As the core components directly involved in cutting processes in machine tools, cutting tools' performance status directly affects machining efficiency, workpiece quality, and production costs. During metal cutting, intense friction and high-temperature interactions between the tool, workpiece, and chips inevitably cause tool wear. Scientific life management, however, can maximize tool efficiency. The following constructs a refined management system for the entire life cycle of cutting tools from four aspects: wear types, influencing factors, life evaluation, and optimization strategies.
Tool wear can be classified by location and mechanism as follows:
Flank Wear: Sliding friction between chips and the tool's rake face forms crater wear. When the crater depth reaches 1/3 of the tool thickness, it may cause edge chipping. This type of wear is particularly prominent in high-speed cutting of plastic materials (e.g., aluminum alloys, low-carbon steel).
Flank Wear: Contact friction between the tool's flank face and the machined surface of the workpiece produces a uniform wear land. The wear land width (VB value) is typically used as a criterion (e.g., carbide tools need replacement when VB reaches 0.3mm).
Boundary Wear: Localized wear at the junction of the main cutting edge and the workpiece's unmachined surface, caused by uneven material hardness or insufficient cooling. Common in machining high-hardness castings or interrupted cutting scenarios.
Thermochemical Wear: At high temperatures (exceeding 800°C), chemical reactions (e.g., oxidation, diffusion) between the tool material and workpiece material degrade the tool's surface properties. This is common in high-speed cutting of difficult-to-machine materials like titanium alloys and superalloys.
Tool wear exhibits typical 阶段性特征 (phased characteristics):
Initial Wear Stage: A new tool's sharp edge has a small contact area with the workpiece, resulting in rapid wear, usually completing within 5-10 minutes of cutting, accounting for 10%-20% of total wear.
Steady Wear Stage: The contact between the cutting edge and workpiece stabilizes, with slow and uniform wear. This is the tool's main effective working stage, accounting for 70%-80% of total life.
Accelerated Wear Stage: When wear reaches a critical value, the tool's geometric parameters deteriorate severely, cutting force increases sharply, and machining quality declines rapidly. Continued use may cause workpiece scrapping or tool chipping.
Cutting Parameters: Cutting speed has the greatest impact on wear. According to Taylor's formula, a 20% increase in speed may reduce tool life by over 50%. Increased feed rate exacerbates flank wear, while excessive cutting depth increases impact load on the tool.
Cooling and Lubrication: Adequate cooling can reduce cutting zone temperature (e.g., emulsion can lower temperature by 100-300°C), reducing thermochemical wear. Insufficient lubrication increases friction coefficient, accelerating crater formation on the rake face.
Cutting Fluid Type: Water-soluble cutting fluids have good cooling performance, suitable for high-speed cutting; oil-based fluids have excellent lubrication, suitable for heavy-load cutting. Improper selection can exacerbate wear (e.g., sulfur-containing fluids may cause chemical corrosion when machining aluminum alloys).
Tool Material Properties: High-speed steel tools have good toughness but poor heat resistance (maximum temperature ≤600°C), suitable for low-speed finishing. Carbide tools have excellent heat resistance (800-1000°C), suitable for high-speed cutting. Ceramic tools have high hardness but brittleness, only suitable for continuous cutting of high-hardness materials.
Workpiece Material Attributes: Machining high-hardness (HRC＞40), high-plasticity, or high-wear-resistance materials (e.g., high-manganese steel, stainless steel) accelerates tool wear, requiring higher-performance tool materials (e.g., CBN cubic boron nitride tools).
Blunting Criteria: Quantitative indicators based on machining requirements, such as flank wear land width (VB), crater depth (KT), and radial wear (NK). For finishing tools, VB=0.1-0.2mm is typical; for roughing tools, it can be relaxed to VB=0.3-0.5mm.
Cutting Time: In mass production, tool replacement cycles are determined by 统计 (statistical) effective cutting time under the same conditions (e.g., one tool can machine 500 workpieces), suitable for highly standardized production lines.
Machining Quality Degradation: Tools are deemed end-of-life when workpiece surface roughness (Ra) exceeds 1.5 times the drawing requirement, dimensional errors exceed tolerances, or obvious chatter marks appear.
Direct Monitoring: Visual sensors (e.g., industrial cameras) capture images of the tool edge, and image processing algorithms calculate wear, with response time controlled within 0.5 seconds to avoid disrupting machining rhythm.
Indirect Monitoring: Changes in cutting force (＞20% rate of change), spindle current (＞15% fluctuation), or vibration signals (abnormal frequency peaks) are used to indirectly determine tool wear status. This method is suitable for harsh cutting environments.
High-Speed Cutting Strategy: Increase cutting speed within the range allowed by tool materials (e.g., 150-300m/min for carbide tools machining steel), reducing total wear by shortening cutting time, but requiring matching high-performance cooling systems.
Feed Rate and Depth Matching: Adopting "high feed, small depth" reduces flank wear. For example, increasing feed rate by 50% while reducing depth by 30% in milling can extend tool life by over 20%.
Grinding Quality Control: Reground tools must ensure edge radius (rε=0.05-0.1mm) and accuracy of rake and relief angles, with grinding surface roughness ≤Ra0.4μm to avoid accelerated early wear due to edge defects.
Coating Technology Application: PVD or CVD coatings (TiN, AlTiN) on tool surfaces can increase hardness to over 2000HV and improve wear resistance by 3-5 times, with coating thickness typically 3-10μm.
Tool Database: Record cutting parameters, wear data, and life cycles for different tool-workpiece combinations, forming a process knowledge base to provide parameter references for new workpiece machining.
Hierarchical Replacement System: Develop differentiated strategies based on process importance—critical processes use "timed replacement + online monitoring"; non-critical processes use "count-based replacement" to balance quality and cost.
Tool Inventory Optimization: Predict tool demand based on production plans and life data, maintaining safety stock (typically 3-5 days' supply) to avoid downtime from stockouts or excessive inventory.
The core of tool life management is "accurate prediction, timely replacement, and maximum efficiency". Establishing a closed-loop mechanism of wear monitoring and parameter optimization can reduce total tool costs by 15%-30% while reducing quality accidents caused by tool failure. For different machining scenarios, targeted strategies are needed: precision machining focuses on wear accuracy control, heavy machining emphasizes impact resistance, and difficult-to-machine materials require multi-dimensional optimization of tool materials, coatings, and cooling. Scientific tool management is not only a means to reduce costs and increase efficiency but also a key link in ensuring production continuity and stability.
