Foundry: A comprehensive read
What is a Foundry?
A foundry is one of its kind factory or production facility which produce metal castings and offer similar casting related services. Foundries on a broader view follows a similar process: solid metal is melted into liquid, poured into a mold with cavity of shape of the finished product, which is allowed to solidify. On the other end, what comes out is a near finished casting product which after a few finishing operations is ready to be used in anything under the sun. Look around and you will find out that you are surrounded by casting products, from the car you used to commute to work or college this morning to the bridge you passed from and the skyscrapers forming the astonishing city skyline, all of which have these casting products as their backbone.
Some of metals used in the casting process by the foundries are, aluminum and cast iron being the most common ones and few other metals, like bronze, brass, steel, magnesium, and zinc.
“Don’t judge someone until you’ve stood at his forge and worked with his hammer.”
– Rick Riordan
Following are some of the common terms that you might come across while reading this article or strolling through a foundry.
These are structures within which molten metal is poured to form a casting. Molds can be classified into temporary (sand molds) made using patterns or permanent (steel molds) machined.
2. Cope & Drag
Generally, in the case of sand casting, molds are made into two halves, the upper half being called cope and the lower half called drag. This cross-section allows insertion of core/s in the mold.
Cores are apparatus used to generate hollow cavities or internal features which cannot be formed using pattern alone in molding, cores are majorly made using sand, but some processes also use permanent cores made of metal.
Like any other industrial product, castings also are subjected to industry-standard tolerances. Tolerance can also differ varyingly depending on the process used. Some casting methods provide more control over tolerances than others.
5. Surface Finish
This basically refers to how the surface feels at the end of the process or when the casting product is ready. Surface finish can be classified into lay, waviness, and roughness.
More terms will be added in our next update.
Casting process in the foundry
Like mentioned before, irrespective of the finished product, the crux of the process remains standard. The stages of the casting process in a foundry are as following:
1. Melting: As the name suggests, the process involves the melting metal in a furnace. The inputs may include internal scrap, external scrap, and virgin materials. A crucible is used to transfer the molten metal from the furnace to the prepared molds.
2. Degassing: Gases can form in castings due to either chemical reactions in the materials or due entrapment during the casting process.
3. Mold Making: Molds are the parent structures in which molten metal is poured. Molds are made using patterns that are machined in the shape of the desired finish cast product. The pattern usually has two sections, upper or cope and lower or drag. The pattern makes an impression in the parent material and allows the placement of cores.
4. Core Making: Cores are inserted in the mold to facilitate hollow cavities in the finished product. The cores are made using core boxes which are designed as per the requirement of a particular product. Core boxes are installed in core shooting or blowing machines which produces the desired cores with efficiency.
5. Mold Assembling: Depending on the design of the casting product, a certain assembling is required. This is usually the case in molds with multiple and complex cores. Materials like adhesives, filters, and others are used in the assembling process.
6. Pouring: Metal has been melted, molds are assembled, now it’s time for the pour. Molten metal is transferred to the molds in a crucible. And the pouring begins one mold at a time. Pouring is a risky job, Modern foundries use automatic pouring machines for the process.
7. Shakeout: Once the molten metal sets in the molds and solidifies, the molds are sent for shakeout. The step is particularly used in the sand casting process, where the sand mold and sand cores are removed from the casting product using a shaking or vibrating machine.
8. Degating: This step includes the removal of risers, runners, and gates. Formed as per the design of the mold, these parts are formed with the cast product, they are removed using myriad tools like sledgehammers, cutting torches, knockoff machinery, etc. These parts are again sent for melting as internal scrap as mentioned in the first step.
9. Heat Treatment: This treatment is necessary to change to the physical and chemical composition of the material. Treatment includes heating and chilling to extreme temperatures, to get the desired hardening or softening of the material.
10. Cleaning & Finishing: After all the above steps, surface cleaning of the casting is done to remove any sand granules or other unwanted substances. Finishing involves sanding, grinding, and machining of the casting. This is done to achieve the accuracy of the finished product and to comply with the tolerances.
Types of casting processes
All foundries produce casting products, but they are differentiated by the process they use to produce those finished castings. Selection of process is a complex task in itself and require considering many factors. Therefore, most foundries usually specialize in single process and foundries engaging in multiple processes are usually uncommon.
1. Sand casting
Sand casting deserves a separate article of its own, of course. Being the oldest form of casting process, it still hasn’t lost its charm. Cost-efficient, tolerance control options, widest range of applicability and flexibility in size are some of the few features which still makes this process one of the most feasible and used process across the world.
Though the above mentioned characteristics have evolved to fulfill current eras requirement, but the fundamental process still remains the same. As the name suggests, Sand is an integral part of the process, basic process involves making a cavity in sand using a pattern, adding a core for hollow cavity inside the casting and then pouring the molten metal, allow this to cooldown and remove the sand using shakeout process. Repeat this process a few thousand times to achieve economies of scale.
2. Die Casting
This process of casting is similar to injection molding, wherein the molten metal is injected with pressure inside a mold or die. Unlike the sand molds used in sand casting, die casting involves steel dies to create a mold cavity.
More casting processes will be added in our next update.
Here are some of the standard equipment you will find in any foundry:
Furnaces are at the heart of any foundry; they are used for melting metals to desired consistency. These furnaces melt as per their capacity and then on a batch basis, the molten metal is taken to the pouring station using crucibles.
2. Molding machine
Ideally used in sand casting foundries, these machines ensure the supply of molds for the production line. Modern foundries incorporate them within a larger reclamation system which ensures automatic, circular, and continuous supply of molds.
3. Core Shooter
Like molding machines, the core shooter ensures a steady supply of sand cores to the production line. But instead of patterns, a core box with the desired internal cavity is used for blowing purposes.
Like any other industry, foundries require a supply chain for raw materials and other inputs including but not limited to scrap or virgin materials, metals and minerals, machinery, conveyor systems, reclamation systems, furnaces, crucibles, spare parts, and other foundry consumables.
The majority of these requirements are fulfilled by foundry suppliers. These standalone businesses bridge the gap and ensure an uninterrupted supply of inputs to keep the production running. If your foundry is located in an industrial cluster, chances are you are already dealing with either single or multiple foundry suppliers. Another source of inputs is dealing directly with the manufacturer, this is ideally the case for machinery and automatic systems which require sizable investments and usually are handled on a case-by-case basis.