24/04/2007
A win on points: bar peeling vs. turning
Including a report showing a practical example: bar peeling with CERATIZIT tools at BGH Edelstahl |
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From the raw forged blank to the polished bar – the carbide expert CERATIZIT proves its expertise in the field of bar peeling with practical examples. The mechanical engineering segment in the CERATIZIT cutting tool division / BU end-users focuses on the development of tools for bar peeling, an important area in the field of cutting tools.
Bar peeling is a machining method where producing heavy swarf. It is the machining of forged bars to remove oxide, chilled skin and surface cracks. During the peeling operation the bars are given the requested surface quality, dimensional accuracy and roundness. Bar peeling is suitable for the machining of various material types: for example tempered steel, bearing steel, tool steel, high-speed steel and spring steel, high alloyed also stainless steels, and even for titanium. The results are semi-finished products which are mainly delivered to the oil industry and the general mechanical engineering sector. Automatic lathes produce the most varied turned parts. Later the bars may be machined as mandrels, axles for wind turbines, gears, piston rods and shafts.
Bar peeling: from the blank steel to the machined bar
During the peeling operation the bar is moved through a rotating peeling head, with a radial direction of cut. The peeling head in this case has four cartridges, each with one to three inserts which are all in contact with the bar. The inserts serve for roughing and finishing.
Bar peeling in detail
1. Heating the blank steel in a furnace
2. Forging or rolling of the hot bars
3. Annealing and pre-alignment of the bars
4. Taking samples for quality assurance
5. Elimination of oxide, chilled skin, and surface cracks in the peeling facility taking into account the required dimensional accuracy and surface treatment
6. Straightening of the bar in the press to balance stress and strains which are caused by bar peeling.
7. Final ultrasonic checking of the peeled bar for cracks and other imperfections
8. Available upon request: grinding of the bar in a belt grinding machine
A practical example: bar peeling at BGH Edelstahl in Siegen, Germany
Boschgotthardshütte (BGH) Edelstahl in Siegen has been a CERATIZIT customer since 2005. BGH produces stainless steel and special alloys suitable for the toughest applications. At BGH in Siegen bars up to 18 metres long, are turned by a Kieserling & Albrecht machine with a length of 50 m. With this facility BGH machines around 4,100 tons of bars per month, producing 350 tons of swarf. CERATIZIT makes the roughing insert RNMH 5018MOS00-R50 CTC1635, which is applied up to a cutting depth of 7 mm, and the finishing insert, YNUF 201220S50-M50 CTC1125, which thanks to its positioning in the cartridge achieves a constant cutting depth of 1.5 mm.
Interview with Jost Kretzer, works manager at BGH Edelstahl
When is peeling applied instead of turning?
Kretzer: Peeling is mostly applied for long cylindrical work pieces, i.e. bars. Shafts with a step or bars with a diameter larger than 300 mm are turned.
What are the advantages of bar peeling?
Kretzer: One of the main advantages is the simultaneous application of four tools; this means feed rates four times higher than with turning. There is also reduced vibration in peeling because the bar is held closer to the cutting tools. The entire peeling process is considerably more stable and thus more resistant to vibration, through which performance is also increased.
Furthermore the material allowance for bar peeling is smaller compared to classic centre turning. The bar is held centrally, extra support such as fixed stays or change of clamping as in turning are not necessary.
What are the risks in bar peeling?
Kretzer: Clearly, the breakage of the insert. If an insert breaks at a feed rate of 15 to 18 mm per revolution, the entire cartridge is ruined, or even all four cartridges. The higher forces which can occur after the insert breakage cause the peeling head to start turning the bar instead of peeling it. This leads to very high costs as the 22 guide rolls of the peeling machine and the bar are damaged. But before the insert breaks, the pressure rises and the facility requires more power, which can be heard very well. In this case sensitivity is necessary: it is important to change the insert at the right moment to avoid this risk.
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