Quick Return Mechanism

QUICK RETURN MECHANISM

  

What is a quick return mechanism?

A quick return motion mechanism transforms circular action into reciprocating motion in the shaper and slotter machine, enabling the slider to travel forward and backward. Cutting only happens when moving forward; there is no matching cutting when moving backward. A device that produces a reciprocating motion in which the return stroke takes less time than the forward stroke is known as a quick return mechanism. It employs a system of connections that is powered by a circular motion source and has three turning pairs and a sliding pair (usually a motor of some sort). A slider-crank linkage is a subclass of a quick-return mechanism with an offset crank.

 

                      Reference:- https://en.wikipedia.org/wiki/Quick_return_mechanism

Purpose of quick return mechanism:

We employ a quick recovery mechanism to allow the backward stroke to run at a faster speed than the forward stroke since it is frequently desirable to reduce the non-productive time in machining.

Applications of quick return mechanism:

In the engineering sector, quick return mechanisms are widely used in machines.

1. It flattens the workpiece inside the shaper machine.

2. The same is employed in the planer and slotter machines.

3. It is also utilised in the Rotary Internal Combustion Engine, Mechanical Actuator, and Screw Press.

Components of quick return mechanism:

The essential elements of a quick return mechanism are as follows:

1. Crank: The crank revolves at a fixed angle and is fastened to the pinion wheel or motor.

2. Slider and Slotted Bar: At the end of the crank, the slider pivots. The slotter bar allows for unfettered movement of this slider. This part is in charge of turning the crank’s circular motion into the oscillating motion of the slotted bar.

3. Connecting rod: The connecting rod converts the oscillating motion of the slotted bar into reciprocating motion.

4. Ram: The ram reciprocates in a horizontal direction along the stroke line.

Types of a quick return mechanism

There are three types of Quick return mechanism:

1. Hydraulic Drive

2. Whitworth Quick Return mechanism

3. Crank and Slotted Link Mechanism

1. Hydraulic Drive

Inside the hydraulic cylinder, there is a reciprocating piston for the hydraulic drive. The piston rod is located in between the ram and the piston. The piston therefore moves back and forth with the ram. The diagram depicts two entries at the end of the cylinder. Below it is a control valve with four passageways. Through a reservoir, the last two entries from the cylinder to the control valve are joined.

Fig: Hydraulic drive , Reference:-learnmechanical.com/quick-return-mechanism/

2. 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. 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 than the forward stroke in this mechanism.

 Fig: Crank and slotted link mechanism , Reference:-learnmechanical.com/quick-return-mechanism/

3. Whitworth Quick Return mechanism

The spinning motion is transformed to produce the oscillatory motion. This gadget, which has a crank pinion, makes use of the bull gear. The connecting rod joins the crankpin at one end to the ram, which slides over the crankpin and into a crank plate’s groove, at the other end. The gear is rotated by a pinion that is driven by the electric motor shaft. Now that the crankpin and bull gear are rotating together, the sliding block is moved into the crank plate’s groove. This action causes the ram to move up and down thanks to the connecting rod. View the illustration below:

 Fig: Whitworth quick return mechanism , Reference:-learnmechanical.com/quick-return-mechanism/

Working Principle of quick return mechanism:

Fig:- Quick Return Mechanism Working principal, Ref: learnmechanical.com/quick-return-mechanism/

 

There are four links, as shown in the diagram, and they are the Slider, Crank, Frame, and Slotted Lever. Additionally, it is related by a pair, which includes:

1. Turning pair: Frame and slotted lever

2. A Turning Pair: Frame and Crank

3. The Turning Pair, Crank and Slider

4. Sliding Pair: Slider and Slotted Lever

One sliding pair and three turning pairs are present. It is sometimes referred to as the Single Slider Crank Chain Mechanism Inversion. Here, the connecting rod is secured.

The upper end of the slotted lever is connected to the ram of the shaper machine through a linkage, and the lower end of the slotted lever is free to slide in the slider. The slotted lever and the crank are attached to the frame at points A and B, respectively. The slotted lever and crank are linked together by a slider.

As soon as the power is turned on, the crank begins to turn, transmitting the motion to the slider, which is inserted inside the slotted lever and begins to oscillate. Now that ram is travelling forward, it creates a beta angle that is noted, and as it turns around, it creates an alpha angle that is also noted.

The graphic shows that the beta angle is greater than the alpha angle. We might therefore conclude that cutting strokes take longer than returning strokes.

Advantages:

Among the benefits of the Quick return method are the following:

1) The procedure is computerised.

2) The mechanism’s construction is not very difficult.

It has the ability to cut, flatten, and slot the workpiece, among other things.

4) Because of the quick returning stroke, the idle time is decreased.

5) The return stroke is characterised by quick movement.

6) Rotating motion can be changed into reciprocating motion using it.

7) In some machines, the material removal process is only performed during the forwarding stroke. The machine’s overall operating time is thereby decreased by the quicker return stroke.

Disadvantages:

The following negative aspects of the quick return mechanism:

1) It requires more energy to carry out operations.

2) The slider and the piston are in contact with one another.

3) The piston won’t operate endlessly because of the heat it produces, and wear and tear could happen.

Conclusion:

A method known as the rapid return mechanism is employed to change circular motion into reciprocating motion, enabling the slider to travel both forward and backward. Cutting only happens when moving forward; there is no matching cutting when moving backward. That concludes this article’s explanation of quick return mechanisms’ definition, applications, diagram, parts, types, operating principle, and advantages and disadvantages.

 

Guided By:-Prof. Dr. Umesh Chavan.

By:- Om Panchal, Parth Gupta, Rohit Patil, Vishal Patil, Mayuri Pawar