How to choose the suitable turning insert

When we choose the turning insert, we should consider many parameters such as the insert geometry, insert grade, insert shape, and insert size, nose radius and entering angle to achieve good chip control and machining performance.

First, we need know the inserts will be used for roughing, finishing or just doing some general turning. For roughing and general turning applications, Negative inserts are the strongest and the best option as it will allow deeper depths of cut and higher feed rates due to strong insert shapes and thickness.

Negative turning insert

• Double and/or single sided
• High edge strength
• Zero clearance
• First choice for external turning
• Heavy cutting conditions

If you are finishing, positive inserts are always the best option as these create less cutting forces and can therefore get away with lower depths of cut, eliminating vibration.

Positive turning insert

• Single sided
• Low cutting forces
• Side clearance
• First choice for internal turning and for external turning of slender components

 

• CNMG, DNMGand WNMG are the most popular roughing inserts. For heavier roughing operations, SNMGs are an excellent choice with a 45-degree approach angle allowing for larger depths of cut and reduced cutting loads.
• CCMT,DCMT, VCMT or VBMT are the most popular finishing inserts.
• For roughing applications, you would usually opt for a 0.8mm or 1.2mm radius depending on your machine’s horsepower and the depth of cut you plan on taking.
• For finishing operations, 0.4mm or 0.2mm rad would be the best option. This allows you to take the smallest depth of cut without causing vibration.

 

Second, confirm the turning insert grade

• The insert grade is primarily selected according to:
  • Component material (ISO P, M, K, N, S, H)
  • Type of method (finishing, medium, roughing)
  • Machining conditions (good, average, difficult)

  The insert geometry and insert grade complement each other. For example, the toughness of a grade can compensate for lack of strength in an insert geometry.

  Last, Turning inserts shape

  ​The insert shape should be selected relative to the entering angle accessibility required of the tool. The largest possible nose angle should be selected to provide insert strength and reliability. However, this has to be balanced against the variation of cuts that need to be performed.

  A large nose angle is strong, but requires more machine power and has a higher tendency for vibration.

  A small nose angle is weaker and has a small cutting edge engagement, both of which can make it more sensitive to the effects of heat.

   

• I would always express to my new recruits that there isn’t really any bad turning grades, but instead turning grades wrongly applied. You can have the best insert geometry and chipbreaker, but if the grade of carbide doesn’t suit the material you’re cutting, you’ll just be wasting your time.

  Once you have selected the material-specific grade of carbide, we then need to determine whether you are roughing, medium or finish turning.

  The below guide should give you a good grounding in which grade suits which material / application.

  A roughing grade is very tough and will run at slower surface speed but withstands intermittent cuts well. However, your roughing may be very different to someone else’s roughing. For example, a turner on a VTL turning large stainless steel castings will be taking 5mm+ depth of cut, whereas a turner on a smaller lathe will be roughing with much smaller depths of cut.

  In these cases, it may be useful to talk to one of our engineers and discuss your requirements using information like:

  • Diameter of workpiece.
  • Shape (e.g. rough, hexagon).
  • Machine capability.
  • From this, they can make a quick assessment of the most suitable grade of carbide for your job.
  • A finishing grade will be the hardest grade run at higher surface speed. This will not work well under vibration or heavy intermittent cuts.

  Zhuzhou Xinhua Cemented Carbide industrial Co Ltd is located in zhuzhou city, the largest cemented carbide products manufacturing center in Asia. We manufacture all kinds of carbide inserts for more than 20 years with good quality and pretty competitive price.

  If you have any inquiry or questions, pls feel free to contact 86 181 0733 2178 or email to carbidesales1@zxhcc.com

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