What is a deburring machine?
The ISLAND (WORKSTATION)
We find often in the sector the word ISLAND to identify a robotic machine.
Let me start from this misuse of the word to explain how a robotic machine is composed of.
In the early robots (in the 90s) we hadn’t to follow standards to build a machine, it was enough that it could produce pieces.
So, the robot was in the spotlight of the manufacturer and the user.
The robot was the highest palm tree of the ISLAND (workstation) at the centre of ISOLA. The robotic machine was stationary (not connected to anything else in the factory) and the robot was the focal point of the machine.
All equipment were under of the robots and their safety study had still to follow.
Nowadays everything has changed.
Let’s go step by step.
How is a deburring machine composed of?
IS IT COMPOSED OF
There is no a precise scheme to build a machine for deburring machine. All depends on the material to be worked and how the machine fits with the factory system.
The elements of the machine are:
- Loading system
- Work unit
- Discharge system
- Protections (safety cabin)
- Supervisor and inspection system
The machine generally works like this:
- The robot takes the piece through a pneumatic clamp
- The piece gets in contact with different cutting tools
- The tools remove the burr while the robot moves
- The robot leaves the piece and starts from the beginning
The operator is always out of the robot safety cabin, away from the noise, dust and vibration.
The tools (and therefore the units) can be of different types. Substantially are divided into 2 groups:
- Cutting tools
- Grinding tools
The cutting tools are cutters and blades, i.e. tools that remove material by chip removal.
Grinding tools are all tools that remove material by making dust.
There are many types of abrasive tools. Each of these tools have its own peculiarities. There are more “aggressive” tools that acta s a cutting tool or tools that are almost finishing gloss (type scotche brite).
The grinding tools are constantly changing, and every year producer develop new solutions that modify considerably the work cycles.
SOMETHING TO EVERYONE
Depending on the material to be machined the forces are changing and the machine has to be different.
The machine can not be too oversized, otherwise it will be slow in the movements (and therefore it will affect the cycle time).
Then depending on the material to be processed there are established performance limits.
There is no policy to understand the forces for in a loop or a manual one to follow.
Because everything depends on the “general conditions”: everything depends on the vibrations, the thickness of the burr, the rigidity of the piece, the power of the unit.
Let’s take for example a milling application. All milling user’s handbooks we find
Vf = fz x n
Vf = Feed speed
Fz = removal for cutter tooth
n = Cutter speed
If we take the same piece ad we work it on a work centre, then replicate the same situation with a robotic machine, the results will be very different.
The robot is an elastic machine and with more approximate trajectory control than the machining centre
If a robot meets the same conditions it starts vibrating.
The vibration is a constant to keep in consideration. It is a prerogative not deletable.
So keeping the same milling parameters on the working center, but by introducing the vibration the teeth of the cutter are to remove sometimes a lot of material and sometimes very little.
TYhis makes the operating cycle unstable and uncertain quality.
How do you solve the problem?
There are 2 strategies:
- Change way
- Be more ridgid
It all depends on what you have to do. It is often better to change the approach and use tools tat give less problems to the robot.
Other times you can use a big-sized robot and contain vibrations: the greater is the inertia of the robot, the lower are the vibrations generated.
Everything is a performance balacing cycle time.
Ultimately it all depends on the loop target you want to reach. The question is: is the hippopotamus better or the Gazelle?
The reasoning we did here on a milling processi s then repeated on all types of tools.
I spoke about a milling process because about this topic there is a lot oh knowledge and there is a lot of written material.
You can imagine the difficulty in finding the right work parameters with new tools, without knowing anything because nothing is written, where maybe you are the first to test them in a particular application.
Building a safe machine is not complicated.
To be able to certify the machine CE it is necessary to follow the machine directive (2006/42/CE).
To meet the machinery directive and therefore to mar kit with the CE marking it is necessary to follow a series of standards.
First of all the risk assestment en iso 12100, then you have to consider the standards for industrial robots EN 10218-2 and the standard EN 13857 for safety protections. We do not have to forget the details, such as the stairs (if there are any) that have to comply EN 14122-3.
It all sounds simple, just do everything according to the rules and Bob’s your uncle.
Buti t doesn’t work this way.
In reality it is not so, just with one assestment mistake, you may apply standards incorrectly and the machine is no longer safe.
If the risk is assessed incorrectly (because every machine is made differentely to work different types of material) then the risk reduction will be insufficient or made diametrically opposite.
It is important to remember that the machines should not only be safe, you should be able to use them.
To make a safe robotic machine, just make sure that when the machine has the door open, everything stopes safely.
But how do you program it? How do I see that the robot is moving and is working in the right way?
If you make a robotic deburring machine that inhibits any open door function, you are putting a huge risk at stake!
If I don’t give the possibility to the programmer to work, he will find a way to do it.
Instead of always staying out of the machine and taking a long time to program the work cycle, he will enter into the machine and will find the way to access (dismantling machine parts, cutting them or touching safety sensors
The injury happens.
And whose fault is it?
Formally the fault lies with the programmer who tampered the machine.
Ùthically the fault lies with the manufacturer.
During the design and construction of the machine, we must think about the various work steps on the machine.
At the beginning I spoke about the ISLAND (workstations). Actually there are many ISLANDS (workstations). The factories are integrated. Deburring machine has to be integrated into the production process. If the integration is done without knowledge of the facts, there will be less safety.
For example, if a machine works aluminium it makes dust, so the area is potentially explosive.
The dust should be taken over by a suitable sunction device and in case of explosion the machine must stop immediately.