Inserts for turning

The selection of a turning insert is a crucial part of an efficient machining process, involving several considerations. Choosing the right cutting geometry, insert grade, shape, size, corner radius, and setting angle significantly affects the results. The first step is to determine the insert geometry according to the machining phase – finishing, medium roughing, or heavy roughing. Similarly, the insert shape, especially concerning the cutting edge angle, should be optimized to maximize insert strength and economy.

Rough turning demands large cutting depths and feeds, requiring edge strength. Medium roughing allows for variable feeds and cutting depths, while finish turning focuses on controlling small cutting forces for precise and high-quality machined surfaces. Special attention should be paid to the wiper cutting geometry, which enables improved surface roughness or significantly higher cutting feed while maintaining a quality surface finish. Experience shows that more positive wiper geometries reduce cutting forces and are beneficial, especially in vibration-sensitive tasks.

The insert grade is chosen based on the material being machined, such as alloyed or non-alloyed steel, stainless steel, cast iron, superalloys, or non-ferrous metals. Each material has its specific requirements for turning. For example, for non-ferrous metals like aluminum, positive and sharp-edged cutting tools are used.

The choice of insert shape is significant as it determines the setting angle and affects the depth of engagement with the workpiece. A larger cutting edge angle increases tool strength but may cause vibration susceptibility. A smaller insert's cutting edge angle improves reach but weakens the cutting edge durability.

The size of the insert should be chosen according to the job and machining space. Heavy turning requires large inserts for support, while finishing can use smaller inserts depending on the situation. The corner radius, RE, is also a critical insert parameter; small corner radii are ideal for reducing vibration, while larger radii allow for deeper cutting depths and provide high edge strength.

When making a selection, remember that the relationship between cutting depth and corner radius is crucial in controlling vibration sensitivity. The balance between radial and axial cutting forces affects vibration sensitivity and thereby the quality of the final result. A positive turning insert is chosen for applications with a risk of workpiece vibration, while a negative one is more suitable for rough turning.

The setting angle is one of the most significant factors in turning as it affects the direction of cutting forces and the length of the cutting edge. A correctly selected setting angle ensures that cutting forces direct vibrations affecting tool and workpiece setups and guarantees smooth chip formation.

The turning of materials such as steel, stainless steel, and superalloys requires machinists' expertise and carefully selected insert grades and geometries. In this context, superalloys pose special challenges in machinability, and choosing the optimal geometry is key to a flawless outcome. This is especially true in situations where controlling cutting forces is challenging.

Experienced machinists use various method strategies in turning, such as the one-pass strategy, which covers single-phase machining and combines roughing and finishing in general machining. This can save machining time and tool costs, though achieving precise tolerances may require compromises. Alternatively, the roughing and finishing strategy allows for fine-tuning surface quality and longevity. It requires two turning tools but offers a well-controlled process and the potential for longer production runs with a single turning tool.

It is also noted how cutting speed, feed, and depth of cut directly affect tool durability and the efficiency of the machining process. These parameters can be best managed by ensuring that the turning tool and machine are properly maintained, enabling them to operate optimally. Choosing turning tools significantly impacts product quality and production costs, requiring carefully considered decisions.