XPF form tap eliminates frequent tool breakage in differential housing
Marco Túlio Bianchi Furtado | OSG Sulamericana
Truck manufacturing may be a small segment within the automotive industry, but it is still one of the most economical methods for transporting raw materials and finished goods. Similar to passenger vehicles, heavy-duty trucks have greatly evolved over the past century, with an increased emphasis on the total cost of ownership, fuel efficiency, cleaner emissions, and safety. To comply with these requirements, OEMs and manufacturers of heavy-duty truck components are constantly in search of new innovative solutions to further improve efficiencies, quality and stability of their manufacturing process.
Founded in 1891, Scania AB is a leading Swedish manufacturer of commercial vehicles, specifically heavy trucks, buses and coaches. It also manufacturers diesel engines and provides transport solutions for industrial and marine applications as well as power generation. The company’s headquarters is located in Södertälje, Sweden, employing approximately 5,600 staff. As of 2015 Scania has a sales and service organization spanning more than 100 countries, with a total of 45,000 employees, accordingly to the company’s official statement.
Scania has production facilities and assembly plants globally, including one in Brazil that dedicates to assembly, bodywork and fitting locally adapted vehicles. Scania first began its activities in Brazil in 1957. Nearly 60 years later, the Brazilian division has established itself as one of the main subsidiaries of the Scania group worldwide. Scania’s production facility in Brazil is located in São Bernardo do Campo, a region also known as the Greater São Paulo, and has been attended by OSG’s South American division – OSG Sulamericana, for over 20 years. Scania’s Brazil production plant produces drive assemblies, differential housings, and assembles several models of trucks, as well as chassis production for buses. Altogether, the plant has an annual production between 30,000 and 50,000 products per year.
Differential housings, which is the cover unit of the differential gear train that controls the speeds of driving wheels, have been produced at Scania’s Brazil production plant for the past 10 years. The differential housing is made of forged steel with low carbon and high manganese. There are eight holes per housing that require internal threading. Each hole has a diameter of 16.8 mm, thread length of 35 mm, tolerances of 6H and hole types of both through and blind holes. Scania’s Brazil production plant manufactures approximately 2,736 pieces of the differential housings annually, requiring the threading of over 20,000 holes in total.
The threading used to be processed by cut taps in the size of M18 x 2.5 using soluble oil (5% to 10%) in Scania’s GROB BZ1000 CNC machine. With the spiral cut tap, Scania was experiencing frequent tool breakage, low yield, and consequently low productivity. Hoping to increase tool life and avoid tool breakage, Daniel Prado, Tool Analyst responsible for the application, consulted with OSG Sulamericana’s Applications Specialist Marco Túlio Bianchi Furtado on the possibility of processing the internal threads by rolling. Upon a detail evaluation of the application, Furtado recommended OSG’s XPF forming tap (OIL-S-XPF M18 x 1.25 DIN376) and also a special step-drill 16.75 x 20 mm for pre-drilling.
OSG’s XPF represents a new evolution in forming tap technology. This series is engineered to generate up to 50 percent less torque versus other forming taps, making it feasible to tap materials up to 35 HRC and sizes up to M45 in diameter. Its low-torque design allows for longer tool life at faster speeds. With the addition of OSG’s proprietary V coating, wear resistance can be further enhanced. The XPF is available with or without coolant holes, and in standard or long shank style.
With some experience in forming tap, Prado took the recommendation and put the XPF up for trial. Immediately after the first parts, the better finishing of the threads was evident. After the completion of the first batch of parts, the wear on the XPF had proven to be negligible. The parameters used hitherto been very low in an attempt to minimize the problem of frequent tap breakage. With no apparent cutting wear troubles, Furtado proposed to increase the rotation of the threading of 210 rpm to 390 rpm to further enhance productivity.
At the end of the trial, the XPF presents a gain of 43.14 percent in the cost per part, and 46.11 percent in tapping time. Although the initial tooling cost is more expensive than the previous competitor cutting tap, the XPF is able to demonstrate benefits in all directions, especially in process stability, significantly minimizing the occurrence of tool breakage. The reduction of tool breakage is critical in this application. The previous cut tap averaged 45 parts per tool and was reground up to five times, but the yield of the reconditioned tool was greatly reduced, capable of only completing 10 pieces of differential housing, requiring frequent tool change due to cutting wear and breakage. The XPF, on the other hand, averages 360 parts per tool and is removed from the machine only by natural wear. The XPF clearly outperforms the previous competitor cut tap in the categories of cost efficiency and productivity. More importantly, it is able to provide complete confidence to the operators at Scania, knowing that the XPF they put into their spindle will always provide satisfactory results equivalent to their quality standard.
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