Quick Return Mechanism: application, parts, types, working, Advantages & More

What is the Quick Return Mechanism?

The quick return mechanism is a mechanical linkage that converts rotational motion into reciprocating motion, with the returning stroke being faster than the forward stroke. It is commonly used in machines such as shapers, slotters, and some types of presses, where a rapid return stroke is required to increase productivity.

The basic principle of the quick return mechanism is that a rotating crank is used to drive a connecting rod, which is then used -to drive a sliding ram or tool. However, instead of the crank being mounted directly on the main shaft, it is offset to create a varying eccentricity. This means that during the forward stroke, the ram moves slowly, while during the return stroke, the ram moves rapidly due to the increased eccentricity of the crank.

The quick return mechanism allows for the efficient shaping of materials such as metal or wood, as the rapid return stroke ensures that the tool or cutter is quickly repositioned for the next cutting operation. Additionally, it can be used to create complex shapes and profiles by varying the shape of the cutter or tool and the path of the sliding ram.

Types of Quick Return Mechanism:

There are several types of quick return mechanisms, each with its own advantages and disadvantages. Here are some common types:

1. Whitworth Quick Return Mechanism: This is the simplest type of quick return mechanism, and it consists of a crankshaft with an eccentric and a connecting rod that drives a sliding block. During the forward stroke, the sliding block moves slowly, while during the return stroke, it moves rapidly due to the increased eccentricity of the crank.
2. Crank and Slotted Lever Mechanism: This mechanism uses a crankshaft with an eccentric to drive a slotted lever, which in turn drives a connecting rod and a sliding ram or tool. The length of the slot in the lever determines the stroke length and the speed of the return stroke.
3. Whitworth-Diagram Mechanism: This mechanism uses two crankshafts with eccentrics and connecting rods that drive a parallelogram linkage. During the forward stroke, the linkage moves slowly, while during the return stroke, it moves rapidly due to the changing orientation of the parallelogram.
4. Hydraulic Quick Return Mechanism: This mechanism uses hydraulic cylinders to control the movement of the ram or tool, with a control valve that regulates the flow of hydraulic fluid. By adjusting the valve, the speed and stroke length of the ram can be varied.
5. Scotch Yoke Mechanism: This mechanism uses a rotating disk with a slot that drives a sliding block or yoke, which in turn drives a connecting rod and a sliding ram or tool. During the forward stroke, the yoke moves slowly, while during the return stroke, it moves rapidly due to the shape of the slot in the disk.

Each of these types of quick return mechanisms has its own advantages and limitations, depending on the specific application and requirements.

Components of a Quick Return Mechanism

The components of a quick return mechanism may vary depending on the specific design and application, but typically include the following:

1. Crankshaft: The crankshaft is the primary rotating component of the mechanism, which converts rotary motion into reciprocating motion.
2. Eccentric: The eccentric is an off-center component attached to the crankshaft, which provides the variable distance or throw necessary for the reciprocating motion.
3. Connecting Rod: The connecting rod connects the eccentric to the sliding block or other reciprocating component, transmitting the motion from the crankshaft.
4. Sliding Block: The sliding block is the component that moves back and forth in response to the motion of the connecting rod and eccentric, providing the reciprocating motion necessary for the machine or tool.
5. Flywheel: The flywheel is a rotating mass that helps to smooth out the motion of the mechanism, providing a more constant and consistent output.
6. Bearings: Bearings are used to support the rotating components of the mechanism, reducing friction and wear.
7. Control Mechanisms: Control mechanisms, such as hydraulic valves or electronic controllers, may be used to regulate the speed and stroke length of the mechanism, or to control other parameters such as force or pressure.

Overall, the specific components of a quick return mechanism will depend on the specific application and requirements, but the above components are typically present in most designs.

Working principle of Quick Return Mechanism

The working principle of a quick return mechanism involves converting rotary motion into reciprocating motion using a crankshaft and eccentric. The crankshaft rotates, driven by a motor or other power source, and the eccentric is mounted off-center on the crankshaft. As the crankshaft rotates, the eccentric moves in a circular path, transmitting motion to the connecting rod.

The connecting rod is connected to a sliding block or other reciprocating component, which moves back and forth in response to the motion of the eccentric. The distance or throw of the reciprocating motion is determined by the distance between the center of the crankshaft and the center of the eccentric. This distance is variable and can be adjusted to control the stroke length of the mechanism.

The quick return mechanism is designed to provide a faster return stroke than the forward stroke, which allows for more efficient cutting or forming operations. This is achieved by designing the mechanism so that the distance between the center of the crankshaft and the center of the eccentric is shorter on the return stroke than on the forward stroke. This causes the sliding block to move more quickly on the return stroke, allowing for faster processing and increased productivity.

Overall, the working principle of the quick return mechanism involves converting rotary motion into reciprocating motion and controlling the stroke length and speed of the reciprocating motion to achieve faster, more efficient processing of materials or other operations.

Applications of Quick Return Mechanism:

The quick return mechanism is commonly used in a variety of machines and applications that require fast and efficient reciprocating motion. Some common applications include:

1. Shaping Machines: The quick return mechanism is commonly used in shaping machines to move the cutting tool back and forth rapidly, allowing for efficient shaping of metal, wood, or other materials.
2. Slotting Machines: Slotting machines use the quick return mechanism to move a slotted cutting tool up and down rapidly, allowing for precise and efficient cutting of slots and other shapes in metal or other materials.
3. Presses: Mechanical presses use the quick return mechanism to rapidly move the ram up and down, allowing for efficient stamping, punching, and other forming operations.
4. Shearing Machines: Shearing machines use the quick return mechanism to move a blade rapidly back and forth, allowing for efficient cutting of metal or other materials.
5. Saws: Some types of saws use the quick return mechanism to move the saw blade up and down rapidly, allowing for efficient cutting of wood, metal, or other materials.

Overall, the quick return mechanism is widely used in manufacturing, machining, and other industrial applications where fast and efficient reciprocating motion is required.

Advantages and Disadvantages of Quick Return Mechanism:

Advantages of Quick Return Mechanism:

1. High Productivity: The main advantage of the quick return mechanism is that it enables high productivity due to the rapid return stroke. This allows for more efficient cutting or forming operations, which can result in faster production rates and increased output.
2. Precision: The quick return mechanism can be designed to provide precise control over the stroke length and speed, which can result in higher accuracy and better quality finished products.
3. Versatility: The mechanism can be used in a variety of machines and applications, making it a versatile option for manufacturers and other industrial users.
4. Reduced Operator Fatigue: The use of quick return mechanism reduces the operator's fatigue, making it more convenient to work on the machine.

Disadvantages of Quick Return Mechanism:

1. High Initial Cost: The cost of designing and implementing a quick return mechanism can be higher than that of other types of mechanisms due to its complexity.
2. Increased Maintenance: The mechanism may require more frequent maintenance due to the higher speeds and forces involved, which can increase maintenance costs and downtime.
3. Limited Stroke Length: The quick return mechanism is typically limited in the length of the stroke that can be achieved, which can be a disadvantage in certain applications.
4. Noise and Vibration: The rapid movement of the mechanism can generate high levels of noise and vibration, which can be a concern in certain work environments.
5. Safety Hazards: The high speeds and forces involved in the quick return mechanism can pose safety hazards if not properly designed, operated, and maintained.

Quick Return Mechanism Calculations

The calculations involved in designing a quick return mechanism will depend on the specific application and requirements. However, some common calculations include:

1. Stroke Length: The stroke length of the mechanism is determined by the distance between the center of the crankshaft and the center of the eccentric. This distance can be calculated based on the desired stroke length and the dimensions of the mechanism.
2. Velocity Ratio: The velocity ratio of the mechanism is the ratio of the velocity of the cutting tool or other working component to the velocity of the sliding block. It is typically calculated using the formula VR = (1 + r)/(1 - r), where r is the distance between the center of the crankshaft and the center of the eccentric, divided by the length of the connecting rod.
3. Cutting Speed: The cutting speed of the tool or other working component is calculated based on the surface speed of the workpiece and the desired feed rate.
4. Feed Rate: The feed rate of the tool or other working component is calculated based on the cutting speed and the desired depth of cut or material removal rate.
5. Power Requirements: The power requirements of the mechanism are calculated based on the force required to perform the cutting or forming operation, the velocity of the working component, and other factors such as friction and efficiency.

Overall, the calculations involved in designing a quick return mechanism can be complex and will depend on the specific requirements of the application. It is important to carefully consider factors such as stroke length, velocity ratio, cutting speed, and power requirements to ensure that the mechanism will provide the desired performance and productivity.

How to make Quick Return Mechanism

The process of making a quick return mechanism will depend on the specific design and requirements, but some general steps to follow are:

1. Determine the design specifications: Before starting the construction process, determine the specific design requirements for your quick return mechanism. This will include factors such as the desired stroke length, velocity ratio, cutting speed, and power requirements.
2. Select the materials: Choose materials that are strong, durable, and able to withstand the forces and stresses of the mechanism. Common materials for the crankshaft, connecting rod, and eccentric include steel or aluminum.
3. Fabricate the crankshaft and eccentric: Use a lathe or other metalworking tools to create the crankshaft and eccentric. The crankshaft should be machined to a smooth finish, with a precise center hole and appropriately sized journal bearings. The eccentric should be mounted off-center on the crankshaft, with the distance between the center of the crankshaft and the center of the eccentric determined based on the desired stroke length.
4. Fabricate the connecting rod: The connecting rod should be machined to the appropriate length and shape, with a hole at each end for mounting to the eccentric and sliding block.
5. Fabricate the sliding block: The sliding block should be machined to the desired shape and size, with holes at each end for mounting the connecting rod.
6. Assemble the mechanism: Assemble the crankshaft, eccentric, connecting rod, and sliding block according to the design specifications. Use appropriate bearings or bushings to reduce friction and wear.
7. Test and adjust: Once the mechanism is assembled, test it to ensure that it functions properly and meets the desired design specifications. Adjust as necessary to optimize performance.

Overall, the process of making a quick return mechanism requires careful planning, precise machining, and testing to ensure that it functions properly and provides the desired performance.

Whitworth Quick Return Mechanism

The Whitworth Quick Return Mechanism is a type of quick return mechanism named after its inventor, Sir Joseph Whitworth. It is a modification of the basic slider-crank mechanism and is commonly used in shaping and cutting machines.

The Whitworth Quick Return Mechanism is similar to a basic slider-crank mechanism, with the addition of an intermediate link between the connecting rod and the slide. The intermediate link is connected to the slide at one end and to the connecting rod at the other end. The crankshaft and eccentric are mounted on the same axis, with the eccentric offset from the centerline of the crankshaft. As the crankshaft rotates, the eccentric imparts a reciprocating motion to the intermediate link, which in turn causes the slide to move in a quick return motion.

The Whitworth Quick Return Mechanism provides a faster cutting or shaping stroke and a slower return stroke, which improves the efficiency and productivity of the machine. It also reduces the shock and vibration of the mechanism, which can improve the quality of the workpiece.

However, the Whitworth Quick Return Mechanism can be more complex and difficult to manufacture than other types of quick return mechanisms. It also requires careful adjustment and maintenance to ensure that it operates smoothly and reliably.