Abstract
Minik N. V., Matvienko S. A., Gorbyliova E. V. The main directions of increasing durability of cam mechanisms of land-transport vehicles. Some classification, application areas and technological methods for improving the total running period of cam-operated mechanisms are considered. The application of functionally oriented combined methods of surface treatment of cam-operated mechanisms is proposed with the purpose to increase their durability. There have been considered different characteristics of cams in overall mechanisms. Attention is drawn to existing drawbacks of cam mechanisms and some ways of increasing their fatigue and wear resistance.
Keywords. cam mechanism, longevity, functionally-oriented approach, technological method.
In the report given we have considered some classifications, application areas and technological methods for improving total running time of cam-operated mechanism. The purpose of the research study at this stage is to find some ways of increasing durability of cam-operated mechanisms by using functionally orientedcombined methods of their surface treatment.
Cam-operated mechanisms are widely used in transport, technological and other machines. Cam mechanisms are used in the mechanisms of feeding metalworking machine-tools, in the mechanisms of moving working parts of these machine tools, in internal combustion engines for regulating their working parts, in internal combustion engines for regulating fuel supply in the cylinders and for removing exhaust gases, in calculating devices and technological machines, etc. [1] They are also used in machines for food industry in which cam mechanisms perform a programmed operation, as well as in automated machines, in which they perform control functions connecting and disconnecting working parts at the proper moment.
A cam mechanism usually consists of two moving parts and a fixed part. Cam mechanisms produce any type of motion of a driven element with continuous motion of a drive element. Cam mechanisms are compact and may be easily introduced into a general scheme of a machine. No other mechanism as versatile and straightforward in design. However, a cam may be difficult and costly to manufacture and it is always too noisy and susceptible to wear, fatigue and vibration. Thus, some of the drawbacks are heavy wear of double action kinematic pair. To reduce wear the elements of cam mechanisms are made of high quality steel.
Mechanisms that utilize cams are typically designed to transform rotational motion into consistent reciprocating linear motion. Perhaps the most common example of a cam is an internal combustion engine. Car motors operate through a system of cams mounted on a cam shaft that open and close valves to regulate inputs (air and fuel) and outputs (exhaust) within the piston-cylinder assembly.
The characteristics of the linear motion are dictated by the shape of the cam and the cam follower. The profile of the cam can be altered to achieve different characteristics in the overall mechanism. For example:
- Frequency: Cams are usually fairly small which helps to accomplish more rapid reciprocating motion. The larger the circumference, the longer it will take to rotate a full 360 degrees and the less frequent will be the resultant linear motion in the cam follower.
- Distance: The linear distance of travel in the cam follower is equivalent to the follower radius. Stated differently, the linear motion in the cam follower is represented by the difference between the highest point in the cam (the largest or prime radius) and the lowest point in the cam (the smallest or base radius). If you need more or less reciprocal motion simply increase or decrease the follower radius.
- Quickness of Motion: Using a sharp drop off from the largest (prime) radius to the smallest (base) radius of the cam will cause a quick dropping or punching type action of the cam follower. This type of profile can be used to achieve a quick release or quick return feature. Additionally, designing the cam with multiple changes in radius in order to achieve rapid linear displacements of the follower [4].
The reliability of the cam-operated mechanisms is mainly determined by the durability of the cams. The working surface of cam-operated mechanisms loses its total running period due to contact and impressive wear during its operation. The longevity of the cam-operated mechanisms can be improved by modifying the axial profile of the cam and use of innovative surface treatment technologies.
The development of technological methods that provide a modified profile of axial section of the cam and formation of a functionally oriented quality of the surface layer of cam surfaces is task of paramount importance [2]. The issues of increasing the durability of cam mechanisms were studied by the following scientific researchers such as Korolyov P. A, Shoev A. N. and others.
Currently there is the following classification of cam-operated mechanisms:
- According to the type of links movement:
- flat (movement of the cam and pusher in one or parallel planes) (Fig. 1a, b, c, d, e);
- spatial (Figure 1 e);
- According to the type of the driven link movement:
- reciprocating (pusher) (Fig. 1a, b, c, e);
- return-rotational (rocker arm) (Fig. 1d, d);
- complex plane-parallel;
- According to the type of leading link movement:
- rwith a rotating cam (Fig. 1a, b, c, d, d);
- with a translationally moving cam (Fig. 1e);
- According to the form of working part of the driven link:
- with a pointed pusher (Figure 1 a);
- with a roller pusher (Fig. 1 b, d);
- with a pop-up plunger (Tigure 1c);
- with a mushroom-like pusher (Figure 1 e);
- According to the way of closing the higher kinematic pair
- open (force closure);
- closed (with a geometrical closure);
- According to synchronicity of movements:
- single (for one cycle of the cam of the driven link, it also performs 1 cycle);
- multiple (in a single cycle the cam of the follower link performs several cycles, for example, a two-fold pattern 1b) [3].
Figure 1 – Types of cam mechanisms
The main technological methods for improving durability include the following:
- Ensuring the extremely important accuracy of manufacturing parts;
- Ensuring optimum quality of working surfaces;
- Increasing of wear resistance, static and cyclic strength of parts by heat treatment;
- Hardening of parts by chemical-thermal treatment;
- Hardening of parts by surface plastic deformation;
- Putting wear-resistant coatings on wear surfaces of machinery parts.
The scientific novelty of the study lies in the application of a functionally oriented approach while developing technological methods of surface processing of cam mechanisms critical workpieces. The cam mechanisms are designed to take into account operating conditions and operational factors distribution on the working surfaces of workpieces.
The development and diversification of machines and mechanisms with application in different transport fields requires new scientific research for systematization and improvement of existing mechanical systems by creating new ways of increasing fatigue and wear resistance of some parts of a mechanism to be adopted to modern requirements. Our study has revealed that it is possible to increase the longevity of cam mechanisms at the designing, final or strengthening treatment stage using functionally oriented combined methods of treatment.
References
1. Методические указания по проектированию кулачковых механизмов/ сост. Т. Ф. Соловьёва, И. В. Костюк, С. В. Зубова. – М: МАДИ, 2011. – 43 с.
2. Шоев, А. Н. Технологическое повышение долговечности кулачковых механизмов// Справочник. Инженерный журнал.– 2010, № 6. – С. 10-12.
3. Ефанов А. М., Ковалевский В. П., Теория механизмов и машин: Учебное пособие. – Оренбург: ОГУ, 2004. – 267 с.: ил. 198.
4. Engineeringmechanisms: cams [Электронный ресурс]. – Режим доступа: https://www.creativemechanisms.com/cams.