Single point threading saves the day

Switching from a full form thread mill to a Horn R108 single point thread milling tool to produce NPT threads has reportedly saved nearly 20 machine hours per batch of 400 components for Daventry-based hydraulic equipment manufacturer Hi-Force.

As well as reducing machining time from three minutes to around 10 seconds per thread, thread quality and tool life have improved. In addition the replacement cost for the Horn thread milling insert is significantly lower than the previous tooling.

Shane Cross, workshop manager at Hi-Force, comments: “Frankly, the gain in performance using the Horn tooling is remarkable. Previously we had a slow process that needed constant attention to achieve the desired quality. Now we have a fast, highly reliable means of doing the same job.”

Hi-Force is a successful supplier of hydraulic tooling to a wide range of industry sectors. From its start-up in the 1980s it initially went on to become one of the leading suppliers of hydraulic tooling in the UK, but since 1991 it has developed as a global organisation and now exports around 85% of its output to 100 countries worldwide.

Its current network of sales and distribution centres in Europe, the Middle East, South-East Asia, South Africa and Australia has grown on the back of innovative product development and high quality manufacturing under an ISO9001 approved quality system. By late 2010 the company will have consolidated its UK operation into new purpose-built 50,000ft² premises in Daventry.
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 machineability index of 29% compared with 55% for mild steel.

Machining is carried out in two operations. The first produces axial features including an internal thread, a through bore and an externally threaded spigot which are produced on a CNC turning machine. A vertical machining centre is then used to drill, chamfer and tap a thread on the top face and 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 3/8 inch or ½ inch NPT with all NPT threads tapering at a rate of 1:16. The previous thread milling process utilised a full form single insert thread mill.

“The combination of the taper and moderately tough material caused problems for the full form thread mill,” Mr Cross reports. “Issues with push-off compromised the consistency of the thread form, so two passes were needed to achieve the required quality. 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.”

An important factor in the success enjoyed by Hi-Force since its formation has been the efficiency of its manufacturing operations and this has been promoted through a combination of ongoing investment in modern capital equipment and a diligent approach to methods improvement.

“We recognised that the existing method of producing the thread offered potential for improvement,” recalls Mr Cross. “However the results obtained using the Horn tooling exceeded our expectations.”

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

Particularly on tapered threads, the single point process enables significant 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 whilst feed rate (vf) increased from 30mm/minute to 159mm/minute. This allows threads to be generated in less than ten seconds compared to around three minutes previously. In addition, tool life has increased from 100 threads to 150.

“In practice it now takes less time to produce the thread than it does to screw a thread gauge into it,” Mr Cross confirms. “Equally important is the consistency of the thread that the Horn tooling produces. We've gained significant advantages on productivity, quality and manufacturing cost and the Horn inserts themselves cost less than the ones we previously used. It has been a very successful project and has encouraged us to look at how Horn can contribute elsewhere.”

Horn Cutting Tools
www.phorn.co.uk