one unique no to diffrent item during production

Hi

My client just do assembly work. He assembles the ambulance.

Process is :

Vehicle received from customer.

Welding stage:Welding done on it.

Insulation stage:Insulation done on it.

Painting stage: Painting done on it.

Final fitting.

I have to keep track during each production stage.i.e how many items are issued at which stage and at particular time where the vehicle is present. To solve this problem i am defining item as

1. Vehicle 2.Welded Vehicle 3. Insulated Vehicle 4.Painted vehicle 5. Ambulance

In this way step by step vehicle will be changed to ambulance in production process.

The vehicle is received at the gate from the customer.I want to alot a unique no. to the vehicle and want that it should be alloted to vehicle,welding vehic,insul vehic, paint vehic, final fitt vehic and ambulance finally, as long as process carry on this will act as registration no. which will be same up till this ambulance is delievered and invoiced

How this possible?

Plz suggest me.

Thanks