Advantages and Applications of the Precitech Hydroround CNC B Axis

Many customers are rediscovering B axis technology as a cost-effective and enabling technology. The latest CAM tools now support new uses of coordinated motion of the B and Z or B and X axes. Thanks to sophisticated control capabilities, the additional setup time required to configure tools for use on a B axis has been eliminated. This article discusses the advantages as well as current applications of B axis technology.

Before the advent of controlled waviness diamond tools, the B axis on a diamond turning machine was mainly utilized to support single-point diamond turning. Rotating the tool under computer numerical control (CNC) ensures that the tool is in the same angular relationship to the surface normal vector and that the same spot on the tool remains in contact with the surface. When utilized in this manner, the form precision of the turned surface is not affected by the edge waviness of the diamond tools.

With the availability of cost-competitive controlled waviness diamond tools, the need for the B axis technology has reduced significantly. However, new developments in CNC controller technology have made it possible to setup tools at the center of B axis quickly and precisely, similar to the setting of fixed tools.

Hydroround B axis

Precitech’s Hydroround B axis is one of the most versatile machine options available on high-precision systems. With its precision, stiffness, and damping characteristics, the Hydroround B axes enable users to get the most from their B axis technology. it comes in two sizes: the Large Hydroround is utilized on Freeform 700 and Nanoform 700 systems; and the Small Hydroround is utilized on drum roll lathe and Nanoform 250Ultra systems.

Eight Ways Hydroround B Axis Improves Profits and Increases Capabilities

B Axis Applications Related to Processing Crystalline Infrared Materials

Rapid development of Germanium lenses: The Hydroround B axis enables customers to utilize extremely large radius tools to manufacture Germanium lens at three times to five times the normal feed for each revolution.

Selective use of diamond tools when cutting Silicon: When compared to other materials, Silicon abrades diamond tools much faster. The hardness of the edge of diamond tools is not homogeneous around the sweep angle of the tool’s edge owing to the diamond’s crystal orientation. By means of tool normal cutting, users can control which section of the sweep angle is utilized to cut parts and remove the influences of crystal orientation on cutting results.

Reduced subsurface damage and better yields when cutting Germanium and Silicon: In order to obtain the desired surface finish from diamond turning Silicon or Germanium, the material should be cut in a ductile state and the volume of material removed by brittle fracture should be reduced.

When fixed tools are used, the effective negative rake angle becomes shallower when the contact point between the tool and the surface shifts away from the tool’s axis. This reduction raises the degree of brittle fracture taking place, resulting in subsurface damage and substandard surface finish. Tool normal machining coupled with the Hydroround B axis enables users to cut the whole surface at a consistent and optimal negative rake angle.

B Axis Applications Related to the Processing of all Optical and Mold Materials

Enabling the development of steep surfaces: Steep surfaces can be quite complex to make using fixed tools. It is important to ensure that the sweep of the controlled waviness edge of a fixed tool have the complete range of slopes on the surface being cut. A Hydroround B axis from Precitech enables users to rotate the tool so as to track the surface slope, ensuring one spot on the tool remains in contact with the surface. This is called as tool normal machining.

Improving yields related to form while reducing the cost of diamond tools: Tool normal machining removes the waviness in the edge of the tool, which is a major source of error in form. When turning with a fixed tool, users normally purchase costly controlled waviness tool to reduce the effect of tool waviness on form precision. In contrast, the Hydroround B axis helps in enhancing form precision and uses non-controlled-waviness tools that are less expensive.

Increasing diamond tool utilization and lowering tool maintenance costs: The Hydroround B axis not only improves productivity by reducing tool changes, but also extends tool life. A single zone of the edge of the tool can be utilized for roughing, while a different zone can be kept for finishing. All passes can be carried out by a single location on a tool, and when this location becomes dull the tool is pivoted to use a fresh spot.

Improving the efficiency of diffractive optics and reducing manufacturing time: When the Hydroround B axis with a split radius tool is used, highly efficient diffractive optics can be developed with lower cycle times. The diagram in Figure 1 demonstrates the loss of a diffractive surface or transmission blockage owing to the tool radius. Equation 1 assesses the overall loss.

Transmission blockage due to the tool radius.

Figure 1. Transmission blockage due to the tool radius.

   

Equation 1

where:

D = Lens Diameter
d = Maximum Step Size
RT = Tool Radius
nr total = Total Transition Steps

In case of a static tool, losses are kept to a satisfactory level by utilizing a small radius tool. A split radius tool includes a large radius edge, which is truncated at the middle line of the tool by a single flank of the diamond tool. The intersection of the radius and the flank forms a corner that has a relatively smaller radius.

Using the large radius part of the split radius tool, the refractive zones of a diffractive lens can be rotated at high speeds. As the tool nears the diffractive or transition step, it is rotated so that the sharp corner radius creates a small radius at the step’s base. This yields a quality diffractive optic that can be produced easily and efficiently.

Using the B axis as a tool turret to increase production efficiency: When customers use their Hydroround B axis as a turret, they normally employ a person who mounts and sets a number of tools for upcoming production shift. When different tools are needed or as the tools wear, the operators have the required tools available for use.

The CAD layout in Figure 2 displays a Small Hydroround B axis on a Nanoform 250 Ultra system. The B axis table top offers sufficient space so that a wide range of tool configurations can be easily mounted. The dual tool holders include the tools that are slightly moved away from each other so that they do not obstruct each other when large convex optics is being cut. This layout comprises five diamond tools, an UltraComp probe, a part centering accessory, a dual tool shroud, and a front surface probe.

CAD layout

Figure 2. CAD layout

Precitech’s Hydro-lock Technology

When customers need to lock their B axis in place, Precitech’s Hydro-lock offers a suitable solution. With the help of Hydro-lock, the Hydroround B axis is securely locked in place by applying hydraulic pressure to one part of the Hydroround bearing. After the B axis is Hydro-locked, it is capable of resisting up to 80ft-lbs of torque.

Other products associated with Precitech’s Hydroround B axis include Virtual Center Technology (VCT) that minimizes set-up time for tool normal machining; and ultra-mapping, B axis radial error compensation

Conclusion

This article broadly describes the benefits and applications related to the Precitech Hydroround CNC B axis. The Hydroround B axes have excellent stiffness, accuracy and damping characteristics, enabling users to get the greatest benefit from B axis technology.

This information has been sourced, reviewed and adapted from materials provided by Precitech.

For more information on this source, please visit Precitech.

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