How To Create Composite Primary Key

I have a rather interesting situation involving creating a primary key. Basically I have two tables.

Table 1

Date, Customer, Part Number, Work Order, Qty tested, qty failed, tech name

Table 2
Defect, reference, quantity(defect), defect cause, part number, work order

The ideal relationship I want to create is that for every Table 1 there are multiple table 2. Regular one to many relationship. The problem is that in the first table it is possible and probable that there will be duplicate records because of the process. The test parts by individual carts, but often they're exactly the same parts with same work orders and same everything else. How should I go about doing this. I don't want to just create an autonumber for each record if possible. Any suggestions?