Machines Theory

Understanding Quick Return Mechanism

Quick return mechanism is a common principle on shaper and slotter machines. This principle helps to change circular motion into reciprocating motion which in return move the ram forward and backward. In this article, you’ll get to know the definition, applications, diagram, parts, types, working principle, advantages, and disadvantages of the quick return mechanism.

What is a quick return mechanism?

In the shaper and slotter machine, a quick return motion mechanism converts circular motion into reciprocating motion, allowing the slider to move forward and backward. The cutting process occurs in the forward motion, but there is no corresponding cutting in the reverse direction. A quick return mechanism is a device that generates a reciprocating motion in which the return stroke takes less time than the forward stroke. It uses a system of links with three turning pairs and a sliding pair to be driven by a circular motion source (usually a motor of some sort). With an offset crank, a quick-return mechanism is a subclass of a slider-crank linkage.

Read more: The various parts of a shaping machine and their functions

Applications of a quick return mechanism

Machines with quick return mechanisms can be found all over the engineering industry. Below are the applications of a quick return mechanism.

  • Shaper
  • Screw press
  • Power-driven saw
  • Mechanical actuator
  • revolver mechanisms
  • rotary combustion internal engine
  • air compressor
  • mechanical cutter.

Components of a quick return mechanism

The following are the key components of a quick return mechanism:

  1. Crank: The crank is attached to the pinion wheel or motor and rotates at a constant angle.
  2. Slider and Slotted Bar: The slider pivots at the crank’s end. This slider is free to move within the slotter bar. This component is responsible for converting the crank’s circular motion into the slotted bar’s oscillating action.
  3. Connecting rod: The connecting rod’s job is to transform the slotted bar’s oscillating action into reciprocating motion.
  4. Ram: The ram reciprocates along the stroke line in a horizontal direction.

Types of a quick return mechanism

The following are the various types of quick return mechanisms:

Whitworth Quick Return Mechanism:

The oscillatory motion is created by converting the rotating motion. The bull gear is utilized in this device, which features a crank pinion. The connecting rod connects the pin at one end to the ram at the other end of the connecting rod, which slides over the crankpin and into the slot of a crank plate. A pinion is driven by the electric motor shaft, which rotates the gear. The bull gear now rotates in tandem with the crankpin, and the sliding block moves into the crank plate’s groove. As a result of this operation, the connecting rod causes the ram to travel up and down. View the diagram below:

Whitworth Quick Return Mechanism

Read more: Working principle of a slotter machine and its mechanism

Crank and Slotted Link Mechanism:

Whitworth devised this system in the 1800s. A slider, crank, fixed link, slotted lever, connecting rod, and ram make up the mechanism. The slider and fixed link are connected to the crank. When the cranks begin to rotate, the connecting rod pushes the ram forward and backward. From rotational motion, the motion is translated to linear motion here. Crank and slotted link mechanisms are commonly employed in shaping machines such as slotters and shapers to produce flat surfaces on workpieces. In this mechanism, the return stroke is substantially faster than the forward stroke. See diagram below:

Crank and Slotted Link Mechanism

Hydraulic Drive:

The hydraulic drive has a reciprocating piston inside the hydraulic cylinder. Between the ram and the piston lies the piston rod. As a result, the piston reciprocates with the ram. There are two entries at the cylinder’s end, as shown in the diagram. A control valve with four passages is installed below it. The remaining two entries from the cylinder to the control valve are connected through a reservoir.

Hydraulic Drive

Working principle

working of quick return mechanism

Considering the above diagram, a quick return mechanism is made up of two strokes: forward and reverse strokes.

Forward stroke: The crank ‘B’ must move in a clockwise direction from point ‘B1’ to ‘B2’ for forwarding stroke. A green dotted line marks the forward path of crank ‘B’ in the diagram above. The end of the slotted bar goes from ‘P1’ to ‘P2’ in a clockwise motion at the same time and the ram ‘R’ advances from position ‘R1’ to ‘R2.’

Return stroke: The slider ‘B’ rotates clockwise from position ‘B2’ to ‘B1’ during the return stroke. The return path for crank ‘B’ is indicated by a red dotted line in the diagram above. The slotted bar’s end ‘P’ goes from position ‘P2’ to ‘P1’ in an anticlockwise direction at the same time. In the opposite direction, the ram ‘R’ goes from ‘R2’ to ‘R1’.

Read more: Difference between shaper and planer machine

Watch the video below to learn more about the working of a quick return mechanism:

Advantages and disadvantages of a quick return mechanism

Advantages:

The following are some of the advantages of the Quick return mechanism:

  1. During the return stroke, there is rapid movement.
  2. It can be used to convert rotary motion into reciprocating motion.
  3. The material removal operation is only carried out in forwarding stroke in some machines. As a result, the machine’s overall working time is reduced by the faster return stroke.

Disadvantages:

The quick return mechanism has the following drawbacks:

  1. Because there is no contact with the work during the returning stroke, no cutting occurs, and the operation takes a long time to complete.
  2. In comparison to the return stroke, the forward stroke takes a long time.
  3. To carry out operations, additional power is required.
  4. Friction exists between the slider and the piston.
  5. Because of the heat generated inside the piston, it will not perform indefinitely, and wear and tear may occur.
  6. Because this gadget is also linked to links, balancing the linkage is a key issue.

Read more: Understanding slotter machine

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Conclusion

The quick return mechanism is known as a principle used to converts circular motion into reciprocating motion, allowing the slider to move forward and backward. The cutting process occurs in the forward motion, but there is no corresponding cutting in the reverse direction. That is all for this article, where the definition, applications, diagram, parts, types, working principle, advantages, and disadvantages of quick return mechanisms are being explained.

I hope you get a lot from the reading, if so, kindly share with other students. Thanks for reading, see you around!

 

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