How to choose the right fixture for CNC machining
Why is there several times difference in productivity of the same CNC machine? Most likely because of the difference in fixturing, unsuitable fixtures reduce the productivity of CNC machines.
Fixturing the blanks or workpieces is an essential step in CNC machining. There are many types of fixtures for CNC machine tools. Once the fixture is not properly selected, it may cause vibration, impact, broken tool tips, loose workpieces, etc., thus damaging the workpieces and tools and leading to errors in the processed products.
A common fixture is a clamping device that is generally designed in two parts, one fixed to the machining platform and immovable, and the other consisting of one or more moving parts that can be used to hold the stock or workpiece. It is usually made of mild steel, stainless steel and other alloy steels.
Before choosing a CNC fixture, it is important to understand the characteristics of machining and the types of CNC fixtures. Machine manufacturing is divided into three types, such as single-piece, multi-species small batch, and multi-species large batch.
Generally speaking, modular fixtures are suitable for small batch production.
Block/combination clamps
Combination fixture, also called “building block fixture”, consists of a series of standardized design, different functions, different specifications and different sizes of clamp components. The “building blocks” (various machine tool clamps) can be assembled quickly according to machining requirements.
The modular fixture saves design and manufacturing time, thus greatly reducing production preparation time, which effectively shortens the cycle time of small batch production and improves production efficiency.
In addition, modular fixtures have the advantages of high positioning accuracy, high fixture flexibility, reusability, energy and material savings, and low cost of use.
In high volume production, the clamping time of workpiece may take 10-30% of the whole machining cycle. Therefore, for high-volume machining, it is necessary to use special fixtures with fast positioning and fast clamping (loosening), and three types of machine tool fixtures can be preferred: hydraulic/pneumatic fixtures, permanent magnet fixtures and fixture holders.
Hydraulic / pneumatic fixture.
Hydraulic/pneumatic fixture is a special fixture that uses hydraulic or pneumatic components as the power source to position, support and compress the workpiece through hydraulic or pneumatic components. The mutual position of the workpiece, machine tool and tool can be determined accurately and quickly.
The positioning accuracy of the workpiece is guaranteed by the fixture, with high machining accuracy and fast positioning and clamping process, which saves a lot of time for workpiece clamping and loosening. It also has the advantages of compact structure, multi-station clamping, high-speed heavy cutting and automatic control.
Due to the above advantages of hydraulic/pneumatic clamping, it is suitable for CNC machine tools, machining centers, flexible production lines, and especially for high-volume machining.
Electro-permanent magnetic clamping
Electromagnetic permanent magnetic clamping is a new type of clamping designed by using the latest magnetic circuit principle, using new permanent magnetic materials such as neodymium iron boron as the magnetic source. The clamping and unclamping process takes only about 1 second, which greatly reduces the clamping time. These clamps are suitable for small-scale and large-scale production with clamping force above 450Kgf.
Electromagnetic permanent magnet clamps can greatly reduce the clamping time, reduce the number of clamping times and improve the clamping efficiency. Many machining methods have shown that electromagnetic permanent magnet fixtures can greatly improve the overall machining efficiency of CNC machine tools and machining centers. Traditional machine tool fixtures have positioning and clamping elements that take up a lot of space, while electromagnetic permanent magnet fixtures lack these space consuming components.
It has the advantages of fast clamping speed, easy to realize multi-station clamping, multi-face machining, stable and reliable clamping, energy saving, automatic control, etc. It is not only suitable for small batch production, but also for large batch production.
Clamping base
Smooth clamping base can effectively shorten the manufacturing cycle of special fixture and shorten the manufacturing preparation time, thus shortening the whole cycle of mass production and improving the production efficiency. It can also reduce the manufacturing cost of special fixtures. Therefore, smooth clamping bases are particularly suitable for high volume production with tight cycle times.