Development and application of gear processing technology (4)

Gleason has developed a new process that can be machined on its CNC-controlled Phoenix series of freeform machines using straight-cone Coniflex tools to process straight bevels or hypoid gears. Bevel gears. According to Stadtfeld, machining spur gears on Phoenix machines can significantly reduce cycle times and increase machining efficiency by 100% to 120% compared to mechanical machines.

Gear cutting machines are multi-axis machines that are usually driven by direct-drive motors (replacement of two sets of drive gears on the table and the nip head).

Liebherr, which specializes in the development and development of parallel shaft gear machines, also offers CNC-controlled hobbing machines with direct drive, gear drive or worm drive systems. According to Christoph Bunsen, development and design manager for gear cutting machine tools at Liebherr, although many people believe that the use of direct drive motors on hobbing machines has become a trend, there are still good reasons to consider the use of gears or worm gear drives on gear hobbing machines. The direct drive approach provides greater flexibility and usually requires less maintenance and is faster and more accurate than gear drives. On the other hand, gear or worm gear drives provide more torque at low speeds, while direct drives are less likely to do so.

For example, comparing a similar gear hobbing machine produced by Liebherr: a direct drive gear hobbing machine with a rated power of 23 kW, the hobbing head can produce a torque of 130 N·m at a spindle speed of 7000 r/min. The gear-driven hobbing machine with a rated power of 20 kW produces a torque of up to 270 N·m at a spindle speed of 500 r/min.

Bunsen explained, “Sometimes this is a trend-changing issue. Some users insist on direct drive, and we don’t know why they are. For processing, sometimes gear drive may be a better option.”

Nowadays, users have higher and higher requirements for machine tool accuracy and require a higher processing capability index (in Cp or Cpk). To this end, gear machine tool suppliers are deeply concerned about the need to propose appropriate machine accuracy.

Grison's Maiuri said, "With 6 sigma analysis, the processing capacity index Cp and Cpk requirements are usually 1.66, although some users require Cpk = 2. In some cases, users require 8 sig Ma or 10 sigma analysis, although the current 6 sigma analysis is increasingly becoming the standard method." He said that the user's proposed accuracy requirements are getting higher and higher, and requires more gear parameters to be tested before the acceptance of the machine. For example, a typical car planetary pinion has a three-needle measurement dimensional tolerance of about 50 μm. In addition, more workpiece designs (ie more workpiece quantities) must be evaluated before the machine is accepted. He pointed out that the number of workpieces used for machining capability research is usually 25 to 30, although some users require up to 150 workpieces.

Liebherr's Oliver Winkel explains how to reduce the tolerance of a 60μm marked on the part drawing to a specific CmK=1.67 (CmK is the Cpk that is only applied to the machine itself, not under actual production conditions). A 25mm effective hobbing tolerance. As is known from experience, an increase in CmK usually causes the tolerance to decrease linearly. “Requires dimensions within 100% of a given tolerance is not the same as requirement for CmK=1.0 for the same tolerance.” Winkel explained that requiring CmK=1.0 resulted in a 30% to 40% reduction in effective tolerance. The effective tolerance is determined by all data points that converge between the tolerance bands of the X-bar–R chart, which are more stringent than the upper and lower control tolerances, only the part drawing Label the half of the tolerance. The tolerance band for effective tolerance is determined by the Six Sigma analysis and is tighter than the part icon tolerance band. Although there may be some changes in the results depending on the processing conditions, the trend shown in Figure 4 is universal.

“In Germany, we have a saying: Parts should only be made as good as they are needed, and should not be made as good as possible,” Winkel said. “Unnecessarily tightening the tolerance band will result in longer processing times and will Increase processing costs."

Previous page

Slot Diffusers

Slot Diffusers,Slot Air Diffuser,Slot Diffuser Grill,Ceiling Slot Diffuser

Guangzhou Jointair Co., Ltd. , http://www.jointairaccessories.com