I am wondering that is there any fixed sequence for fillets???
Like linear or lateral or any other stander sequence
When you say sequence, do you mean sequence in selecting vertical edges and horizantal Edges?
If it is what you mean, then, yes and no. No because it's not a written rule. Yes because it save a lot time. How? Imagine a PAD of hexagon, we have 6 vertical edges, if you give Fillet to horizontal edges, (on each face) you need to select all the top face edges (6 edges) and then if you want to create fillers around it in vertical edges we need to select them separately (6 more edges).
Let's assume the situation in which you have given fillets in the vertical edges. Then, for the top face edges select one edge and use tangents propagation and all the six(remaining five) will be taken in tangents propagation and will be fileted automatically. It saves time. So, it's smart way of doing job.. Select vertical edges for fillets rather than horizontal edges..
Oh, ok, as far as my knowledge fillers are used in castings and chamfer in machining.
The reason for using these are simple,
When ever you have a sharp corner then we have stress concentration, when we go for the fillers we are removing the edge and there by stress concentration, fillets are used in castings because of manufacturability, where as chambers can lead to mould breakage.
And coming to chamfer, we are removing one edge and replacing by two edges and hence stress concentration reduced by half. Chamfer is used in machining as the cost is almost same as that of giving Fillet, but chamfer needs only one tool, but fillets need different tools for different radii, hence we prefer chamfer.