Many products observed in day-to-day life, are commonly made by putting many parts together may be in subassembly. For example, the ball pen consists of a body, refill, barrel, cap, and refill operating mechanism. All these parts are put together to form the product as a pen. More than 800 parts are put together to make various subassemblies and final assembly of car or aero plane. A complete machine tool may also require to assemble more than100 parts in various sub assemble or final assembly. The process of putting the parts together to form the product, which performs the desired function, is called assembly. An assemblage of parts may require some parts to be joined together using various joining processes. But assembly should not be confused with the joining process. Most of the products cannot be manufactured as single unit they are manufactured as different components using one or more of the above manufacturing processes, and these components are assembled to get the desired product. Joining processes are widely used in fabrication and assembly work. In these processes two or more pieces of metal parts are joined together to produce desired shape and size of the product. Such requirements usually occur when several pieces are to be joined together to fabricate a desired structure of products. These processes are used developing steam or water-tight joints. Temporary, semi-permanent or permanent type of fastening to make a good joint is generally created by these processes. Temporary joining of components can be achieved by use of nuts, screws and bolts. Adhesives are also used to make temporary joints. Some of the impotant and common joining processes are:
(1) Welding (plastic or fusion), (2) Brazing, (3) Solding, (4) Riveting, (5) Screwing, (6) Press fitting, (7) Sintering, (8) Adhesive bonding, (9) Shrink fitting, (10) Explosive welding, (11) Diffusion welding, (12) Keys and cotters joints, (13) Coupling, (14) Nut and bolt joints.
SURFACE FINISHING PROCESSES
Surface finishing processes are utilized for imparting intended surface finish on the surface of a job. By imparting a surface finishing process, dimension of part is not changed functionally either a very negligible amount of material is removed from the certain material is added to the surface of the job. These processes should not be misunderstood as metal removing processes in any case as they are primarily intended to provide a good surface finish or a decorative or protective coating on the metal surface. Surface cleaning process also called as a surface finishing process. Some of the commonly used surface finishing processes are:
(1) Horning, (2) Lapping, (3) Super finishing, (4) Belt grinding, (5) Polishing, (6) Tumbling, (7) Organic finishes, (8) Sanding, (9) Deburring, (10) Electroplating, (11) Buffing, (12) Metal spraying, (13) Pointing, (14) Inorganic coating, (15) Anodizing, (16) Sheradising, (17) Parkerizing, (18) Galvanizing, (19) Plastic coating, (20) Metallic coating.
PROCESSES EFFECTING CHANGE IN PROPERTIES
Processes effecting change in properties are generally employed to provide certain specific properties to the metal pieces for making them suitable for particular operations or use. Some important material properties like hardening, softening and grain refinement are needed to jobs and hence are imparted by heat treatment. Heat treatments affect the physical properties and also make a marked change in the internal structure of the metal. Similarly the metal forming processes affect on the physical properties of work pieces. Similarly shot peening process, imparts fatigue resistance to work pieces. A few such commonly used processes are given as under;
(1) Annealing, (2) Normalizing, (3) Hardening, (4) Case hardening, (5) Flame hardening, (6) Tempering, (7) Shot peeing, (8) Grain refining, (9) Age hardening.
In addition, some allied manufacturing activities are required to produce the finished product such as measurement and assembly.
Inspection and Quality Control
A Product is manufactured to perform desired function. It must have a specified dimension such as length, width, height, diameter and surface smoothness to perform or accomplish its intended function. It means that each product requires a defined size, shape and other characteristics as per the design specifications. For manufacturing the product to the specified size, the dimensions should be measured and checked during and after the manufacturing process. It involves measuring the size, smoothness and other features, in addition to their checking. These activity are called measurement and inspection respectively.
In the era of globalization, every industry must pay sufficient attention towards maintaining quality because it is another important requirement or function of a production unit. If a manufacturing concern wants to survive for longer time and to maintain its reputation among the users, it should under all condition apply enough efforts not only to keep up the standard of quality of its products once established but to improve upon the same from time to time. For this, every manufacturing concern must maintain a full-fledged inspection and quality control department which inspects the products at different stages of its production. Vigilant inspection of raw materials and products depends upon the entire process of standardization. The production unit of manufacturing concern must produce identical products. However a minor variation may be allowed to a predetermined amount in their finished dimensions of the product. The two extremities of dimensions of the product are called limits. All the parts of which the finished dimension lie within these are acceptable parts. This facilitates easy and quicker production, easy inspection, requires less skill on the part of worker and accommodates a slight inaccuracy in the machine as well, resulting in an over all reduction in the production cost of the part.
Mechanization And Automation
Mechanization means something is done or operated by machinery and not by hand. Mechanization of the manufacturing means is milestone oriented trend towards minimizing the human efforts to the extent of its possibility, by adopting mechanical and electrical means or methods for automating the different manufacturing processes. Such a trend may be in the area of automating and mechanizing the processes material handling, loading and unloading of components, actual operations performed on the job or transportation, etc. But, no feedback is provided process, operation or machinery. Extension of mechanization of the production process is termed as automation and it is controlled by a closed loop system in which feedback is provided by the sensors. It controls the operations of different machines automatically. The automatic control may be applied for some operations or for all the operations of a machine or group of machines.
Every machine should involve some automation, may be to a lesser degree or to a higher extent to which is mainly governed by economic considerations. Automation means system in which many or all of the processes in the production, movement, and inspection of parts and material are performed under control by the self operating devices called controllers. This implies that the essential elements of the automation comprises of mechanization, sensing, feedback, and control devices. The reasons why one should go for automation are:
1.Increased productivity
2. Reduced cost of labor and dependence on labor shortages
3. Improved quality
4. Reduced in process inventory
5. Reduced manufacturing time
6. Reduced dependence on operator skills
7. Increased safety or reduced risk of humans.
Automation can be classified into three categories
1. Fixed automation
2. Programmable automation
3. Flexible automation
Fixed automation
It is also known as hard automation which is utilized to produce a standardized product such as gears, nuts and bolts, etc. Even though the operating conditions can be changed, fixed automation is used for every large quantity production of one or few marginally different components. Highly specialized tools, devices, equipment, special purpose machine tools, are utilized to produce a product or a component of a product very efficiently and at high production rates with as low unit costs as possible relative to other alternative methods of manufacturing.
Programmable Automation
In programmable automation, one can change the design of the product or even change the product by changing the program. Such techniques is highly useful for the low quantity production of large number of different components. The equipment’s used for the manufacturing are designed to be flexible or programmable. The production normally carried out in batches.
Flexible Automation
There is a third category possible between fixed automation and programmable automation that is called flexible automation using Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM) activities. This is also called as Flexible Manufacturing System (FMS). It allows producing different products on the same equipment in any order or mix. One important example of programmable automation, in discrete manufacturing, is numerical control. Robot is another example of programmable automation. Robot being integral part of FMS and Computer Integrated Manufacturing (CIM) system can do a large number of manufacturing tasks for replacing the human labor.
In the present globalized manufacturing scenario, the advancements of hardware and software concepts using the mechatronics for fast mechanization and automation of manufacturing processes have become essential to be incorporated in the manufacturing areas.
Computer Aided Manufacturing (CAM)
The computer aided manufacturing implies manufacturing itself, aided or controlled by computers. In a wider sense, it denotes all the activities in the manufacturing environment like use of computers inventory control, project management, material requirements planning, data acquisition, testing and quality control. Improved reliability in view of the better manufacturing methods and controls at the manufacturing stages, the products thus manufactured as well as of the manufacturing system would be highly reliable. Since most of the components of a CAM system would include integrated diagnostics and monitoring facilities, they would require less maintenance compared to the conventional manufacturing methods. When there is a large variety of products or minor changes required in the existing production programme, CAM can easily manage the necessary changes or alterations. Following are the main advantage of using CAM.
1.Greater Design Freedom
Any changes that are required in design can be incorporated at any design stage without worrying about any delays, since there would hardly be any in an integrated CAM environment.
2.Increased Productivity
In view of the fact that the total manufacturing activity is completely organized through the computer, it would be possible to increase the productivity of the plant.
3.Greater Operating Flexibility
CAM enhances the flexibility in manufacturing methods and changing of product lines.
4. Shorter Lead Time
Lead times in manufacturing would be greatly reduced.
The integration of CAD and CAM systems is called computer integrated manufacturing system. The role of computer in manufacturing may be in two major groups namely computer monitoring and control of the manufacturing process and manufacturing support applications, which deal essentially with the preparations for act of manufacturing and post manufacture operations. Computers are used in controlling machine tools and other material handling equipment’s.