Joining is an integral part of manufacturing as it facilitates easy, efficient and economic production of intricate shaped parts. Basic purpose of joining is to assemble two or more solid components together in such a way that it can form a single unit and can subsequently perform intended functionalities. To serve this purpose, a number of joining processes has evolved throughout the ages that can join structural members in different ways. Broadly such processes can be classified as temporary and permanent joining processes. A temporary joint allows disassembly of joined parts without breaking them; while, a permanent joint does not allow easy dismantling of joined components without breaking them.

Both weld joint and rivet joint are considered as permanent joints; but their joining techniques, features of joint as well as application areas are different. By definition, welding is one type of permanent joining process by which two or more components can be joined together by coalescence formation with or without the application of heat, pressure and filler material. So here intended joining is obtained by the formation of weld bead or coalescence between two components.

On the other hand, riveting is also one permanent joining process where two components can be joined by means of long cylindrical rivets inserted through holes, which are drilled on the components prior to riveting. While welding requires edge preparation when plate thickness is more, riveting always requires pre-drilled holes on the component, which reduces load bearing capability of joined structure. However, performance of weld joint decreases when subjected to vibrations; but rivet joints exhibit excellent performance under same situation. Various differences between weld joint and rivet joint is provided below in table format.

Table: Differences between weld joint (welding) and rivet joint (riveting)

Requirement of holes on components: Welding requires no hole or slot to be made on the parent component; however, edge preparation is desired if component thickness is more. Such prepared edges are again filled by filler metal during welding. Riveting requires holes to be made on the component for passage of rivets. Such holes are actually weak portions and reduce overall strength of components, as discussed in the following section.

Strength of joint and load carrying capacity: A sound welded joint is considered to have 100% strength; in fact, strength of defect-free joint is more than that of the component. So welded assembly has same strength to that of the parent components. But riveted joints have significantly lower strength because of the presence of series of holes drilled on the components for passage of rivets. Such holes actually reduce resultant cross-sectional area of the assembled part. Rivets, itself, do not contribute in the overall strength of the joined structure. These areas are also mechanically weak portions due to immense stress concentration. Since strength is proportional to load carrying capacity of the solid member, load bearing capacity of welded structure is considerably higher than that of riveted structure.

Changes in metallurgical properties: Metallurgical changes are inherent to many welding processes mainly because of heating at an elevated temperature and subsequent cooling. Most fusion welding processes (such as arc welding, gas welding, resistance welding and intense energy beam welding) and certain solid state welding processes (where temperature rise is considerably high like friction welding) tend to alter various metallurgical properties like grain structure, grain orientation, level of crystalline defects, etc. Such changes can be observed on the weld bead as well as surrounding the bead in heat affected zone (HAZ). In most occasions, such changes are undesirable and disadvantageous. On the other hand, rivet joining does not affect metallurgical properties of the basic component as no heat is induced on parent metal.

Performance under vibration: Welded joints are prone to failure under incessant vibration. For this reason it is not preferred for various joining in bridge construction. However, with the extensive development of welding field in last few decades and emergence of many modern welding techniques, now weld joints can be applied for such applications without much problems. Rivet joints exhibit excellent performance under vibration and thus it is traditionally used in applications like bride construction, casing of machineries, etc.

Requirement of accessories and resultant weight: Rivet joint mandatorily requires additional strap plates, either in one side or in both sides of the joint. Such plates increase weight of overall structure. Rivets also contribute in increasing weight as a single rivet is heavier than that of component material removed by drilling for passage of rivets (because of rivet head and protruding end of shank). Welding, on the other hand, does not use additional plates and thus welded assemblies are lighter in weight. In homogeneous and heterogeneous welding methods, filler material is used; however, it only fills the root gap present in between two components and thus does not contribute in increasing structure weight.

Increase in dimension, joint appearance and sliding motion: Because of strap plates, rivet heads and hammered end in protruding part of shank, overall dimension of riveted assemblies increases significantly. Such protruding parts also hamper appearance and also restrict sliding motion on the surface. This sometime imposes restriction on its application. Contrary to this, defect-free welded assemblies offer apparently good joint with no changes in component dimensions. Reinforced metal, if present on joint due to application of excess filler metal, can be easily removed by grinding after the process. Apart from improving appearance, this also enhances sliding properties of the surface.

Time required for designing and processing: Design for welded assembly is easier as well as time and cost efficient. Welding process is also faster so it is more productive. Riveting requires lot of calculations to find out optimum number of rivets require, their size and position, etc. Thus designing is more complicated and time consuming. Moreover, drilling a number of holes on the component at exact locations and hammering of the protruding end of rivets require considerable amount of time, especially when it is directly performed by human operator. Thus riveting is also more time consuming than welding.

Possibility of joining various materials in different ways: Welding can be advantageously applied for joining a wide variety of materials including metals, ceramics, plastic and composites. A large number of welding processes exists to fulfill this requirement. Moreover, joining in different orientations like lap joining, butt joining, T-joining, cylindrical joining, etc. are possible by welding. Riveting is preferred for assembly of metallic materials in butt joining mode as lap joining requires additional plates that may not be feasible in all cases.

Areas of applications: With the extensive development of welding over last few decades, now-a-days a large number of welding processes exist which can be used for a wide variety of fabrication purposes. Its applications include, but not limited to, common household joining, automobile industries, electrical and electronic industries, civil construction, aerospace joining applications, etc. It can be profitably used for joining various shapes like sheets, plates, rods, pipes, etc. Compared to this, riveting has narrower field of application. Typical areas where riveting are commonly used are bride construction, pressure vessel, boiler, ship tussle, household frames, etc. However, now-a-days riveting is mostly superseded by welding as the later one offers a sound, strong, reliable and leak-proof joint.

Scientific comparison among weld joint and rivet joint is presented in this article. The author also suggests you to go through the following references for better understanding of the topic.

• Welding Processes Handbook by Klas Weman (1^st edition, CRC Press).
• Springer Handbook of Mechanical Engineering, Volume 10 edited by K. H. Grote and E. K. Antonsson (Springer Science & Business Media).
• An Introduction to Metallurgical Laboratory Techniques by P. G. Ormandy (1^st edition, Pergamon Press).
• Welding and Joining of Aerospace Materials edited by M. C. Chaturvedi (1^st edition, Woodhead Publishing).