POWER SKIVING – AN INNOVATIVE GEAR MACHINING OPTION
It is expected that the machining of automobile transmission gears will continue into the future with 7-speed and 8-speed transmissions, even with the introduction of EV reducers. The core component of these gears and reducers is the planetary gear set, with the power skiving being an innovative method for machining ring gears.
Power skiving was conceived in the beginning of the 20th century. Though highly productive and flexible, this method was difficult to implement because it required precision equipment and tools. Today, however, the development of new geometries and grades of tools, as well as improved machine control, makes the power skiving process an interesting alternative for gear manufacturing.
Power skiving is basically an operation where a workpiece is machined into the shape of a desired gear. The two axes rotate according to the gear ratio, due to the intersecting angle between the gear axis and the tool axis, resulting in skiving cutting in the direction of the gear’s tooth line, and continuous skiving cutting occurs with a combination of hobbing and shaping.
Advantages of Power Skiving Machining Method
The advantages of the power skiving machining method are as follows:
Power skiving replaces most of the conventional gear machining methods: Such methods include broaching, shaping and hobbing, which are used depending on internal/external gear machining and interference issues. Power skiving is more flexible than broaching, because it can be applied to blind and through hole gears. Hobbing can only be applied to external gear processing but cannot be applied if there is interference, whereas power skiving can also be applied when there is interference with internal/external tooth processing. In shaping, compared to power skiving, the tool has a longer contact time with the workpiece and generates much cutting heat, which is disadvantageous to tool life. Another advantage to power skiving is its excellent profile accuracy in the lead direction.
High productivity: In the power skiving process, the cutting speed is in the tooth line direction of the gear, so the milling rotation speed of the cutter must be multiplied by sinΣ (intersection angle).
Although there is a difference, depending on the angle of intersection, the revolutions per minute (RPM) of the spindle must be about 4 times faster than that of conventional milling in order to obtain the desired speed with a carbide tool.
At this time, the workpiece rotates according to the gear ratio, and since continuous cutting is performed according to the way the gear is generated, the cutting speed becomes very fast.
Power skiving differs depending on conditions, such as the module and pressure angle, but it is generally 4 times faster than hobbing and about 10 times faster than shaping. Therefore, it is possible to significantly reduce the number of machines used in the machining process. For example, one power skiving machine can do the work of 10 installed shaper machines. This is the basis for reducing space, minimizing equipment investment and reducing manpower costs.
One machine for turning, milling and gear machining: Traditional gear machining requires separate machines for each process; for example, shaping is usually done on the shaping machine and hobbing is done only on the hobbing machine. However, in the case of power skiving, all the work is done on one 5-axis multitasking machine, making it possible for the operator to complete turning, grooving, milling, drilling and chisel machining, all in one setting. This eliminates the need for separate setup time and can dramatically shorten the cycle time.
High compatibility: With the same module and pressure angle tool, power skiving processes of spur gears and helical gears are machined within the range of formed crossing angles in the production of internal and external gear teeth. In addition, it is also able to machine the various numbers of teeth.
Less interference when machining: Hobbing can only be applied to external teeth and cannot be applied when there is workpiece interference, but power skiving can reduce the component size and weight when machining gear parts. Gear tooth profiling using shaping has relatively even less interference than hobbing, but the productivity is low and undercutting is essential when machining blind hole types. However, power skiving avoids this issue with a programmed tool path, even if there is no undercutting required.
Hard power skiving for internal gears: After gear cutting, partial deformation occurs when heat treatment is performed to increase the hardness of the gear surface. Hard power skiving refers to finishing the deformed part with a carbide power skiving tool. Previously, there was no way to efficiently process heat-treated small and medium-sized internal gears, therefore, power skiving will become a game changer in gear cutting in the future.
TaeguTec’s Power Skiving Tool Technology
TaeguTec is a leader and innovator of advanced metal cutting tools including insert types and head changeable solid carbide tools with advanced technology in the production of power skiving tools.
Essentially, carbide tools have very high cutting speeds and high hardness, compared to HSS tools; this reduces machining time and increases tool life. The insert type is applied to gears in large sizes with the diameter of the tool being relatively large. In addition, the head changeable solid carbide tool is suitable for the gear processing of small sizes, such as automobile parts.
Usually, there is a high probability of problems, such as chip tangling, due to the rotation of the workpiece during internal gear processing, but TaeguTec’s cutting tools solve these challenges using an internal coolant supply. The head changeable type solid carbide tools not only guarantee high-precision because of its rigid and precise fastening structure but also eliminates the need for setup intervals, due to simple indexable head replacement, which enables high cost reduction.
For more information, please contact TaeguTec – Tel: 011 362-1500.
