Threading Options for Hard Materials

Source: Modern Machine Shop September 20, 2017 2:04 pm

Here are three approaches to threading hardened components.

Article From: 7/20/17 Modern Machine Shop, Derek Korn, Executive Editor

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Shops have options when it comes to hard threading. However, Seco Tools says most of them involve multiple operations and tools, each of which presents the risk of human error, a possible increase in cycle times and a probable hindrance of part consistency.

Here, the company highlights three such tooling options, along with their limitations:

1. A tungsten-carbide-tip insert brazed onto a steel, stick-type tool.

  • Every tool change requires datums to be set again, which extends downtime.
  • Material has to be annealed prior to machining and re-hardened afterward,which increases the risk of thread distortion.
  • Tool life is short and cutting speed is typically limited to approximately 40 m/min.
  • Long cycle times, often measured in days, occur because of multiple operations.

2. A brazed-tungsten-carbide or polycrystalline-boron-nitride (PCBN) grooving tool for roughing, and an insert made from either of those materials to finish profile.

  • This time-consuming, two-tool operation requires annealing the workpiece if using the tungsten-carbide tool.
  • The brazed tool joint needs coolant, and it limits cutting speed because of heat.
  • Low cutting speeds extend cycle times (a 33-mm-pitch Acme thread can take as long as five hours).
  • Rapid flank wear and built-up edge (BUE) occur due to low cutting speeds.

3. PCBN-tipped insert brazed to a steel shank.

  • Every tool change requires datums to be set again, which extends downtime.
  • The brazed tool joint needs coolant, and it limits cutting speed because of heat.
  • Low cutting speeds extend cycle times (a 33-mm-pitch Acme thread can take as long as three hours).
  • Rapid flank wear and BUE occur due to low cutting speeds.
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Threading hardened materials such as this one that requires an ACME thread presents a range of challenges.

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Article From: 7/20/17 Modern Machine Shop, Derek Korn, Executive Editor

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