There are many ways to merge these files. Let me show you two popular ways
a) Using cat to merge
cat file.1 file.2 file.3 > file
Using split to well, split
split [OPTION]... [INPUT [PREFIX]]
-b, stands for binary files
It's easy to write a shell script that takes in filename, chunk size, destination etc as parameters. But why not save the trouble and use the second alternative.
b) Using Gnome split
As the name suggests, you can merge, split files right from Gnome.
It also has some cool features like deleting the chunks after merge is completed etc.
Great. That was easy, wasn't it. I haven't found any KDE alternatives yet. Feel free to share them in the comments. Thanks.