Challenge:
-Create a customized solution capable of grinding two mating metal components with a tight clearance between surfaces.
-Adhere to manufacturing requirements for a powered arthroscopic shaver for use in orthopedic joint surgery.
Solution
Utilizing MMT’s Glebar GT-610 CNC High Precision Automated Infeed/Thrufeed Centerless Grinding Machine, the following efficiencies were achieved:
-Provided a minimum gap between assembled parts to prevent debris catch between the two surfaces while maintaining a +/‐0.0002” tolerance on tip dimensions
-Delivered a new and tailored process, completed in less than 20 seconds
-Reduced previous scrap rates significantly
Process
In this application, two tubes are assembled with a minimal gap between them—sometimes as small as 0.0005 inches. This allows the inner tube to move freely within the outer tube while preventing debris from getting trapped between the surfaces. The tips of the tubes typically feature a rounded guiding surface, while the outer tube has a window cut into it to expose the sharp edges of the inner tube.
Using MMT’s Glebar GT‐610 CNC to infeed grind the shape of the inner tube, a +/‐ 0.0002” tolerance was maintained on the tip dimensions. In addition, 3 diameter features were ground to within 0.0002” per diameter, maintaining a TIR of 0.0001” and producing a smooth 9 Ra surface finish on 304V stainless steel with a +/‐0.001” wall thickness. Removed were 0.012” in stock for the majority of the part and 0.004” from the tip geometry. The updated, fully automated process is now completed in less than 20 seconds, which adjusts for part length variation, heat expansion, and a near-zero tip geometry requirement.
Results
This solution vastly reduced previous scrap rates due to tip geometry imperfections and eliminated an extra step in the previous manufacturing method, which left unacceptable tool marks on the surface. For the outer sleeve, the GT‐610 Thrufeed Grinder was used to grind the OD of the blank tubes, maintaining a surface finish between 3‐6 RMS and a comfortable 2‐3 Cpk on the outside part diameter. Material removal of 0.005” with a tolerance requirement of +/‐ 0.0005” was met easily in a fully automated turnkey process.
