What Causes Burrs in CNC Machining and How to Eliminate Them?

 Burrs in CNC machining are tiny yet destructive defects—they not only ruin part precision (rendering 5-15% of finished components out of tolerance) but also pose safety risks (sharp edges can cut workers or damage mating parts during assembly). For manufacturers producing high-precision components (e.g., medical devices, aerospace parts), burr removal can add 20-30% to production costs if not controlled at the source. Unlike surface scratches, burrs form due to complex interactions between tools, materials, and processes—making their elimination require a systematic approach, not just post-processing. This article systematically breaks down burr types, root causes, preventive strategies, and removal methods—backed by data and real-world cases—to help you build a burr-free CNC machining workflow.

Table of Contents

• 1. Classification of Burrs in CNC Machining: Understand the Enemy First
• 2. Root Causes of Burrs: A Chain of Interconnected Factors
  • 2.1 Tool State & Geometric Design: The First Line of Failure
  • 2.2 Cutting Parameter Mismatch: The Most Adjustable Factor
  • 2.3 Material Properties: The Inherent Challenge
  • 2.4 Process Planning & Equipment Performance: The Hidden Influencers
• 3. Preventive Strategies: Stop Burrs at the Source
• 4. Burr Removal Methods: Efficiently Clean Up Residual Burrs
• 5. Real-World Case Study: Eliminating Burrs in Aerospace Part Machining
  • 5.1 Problem Analysis
  • 5.2 Solution Implemented
  • 5.3 Results
• 6. Yigu Technology’s Perspective on Burrs in CNC Machining
• 7. FAQ: Common Questions About Burrs in CNC Machining
  • Q1: Can I completely avoid burrs in CNC machining, or is some post-processing always needed?

1. Classification of Burrs in CNC Machining: Understand the Enemy First

Not all burrs are the same—their shape, location, and formation mechanism vary based on the machining process and material. The table below categorizes common burr types, their characteristics, and typical occurrence scenarios:

Burr Type	Visual Characteristics	Formation Scenario	Impact on Production
Continuous Burrs	Long, thin, thread-like projections (0.1-1mm in length) that follow the cutting path	Machining ductile materials (aluminum alloy, copper) with worn tools or high feed rates	Easy to entangle with cutting tools or workpieces, causing secondary scratches; Equipment jamming may occur in automated production lines, resulting in a loss of 500 to 2000 per malfunction
Jagged Burrs	Short, irregular, tooth-like fragments (0.05-0.3mm) with sharp edges	Machining work-hardening materials (stainless steel 304, titanium alloy) with insufficient cutting speed	Difficult to remove with conventional deburring tools, requiring manual polishing (adding 10-15 minutes/piece of work time); Easy to scratch the seals during assembly, resulting in leakage
Flanging Burrs	Wavy, folded metal edges (0.2-0.8mm) that form a “lip” on the workpiece surface	Machining low-carbon steel or mild steel with excessive cutting depth or improper tool rake angle	Destroying the flatness of the parts (deviation can reach 0.1-0.2mm), affecting the subsequent welding or bonding accuracy; Increasing material waste in coating processes
Location-Specific Burrs	Small, concentrated burrs (0.03-0.1mm) at acute angles, hole edges, or tool path transitions	Complex cavity machining (e.g., mold cores) with no arc interpolation; abrupt tool direction changes	Precision fitting parts (such as bearing seats) can cause excessive clearance (exceeding the design tolerance of 0.02mm), leading to abnormal noise or accelerated wear

2. Root Causes of Burrs: A Chain of Interconnected Factors

Burr formation is never a single-factor issue—it stems from the interplay of tool performance, cutting parameters, material properties, and process design. This section uses a causal chain structure to break down core causes, with specific data and examples.

2.1 Tool State & Geometric Design: The First Line of Failure

Tools are the direct interface with the workpiece—their condition determines whether burrs form:

• Tool Wear & Passivation: A worn tool (flank wear ≥0.2mm) loses its ability to shear material cleanly, causing metal to undergo plastic flow instead of brittle fracture. For stainless steel machining, tool passivation increases burr occurrence by 40-60%—a 10mm diameter end mill with 0.3mm flank wear produces continuous burrs on 80% of parts, vs. 15% for a new tool.
• Unreasonable Geometric Parameters:
• Excessive rake angle (>15° for aluminum): Reduces edge strength, leading to tool vibration and uneven cutting—forming wavy flanging burrs on thin-walled parts.
• Insufficient rake angle (<5° for steel): Increases friction between the tool’s rear face and the workpiece, squeezing material to form burrs at the cutting edge.
• Poor Rigidity: Long, slender tools (length-to-diameter ratio >8:1) chatter during cutting, causing the tool path to deviate by 0.05-0.1mm. This deviation leaves uncut material fragments—location-specific burrs—at cavity corners or hole edges.