Water jet cutter

A water-jet cutting machine is a machine tool for cutting materials using a high pressure water jet.

• 3.1 Machine frame
• 3.2 beam annihilator
• 3.3 high pressure pump
• 3.4 Disposal
• 3.5 control

Method

With waterjet cutting, the material to be processed is separated by a high pressure water jet. This jet has a pressure of up to 6000 bar and reaches the outlet speeds of up to 1000 m / s The sliced ​​barely heats up. Therefore, the process is, in contrast to the laser cutting, including cutting of hardened steel. The high pressure is the cutting water germ-free (high pressure sterilization). The water quality must meet certain minimum requirements. For optimum pump and component life, a special treatment is given if necessary, which requires a lot of experience and intuition because of the extremely high pressures; Standard methods such as water softeners or reverse osmosis systems often generate more problems than they solve. Due to the high exit velocity of the water produced during cutting, a sound pressure of up to 120 dB. By cutting under water, for example by increasing the water level in the beam catcher and by surrounding the nozzle with a water bell, the sound emission can be significantly reduced.

Clean water cutting ( Purwasserschneiden )

When pure water cutting the beam energy of the water is only exploited. The cutting performance in hard materials is very limited. However, amount to only 0.1 mm in soft materials, the kerf. For beam focusing polymers may be added. Latest technology in the high pressure pump sector even hard materials such as aluminum to about four millimeters in thickness without the use of abrasives with a 6000 bar water jet can be separated today.

Abrasive

To increase the cutting performance of the water is a cutting means, a so-called abrasive often added. Only through the incorporation of such an abrasive, (such as garnet or corundum), it is possible to cut harder materials with pure water jet is not separable, or their processing with pure water is not economical or where demands a higher quality of cut will.

In order to abrasive cutting, water jet system shall have a cutting head, which consists of three components mainly:

• Reinwasserdüse,
• Abrasive mixing chamber,
• Abrasivfokussierdüse / focusing tube

First, the highly compressed water is formed into a beam of about 0.25-0.4 mm ( nozzle- dependent) by the Reinwasserdüse. This beam shoots through the mixing chamber with up to 1000 m / s and thus creates a negative pressure in the cutting head. Through a small opening in the cutting head abrasive can now be sucked into the mixing chamber and mixed with the water jet. The water - abrasive mixture is then focused by the downstream Abrasivdüse and occurs with a diameter of typically 0.8 or 1 mm.

The abrasive can be dosed CNC - controlled normally, and the cutting head can be supplied with either air as a carrier or an emulsion. The feed rates for waterjet cutting include dependence on parameters such as material type and thickness, pump capacity (flow and pressure), nozzle combination (pure water and Abrasivdüsendurchmesser ).

Micro water jet cutting

The Micro Waterjet cutting is a process with a much higher component accuracy (± 0.01 mm), the angle error goes to zero. When micro water jet cutting with abrasives beam diameter can be produced from 0.2 mm (as of today's technology ). The maximum material thickness is dependent on the focusing tube inserted, but can be as long as 40 mm. The maximum workpiece size is about 990 × 590 × 140 mm. The method is particularly suitable for components where the conventional water jet cutting process is reaching its limits and higher accuracies parts and geometry are required. When pure water cutting, a cutting gap of 0.06 mm can be produced. Thus soft materials can be processed more accurately.

Applications

With the high pressure water jet process almost all materials can be processed, starting with the foam through to sapphire. The focus is on plastic processing, metal processing, leather processing and stone processing. Due to the possibility of pivoting of the cutting head ( 3D machining ) by means of a cutting vector control almost any complicated shapes can be cut even in the room.

It can be accuracies up to 0.005 mm / m working length reach. However, it must be conditioned to the processing room.

In addition to disconnecting the water jet cutting is also used for deburring.

An important aspect that speaks for cutting with abrasive waterjet is that structural changes ( material structure changes; see iron-carbon diagram ) can be excluded at the cut edges. The abrasive water jet cutting is therefore used with high success in materials science and engineering. A good way offers waterjet cutting, when it comes to cut dissimilar workpieces, such as ceramic-metal mixtures. The technology of waterjet cutting is therefore used for years in research institutions.

A standard application of waterjet cutting is now the trimming of composite layers plastic dashboards for cars by means of a five-axis robot, including water jet.

Machine components

A water jet cutting machine is comprised of various components which can be combined in different ways. Components include: memory, high pressure tubing, CNC transfer machine, pressure booster, oil tank, oil pump, electric motor, valve and nozzle

Machine frame

The machine frame, which is usually assembled from steel pipe of different sizes, bears the individual axes of the machine. The guides are stress relieved for high-quality machines, milled, ground or scraped. Thereafter, the straightness of the frame and the guide tracks is tested by means of a laser interferometer. The orientation of the frame via fixators or anchor elements. Standard design waterjet cutting the so-called portal construction is wearing ( as a flat bed for standard tasks or as high gantry system for workpieces with extreme dimensions ) on which two axes without connecting the crossbar. These types can be almost arbitrarily large machines realize ( spans the portal to about 5,000 mm). In portal machines, the two guide shafts ride in a so-called gantry grouping, and are thus coupled through the CNC control (two axes behave as a single ). In addition to the portal or the design variation exists as a carrying arm, in which the cross bar is carried out only on one side. This design is cheaper to manufacture and has an advantage because of the particularly good access from three sides of the cutting area. She was a long time but technically inferior to the portal design and less suitable for precision cutting, because the Tragarmbauweise generally tended to oscillate. Current quality support arm systems are designed using finite element analysis in terms of vibration so stiff that the same tight tolerances are achieved as with a portal machine.

Beam annihilator

The residual energy of the water jet which remains after the payment cutting work can be reduced in various ways. The most common variant is a pool of water that acts as a " beam dump ". The water tank should have sufficient water column of about 600 mm, so that the residual energy of the water jet can be converted into heat. The water tank should be constructed with absolutely no mechanical connection to the lead machine, because even the larger pool of water can heat in two -digit degree range after a few hours of cutting time. If now lead machine and water basins are one unit, such heating leads to significant changes in the machine geometry. The consequences are straightness, material expansion and thus inaccuracies in the parts manufacturing. Tolerances in the range of several tenths of a millimeter are not uncommon. However, the warming influence on the behavior of the workpiece and in a timely manner it may be necessary for higher accuracy requirements included in the calculation are (Online CNC correction).

In addition to using a fixed pool of water, there is also another variant, namely the so-called " Catcher ". A catcher called for waterjet cutting a wheeled narrow water catch basin, which moves synchronously with the movement of the cutting axis. These catchers are often filled with ceramic balls that are to convert the residual energy. The main disadvantage of these catchers are extreme airborne noise emissions from the non-water -covered top, and a high proportion splash. As a result of significantly lower amounts of water in circulation in the heating Catch heritage instinct is, however, much faster decoupled from the workpiece.

High-pressure pump

The high pressure pump is used to generate a high-pressure water jet pulsation as possible. Simple designs are operated by compressed air, which provide the high pressure via a pressure intensifier. Due to the poor efficiency but this is only for systems in the low-end applications in particular. In general, high pressure pumps are used in water jet cutting, using a hydraulic unit [ the efficiency is about 65 %]. These units produce oil hydraulically an upstream pressure of up to about 200 bar. The pressure is greater at any abregelbar pump a proportional valve. The compressed oil is pumped into the hydraulic cylinder of the high- pressure booster. Here, the oil acts on a piston rod with a ratio of about 20:1 - 40:1 ( hydraulic surface to the water surface ). Thus, pressures can produce up bar in the range of about 6500. The high-pressure water leaving the high-pressure cylinder, reaches a so-called pulsation damper. This is a gas high pressure reservoir, a " buffer cylinder " (typically one or two liters capacity ), which is to damp the pressure fluctuations in reversal of the hydraulic piston. The larger the buffer container, the better the cutting performance and quality. HD pumps can have more than one high-pressure intensifier and buffer bottles. The power of today's systems is between about 11-149 kW. The flow rate may be up to 15.2 liters per minute. Recently, cutting pump units are used which produce a pressure of 3800 bar by means of plunger pumps. This can be dispensed with going through the hydraulic system. These waterjet cutting pumps have the high pressure pump is directly driven, so that an efficiency of over 90 % is achieved. Due to the triplex characteristic pulsation is so small that can also be dispensed with Pulsationdämpfer. In the power range can be implemented with this technique up to 750 kW propulsion power, while a volume flow up to 100 l / min are generated at 3800 bar.

Disposal

The blended with cutting material and abrasives cutting water must be removed from the beam annihilator. This is done manually, either continuously or at intervals by disposal. The continuous disposal consists of either a scraper conveyor which removes the cutting residues from the beam annihilator, or from a water circulation that segregates the residues from the beam annihilator. The water from the beam annihilator is then filtered and fed to the cutting tank again.

Control

Waterjet cutting systems are consistently equipped with CNC controls. In addition to the simplest designs that allow only a plotter, have higher quality machines to control, which interpolate all the axes as both can also perform an adaptive feed rate reduction depends upon the cutting process. Here exists alongside a CAD interface also often a CAM connection. For several years, PC controllers on the market that offer the advantage of easy incorporation for CNC operators are ignorant.

History

Since about 1900 the water jet was used for digging in gravel and clay deposits. In Soviet and U.S. mines the possibility of using a high pressure water jet for the coal and ore mining has been studied in the 1930s. As composites were introduced in aircraft in the 1960s, the Boeing suggested the use of a water jet for processing such materials. The company Ingersoll Rand, today KMT (Sweden), delivered in 1971, the first operational water jet cutting machine. In the late 1990s brought FLOW a new method on the market, which is now called Dynamic Waterjet. With this method it is possible to correct the damage caused by the beam divergence angle error of the cutting edge, so you can cut very precisely even with thick workpieces. Through these corrections accuracies in the range of ± 0.04 mm are achievable. However, accuracies better than 1 /10 mm can be reached by any high-quality 3-axis system.