Metals and materials science for industrial technicians

The metal in the workpiece determines much more than you think. It determines which rake you should use, how fast you can cut, how the chip breaks and how the surface ends up at the end. An industrial technician who knows the materials can foresee problems before they arise — and corrects cutting data instead of guessing when something goes wrong.

§Steel — the trade's workhorse

Steel is an alloy of iron and carbon, and the carbon content greatly determines it: the more carbon, the harder and more brittle the steel becomes. Common structural steel is relatively easy to machine and is used for everything from machine parts to fittings. Alloyed steel, where e.g. chromium, nickel or molybdenum is added, has improved properties such as strength, toughness or wear resistance, but often requires sharper tools and more careful cutting data. Hardened steel makes even greater demands — here one often works with hard metal or ceramic tools because ordinary steel tools quickly become dull.

§Aluminum – light and quick to process

Aluminum weighs about one-third of steel and conducts heat well, making it ideal for parts where weight matters, such as in transportation and aviation. The material is soft compared to steel, which means you can typically cut faster, but aluminum is also prone to 'sticking' to the blade if the geometry and cutting data don't fit. Therefore, blades with sharp cutting angles and often plenty of cooling lubricant are used so the chip glides away easily instead of building a burr on the tool.

§Stainless steel — corrosion resistance has a price

According to the standard DS/EN 10088-1, a steel can first be called stainless when it contains at least 10.5% chromium and at most 1.2% carbon. The chromium forms an invisible, self-repairing oxide layer on the surface that protects against rust. Many grades are also alloyed with nickel and molybdenum, where a high molybdenum content gives the so-called acid-resistant grades, which tolerate more aggressive environments. The downside when processing is that stainless steel is often tough and hardens at the surface during cutting, which requires stable cutting data, sharp tools and good cooling — otherwise thermal damage and poor surface quickly occur.

§Brass and copper — good for fine mechanics and electrical conductivity

Brass is a copper-zinc alloy and is known for being easy to work with a beautiful, smooth surface — it is used for fittings, valves and fine mechanical parts among other things. Pure copper conducts electricity and heat exceptionally well and is therefore especially used for electrical components and heat exchangers, but it is softer and can be more difficult to cut cleanly because it easily smears out over the tool instead of breaking into neat chips.

§Heat treatment and hardening

Many steel alloys can change properties markedly through heat treatment. Hardening makes the steel harder and more wear-resistant through rapid cooling from high temperature while a subsequent tempering adjusts the balance between hardness and toughness so the part does not become too brittle. Some parts are finished before hardening others require a final very precise grinding or finishing after hardening because the part can 'move' slightly during the process. Knowing the material's condition — annealed hardened or tempered — is crucial for choosing the right cutting data.

“The same lathe, the same blade and the same rpm give vastly different results depending on whether the item is aluminium, soft steel or hardened stainless. The material is the invisible player in any machining.”