Phantoms
Sometimes engineering drawings and bills define transient product items that exist independently for a relatively short time and are not stocked. Instead, they are immediately consumed by higher-level products. These are called phantom structures.
Example: Frames for sunglasses are assembled or purchased, but before final assembly, the company name is printed on the side. An engineering drawing specifies the exact location. The product structure now has one more level—a labeled frame. In practice, when the sunglasses are being manufactured, the labeling and final assembly processes may be so close together that the labeled frames (without lenses) exist only briefly.
A product that starts out as a normal subassembly that is kitted, manufactured, and stocked can later evolve into a phantom. If manufacturing engineering can support changes to the manufacturing flow, you can use phantoms to reduce inventory movement, shorten lead times, and effectively reduce the levels in a bill of material.
Using phantoms may require changes in manufacturing technology, or something as simple as introducing kanban to control the movement of components and phantoms.
Use Item Planning Maintenance (1.4.7) to identify an item as a phantom for all sites. When an item is a phantom at one site but not at another, indicate exceptions in Item-Site Planning Maintenance (1.4.17). Items that are marked as phantoms using either of these two programs are known as global phantoms.
If an item is a phantom only when assembled as a component of a specific parent item, use a structure type of X within the product structure or formula. Such a phantom is known as a local phantom, since its use as a phantom depends on a particular bill of material.
When Material Requirements Planning (MRP) plans requirements, it always ignores a local phantom and creates planned orders for its components. This process of driving requirements from the components is sometimes referred to as blowing through a phantom.
If there is a quantity on hand of a global phantom, MRP uses it to fill requirements before creating additional requirements for the components.