Tackling long drill production challenges

How linear motion solutions help one CNC machine manufacturer solve the problem of machining long drills.  

Russell Riddiford 
President of ANCA Americas 
ANCA CNC Machines

Linear motion components play a central role in CNC machines. From linear actuation to bearings to the drive and control system, these components are key to the motion system of CNC machines and their operations.

The benefits of CNC machining are that they produce parts with high levels of accuracy and consistency, and typically better surface finishes. They use software programming to produce parts faster than other manual methods. Types of CNC machines include routing and milling machines, lathes, and laser cutters that work on steel, aluminum, plastic, and composite materials.

One use of CNC machining is in the manufacturing of long drills. The machining of long drills presents several difficulties and challenges in the production process. Their elongated physical size is not the only concern; ensuring accuracy throughout the entire length of the tool can be equally challenging. The extended nature of these drills introduces a host of potential issues that need to be addressed.

One challenge is the need to control grinding forces consistently throughout the entire length of the tool. This is crucial because long drills are designed to create holes that are not only accurate but also maintain their straightness over extended distances. The reduction of deflection caused by grinding forces is important. When fluting the drill in the shortest possible time, high feed rates and forces are necessary. It becomes crucial to find ways to minimize deflection while maintaining the required machining efficiency.

Another concern is runout, which refers to the error that occurs when the tool deviates from the center axis at an angle. While a standard setup may allow for an acceptable 5-µm runout for a 100-mm tool, the same setup could result in up to 40-µm runout for a 400-mm tool. Achieving acceptable runout becomes a priority when dealing with such lengthy tools, as it directly impacts the performance of the tool.

Additionally, long drills often feature coolant holes integrated within their bodies. To ensure proper functioning, these coolant holes must be correctly identified by the machine during the machining process, avoiding any damage that could impede their functionality. Managing grinding forces and preserving the integrity of coolant holes are critical considerations when working with long drills.

Addressing the challenges of tool deflection, runout, fluting, and coolant holes, integrated solutions and software capabilities provide a comprehensive approach to effectively produce long drills with accuracy and efficiency.

Spindle solution
ANCA’s TX7 CNC machine integrates a number of solutions to solve the challenge of producing long drills. First of all, the machine’s 37-kW (49-hp) direct-drive spindle facilitates the efficient grinding of long drills without putting excessive strain on the machine. It boasts a spacious working envelope and a 6th axis with a traveling steady support that can be positioned strategically to provide support in the grinding zone, allowing for the accommodation of tool lengths of up to 480 mm. This setup eliminates deflection and minimizes vibrations caused by grinding forces on the tool. It also addresses the issue of runout, as the steady supports enable compensation control to mitigate runout errors effectively.

At the heart of the spindle’s design is a 37-kW direct-drive motor, engineered to provide high reliability with optimal power and torque for a wide range of applications. The direct-drive configuration eliminates the need for belts or gears, reducing mechanical complexity and enhancing reliability. Plus, ANCA has recently introduced its patented Motor Temperature Control (MTC) product, which can be applied to the spindle to actively regulate spindle temperatures. This innovative technology acts preventively, mitigating inaccuracies and inconsistencies caused by spindle growth when operating over a range of spindle loads and speeds throughout production. By proactively addressing temperature variations, the spindle ensures consistently precise machining results.

The TX7 spindle is crafted to not only accommodate standard wheels and tools but also to address the specific demands arising from grinding tools with larger wheel diameters. The machine is often deployed in contexts where larger machine sizes are used: for instance, production of larger tools necessitating the need for larger grinding setups, including a 12-in. wheel that can weigh over 20 lb. These scenarios often involve longer cycle times and/or frequent wheel dressing, where larger wheels offer a great advantage over smaller ones in batch production. Applications such as punch grinding, fir tree cutters, and tap grinding to name a few, commonly encounter such requirements. The spindle has been engineered with a robust high-torque design, enabling it to effortlessly handle these challenges and deliver consistent precision in grinding operations.

Linear motors drive linear axes
LinX linear motors drive all the linear axes, with a unique counterbalance design to counter gravity for the Z-axis. These linear motors have a number of advantages compared to ballscrews or flatbed linear motors. Flatbed-style linear motors used in grinding machines typically have a back iron in their magnetic circuit, which increases the down-forces and creates cogging. Cogging results in reduced surface finish quality. This tremendous down-force on the bearings can cause components to wear faster, decreasing efficiency.

The LinX linear motor’s even force over the entire stroke provides superior motion performance, and because of its direct drive nature, the motor can track motion commands more accurately and repetitively to achieve a better surface finish. The LinX linear motor also enhances the cycle time due to its higher acceleration and faster traverse speed.

The key is the cylindrical design. The LinX linear motor consists of a shaft containing magnets and a forcer containing wound copper coils. The symmetric design results in zero attractive forces between the forcer and shaft, greatly reducing the loading requirement on support bearings. The thermal barrier design separates and removes heat from the motor, eradicating thermal growth for the machine.

The LinX’s simple construction, non-critical air gap, and no physical contact between the shaft and forcer lets machine manufacturers greatly simplify installation, reduce maintenance, and extend machine life.

Due to its simple construction, only one or two supports are required at the shaft ends depending on its orientation. Not only has the axis installation time been reduced by more than 200 percent when compared to ball screws, but the installation of LinX motors is much safer than flatbed linear motors.

Specialized software
ANCA offers several software solutions for long drill production. The first is ToolRoom, which provides a drill wizard as a standard feature. This wizard is a great starting point and includes convenient features like wheel pack auto-select. Users can easily add and define coolant holes in the blank editor for simulation. The software also includes runout compensation capabilities, providing further adjustments to compensate for runout errors.

For formed flutes, ANCA offers iFlute software. Long drills often require specific flute forms, and iFlute simplifies the process. Users can simply import their DXF file, and iFlute will determine the wheel profile and grinding paths accordingly.

To simulate the tool grind and account for machine features, ANCA provides CIM3D. Users can add all the necessary machine features to the simulation, including a 6th axis, to determine the setup and control before proceeding to the actual grinding process. Not only can users set up the required operations, but they can also optimize the grind from their desk with accurate simulations of all features. CIM3D includes intuitive coolant hole collision detection within the simulation, ensuring that potential issues are identified and addressed beforehand.

ANCA CNC Machines
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