Medical Micro-Milling & Micro-Drilling of AISI-420 Stainless Steel

🕜 Efficiency & Yield Rate- elimination of manual refining process, and product yield rate was raised from under 10% to 100% | 📈 Quality - great improvement in surface roughness with no obvious feed marks or burrs, and have great roundness in micro-drilling on cruved surface without pilot drilling process.
  • Difficulties in Machining
  • HIT Achievements
  • Industry Application
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What makes AISI-420 Stainless Steel difficult to machine?



AISI-420 Stainless Steel is a martensitic stainless steel which has excellent corrosion resistance, high hardness and strength, and is commonly used across various industrial applications.

AISI-420 Stainless Steel has a high hardness level.  It can achieve a hardness of approximately HRC 50-55 after heat treatment.  Along with its work-hardening material property, it has brought great challenges in CNC machining of this kind of material.

Especially when micro-milling and micro-drilling AISI-420 stainless steel for extremely small medical spare parts, high cutting forces would cause vibration when the tool started pushing and squeezing out the material.  This eventually left obvious feed marks on the surface of workpiece.  The work-hardening characteristic of stainless steel made the cutting ability from the chisel (of ball end mill) unable to overcome the plastic deformation of the material.  The tool failed to cut off the material, which left serious tool marks and massive burrs on the workpiece.

Since the final product was minimally invasive surgical spare parts, the full length of the workpiece was only 4mm, with the slot width only 0.8mm.  The extremely small workpiece had obvious tool marks and massive burrs after CNC machining process, which would then require manual refining process (blasting and manual deburring) under microscope.

However, the tool marks were often impossible to fully remove after blasting.  The micro-features of the spare parts would even get severely damaged during the manual deburring process, which resulted in terribly low product yield rate (under 10%).  Moreover, the manual refining process could not fix the poor roundness of the drilling holes on a curved surface due to high cutting forces.  These factors have caused serious risks of failing to deliver the order for our customer.

 

☑️ AISI-420 Stainless Steel Machining Information

 
   AISI-420 Stainless Steel Machining Information     
  Material   AISI-420 Stainless Steel
 
*Hardness over HRC50 after heat treatment
  Feature   Fine milling on slot bottom, fine milling on slot lateral wall, bottom milling on the shank, Φ0.26 x 0.8mm micro-drilling (through holes)
  Process   Micro-milling & micro-drilling  
  Ultrasonic Tool Holder           BT30-R02-06
  Rotating Speed   13,000 ~ 17,000rpm
  Tool Selection   R0.1 ball end mill, R0.15 ball end mill, Φ0.26 drill bit  


 

HIT BT30 ultrasonic machining module was used for micro-milling and micro-drilling of AISI-420 stainless steel medical spare parts
(Figure 1. HIT BT30 ultrasonic machining module was used for micro-milling and micro-drilling of AISI-420 stainless steel medical spare parts)



 

HIT's Goal in Machining AISI-420 Stainless Steel


The ultimate goal is to help enhance product yield rate for our customer.  Through the assistance of HIT Ultrasonic, customer could eliminate the manual refining process and achieve even better surface quality with great reduction in burrs.



 

Ultrasonic-Assisted Machining AISI-420 Stainless Steel Results

 

AISI-420 Stainless Steel Micro-Milling & Micro-Drilling : Workpiece Quality


HIT ultrasonic-assisted micro-milling and micro-drilling of AISI-420 stainless steel for medical spare parts can improve surface quality, greatly reduce burrs, and have better hole roundness without pilot drilling process
(Figure 2. HIT ultrasonic-assisted micro-milling and micro-drilling of AISI-420 stainless steel for medical spare parts can improve surface quality, greatly reduce burrs, and have better hole roundness without pilot drilling process)

 
  • Without ultrasonic, high cutting forces appeared at the chisel of ball end mill.  This caused vibration when the tool started pushing and squeezing the material, and eventually left obvious feed marks on the surface of workpiece.
  • Along with the work-hardening characteristics of stainless steel, the cutting ability of the chisel could not overcome the plastic deformation of stainless steel.  The tool failed to cut off the material, which left serious tool marks and massive burrs on the workpiece.
  • With HIT ultrasonic, the high frequency micro-vibration helped reduce the cutting force at the chisel of ball end mill.  This allowed the tool to cut off the material with easier chip removal, which helped improve the surface roughness of workpiece and have great reduction in burrs.
  • Especially when micro-drilling on a curved surface, the lowered cutting force also prevented the tool from deflection.  As a result, with HIT ultrasonic, there could be better roundness in drilling holes without pilot drilling process.



 

AISI-420 Stainless Steel Micro-Milling & Micro-Drilling : Efficiency & Yield Rate


HIT ultrasonic-assisted micro-milling and micro-drilling of AISI-420 stainless steel for medical spare parts can successfully eliminate the manual refining process, and enhance the product yield rate from 10% to 100%
(Figure 3. HIT ultrasonic-assisted micro-milling and micro-drilling of AISI-420 stainless steel for medical spare parts can successfully eliminate the manual refining process, and enhance the product yield rate from 10% to 100%)

 
  • Without ultrasonic, the surface of workpiece was terrible with massive burrs after CNC machining process.  It would then require blasting and manual deburring process in order to refine the workpiece quality.
  • Since the workpiece size was extremely small, manual deburring process could cause risks including damages to the micro-features or failing to remove tool marks after blasting.
  • Moreover, the refining process could not overcome poor roundness in micro-drilling on a curved surface.
  • The true benefit that HIT ultrasonic brought to the customer regarding the machining process was the increase of product yield rate to 100% by CNC machining process.
  • Without having to face the risks of poor yield rate due to manual refining process, the products could achieve customer's standards and even exceed their expectation.



 

HIT Ultrasonic Machining Technology Achievements


🕜 Efficiency & Yield Rate - elimination of manual refining process, and product yield rate was raised from under 10% to 100%
📈 Quality - great improvement in surface roughness with no obvious feed marks or burrs, and have great roundness in micro-drilling on cruved surface without pilot drilling process


 

AISI-420 Stainless Steel Machining in Industry Application



Micro-milling and micro-drilling AISI-420 Stainless Steel is applied in the Medical industry, especially for minimally invasive surgical spare parts, such as biopsy forceps, grasping forceps, etc.


AISI-420 Stainless Steel is a martensitic stainless steel that is commonly used in various industrial applications, including surgical instruments, cutlery, moulds, shafts, valves, and wear-resistant parts.

AISI-420 Stainless Steel has a high hardness level.  It can achieve a hardness of approximately HRC 50-55 after heat treatment.  Along with its good corrosion resistance, it can be a great challenge to CNC machining of this kind of material.


That was when HIT's Ultrasonic Machining Module came to help!  HIT offers a comprehensive solution in machining advanced materials.  With the assistance of HIT's Ultrasonic Machining Technology, clients stopped worrying about poor workpiece quality which resulted in poor product yield rate due to high cutting force.  HIT assures its clients of not only matching up with their requirements, but also achieving even better outcomes!




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