Techniques for processing stainless steel materials with end mills

In the processing of stainless steel materials, end mills need to be optimized in combination with tool design, cutting parameters and process strategies to address challenges such as chip adhesion, work hardening and fluctuations in cutting force in stainless steel. The following are key techniques:

First, optimization of tool design

Material and grade selection

For the characteristics of stainless steel, it is recommended to use ultra-fine-grained cemented carbide tools containing TaC or NbC, such as grades YG8X and YW2, which have a better balance between hardness and toughness. For instance, when processing 304 stainless steel, the durability of YG8X carbide end mills is 40% higher than that of ordinary YG8. For high-hardness stainless steel (such as 316L), hard alloy tools with a cobalt content of more than 8% can be selected to enhance the anti-chipping performance.

Geometric parameter design

Large helix Angle design: It is recommended to adopt a helix Angle of 45°-50°, which can increase the working rake Angle to more than 27°, making the cutting process smooth and increasing the tool durability by more than twice. For instance, when processing 316 stainless steel, the cutting force of an end mill with a helix Angle of 45° is 15% lower than that of a 30° tool.

The chip containment tank needs to be enlarged by 15% compared to the conventional design to address the chip issue of stainless steel long coils. For instance, when processing 2205 duplex stainless steel, the chip removal efficiency of end mills with larger chip grooves is increased by 30%, preventing tool wear caused by chip blockage.

Edge treatment: A sharp edge design with negative chamfering is adopted, with a chamfering width of 0.05-0.1mm, which can enhance the edge strength and reduce the risk of chipping. For instance, when processing 304 stainless steel, the service life of end mills with negative chamfers is 50% longer than that of ordinary cutting edge tools.

Application of Coating Technology

It is recommended to use TiAlN or AlCrN coatings, which have an anti-oxidation temperature of up to 800℃ and a hardness of up to 3200HV, effectively reducing the coefficient of friction to below 0.3. For instance, when processing 316L stainless steel, the cutting temperature of TialN-coated end mills is 100℃ lower than that of uncoated tools, and the tool life is increased by three times. For high-speed processing (Vc > 100m/min), nano-multilayer coating technology can be adopted to further enhance the adhesion and wear resistance of the coating.

Second, matching of cutting parameters

Linear speed and feed rate control

Rough machining: The linear speed is recommended to be 60-90m/min, the feed rate per tooth is 0.08-0.12mm/z, and the axial cutting depth should not exceed 0.8 times the tool diameter. For instance, when machining 304 stainless steel with a φ12 four-edge end mill, with a spindle speed of 1800rpm, a feed rate of 900mm/min, and a layer-by-layer cutting depth of 3mm, efficient cutting can be achieved.

Finishing: The linear speed can be increased to 90-120m/min, the feed rate per tooth is 0.05-0.08mm/z, and the residual height is controlled within Ra1.6. For instance, when using a φ10 ball-end milling cutter to process a 316 curved surface, with a rotational speed of 2500rpm and a feed rate of 600mm/min, combined with micro-lubrication technology, a surface quality of Ra0.6μm can be achieved.

Optimization of cutting depth and step distance

Axial cutting depth: It is recommended to be 60%-80% of the tool diameter during rough machining, and no more than 30% during finish machining. For instance, when processing the end face of a stainless steel valve, a φ20 end mill is used with a cutting depth of 2mm, which can balance efficiency and surface quality.

Radial step distance: It is recommended to be 50%-70% of the tool diameter during rough machining, and no more than 30% during finish machining. For instance, when processing stainless steel medical device parts, adopting a reciprocating tool feed strategy with a 75% radial step can reduce vibration and enhance surface consistency.

Intermittent cutting and hardened layer treatment

Intermittent cutting: When encountering intermittent surfaces such as keyways, the linear speed should be reduced by 20%. Unequal pitch tools should be preferred, and the entry Angle should be controlled between 5° and 8°. For instance, when processing stainless steel keyways, using end mills with unequal pitch can reduce the impact load and prevent tool chipping.

Hardened layer treatment: For the already machined hardened surface, brand-new tools should be used, the linear speed should be increased to 120m/min, and the hardened layer should be broken through by using a large cutting depth (0.8-1.2mm) and a small feed rate (0.05-0.1mm/z). For instance, when processing stainless steel stirring shafts, this strategy can reduce tool wear and extend service life.

Third, adjustment of process strategies

Cooling and lubrication method

Spray cooling: In high-speed machining, spray cooling can significantly reduce the cutting temperature and enhance tool durability. For example, when processing stainless steel, the use of spray cooling can increase the tool life by more than double.

Micro-lubrication (MQL) : In finish machining, MQL technology can reduce the friction between the tool and the workpiece and improve surface quality. For example, when processing stainless steel curved surfaces, the use of MQL technology can increase the surface roughness Ra value from 1.8μm to 0.6μm.

Tool path optimization

Helical cutting: Changing the conventional equal-height cutting to a helical cutting method can reduce the impact of entry and extend the tool life. For instance, when processing deep cavities in stainless steel, the helical cutting method is adopted, reducing the single-piece processing time by 25% and improving the uniformity of tool wear by 40%.

Layered ring cutting: For thin-walled parts (wall thickness < 1mm), a layered ring cutting strategy is adopted, with each layer’s cutting allowance not exceeding 0.05mm, which can avoid vibration and deformation. For example, when processing thin-walled stainless steel tubes, the wall thickness tolerance can be controlled within ±0.02mm through this strategy.

Vibration control and chip removal

Vibration control: When the amplitude exceeds 5μm, the feed per tooth should be increased by 0.02mm/z, while the rotational speed should be reduced by 100rpm. The tool overhang should be shortened to within four times the diameter. For instance, when processing stainless steel stirring shafts, the vibration problem can be completely eliminated by adjusting the parameters.

High-pressure chip removal: During deep groove processing, the coolant pressure must be no less than 8MPa, and the tool must be completely withdrawn for chip removal every 10mm of processing depth. For instance, when processing deep grooves of stainless steel, high-pressure chip removal can increase the tool life by 30%.