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Explain the difference between BOM and Assembly? By: Tim I wrote this a while ago. It should be a bit helpful for you. It also talks about construction type. Some people link a maintenance assembly material as the construction type but I disagree with this because they are missing the point of the construction type. Assemblies The term "assembly" can mean a lot of things. In general, an assembly is a group of parts that, together, form another larger part. This also describes a BOM and so a BOM and an assembly, in essence, are the same things. (You can see this in transaction CS03 - look for the "A" column). There is also a material type called "Maintenance Assembly". This type of material has no purchasing or valuation information and is not linked to a plant. In other words it doesn't really exist. The concept of a maintenance assembly is a collection of parts that cannot be purchased as a single entity. In other words, if the motor you see can be fixed then it's probably a BOM (aka, an assembly) and if the motor itself can be purchased as a spare part then the whole "assembly" is a normal material BOM. If the motor cannot be purchased then it would be a maintenance assembly - a collection of parts that can be fixed but not purchased nor replaced as a single, complete entity. When you create a BOM for PM usage (normally usage "4") there is special logic in the code that allows special scenarios. Normally you cannot create a BOM linked to a plant unless the parent material actually exists in the plant but a BOM with PM usage will allow it (compare this in CS01 using usage "3" versus usage "4"). This is because a "Maintenance Assembly" does not have a plant and would fail this check. The same thing goes for adding BOM items. The BOM items must exist in the plant for the BOM. This means that you cannot add a Maintenance Assembly to a BOM and yet you need to do this (for functional location or equipment BOMs mainly). For this reason there is a "PM Structure Element" category for BOM items which turns off the plant check allowing you to add components to a BOM that don't exist in that plant. There is also a "PM Assembly" which you see in IH01 as a yellow item. This "PM Assembly" is actually a normal material BOM that has been flagged as a "PM Assembly". Any material BOM can be flagged this way but by default all BOMs built from "Maintenance Assemblies" are automatically flagged as such. This further re-inforces the link between a "Maintenance Assembly" material and a BOM as an assembly. If you experiment with these concepts you will find that you can get away with a lot and do almost anything so you must be aware of what you are doing and how it works for the company and other processes (both yours and other SAP transactions). If you "cheat" then just be aware of the benefits and consequences. The same holds true for construction type. You can
use a maintenance assembly in there but if you use a legitimate material
(that can be purchased) then you can purchase equipment (as materials),
use valuation (for broken and refurbished equipment/material), and track
equipment as swappable materials (spare parts). You can't do all
that if the construction type is a maintenance assembly. Anyway,
consider that in the IMG there is an option to synchronize the construction
type to the serial material of an equipment. In other words the idea,
in general, was for the equipment to be linked to a normal material to
show that the equipment is made of that material but more importantly you
would link the equipment to a serialized material that can be purchased,
stocked, and swapped with any other material of that same type.
An example with exactly what I don't recommend to do : Assemblies as Construction type. The thing is that SAP lets you do a lot of things and the question is, is this allowed? Sure, if you can do it then technically it's ok to do. I mention the construction type scenario because there is some SAP documentation on the help site where you configure the construction type to be linked to a serialized material. Assuming that you follow all the documentation and set up your system correctly here is what would happen. The idea is that you need to buy 5 pumps. Each are of the same material number so you create a purchase order for 5 pumps. When you receive the pumps you assign serial numbers to them. Doing this will automatically create equipment master records where the material information is copied over. Also, this equipment shares certain aspects of the material (like its BOM). There are two reasons why I don't like the construction type linked to a maintenance assembly. 1. In SPRO the construction type and serialized material
number can be "force-linked" together.
In both cases we are talking about the construction type being a physical material, something that can be purchased and stocked. However, the point of the maintenance assembly is a non-physical structural or organizational mechanism, hence the reason it cannot be purchased nor stocked.
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