Cutting speed with HSS tools: For which material is the recommended cutting speed generally the highest when machining with high-speed steel tooling?

Introduction / Context:
Cutting speed guidelines depend on tool material and work material. With high-speed steel (HSS) tools, soft, thermally conductive, non-hardening materials typically permit the highest surface speeds before tool softening and wear mechanisms become limiting. Among the listed options, aluminium commonly allows the highest speeds.

Given Data / Assumptions:

• Dry or light coolant conditions.
• Sharp HSS tooling, conventional turning/milling.
• Average machinability grades for each material class.

Concept / Approach:
Aluminium alloys have good machinability, low yield strength, and high thermal conductivity, enabling higher safe cutting speeds with HSS. Brass also machines well but is often run somewhat slower than aluminium with HSS to avoid smearing and to maintain edge integrity. Cast iron and steels require lower speeds due to abrasive constituents, higher strength, and heat generation. Austenitic stainless steels are the most speed-limited due to work-hardening and poor thermal conductivity.

Step-by-Step Solution:

Verification / Alternative check:
Shop charts often show aluminium with HSS in the 90–200 m/min range (or higher in favorable cases), brass in moderate-high ranges, mild steel lower, and stainless/cast iron lower still.

Why Other Options Are Wrong:
Cast iron and steels have lower allowable speeds due to wear and heat; brass is good but typically below aluminium with HSS; austenitic stainless is notably speed sensitive.

Common Pitfalls:
Running too slow on aluminium causing built-up edge; using unpolished cutting edges that smear aluminium; neglecting coolant or chip evacuation leading to poor finish even at proper speeds.

Final Answer:
Aluminium