In machine tool machining, cutting tool costs account for 15%-20% of total production costs. However, many factories suffer significant waste due to chaotic tool management, such as frequent tool chipping caused by improper selection, capital occupation from excessive inventory, and shortened service life due to non-standard reconditioning. This article breaks down efficient management methods for machine tool cutting tools throughout the entire process of "selection - use - reconditioning - inventory - scrap", helping you reduce waste, cut costs, and ensure machining quality simultaneously.
The core of tool selection is to "match machining requirements" rather than blindly pursuing high-end materials. Choosing the wrong tool not only increases costs but may also lead to part scrapping and machine tool wear.
Workpieces of different materials have vastly different requirements for tool hardness, wear resistance, and toughness – this is the foundation of selection.
Machining Soft Materials (Aluminum, Copper, Plastic): Prioritize high-speed steel (HSS) tools or ordinary cemented carbide tools. These materials have low cutting resistance; HSS tools are cost-effective and tough, suitable for small-batch to medium-batch machining. For improved efficiency, coated cemented carbide tools (e.g., TiN coating) can be used to enhance surface finish.
Machining Medium-Hardness Materials (45# Steel, Cast Iron): Cemented carbide tools (e.g., WC-Co alloy) are the first choice. With high hardness (HRC 70+) and strong wear resistance, they can withstand moderate cutting intensity. For interrupted cutting (e.g., machining grooved steel), ultra-fine grain cemented carbide with good impact resistance is required to reduce chipping risks.
Machining Hard Materials (Stainless Steel, Mold Steel, Titanium Alloy): High-performance tools such as coated cemented carbide (AlTiN coating, with excellent high-temperature resistance), ceramic tools, or CBN (cubic boron nitride) tools are a must. For example, when machining hardened steel above HRC 55, CBN tools enable high-speed cutting and have a service life 5-10 times that of ordinary cemented carbide. Although their unit price is high, the overall cost is lower.
The machining method (turning, milling, drilling, boring) determines the tool structure. Choosing the wrong structure leads to low efficiency and poor precision.
Turning: For external turning, select "external turning tools", paying attention to tool shank rigidity (thick shanks for rough turning, slender shanks for finish turning). For internal turning, use "internal turning tools" – the shank length should be 5-10mm longer than the hole depth to avoid vibration. For thread turning, choose "thread turning tools" matching the thread profile (triangular, trapezoidal).
Milling: For face milling, select "face mills" – more inserts mean higher efficiency (but must match machine tool power). For contour milling, use "end mills"; for closed slot machining, choose "slot drills" (capable of axial feed). For complex curved surface milling, "ball nose end mills" are used to ensure surface smoothness.
Drilling: For ordinary through-holes, select "twist drills"; for deep holes (hole depth > 5×hole diameter), use "deep hole drills" (with internal cooling channels for smoother chip evacuation). For blind hole machining, "flat-bottom drills" are necessary to avoid residual stock at the hole bottom.
Tool precision is categorized into "ordinary grade (IT8-IT10)", "precision grade (IT5-IT7)", and "ultra-precision grade (IT3-IT4)". Higher precision means higher price, so selection should be based on actual needs.
Rough Machining (e.g., stock removal, blank forming): Ordinary grade tools are sufficient; there’s no need to pursue high precision, which reduces costs.
Semi-Finishing (tolerance ±0.05-0.1mm): Precision grade tools are selected to ensure uniform stock for subsequent finishing.
Finishing (tolerance ±0.005-0.02mm, surface roughness Ra ≤1.6μm): Ultra-precision grade tools are required, and attention should be paid to tool runout (runout after installation ≤0.005mm).
70% of abnormal tool wear (such as chipping, excessive wear, and tool burning) stems from improper use. Mastering the following 3 details can extend tool life by 20%-30%.
Cutting parameters (cutting speed vc, feed rate f, depth of cut ap) directly affect tool wear and must be matched based on "tool material - workpiece material" rather than experience.
Excessively High Cutting Speed: Easily causes "tool burning" (surface blackening and accelerated wear). For example, when machining 45# steel with cemented carbide tools, if vc exceeds 120m/min, tool life drops by 50%.
Excessively High Feed Rate: Prone to "chipping" (especially when machining hard materials). It is recommended to select a feed rate of 0.2-0.5mm/r for rough machining and 0.05-0.1mm/r for finishing.
Excessively Large Depth of Cut: Increases tool load, causes tool shank deformation, and affects precision. The depth of cut for rough machining should not exceed 1/3 of the tool diameter, and for finishing, it should not exceed 0.1mm.
Tip: When using a new tool for the first time, reduce the standard cutting parameters by 10%-15% for "running-in", then restore to normal parameters afterward.
Improper tool installation causes runout, leading to uneven cutting forces and rapid local wear.
During Tool Installation: The length of the tool shank inserted into the tool holder should be ≥3 times the tool shank diameter (e.g., for a 10mm diameter shank, insertion length ≥30mm) to avoid excessive overhang. When tightening the tool holder bolts, tighten them in diagonal order in stages to prevent shank tilting.
During Tool Setting: Use edge finders or tool setters for tool setting; avoid tool collision due to operational errors when using the "trial cutting method". After tool setting, verification is necessary (measure dimensions after machining 1-2 parts and confirm correctness before mass production).
During cutting, chips accumulating on the tool edge form a "built-up edge", which degrades surface roughness and accelerates tool wear.
Chip Evacuation: When machining deep cavities or blind holes, pause machining regularly to clean chips. Use "helical flute tools" (e.g., helical end mills) to evacuate chips using the helix angle and reduce accumulation.
Cooling: Select cooling methods based on machining scenarios. Use "flood cooling" for ordinary machining (coolant should be directed at the cutting area); use "internal cooling" for high-speed cutting and deep hole machining (coolant reaches the cutting edge directly through internal tool channels, improving cooling effectiveness by 3x). For materials prone to tool adhesion such as aluminum alloys, "emulsions" (with good lubricity) can be used; for steel machining, use "cutting oils" (with good cooling properties).
The reconditioning quality of regrindable tools (e.g., HSS tools, cemented carbide brazed tools) directly determines their reusability. Incorrect reconditioning methods (such as excessive grinding and uneven cutting edges) drastically shorten tool life.
Tool wear is mainly concentrated on the "flank face" (contacting the machined surface of the workpiece) and the "cutting edge" (blunt or chipped edges). If the rake face (contacting chips) shows no obvious wear, grinding is unnecessary.
Observation with Magnifying Glass: When flank wear exceeds 0.2mm (for ordinary machining) or 0.1mm (for precision machining), reconditioning is required.
Abnormal Phenomena During Cutting: When "abnormal noise", "deteriorated surface roughness", or "increased cutting force" (elevated machine current) occur, the tool is worn and should be stopped for inspection and reconditioning.
Grinding methods vary by tool type. Take the most common "external turning tool" as an example:
Select "green silicon carbide grinding wheels" (suitable for grinding cemented carbide tools) or "aluminum oxide grinding wheels" (suitable for grinding HSS tools).
Grind the Flank Face First: Press the tool flank against the grinding wheel, maintain the main relief angle (5°-8° for ordinary turning tools), move the tool at a constant speed, and grind until the flank face is flat without burn marks (no blue or black oxide layers on the surface).
Then Grind the Rake Face: Maintain the rake angle (15°-20° for ordinary turning tools), grind until the rake face transitions smoothly with the cutting edge.
Finally Dress the Cutting Edge: Gently rub the cutting edge with a fine grinding wheel to remove burrs and avoid chipping (a small edge of 0.05-0.1mm can be chamfered on the cutting edge to enhance strength).
Reground tools must pass 3 inspections before use:
Visual Inspection: Use a magnifying glass to check for no chipping, cracks on the cutting edge, and no burns on the rake or flank faces.
Angle Inspection: Use an angle gauge to measure the side cutting edge angle, main relief angle, and rake angle, with an error not exceeding ±1°.
Runout Inspection: Install the tool in the tool holder and measure the cutting edge runout with a dial indicator – ≤0.01mm for ordinary machining and ≤0.005mm for precision machining.
Many factories face issues of "excessive tool inventory (capital occupation)" or "insufficient inventory (production downtime due to tool shortage)". Through "classification management + dynamic replenishment", inventory capital occupation can be reduced by 30%.
Classify tools into "frequently used tools", "backup tools", and "emergency tools", store them in tool cabinets, and label them clearly (indicating tool model, specification, and quantity):
Frequently Used Tools (e.g., main end mills, turning tools for key processes): Place in easily accessible upper layers of the tool cabinet, with inventory equal to "3 days of usage".
Backup Tools (e.g., infrequently used but necessary special tools such as form mills): Place in middle layers, with inventory equal to "1 week of usage".
Emergency Tools (e.g., high-precision tools, imported tools with high prices and long procurement cycles): Place in locked lower layers, with inventory of "1-2 pieces" to avoid waste.
Implement a system of "who issues, who registers, who returns". Registration content includes: tool model, issue date, quantity issued, purpose (machined part number), and return date (for regrindable tools).
Equip each operator with a "personal tool box" to store their frequently used tools, reducing confusion caused by cross-issuance.
Set a "tool wear quota" (e.g., 1 cemented carbide turning tool is allowed to wear out for every 100 pieces of 45# steel parts processed). Reasons must be provided for exceeding the quota to avoid arbitrary waste.
Assign a dedicated person to conduct weekly tool inventory checks, focusing on the "safety stock level" (i.e., replenishment must be initiated when inventory falls below this level):
Frequently Used Tools: Set the safety stock level to "1 day of usage". With short replenishment cycles (1-2 days for local suppliers), there’s no need for excessive inventory.
Imported Tools or Special Tools: Set the safety stock level to "2 weeks of usage". Due to long procurement cycles (usually 2-4 weeks), advance replenishment is required.
Establish a "supplier file" recording delivery cycles and quality stability of each tool supplier. Prioritize suppliers with fast delivery and reliable quality to shorten replenishment waiting time.
Tools are not "scrapped after one grind" nor should they be "used until chipping". Clear scrap standards must be established to achieve "maximum utilization".
Tools can be scrapped if any of the following conditions are met:
The cutting edge is chipped by more than 1/3 of its length and cannot be repaired by reconditioning.
The tool shank has cracks or deformation (e.g., turning tool shank bending exceeds 0.1mm/m), affecting rigidity.
After 3-5 reconditioning cycles, the tool size is smaller than the minimum usable specification (e.g., an end mill ground from 10mm to 8mm can no longer meet machining size requirements).
Runout still exceeds 0.02mm after reconditioning, failing to ensure machining precision.
Tools can be scrapped if any of the following conditions are met:
Flank wear of inserts exceeds 0.3mm (for ordinary machining) or 0.1mm (for precision machining).
Inserts have chipping or cracks (even small chipping causes cutting vibration and affects precision).
Machined surface roughness deteriorates suddenly (Ra value is more than twice the normal level) with no improvement after adjusting cutting parameters.
Cutting force increases significantly (machine current is 30% higher than normal), indicating excessive tool wear.
Scrap tools are not completely useless; they can be classified and processed to create additional value:
Tool Shanks (e.g., cemented carbide turning tool shanks, end mill shanks): If there is no deformation or cracks, they can be reused after replacing inserts or tool heads.
Scrap Inserts and Drills: Collect and sell to professional recycling manufacturers for cemented carbide raw material recovery, reducing waste.
Short Scrap Tools (e.g., ground-down small-diameter end mills): Can be converted into "marking tools" or "deburring tools" for non-precision marking and deburring work.
Tool management is not limited to a single link but involves full-process control from "selection - use - reconditioning - inventory - scrap". The key is to do three things well:
Precise Selection: Avoid "over-engineering" or "under-engineering" and match tools to machining requirements.
Standardized Use: Extend tool life through reasonable parameters, proper installation, and effective cooling.
Rational Inventory: Meet production needs with "minimum safety stock" to reduce capital occupation.
By implementing these three points, not only can tool costs be reduced by approximately 30%, but downtime and scrap caused by tool issues can also be minimized, achieving the dual goals of "cost reduction and efficiency improvement".
