Machine Design theory.

What is machine design ? 

Mechanical Design or Machine Design is the branch of Engineering Design. Machine design can lead to the formation of the entirely new machine or it can lead to improvement of the existing machine.

●      To understand what exactly machine design or mechanical design is let us consider the example of the gear box of the car. The gear box transmits the motion and the power of the engine to the wheels of the vehicle. The gearbox comprises group of gears which are subjected to not only motion but also the load of the vehicle. For the gears to run at desired speeds and take desired loads it is important that they should be designed. During designing various calculations are performed considering desired speeds and loads and finally the gear of particular material and specific dimensions that can take all loads and that can be manufactured at least possible cost giving optimum performance is designed. In similar fashion all the components of the car, including engine, have to be designed so that they optimally meet all the functional requirements at lowest possible cost. This whole process of designing is called as machine design or mechanical design.

●      Machine Design or Mechanical Design can be defined as the process by which resources or energy is converted into useful mechanical forms, or the mechanisms so as to obtain useful output from the machines in the desired form as per the needs of the human beings. Machine design can lead to the formation of the entirely new machine or it can lead to up-gradation or improvement of the existing machine. For instance if the existing gearbox is too heavy or cannot sustain the actual loads, entirely new gearbox can be designed. But if the same gearbox has the potential to lift more loads, it can be upgraded by making certain important changes in its design.

Factors to be considered during Machine Design. 

When the designer designs the elements of the machine or the complete machine, they have to consider several important parameters. Here are some of the important factors to be considered while doing machine design:

● 1

 Cost: Cost has always been the major factor of consideration while designing the machine elements or machine and in this age of competition it has become more important. The best machine design is the one which helps get the finished product with all the major functionalities and highest possible quality at the lowest possible cost. 

● 2

 High output and efficiency:Earlier machines used to be very heavy and consume lots of power. Now the trend is of full functional machines consuming low power and giving high output in terms of the number of the of products manufactured. Some computer controlled machines can manufacture the components very fast and are highly efficient.

●3

 Strength: The machine elements or the machine should be strong enough to sustain all the forces it is designed for so that it is not damaged or permanently deformed during its life time. Right at the time of the designing the machine the designer should consider the force machine can be applied to and consider all the relevant factors that could affects its life.

●4

 Stiffness or rigidity: The machine should be rigid enough so that under the effect of applied forces for which it is designed there is no deformation of the machine or machine elements beyond the specified limits

● 5

 Wear resistance: Wear is the removal of the material from the metallic surface when two surfaces rub with each other. If there is more removal of the material, the component will become weaker and eventually break. The wear of the contacting surfaces can be reduced by the lubrication of the surfaces, increasing the strength or the hardness of the working surfaces.

●6

 Lubrication: Lubrication between the two mating surfaces of the elements of the machine help reducing friction between them and wearing of the two surfaces, which results in the increase in life of the components of the machine.

● 7

 Operational safety: For the safety of the operator of the machine, the hazard producing things from the machine should be eliminated and the design should confirm to the safety codes.

● 8 

Ease of assembly: The elements of the machine should be such that the machine can be assembled very easily. For the mass production of the complex machines like automobiles, type writers etc, the concept of unit assemblies are common. The unit assemblies are assembled together to form the complete machine.

●9 

Ease and simplicity of disassembly: Like assembly, the disassembly of the machine also should be easy so as to easily carry out replacement of the parts, and repair and maintenance of the machine and machine elements.

● 10 

Ease and simplicity of servicing and control: The machine and its element should be simple enough so that very little maintenance and servicing is required. The repair and maintenance of the machine should be easy and cheap and simple replacements should be available.

●11

 Light weight and minimum dimensions: The machine elements and machine should be strong, rigid and wear resistant with minimum weight and least dimensions. This can be achieved by using light weight rolled sections and hardening the metals. Using high strength grades of cast iron and light alloys can further help getting light materials and minimum dimensions of the machine elements. Improving the design in this direction is very important.

● 12 

Reliability: The reliability of the machine is a very important if the machine has to find the huge market in the business.

● 13 

Durability: The longer the life of the machine more it develops the reputation of being the dependable machine and more will be its sale. Hence the right at the time of designing reliability and durability should be given priority. 

● 14 

Economy of performance: For the proper economic performance of the machine correct mechanical, hydraulic, thermodynamic and other principles should be applied while designing the elements of the machine and the whole machine.

●15 

Accessibility: The machine elements and machine the whole should be easy to handle and access.

● 16

 Processability: The shape and the materials for the elements of the machine should be such that they can the processing costs and labor costs are lowest possible.

● 17

 Compliance with state standards: Following the standards makes designing easier and availability of various parts faster and easier.

●18 

Economy of repairs and maintenance: While designing the machine elements and machine the designing should be such that least amount of repairs and maintenance will be required for the machine.

●19 

Use of standard parts: There should be maximum possible standard parts in the design of the machine. This will help reduce the cost of the machine and ensure easy availability of the parts. With standard parts the design can be modified easily.

● 20 

Use of easily available materials: Materials selected for the machine elements during the design should be available easily and lowest possible costs.

●21 

Appearance of the machine:While designing the machine the aesthetics and ergonomics of the machine should be given due consideration without affecting its functionality.

● 22 

Number of machines to be built: Designing of the machine will depend a lot on the number of machines to be manufactured. If few numbers of machines are to be manufactured then expensive materials and high production costs can be considered, but for the mass production economy of the machine should be top priority

Machine Design Procedure

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.

●      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. The designer who develops the habit of following a fixed line of steps for designing the machine or machine elements cannot come out with the best product. 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.

Important Steps of Designing Machine

  Though the machine design procedure is not standard, there are some common steps to be followed; these can be followed as per the requirements wherever and whenever necessary. Here are some guidelines as to how the machine design engineer can proceed with the design

●1

 Making the written statement: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. If you want to develop the new produce write down the details about the project. This statement is sort of the list of the aims that are to be achieved from machine design.

●2

 Consider the possible mechanisms: When you designing the machine consider all the possible mechanisms which help desired motion or the group of motions in your proposed machine. From the various options the best can be selected whenever required.

●3

 Transmitted forces: Machine is made up of various machine elements on which various forces are applied. Calculate the forces acting on each of the element and energy transmitted by them.

● 4

 Material selection: Select the appropriate materials for each element of the machine so that they can sustain all the forces and at the same time they have least possible cost.

●

5 Find allowable stress: All the machine elements are subjected to stress whether small or large. Considering the various forces acting on the machine elements, their material and other factors that affect the strength of the machine calculate the allowable or design stress for the machine elements.

● 6

 Dimensions of the machine elements: Find out the appropriate dimensions for the machine elements considering the forces acting on it, its material, and design stress. The size of the machine elements should be such that they should not distort or break when loads are applied.

●  7

 Consider the past experience: If you have the past experience of designing the machine element or the previous records of the company, consider them and make the necessary changes in the design. Further, designer can also consider the personal judgment so as to facilitate the production of the machine and machine elements.

Skills a Good Machine Designer should possess

Machine designer is the one who designs the machine and its various elements. A good machine designer possesses some skills that help him/her design the machine elements and machine that meet all the needs of the designer and that helps develop the high quality machine at lowest possible costs.Here are some important skills that a good machine designer should possess.
● 1

 Inventiveness: This skill is the foundation stone for a good machine design engineer. Any new design starts with the need or some objective. A good designer should have inventiveness, which is the ability to think of or discover valuable and useful ideas or concepts for the things or processes to achieve the given objective. Without inventiveness the designer cannot start the process of machine design.
●2

  Engineering analysis: Engineering analysis is the ability of the designer to analyze the given component, system or the process using engineering and scientific principles. The designer who possesses this skill will be able to find answer to the engineering related problems very quickly for he or she knows what exactly the problem is and where it is.
●  3

  Engineering science: This is another skill without which the designer will just not be able to do any designing. A good designer is the one who has thorough knowledge of and in depth training in the engineering science in which they are doing designing. For instance, if the person doesn’t know what the refrigerator is and other basics of mechanical engineering how will they be able to design the refrigerator?

●  4

 Interdisciplinary ability: A good design engineer is the one who has the ability to solve the problems not only those related to his/her specialty, but also have the ability to competently and confidently deal the basic problems or ideas from other disciplines which are in some or the other manner linked to the machine they are designing.
● 5

 Mathematical skills: All types of designs involve lots of mathematical calculations and iterations. A good designer should have the knowledge of all the basics and advanced mathematical concepts so that they can be applied fruitfully and effectively wherever required.
● 6

Decision making: During designing many times a number of uncertain situations arrive, in such cases the designer should be able to take the decision with balanced mind considering all the relevant factors involved. If the person doesn’t maintain the balance of mind and doesn’t consider all the relevant factors there are greater chances of taking the wrong decision.
●7

 Manufacturing processes: The design engineer should have the knowledge of the manufacturing process like cutting, drilling, milling etc and the knowledge of all the machines. They should also the knowledge of potential and limitations of all the machines and manufacturing processes which may be old or new.
● 8

Communication skills: Communication skill is the ability of the design engineer to express oneself clearly and persuasively orally, graphically as well as in writing.
● 9

These are the important skills that the machine design engineer or rather any designer should posses. Apart from this there are many other skills desired from a good designers, these are: skill in design, good judgment, simulation skill, measurement skill, thought skill, work in team, ability to make conclusion etc.

Laminated Leaf Spring Design Procedure

You can find leaf springs in almost all four wheelers. In this article we discuss how to design a leaf spring and the typical guidelines for a leaf spring.

●      A leaf spring protects a four wheeler from the unevenness of the road. Thus a leaf spring necessarily serves the following purposes:

○      Increase service life of a four wheeler

○      Increase user comfort

             Formula to be used

●      Leaf spring design is based on thefundamental beam theory. I already have an article on how to design plates based on beam theory.

●       You have to use the following two formulas for the leaf spring design process:

○      Bending stress produced in the whole spring:

●      Tb= (3*W*L)/ (b*N*t^2)………………………………eqn1.1

○      Maximum deflection in the whole spring:

●      X= (6*W*L^3)/[{(2+(n/N)}*E*N*b*t^3]……………eqn1.2

●      Where,

●      Tb – maximum bending stress in the leaf spring

●      W – Applied load on the spring

●      t – Thickness of the individual leaves

●      X – Maximum deflection of the spring due to applied load

●      L – Span of the leaf spring

●      n – Number of full-length leaves

●      N – Number of graduated-length leaves

●      b – Width of the spring

●      E – Young’s modulus of the spring material. 

     Leaf Spring Design Procedure

●      Let’s start with a leaf spring design problem. We have the following data as input:

●      W= 24516 N

●      L= 0.445 M

●      N= 8

●      n= 2

●      E= 2.1E+11 N/m2

●      X= 0.13 M

●      Sa= 600000000 N/m2

●      Sa is the allowable bending stress for the spring material.

●      You have to find out the width (b) and the thickness (t) of the spring.

●      W= 24516 N

●      L= 0.445 M

●      N= 8

●      n= 2

●      E= 2.1E+11 N/m2

●      X= 0.13 M

●      Sa= 600000000 N/m2

●      Sa is the allowable bending stress for the spring material.

●      You have to find out the width (b) and the thickness (t) of the spring.

                            Solution 

●      Apply the eqn1.1 and you will get the value of:

●      b*t^2 = 6.81 * 10^-6…………eqn1.3

●      Now, apply the eqn1.2 and you will get the value of:

●      b*t^3 = 2.63 * 10^-8………….eqn1.4

●      By solving the eqn1.3 and eqn1.4 you will get:

●      t = 0.0038 m

●      b = 0.455 m...