Tap Performance Troubleshooting - Part 3: Excessive Wear

June 5, 2019 2:20 pm

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A series from Walter Tools USA

 

The following is one part in a series of articles regarding performance problems associated with the tapping process.  The solutions focus on specific actions to counter specific issues.

This article addresses remedies for the issue of Excessive Wear.  We are offering suggestions and changes that can be made to counter the effects of premature wear.  For further information regarding chip control, please see other articles in this series such as insufficient tool life, chip control or fractures.

Action to correct excessive wear will depend on the type of wear that we see, and in which part of the tap the wear is occurring.  It’s important to examine the used tool to determine which type of wear the tool is experiencing.

 

Tap wear

Anatomy of a spiral point tap and a spiral flute tap

 

 

Let’s take a look at the different types of wear that we expect to see.

 

Excessive Wear on the First Tooth

Excessive wear on the first tooth

Excessive wear on the first tooth means that the tap hole has been hardened by the drilling process

Cause

Edge zone hardening caused by the core hole drill

 

Solution

Optimize the core hole drilling process by incorporating as many of the following changes as possible.

  • Improve the coolant supply by adding internal coolant to the drilling process if not using already. If internal coolant supply is already being applied, increasing the coolant supply pressure or even the concentration level of water-soluble coolant to increase lubricity.
  • Reduce the cutting speed of the drill operation
  • Reduce the advance per revolution (feed rate) of the drill
  • Replace worn drills sooner

 

Wear in the Chamfer Area

Wear in the chamfer area

Wear in the chamfer area means that there is friction between the tool and the workpiece

Cause

Friction between tool and work piece. This could be considered typical wear and is not necessarily indicative of a problem.

 

Solution

  • Use a tool that is more wear resistant such as solid carbide taps
  • Increase the flank relief angle. This could have a negative side effect and may result in axial miscut or built up edge.  The trade-off has to be evaluated to determine if  the net effect to the operation is beneficial.
  • Improve the coolant supply by adding internal coolant if not using already. If internal coolant supply is already being applied, increasing the coolant supply pressure or even the concentration level of water-soluble coolant to increase lubricity.
  • Reduce the cutting speed of the tapping process
  • When machining materials with spring back effect, make sure that the tool cuts free (large rake and helix angle, sharp cutting edges)

 

 

Wear in the Guidance Part

Wear in the Guidance part

Wear in the Guidance part means that there is friction between the part and the relief angle

Cause

Friction between the relief face and the component. Wear on the first full tooth of the guidance section of the tap leads to wear on the subsequent teeth in the guidance area. The thread then becomes tighter and tighter. This could be considered typical wear and is not necessarily indicative of a problem.

 

Solution

  • Use a more wear resistant substrate such as solid carbide taps
  • Improve the coolant supply by adding internal coolant if not using already. If internal coolant supply is already being applied, increasing the coolant supply pressure or even the concentration level of water-soluble coolant to increase lubricity.
  • When having excessive wear on the outer diameter of the guidance part, a tap with a relief angle on the outer diameter should be chosen. Workpiece materials with spring back effect and abrasive materials require such a relief angle.

 

Crater Wear

Crater Wear

High cutting speeds is one of the causes of Crater Wear

Cause

Crater wear can be caused by a number of different scenarios.  To some extent, this can be considered typical wear, but the following scenarios can be the root cause that needs to be addressed.

  • high cutting speeds
  • tough materials
  • Tools are being run too long
  • tool substrates that are prone to wear
  • insufficient coolant conditions

 

Solution

  • Use tool that is more wear resistant such as solid carbide taps
  • Reduce the cutting speed
  • Improve the coolant supply by adding internal coolant if not using already. If internal coolant supply is already being applied, increasing the coolant supply pressure or even the concentration level of water-soluble coolant to increase lubricity.

 

Rounding of the Cutting Edge

Rounding of the cutting edge

Rounding of the cutting edge is caused by a combination of crater wear and wear in the relief area.

Cause

Combination of crater wear and wear in the relief area. This could be considered typical wear and is not necessarily indicative of a problem.

 

Solution

  • Use a tool that is more wear resistant such as solid carbide taps
  • Reduce the cutting speed of the tapping process

 

Didn’t find a solution to your issue? For a remedy that does not involve such a direct customization, try a tap designed around a universal application range and can be appropriate for a wide range of materials.  You can also find additional details in this Threading Handbook.

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