Gears for waterjet cutting heads

     Various technologies have been used in material cutting. Saw cutting is the best known amongst them, used however only for a simple material dividing. Waterjet, plasma, or laser cutting have been used for cutting various complicated shapes. The design and principle of these cutting machines are more or less similar, with the cutting medium type being the main difference. Machine properties such as cutting speed and quality, the width of the cutting gap, the maximum thickness of the cut material, procurement costs, and operating costs depend on the used medium. Each one of these technologies has some pros and cons, and technology choice depends on the machine application and the purpose. 

     Plasma and laser cutting technology is thermally based, i.e. the material is cut by melting. Therefore these technologies cannot be used for cutting heat-sensitive materials (wood, thermoplastic materials, laminates, etc.). Waterjet cutting operates on the basis of hydro- erosive dividing by high-energy water jet. The cutting edge is not affected by thermal deformation, thus it demonstrates high quality and precision of the cut.  It is the most universal method of cutting, covering all material types including paper and food products. The abrasive component is added in case of cutting hard and sturdy materials.

     Cutting is divided into two fundamental methods, namely two-dimensional (2D) and spatial (3D) cutting. Three-axis machines are used for 2D cutting with cutting head moving in two basic axes X and Y. The axis Z serves for the adjustment of the distance between the cutting head and the material to be cut. Five-axis machines are used for 3D cutting with added two rotating axes, along with linear axes X, Y, and Z, which allow for the cutting head to be tilted and thereby create three–dimensional spatial cutting. 

     However, there is a trend in waterjet cutting to apply 5 axis machines also to 2D cutting. The reason is that the waterjet coming out of the cutting head orifice at high pressure has a conical shape. Accordingly, the cutting edge is not perpendicular to the cut material surface. Moreover, cutting is delayed here (water jet bending) between the material surface and its bottom part, resulting in an uneven cut and worsened quality of the cut surface.  Taper Control system technology has been used to remove these deficiencies, compensating them with cutting head tilting at a certain angle.

     Reduction gears used in the fourth and fifth axis largely affect the cutting machine properties. Applying the Taper Control system to the cone compensation causes very small movement in these axes. Therefore gears should be used here with high rigidity and low friction in the gearing, resulting in the elimination of the so-called stick-slip effect that causes jerky movement and thereby reduces the quality of the cut. Cycloid gears TwinSpin® were proved successful in these conditions with very smooth running also at very low speed.

     TwinSpin® reduction gears are typical with high precision that demonstrated favorable impact on the machine cutting accuracy. The gears are also characterized by high torsional and tilting stiffness which are very important since the water jet is sprinkling through the orifice onto the cut material at high pressure and this further tends to wobble the cutting head, which would adversely affect the precision and quality of the cut.   

     Moreover, reduction gears TwinSpin® have high gearing ratio and small dimensions, which allows creating a very compact cutting head design and thus reduce its total inertia, showing the favorable impact on the movement dynamics, reduction of secondary times (actions aside of cutting, i.e. cutting head repositioning), and thereby improving the machine productiveness.   

     The use of actuators DriveSpin® represents also a  very interesting solution of the cutting head drive node, especially the hollow shaft version that allows for even more compact and simpler cutting head design, reducing the drive node dimensions, facilitating the assembly and increasing the machine reliability and safety thanks to the power and control signal transmitting cables that can be led through the actuator inside the cutting head, avoiding the exposure to threatening external mechanical damage. 

            Along with waterjet cutting machines, these excellent properties of reduction gears TwinSpin® and actuators DriveSpin® made by company SPINEA, s.r.o. have been demonstrated also in the cutting heads during 3D plasma and laser cutting.