Design of a clamping and holding fixture

 To meet the stringent requirements for workpiece clamping and holding capability in modern precision manufacturing, a novel clamping fixture has been developed, detailing its structure and operating principles.

Through an ingenious structural design, this fixture achieves efficient and stable clamping of workpieces.

It not only addresses the shortcomings of traditional clamping fixtures in clamping force stability and reset accuracy but also enhances compactness and durability through an integrated design.

In modern precision manufacturing, particularly in high-precision operations like micro-grinding of minute rods, the clamping and holding capability of workpieces directly impacts machining accuracy and production efficiency.

Traditional clamping fixtures exhibit numerous shortcomings in clamping force and stability, such as uneven clamping force, unstable holding power, and poor reset accuracy, making them inadequate for modern precision manufacturing demands.

As shown in Figure 1, small-diameter cutting tools made of high-speed steel or cemented carbide feature extremely narrow cutting edges (0.05–1.0 mm) and lengths up to 20 mm, requiring grinding of both primary and secondary cutting surfaces at the tool tip.

In actual production, elastic collets are commonly used to clamp the shanks of small-diameter tools.

Due to the small diameter and length of the tool shank, it is difficult to ensure uniformity and stability of the clamping force. This often leads to tool tilting, deformation, damage, or even breakage during machining, severely impacting processing quality and efficiency.

Therefore, designing a novel clamping fixture that significantly enhances workpiece clamping retention capability is critical.

Figure 1 Small-Diameter Tool

The primary technical challenges to be addressed are as follows:

(1) Uniformity and Stability of Clamping Force

Traditional clamping fixtures often suffer from uneven clamping force distribution and instability, causing workpiece deformation or displacement during machining.

Ensuring uniform distribution and stable control of left-right clamping forces throughout the process to prevent workpiece deformation or displacement is the primary technical challenge.

(2) Reset Accuracy

During machining, the fixture's reset accuracy directly impacts workpiece machining precision.

Traditional fixtures employ relatively simple reset mechanisms, making high-precision reset difficult to achieve.

Designing a rational clamping structure and transmission mechanism to ensure fixture reset accuracy during operation is key to improving machining quality.

(3) Adaptability

Considering the varying clamping requirements for workpieces of different specifications, the clamping mechanism must offer excellent versatility and adjustability.

A primary design consideration is how to achieve stable clamping of multiple workpiece specifications through optimized structural design and other means.

Structural Design of Clamping and Holding Fixtures

Addressing the above issues, engineers developed a novel small-diameter tool clamping and holding fixture. Mounted on the DTMA1200 micro four-station grinding machine, it grips the tool shank while assisting the collet in keeping the tool handle.

Through a sophisticated structural design and optimized transmission mechanism, it achieves stable and reliable workpiece clamping.

The clamping fixture's gripping mechanism is illustrated in Figure 2. The physical fixture is shown in Figure 3, with its 2D view depicted in Figure 4 and 3D view in Figure 5.

Figure 2 Clamping Fixture Holding Diagram

Figure 3： Actual Clamping Fixture

Figure 4：  Clamping Fixture 2D Drawing

Figure 5:  3D Drawing of Clamping Fixture

Key Component Design

This clamping fixture primarily consists of four critical sections: the mounting section, the first clamping arm section, the second clamping arm section, and the drive plate section. Through precise mechanical design and ingenious connection methods, these components collectively achieve efficient clamping and holding functionality.

(1) Mounting Section Design

Serving as the fixture's foundation, the mounting section features a stable structure capable of withstanding various forces during machining processes.

It features precise mounting surfaces and locating holes for accurately installing and positioning the first clamping arm assembly, second clamping arm assembly, drive plate assembly, and other necessary accessories.

(2) First Clamping Arm Assembly and Second Clamping Arm Assembly Design

The first and second clamping arm assemblies constitute the core gripping components of the fixture. Positioned on opposite sides of the mounting section, they connect to it via elastic joints.

Each clamping arm consists of a front end and a rear end. The front end mounts grippers or fixtures for direct contact with the workpiece, while the rear end connects to the drive plate section, enabling the clamping arm's opening and closing motion through deformation of the drive plate section.

Specifically, the first clamping arm includes a first front end and a first rear end, while the second clamping arm comprises a second front end and a second rear end.

The first and second clamping arms are elastically connected to the mounting section via their respective elastic arms (first elastic arm and second elastic arm). This design allows the clamping arms to undergo elastic deformation when driven, enabling better adaptation to the workpiece's shape and dimensions for tighter gripping.

(3) Drive Plate Assembly Design

The drive plate assembly serves as the critical component connecting the first and second clamping arm assemblies. It controls the opening and closing of both clamping arm assemblies through elastic deformation.

When driven by a power source (such as a pneumatic cylinder or electric motor), the drive plate assembly undergoes elastic deformation. This deformation propels the first and second clamping arm assemblies to move toward or away from each other, thereby achieving workpiece clamping or release.

The design of the drive plate section thoroughly considers structural stability and deformation capacity. Through a meticulous design of hollowed-out gap sets (first hollowed-out gap set and second hollowed-out gap set), deformation capacity is enhanced without compromising overall strength. This ensures more uniform and adjustable clamping force.

Structural and Detail Design

To further enhance the performance of the clamping fixture, multiple structural and detail designs are incorporated here.

(1) Elastic Arm Design

Based on the clamping force required for the workpiece, the widths of the first and second elastic arms are precisely controlled between 0.05 and 0.5 mm. This ensures sufficient deformation capability while maintaining structural stability.

Additionally, the number of elastic arms can be adjusted according to actual needs. This design incorporates at least two elastic arms to enhance clamping uniformity and reliability.

(2) Hollow Slot Array Design

A finely crafted hollow slot array positioned between the mounting section and clamping arm section not only reduces overall mass but also improves deformation efficiency and precision. The symmetrical or asymmetrical configuration of this array can be flexibly adjusted based on the shape and dimensions of the workpiece being clamped, achieving optimal clamping results.

(3) Positioning and Adjustment Mechanism

The design incorporates positioning grooves and adjustable components to ensure precise alignment and stable power transmission during operation. The introduction of an adjustment mechanism allows for fine-tuning of clamping position and force according to specific requirements, further enhancing the fixture's adaptability and flexibility.

(4) Integrated Forming Design

Key components—including the mounting section, first clamping arm section, second clamping arm section, and drive plate section—adopt an integrated design philosophy. These are formed by cutting a single metal plate with elastic deformation capability. This approach minimizes clearance gaps and potential looseness between components, enhancing the overall structure's compactness, stability, and precision.

Structural Design Features

(1) Stable and Reliable Clamping Force

Through the ingenious design of the elastic arms and drive plate assembly, this clamping fixture delivers stable and reliable clamping force output when activated by the drive mechanism. The clamping force is maintained not only by the drive mechanism but also by the deformed drive plate section and elastic arms. Even with minor stroke errors in the drive mechanism, the drive plate section and elastic arms do not undergo significant direct deformation, ensuring relatively stable clamping force. This eliminates the substantial clamping force fluctuations caused by stroke errors in traditional clamping fixtures.

(2) High Adaptability

The fixture's structural design fully accommodates clamping requirements for workpieces of varying shapes and dimensions.

By adjusting parameters such as the number and width of elastic arms, along with the layout of hollow gap assemblies, it flexibly addresses clamping challenges for complex workpieces. The introduction of positioning and adjustment mechanisms further enhances the fixture's adaptability and flexibility.

(3) Excellent Reset Accuracy

During machining, the fixture's reset precision directly impacts workpiece accuracy.

Through sophisticated structural design and elastic reset components, this fixture achieves precise arm reset, significantly improving positioning accuracy.

(4) Compact and Durable Structure

The integrated design philosophy results in a more compact and durable fixture structure.

Critical components are fabricated from high-strength materials and undergo surface treatments to enhance wear resistance and corrosion resistance, effectively extending the fixture's service life.

(5) Simple Operation

This clamping and holding fixture offers simplified and efficient operation. The use of elastic connections and an integrated design concept enables smoother and less labor-intensive clamping and releasing of workpieces.

Simultaneously, the introduction of an adjustment mechanism makes modifying the clamping position and force more intuitive and user-friendly.

Working Principle of the Clamping Fixture

During operation, this clamping fixture achieves relative movement between the first and second clamping arms through controlled elastic deformation of the drive plate section, thereby completing workpiece clamping and release. The specific process is as follows.

(1) Initial State

In the initial state, the drive plate section remains in its natural state without external force.

At this point, the first and second clamping arm sections naturally open to a certain angle under the action of their respective elastic arms, forming an opening gap to await workpiece placement.

The mounting section securely supports the entire fixture, ensuring stability during operation.

(2) Workpiece Placement and Clamping

After the workpiece is placed within the “gap” between the first and second clamping arms, the drive mechanism activates. This causes the drive plate assembly to undergo elastic deformation under applied force.

During this deformation, the drive plate pushes the rear ends of the first and second clamping arms toward each other. Since the clamping arms are connected to the mounting section via elastic arms, the movement of the rear ends causes the front ends of both arms to move inward accordingly, achieving clamping of the workpiece.

At this stage, the degree of deformation in the drive plate section directly determines the clamping force of the clamping arm section. By precisely controlling the output force of the drive mechanism, the clamping force can be finely adjusted to meet the holding requirements of different workpieces and machining needs.

(3) Clamping Maintenance During Machining

During the machining process, the combined clamping action of the elastic arms and the drive plate section enables the fixture to continuously provide a stable and reliable holding force for the workpiece.

Even when vibrations or impact forces occur during machining or minor stroke errors exist in the drive mechanism, the elastic deformation of the drive plate and elastic arms provides a degree of tolerance. Consequently, the clamping force remains relatively stable without significant variation. This effectively prevents workpiece displacement or deformation caused by uneven force distribution, ensuring stability throughout the machining process.

(4) Workpiece Release and Reset

Upon completion of machining, the drive mechanism reverses direction, gradually restoring the drive plate assembly to its initial natural state.

As the drive plate section regains its shape, the first and second clamping arms gradually open, releasing the clamping force on the workpiece.

At this point, the workpiece can be easily removed with the assistance of the manipulator. After release, the clamping arms automatically reset to their initial open state under the action of the elastic arms, awaiting the next clamping operation.

Conclusion

This fixture features an ingenious design that effectively addresses issues common in traditional clamping fixtures, such as uneven clamping force, unstable holding power, and poor reset accuracy, significantly enhancing clamping retention capability.

Through the precise coordination between the elastic arms and the drive plate assembly, clamping force remains relatively stable even when minor errors occur in the drive mechanism's stroke, thereby ensuring machining precision and product quality.

Furthermore, this fixture demonstrates exceptional adaptability. By adjusting parameters such as the number and width of elastic arms, along with the layout of the hollow gap assembly, it flexibly accommodates clamping requirements for workpieces of various shapes and sizes, significantly enhancing the fixture's versatility and adjustability.

Simultaneously, the ingenious structural design and application of elastic reset components ensure precise reset accuracy, further improving stability and reliability during the machining process.

In actual production, testing has confirmed that using this clamping fixture achieves repeatable positioning accuracy of ±0.002mm for small-diameter tools and a grinding yield rate exceeding 99.2%.