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Zero-point clamping system

What is a zero-point clamping system?

A zero-point clamping system is an extremely precise workpiece clamping system that allows a workpiece to be positioned repeatedly in exactly the same place in all directions. The key advantage of zero-point clamping is its repeatable accuracy, which can be as good as 0.005 mm between clamping cycles. Zero-point clamping offers significant benefits, especially due to its short setup time, which can reduce setup times by up to 90% compared to traditional clamping methods. The clamping takes place in a system of pull studs and cylinders, where the pull studs precisely secure the workpiece in position within the cylinder, using either a hydraulic or pneumatic locking mechanism.

Zero-point clamping system components

The main components of a zero-point clamping system are the cylinder installed in the machine tool and the pull stud attached to the workpiece. The cylinder acts as the zero point for the entire clamping system, providing exact positioning for the workpiece and ensuring the secure fastening of the pull stud and the part. Cylinders are often made of stainless steel, and the locking mechanism can be implemented in various ways, such as with ball locks, sleeve locks, or claw locks. The locking system does not require an external power source to maintain, as the lock is held by spring force, but releasing the lock requires either hydraulic or pneumatic pressure.

The pull stud is attached to the workpiece or a fixture plate and enables the workpiece to lock into the cylinder. The pull stud has a notch or shoulder that matches with the cylinder’s locking element and retracts into the cylinder with a certain force during locking. This ensures the piece stays tightly against the cylinder’s face. To ensure different levels of positioning accuracy, there are three types of pull studs: centering studs, aligning studs, and guiding studs.

Different types of zero-point clamping cylinders

Cartridge-type cylinders are designed to be permanently installed as part of the machine tool frame. The cylinders are mounted by machining an opening matching the cylinder’s base dimensions, allowing the cylinder to be installed flush with the machine table surface. Hydraulic and pneumatic connections are located at the bottom of cartridge-type cylinders. The cylinder features a built-in uncoupling system and oil reservoir, as well as channels for sensors.
Flange-mounted cylinders differ from cartridge types due to their shallower mounting depth. This means the top of the cylinder remains visible above the surface of the machine table. The shallow mounting depth makes these cylinders suitable for thinner tables and pallets. Embedded cylinders do not have an internal oil reservoir; instead, the oil space is formed between the cylinder and the bottom of the mounting hole. This solution enables the hydraulic or pneumatic unlocking from the base of the cylinder.
Surface-mounted cylinders are especially suitable for upgrading older machine tools, as they can be installed directly onto existing clamping tables, like T-slot tables or grid plates. This makes them a flexible choice for many different machines, reducing the need for recalibration and extensive installation modifications.
Wall-mounted cylinders are specifically designed for use in setups such as angle shelves or fixture towers, where the part is loaded with a crane. The hook protruding from the cylinder helps the pull stud to align with the groove, and when locked, the hook pulls the pull stud inside the cylinder and locks it in place.
Indexing cylinders feature a mechanism that allows the workpiece to be positioned at specific angles using grooves on the cylinder’s face. This enables high-precision clamping at different angles. For example, notched cylinders and their holes ensure the piece stays exactly in position and prevent unwanted rotation, which is particularly important for work involving high machining forces.

Different types of pull studs in a zero-point clamping system

Pull studs are a central part of the zero-point clamping system, responsible for locating and securing the part in the cylinder. Different pull studs have specific features that ensure accuracy and reliability in various applications.

Centering stud

The centering stud defines the zero point of the clamping and is a critical component for achieving high clamping accuracy. This pull stud is designed to fit precisely into the center hole of the cylinder, ensuring the part is positioned exactly in place.

Feature: The guiding surface of the centering stud is machined to a highly precise fit.
Use: Typically used in applications that require a single stud, which must be a centering type. More than one centering stud cannot be used for a single part, as it could lead to excessive clamping force and inaccuracies.

Aligning stud

The aligning stud determines clamping in a specific axis direction. It is designed to support and accurately align parts in a direction other than the one guided by the centering stud.

Feature: Two narrow surfaces are machined on opposite sides of the stud’s guide surface, while the rest of the surface is undersized.
Use: The aligning stud acts on the y-axis when the centering stud acts on the x-axis, allowing for thermal expansion of the part along the x-axis.

Guiding stud

The guiding stud is primarily used to secure the part and keep it in position. The locating surface of the guiding stud is undersized, meaning it does not affect the positioning of the part.

Feature: The locating surface is fully undersized by about 0.5–1.5 mm.
Use: Used when the part needs to stay in place but precise positioning or indexing is not required. The guiding stud only securely clamps the piece.

Pull stud attachment methods

Pull studs are attached to the part or pallet in several ways, depending on the part’s shape and requirements:

Screw fastening: One of the most common methods, where the pull stud is attached to the part being machined with a screw.
Embedding: The pull stud is embedded into a precisely machined hole according to manufacturer tolerances.
Special screws: In certain cases, specially designed screws are used to fasten the pull stud.

Different pull stud structures

Ball-bearing and sleeve-type structures are common technologies for pull studs:

Ball bearings: Steel balls lock the pull stud into the cylinder. The balls fit into the groove of the pull stud and, under spring force, lock the stud in place.
Sleeves: The sleeve has flexible claws that lock around the pull stud. The sleeve presses against the shoulder of the stud, providing a strong hold.
Claw locking: In claw locking, two spring-loaded claws slide along the axis of the cylinder. Unlocking is performed by retracting the claws out of the pull stud groove.

Advantages of zero-point clamping

There are numerous advantages to using zero-point clamping systems:

High repeatability: Zero-point clamping systems offer repeat accuracy of up to 0.005 mm between clamping cycles, allowing for extremely precise positioning and reducing the need for adjustments.
Fast setup times: Zero-point clamping enables extremely rapid setups, shortening setup times by up to 90% compared to conventional methods. This improves machine utilization and production efficiency.
Consistent clamping: Zero-point clamps can be used across different machines without having to recalibrate the fixture. This makes it easier to transfer parts between machines.
Versatility: The clamped part is generally free on nearly all of its surfaces for machining, allowing for five- or even six-side machining in a single setup.
Suitable for automation: Zero-point clamping is well-suited for unmanned and automated production, reducing labor costs and the chance for errors.
Low part tension: Zero-point clamps often exert less stress on the clamped part than traditional clamping methods, potentially improving part quality.
Work safety: More reliable clamping reduces the risk of the part coming loose or shifting during machining, improving workplace safety.

Disadvantages of zero-point clamping

Although zero-point clamping offers many advantages, there are also certain drawbacks and limitations:

High investment costs: Purchasing and implementing a zero-point clamping system can be a significant investment, especially for small machine shops. The cost of the clamps and associated hydraulic or pneumatic systems is relatively high.
Need for hydraulic and pneumatic systems: Releasing the lock of the zero-point clamping system generally requires hydraulic or pneumatic pressure. This may require infrastructure upgrades or additional system purchases for the shop.
Sensitivity to contamination: Chips and other contaminants can disrupt the function of zero-point clamps. Cleaning systems and preventive measures are essential to ensure reliable clamping.
Machining requirements: Installing a pull stud directly onto the part to be clamped requires additional machining steps, increasing manufacturing costs and production time.
Shape limitations: The attachment and positioning requirements of pull studs may restrict the shape of the workpiece. This can make it challenging to use zero-point clamping for more complex geometries.
Weight limits: Clamping very large and heavy parts can be problematic, as zero-point clamping systems have limits to their locking and holding forces. Although there are special zero-point systems for large parts, even they face restrictions regarding size and forces.

Applications of zero-point clamping

Zero-point clamps are highly versatile and well-suited to various needs in the metalworking industry:

Machining: Zero-point clamps are particularly useful in CNC machining. Their high accuracy and short setup times enhance production efficiency and part quality. Zero-point clamping can also secure a workpiece so machining can be performed from five sides, significantly reducing handling and manufacturing time.
Welding: In welding, zero-point clamping ensures precision and reduces setup times. Accurate clamping improves weld quality and reduces potential errors.
Automated production: Zero-point clamping is ideal for automated production lines where parts are changed frequently and rapidly. The clamps provide high repeat accuracy and reduce human error risk.
Jigs and assembly tools: Zero-point clamps can be used in various jigs and assembly tools, such as on assembly lines where their quick clamping and release are an asset.
Testing and measurement: Zero-point clamps are valuable for quality assurance, measurements, and testing, where precision and repeatability are essential requirements.
Prototype manufacturing: Prototyping often requires quick clamping and release. Zero-point clamping enables effective and rapid prototype manufacturing and modification.

When selecting and using zero-point clamping, it’s important to consider the benefits it provides and its potential applications to improve production efficiency and quality. While upfront investment may be higher, the speed, accuracy, and versatility of clamping can lead to significant savings and improved productivity over time.

Summary

The zero-point clamping system is an advanced and efficient solution for positioning and securing workpieces. It combines high accuracy, short setup times, and versatility, making it an excellent fit for the needs of modern machine shops. Its use can greatly improve production efficiency and reduce setup times in manufacturing processes, making it a recommended choice for a variety of workholding needs. The challenges are mainly the higher investment costs and the installation of necessary hydraulic or pneumatic systems, but in the long run, the savings in setup time and improved accuracy can bring significant cost benefits.