ID Turning
Internal turning, an essential yet challenging process for many machinists, is a method where precision and diligence are rewarded. Discussing internal turning often involves a technically demanding task where control of tolerances and process fluidity is key. The most typical and challenging situations in internal turning relate to the long tool overhangs and chip removal, both of which can present various problems during the process.
When turning a long internal diameter, one of the first challenges is managing tool deflection and vibrations. The smaller the internal turning tool’s shaft and the further it must extend, the higher the risk that the tool will start vibrating during the turning process. This vibration can be detrimental in many ways: it might impair the workpiece's dimensional accuracy and surface finish, accelerate tool wear, or in the worst case, cause tool breakage.
To mitigate vibrations, it's important to use suitable cutting speeds and feeds and to select the appropriate cutting tool geometry for the task at hand. Available options include carbide or vibration-damped tool holders, which help reduce vibrations stemming from long tool overhangs.
Another common challenge in internal turning is chip removal. Inefficient chip removal can cause a myriad of issues such as excessive tool wear, workpiece damage, or even tool breakage. If chips do not efficiently exit the turned hole, it can degrade surface roughness, lowering the quality of the manufactured part.
To improve chip removal, selecting the correct insert and tool material is crucial. The chip formation and removal mechanisms can vary significantly when machining different materials, highlighting the importance of insert selection. Effective chip removal also requires continuous attention to chip formation and potential chip breakers, which help break chips into smaller pieces, facilitating their removal. Through-coolant tool holders and adequate cutting fluid pressure help transport chips out of the machined hole.
Internal Longitudinal Turning
Internal longitudinal turning is a complex process where tool selection and use are critically important for achieving a successful outcome. In this process, the internal diameters of a workpiece's holes are turned, and to ensure optimal efficiency and accuracy, the tool's shaft size and overhang must be optimal relative to the bore length and diameter being machined. A general rule of thumb is to minimize the overhang length of the internal turning tool and increase the tool size where possible. This approach reduces tool deflection and susceptibility to vibrations, enhancing turning accuracy.
When selecting an appropriate tool for internal longitudinal turning, several factors need consideration, among which the insert shape is crucial. Positive inserts are preferred in internal turning, as they generate lower cutting forces compared to negative inserts. Furthermore, a small lead angle and nose radius help reduce cutting forces, affecting not only work quality but also tool durability.
The insert's orientation angle also significantly influences the success of the turning process. This angle affects the direction and magnitude of cutting forces. Ideally, the orientation angle should be close to 90 degrees to maximize axial cutting force, while a smaller angle increases radial cutting force. This factor is particularly critical when machining workpieces that require high precision and good surface quality.
Attention should be given to the choice of holder in internal turning. For machining shoulders within a workpiece, using an orientation angle between 91–95 degrees is recommended, as this helps avoid unnecessary errors and improves the quality of the outcome. Employing triangular or D-shaped (55°) inserts is also advisable. When stronger insert edges are needed, choosing a C-shaped (80°) insert is appropriate. A square insert with a 75-degree orientation angle (rake angle adjustment of 15°) can enhance productivity if conditions are stable and there is no shoulder present.
Internal Shaped Turning
Internal shaped turning is a precision-demanding process where the tool is subjected to both radial and tangential cutting forces. Radial cutting forces tend to shift the tool away from the workpiece, while tangential forces apply torque to the tool away from the centerline. Such forces impose requirements on both tool geometry and settings, and optimizing these aspects is key to achieving a quality outcome.
When working with the machining of small bores, paying special attention to the tool's back taper is important. A sufficient back taper ensures that the tool does not make contact with the workpiece wall, minimizing tool wear and potential manufacturing errors. When selecting the tool geometry, factors like depth of cut, feed rate, and cutting speed should be considered, choosing a lead angle that best supports this combination. Generally, larger lead angles, typically 55° and 35°, are favored as they provide the best combination of tool strength, cost-effectiveness, and reach.
The significance of orientation angle and nose radius concerning reach is also noteworthy. Choosing a suitable insert angle determined by the workpiece shape helps achieve precise results. At least a 2° clearance should be left between the insert and the workpiece, but to ensure the best surface roughness and tool longevity, a minimum clearance angle of 7° is recommended.
When selecting a holder, turning tool holders with a 93° orientation angle and D-shaped (55°) inserts often emerge as primary options. If there is a need for a greater lead-in angle, a V-shaped (35°) insert might be a more suitable choice. In special cases, such as shaped turning of the endpoint and face groove machining, an internal turning tool holder with an orientation angle of 107–117° (rake angle adjustment of –17...–27°) can be employed. These tools are specifically designed for back turning and machining shoulders in the opposite direction, offering additional flexibility and precision for various machining needs.
