Hi Carol
When you add a component with a negative quantity on the BOM and post a confirmation on CO11N, a goods receipt with movement 531 is posted. This is a goods receipt of a by-product, which is generally used for scrap.
If you want to use a different mov. type, you can replace 531 on the customizing transaction OPKA.
Otherwise, you can try to use WORKORDER_GOODSMVT to change the movement type.
BR
Caetano