Logistics News: Can You Ever have too Much Accumulation Conveyor?

The obvious solution would appear to be adding more accumulation conveyor.  But, not so fast!  Zero Pressure Live Roller Accumulation Conveyor, and that’s what we’re talking about adding, is the most expensive type of case handling conveyor in the system.  When planning a new system, you could be easily adding $25,000 to $30,000 for each additional 100 lineal feet of conveyor.  For a system that is already installed, the cost will be considerably higher.  If cases are accumulating at say 40 per minute, and the average case is 15 inches long, you’re gaining 2 minutes of accumulation for each additional 100 feet of conveyor.  We’re talking $15,000 per minute or more.  That can quickly add up to some serious cash.  And worse yet, it may not substantially improve system performance.

So, what’s causing the backups and how can it be solved?

There can be several operational factors contributing to the problem.  As an example, let’s look at a wave picking, sorting, and manual palletizing system operation commonly found in order fulfillment distribution centers throughout the industry.  In this type of operation it is critical to maintain proper timing between the picking and palletizing operations.  If not, you can expect the following problems to occur:

• Because pickers pick ahead of the palletizers, cases belonging to large orders from older waves (or batches) will frequently end up accumulating behind cases belonging to newer waves.  Thus, orders from older waves cannot be completed.  Consequently, some of the after-sort palletizing/shipping lanes will not be available for a new order and a new wave.
• Cases, belonging to later waves start accumulating on the sorter recirculation loop until it becomes full, which then interrupts inbound case flow to the sorter causing those conveyor lines to backup.
• Although pickers are being effectively utilized, palletizers are standing idle waiting for the system to sort through cases belonging to multiple waves thus reducing system throughput.
  

The congestion caused by the above operation left unchecked will quickly fill up the available accumulation.  Adding more accumulation conveyor will delay the problem, but not solve it.  It may be better, certainly less expensive, to test different wave picking strategies like limiting the pickers to no more than two waves at a time. You may also want to review critical path conveyor speeds to determine if they can and should be increased. And, make sure that the right amount of labor is at the right place at the right time.

In the typical distribution system, the rate at which cases are introduced into the system from receiving, cross docking, warehousing, picking, special processing, and staging areas, varies greatly throughout the production cycle.  By analyzing each of these inbound production areas it is possible to estimate how much accumulation is required under various flow scenarios to keep all areas running at their target design rate.  Sometimes computer simulations can be effective tools for companies to use to better understand system performance, test design alternatives, identify potential bottlenecks, and understand the likely result of changes to an existing system.

For medium to high throughput systems, consideration should be given to software systems that include wave overlap and waveless picking strategies, which can eliminate bottlenecks and optimize dynamic accumulation requirements.  For more info on this approach, checkout the SCDigest article How to Improve Wave Picking System Productivity.

Agree or disgree with Holste's perspective? What would you add? Let us know your thoughts for publication in the SCDigest newsletter Feedback section, and on the website. Upon request, comments will be posted with the respondent's name or company withheld.