Machining is the subtractive manufacturing process where tools’s edges directly make contact with the workpiece and remove the materials to form the desired parts or products. It has been more efficient and fast with the advancement of CNC and AI automation in factories, but not completely free from defects. The machining defects list goes from tool setting issues and program crashes to burrs in machined parts.
Understanding different machining defects and their causes helps to identify and avoid them. Furthermore, we will discuss cutting defects, tool wear, chatter marks, and other various machining issues, their causes, and how you can avoid them.
Defects Due to Machine and Tool Wear
CNC tool wear
The conditions of the machine(conventional or CNC) you are using directly impact the final part’s dimensional accuracy and finish quality. Wear on chuck or work holding jaws, machine stability, vibration, and other issues are the main causes behind this. Similar to machines, tool wear also causes dimensional defects, low finish quality, and marks on the surface. Therefore, you need to ensure the sharpness and no wear on the cutting tool before proceeding with machining cycles.
| Defect | Causes | Prevention |
| Tool Chipping or Breakage | Excessive cutting tool wear or improper tool material | Inspect the tool periodically and choose compatible tool material |
| Tool Strength Issues | Low strength of tool compared to cutting force. | Consider the tool length and material type during selection. |
| Surface Roughness Issues | Dull cutting tools or vibration during machining | Replace or sharpen your tools and ensure machine rigidity |
| Dimensional Inaccuracy | Tool wear leads to inconsistent material removal | Adust CNC program or replace the old tool |
| Excessive Burr Formation | Dull tools or excessive tool wear during cutting | Use sharp tools and inspect the wear regularly |
Defects Due to Programming Mistakes
Programming mistakes refer to errors in CNC G and M codes used to control the tool movement and auxiliary systems like coolants. Essentially, they are the lines of codes instructing the control system to guide movement and other functions according to the desired 3D shape. If any lines have format or value errors, it brings several machining defects during the execution.
Error in CNC program
Some typical examples of programming mistakes are safety height, blade length and cutting depth alignment, and incorrect cor-ordinate setting. The machining defects list due to these programming mistakes is as follows;
- Dimensional inconsistencies
- Tool path collision
- Overcutting issues
- Marks on the surface
Next, the table below outlines the causes and prevention strategies for the machining defects lists that are mentioned above;
| Defect | Causes | Prevention |
| Incorrect Dimensions | Incorrect input of dimensions | Verify program dimensions using simulation software before execution |
| Toolpath Collisions | lack of analytic toolpath planning | Use CAD/CAM simulation tools to identify and resolve toolpath issues |
| Overcuts or Undercuts | Depth or tool compensation error in the program | Double-check tool compensation parameters and depth settings |
| Surface Finish Defects | Incorrect feed rate or spindle speed | Optimize feed rate and spindle speed based on material properties and tooling |
Additionally, the malware and viruses in CNC software can also cause these programming related defects. So, update all related software regularly.
Defects Due to Machine Setup and Variables Error
Tool breakage
Several CNC cutting defects are caused by errors in machine and machining variables. If any misalignment happens between cutting edges and the work surface, it can result in inaccuracy or even nonfunctional parts. Therefore, machining parameters like spindle speed, feed rate, cutting force, and cutting depth should be set according to the work material, tooling, and type of machining operations you are executing.
| Defect | Cause | Prevention |
| Dimensional inaccuracies | Incorrect tool offsets or workpiece misalignment. | Regularly calibrate tools, perform test runs, and ensure secure clamping. |
| Poor surface finish | Inadequate feed rate, spindle speed, or improper tool selection. | Optimize machining parameters based on the work material’s properties. |
| Tool wear or breakage | Excessive cutting speed or improper depth of cut. | Monitor tool life, adjust cutting force, and use suitable tool coating. |
| Thermal distortion or burn marks | Insufficient coolant or high spindle speed generating heat. | Use the right coolant type and flow, and install a temperature control setup. |
| Chatter mark Defect | Vibrations due to loose machine components or inappropriate feed rates. | Tighten your machine components and adjust feed rates. |
Defects Related to Operation Handling
Sometimes operator might input the wrong setup codes, forget some steps of procedures, lack attention to the monitoring screen, or calibration errors in centering. All these minor details cause so many machining and cutting defects or even complete failure.
Here is the machining defects list related to operator error;
- Burrs and uneven surface
- Inconsistent parts across batches
- CNC machine-crash
- Fracture or failure of workpiece
- Rapid wear and tool breakage
These defects are heavily influenced by the experience of the operator and the technology used in the CNC machines. Additionally, natural human errors and the accuracy of calibration equipment are two other causes.
Conclusion: The Combined Machining Defects List
Machine and tool setup, CNC programming, and machining handling are the main areas that you should keep an eye on to avoid all machining defects in the list below;
- Surface Burns
- Chatter Marks.
- Tolerances failure or dimensional inaccuracies
- Burr Formation
- Tool Marks on machined surface or rough finish
- Work material wrapping
- Chatter mark defect
- Clamping marks and dents
Moreover, it is recommended to perform the test run before actual machining even if you are considering all the causes and prevention strategies.