In the CNC machining center's machining process, tool damage is a common issue that can affect the quality of the parts being produced and may even lead to work interruptions. Tool failure typically manifests in various types of wear and damage to different parts of the tool. Here are some primary causes of tool damage and how they occur:
- Flank Wear: Flank wear is friction-induced wear occurring on the rear face of the tool. It often results from factors such as soft tool materials, insufficient tool relief angle, high cutting speeds, and low feed rates. These factors lead to excessive wear on the tool's rear face, impacting the dimensional accuracy and precision of the machined surface. To mitigate flank wear, it's advisable to select tool materials with high wear resistance, reduce cutting speeds, increase feed rates, and enhance the tool's relief angle.
- Edge Wear: Edge wear typically occurs at the point of contact between the primary cutting edge and the workpiece. It is often caused by the friction generated due to workpiece surface hardening and serrated chip formation. To minimize edge wear, you can lower cutting speeds and feed rates, choose tools made of wear-resistant materials, and increase the tool's rake angle to enhance the cutting edge's sharpness.
- Face Wear: Face wear is the result of friction and diffusion processes on the tool's face. It primarily arises from contact between chips, workpiece material, and heat diffusion in the cutting zone. Soft tool materials, high cutting speeds, and large feed rates can contribute to face wear. Face wear can lead to tool deformation, chip interference, and reduced cutting edge strength. To reduce face wear, decrease cutting speeds and feed rates, select tool materials with coatings, such as hard alloys.
- Plastic Deformation: Plastic deformation occurs when the cutting edge deforms under high temperature or high stress conditions. Factors contributing to this include excessive cutting speeds, high feed rates, hard inclusions in the workpiece material, soft tool materials, and elevated cutting edge temperatures. Plastic deformation affects the quality of chip formation and may lead to tool chipping. To mitigate plastic deformation, lower cutting speeds, use materials with high wear resistance and good thermal conductivity, and ensure suitable tool conditions.
- Built-up Edge (BUE): BUE is the adhesion of workpiece material onto the tool. BUE significantly degrades the quality of the machined surface, alters the cutting edge shape, and can ultimately lead to chipping. To reduce BUE formation, increase cutting speeds, select tools with coatings made of hard alloys or metal ceramics, and use cooling fluids during machining.
- Edge Chipping: Edge chipping refers to the appearance of small notches and uneven wear on the cutting edge. It is typically caused by interrupted cutting and inadequate chip evacuation. To prevent edge chipping, reduce the feed rate, select tools made of tough materials, and use cutting edges with high strength.
- Chipping: Chipping results from excessive wear and high machining forces. It can also occur due to tool materials being too hard, insufficient cutting edge strength, and excessive feed rates. To reduce chipping, choose tool materials with good toughness, reduce the feed rate and cutting depth, and opt for high-strength or large-radius cutting inserts.
- Thermal Cracks: Thermal cracks occur due to temperature fluctuations during interrupted cutting, resulting in cracks perpendicular to the cutting edge. These cracks reduce the quality of the machined surface and can lead to edge chipping. To minimize thermal cracks, select materials with good toughness, lower the feed rate and cutting depth, consider dry cutting, or use ample coolant in wet cutting processes.
In CNC machining, tool damage is an ongoing concern that demands constant attention and mitigation strategies. By selecting appropriate tool materials, cutting parameters, and machining conditions, tool life can be maximized, and machining quality can be improved.
