Tungsten carbide cutting tools, CNC milling cutters, drills and turning inserts are core consumables for metal machining. Unqualified hardness, poor coating adhesion and insufficient cutting durability will lead to frequent tool chipping, rapid wear, unstable workpiece dimensional accuracy and increased production cost. A complete set of factory inspection standards covering hardness detection, coating adhesion test and actual cutting durability evaluation is formulated to screen unqualified products before delivery and guarantee consistent machining performance of cutting tools for end users.

1. Pre-Inspection Preparation & Basic Appearance Inspection

Before performance testing, all finished cutting tools shall pass full visual inspection. Check the tool surface for scratches, burrs, edge collapse, uneven coating, stains and deformation; inspect the cutting edge grinding finish to ensure no micro-cracks. Tools with obvious appearance defects are directly rejected without subsequent performance tests. All test samples are randomly selected from finished batches according to fixed sampling ratio, and test records are marked with batch number, tool model and production date for traceability.

2. Hardness Inspection Standard for Cutting Tool Substrate

2.1 Test Equipment & Test Position

Use Rockwell Hardness Tester HRA to detect the hardness of carbide substrate; test points are set on the tool flank surface, avoiding coating layers and edge fragile areas. Each sample takes 3 groups of effective data and calculates the average value as the final hardness result.

2.2 Hardness Classification Acceptance Criteria

Ultra-fine grain carbide tools for precision finishing: HRA 92.5–94.0; General milling & turning carbide inserts: HRA 91.0–92.5; Tough heavy-cutting tools for thick steel removal: HRA 89.0–91.0.

If the average hardness is lower than the lower limit, the substrate has insufficient wear resistance and will wear rapidly during cutting; if hardness exceeds the upper limit excessively, the tool toughness declines, resulting in easy edge chipping under impact cutting. Both non-compliant conditions are judged unqualified.

2.3 Auxiliary Microhardness Test

For tiny drills and micro end mills, Vickers microhardness tester is adopted to measure the hardness of thin cutting edge, so as to avoid crushing small tool samples during Rockwell test.

3. Coating Adhesion Inspection Standard

Tool coatings such as TiN, TiCN, AlTiN, DLC directly determine high-temperature oxidation resistance and anti-built-up-edge performance. Poor adhesion will cause coating peeling in cutting process and lose protection effect.

3.1 Scratch Test Method (Mainstream Factory Inspection)

Adopt automatic coating scratch tester with diamond indenter. Gradually increase loading force until continuous coating peeling cracks appear on the tool surface, record the critical load value. Acceptance standard: conventional metal cutting tools critical load ≥80N; high-end multilayer composite coating tools critical load ≥120N. Low critical load indicates weak bonding between coating and substrate, easy to peel off under high temperature friction.

3.2 Grid Cross-Cut Auxiliary Test

For flat insert surfaces, use special cutting knife to draw uniform grid scratches on coating, paste high-viscosity adhesive tape and tear off rapidly. Observe coating shedding condition: no coating peeling at grid intersection is qualified; massive flaking means unqualified adhesion.

3.3 Post-Coating Micro Observation

Observe the coating cross-section under metallographic microscope to check coating thickness uniformity, no internal bubbles and separation gaps between coating and substrate.

4. Actual Cutting Durability Performance Test

Laboratory hardness and coating tests can only reflect static physical properties; real cutting durability test simulates actual workshop working conditions to verify comprehensive service life.

4.1 Test Machine & Workpiece Material Matching

Install test cutting tools on standard CNC machining center. Select matched workpiece blanks: 45# carbon steel for general-purpose tools, 304 stainless steel for anti-corrosion cutting tools, 6061 aluminum alloy for non-ferrous processing tools. Blank hardness and material grade are fixed to ensure test comparability of different batches of tools.

4.2 Unified Fixed Cutting Parameters

Set fixed spindle speed, feed rate, cutting depth and coolant condition according to tool model specification. All batch samples adopt identical cutting parameters to eliminate test deviation caused by different processing conditions.

4.3 Durability Judgment Standard

Continuous cutting until the flank wear width reaches the specified failure limit (conventional tool failure standard VB=0.2mm). Record total effective cutting length / processing quantity. If the cutting life is lower than the standard value of the product model by more than 10%, the batch is unqualified.

During cutting process, record abnormal failure phenomena in real time: edge chipping, coating peeling, severe built-up edge, workpiece vibration and burr surge. Any abnormal failure in advance indicates unqualified tool comprehensive performance.

5. Auxiliary Supporting Inspection Items

5.1 Dimensional Tolerance Test: Detect tool diameter, length, edge angle tolerance with micrometer and tool presetter to ensure interchangeability during machining.

5.2 Surface Roughness Inspection: Ra value of cutting edge flank is controlled within the standard range to reduce friction and built-up edge.

5.3 High Temperature Oxidation Resistance Auxiliary Test: Simulate cutting high temperature environment to check coating anti-oxidation performance for high-speed cutting tools.

6. Batch Re-Inspection & Disposal Rules for Unqualified Products

If single sample fails hardness, coating adhesion or durability test, double sampling re-inspection is carried out. If re-inspection still fails, the whole production batch is isolated and reworked or scrapped. All test data, equipment records and sample photos are archived for more than one year to realize production quality traceability.

Conclusion

Hardness test controls the basic mechanical performance of cutting tool substrate, coating adhesion test verifies the bonding stability of functional protective film, and cutting durability test comprehensively inspects the actual service life under real machining load. Combined with appearance, dimensional and roughness auxiliary inspection, this complete factory inspection standard effectively eliminates defective cutting tools, stabilizes product quality consistency, and reduces tool wear and failure risks for downstream metal processing manufacturers.