What is Metal Processing? Beginners Guide

Metal processing consists of metal extracting, metalworking, and metal recycling. While metal extracting is an industrial application where the metal is extracted from its ore, metalworking and metal recycling can be performed in workshops equipped with proper metalworking tools. Cutting, casting, forming, and joining are some popular metalworking processes.

This article discusses the metal processing techniques commonly used in the industry to extract, shape, and recycle metals. 

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Metal Processing Explained

The journey of a metal workpiece from its ore to the final product involves various metal processing techniques to extract the metal, shape the metal, and finally recycle the scrap metal.

Each metal processing method adds value to the metal workpiece. However, performing an improper operation can ruin the workpiece and render it useless.

Generally, metal processing such as casting, forging, cutting, bending, joining, etc., are commonly used for metalworking hobby projects.

Each process requires specific tools such as casting requires metal melting tools, forging requires power hammers, and cutting requires CNC mills and lathes to perform the desired operations.

Unlike non-metals, the processing of metals require stronger cutting, shaping, and forming forces, and, therefore, it is important to always wear safety gear during metalworking.

Furthermore, there are various heat treatments that can be performed to alter the properties of metal.

Annealing improves ductility while releasing internal stress, improving the machinability of metals such as steel, copper, aluminum, brass, etc.

Similarly, normalizing and tempering can be performed to improve various properties such as the toughness and abrasion resistance of metal workpieces.

Apart from that, metal processing also involves the recycling of metal and extracting metals from their ores.

Metal Processing Techniques

Processing Techniques For Metalworking 

Process	Overview
Forming	Shaping metals using compressive and tensile forces
Casting	Pouring molten metal into molds of the required shapes
Cutting	Removing excess material using machining processes
Joining	Process of joining different pieces together

Metalworking is a group of diverse processes that use various tools to shape and form metals.

These processes are actively used in almost every metal manufacturing industry to produce parts of different scales and for different applications.

The processes have evolved over the years from simple hand tools to advanced machines that can perform complex operations like machining and welding.

Metal Forming

Forming is a process of shaping metals by applying compressive and tensile forces. Forging and stamping are common operations used to manufacture metallic components. 

Forging metals involves applying a high compressive force to metal blanks to get the required shape using open or closed dies.

The metal can be hot or cold forged, and the metal blanks go through multiple compressions to attain the shape of the die cavity. 

Some of the popular types of forging techniques include drop forging, press forging, open die forging, closed die forging, etc.

Stamping is used for shaping metal sheets into specific shapes by using a stamping tool or die and applying pressure using a stamping press which shapes and shears the material into the desired form.

It usually involves multiple successive operations to get the final geometry.

One of the greatest advantages of forging over other processes is its ability to produce parts with high strength and reliability.

Metal Casting

Casting is a process of manufacturing metal components by pouring molten metal into a mold having a cavity in the shape of the part to be produced.

The molten metal fills the mold cavities, cools down, and solidifies in the required form.

Generally, the cast metal workpieces require further processing to remove excess material from the workpiece and to enhance their surface finish.

It is majorly used for making complex shapes that are difficult to produce with other metalworking processes such as forging or machining.

Some of the popular casting techniques include gravity casting, sand-mold casting, investment casting, etc.

For DIY applications, aluminum casting is preferable due to its low melting point and cheaper cost.

Metal Cutting

Metal cutting is a collection of subtractive manufacturing processes where the excess material is removed from the stock to achieve the desired shape and form.

The excess material can be removed using machining operations such as milling, turning, boring, drilling, knurling, threading, etc.

Machines such as CNC mills, CNC routers, CNC lathes, die punches, etc., are used to perform metal-cutting applications.

Generally, thin metal workpieces are cut by sheet metal tools, like die punches, that involve sheet metal shearing to get the desired cut.

Apart from that, metal cutting can also be achieved by using advanced metal cutting tools such as plasma cutting, laser cutting, waterjet machining, or wire EDM.

Metal Joining

Joining is a collection of fabrication processes used to combine pieces of metals. Various techniques are used to join metals depending on the type of metal to be joined. 

Welding is the most widely used technique to join metals, and it involves melting the material at the weld area and adding filler material.

The molten mixture cools down and solidifies to form a strong joint. The metal can be melted through various methods such as gas welding, electric arc welding, fiber laser welding, ultrasound welding, etc.

Brazing and soldering are also joining processes that involve the melting of filler material to join the metals.

Unlike welding, the base metals are not melted in these processes. Instead, the molten filler material metallurgically reacts with the solid workpiece and solidifies to form a joint.

Brazing and soldering use different filler materials and brazing results in stronger joints than soldering.

Apart from these, rivets, nuts, and bolts are also used to join metal workpieces. However, these joints are generally temporary joints and can be removed easily.

Whereas welding, brazing, and soldering produce permanent joints which cannot be removed without damaging the workpiece.

Processing Technique For Recycling Metals

Steps Involved	Overview
Collection & Sorting	Collecting scrap from various sources and separating different materials based on the type
Processing	Compacting and cutting scrap into smaller pieces
Melting	Melting the scrap metal to separate it from impurities
Refining	Used to increase the purity of the metal
Solidifying	Cooling and shaping the metal into various forms like blocks, sheets, etc.

Metal recycling refers to collecting and processing used or scrap metal to reuse it as raw material for making new products.

Almost every metal, except some radioactive and toxic metals, can be recycled again and again, without any significant derogatory effect on their quality.

Every metal recycling process consists of some simple steps, but the process parameters can vary from one metal to another.

Step 1: Collection and Sorting 

The scrap metal is collected from various domestic and industrial sources and taken to a scrap yard for processing. Scrap yards use multiple methods to separate the metal from other materials. 

Sorting is done through visual inspection, electro-magnets, spectrometers, etc. Sorting prevents mixing with other metals and materials, ensuring the purity of recycled metals.

Therefore, when collecting the metal scrap or chips from your workpiece for recycling, make sure that you sort them carefully to prevent the inclusion of impurities.

Step 2: Processing the Scrap Metal

Processing scrap metals involves shredding and breaking them into smaller pieces using hydraulic machines. It is further broken down into smaller pieces using hammer mills. 

This is done to increase the surface-to-volume ratio, increasing the melting process's efficiency.

However, this step can be skipped when recycling small metal chips from your workshop.

Step 3: Melting the Metal

After processing the metal scrap, it is melted in a furnace. The choice of furnace varies from one metal to another and depends upon the required purity.

Generally, an induction furnace is preferred for melting gold and silver as it assures minimal contamination of the molten metal, whereas a crucible furnace is suitable for DIY applications.

The volume of the metal and the capacity of the furnace determines the time taken for the melting process.

Step 4: Refining of Recycled Metal

Although insoluble impurities rise to the top of the molten metal and can be easily separated, there are various microscopic impurities that can get trapped on the surface of the recycled metal.

The recycled metal undergoes a refining process, such as electrolysis, to improve its purity, helping to achieve properties very close to base metal made from ores.

Step 5: Solidifying The Recycled Metal

After the metal is free from impurities and other contaminants, it is poured into dies and shaped in various forms while solidifying. Some chemicals are also added to achieve desired properties. 

Generally, the recycled metal is shaped into bars and billets, which can later be used with different metalworking processes.

However, you can also use molds of complex shapes to directly cast the recycled metal into the desired part.

Processing Techniques For Metal Extraction

Process	Overview
Hydrometallurgy	Aqueous solution is used to recover metal from their ores
Pyrometallurgy	High temperatures are used to treat ores to enable metal extraction

Metals exist in nature as mineral deposits from which valuable metals can be extracted through a series of processes.

These mineral deposits are called ores, and the extraction process depends upon the kind of ore, the metal to be extracted, and the impurities present in the ore.

The ore is mined and sent for extraction, where it undergoes the enrichment process or ore concentration, in which the undesirable impurities known as gangue are removed from the ore. 

Generally, the ores are subjected to a ball mill, which breaks the ore into finer pieces, separating the impurities from the metal.

After ore enrichment, the concentrated ore is sent for further processing, where the minerals are extracted from the ore and refined to get pure metal, known as extractive metallurgy.

Generally, there are two main extractive metallurgy techniques: hydrometallurgy and pyrometallurgy

Hydrometallurgy

Hydrometallurgy uses an aqueous solution to recover metals from their concentrated ores.

The metal to be extracted gets dissolved in the aqueous solution leaving behind other solid impurities. This hydrometallurgical process is known as leaching.

The solution is separated from the solid impurities, and then the solution is concentrated and purified using various methods such as adsorption, distillation, etc.

Finally, the pure metal is recovered from the solution by using various techniques, such as, electrolysis, precipitation, and gaseous reduction.

Pyrometallurgy

Pyrometallurgy uses high temperatures to treat minerals and concentrated ores, resulting in physical and chemical changes enabling metal extraction.

Pyrometallurgical processes consist of three main categories: calcination, roasting, and smelting.

Calcination is thermally treating a solid material under a controlled oxygen supply to remove impurities without melting it.

Roasting involves heating sulfide ore to high temperatures so that it reacts to form sulfur dioxide gas leaving behind solid metal oxide.

Smelting is the process where metal oxides are heated above melting point with coke or charcoal, reducing the metal oxide to form carbon dioxide and refined metal.

Further refining is carried out to remove the remaining impurities.

Final Thoughts

Metal processing employs various techniques, including metal extraction from ores, shaping and forming metals, and recycling used metal components.

However, the shaping and forming of metals are the most important processing techniques for DIY metalworking projects.

While casting and forging require metal melting tools such as furnaces, tongs, etc., cutting and bending of metal workpieces can be achieved by using various manual or CNC machines.

You can also use metal melting tools to recycle the scrap metal produced during the machining process, thereby minimizing wastage and enhancing productivity.

Frequently Asked Questions (FAQ)

Is casting preferable over forging?

Yes, casting is preferable over forging to produce metal parts with complex geometries. However, forging is ideal for producing simple parts with high strength and durability. Therefore, both processes have their pros and cons, and selecting the right process depends upon your application.

What is photochemical machining?

Photochemical machining is a milling process that uses chemicals to corrosively machine sheet metal components. It is used for making complex and precise sheet metal parts. The tooling is relatively cheap and can be easily modified as per requirements, making it suitable for prototypes.   

What is the meaning of metal reduction?

Metal reduction is when the metal oxide loses its oxygen to form elemental metal. This process is the opposite of oxidation. Metal reduction is used in pyrometallurgy in the smelting process using a reducing agent in the form of carbon. The carbon acts as a reducing agent and gets oxidized, leaving behind the elemental metal.