What do we mean when referring to raw material as Ductile, Malleable, or mild?
Ductility is defined as the amount of plastic deformation the material can absorb before failure. In simple words, it describes how “Soft” is the raw material.
Why is it important in machining?
You will often come across terms like:
- Malleable cast iron.
- Mild steel.
- Ductile material.
- Gummy material.
- Soft stainless steel.
All the above mean that the material we are about to machine is soft. An inexperienced machinist might think that machining soft raw materials is more straightforward; however, it presents several unique challenges.
Chip Control
It isn’t easy to break the chip when machining ductile materials. Chip breaking is achieved when the chip breaker forces the bending of the evolving chip until it breaks. When the material is ductile, the chip bends without breaking, leading to very long chips.
Build-up edge
Built-Up Edge (Nicknamed BUE) is a wear mechanism that can occur on both milling and turning operations. It is caused by the welding of chips to the insert body.
Best practices when machining ductile materials
- Utilize an insert/tool with a sharp and positive cutting edge, preferably ground.
- Work with polished or post-treated inserts.
- Use an aggressive/tight chip breaker with a deflector that is very close to the cutting edge.
- Use high coolant pressure.
- Raise the cutting speed to generate enough heat.
- Adopting some or all of the above tips will increase your chances to break the chips and decrease or postpone the forming of the build-up edge.
