Ok, here in brief how I achieve this. It is standard available in OpenERP.
Step1: Configure your 5 Parts (Products), these are products configured as type Stockable, procurement is set to "Make to order" and supply method is set to "Buy"
Step2: Make sure that these 5 parts have a supplier rule defined, and disable the selection "Can be sold"
Step3: Make your production product which you want to produce, set it to type Stockable, procurement is set to "Make to stock" and supply method is set to "Manufacture".
Step4: Set a minimum and maximum stock on your production product to 50
Step5: Setup your Bill of Material (BOM). Link it to the product you wish to produce
Step6: Add all 5 parts to your Newly Created BOM
Step7: Goto Warehouse - Scheduler, and click Run Schedulers. Enable the "Automatic orderpoint" selection and proceed
Result1: In your manufacturing order you'll find an order to produce 50 pieces of your production product. Waiting for availability. So you can't start production yet.
Result2: In your purchases - quotqtions you'll find requests for quotes to your default suppliers for all of these 5 products. These should be confirmed and send to your suppliers as an order.
Result3: When your products arrive in your warehouse, the production orders will be set to ready to produce whenever sufficient stock became available.
Remark. When you sell 1 production production product, the scheduler will make a second production order, and purchase quotations because your minimum stock drops below 50. That is why I mostly set the parts also to the procurement type of "Make to stock" and make sure I always have enough stock available to produce if there is an sales order of that product. But it all depends on the value of your parts of course. In some cases it advisable to buy parts not to quickly.