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How to design a machine?

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step by step procedure of machine design

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How to design a machine?

  1. 1.  A machine is made up of mechanisms that work together to satisfy the requirements of what the machine needs to accomplish. & Machine design is the process of engineering design. Creation of new and better machine Improving existing one Implimantation of our idea in machine What is the importance of Machine Design for engineers? What is the Machine and Machine Design?
  2. 2. How to design a Machine?  There is no fixed machine design procedure for when the new machine element of the machine is being designed a number of options have to be considered.  When designing machine one cannot apply rigid rules to get the best design for the machine at the lowest possible cost  When the new product is to be developed the problems keep on arising at design stage, and these can be solved only by having flexible approach and considering various ways. Though the machine design procedure is not standard, there are some GENERAL PROCEDURE to be followed; these can be followed as per the requirements wherever and whenever necessary.
  3. 3. Recognition of need  Make the written statement of what exactly is the problem for which the machine design has to be done.  This statement should be very clear and as detailed as possible.  This statement is sort of the list of the aims that are to be achieved from machine design.
  4. 4. Specification of products  Making a complete list of requirements of product, it includes  Outer  Capacity of Machine  Service life  Overall dimensions  Weight  Cost  Reliability
  5. 5. Specification of products For example, While designing a Machine the list of the specification will be as follow; i. Fuel consumption = 45km/l ii. Maximum speed = 180km/hr iii. Carrying capacity = three persons with 4kg luggage iv. Overall dimensions Width = 750mm Height = 1100mm Length = 1800mm Weight = 100kg Cost = Rs 55000 to Rs 60000 For example, While designing a Machine the list of the specification will be as follow;  Fuel consumption = 45km/l  Maximum speed = 180km/hr  Carrying capacity = three persons with 4kg luggage  Overall dimensions Width = 750mm Height = 1100mm Length = 1800mm  Weight = 100kg  Cost = Rs 55000 to Rs 60000
  6. 6. Proper Mechanism  As per requirement, one can go to prepare rough sketches of different possible mechanism  Select the possible mechanism or group of mechanisms which will give the desired motion.  The various mechanisms are compared with each other and also with the mechanisms of product which are readily available in the market.  From all the mechanisms one can choose the mechanism depending on the cost competitiveness, availability of raw material and manufacturing facility.
  7. 7. Proper Mechanism  For example; while designing a blanking or piercing press, the following mechanism are possible  A mechanism involving the crank and connecting rod , converting the rotary motion of the electric motor into the reciprocating motion of the punch.  A mechanism involving nut and screw , which is a simple and cheap configuration but having poor efficiency and  A mechanism consisting of a hydraulic cylinder , piston and valves which is a costly configuration but highly efficient.
  8. 8. Selection of material
  9. 9. General layout of Configuration The next step in the design procedure is to prepare a block diagram showing the general layout of the selected configuration. For example , the layout of an Electrically operated Overhead Travelling(EOT) crane will consist of the following components;  Electric motor for power supply  Flexible coupling to connect the motor shaft to the clutch shaft  Clutch to connect or disconnect the electric motor at the will of operator  Gear box to reduce the speed from 1440rpmto about 15 rpm  Rope drum to convert the rotary motion of the shaft to the linear motion of the wire rope  Wire rope and pulley with the crane hook to attach the load  Brake to stop the motion
  10. 10. General layout of Configuration  In this step , the designer specifies the joining methods , such as riveting , bolting or welding to connect the individual components .  Rough sketches of shapes of the individual parts are prepared .
  11. 11. Design of individual elements  The design of individual components or machine elements is an important step in a design process . This step involves detailed stress and deflection analysis.  It consists of the following stages :  Determine the forces acting on the component.  Select proper material for the component depending upon the functional requirements such as strength , rigidity , hardness and wear resistance.  Determine the likely mode of failure for the component and depending upon it , select the criterion of failure , such as yield strength , ultimate tensile strength , endurance limit or permissible deflection.  Determine the geometric dimensions of the component using a suitable factor of safety and modify the dimensions from assembly and manufacturing considerations.
  12. 12. Testing & Modification  From all the steps till now we have seen , make a prototype model of the machine for testing and considering this experimental results we can do further modification.  The geometric dimensions of the machine element are modified from assembly and manufacturing considerations.  For ex , the transmission shaft shown in fig. Revised calculations are carried out for operating capacity , margin of safety at critical cross section s and resultant stresses taking into consideration . When this value differ from desired values , the dimensions of the component are modified . This process is continued till the desired values are obtained.
  13. 13. Detailed drawing  The last stage in a design process is to prepare drawing of the assembly and the individual components  On this drawing , the material of the components , its dimensions , tolerances , surface finish grades and machining symbols are specified.  The working drawing must be clear , concise and complete.  It must have enough views and cross sections to show all details.  The designer prepares two separate lists of components :  Standard components to be purchased directly from the market.  Special components to be machined in the factory.  All the dimensions that are imported for proper assembly and interchangeability must be provided with tolerances.  The main view of machine elements should show it in position , it is required to occupy in service.
  14. 14. Production  The component, as per the drawing, is manufactured in the workshop.

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