Robotic cell polishes steam turbine blades
January 30th 2009 04:15 am By Web Development in India
A robotic grinding and polishing cell is finishing a wide variety of alloyed stainless steel steam turbine blades - ranging from 4in to 20in long - after CNC machining.
A major US manufacturer has taken delivery of a robot cell for grinding and finishing large steam turbine blades for power generation.
1- The blades are new.
2- They range from 4in up to 20in in length and are straight.
3 The blades are machined out of stainless steel on Swiss made CNC machines.
4 With the off-line programming system, after the CAD model is imported into the Robot Studio software with the Robo Foil module, it takes 15 to 20 minutes to generate a grinding program.
The exact time depends on the size of the blade.
The following sequence of operation is generated: a) The robotic cell is equipped with two linear transducers for gauging or measuring the blade and checking the orientation of the blade on the gripper.
First the robot takes the blade to the first linear transducer and checks the orientation of the blade on the gripper and compares it to the CAD model.
If the orientation does match well the CAD model the software will calculate an offset and change the position of the blade accordingly.
The robot then goes to the second linear transducer and runs a gauging program to check the dimensions of the blade.
From this information the software determines how many passes it has to make on each belt to remove the correct amount of material.
b) After grinding it checks the dimensions of the blade again to make sure it is within tolerance.
c) The robot first grinds the inside radius with a small A 20 durometer contact wheel 1.5in in diameter by 2ins long.
The first belt is a grit 80 ceramic aluminum oxide belt 2in wide by 132in long.
It moves to the bottom unit and grinds the outside radius using a 350mm dia x 90mm wide Vulkolan VLS contact wheel with a Ceramic aluminum oxide belt, 80 grit, and 90 mm wide by 132in long.
d) The finishing operation uses the same size belts and contact wheels.
The belts used for finishing are structured abrasive belts, grade X30.
e) After finishing, the robot checks the dimension of the blade.
If it is not in tolerance it will go back and grind the part again.
f) If the blade is in tolerance it will place it back on the magazine.
g) The robot uses belts only.
h) The most important dimension is the trailing edge thickness of the blade where the tolerance is +0.127mm or 0.0005in.
On the remaining surface of the blade the tolerance is +0.010in or 0.254mm.
After grinding the bottom of the blade is cut off and the blade is welded into a ring,the first stage of the steam compressor Because this Company uses all different size stock to machine the blade from we used a pallet or adapter that is attached on the blade.
This adapter is adjustable for different widths and is picked up by the gripper on the robot.
We have also tested refurbished or repaired blades that have a metal coating.
The blades are for aircraft.
The problem with the repaired blade is the thickness of the coating varies considerably from one blade to another.
What we did was to start with the program barely touching the blade.
Every pass the robot would increment the program in 0.5mm.