OD Turning

External turning is one of the most central processes in machining, where the outer diameter of the workpiece is modified to achieve the desired shape and dimensions. By using different turning tools, this method allows for the production of a wide range of parts, from simple shafts to complex shapes. The demands for quality, efficiency, and cost-effectiveness in the external turning process are constantly increasing, making an understanding of its basic principles and the use of modern techniques key.

The basic methods of external turning include longitudinal turning, form turning, and facing. In longitudinal turning, the focus is on modifying the longitudinal diameter of the workpiece, whereas in form turning, complex shapes are created on the surface of the workpiece and in facing, the end surfaces of shoulders or the face of the shaft are flattened. The use of each method depends on the requirements of the workpiece and the type of component being manufactured.

In recent years, the PrimeTurning™ method has brought a significant innovation to the field of external turning. With this technology, turning can be performed in all directions, offering significant advantages over traditional methods. One of the biggest benefits is the ability to produce a higher chip flow, accelerating the machining process and thereby significantly improving productivity. Additionally, PrimeTurning™ enables more efficient chip control, which reduces tool wear and enhances process reliability.

Chip control is particularly important in external turning, as suboptimal chip formation and removal can cause tool wear, degrade surface quality, and even lead to interruptions in the machining process. Well-designed chip control improves workpiece quality and extends tool life, which is particularly important for large series and demanding materials.

Another essential factor in external turning is process reliability. Modern machining centers and turning methods (PrimeTurning™) offer advanced controls and tools that ensure a high level of process reliability. This is especially important when producing high-quality parts according to strict tolerances and surface quality requirements.

Longitudinal Turning

Longitudinal turning is the most common turning method characterized by the feed motion of the tool parallel to the workpiece's axis. This action results in the workpiece's diameter reducing as the work progresses. Although the process may sound straightforward, its efficiency and quality depend on many factors, such as the selection of the right tool. Here, we discuss how to choose the appropriate tool for longitudinal turning and what factors are essential to consider.

The first step is to select the tool clamping system. This choice primarily depends on the machining stage. Different stages, such as roughing and finishing, require different clamping systems. Additionally, the size of the workpiece affects the choice of clamping system. Generally, machining large workpieces demands a more robust clamping system than the precise finishing of small workpieces.

Key factors in tool selection include the shape of the tool and the setting angle. Regarding the tool shape, it is important to choose the largest possible tip angle. This improves the tool's strength and makes machining more economical. The setting angle directly affects chip formation. A 90-degree setting angle produces a chip whose thickness corresponds to the feed rate. A smaller setting angle, such as 75-45 degrees, reduces chip thickness, allowing for an increased feed rate.

In addition to these general guidelines, the choice of holder, that is, the orientation of the tool relative to the workpiece, must be considered. When working opposite shoulders, a setting angle of 91–95 degrees is recommended. Typically, model C (80°) is recommended as it offers a good balance between efficiency and versatility. The D model (55°) allows both form turning and face turning.

If there are no shoulders, productivity can be increased by choosing a square-shaped insert and a 75-degree setting angle. In this case, the additional setting angle is 15 degrees, which enhances chip formation and allows for a higher feed rate.

Selecting the tool for longitudinal turning is not a straightforward decision. Considering many different factors—from the tool clamping system, its shape, and variations in the setting angle—is crucial for achieving a quality and efficient result. The right tool not only speeds up the work process but also improves the surface quality of the processed part and extends the tool's life. In machining, expertise, experience, and the right tools together ensure the best result.

Form Turning

Form turning is a turning method that differs from traditional turning as the shape of the part being machined, the depth of cut, the feed, and the speed vary. This makes form turning more challenging because the turning direction and the diameter of the part can vary greatly, which places high demands on the tools. The tools must be able to withstand varying cutting forces and depths.

The tool and its characteristics play a significant role in the quality of the final result in form turning. In choosing the shape of the tool, it is crucial to find a balance between the tool's strength and economy. Common tip angles are 35° and 55°, where the larger tip angle offers better strength, but it is not as suitable for various shapes as the smaller tip angle. The tip angle of the tool directly affects its reach, which is important to consider when form turning complex shapes.

In choosing the setting angle, the shape of the workpiece must be considered. The aim is to enable high-quality surface finishing and optimize the tool's lifespan. Typically, a clearance of at least 2° is left between the tool and the workpiece, but for better surface roughness and longer tool life, it is recommended to use at least 7° clearance. This means that the setting angle (additional setting angle) would be 83°, helping to reduce wear on the tool and improve work quality.

The clamp is selected based on how the tool best operates with the part. Typical choices include a clamp with a 93° setting angle (additional setting angle –3°), which is suitable for most form turning tasks, and a D model (55°) tool, which offers good strength and economy. When the tool is required to be fed at an oblique angle into the workpiece at a steep angle, a V model tool (35°) is the better choice. If the clamp is required to work in the opposite direction of the form turning and face groove machining, a setting angle of 107–117° (additional setting angle –17...27°) is chosen.

Facing

In facing, also known as cross-turning, the tool is fed radially towards the center of the part. This is one of the most common turning methods, but its implementation requires precision and the right tool choices. In this method, radial cutting forces are significant, which can cause the workpiece to bend and vibrate, compromising the quality of the work.

The shape of the selected tool greatly depends on the required setting angle and the reach or versatility required from the tool. It is essential to choose the largest possible tip angle to ensure the strength and cost-effectiveness of the tool are optimal. For example, the profile you want to machine into the workpiece directly influences the choice of tool.

The setting angle greatly impacts the success of facing. A setting angle of 75° (additional setting angle 15°) is often the starting point used, but by reducing the setting angle (and thus the additional setting angle), some of the radial forces can be directed axially towards the chuck. This better supports the machining and reduces the tendency for vibration. Therefore, a smaller setting angle can be advantageous in some cases, especially if the workpiece is prone to bending.

In optimizing machining, the choice of holders is as important as the choice of tool. A square-shaped insert combined with a 75° setting angle (additional setting angle 15°) offers a good general solution for many turning tasks. Other versatile solutions include an 80° rhombic insert or a trigon insert combined with a 95° setting angle, where the additional setting angle is –5°. The choice of these depends on the material being machined and the geometry of the workpiece. The holder is often chosen based on the ease of tool change and how securely the tool is fastened in the holder during turning.