Thread forming with multi-groove
Thomas Deschle, BASS GmbH & Co. KG and Magnus Hoyer, OSG GmbH
By nature, roll tapping forms screw threads through plastic deformation of the work material. Because no cutting chips are created, thread forming stands out as a clean machining method. As opposed to cutting taps, thread forming tools can offer advantages such as long tool life and high process reliability even in large thread depth applications. However, when using minimum quantity lubrication (MQL) during thread forming, a negative effect may occur – the contamination of part and tool during machining. This condition is especially apparent in MQL processing, whereas most contaminants are removed by the cooling lubricant in wet processing. In addition to requiring subsequent component cleaning, the contaminants may also increase abrasive wear of the tool and reduce its service life.
BASS’ manufacturing plant is located in the city of Niederstetten, Germany, with an estimated production floor of 6,500-square-meter.
The cause for this contamination is small material particles moving out of the ridges of the furrow of the tapped thread during processing. These particles accumulate in the grooves of the roll tap and will gradually contaminate both the tool and the part. To reduce this contamination, BASS has taken extensive series of tests. Several years of development work have resulted in the internationally patented multi-groove as shown in figure 1. Due to the special geometry of this new groove shape, contamination of the threading tool used under MQL conditions can be eliminated almost completely.
Figure 1. BASS’ internationally patented multi-groove tool geometry for longer tool life and clean parts.
The special form of the multi-groove absorbs dispersed material particles from the ridges of the furrow. At the same time, it also increases the cleansing effect of the cooling medium, whether it is MQL or cooling lubricant, allowing the unwanted material particles to be removed from the grooves and thus from the tool and part, enabling both to come “clean” from the machining process.
An important factor during MQL-machining is to evacuate the air from the blind hole. In this case, traditional roll taps have a crucial disadvantage. The air contained in the blind hole of the conventional straight groove can only escape with a delay during thread forming. While the tool is entering the hole and forming the thread, the air within the bore hole is displaced and compressed to the bottom, with the cooling lubricant being pressed against a “wall” of air. Due to this “counterpressure,” the coolant is unable to wet the machining area sufficiently to maximize its lubricating effect. This is where the multi-groove comes in.
The larger volume of the multi-groove allows for the enclosed air to escape more quickly and for the bore hole surface to be better wetted as depicted in figure 2. The result: up to 30 percent longer tool life and a drastically enhanced process reliability.
Figure 2. The multi-groove’s functional principle: With the traditional groove form as depicted on the upper half of figure 2, air within the bore hole (highlighted in blue) is compressed to the bottom. Whereas the multiple groove configuration allows more air to escape and for the MQL-aerosol (highlighted in yellow) to sufficiently wet the bore hole wall. The result is an improved washing effect of the multiple groove, where the outgoing air immediately removes material particles from the part during machining.
The logical conclusion: the deeper the blind hole (> 2xD), the greater amount of air has to escape – and thus the greater the effect of the multi-groove.
BASS has developed an internationally patented multi-groove geometry to control contamination during roll tapping. The multiple groove configuration increases the cleansing effect of the cooling medium, allowing unwanted material particles to be removed from the grooves and thus from the tool and part.
Another factor influencing the effectiveness of the multi-groove is the pressure in which the aerosol is blown to the processing point. The usual ambient air pressure is 1 bar. Through compression within the blind hole, the aerosol thus pushes against the “wall” of air with more than 1 bar. If the pressure of the aerosol is just slightly higher, a sufficient wetting of the bore hole wall by the aerosol cannot be ensured. Thus, the tool life drastically decreases and contamination increases. Particular for this reason, the multi-groove offers great potential especially under poor processing conditions.
BASS GmbH & Co. KG is a dynamic, medium-sized family manufacturer based in Niederstetten, a German town located near the medieval tourist site Rothenburg ob der Tauber. Ever since the company’s founding by the toolmaker Kurt Bass in 1947, BASS has focused on the development, production and sales of powerful threading tools. In 2019, BASS was acquired by OSG Corporation to reinforce its strength in the European market and global affiliated companies.
BASS GmbH & Co. KG’s headquarters in Niederstetten, Germany.
BASS is renown worldwide for its high-quality taps, especially for its roll taps and special tools. A commitment to exceed customer expectation in products, services and delivery time is the core philosophy of BASS’ 150 employees. Driven by innovation, BASS serves clients from all fields – ranging from automotive, mechanical engineering and medical applications up to the machining of nuts, and manufacturers of windmill turbines.
For more information on BASS GmbH & Co. KG
Combination with OSG’s ADO-TRS ‘Triple Revolution’ 3-flute coolant-through carbide drill to achieve flawless holes for perfect threading
The ADO-TRS is one of OSG’s latest drilling innovations for ultra-machining efficiency in a wide range of materials. This 3-flute coolant-through carbide drill series is highly recommended to be used in combination with BASS’ multi-groove forming taps. The ADO-TRS’ 3-flute specification offers greater balance than 2-flute drills, which are more prone to chattering. Moreover, the ADO-TRS enables superior roundness and improved positioning in terms of hole precision. With capability to excel under high-feed condition, the ADO-TRS is able to minimize contact time with the workpiece material, which reduces the probability of work hardening.
The ADO-TRS is available from diameter 3 mm up to 20 mm, in processing depth of 3xD and 5xD, and is suitable for applications in carbon steels, alloy steels, mild steels, cast iron and hardened steels.