How to Select Appropriate Carbide CNC Inserts

I. Clarify Processing Requirements: Define Core Parameters

1. Workpiece Material Properties

Material Type

• Steel (Carbon Steel / Alloy Steel): Give priority to insert grades containing titanium (TiC) or tantalum (TaC) (such as YG6X, YT15) to balance wear resistance and chipping resistance. When machining quenched and tempered steel (hardness > 30HRC), fine – grained cemented carbide with higher hardness (such as sub – micron WC – Co alloy) is required.
• Aluminum and Aluminum Alloys: Select inserts with high hardness and low friction coefficient (such as pure WC – Co alloy, avoid titanium – containing coatings to prevent sticking). The cutting edge needs to be sharp (rake angle 10° – 15°) to reduce cutting resistance.
• High – temperature Alloys (such as Inconel, Titanium Alloys): Require coatings resistant to high – temperature oxidation (such as Al₂O₃, CVD diamond coatings), and the insert substrate needs to have high strength (cobalt content 8% – 12%) to avoid insert softening due to high temperatures during machining.

Cast Iron: Choose coarse – grained inserts with strong wear resistance (such as K10 – K30 grades), and the cutting edge can be designed with a chamfer (0.2mm×20°) to enhance impact resistance.

• Material Hardness
• For low – hardness materials (<25HRC), focus on sharp cutting edges and processing efficiency (such as large rake angles, thin coatings).
• For high – hardness materials (>50HRC), an ultra – fine – grained substrate (grain size < 1μm) + thick coating (such as PVD TiAlN coating with a thickness of 3 – 5μm) is required to improve wear resistance.

2. Processing Technology Types

• Turning: Select the insert shape according to the processing form (for example, choose the DNMA type for a 90° external turning tool and the WNMA type for a facing tool). For roughing, choose a large tip radius (R0.8 – R1.2mm), and for finishing, choose a small radius (R0.4 – R0.8mm) to control the surface roughness (Ra≤1.6μm).
• Milling: For face milling, select dense – tooth inserts (to increase the feed rate). For cavity milling, select ball – nose or rounded – corner inserts (R5 – R10mm). For high – speed machining (HSM), an insert design with optimized dynamic balance (such as symmetrically distributed screw counter – bores) is required.

Drilling / Boring: For deep – hole machining (length – to – diameter ratio > 5), inserts with chip – breaking grooves (such as V – shaped grooves with a width of 2 – 3mm) are required. For precision boring (tolerance ±0.01mm), a fine – adjustment insert clamping system (such as a heat – shrinkable tool holder supporting high – precision inserts) is required.

II. Analyze Key Performance Parameters of Inserts

1. Selection of Substrate Material and Grade

• WC – Co Alloy: A general – purpose type. The higher the cobalt content (such as 15% Co), the better the toughness, which is suitable for interrupted cutting. The lower the cobalt content (6% Co), the higher the hardness, which is suitable for high – speed finishing.
• Coated Cemented Carbide
• TiN Coating: A general – purpose type that increases surface hardness (2300HV) and is suitable for medium – speed machining of steel parts (cutting speed V≤150m/min).
• TiCN Coating: It has higher hardness (3000HV) and strong anti – adhesion properties, which is suitable for machining stainless steel (such as 304/316) to reduce built – up edges.
• Al₂O₃ Coating: It is heat – resistant (oxidation temperature > 1000℃) and suitable for high – speed machining of high – temperature alloys (V>200m/min), and can be combined with a cermet substrate (such as Cermet inserts, TiC/TiN – based).

Diamond Coating (PCD): It is used for aluminum and non – metallic materials (such as carbon fiber), and the surface roughness can reach Ra≤0.2μm, but it is brittle and requires a stable processing system.

2. Geometric Parameter Design

• Rake Angle (γ₀): A positive rake angle (+5° – +15°) reduces cutting force and is suitable for soft materials. A negative rake angle (-5° – - 10°) enhances the cutting – edge strength and is suitable for hard materials or interrupted cutting.
• Clearance Angle (α₀): For finishing, select a large clearance angle (10° – 15°) to reduce friction. For roughing, select a small clearance angle (5° – 8°) to improve the cutting – edge rigidity.
• Tip Radius (R): The larger the R, the higher the surface roughness (Ra∝R²), but the stronger the impact resistance. It is necessary to select according to the processing accuracy requirements (for example, for IT6 – level accuracy, select R≤0.8mm).

Chip – Breaking Groove Design: Shallow grooves (groove depth 0.5mm) are used for chip – breaking of low – carbon steel, and deep grooves (groove depth 1.5mm) are used for chip – breaking of high – alloy steel. The groove shape needs to match the feed rate (for example, f = 0.2mm/r corresponds to a medium – width groove).

III. Match Machine Tools and Processing Conditions

1. Equipment Performance Adaptation

• Machine Tool Rigidity: For machine tools with insufficient rigidity (such as small machining centers), avoid using a large cutting depth (ap>5mm) and select thin – edge inserts (thickness 3 – 4mm) to reduce radial force.
• Speed Range: For high – speed machine tools (spindle speed > 10,000rpm), lightweight inserts (such as aluminum alloy tool bodies with carbide inserts) are required to balance the centrifugal force. For low – speed machine tools (<3,000rpm), inserts with high toughness (cobalt content above 12%) can be selected.

Tool Holder Interface: Confirm the interface type (such as ISO BT50, HSK – A63) to ensure the insert clamping accuracy (run – out ≤0.01mm). Hydraulic tool holders are suitable for high – precision machining, and mechanical clamping types are suitable for heavy cutting.

2. Optimization of Cutting Parameters

• Cutting Speed (V): Refer to the formula V = πDN/1000 (D is the workpiece diameter, N is the spindle speed). For steel machining, V = 80 – 200m/min, and for aluminum parts, V = 300 – 600m/min. It is necessary to combine with the heat – resistant limit of the insert coating (such as for TiN coating, V≤150m/min).
• Feed Rate (f): For roughing, f = 0.3 – 0.8mm/r, and for finishing, f = 0.05 – 0.2mm/r. It is necessary to match with the chip – breaking groove (for example, select a narrow groove for small feed and a wide groove for large feed).

Cutting Depth (ap): Do not exceed 1/3 of the effective cutting – edge length of the insert (for example, if the edge length is 12mm, ap≤4mm) to avoid edge overload and chipping.

• IV. Practical Selection Steps (with Decision – making Flowchart)
• Define Processing Objectives: Clearly define the workpiece material (such as 42CrMo4, hardness 35HRC), processing type (finish – turning the outer circle, Ra≤0.8μm), and equipment model (Mazak VTC – 200C).
• Preliminary Grade Screening: For semi – finishing of steel parts, select a medium – cobalt content (10% Co)+TiCN coating (such as Sandvik Coromant’s GC4325 grade).
• Geometric Parameter Matching: For finishing, select a positive rake angle (+10°), a small tip radius (R0.6mm), and a shallow chip – breaking groove (suitable for f = 0.15mm/r).
• Verify Compatibility: Confirm that the tool – holder interface (Mazak’s standard BIG – PLUS BT40) matches the insert size (DNMG 150608), and set the cutting speed V = 150m/min (corresponding to N = 1500rpm).

Trial – processing Adjustment: If chipping occurs, increase the clearance angle to 8°. If chip – breaking is poor, replace the insert with a deep – groove type. If the surface roughness exceeds the standard, reduce the tip radius to R0.4mm.

V. Avoid Common Selection Mistakes

• Mistake 1: Blindly Pursuing High – Hardness Inserts High – hardness (such as fine – grained WC – Co) inserts are prone to chipping during interrupted cutting. A negative rake angle and edge strengthening (such as chamfer treatment) need to be combined, rather than simply relying on material hardness.
• Mistake 2: Ignoring the Matching of Coating and Substrate Thick coatings (such as CVD Al₂O₃ with a thickness of 10μm) need to be combined with a high – strength substrate (cobalt content ≥10%), otherwise the coating is easy to peel off. Thin coatings (PVD TiAlN, 2μm) are suitable for high – precision machining, but their heat resistance is limited.
• Mistake 3: Ignoring the Balance between Insert Life and Cost Although super – hard inserts (such as PCD) have a long life, they will wear rapidly due to chemical affinity when machining steel parts. At this time, choosing conventional cemented carbide (such as YG8) is more economical.

ConclusionSelecting carbide CNC inserts is an art of balancing technology and economy. Through a systematic analysis of the three core elements of workpiece material, processing technology, and equipment performance, combined with the precise matching of insert substrate, coating, and geometric parameters, an optimization goal of increasing machining efficiency by 20% – 30% and reducing tool costs by 15% – 25% can be achieved. It is recommended that manufacturers establish an insert selection database, record the best practices under different material – process combinations (such as the preferred solution for machining aluminum alloy 6061: YG6X substrate + uncoated + rake angle 15°+R0.8mm), and form a standardized selection process through continuous iteration to provide a reliable tool solution for precision machining.