ALL GATE CONCEPTS MECHANICAL THEORY Production

Types of Fits (3)-Clearance Fit,Transition Fit, Interference Fit,Selective Assembly,FMS

Types of Fits (3)-Clearance Fit, Transition Fit & Interference Fit Every Engineer must know: The relationship between the hole and the shaft during the Assembly is called Fit. The various parameters that can be included are Maximum Interference, Minimum Interference, Maximum Clearance, minimum clearance, etc.

Fit obtaining parts are either movable or fixed joints.

Ex: Shaft and Bearing assembly.

In this article, I will be defining all these parameters w.r.t. the hole and shaft assembly. Each Fit in this article is represented by a condition which needs to be satisfied and extreme cases are shown w.r.t.the assembly. Read this article till the end so that you can understand 3 types of fits briefly.

3 Types of Fits-Clearance Fit,Transition Fit & Interference Fit Every Engineer must know-Interview

Contents: Click on the links to Navigate

1.Clearance Fit

1.1 Clearance Fit: Maximum Clearance

1.2 Clearance Fit: Minimum Clearance

1.3 Types of Clearance Fits

2.Interference Fit

2.1 Interference Fit: Maximum Interference

2.2 Interference Fit: Minimum Interference

2.3 Types of Interference Fits

3.Transition Fit

3.1 Types of Interference Fits

3.2 Applications of Interference Fits

4.Numerical on Limits, Fits, and Tolerance

5.Types of Assemblies used in Manufacturing

6.Flexible Manufacturing System

3 Types of Fits-Clearance Fit, Transition Fit & Interference Fit:

The brief explanation of all these types of fits was presented below.

1.Types of Fits-Clearance fit:

The dimensions of the hole and shaft are such that always clearance or gap is existing between hole and shaft called Clearance fit.

Condition: Hole size must be greater than Shaft size.

Clearance fit
Clearance fit

Extreme Cases:

  • L.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • L.Hole v/s H.Shaft –>H>S—–>Clearance Fit
  • H.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • H.Hole v/s H.Shaft –>H>S —->Clearance Fit

Here,

L.Hole represents Lower Limit of Hole &

H.Hole represents Higher(Upper) Limit of Hole

H Represents Hole

S Represents Shaft

As Hole size is greater than Shaft size, it is called as Clearance Fit.

Ex: Used in all the mating assemblies.

1.1 Clearance Fit: Maximum Clearance

Maximum Clearance = higher limit of the hole lower limit of the shaft

                                        = Difference between minimum material limits.

Maximum clearance is also called as worst-case clearance in the clearance fit.

1.2 Clearance Fit: Minimum Clearance

Minimum Clearance = lower limit of the hole higher limit of the shaft.

                                       = Difference between maximum material limits.

1.3 Types of Clearance Fits:

The most commonly used fits of the clearance type are.

  1. Slide fit
  2. Running Fit
  3. Slack running Fits
  4. Easy Slide
  5. Loose Running Fits

Explanation on Types of Clearance Fits:

1.Slide-Fit:

  • Slide fit has a very small clearance between two mating  parts i.e. almost to zero
  • By this, we can say that the sliding fit is too closed to a transitions fit.

Example of Slide fit :

 The tailstock spindle in a lathe machine.

2. Running Fit :

  • At moderate speeds, the running fit is employed in engineering for rotation of components.
  • The clearance provides the required space for couplings.

Ex: couplings, Gears, etc…

3.Slack running Fits

4.Easy Slide Fit:

  • As the name implies, it provides a small clearance between the shaft and hole.
  • It is applicable for slow regular motion and non-regular motions

Ex: Piston.

5.Loose Running Fits:

  • As the name implies, Loose Running fits have the largest clearance and employed for rotation at high speeds of the components.

Ex: Plummer block, Idler Pulleys, etc.

2.Types of Fits-Interference fit:

Dimensions of hole and shaft are such that without the interference of external agency the Assembly of hole and shaft is not possible.

Condition: Shaft size must be greater than the Hole size.

interference fit
interference fit

External agency for assembly:

a.Force/Pressure: that is by the application of force or pressure we can get the push fit.

b: Heating or Cooling: i.e. by the application of Heating or Cooling, we can get the shrink fit.

Extreme Cases:

  • L.Hole v/s L.Shaft –>S>H —->Interference is Required
  • L.Hole v/s H.Shaft –>S>H —->Interference is Required
  • H.Hole v/s L.Shaft –>S>H —->Interference is Required
  • H.Hole v/s H.Shaft –>S>H —->Interference is Required

Here,

L.Hole represents Lower Limit of Hole &

H.Hole represents Higher(Upper) Limit of Hole

H Represents Hole

S Represents Shaft

According to the Transition Fit, in all the 4 cases interference is required. Let’s look at the Interference fit.

Ex: Used in non-mating assemblies like bearing bushes fitted into the bearing housing, key fitted into the keyway, etc.

2.1 Interference Fit: Maximum Interference:

Maximum Interference = higher limit of the shaft – lower limit of the hole.

                                              = Difference between maximum material limits.

2.2 Interference Fit: Minimum Interference:

Minimum Interference=lower limit of the shaft – higher limit of the hole.

                                            = Difference between minimum material limits.

The power transmission capacity of interference fit is defined based on minimum interference only.

2.3 Types of Interference Fits:

Interference Fit is further Classified into the following types.

  1. Force Fit
  2. Tight Fit
  3. Shrink Fit

3.Types of Fits-Transition Fit:

The dimensions of hole and shaft are such that sometimes the Clearance fit and sometimes the Interference fit is produced called as Transition fit.

transition fit-Types of fit
transition fit-Types of fit

Condition:

According to the latest definition, if one of the components is lying in between higher and lower limits of the Other component produces transition fit.

Extreme Cases:

Case 1:

  • L.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • L.Hole v/s H.Shaft –>H<S—–>Interference Fit
  • H.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • H.Hole v/s H.Shaft –>H>S —->Clearance Fit

Case 2:

  • L.Hole v/s L.Shaft –>H<S —->Interference Fit
  • L.Hole v/s H.Shaft –>H<S—–>Interference Fit
  • H.Hole v/s L.Shaft –>H>S —->Clearance Fit
  • H.Hole v/s H.Shaft –>H<S —->Interference Fit

Here,

L.Hole represents Lower Limit of Hole &

H.Hole represents Higher(Upper) Limit of Hole

H Represents Hole

S Represents Shaft

According to the above cases, the Transition fit sometimes produces Clearance Fit and Sometimes it is producing Interference Fit.

3.1 Types of Transition Fits:

The transition fit is classified into two types

  1. Wringing Fit
  2. Push-fit

Therefore it is called Transition Fit.

3.2 Applications of Transition Fit:

Used for producing non-mating assemblies like fit between Piston and Piston rings of IC engine, coupling, and coupling rings, etc.


4.Numerical on Limits, Fits, and Tolerance:

Problem:

For a Shaft designated as 40 H8/f7, Calculate the tolerances?

Solution:
Given:

Shaft designation = 40 H8/f7

The above equation(shaft designation) means that the

The basic size is 40 mm

Tolerance grade for the hole is 8 ( i. e. I T 8)

Tolerance grade for the shaft is 7 ( i. e. I T 7).

Since 40 mm lies in the diameter steps of 30 to 50 mm, therefore,

The geometric mean diameter,
D = Square root of (30 x 50) = 38.73 mm

As,we know that

Standard Tolerance Unit (i) = 0.45 x Cube root of (D) + 0.001 D
                                               i = 0.45 × 3.38 + 0.03873 = 1.559 73 or 1.56 microns
                                               i = 1.56 × 0.001 = 0.001 56 mm         Since(1 micron = 0.001 mm)
The standard tolerance for the hole of grade 8 (IT8)= 25 i 
                                                                                             = 25 × 0.001 56 = 0.039 mm
The standard tolerance for the shaft of grade 7 (IT7)= 16 i 
                                                                                             = 16 × 0.001 56 = 0.025 mm


5.Types of Assemblies Produced in the Manufacturing Industry(Fits):

1. Make to suit assembly:

Out of the hole and shaft, one component is made first approximately near to the required dimension and the second component is made slowly such that it can be assembled into the first component according to the requirement assembly conditions.

Advantages:

because of no limits and no tolerances are provided on the component, there is no rejection of components will be present.

Disadvantages:

During usage of the assembly, if one component fails in the Assembly, the total assembly has to be brought it to one of the manufacturing industry and get it to manufacture the failure component which is difficult sometimes.

2.Interchangeable Assembly:

The parts manufactured under similar conditions by a company or a factory at any corner of the world can be interchangeable.

During usage of the Assembly, if M6 Bolt fails in the Assembly, simply bring another M6 bolt from the spare parts shop and replace it.

With interchangeable assembly, the customer is not facing any problem but when the components are manufactured in the industry with limits and tolerances, there must be some amount of rejection of components will be present.

3.Selective Assembly:

It is also one type of interchangeable assembly but only a selected group of components can be interchangeable.

During usage of assembly, if group A, M6 Bolt fails in the Assembly, it has to be replaced by using another group A, M6 Bolt only.

Therefore it has the limited interchangeability hence when compared to interchangeable Assembly the selective assembly is inferior.

The selective assembly has been developed for manufacturing of very small tolerance components on a machine which has process capability.

It is the minimum tolerance of components which can be produced on a machine with more than 99% of acceptability.

Lowered the minimum tolerance indicate good process capability machining.

Procedure:

In selective assembly, by keeping one of the limits of a component remains constant, it enhances the tolerance of the component such that tolerance of the component should be greater than or equal to process capabilities of machining.

Manufacturing the components accordingly. Inspect them and after inspection divide the acceptable components into a number of groups such that each group of components will have tolerance less than or equal to the original tolerance.

Assemble the corresponding related group of a component so that the Assembly components are better than or same as that of original assembly conditions.

Advantages of selective assembly:

It is possible to produce very small tolerances components on a machine which has very poor process capability.

limitations of selective assembly:

Because of a number of components produced in each group or random, some group of components will get accumulated.

During usage of the assembly, if one component fails in assembly, first referred the manual of the assembly and identify the group to which the failure component belongs and then search in the different spare parts shop until the required group of the component is made available.

In spite of limitations, the selective assembly is used for manufacturing of ball bearing assemblies.


6.layers(3) of Manufacturing Flexibility in Flexible Manufacturing System(FMS):

An FMS is a form of flexible automation in which several machine tools are linked together by a material handling system and all aspects of the system are controlled by means of a central computer. This is called a Flexible Manufacturing System. In this article, I am going to explain the 3 layers of Manufacturing Flexibility in FMS.

 

Manufacturing Flexibility in FMS(Flexible Manufacturing System) include:

    • Features of FMS
    • Characteristics
    • 3 levels of manufacturing flexibility
    • Major historical developments
    • Components of the FMS system
    • Benefits & Dis-Advantages of FMS
    • Future benefits of FMS
    • Difference between FMS and FMC, etc.

3 layers of Manufacturing Flexibility in Flexible Manufacturing System:

1.Basic Flexibilities

  • Machine Flexibility
  • Material Handling Flexibility
  • Operation Flexibility

2.System Flexibilities

  • Volume Flexibility
  • Expansion Flexibility
  • Routing Flexibility
  • Process Flexibility
  • Product Flexibility

3.Aggregate Flexibilities:

  • Program Flexibility
  • Production Flexibility
  • Market Flexibility

 Components of Flexible Manufacturing System:

  • Robotics
  • Computers
  • Controllers
  • Networks
  • Software
  • Material Handling/Transport
  • Machines
  • Manual or Automated Assembly cells etc.

These are the different components of Flexible Manufacturing System.

The remaining contents mentioned above are presented in the form of a video which is shown below.

                                               

This is the complete explanation of the 3 layers of Manufacturing Flexibility in FMS which is shown in a detailed manner. If you have any doubts, feel free to ask from the comments section. Please Share and Like this blog with the whole world so that it can reach to many.

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This is the complete explanation of all the 3 types of fits which are proved by the conditions and Extreme cases.

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