MACHINE DESIGN
Machine design is defined as the use of scientific principles, technical information and imagination in the description of a machine or mechanical system to perform specific functions with maximum economy and efficiency. This definition of machine design contains the following important features;
(1) A designer uses principles of basic and engineering science such as physics, mathematics, statics and dynamics, thermodynamics and heat transfer, vibrations and fluid mechanics. Some of the examples of these principles are
(a) Newtons laws of motion,
(b) D’ Alembert’s principle,
(c) Boyles and Charles laws of gases,
(d) Carnot cycle
(e) Bernoulli’s principle.
(2) The designer has technical information of the basic elements of a machine. These elements include fastening devises, chain, belt and gear drives, bearings, oil seals and gaskets, springs, shafts, keys, couplings, and so on. A machine is a combination of these basic elements. The designer knows the relative advantages disadvantages of these basic elements and their suitability in different applications.
(3) The designer uses his skill and imagination to produce a configuration, which is a combination of these basic elements. However, this combination is unique and different in different situations. The intellectual part of constructing a proper configuration is creative in nature.
(4) The final outcome of the design process consists of the description of the machine. The description is in the form of drawings of assembly and individual components.
(5) A design is created to satisfy a recognized need of customer. The need may be to perform a specific function with maximum economy and efficiency. Machine design is the creation of plans for a machine to perform the desired functions. The may be entirely new in concept, performing a new type of work, or it may more economically perform the work that can be done by an existing machine. It may be an improvement or enlargement of an existing machine for better economy and capability.
BASIC PROCEDURE OF MACHINE DESIGN
The basic procedure of machine design consists of a step-by-step approach from given speciications about the functional requirements of a product to the complete description in the form of drawings of the final product. A logical sequence of steps, usually common to all design projects, is illustrated. These steps are interrelated and interdependent, each reflecting and affecting all
> Market survey
> Define specification of product
> Study alternative mechanisms for product and select proper mechanism
> Prepare general layout of configuration and select joining methods between individual components of product
> Design individual components
> Prepare assembly and detail drawings and modify drawings after testing prototype model
other step. The following steps are involved in the process of machine design.
Step 1: Product specifications
The first step consists of preparing a complete list of the requirements of the product. The requirements include the output capacity of the machine, and its service life, cost and reliability. In some cases, the overall dimension and weight of the product are specified. For example, while designing a scooter, the list of specifications will be as follows:
- Fuel consumption =40km/hr
- Maximum speed = 85km/hr
- Carrying capacity = two persons with 10 kg luggage
- Overall dimensions
Width =700mm
Length =1750mm
Height =1000mm
5. Weight =95kg
6. Cost = Rs 40000 to 45000
In consumer products, external appearance, noiseless performance and simplicity in operation of controls are important requirements. Depending upon the type of product, various requirements are given weightages and a priority list of specifications is prepared.