Lecturas

E-05

Jim Robison, CFPIM, CIRM, C.P.M.

A New Model for Solving, and Resolving, Inventory Problems
INVENTORY
Inventory is a wonderful thing. Inventory allows us to meet seasonal spikes in demand with level annual production. Inventory allows us to offer a wide range of products and options while manufacturing in large, efficient batches. Inventory allows us to provide high order fill rates,despite random variations in demand, and to continue production despite random variations in supply. Inventory even allows us to decouple, and optimize, sequential production processes. Yes, inventory is a wonderful thing. But, you know, nothing is free. For all of the benefits inventory provides, we must pay a lofty price. Inventory is a hungry beast. Inventory consumes shelf or floor space.Inventory steals our flexibility and robs us of future opportunities. And inventory devours our working capital. We profess to be inventory managers, but some could argue we are lion handlers, attempting to train—though never tame—the savage beast. Using the tools of the trade, blank-pistols, chairs, and whips, we cause the lion to sit on the pedestal or jump through the hoop, all for the benefit ofour customers and the enrichment of our enterprise. But enough of the analogies. What are the tools of the inventory management trade? Before we can select the appropriate tool, we must clearly understand the task to be performed. What are some typical inventory problems? I asked this question at the 1999 conference, and I will ask it again now. By a show of hands, how many of you have had, at onetime or another, too much inventory? Now, who, at one time or another, has not had enough of some inventory item? And, who has had too much of something and not enough of something else at the same time? Well, it looks like defining our inventory problems might be a little complicated. What is it like in the typical life of an inventory manager? Is everything going smoothly? How about when oneitem needs expedition? Maybe we have just a little too much of a couple items. Does that sound typical to you? Okay. How about inventory turns are down, backorders are up, on-time deliveries are down, receipts from vendors are late, and cycle count variances are up, all at the same time. Does that sound more like your current reality? Wow! Where do we start? Wouldn’t it be great to have a magic wandlike Harry Potter, with which we could identify and solve every problem? Well, I don’t have a magic wand, but I do have an all-purpose inventory tool. We’ll talk about that tool in a while, but for now, let’s dig into our current problem. Okay, let’s look at this in detail. We’ll start with the inventory turns, which are down. That means we have more inventory, compared to sales, than we did insome prior period, such as last month or this period last year, or maybe compared to our budget or plan for this period. But what does that really mean? Was last year a fluke? Is there an error in the budget formula? Should we have less inventory or should we have more sales?

THE CLASSIC CAUSE AND EFFECT DIAGRAM
A good tool to use in a situation like this is an Ishikawa diagram, also known as acause-andeffect diagram or a fishbone diagram. We will state our problem, “inventory turns are down compared to the same period last year,” in the head of the fish. This is the “effect.” Next we will list the major possible causes as branches off the spine. Comparable periods, computations, excess inventory, and insufficient sales, among other possible causes, will be added. For each major cause,we now add all possible minor causes. For example, under comparable periods, we might look for abnormalities in the two periods—last year and this year. In each of these, we might look for changes in either inventory or sales plans. We might find that there was an unusually large sale last year caused by a new customer placing their initial stocking order. If our policy is to remove atypical...