EP2422898B1

EP2422898B1 - Method for plastic forming of toothed shafts

Info

Publication number: EP2422898B1
Application number: EP20110461501
Authority: EP
Inventors: Zbigniew Pater; Janusz Tomczak
Original assignee: Politechnika Lubelska
Current assignee: Politechnika Lubelska
Priority date: 2010-08-30
Filing date: 2011-01-03
Publication date: 2013-11-13
Anticipated expiration: 2031-01-03
Also published as: PL216309B1; EP2422898A1; PL392276A1

Description

This invention relates to a method for plastic forming of toothed shafts, in particular of hollow shafts. The notion of "hollow shaft" is to be understood as a shaft which has a cylindrical or shaped hole located centrally along its axis.
US-A-2 906 146 discloses a method, in which teeth are formed on a preformed step of a shaft by rolling the blank between three working rolls.
A vast number of methods for forming toothed shafts have been developed so far. The ones that are most widely used in industries include, among others, mechanical working processes - metal machining, in which the required shape of the formed part is obtained by removing consecutive material layers. A shaft profile is first obtained in rolling and then teeth are cut on the shaft. Mechanical working processes of toothed gears have been described in the literature (K. Ochduszko "Koa
a z
bate. Wykonanie i montaż," Vol. 2. WNT, Warszawa 2009). Mechanical working processes of toothed gears can be divided into two groups depending on tool shape as well as product and tool motion kinematics. The first group includes shaping methods consisting in the use of machining tools which working part is in the shape of tooth space of the machined toothed wheel - a toothed gear. This group also comprises such processes as roller milling, finger milling, chiseling, or pull broaching. The other group includes rotary methods for cutting gear teeth based in cooperation between the tool and the gear to be formed. The tooth profile is made when the gear and the tool mesh. The most common rotary methods for machining toothed gears include, for instance, the Maag method of rotary chiseling, in which the tool in the shape of a toothed bar moves to and fro, while the gear rotates and moves in a translational manner towards the tool. Another method for rotary machining of toothed gears is the Sunderland method of chiseling, in which the tool in the shape of a toothed bar translationally moves to and fro towards the gear, while the toothed gear moves in a rotary manner. One more very commonly used method for rotary machining of toothed gears is the Fellows method of rotary chiseling, in which the tool in the shape of the toothed gear moves to and fro and rotates. The machined toothed gear performs at the same time rotary and translational motion towards the tool. The Gleason method of toothed gear rotary milling has also been widely used. With this method the tool is worm-shaped and has grooves cut along the axis. In the normal section the worm is in the shape of a rack. The tool moves in a rotary manner, while the formed toothed gear moves in a rotary and translational manner towards the tool. Plastic methods for toothed gear generating are also known, and they include such processes as forging and toothed gear rolling. The processes for plastic forming of toothed gears have been described in the literature (A. Turno, M. Romanowski, M. Olszewski "Obróbka plastyczna kó z
batych," WNT, Warszawa 1973). Forging processes are most commonly used for forming bevel gears, plate gears, and special gears. The forging process consists in that the blank is pressed by the tools the internal shape of which corresponds to that of the forging. As a result of the pressure, metal fills in the tool impression, owing to which a toothed gear is formed. One characteristics of toothed gear forging is that obtained products mirror, or constitute a negative image of the tools. Another method for toothed gear forming is the rolling process in which the product shape is a boundary of consecutive points marked by the teeth of the rotating tool. The forming process is gradual, and the maximal thrust necessary to form teeth is considerably lighter than it is in the case of forging. Depending on process kinematics, a few methods for teeth rolling can be distinguished. In cold rolling of teeth, three non-powered rolls are used. Preforms in the form of pack or rod are positioned in the lathe chuck and propped with a center. Three toothed rolls of constant axle base move along the material which rotates and drives the working rolls. The tools in the form of toothed rolls have a special shape. They have two cones: an entrance cone and an exit one, as well as a cylindrical sizing part. This forming method is used for rolling teeth of small gears only out of preforms prepared in advance. Another method for tooth rolling is tangential rolling, which consists in tangential shifting of the rolled gear between two rotating rolls of constant axes. This method is predominantly used for rolling teeth of small dimensions. Another process for tooth rolling is the one in which three rolls moving in the same direction are used with the formed material put between them. Within such rolling system counter rolling and deep rolling can be distinguished. In the case of the first type of rolling, the roll axis distance does not change its position and tooth rolling is done by pushing the material between the rotating rolls. In the second type of rolling, the material does not move, but it is one of the rolls or all of them that are moved to the centre. The rolling process in a three-roll system is predominantly used for cold forming of threads, of straight and helical teeth as well as multi-toothed ones of small dimensions. The currently known methods for toothed gear rolling can be characterized in that the teeth are formed only on gears which require that preforms have to be specially prepared beforehand in mechanical machining.
The essence of plastic forming of toothed shafts, particularly of hollow shafts, is that the blank to be formed - in the form of a rod or tube section, is positioned between three identical stepped working rolls with teeth which rotate in the same direction with a first constant velocity and move radially to the product axis with a same second velocity, as a result of which a toothed stepped shaft is formed, and three working forming rolls with teeth - the tools, are positioned on the perimeter at every 120° +/- 20°, the preferable position being that at every 120°, the three rolling tools shift in the radial direction forming first steps of different diameters on the blank, and then teeth are formed on one of the steps, and when the working rolls - the tool, reach their final position, the radial plane motion is stopped, while the working rolls still rotate and correct shape inaccuracies of the part - a toothed shaft. The process for forming hollow toothed parts is done with or without mandrel, which allows obtaining accurate cylindrical or shaped holes. The process is done either cold or hot. The process is used for forming toothed shafts with straight, helical, arc, herringbone teeth as well as other shafts with multi-toothed or spline steps.
A beneficial effect of the present invention is that it allows for the application of simple forming tools, manufacture costs of which are relatively low to produce such parts as stepped shafts - especially the hollow ones which have toothed steps all over their length with straight, helical, herringbone teeth as well as a variety of profiles such as splines and multi-toothed ones. Hollow parts are more and more often used in machine constructions, in automotive industry, and particularly in aerospace industry. Owing to the use of such parts, the construction mass of elements can be decreased, while their strength and functional properties are at the same time retained. For forming hollow shafts, thick-walled tubes can be used as the blank, which makes additional drilling operations unnecessary as well as eliminates material loss which occurs during machining. Additionally, the finished product - a stepped shaft, can be obtained from the blank in the form of a tube section within one plastic forming operation. Owing to the use of rotational forming tools - the rolls, it is possible to roll products of different diameters by means of the same set of working rolls. The formed toothed shaft - either full or hollow, has a more advantageous structure, which improves strength properties of the part.
The method for plastic forming of toothed shafts has been schematically presented in three figures, where Figure 1 shows the beginning of the process in which a hollow toothed stepped shaft is formed, and Figure 2 illustrates the end of the rolling process of a hollow toothed stepped shaft, and Figure 3 shows a view of a sample blank as well as the product obtained from the forming process.
The method for plastic forming of toothed shafts, especially of hollow shafts, consists in that the blank 1 in the form of a rod or tube section is positioned between three identical stepped working rolls 2. Next, the working rolls 2 begin to rotate in the same direction with the constant first velocity n ₁ and move radially and translationally with the second velocity V towards the axis of the blank 1. Three working forming rolls 2 - the tools -, are positioned on the perimeter at every 120° +/- 20° relative to the blank 1, the preferable position, however, being that at every 120°. The radial shift of the rolling tools 2 results first in shaping shaft steps and then in forming teeth, in effect of which the part 3 is obtained - a hollow toothed stepped shaft. In the final phase of the process, once the part 3 reaches the assumed dimensions, the translational motion of the working rolls 2 is stopped, the working rolls 2 are, however, still allowed to rotate, which results in eventual shaping of the plastically formed part 3 - the toothed shaft, and in correcting shape inaccuracies which have occurred at the beginning of the process. The shape of the rolling tools 2 is designed in such a way that at any moment of contact reflect the geometry of the finished product 3 - the hollow toothed shaft. The shape of the rolled toothed shaft 3 is the is formed as the contact boundary of consecutive points of the rotating tools - the working stepped rolls 2, which allows for rolling parts of different diameters.

Claims

A method for plastic forming of toothed stepped shafts characterized in that a blank to be formed (1) in the form of a rod or tube section is positioned between three identical toothed stepped working rolls (2) which rotate in the same direction with a first constant velocity (n ₁) and move radially to the product axis with a same second velocity (V), as a result of which a toothed stepped shaft (3) is formed, and the three working forming rolls (2) with teeth - the tools, are positioned on the perimeter at every 120° +/- 20°, the preferable position being that at every 120°, the three rolling tools (2) shift in the radial direction forming first steps of different diameters on the blank (1), and then teeth are formed on one of the steps, and when the working rolls (2) - the tools, reach their final position, the radial plane motion is stopped, while the working rolls (2) still rotate and correct shape inaccuracies of the part (3) - the toothed shaft.
The method according to claim 1, characterized in that the process for forming of hollow toothed parts (3) is done with or without mandrel, which allows obtaining accurate cylindrical or shaped holes.
The method according to claim 1, characterized in that the process is done either cold or hot.
The method according to claim 1, characterized in that the process is used for forming toothed shafts with straight, helical, arc, herringbone teeth as well as other shafts with multi-toothed or spline steps.