Quick Return Mechanism

          

 Bansilal Ramnath Agarwal Charitable Trust's

Vishwakarma Institute of Technology

(An Autonomous Institute affiliated to Savitribai Phule Pune University

Department of Mechanical Engineering 2020-21

In this blog, we are going to give you an in-depth overview of the Quick Return Motion Mechanism. Hope so you guys enjoy reading it! So let's get started!

Page Contents

• 1) What is Quick Return Mechanism?
• 2) Quick Return Mechanism Types:
• 3) Quick Return Mechanism Working Principles:
• 4) Simulation and Calculations:-
• 5) Applications of Quick Return Mechanism:
• 6) Advantages of Quick Return Mechanism:
• 7) Disadvantages of Quick Return Mechanism:
• 8) Conclusion:

1) What is the Quick Return Mechanism?

A quick return motion mechanism is used in the shaper and slotter machine in which the circular motion is converted into reciprocating motion so that the slider moves forward and backwards. In the forward direction, the cutting process occurs while in return there is no such cutting.

2) Quick Return Mechanism Types:

There are three types of Quick return mechanism: 

      I) Whitworth Quick Return mechanism

      II) Crank and Slotted Link Mechanism and

      III) Hydraulic Drive

      I) Whitworth Quick Return Mechanism:

Here the rotary motion is converted into the oscillatory motion. In this mechanism, the bull gear is used and It has a crank pinion. 

The sliding block slides over the Crankpin and slides inside the slot of a crank plate and The connecting rod connects the pin at one end and ram at the other end.

The electric motor shaft drives the pinion and rotates the gear. Now the bull gear is also rotating along with the crankpin and the sliding block slides on the slot provided on the crank plate.

So this process makes the ram move up and down by the connecting rod.

Whitworth Quick Return Mechanism Diagram

     II) Crank and Slotted Link Mechanism:

This mechanism was invented by Whitworth in the 1800s. The mechanism consists of a slider, crank, fixed link, slotted lever, connecting rod and ram.

The crank is connected with the slider and fixed link. When the cranks start rotating the connecting rod pushes forward and backwards the ram.

Here the motion is being converted into linear motion from rotary motion.

To understand it clear please see the diagram.

The crank and slotted link mechanism are widely used in shaping machines like slotter, shaper Machine for producing flat surfaces on the workpiece. 

The return stroke is much faster then the forward stroke in this mechanism.

Crank and Slotted Link Mechanism Diagram

      III) Hydraulic Drive:

In the hydraulic drive, there is a piston inside the hydraulic cylinder that reciprocates. The piston rod is connected between ram and piston. Therefore ram reciprocates with the piston.

In the diagram, you can see there are two entries at the end of the cylinder. And below a control valve is attached which has four passes.

Two entries from cylinder to control valve and the remaining two are connected through a reservoir.

Hydraulic Drive Mechanism Diagram

3) Quick Return Mechanism Working Principle:

Quick Return Mechanism Working Principle

As you can see in the diagram there are four links and those are Slider, Crank, Frame, and Slotted Lever. And also it is connected through pair and those are:

1. Frame and Slotted lever: Turning Pair
2. Now Frame and Crank: Turning Pair
3. Crank and Slider: Turning Pair
4. Now Slider and Slotted lever: Sliding Pair

There are three turning Pairs and one sliding pair. It is also known as the Inversion of the Single slider crank chain mechanism. The connecting rod is fixed here.

1. The slider is free and it can slide in the slotted lever and the upper end of the slotted lever is attached to the ram of the shaper machine through a linkage.
2. The crank and the slotted lever is fitted to frame at point A and B respectively.
3.  Through a slider, the crank and slotted lever are connected to each other.

Now when the power is supplied, the crank starts rotating and the motion is transmitted to the slider and it is fitted inside the slotted lever therefore it starts oscillating.

Now ram moving forward and it makes an angle of beta which is noted and In the return it makes an angle alpha which is also noted.

From the diagram you can see that the beta angle is more than the alpha. So we can say that cutting strokes takes more time than returning strokes.

4) Simulation and Calculations :-

Whitworth Quick Return Mechanism in Solidworks

              

                  Calculations :-

     i) Return Stroke Angle = 154.26 deg

        Therefore, % return stroke = (154.26/360)*100%

                                                      = 42.85%

      ii) Cutting Stroke Angle = 205.74 deg

          Therefore, % cutting stroke = (205.74/360)*100%

                                                          = 57.15%

      iii) Efficiency = (% cutting stroke - % return stroke)/2

                             = (57.15% - 42.85%)

                             = 14.3%

5) Applications of Quick Return Mechanism:

These are the following applications of Quick return mechanism:

1. It is used in the shaper Machine for flattening the workpiece.
2. Same used in the Slotter and Planer Machine.
3. It is also used in the Screw press, Mechanical actuator and Rotary combustion Internal Engine.

6) Advantages of Quick Return Mechanism:

These are the advantages of Quick return mechanism:

1. The process is automated.
2. The construction of the mechanism is not so complicated.
3. It can perform operations like cutting, flattening and slotting the workpiece.
4. The idle time is reduced because of the fast returning stroke.

7) Disadvantages of Quick Return Mechanism:

Disadvantages of Quick return mechanism are:

1. In the returning stroke, there is no contact with the work so no cutting takes place hence the process takes much time to complete.
2. The forward stroke takes much time compared to the return stroke.
3. It takes more power to perform operations.
4. There is friction in the slider and Piston.
5. Continuous it won’t work because of heat generated inside the piston and wear and tear can happen.
6. Balancing of linkage is also a major problem as this device is also linked to linkages.

8) Conclusion:

  i) It is confirm that the quick return motion may increase the efficiency of the machine tool        because it can reduce the rotation angle for the return stroke.  This is because; the time          taken for the slider to return to its initial position is less than the time taken for the slider to        accomplish the cutting operation with the same distance.

  

  ii) Efficiency of Whitworth's Quick return Mechanism is 14.3%

  iii) The cutting stoke occupied 57.15% of the motion compared to return stroke which                contributes only 42.85%. The simulation also verified that the motion does have a quick            return stroke and a slow cutting or forward stroke.