Whitworth quick return mechanism : Definition, Working, Advantages

What is whitworth quick return mechanism ?

The Whitworth quick return mechanism is a mechanical device that converts rotational motion into reciprocating motion. It was invented by Sir Joseph Whitworth, a prominent British engineer, in the 19th century.

Table of Contents

The mechanism consists of a rotating crankshaft connected to a connecting rod, which is in turn connected to a sliding block or slider. The slider moves along a straight guide or slider crank, creating a back-and-forth motion.

The distinguishing feature of the Whitworth quick return mechanism is that the forward stroke of the slider is faster than the return stroke. This speed difference allows for efficient operation in certain applications, such as shaping machines or slotting machines.

The mechanism works as follows: as the crankshaft rotates, the connecting rod translates the circular motion of the crankshaft into linear motion, causing the slider to move forward. However, during the return stroke, the connecting rod is configured in such a way that it creates a longer path for the slider to travel, resulting in a slower return speed.

The Whitworth quick return mechanism finds its application in various machines where a reciprocating motion is required, with a quick forward stroke and a slower return stroke. It has been widely used in shaping machines, slotting machines, and other industrial equipment.

Overall, the Whitworth quick return mechanism is a mechanical innovation that allows for efficient and controlled reciprocating motion, enabling the operation of various machines and tools in industries such as manufacturing and metalworking.

history

The Whitworth quick return mechanism was invented by Sir Joseph Whitworth, a prominent British engineer and inventor, in the 19th century. Joseph Whitworth was born in 1803 in Stockport, England, and he made significant contributions to the field of engineering during his lifetime.

Whitworth developed the quick return mechanism as a means to convert rotary motion into reciprocating motion with a speed difference between the forward and return strokes. The mechanism was specifically designed to improve the efficiency and productivity of machines used for shaping and cutting operations.

The invention of the Whitworth quick return mechanism is believed to have taken place in the mid-1840s. Whitworth’s innovative design incorporated a rotating crankshaft, a connecting rod, and a sliding block or slider that moved along a straight guide or slider crank. The mechanism enabled a faster forward stroke and a slower return stroke, resulting in more efficient machining processes.

The Whitworth quick return mechanism quickly gained recognition and was widely adopted in various industrial applications. It revolutionized the performance of shaping machines, slotting machines, and other machines that required reciprocating motion.

Joseph Whitworth’s contributions to engineering extended beyond the quick return mechanism. He was a proponent of standardization in engineering and played a crucial role in establishing the British Standard Whitworth (BSW) thread system, which became widely used in the manufacturing industry.

Whitworth’s dedication to precision engineering and his inventions left a lasting impact on the industrial landscape. His work influenced advancements in machinery, manufacturing processes, and engineering standards, and he is regarded as one of the leading figures of the Industrial Revolution.

The Whitworth quick return mechanism remains an important mechanical innovation, and its principles are still utilized in various machines and industrial applications today. It stands as a testament to Joseph Whitworth’s ingenuity and his contributions to the field of engineering.

parts of Whitworth quick return mechanism

Certainly! Here is an expanded description of the parts of the Whitworth quick return mechanism:

Crank: The crank is a crucial component of the Whitworth quick return mechanism. It is typically attached to a motor or pinion wheel and rotates at a constant angle. The rotational motion of the crank serves as the driving force for the mechanism.
Slider and Slotted Bar: The slider is a movable component that pivots at one end of the slotted bar. The slotted bar features a slot or groove in which the slider moves. As the crank rotates, the slider follows the circular motion, resulting in an oscillating action within the slotted bar.
Connecting Rod: The connecting rod plays a vital role in transmitting motion from the slider to the ram. It connects the slider to the ram and converts the oscillating motion of the slider into reciprocating motion. The length and configuration of the connecting rod influence the stroke length and motion characteristics of the mechanism.
Ram: The ram is a key part of the Whitworth quick return mechanism. It is connected to the connecting rod and moves back and forth in a reciprocating motion. The ram carries out the desired action, such as shaping or cutting, during the forward stroke. The reciprocating motion of the ram is synchronized with the oscillating action of the slider and slotted bar.

By working together, these four parts create an efficient and controlled reciprocating motion in the Whitworth quick return mechanism. The rotational motion of the crank is converted into an oscillating motion by the slider and slotted bar. The connecting rod then transmits this motion to the ram, enabling it to perform the desired action during the forward stroke.

components

Here is a simplified version:

In the diagram above, the part labeled AC is fixed and doesn’t move.
The part labeled AB is a crank that rotates around point A with a steady speed.
The slider, labeled b, is attached to the end of the crank AB and slides into the slotted bar.
The slotted bar is connected to point C and can rotate around it.
At the end of the slotted bar, there is a connecting rod that converts the rotational motion into back-and-forth motion.
The ram is connected to the end of the connecting rod. It moves back and forth and has a cutting tool mounted on it.

how does Whitworth quick return mechanism works

The Whitworth quick return mechanism operates as follows:

The crank, attached to a motor or pinion wheel, rotates at a constant speed.
As the crank rotates, it causes the slider, connected to the crank, to move back and forth within the slotted bar.
The slotted bar is pivotally attached at one end and rotates around that pivot point.
The connecting rod, connected to the other end of the slotted bar, converts the rotational motion of the slotted bar into reciprocating motion.
The reciprocating motion of the connecting rod is transmitted to the ram, which moves back and forth in a straight line.
The ram carries a cutting tool or performs a specific action during the forward stroke, such as shaping or cutting a material.
The return stroke of the ram is slower than the forward stroke due to the design of the mechanism, which allows for a quick forward action and a slower return motion.

This continuous rotation of the crank drives the reciprocating motion of the ram, allowing for efficient and controlled operation in various applications, such as shaping machines, slotting machines, and other industrial processes.

Whitworth quick return mechanism working:

The Whitworth quick return mechanism operates in two strokes: the forward stroke and the return stroke.

Forward Stroke:
During the forward stroke, the crank AB moves in a clockwise direction from point B2 to B1.
At the same time, the point X on the connecting rod moves in a clockwise direction from B1 to B2, and the ram moves forward from point Y1 to Y2.
The forward stroke is shown in the figure with a green dotted line.
In the forward stroke, the crank AB completes an angle α.

Return Stroke:
During the return stroke, the crank AB moves in a clockwise direction from point B1 to B2.
At the same time, the point X on the connecting rod moves in a clockwise direction from B2 to B1, and the ram moves in the opposite direction from point Y2 to Y1.
The return stroke is shown in the figure with a red dotted line.
In the return stroke, the crank AB completes an angle β.

This alternating motion of the crank, connecting rod, and ram allows for efficient back-and-forth movement. The forward stroke accomplishes a specific action, and the return stroke resets the mechanism for the next cycle.

Relation between time takes for forward & reversed stroke:

Here is the explanation in English:

1.During the crank’s clockwise movement from B2 to B1, the ram moves forward from Y1 to Y2. The time taken for the forward stroke of the ram is equal to the time taken for the crank to complete angle α.

2. When the crank moves clockwise from B1 to B2, the ram moves in the opposite direction from Y2 to Y1, completing the return stroke. The time taken for the return stroke of the ram is equal to the time taken for the crank to complete angle β.

From the given figure, we can observe that β is smaller than α. This means that the ram moves faster during the return stroke, while it takes more time for the forward stroke.

The ratio of the time taken for the forward stroke to the time taken for the return stroke can be expressed as:

Time for forward stroke / Time for return stroke = α / β

Alternatively, it can be written as:

Time for forward stroke / Time for return stroke = α / (360 – α)

This ratio indicates that the time taken for the forward stroke is longer compared to the return stroke, as α is greater than β. The specific values of α and β depend on the design and configuration of the mechanism.

application of Whitworth Quick Return Mechanism

The Whitworth quick return mechanism has found applications in various machines and industrial processes. Some of the notable applications include:

Shaping Machines: The Whitworth quick return mechanism is commonly used in shaping machines, which are used to remove material from workpieces to create flat surfaces, slots, and contours. The mechanism enables the cutting tool to have a quick forward stroke for the cutting action and a slower return stroke for repositioning.
Slotting Machines: Slotting machines are used to create slots and grooves in workpieces. The quick return mechanism is employed in these machines to move the cutting tool rapidly during the cutting stroke and return it at a slower speed.
Reciprocating Pumps: In certain types of reciprocating pumps, the Whitworth quick return mechanism is utilized to convert the rotary motion of the drive shaft into reciprocating motion of the pump piston. The mechanism ensures a faster suction stroke and a slower discharge stroke for efficient pumping action.
Guillotine Shears: Guillotine shears are used for cutting sheet metal or other materials. The quick return mechanism is employed in these machines to power the cutting blade, enabling a fast downward cutting stroke and a slower upward return stroke.
Riveting Machines: Riveting machines use the quick return mechanism to rapidly apply force for the riveting process. The mechanism allows the rivet to be driven quickly during the compression stroke and then retracted at a slower speed.
Stamping Machines: Stamping machines, which are used for cutting, shaping, or embossing materials, often incorporate the Whitworth quick return mechanism. This enables a fast downward stroke to apply the stamping force and a slower upward return stroke for repositioning.

These are just a few examples of the applications of the Whitworth quick return mechanism. Its ability to provide a quick forward stroke and a slower return stroke makes it suitable for various machines that require reciprocating motion with differing speeds for specific operations.

advantages of Whitworth Quick Return Mechanism

The Whitworth quick return mechanism offers several advantages in its applications. Some of the key advantages are:

Increased Efficiency: The mechanism allows for a quick forward stroke and a slower return stroke. This speed difference improves the overall efficiency of the machine by reducing the idle time and maximizing the productive cutting or shaping time during the forward stroke.
Enhanced Productivity: The quick forward stroke of the mechanism enables faster cutting, shaping, or other operations, leading to increased productivity. The rapid motion reduces the cycle time required for each operation, allowing more work to be completed in a given timeframe.
Improved Cutting Performance: In machines like shaping machines or slotting machines, the quick forward stroke of the Whitworth mechanism results in a more aggressive cutting action. This can lead to improved cutting performance, especially when working with harder or tougher materials.
Precision and Control: The Whitworth quick return mechanism offers better control over the reciprocating motion. The speed difference between the forward and return strokes allows for more precise positioning and control of the cutting tool or workpiece. This can lead to higher accuracy and improved quality in the machining or shaping process.
Versatility: The mechanism can be adapted to different machines and applications, making it a versatile choice. It can be incorporated into various types of machines such as shaping machines, slotting machines, pumps, shears, and stamping machines, among others, to provide efficient reciprocating motion.
Reliability: The Whitworth quick return mechanism is a simple and well-established mechanical design. Its simplicity and robustness contribute to its reliability and ease of maintenance. It has been widely used for many years, proving its durability and dependability in industrial settings.

Overall, the advantages of the Whitworth quick return mechanism include increased efficiency, enhanced productivity, improved cutting performance, precision and control, versatility, and reliability. These advantages make it a popular choice for applications where efficient reciprocating motion is required.

disadvantages of Whitworth Quick Return Mechanism

While the Whitworth quick return mechanism offers several advantages, there are also some disadvantages associated with its use. Here are a few of the notable disadvantages:

Uneven Wear: The quick return mechanism can lead to uneven wear on the sliding block or slider and the guide due to the varying speeds during the forward and return strokes. This can result in increased friction, accelerated wear and tear, and the need for more frequent maintenance and replacement of components.
Limited Speed Range: The mechanism is not suitable for high-speed applications. The speed of the forward stroke is limited by the design and configuration of the mechanism. As a result, it may not be ideal for processes that require very high-speed reciprocating motion.
Reduced Stability: The quick return motion can introduce vibrations and oscillations in the machine. These vibrations can affect the stability of the machine and potentially impact the quality of the workpiece. Additional measures may be required to mitigate these vibrations and ensure stable operation.
Complexity in Design: While the basic concept of the Whitworth quick return mechanism is relatively straightforward, the design and implementation can be more complex compared to other types of mechanisms. Achieving the desired speed difference and ensuring proper synchronization between components can require careful engineering and precision manufacturing.
Increased Energy Consumption: The quick return mechanism consumes more energy compared to mechanisms with constant speed reciprocating motion. The acceleration and deceleration during each stroke require additional power input, which can result in higher energy consumption, especially in high-volume production environments.
Limited Stroke Length Control: The stroke length of the reciprocating motion may be limited by the design of the mechanism. Adjusting and controlling the stroke length can be more challenging compared to other mechanisms, which may offer more flexibility in this regard.

It’s important to note that while the Whitworth quick return mechanism has these disadvantages, they may not be significant in every application. The suitability of the mechanism depends on the specific requirements and constraints of the intended use case. Engineers and designers need to carefully evaluate these factors when considering the implementation of the mechanism.

Reference : https://mm-nitk.vlabs.ac.in/exp/whitworth-mechanism/theory.html