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HSS & HSS-Co 4-Flute End Mills for Steel

Professional steel milling cutters engineered for precision. Available in Standard High Speed Steel (HSS) or premium HSS-Co (M35/M42) substrates. Choose between high-performance AlTiN Nano-Coating or Uncoated finishes based on your specific machining requirements. Ideal for finishing, semi-finishing, and light roughing.

HSS / HSS-Co (M35/M42) 4 Flutes AlTiN or Uncoated D6mm - D25mm Versatile Steel Milling
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HSS & HSS-Co 4-Flute End Mills for Steel
HSS & HSS-Co 4-Flute End Mills for Steel

Procurement & Commercial Terms

MOQ1 pc (sample/stock) | 50 pcs (OEM/bulk)
Lead TimeSame day dispatch (standard stock) | 7–10 days (custom/OEM)
InventoryD6mm–D25mm full range in stock. Both standard and extra-long lengths available.
Material & CoatingSubstrate: HSS or HSS-Co (M35 / M42) | Coating: AlTiN (Nano Black) or Uncoated
PackagingIndividual plastic tubes + anti-rust paper | Rigid export cartons (50/100 pcs)
ShippingDHL/FedEx/UPS for samples | Air/Sea freight for bulk. Incoterms: EXW, FOB, CIF, DDP

HSS & HSS-Co 4-Flute End Mill Specifications

Customizable Options: Material: Standard HSS or HSS-Co (M35/M42) | Coating: AlTiN or Uncoated | Tolerance: h6
ModelD (mm)H (mm)d (mm)L (mm)Stock
Standard Length Series
HS-4F-6-19-6-60619660● In Stock
HS-4F-8-25-8-66825866● In Stock
HS-4F-9-25-10-759251075● In Stock
HS-4F-10-25-10-7510251075● In Stock
HS-4F-11-35-12-8511351285● In Stock
HS-4F-12-35-12-8512351285● In Stock
HS-4F-13-35-12-8513351285● In Stock
HS-4F-14-35-12-8514351285● In Stock
HS-4F-15-42-16-9515421695● In Stock
HS-4F-16-42-16-9516421695● In Stock
HS-4F-17-42-16-9517421695● In Stock
HS-4F-18-42-16-9518421695● In Stock
HS-4F-19-50-20-110195020110● In Stock
HS-4F-20-50-20-110205020110● In Stock
HS-4F-21-50-20-110215020110● In Stock
HS-4F-22-50-20-110225020110● In Stock
HS-4F-23-60-20-125236020125● In Stock
HS-4F-24-60-20-125246020125● In Stock
HS-4F-25-60-20-125256020125● In Stock
Extra Long Series (Deep Cavity)
HS-4F-6-25-6-68625668● In Stock
HS-4F-8-38-8-83838883● In Stock
HS-4F-10-45-10-9510451095● In Stock
HS-4F-12-53-12-110125312110● In Stock
HS-4F-14-53-12-110145312110● In Stock
HS-4F-16-63-16-123166316123● In Stock
HS-4F-18-63-16-123186316123● In Stock
HS-4F-20-75-20-141207520141● In Stock
HS-4F-22-75-20-141227520141● In Stock
HS-4F-25-100-20-1602510020160● In Stock

● All sizes in stock | Diameter tolerance: h6 (0/-0.009mm for D≤10, 0/-0.011mm for D>10). Custom sizes available upon request.

Model Naming Convention: HS-4F-[D]-[H]-[d]-[L]. For example, HS-4F-10-25-10-75 indicates a 4-flute end mill with Cutting Diameter (D) = 10mm, Length of Cut (H) = 25mm, Shank Diameter (d) = 10mm, and Overall Length (L) = 75mm.

HSS vs. HSS-Co (Cobalt): Which Substrate to Choose?

Understanding the machining differences to optimize your tooling cost and performance.

Feature Standard HSS (e.g., M2) HSS-Co (M35 / M42)
Cobalt Content 0% (Trace) 5% (M35) or 8% (M42)
Hot Hardness (Red Hardness) Moderate (Softens >600°C) Excellent (Maintains hardness >800°C)
Toughness (Shock Resistance) High (Resists chipping in interrupted cuts) Slightly Lower (More brittle)
Wear Resistance Good Superior
Ideal Workpiece Materials Mild Steel, Aluminum, Plastics, Wood Alloy Steel, Stainless Steel, Cast Iron, Hardened Steels
Best Machining Condition Low/Medium Speed, Unstable Setups, Interrupted Cuts High Speed, Continuous Cutting, Rigid CNC Machines
Cost Efficiency ★★★★★ (Most Economical) ★★★☆☆ (Higher Initial Cost, Longer Life)
When to choose Standard HSS?

Choose standard HSS if you are machining low-carbon steels (like 1018 or A36), aluminum, or non-ferrous metals. It is also the best choice if your machine setup lacks rigidity or if you are performing heavy interrupted cuts where tool chipping is a major concern. It offers the best upfront cost efficiency.

When to upgrade to HSS-Co?

Upgrade to HSS-Co (M35/M42) when machining abrasive or hard materials like 4140 alloy steel, P20 mold steel, or cast iron. The cobalt content prevents the cutting edge from softening under high friction heat, allowing you to run higher cutting speeds (Vc) and significantly extending tool life in continuous CNC production.

Why Choose Our 4-Flute End Mills?

AlTiN Nano-Coating

Forms a stable aluminum oxide layer at high temperatures. Provides exceptional heat resistance up to 800°C, ideal for dry or high-speed machining.

Precision Ground (h6)

100% CNC fully ground from solid blanks. Strict h6 diameter tolerance ensures accurate slot widths and fine surface finishes in finishing passes.

Uncoated Option Available

For specific applications requiring maximum edge sharpness or low-speed machining, our premium uncoated (bright/black oxide) HSS tools deliver reliable performance.

Optimized Helix Angle

30°-45° helix angle designed specifically for steel. Ensures efficient chip evacuation while maintaining a strong cutting edge for fine finishing.

Material & Coating Selection Guide

Application Matrix
Workpiece MaterialRecommended SubstrateRecommended CoatingSuitabilityNotes
Carbon Steel (1018, 1045, A36)HSS or HSS-CoAlTiN or Uncoated◎ ExcellentStandard HSS with uncoated or AlTiN works perfectly for general milling.
Alloy Steel (4140, 4340, 8620)HSS-Co (M35/M42)AlTiN◎ ExcellentHSS-Co + AlTiN is essential to withstand the heat and abrasion of alloy steels.
Mold Steel (P20, 718, H13)HSS-Co (M35/M42)AlTiN◎ ExcellentAlTiN handles the heat generated in mold milling, extending tool life significantly.
Cast Iron (GG20, GG30)HSS-CoAlTiN or Uncoated◎ ExcellentResists abrasive wear from graphite flakes. Use air blast to remove dust.
Stainless Steel (304, 316)HSS-Co (M42 preferred)AlTiN◐ LimitedRequires rigid setup, lower cutting speeds, and abundant coolant to prevent work hardening.
Aluminum / Copper / BrassHSSUncoated or Rainbow✗ Not RecommendedAlTiN is not optimized for non-ferrous metals. Use our dedicated aluminum series.

◎ = Excellent | ◐ = Limited (Requires parameter adjustment) | ✗ = Not Recommended

Typical Applications for HSS 4-Flute End Mills

Mold & Die Making

Pocket milling, profile finishing, and semi-finishing of mold bases and cavities. AlTiN coating maintains edge integrity during long machining cycles.

Precision Part Machining

Finishing of complex contours, slots, and steps in carbon and alloy steel parts. h6 tolerance ensures tight dimensional control.

General CNC Production

High-volume production milling of steel flanges, brackets, and fittings. Excellent balance of tool life and cost-effectiveness compared to solid carbide.

CAM Setup & Cutting Parameters Guidance

Recommended Cutting Data (HSS-Co + AlTiN)
Workpiece MaterialCutting Speed (Vc)Feed per Tooth (fz)Coolant Recommendation
Carbon Steel (< 30 HRC)60 - 90 m/min0.02 - 0.05 mm/toothFlood or Air Blast
Alloy Steel (4140, 4340)50 - 80 m/min0.015 - 0.04 mm/toothFlood Coolant
Mold Steel (P20, 718)40 - 70 m/min0.01 - 0.03 mm/toothFlood or MQL
Cast Iron70 - 110 m/min0.02 - 0.06 mm/toothAir Blast (Dry)

*For standard uncoated HSS, reduce Cutting Speed (Vc) by approximately 20-30% to prevent premature edge wear.

Best Practices for Steel Milling
  • ⚠️ Use Climb Milling - Reduces cutting forces and improves surface finish on steel.
  • ⚠️ Ensure Rigidity - Minimize tool overhang. Use the shortest possible length to prevent deflection.
  • ️ Constant Engagement - Avoid dwell marks by maintaining consistent feed rates.
  • ️ AlTiN Heat Resistance - AlTiN performs exceptionally well in near-dry or dry machining due to its thermal barrier properties.
  • ⚠️ Sharpness is Key - HSS tools must be kept sharp. Dull tools generate excessive heat and cause work hardening in alloy steels.
  • ️ Chip Evacuation - Ensure chips are cleared from the cut zone to prevent re-cutting and edge chipping.

Factory Production & Quality Control

HSS-Co end mill grinding and quality inspection

Manufacturing Process & QA Steps

  • 🔹 Raw Material: Premium HSS and HSS-Co (M35/M42) steel blanks sourced from certified mills.
  • Grinding: 5-axis CNC tool grinders ensure precise flute geometry, helix angle, and h6 diameter tolerance.
  • 🔹 Heat Treatment: Vacuum heat treatment with triple tempering to achieve optimal hardness (64-66 HRC) and toughness.
  • 🔹 Coating: AlTiN nano-coating applied via advanced PVD process for uniform thickness and adhesion (optional).
  • 🔹 Inspection: 100% visual inspection under microscope. Batch sampling for coating thickness, hardness, and cutting tests.

Frequently Asked Questions

Standard HSS is highly tough and cost-effective, making it ideal for low-to-medium speed machining of mild steels and unstable setups where tool chipping is a risk. HSS-Co (M35/M42) contains 5-8% cobalt, which drastically increases its 'red hardness'. This allows HSS-Co to maintain its edge sharpness at high cutting temperatures (up to 800°C), making it essential for continuous high-speed milling of abrasive alloy steels, stainless steels, and cast iron.

Choose AlTiN (Nano Black) for medium to high-speed machining of carbon, alloy, and mold steels, as it provides excellent heat resistance and prevents built-up edge. Choose uncoated tools for low-speed operations, machining highly abrasive materials where coating might wear unevenly, or when maximum edge sharpness is required for specific fine finishing passes.

A 4-flute design provides a larger core diameter than 2-flute tools, resulting in greater rigidity and reduced deflection. This allows for tighter tolerances, better surface finishes, and higher feed rates during semi-finishing, finishing, and light roughing operations in steel.

Upgrade to solid carbide when machining hardened steels above 45-50 HRC, when you need extremely high cutting speeds for mass production, or when ultra-high rigidity is required for micro-machining. HSS-Co remains the most cost-effective and shock-resistant choice for general steel milling, interrupted cuts, and less rigid machine setups.

Request Quote for HSS & HSS-Co 4-Flute End Mills for Steel

Specify your diameter range, material, and monthly volume. We respond with pricing, stock status within 24 hours.

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