (or any other) foundry is, in fact, a service provider (just like a hair salon or a garage), it can perform various manufacturing and finishing services to order. Those are very often confidential, or even top secret activities. After all, large foundries often produce for the defence industry or they make patented products.
Finally, heat treatment of castings
Heat treatment is heating, annealing and cooling to defined temperatures, at defined speeds, just like baking 😀 . Thanks to heat treatment, it is possible to enhance the mechanical properties of a solid aluminium alloy.
Heat treatment causes changes in mechanical properties by changing the metal structure. There are a few types of heat treatment: traditional, chemical and mechanical.