88 | CUTTING TOOLS | Tech Tips
www.shopmetaltech.com april 2017
Stainless steel’s anti-corrosive
qualities makes it perfect for use
in a huge range of environments
and components such as aerospace, general
engineering, consumer, oil and gas, medical
and marine industries. its versatility is
reflected by the fact that there are more
than 150 different grades. The main alloying
element is Chromium. as a general rule,
resistance to corrosion and oxidation increases
with Chromium content. Other alloying
elements such as Nickel and Molybdenum can
be added to change the structure, increase
corrosion resistance and improve strength.
Due to the difficult process of machining
stainless steel, manufacturers have developed
new ways to combat application challenges:
changes to the cutting tool design, new
geometries, improved coolant and stronger
coatings to improve performance and tool life.
For example, drills with thin margins reduce
contact with the hole surface, which in turn
minimizes friction between the cylindrical
land and the hole walls and decreases work
hardening and temperatures. positive point
geometries ensure excellent chip breaking,
while a specially designed web combines the
benefits of maximum rigidity with space for
efficient chip removal.
Here are five key factors to consider.
a generous flow of cutting fluid removes
heat from the chip, helps chip breaking
and improves dimensional stability of the
component. Cutting tools with through coolant
provide instant cooling at the cutting interface,
which helps chip breaking and evacuation.
When using flood coolant, ensure a plentiful
supply, as coolant starvation can cause
temperature fluctuations and thermal cracking,
resulting in reduced tool life. Neat cutting oils
work well but, if using an emulsion, an eight to
ten per cent concentration is recommended.
Machining Stainless Steel
What you need to know when drilling, milling, turning or tapping
by DaN COrMier
Dan Cormier is an
with Dormer Pramet.
Top: Chipbreaker in
action during turning.
Bottom: Cutting stainless steel.
2. Feed Rates
Stainless steels can vary slightly between
different suppliers and batches. When
choosing cutting data it’s a good idea
to begin at the lower region of the
manufacturer’s recommendations. High
feed rates can cause heat transfer in the
cutting tool, increasing tool wear.
3. Work Hardening
Some stainless steels are prone to work
hardening during machining. This can
have a negative effect on tool life and also
reduce the life of subsequent tools used.
To minimize this, avoid using tools with
worn edges, which could accelerate tool
wear and cause breakage. Make regular
checks for signs of wear and change tools
or inserts regularly. also, try to avoid any
dwells or pauses in the cutting process as
this will cause heat build-up and increase
4. Mechanical Properties
The high strength of stainless steels
combined with their high ductility
makes chip breaking more difficult. This
increases the risk of vibration, which can
affect surface finish quality and reduce the
service life of the tool or insert. To address
this, make sure tooling and workpieces
are stable and well clamped. Keep tool
overhang to a minimum, especially when
drilling or internal turning. To help reduce
vibration, use sharp tools or inserts with a
small nose or corner radius.
When tapping stainless steels, tool life can
be increased by pre-drilling the hole 0.1
mm larger than recommended. This will
reduce torque levels encountered during
threading which, in turn, increases tool life
and performance. SMT