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AIM :- Design a different types of Gear using Catia V5 Knowledge toolbar. OBJECTIVE :- Design of tooth using involute profile calculation for different types of gear. INTRODUCTION :- A gear is a rotating circular machine part having cut teeth or, in the case of…
Tejas Metkar
updated on 19 Dec 2020
AIM :- Design a different types of Gear using Catia V5 Knowledge toolbar.
OBJECTIVE :- Design of tooth using involute profile calculation for different types of gear.
INTRODUCTION :-
A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called cogs), which mesh with another toothed part to transmit torque. A gear may also be known informally as a cog. Geared devices can change the speed, torque, and direction of a power source. Gears of different sizes produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be considered a simple machine. The rotational speeds, and the torques, of two meshing gears differ in proportion to their diameters. The teeth on the two meshing gears all have the same shape.
Two or more meshing gears, working in a sequence, are called a gear train or a transmission. The gears in a transmission are analogous to the wheels in a crossed, belt pulley system. An advantage of gears is that the teeth of a gear prevent slippage. In transmissions with multiple gear ratios—such as bicycles, motorcycles, and cars—the term "gear" (e.g., "first gear") refers to a gear ratio rather than an actual physical gear. The term describes similar devices, even when the gear ratio is continuous rather than discrete, or when the device does not actually contain gears, as in a continuously variable transmission.
TYPES :-
1. Spur :-
Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with teeth projecting radially. Though the teeth are not straight-sided (but usually of special form to achieve a constant drive ratio, mainly involute but less commonly cycloidal), the edge of each tooth is straight and aligned parallel to the axis of rotation. These gears mesh together correctly only if fitted to parallel shafts.[18] No axial thrust is created by the tooth loads. Spur gears are excellent at moderate speeds but tend to be noisy at high speeds.
2.HELICAL :-
Helical or "dry fixed" gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Since the gear is curved, this angling makes the tooth shape a segment of a helix. Helical gears can be meshed in parallel or crossed orientations. The former refers to when the shafts are parallel to each other; this is the most common orientation. In the latter, the shafts are non-parallel, and in this configuration the gears are sometimes known as "skew gears".
The angled teeth engage more gradually than do spur gear teeth, causing them to run more smoothly and quietly. With parallel helical gears, each pair of teeth first make contact at a single point at one side of the gear wheel; a moving curve of contact then grows gradually across the tooth face to a maximum, then recedes until the teeth break contact at a single point on the opposite side. In spur gears, teeth suddenly meet at a line contact across their entire width, causing stress and noise. Spur gears make a characteristic whine at high speeds. For this reason spur gears are used in low-speed applications and in situations where noise control is not a problem, and helical gears are used in high-speed applications, large power transmission, or where noise abatement is important.The speed is considered high when the pitch line velocity exceeds 25 m/s.
A disadvantage of helical gears is a resultant thrust along the axis of the gear, which must be accommodated by appropriate thrust bearings. However, this issue can be turned into an advantage when using a herringbone gear or double helical gear, which has no axial thrust - and also provides self-aligning of the gears. This results in less axial thrust than a comparable spur gear.
A second disadvantage of helical gears is also a greater degree of sliding friction between the meshing teeth, often addressed with additives in the lubricant.
3. BEVEL :-
A bevel gear is shaped like a right circular cone with most of its tip cut off. When two bevel gears mesh, their imaginary vertices must occupy the same point. Their shaft axes also intersect at this point, forming an arbitrary non-straight angle between the shafts. The angle between the shafts can be anything except zero or 180 degrees. Bevel gears with equal numbers of teeth and shaft axes at 90 degrees are called miter (US) or mitre (UK) gears.
1. Simple Bevel Gear 2. Spiral bevel gear
4.WORM :-
Worms resemble screws. A worm is meshed with a worm wheel, which looks similar to a spur gear.
Worm-and-gear sets are a simple and compact way to achieve a high torque, low speed gear ratio. For example, helical gears are normally limited to gear ratios of less than 10:1 while worm-and-gear sets vary from 10:1 to 500:1. A disadvantage is the potential for considerable sliding action, leading to low efficiency.
A worm gear is a species of helical gear, but its helix angle is usually somewhat large (close to 90 degrees) and its body is usually fairly long in the axial direction. These attributes give it screw like qualities. The distinction between a worm and a helical gear is that at least one tooth persists for a full rotation around the helix. If this occurs, it is a 'worm'; if not, it is a 'helical gear'. A worm may have as few as one tooth. If that tooth persists for several turns around the helix, the worm appears, superficially, to have more than one tooth, but what one in fact sees is the same tooth reappearing at intervals along the length of the worm. The usual screw nomenclature applies: a one-toothed worm is called single thread or single start; a worm with more than one tooth is called multiple thread or multiple start. The helix angle of a worm is not usually specified. Instead, the lead angle, which is equal to 90 degrees minus the helix angle, is given.
In a worm-and-gear set, the worm can always drive the gear. However, if the gear attempts to drive the worm, it may or may not succeed. Particularly if the lead angle is small, the gear's teeth may simply lock against the worm's teeth, because the force component circumferential to the worm is not sufficient to overcome friction. In traditional music boxes, however, the gear drives the worm, which has a large helix angle. This mesh drives the speed-limiter vanes which are mounted on the worm shaft.
Worm-and-gear sets that do lock are called self locking, which can be used to advantage, as when it is desired to set the position of a mechanism by turning the worm and then have the mechanism hold that position. An example is the machine head found on some types of stringed instruments.
If the gear in a worm-and-gear set is an ordinary helical gear only a single point of contact is achieved. If medium to high power transmission is desired, the tooth shape of the gear is modified to achieve more intimate contact by making both gears partially envelop each other. This is done by making both concave and joining them at a saddle point; this is called a cone-drive or "Double enveloping".
Worm gears can be right or left-handed, following the long-established practice for screw threads.
GEAR TERMINOLOGY :-
METHODOLOGY:-
1. Add new parameter
m = 2 cm
z = 32
Pressure angle (a) = 20 deg
Rp (pitch circle radius) = m * z /2
Ro (Addendum Circle radius) = Rp + m
Rb (base circle radius) = Rp * Cos (a)
Rr (Dedendum circle radius) = Rp - 1.25 * m
2. go to Sketcher and Draw a semicircle with Rb using edit formula.
3. Draw centre axis.
4. Rotate that axis with number of instantence (more the number of pattern of axis more smooth profile you get , here we have 8).
5. then make sure our axis point coincidence with origin point.
6. then angular Spacing with formula
i.e. 2* 1st angle
3* 1st angle
4* 1st angle ...So on.
7. trim the extended axis line so that coincide with base circle.
8. Draw tangent line from every point.
9. length of that point
Rb* that angle * Rb×∠×π180
10. connect with that point with spline.
11. Exit workbench and draw Rp, Rb, Rr , Ro circle with using edit formula.
12. Expolate the involute curve = 2 * m.
13. Now create corner radius = 0.39 * m.
14. we get one curve , for mirror that curve on another side we need plane at right poistion we use symmetry.
15. For that we need to create intersection point at involute curve to pitch circle.
then create point on pitch circle using create point command lenght using formula = 1/z/4.
and reference = intersection point.
that point create plane at perpenicular direction.
16. Create symmetry involute curve and trim in such way that second curve , first curve and addendum circle .
17 . you got one teeth
18. then Circular pattern it with number of teeth using formula.
19. trim dedendum circle. and hide base circle and pitch circle , plane.
20. exit workbench , Pad it with depth of gear dimension.
FOR HELICAL GEAR
1. Offset plane at 250 mm from origin
2. then we project same profile of first gear sketch
3. hide main sketch then isolate second one . and rotate through helix angle (25 deg).
4. then show main sketch , now we have two sketch , just multisection it . we got helical gear.
FOR BEVEL GEAR :-
1. offset plane from main plane with 250 mm.
2. Project main sketch and isolate it.
3. now select second sketch just scale it to 80% (we put 0.8)
4. then show main sketch and multisection it with proper closing point.
fOR SPIRAL BEVEL GEAR :-
1. we need to offset 2 planes at 125 mm , 250 mm from main plane.
2. select first plane and sketch.
3. Scale main sketch with 80 % and rotate with 15 deg.
4. exit workbench
5. select second offset plane and sketch.
6. Select main sketch and scale with 50% and rotate with 30 deg.
7. exit workbench
8. now we have 3 sketches just multisection it with proper closing point.
Conclusion :- In this way we create the different gear using knowledge toolbar for lifetime.
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