Longitudinal turning for efficient machining of small precision workpieces

The trend toward miniaturization of parts continues, and parts in high-tech products are getting smaller and smaller. It is precisely at the same time that the use of parts is more specialized, and the requirements for accuracy and durability are constantly increasing. Original automatic longitudinal lathes, which were mainly used in watch industry with high precision, are now being used in many other industries.

For small and medium batches of workpieces with a diameter of 32 mm or less, automatic longitudinal lathes have many decisive advantages. The Wilhelmi Glasfaseroptik company of Waldsolms in the Hochtaunus region is a professional manufacturer of optical waveguides. The plant is using Cincom automatic longitudinal lathes. This lathe can complete the set of machining tasks quickly and accurately after one set-up, and can be converted in a very short time to process other parts.

The company has 10 employees and can design and manufacture a complete set of fiberglass light guides in small and medium quantities. The technology itself lies in accurate precision connections and the appearance of glass fiber ends polished. A fiber optic cable with 3,000 glass fibers, as long as five of them are damaged, will be considered as waste. Therefore, all Wilhelmi's cars and milled parts are all processed inside the company so that it can ensure high quality for a long time.

200~5000 pieces

In the production of small parts, in addition to high precision, the processing time plays a decisive role. Only by being able to flexibly process all kinds of complex small parts, and strictly guarantee the required quality standards, but at the same time, it can produce quickly and economically to gain a firm foothold in the market. In particular, these requirements are even more important due to the increasing number of component types that result in smaller and smaller batch sizes, or when only a few parts are needed in some special cases.

Fig. 1 The K16 longitudinal feed automatic lathe is equipped with six sets of turning tools for complete sets of machining, four kinds of drive turning tools with a number of revolutions up to 6000 r/min, and four drill tools on the front and rear sides respectively.

If the former Precision Parts were machined using conventional machines, then Wilhelmi discovered the advantages of automatic longitudinal lathes several years ago. Now Wilhelmi uses the Cincom B12 and Cincom K16 automatic longitudinal lathes to machine turn-milled workpieces of various materials. Processed materials include non-ferrous metals, precious metals, stainless steels, titanium alloys, and acid-resistant copper alloys, Arkap, for rods with diameters of 12mm and 16mm, batch sizes typically between 200 and 5000, and minimum internal diameters. The tolerance value is 10 μm and the smallest hole diameter is 0.15 mm.

The main advantage of automatic longitudinal lathes is that they can perform roughing, finishing, punching, deburring and thread rolling on a variety of different workpieces in a very small space. After processing on the spindle, the workpiece can be automatically removed from the opposite axis and then machined on the back. For this purpose, there are a total of six kinds of turning tools on the K16 automatic longitudinal lathe, four driving tools with a rpm of 6000 r/min, and four drill tools on the front and rear sides (see Figure 1). The number of revolutions of the main shaft is 15000r/min, the number of revolutions to the top shaft is 10000r/min, the working area diameter is 12mm, and the length is 200mm.

Fast forward speed up to 34m/min

Due to the fast forward speed of up to 34m/min, the braking and acceleration times for a total of five working axes are extremely short. This means that the automatic longitudinal lathe can be effectively reduced since the front and back sides of the workpiece can be processed synchronously with two tools. The processing time of each workpiece.

Fig. 2 The components used for fiber optic cable processing with longitudinal feed automatic lathes are small and complex and demanding; the machine tool can be retrofitted in a very short time, thus also suitable for small batch processing

In addition, on the K16 model, the new high-speed control unit Fanuc 3li, and specially developed for the Citizen Makros, significantly reduced downtime. Moreover, these two independent machine systems can be moved in overlapping motions when changing tool and thread, further reducing downtime. The use of FMB's bar loading box enables both machines to guarantee the automatic supply of raw materials. In this way, only a few people are required to run each shift, which reduces personnel expenses.

Figure 3 Longitudinal feed automatic lathe guarantees maximum accuracy and repeatability when machining small and complex workpieces

For Wilhelmi, the decisive factor is the constant high quality level of the machined workpiece. In the long run, both Citizen machines have demonstrated high accuracy and absolutely no fluctuations in processing quality. The reason is that the size of the base of the machine tool is quite large, and the main shaft is oil-cooled, which avoids the material expansion caused by the running heat, and thus the automatic longitudinal lathe has particularly high thermal stability. In this way, users will benefit from extremely high accuracy and repeatability during long-term operations. Moreover, these two longitudinally-feeding automatic lathes have very short refitting times and are very flexible in processing. When the raw materials are the same, even if the lot sizes are extremely small, they can be processed economically and rationally.

Add-ons improve efficiency

Compared to conventional transverse feed lathes, longitudinal feed automatic lathes are significantly faster when machining complex, small precision parts (see Figures 2 and 3). In special applications, precision machine tools are equipped with many customer-specific additional components, so that the benefits of longitudinally-feeding automatic lathes can be significantly improved.