by Donald HalasClick image to enlargeby Donald Halas

Increasing threading productivity

 

Threading typically forms the last step in part production, a critical operation that generally can't be redone or repaired. If it fails, it yields a scrapped part that wastes materials and work time. Every decision that goes into a threading operation makes a critical contribution to its success, so to increase threading productivity, follow these tips to make the right decisions before the task begins.

Tool selection and use are critical
The process of threading involves making a thread form on a spiral, with larger spirals on smaller diameter components and smaller spirals on larger diameter parts. To make a proper thread, the tool insert must track the spiral correctly throughout a bore. Start with the proper anvil or helix angle in the toolholder, and if necessary, insert a shim seat underneath the insert to improve tracking, eliminate tool chatter and produce better gauging that creates a better thread.

Machine tool defaults may not be ideal for your task
Machine tools ship with default modes preset on their CNC controllers. Some defaults produce more threading passes than a job may require, leading to unsatisfactory results. Machines also typically make radial in-feed their default cutting mode, inserting the tool straight into the material, which creates high cutting forces. These forces can cause chatter and vibration that affect chip control and damage surface finishes, so it's important to choose a cutting mode that uses only as much cutting force as the job requires. 

Seco threading toolsClick image to enlargeChip control can make or break threading operations
Long, stringy chips that wrap around a toolholder can damage the tool's inserts and reduce their functional lifespan. Of course, re-indexing one or more inserts corrects the chipping problem and enables the threading process to resume, but needless
re-indexing also wastes tool life, and if chips damage the thread itself, they can doom a part to the scrap pile. Additionally, when a chip becomes stuck inside a part during internal threading, an operator can sustain an injury attempting to fish out the chip and rescue the part.

Chip control also becomes essential to automated and lights-out manufacturing. If a robot picks up a part with a chip wrapped around it, the presence of that chip can stop the robot in its tracks and halt overall production. Instead of a full run of parts ready to inspect and ship the next workday morning, the entire process ends prematurely, perhaps without completing so much as a single part.

Look to new threading options for better results
New developments and techniques show promise in improving threading operations in innovative ways. For example, threading carbide or CBN workpieces in a hardened state eliminates the need to thread grind and produces higher part accuracy because the part no longer needs heat treatment after threading, which can distort threads and other part features. Delivering coolant to the nose of the insert or to the cutting edge becomes very important to tool life and success in working with these ultra-hard materials.

Setup choices make or break every threading operation, so it's better to ask questions and clarify the impact of the answers before the job goes on the machine. SMT

Donald Halas is product manager, threading/threadmilling/grooving/MDT for Seco Tools.

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