Small Diameter Thread Forming

Custom VP-NRT forming tap achieves consistent performance and high thread quality in tablet computer shell application

Puhua Xv | OSG Shanghai

With rapid advancement in information technologies, 3C products – the combination of computers, communications, and consumer electronics, have become highly popular due to their superior portability and personalization ability. Information appliances today are ultra-thin and lightweight. With reduced weight and material, the size of screws has also become smaller. The use of AL6 and AL7 aluminum (equivalent to A60 and A70 series aluminum) in China’s 3C product shell market has drastically increased in recent years. However, small diameter tapping is a challenging machining process in these two types of aluminum. M0.8 x 0.2 (special), M1 x 0.25, M1.2 x 0.2, M1.6 x 0.35 and M2 x 0.4 are some of the most common tap sizes for small diameter machining. Breakage can easily occur due to the small size of the tap diameter. As opposed to cutting taps, thread forming tools can offer advantages such as long tool life and high process reliability because a forming tap forms screw threads through plastic deformation of work material with no cutting chips created. Therefore, rather than thread cutting, OSG recommends thread forming for small diameter tapping in 3C applications.

Recently, a part manufacturer of 3C appliances located in Dongguan, Guangdong, China, whose name cannot be disclosed due to confidentiality reasons, was seeking for an improved threading solution for its trial production of tablet computer shells.

Established in 2010, this company specializes in part production of information appliances, mainly producing the metal parts of intelligent terminals and related accessories. Currently, this company has more than 10,000 employees in its two production facilities and its main plant is more than 43,000-square-meter in size.

Left: Inside the production site of the tablet computer shell manufacturer in Dongguan, Guangdong, China.

Right: An image of a tablet computer shell made of AL6R01 aluminum (equivalent to A6061 aluminum).

The tablet computer shells are made of AL6R01 aluminum (equivalent to A6061 aluminum). A total of 28 holes in various diameters are required to be made per part. Each shell includes a mixture of blind holes and through holes with a hole depth between 1 to 2 x D. The accuracy tolerance must be within 5H. Approximately 3,000 to 5,000 pieces are produced per day in the trial production stage. The parts are machined using a FANUC vertical machining center (BT30) with a cutting parameter of 2,000 rpm and a feed rate of 400 mm/min for M1.2 x 0.2. External coolant is applied during machining.

Originally, the end user was using both carbide and HSS forming taps from a domestic tool manufacturer in China. However, there were problems of welding caused by inadequate cooling and high cutting heat. The material melted, flaked and sticked to the cutting tool, even causing the taps to break. The end user was unsatisfied with the result and was seeking a threading solution with consistent performance and excellent thread quality. By the recommendation of the manufacturer’s client, this end user reached out to OSG for support.

After a throughout evaluation of the application, OSG recommended the VP-NRT forming tap for holes in sizes of M1.6 and above. The VP-NRT is a powder metallurgy high speed steel forming tap coated with OSG’s original V coating. The VP-NRT is well known for its durability in a wide range of materials, including carbon steels, alloy steels, stainless steels, copper, brass, aluminum, zinc and alloy casting.

A standard VP-NRT V coated forming tap. In addition to standard items, OSG also offers custom tooling as well as modification and coating services to help manufacturers maximize productivity and quality.

By implementing the VP-NRT forming tap, the surface quality and finish of the machined threads improved significantly versus the competitor tool. However, the VP-NRT could not be used for machining holes below M1.6 because of welding. To improve welding resistance of the tool, OSG recommended to modify the original V coating of the VP-NRT standard product to OSG’s latest DLC coating to correspond to holes smaller than M1.6. Due to its smooth surface and extremely low coefficient of friction, the DLC coating is highly effective against non-ferrous metals such as aluminum alloys, which require welding resistance and lubricity. After the modification, the problem of welding was completed eliminated. The tool customization enabled significant savings in tooling cost, and the client couldn’t be more satisfied with the result.

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