Tap Performance Troubleshooting - Part 1: Insufficient Tool Life

June 5, 2019 2:14 pm

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A series from Walter Tools USA

 

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

In this post, we’ll provide remedies for the issue of Insufficient Tool Life.  The goal is to offer you suggestions and changes that can be made to increase the tool life of the tapping application.  Many times this issue is associated with poor chip control which can also manifest into other issues.  For further information on chip control, excessive wear and fractures, please see other articles in this series.

The first action to take to extend the life of your tapping tool is understanding what’s causing the issue. Although there are multiple factors that can affect the tool life at the same time, we recommend identifying each one of them and address them promptly. The best way to do so is to start by answering the following questions:

 

1. Are fractures or chipping causing the end of tool life?

2. Is it possible to improve the overall process?

3. Can we improve the wear resistance of the tap?

 

Let’s take a look into each question and identify a remedy.

 

Reducing fractures

When having problems with chip control, fractures can occur. Loosely wound chips harm the tool, in the flute area, when being evacuated.

The best way to address this problem is by switching to a standard product with one of the below flute features.

 

Chip formation

Several different features can be added to the tap which affect the way the chips are formed.

 

If you cannot improve the chip control, it’s generally recommended to switch to thread forming or thread milling.

 

Improving the overall process

To maximize the tool life of the tap, it is necessary to improve the complete process.  Threaded holes require a drilled hole first before the tapping process.  Therefore, the drilling process could be affecting how the tap is performing.

Here are a few tips/actions you should take to optimize your process:

  • Check if the core hole drilling leads to a hardened edge zone. You may need to slow the feed and speed of the drilling process or replace the drill sooner.
  • 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.
  • Check if there are welding seams or plasma cut surfaces close to the thread. These processes may have hardened the material in the local area and are having an adverse effect on tool life.
  • Use a synchro chuck with minimum compensation for synchronous threading
  • Maximize the core hole diameter
  • Increase drilling depth so that a tap with a longer chamfer can be used
  • If tool life is more important than machining time, the cutting speed can be reduced
  • Check if the tool has application in the material being machined. Using a tap that was designed for a different material or application is the most common problem when tool life does not match expectations.  Make sure that the tap being used, was designed for that application.

 

Improving the wear resistance of the tap.

In an ideal scenario, we would like to see even and consistent wear of the cutting edge, not a random fracture, determine end of life for the tool.  This leads us in the direction to make the tool from very high wear resistant material.  However, these tool materials can also fracture due to low toughness.  Finding the correct tool substrate to be hard enough to resist wear but also tough enough to resist fracture is the challenge to properly balance the tool substrate for the specific material being machined.

Here are a few recommendations that will help you improve the wear resistance:

  • Try a harder substrate. Solid Carbide taps have more wear resistance, but sometimes a nitriding process or Xtra-treat process can increase the hardness of the tool.
  • Increase the number of cutting edges by increasing the number of flutes or the number of teeth in the chamfer area (the lead). More cutting edges will result in less work being done by each tooth, giving the tap longer tool life.
  • Reduce the helix and/or Rake angle. This will create a stronger cutting edge, but you have to be careful that you are still controlling the chips properly.  A tap with a reduced helix or rake angle will not control the chips as efficiently.
  • Choose the ideal coating for the material.

 

tool coating

Ensuring that the tool coating has an application range in the material being machined can have a big improvement in tool life. 

  

Didn’t find a solution to your issue? For a remedy that does not involve such 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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