Thread Forming Tap with Short Chamfer

VP-SC-NRT short chamfer forming tap improves tool life and machining stability in shaft core production

Sifan Peng | OSG Shanghai

Recently, a manufacturer located in Ningbo, Zhejiang Province, China, whose name cannot be disclosed due to confidentiality reasons, was seeking for productivity improvement in its shaft core production, which is a transmission component for precision machinery. Founded in 2019, this company specializes in the production and sales of precision mechanical parts and automotive components usually made of aluminum alloy die-casting and alloy steel. This company currently employs approximately 30 staff and has a production space of 2,000 to 2,500-square-meter.

In early 2022, this client took over a production project on shaft cores made of SCM 440 alloy steel with a hardness of 23 to 25 HRC. The annual production volume is estimated to be around 200,000 to 300,000 pieces. One M6 x 1 blind hole is required to be threaded. The thread tolerance grade required is 6H and no galling should be visible. The parts are machined using a vertical machining center (BT30) with external coolant. A rigid tap holder is also employed.

At the beginning of the project, the drill hole size was 20 mm and the tapping length was 16 mm. The customer initially used a competitor cutting tap with a chamfer length of 2.5 P for the application. Later on, to enhance thread strength and processing efficiency, a competitor forming tap was employed. Running at a cutting speed of 12 m/min, the competitor tap was able to achieve a tool life of 300 holes. A few months into the project, however, the specification of the product was altered by the product supplier, which also affected the machining requirement of the shaft core. The drill hole size was changed from 20 mm to 17 mm; and the tapping length was changed from 16 mm to 15 mm.

Shaft cores made of SCM 440 with a hardness of 23 to 25 HRC. One M6 x 1 blind hole is required to be threaded per part.

The margin between the drill hole size and the tapping length went from 4 mm to 2 mm with only 2P. In addition, the chamfer length of the tap originally used by the customer was 2.5 P, which would cause the tap to break due to contact with the bottom hole during processing. Therefore, before machining, the customer would regrind the chamfer to the appropriate length on their own. However, due to the unstable quality of the customer’s own regrind, tool life became highly unstable. Tool life would vary between 30 holes to 300 holes, which had a dramatic negative impact on production efficiency and processing stability.

This customer had previously used OSG’s VP-NRT forming tap for processing aluminum alloy, which demonstrated good performance and stable tool life. With this positive experience, the client is confident with the OSG brand and decided to contact OSG through a distributor to troubleshoot their shaft core application. Once in contact, applications engineer Sifan Peng from the OSG Shanghai office immediately followed up by visiting the customer’s production plant. Upon a detail evaluation of the application, Peng recommended OSG’s standard VP-SC-NRT M6 x 1 forming tap (EDP# 8318048) for a test trial.

OSG’s VP-SC-NRT is a short chamfer type forming tap. The VP-SC-NRT is made of powder metallurgy high speed steel and features a special thread form. With the addition of OSG’s original V coating, long tool life is made possible in a wide range of work materials, including carbon steels, alloy steels, stainless steels, copper, brass, aluminum, zinc and alloy casting.

OSG’s VP-SC-NRT is a short chamfer type forming tap.

The short chamfer specification eliminated the need for tool modification before use and avoided tap breakage due to poor quality regrinding. For the cutting test, the VP-SC-NRT was used under identical cutting speed of 12 m/min as the competitor tap. The VP-SC-NRT was able to achieve stable tool life averaging 500 holes, which is 1.6 times more than the competitor tool. By switching to OSG’s VP-SC-NRT, this client is able to eliminate the hassle of tool regrind, improve quality, reduce the frequency of tool change and achieve longer as well as more stable tool life, ultimately leading to greater productivity and cost efficiency.

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