Knowledge

How to increase productivity and reduce reject rates with a well-selected workpiece clamping scenario

Clamping technology is known as the fixing of a workpiece or a tool with which a workpiece can then be machined. The clamping device should clamp the workpiece rigidly in place, i.e. as vibration-free as possible without deforming it. The setup should allow for high repeatability, be quick and easy to use, versatile, easy to replace and ideally not too expensive. 

When does clamping technology increase productivity?

The ideal workpiece clamping scenario reduces setup times and thus increases productivity. Only with excellent workpiece handling during clamping and flexible retrofitting of the clamping technology can productivity be regularly increased by at least 30 percent, in individual cases up to 90 percent. Standardised solutions that are not only precisely tailored to an individual workpiece, but are versatile, also save on procurement and storage costs.

What are the trends in workpiece clamping technology?

  • Increasing machining of composite materials, lightweight components, thin-walled and miniaturised components
  • Smaller batch sizes through increasing customisation of workpieces
  • Fully automated production processes and reliable process monitoring
  • Automated workpiece equipping
  • Networking and unique identification of clamping technology components
  • Implementation of sensor systems for data recording and transmission
  • Online configurators for clamping components

Loading and unloading in industrial applications is becoming increasingly automated; workpiece clamping technology represents a decisive factor for process security and must be equipped with a comprehensive sensor system. Only in this way can clamping pressures be automatically checked and regulated. If the clamping force drops or vibrations occur, the machining parameters can be automatically adjusted to ensure a reliable process and maximum efficiency. To do so, various monitoring options and seamless communication between the clamping device and the machine tool are necessary. 

What benefits does a zero point clamping system offer?

Workpieces, clamping devices and fixtures can be clamped in one operation with accurate repeatability by determining the reference point. Productivity increases if further workpieces outside the machine are set up on the respective clamping system while the machine is processing an order. Once this order is finished, the clamping system can be removed and the next workpiece placed in the zero point clamping system. The machine can run the next program immediately and downtime is therefore reduced.

In modern five-axis machining centres or turning milling machines, the workpiece should also be reliably clamped without hindering free access to the workpiece from all axes. Clamping towers and clamping cubes perform this task extremely efficiently. They provide the option to machine several workpieces that require the same clamping setup at the same time.

If the clamping towers are fitted with zero point clamping bolts again, the entire tower can be set up outside the machine while the workpieces are being machined on another tower in the machine. The complete clamping towers are then exchanged, positioned and secured via the zero point clamping system in no time at all. Alternatively, the workpieces can be pre-fitted on pallets and then secured in the clamping tower.

A marked trend is a combination of the different clamping methods. Zero point clamping technology often forms the basis and is enhanced with hydraulic, magnetic or pneumatic systems as a flexible modular system.

Clamping tower with three zero-point clamping systems. Different vices are mounted on the zero point clamping system.

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How do the individual clamping systems work?

Clamping elements can be divided into mechanical, hydraulic, vacuum or magnetic clamping elements according to the way in which they exert the clamping force:

Mechanical clamping elements

Mechanical clamping elements require time-consuming and precise clamping, but also deliver high clamping forces with self-locking of the clamping elements. Mechanical clamping elements are eccentric levers, machine vices, tilting angle tables or rotary indexing tables. Toggle clamps work with three joints. If these are in alignment with one another, the lever can no longer be pushed back by counterforce - self-locking occurs. Quick-release clamps work according to the same principle in a shorter time and with reduced force. They are suitable for use in welding, drilling and monitoring devices. On eccentric clamps, the centre point of the clamping curve is off centre. These are therefore suitable for turning devices but less so for milling devices, as stronger vibrations than the clamping setup could withstand occur during milling.

Mechanical single vices

Machine vices are used to clamp small and medium-sized workpieces in one-off and small series production. Compared to the other systems, these are far less complex, require less maintenance and are easy to use. For this reason, they are a good and affordable solution for many standard tasks.

Pneumatic clamping elements

Pneumatic clamping cylinders offer quick closing and opening of the clamping device. Due to the low permitted operating pressure, however, they do not generate high clamping forces, and due to the rebound effect of air they give way in the event of overload. If this needs to be avoided, we recommend combining the pneumatic clamp with self-locking toggle clamps.

Hydraulic clamping elements

Hydraulic clamping elements deliver high clamping forces and can build clamping pressure quickly. They are versatile and can also be used for challenging workpiece shapes. The clamping setup is extremely rigid, but can be controlled automatically and delivers uniformly high clamping forces at all clamping points. 

Magnetic clamping devices

Magnetic clamping devices secure the workpiece on permanently magnetic or electromagnetic clamping plates. This means that challenging workpiece shapes can be clamped more easily. However, electromagnetic clamping plates can generate waste heat during operation, which can deform the workpiece. To prevent this, both types of magnet can be combined. After machining, the workpieces must be demagnetised. Magnetic clamping plates and magnetic chucks are used during milling, turning, eroding and grinding. The advantage of magnetic clamping elements lies in the large, definable, concentrated clamping force with comparably low energy consumption and maintenance requirements. 

Vacuum clamping technology

With vacuum clamping technology, thin and elastic materials can also be clamped. These clamping devices are used primarily in wood and plastic machining and come into their own when additive manufacturing with plastics is combined with (subsequent) machining. However, powerful vacuum clamping systems are also used in metal machining and are particularly gentle on the workpiece, especially when machining aluminium and other non-ferrous metals.