The critical importance of sequence in warehouses
Tuesday, March 03, 2015
One aspect of warehousing that is readily overlooked is the order in which tasks are performed. In many warehouses, the sequence is dictated by tradition, or the attitude that "we have always done it that way."
In most cases, the sequence is fine and should not be changed. In many others, however, a change in the order in which things are done can have a material effect on warehouse operations.
A diagnostic examination of warehouse operations should include the consideration of five questions:
- Who does this job?
- Where is this job done?
- How is the task performed?
- When is it performed?
- Why is it done that way?
The last two questions are sometimes overlooked. There is a tendency to assume that the sequence in which work has always been done must be correct. If you want to improve warehouse operations, this tendency to accept the status quo must be resisted.
Let's examine the sequence of work performed in most warehouses:
- value-added services
In many warehouses, product is received in a dock area reserved only for that purpose. A truck is unloaded, and product is staged on the receiving dock where it remains until inspection is completed.
Once inspection is completed, it is then moved to a storage area. If for any reason the inspection is delayed, the receiving area remains cluttered with material that cannot be shipped and has not been stored.
But what if this sequence were changed? Consider this variation: Every inbound shipment has an advanced shipping notice (ASN). Any vehicle arriving with merchandise that cannot be identified with an ASN is not to be unloaded.
A storage planner analyzes each ASN and consigns a location for the received merchandise. The receiving warehouse worker scans the bar codes of each unitized load of the product as it is removed from the vehicle. Each pallet then moves directly from inbound truck to the assigned storage area where the scanner creates a receiving manifest which is compared to the ASN when the putaway is complete.
If there is a discrepancy, the delivering driver and receiver walk into the assigned storage area to mutually verify the discrepancy. If there is no discrepancy, the bill is signed and the delivering truck driver is released.
When vendors are carefully selected and motivated, count discrepancies on receiving should be rare. Vendors with frequent discrepancies should be replaced. Therefore, the number of incidents when a count verification is needed should be infrequent.
Is this the best sequence for your warehousing operation? Is it better or worse than the procedure you now use. Are there special situations in your operation which might create productivity opportunities with a sequence that is different from that just described? It is useful to critically examine the order in which the various receiving tasks are usually performed and questioned.
What is the best sequence for moving merchandise from dock to stock? In many warehouses, the receiving lift operator is provided with a list of locations where the same SKUs are stored today. The operator then selects one or more of these locations as a place to put the newer stock.
In some warehouses, the receiver has no instruction at all, and in that case the person handling the receipt makes a judgement call about the best place to store the inbound item. In other situations, a storage planner works from an advanced shipping notice and plots the best location to store each item on the receipt. Specific storage addresses are provided to the receiver who moves product to the point that was specified.
The sequence of handling putaway will be governed by the type of information available to the receiver. The last of the three options just described probably provides the most rapid and trouble-free movement from dock to stock. As you examine the putaway function in your warehouse, look at the procedure and the sequence of steps.
Some believe no product should ever be rehandled within a warehouse. Rewarehousing the product provides additional risk of damage and increases the cost of warehousing. Yet rewarehousing is clearly a necessity to maximize space utilization and improve your materials handling operations.
What is the proper sequence for rewarehousing? Most relocation of stock is done to save space. A space planner will discover that there are two short rows of the same SKU, and by combining the two into one longer row, a slot is made available for storage of new merchandise.
In other situations, a slow-moving item has now become a fast mover, or the reverse. In either situation, items are moved from the fast-pick area to the slow-moving area or vice versa.
In terms of sequence, rewarehousing to save space is best done on an opportunity basis. Whenever you discover an opportunity to free a storage location, this should be done by moving stock.
Should orders be picked as soon as they are received, or should they be selected just in time to load directly to an outbound truck? We considered a receiving procedure in which merchandise moves directly from inbound truck to storage location, which is sometimes called fluid receiving.
The reverse may happen with order-picking and shipping, with goods moving directly from storage location to the outbound truck, thus saving the space and labor costs of outbound staging. The fluid process requires that order picking and shipping be done on a just-in-time basis.
However, in some warehouses it is necessary (or at least desirable) to pick orders in advance and stage them for shipping at a later time.
Consider the sequence options for order-picking in your warehouse. In some cases, you may want to pick a portion of the order in advance and handle another part of the order on a just-in-time basis. One example of this is an order that marries some material moving from stock with other items received in a cross dock operation.
The sequence options for shipping are similar to order-picking, though there are a few differences. If shipping and receiving operations both use the same docks, it may be desirable to separate the functions by time.
For example, in one warehouse all receiving is done before noon, and the docks are reserved for shipping operations from noon until the end of the work day. In a multiple-shift operation, one shift may be dedicated to receiving and rewarehousing, and another shift is dedicated to shipping.
6. Value-added services
Some warehouses handle kitting, stretchwrapping or final labeling of merchandise. In effect, a new SKU may be created as merchandise is assembled and wrapped. What is the best time sequence for handling this kind of activity?
In some operations, kitting is done in advance, with a bank of new kits developed as soon as the component materials are available. In other warehouses, the kitting is performed on a "just-in-time" basis, with each newly assembled SKU shipped almost immediately after it has been created.
The JIT basis will eliminate the possibility of assembling too many units of the wrong item and later having to perform a dekitting operation. However, if assembly is done on a JIT basis, the workload may exceed capacity during certain peak periods. When that happens, some advance kitting may be necessary in order to keep up with the total workload.
What is the best sequence for handling such value-added operations in your warehouse? There is no one best answer for every operator, though in this situation the advantages of a JIT process are self-evident.
In looking at the sequence of each of the six warehouse operations just described, it is necessary to ask "why" as well as "when." If the answer is that we have always done it that way, this is an invitation to consider a change.
Changing the sequence in which work is performed can have a significant impact on efforts to improve operations in your warehouse.
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