When it comes to the differences between machining stainless steel and brass or softer metals, the difficulty or ease with which a metal can be machined, is one of the main factors affecting a product’s utility, quality and cost. Depending on the application, machinability may be seen in terms of total power consumption, tool wear rate, attainable surface finish and several other factors. It is also crucial that you have the right machine for the job as not all machines are created equal.
Free machining brass is the most versatile copper-alloy and is commonly used. It’s 100% machinability stems from a favourable interaction between the materials structure and the addition of lead.
Brass is incredibly soft, which makes it easier to cut and the metal is more forgiving when it comes to feeds and speed. This makes brass easier and faster to machine than stainless steel. There is also much less negative impact on tool wear, part surface finishes or chip formation.
The power and rigidity of the latest high-speed machine tools have the capability to boost brass workpiece material removal rates in the milling, drilling and turning operations.
Brass rarely needs a coolant but like with other softer metals, it can get gummy. More often than not though, the chips are easy to clear with any sort of cutter.
Machining Stainless Steel
The most frequently machined stainless steels are the austenitic types, such as grades 304 and 316. These are characterised by their high work hardening rates and poor chip breaking properties during machining.
The most common turning stainless steel, free-machining 303, contains added sulfur, the purpose of which is to decrease corrosion resistance in marine environments. In comparison to other 300 series, the sulfur actually improves the machinability of this grade of stainless steel.
When machining stainless steel, any machines used should not be prone to excessive vibration in the machine bed, gearboxes, drives or at the cutting tool or it’s mountings. The machines must also be capable of making the deep cuts required for machining austenitic stainless steel, without slowing down the surface speeds or set feed. Machines intended for machining mild steel, brass etc. are unlikely to cope successfully with the machining of stainless steels.
When machining stainless steel, it is essential to keep cutting tools sharp to preserve tool life, finish, accuracy and tolerances as well as reduce tool breakages. Careful grinding and honing of the tool faces will give accurate and sharp face angels, which are important. Resharpening should be carried out as soon as the quality of the cut has deteriorated.
Due to stainless steel being a poor conductor of heat, the elevated temperatures during machining operations will significantly reduce the life of cutting tools. To help dissipate heat away from the cutting faces, avoid large overhangs of tool shank out of the toolbox. Keep the distance between the cutting tip and toolbox support as short as practical and the shank cross-section as substantial as possible. To provide maximum support, the arbour supports should be as close as possible to the ends of the cutter. While it is fairly normal to have some ‘squealing’ when the metal is being cut, it can also indicate that the tool may be wearing and requires replacement.
Overheating of stainless steel can impair corrosions resistance and also result in distortion, so must be avoided. It is thus essential that cutting fluids are used when machining stainless steels.
Steelmor is the leading supplier and manufacturer of stainless steel in South Africa. Give us a call today on 011 747 5700 for expert advice and top quality products to meet your every need.