If you have a component or assembly, and you want to show the inner mechanics, or find the measurements of parts inside a component or assembly, then you would draw a picture as if it the picture was on a plane that cut through the component or assembly. The material which you cut through, you represent by drawing lines going at 45 degrees, its called 'cross hatching' or 'section lining'.
On your drawing you have got an upper die and lower die (2 components or 2 parts). By having a sectional view, you are looking at how the the inner workings look (in your case how the mold will turn out). On your drawing, you have put lines going in the same direction on both dies. If there are two components, you have to put the lines at 45 degrees on one component, and at -45 degrees on the other, so that it shows a sectional view of two adjacent components (this helps identify two different components). If there is only one component present, you would just have 45 degree lines representing one material section. If you have a 45 degree component, like say a sheet of metal which has been bent at 45 degrees, and you want to show a sectional view, you would then use an angle of 30 degrees for cross hatching as this would help cause less confusion (otherwise your cross hatching lines would line up with the outer lines of your sheet metal).
Sometimes if you have a center line (chain line), you can show a half sectional view on one side of the center line, and the outer body on the other, so that you can view what it looks like on the inside and out, this is called 'Half section'. If you don't want to use your center line to separate sectional views, you can draw a wiggly line followed by hatching on the cut plane.
If you go on amazon, try looking for a book called 'engineering drawing with problems and solutions BY K.R.HART'. I think i payed about three quid (sep-2011). This book is ideal for sectional views, and how to draw mechanical components.
Hope this helps.
Dunk
