Product category:
Polishing, buffing and surface texturing
News Release from: Surtech Surface Technology Products | Subject: Robotic buffing, abrasive belt grind and polishing
Edited by the Manufacturingtalk Editorial
Team on 14 December 2005
Robots abrasively finish, polish femoral
knees
Robotic systems for abrasive belt grinding, buffing and polishing of cast components have also been successfully applied to femoral knee implants as well as turbine blades.
Messrs Intec of Italy have more than 20 years experience of designing robot cells for some of the most difficult parts, i e, surgical implants and turbine blades Over the last five years IIntec have sold more than half a dozen robot installations for finishing surgical implants and turbine blades to US based manufacturers
This article was originally published on Manufacturingtalk on 1 Mar 2004 at 8.00am (UK)
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The following report gives details of an installation for finishing artificial knee joints with a specially adapted robot cell.
The femoral knee finishing process consists of three separate operations: 1 - Gate grinding to net shape.
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3 - Polishing.
* Gate grinding - the gates from the casting process are normally located in the centre of the condyle where the arrow labels the 'distal'.
The gates can be removed with abrasive belts grit 80.
The condyles and the patella track areas can then be ground with abrasive belts grit 150.
This process takes approximately 2 minutes.
Some Companies do not employ abrasive belts to carry out these grinding operations but either mill or use a grinding machine.
After milling robot cells with abrasive belts are used to linish the parts.
* Abrasive belt grinding - the belt grinding operation takes approximately 3.5 minutes, with the exception of the inter condylar gap.
This gap is normally milled, but if it has to be abrasive belt ground the total operation of finishing the knee will take 5 to 6 minutes.
Finishing the inter condylar gap with an abrasive belts is possible but because of the long time taken we recommend this operation to be carried out by milling.
If we use four abrasive belt grinding units and do not finish the inter condylar gap the following finishing sequence is typical: * Abrasive belt grinding unit No 1 - finishes the condyles, condyle tips, lateral and distal sides, the patella track and the patella tip.
with abrasive belts grade X 65.
* Abrasive belt grinding unit No 2 - finishes the condyles, condyle tips, lateral and distal sides, the patella track and the patella tip with abrasive belts grade 45.
* Abrasive belt grinding unit No 3 - finishes the condyles, condyle tips, lateral and distal sides, the patella track and the patella tip with abrasive belts grade X 22.
* Abrasive belt grinding unit No 4 - finishes the condyles, condyle tips, lateral and distal sides, the patella track and the patella tip with abrasive belts grade X5.
* Polishing - after the abrasive belt sequence all parts of the knee are buffed in two stages: No 1 with sisal buffs and cut and colour polishing compo.
No 2 with cotton buffs and colouring polishing compo.
The cycle time for the two buffing operations varies between 3,5 and 5 minutes.
The above finishing sequence is used by one of our customers.
It is typical but we can also design other sequences to satisfy individual requirements.
* JIGS - femoral knees usually have pins, threaded holes or are of a box design.
Grippers are made to suit either of these designs.
In some cases it may be necessary to use two grippers so that all parts of the knee can be finished.
This involves gripping the knee in one position and one gripper and then gripping it in another position with another gripper.
* Three robot cells to finish femoral knees - depending on quantities and finishing specification up to three robot cells are needed to complete the femoral knee finishing process: * No 1 robot cell for gate grinding.
* No 2 robot cell for linishing parts all over.
* No 3 robot cell for cut and colour buffing with sisal buffs, followed by mirror polishing with cotton buffs.
If quantities are small and do not allow a three robot cell operation it is possible to concentrate all operations into either a two robot cell or even a one robot cell operation.
Obviously output will be considerably lower.
* Off-line programming - we can provide customised off-line programming with software options based on the state-of-the- art ABB off-line programming platform ROBOTSTUDIO.
The data input allows the user to use data formats such as CAD model, 3 scanner, a standard workpiece with a portable CMM and CNC path.
Automatic path planning aids optimised tool selection and work-cell design Auto path generation takes into account the experience of the operator A customised calibration method enables us to compensate for the error between the model and a real workpiece.
Simulation by the ABB Virtual Controller technology allows users to see the process and to obtain accurate process time estimation.
Robot linishing and polishing operations for surgical implants save considerable amounts of money.
A properly designed and configured robot cell can do the work of a dozen highly skilled manual operators.
Six axis robots can finish to tolerances below 0.o4 mm and surface finishes below 1.4 micron Ra.
An added bonus is greater consistency and the elimination of vibration induced illnesses and repetitive strain injuries.
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