- Answer
Materials that cannot be directly processed by traditional CNC machine tools mainly include:
High – elasticity/high – toughness materials (such as rubber and silicone. Tools are prone to slipping and the materials are easy to deform);
Non – solid materials (such as liquids, gases, and colloids. They have no fixed shape and cannot be cut);
Some composite materials (such as long – fiber – reinforced plastics. Fibers are easy to break and cause severe tool wear);
Ultra – high – temperature – sensitive materials (such as some low – melting – point metal alloys. The heat generated during processing easily causes them to melt and stick).
- Problem Expansion
Types of Difficult – to – Process Materials and Alternative Solutions
High – elasticity/high – toughness materials (such as natural rubber, polyurethane)
Difficulties: When the tool cuts in, the material will deform significantly (similar to cutting a rubber band with a knife, it is prone to slipping or “clamping the tool”), and there is severe springback after cutting, making it impossible to ensure dimensional accuracy.
Alternative solutions:
Use water – jet cutting (high – pressure water flow + abrasive) or laser cutting (melting the edges with heat);
Conduct cryogenic hardening treatment (such as cooling with liquid nitrogen to – 196°C to make the rubber brittle and then punching).
Non – solid/low – strength materials (such as silicone sealant, soft clay)
Difficulties: They have no fixed shape or are too low in strength to withstand the cutting force of the tool (similar to scooping water with a spoon, unable to form a stable contour).
Alternative solutions:
Indirectly manufacture through 3D printing (such as FDM fused deposition) or injection molding;
If processing is required, solidify first (such as milling after the epoxy resin is cured).
Long – fiber – reinforced composite materials (such as carbon – fiber/glass – fiber – reinforced plastics)
Difficulties: The fibers are high in hardness (carbon – fiber strength reaches 3500MPa) and are distributed disorderly. During cutting, the tool is prone to chipping (similar to cutting a steel – wool ball with a knife, the cutting edge will be “sawed off” by the fibers), and delamination is likely to occur on the processed surface.
Improvement solutions:
Use diamond – coated tools (high hardness and wear – resistant), combined with a low feed rate + high spindle speed (such as a spindle speed of 20000rpm and a feed of 0.05mm/tooth);
Give priority to five – axis linkage processing to reduce the vertical impact of the tool on the fibers (similar to cutting wood at an angle to reduce splitting).
Ultra – high – temperature – sensitive or knife – sticking – prone materials (such as lead – based alloys, low – melting – point solder)
Difficulties: Frictional heat during processing easily melts the material (the melting point of lead is 327°C, and the ordinary cutting heat can reach above 400°C), and it sticks to the tool to form a built – up edge (similar to melted candle wax sticking to the knife), resulting in loss of dimensional control.
Alternative solutions:
Adopt cryogenic cutting (such as cooling with – 100°C cold air) or minimum quantity lubrication (MQL) to reduce the temperature;
Switch to electrical discharge machining (EDM) (non – contact processing, no cutting force and heat accumulation).
Processing Boundaries of Special Materials
Single – crystal diamond: With a hardness of HV10000, it cannot be cut by ordinary tools and requires laser or ion – beam processing (such as semiconductor wafer cutting);
Honeycomb – like materials (such as aerospace aluminum honeycomb): Traditional milling is likely to cause the collapse of the honeycomb walls, and it is necessary to fix with a vacuum fixture or use ultrasonic vibration cutting;
Nanomaterials (such as graphene films): With only atomic – scale thickness, they require nanomanufacturing techniques such as focused ion beam (FIB) or electron – beam lithography.
In summary, the limitations of CNC processing mainly stem from the physical form, mechanical properties, and thermal stability of materials. However, through process innovations (such as hybrid processing, special processing), many “unprocessable” materials are gradually breaking through the limitations and expanding the boundaries of the manufacturing industry.
