How to select the right milling cutter for difficult materials
Have you ever encountered severe sticking of the cutters, when processing stainless steel?
When machining high-temperature alloys, milling cutters wear out rapidly.
Sparks fly everywhere at the processing site when processing titanium alloys.
When processing high-manganese steel, the workpiece becomes increasingly hard.
The above materials are widely used due to their excellent properties such as high strength, high temperature resistance, and corrosion resistance.
But it also poses a huge challenge for processing. Known in the industry as “difficult-to-machine materials” There is no doubt that the selection of carbide milling cutters is particularly important. Choosing the wrong option can result in inefficiency and soaring costs. In severe cases, materials may be scrapped and equipment damaged.
Selecting the right alloy milling cutter is the key to successfully machining these “tough nuts.”
The characteristics and processing difficulties of these difficult-to-process materials.
Firstly, stainless steel materials such as 304 and 316 tend to harden during processing (the surface becomes harder the more it is cut). Thermal conductivity is also poor, with a large amount of heat concentrated on the blade edge. The cutter sticks badly, just like “chewing gum, ” with its toughness. And it easily “sticks ” to the cutting edge of the milling cutter. Causes built-up edge and rough surfaces
This requires the milling cutter to have a sharp cutting edge to cut through the material. Rather than “tearing off “。Good chip evacuation is important to prevent tool sticking. It must also have sufficient edge strength to resist hardening.
Heat-resistant steel and high-temperature alloys have extremely high strength and remain “hard as nails ” even at high temperatures. Severe work hardening and extremely poor thermal conductivity cause heat to concentrate intensely. The material also has some elasticity, which can cause deviations in tool processing.
This requires carbide milling cutters to have extremely high thermal hardness and wear resistance,and requires sharp cutting edges to reduce cutting force. Strong cutting edge and blade structure to resist enormous cutting forces. It also requires excellent chip removal capabilities.
Titanium alloys have extremely poor thermal conductivity, almost all of the cutting heat is transferred to the cutting tool. Chemical activity is also not low. At high temperatures, it is prone to chemical reactions with tool materials, causing sticking. It is also prone to vibration, and the cutting tool may not cut properly.
This type of material requires milling cutters with excellent high-temperature adhesion resistance. Having a sharp cutting edge to reduce cutting heat. Good chip removal ability to carry away heat. Sufficient strength and rigidity to resist vibration.
For high-manganese steel, the more it is cut, the harder it becomes, which means it undergoes extremely severe work hardening. It also has high impact toughness and poor thermal conductivity. This requires carbide milling cutters to have extremely high substrate toughness and wear resistance in order to penetrate the hardened layer. With a strong and resilient substrate material to withstand impact. Cut into the material with a sharp blade before it hardens.
Core selection logic for milling cutters
Milling cutter substrate material:
Ultrafine grain/nanocrystalline hard alloys are the mainstream choice. Because it combines hardness, toughness, and wear resistance. The finer the grain, the better the strength and toughness. Basically suitable for most difficult-to-machine materials. Especially rough/semi-finishing of stainless steel, titanium alloy, and high-manganese steel.
High-speed steel is also an option. It is tough, has a sharp cutting edge, and is relatively inexpensive, making it ideal for low-speed, shallow-cut, and complex-shaped machining. For example, finishing stainless steel and titanium alloys. However, its wear resistance and thermal hardness are far inferior to those of hard alloys.
Metal ceramics have excellent wear resistance and anti-adhesion properties, making them ideal for high-speed precision machining of stainless steel and cast iron. However, it is relatively brittle and susceptible to impact.
Cubic boron nitride, which is second only to diamond in hardness, is also an excellent choice. It has extremely high thermal stability and wear resistance. It is the “magic weapon ” for precision machining of hardened steel, cemented carbide, and high-temperature alloys. However, it is not very cost-effective in terms of price, and its toughness is relatively inferior to that of hard alloy.
Polycrystalline diamond has the highest hardness, exceptional wear resistance, sharp cutting edges, and a very low coefficient of friction. It is the best choice for processing non-ferrous metals, composite materials, graphite, and hard alloys. However, it is important to note that ferrous metals cannot be processed because they will react and dissolve.
Tool Magic Armor: Coating Selection
Coatings play a significant role as protective layers for cutting tools. Can reduce friction and block heat conduction. It can also improve hardness and wear resistance and prevent chemical diffusion.
Recommendation:
TiAlN (titanium aluminum nitride) coatings are highly versatile and have good high-temperature oxidation resistance. Suitable for stainless steel, titanium alloy, steel parts, cast iron, etc.
AlTiN (aluminum titanium nitride) has a higher aluminum content, higher oxidation resistance temperature, and better wear resistance, making it one of the preferred coatings for high-temperature alloys, hardened steel, and titanium alloy processing.
TiSiN/TiAlSiN (titanium silicon nitride/titanium aluminum silicon nitride) coatings have a nanocomposite structure, extremely high hardness, and excellent oxidation resistance. Particularly suitable for high-speed machining of difficult-to-cut materials. For example, high-temperature alloys, titanium alloys, high-hardness steels, etc.
Geometric angle selection and chip removal control
The front angle affects sharpness and strength, so we choose different front angles for different materials. When machining hard, brittle materials (hard alloys, hardened steel), zero or negative rake angles are commonly used to enhance cutting edge strength. When machining soft, sticky materials (such as stainless steel and titanium alloys), a positive front angle is often used to increase sharpness and reduce cutting force.
The rear corner reduces friction with the machined surface. The right rear angle is super important for keeping hardened materials from getting cut again, but it shouldn’t be too big or it’ll weaken the cutting edge.
The helix angle affects cutting balance, chip removal direction, and axial cutting force. A large helix angle of 35°-60° makes cutting smoother, facilitates chip removal, and reduces axial force. Commonly used in stainless steel, titanium alloys, and high-temperature alloys. Small helix angles provide better rigidity, making them suitable for high-hardness materials and intermittent cutting.
The treatment of the cutting edge, with a slight rounding or chamfering, is extremely important. When performing intermittent cutting and machining hard materials, it can significantly enhance cutting edge strength and prevent chipping. However, the amount of passivation needs to be precisely controlled. If it is too large, it will become “dull ” and the cutting force will increase.
As for the design of the chip tray, I recommend that it be large enough and that the tray walls be sufficiently smooth. This ensures smooth chip removal, which is particularly important for sticky materials and long chips. It can also effectively prevent chip clogging from damaging tools and workpieces.
Chip removal is also very important. In general, chip blockage is a common cause of tool failure and workpiece damage.
When it comes to cooling, there is no doubt that high-pressure internal cooling should be chosen, and it is important to ensure that the coolant used has high lubricity and extreme pressure properties. This is very effective in reducing friction and minimizing tool adhesion.
Practical Selection Guide
Remember, there is no real “universal key ” in processing. Different materials, processes, and machine tool conditions require different milling cutters.
Choosing the right milling cutter can maximize processing efficiency. And when we choose a milling cutter, we must have a clear goal.
What needs to be processed?
Is it rough machining or precision machining?
What kind of base material should be selected? Should a coating be applied?
Should internal cooling be used?
These are all factors we need to consider. For particularly difficult materials, You can contact the ZLY technical team, which has extensive experience in processing difficult-to-machine materials. We can definitely provide you with professional milling cutter selection recommendations and processing solution optimization!
We must understand that processing difficult-to-process materials is inherently challenging. However, choosing the right milling cutter is like having a magic sword that can overcome any obstacle.
Understanding the characteristics of materials and mastering the core techniques of tool selection are the absolute core elements for achieving greater efficiency and obtaining superior processing quality.
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