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Horn Cutting Tools’ R108 single-point thread-milling tool has been used by hydraulic equipment manufacturer Hi-Force to reduce machining time in the production of NPT threads.

Switching from a full-form thread mill to a Horn R108 has saved Hi-Force nearly 20 machine-hours per batch of 400 components.

As well as reducing machining time from around three minutes to around 10sec per thread, thread quality and tool life have improved, according to Horn.

In addition, the replacement cost for the Horn thread-milling insert is lower than previous tooling.

The component on which the Horn thread-milling tooling is used is a hydraulic connection block manufactured from EN24T rectangular bar.

This heat-treatable material has a machinability index of 29 per cent compared with 55 per cent for mild steel.

Machining is carried out in two operations.

The first operation produces axial features including an internal thread, a through bore, and an externally threaded spigot, produced on a CNC turning machine.

A vertical machining centre is then used to drill, chamfer and tap a thread on the top face; for this operation three parts per cycle are loaded into a simple fixture and machined consecutively.

Depending on the component specification, the thread required can be either 3/8in or 1/2in NPT; all NPT threads taper at a rate of 1:16.

The previous thread-milling process utilised a full-form single-insert thread mill.

Shane Cross, workshop manager at Hi-Force, said: ‘The combination of the taper and moderately tough material caused problems for the full-form thread mill.

‘Issues with push-off compromised the consistency of the thread form, so two passes were needed to achieve the quality we wanted.

‘As a result, average tool life was around 100 components per insert but we also experienced occasional premature destruction of the insert.

‘Productivity was marginally acceptable as it was taking around three minutes to produce each thread,’ Cross added.

The solution provided by Horn utilises an R108.NP18.02 insert with TI25 abrasion resistant TiCN coating, mounted on a highly rigid vibration-dampening carbide shank.

The insert is ground to the required thread profile which is generated to full depth in a single pass by helical interpolation of the tool.

Especially on tapered threads the single-point process enables productivity advantages over full-form tooling as push-off is eliminated.

In this instance, feed per tooth (fz) increased from 0.0112mm to 0.06mm while feed rate (vf) increased from 30mm/min to 159mm/min.

This allows threads to be generated in less than 10sec compared with around three minutes previously.

In addition, tool life has increased from 100 threads to 150.

Horn Cutting Tools

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