Maintenance and parts inventory
To carry out its mission, the maintenance department must be able to rely on a certain inventory of spare parts. And like all inventories (production, distribution, etc.), they give rise to problems that need to be resolved. When it comes to spare parts inventory, the result is all too often a lack of efficiency, with not inconsiderable economic consequences.
For example, the absence of the parts needed for a job leads to additional delays, resulting in ever-increasing tied-up capital.
Control spare parts inventory
The parts inventory generally comprises all the stocked items needed to optimize the achievement of the maintenance function’s objectives: costs, lead times, safety.
Depending on company policy, this stock will be made up of:
- Parts belonging to the equipment bill of materials and deemed critical, hence the need to keep them in inventory;
- Items such as tooling, equipment, test and inspection materials, etc., required for maintenance work or various projects (fittings,…);
- Miscellaneous supplies specific to maintenance activities (solvents, grease, etc.).
Initially, therefore, a catalog of the items in this stock must be created. The purpose of the catalog is to gather useful information about the items in the stock and make it available to users.
The main information contained in the catalog, apart from indicating the existence of stock items, is the classification of items according to their use:
- common or everyday items;
- multi-purpose spare parts, used by various types of equipment;
- specific spare parts for a particular piece of equipment.
Stock item management requirements generally lead to the assignment of a code to each identified item. This code may or may not be significant, depending on whether it is established for internal use or refers to the number given by the manufacturer.
Parts inventory
Stocks require premises that need to be heated, lit and maintained, as well as management files, equipment and personnel for storage, distribution and handling. Inventories represent tied-up capital that could have earned interest.
Conclusion: inventories are costly to the company, so we need to reduce them as much as possible, in order to move towards stock.
Which item should be kept in stock, and in what quantity?
The decision to keep or not to keep an item in inventory is the result of an analysis that takes into account
lead time
cost of stocked item
the cost of managing the stock
the cost of non-availability of production equipment.
Certain methods for estimating quantities have been established, but only an analysis of actual consumption enables us to manage quantities, since consumption depends on a host of factors linked to its use (the machine on which the used, mode of use, modifications to production equipment, etc.).
Kanban system
The inventory management method based on the Kanban system uses cards for order points and order quantities.
Each type of part is associated with a card (the kanban) which is strategically located in the stock to determine the time of ordering according to the quantity to be ordered. The order quantity is fine-tuned, and the order interval depends on the stock flow.
It’s a visual system.
If you don’t have any data from the equipment manufacturer or supplier concerning the critical parts on the machine, you can always start the analysis with the following procedure, which is very well done when drawing up the data sheets for each machine :
List the machine’s parts and sub-assemblies;
Classify this list into the following categories corresponding to the type of part, and for each category, use the corresponding guide values:
- Connecting parts between fixed and moving parts; mostly wear parts
(bearings, bushings, relays, contacts, etc.); - Regulation and control parts (valves, plugs, springs, rods, connecting rods, etc.);
- Moving parts: shafts and rotors;
- Electronic parts, etc;
- Structural parts: frames, frameworks or supports.
When selecting equipment and quantities, the average workload and number of identical and the number of identical machines.
Thus, with several identical machines working at low load, we could have zero stock (*4 machines running at 75%” are equivalent to ‘3 machines running continuously’).
Historical files can also be used to correct these values. As the causes of repair interventions are noted, it will be easy to judge the nature of the part replacement: wear, accidents, rebuilding, improvements.
