Does your lean manufacturing value stream map include movement of materials between processes?
Value stream mapping is one of the most common and powerful tools used in lean manufacturing . As the name implies, the map visualizes the sequence of processes that create customer value in an enterprise. For manufacturing companies, customer value is predominantly built into the capabilities and features of the product itself. As a result, value stream mapping most often shows the physical processes like machining, painting, assembly, and shipping. What value stream mapping often misses is how those materials move between processes.
Creating a manufacturing value stream map
Value stream maps typically are created from walking the shop floor, interviewing operators and capturing results using sticky notes on a wall. This allows for the flexibility needed, especially when different products have different paths through the manufacturing processes. Lean manufacturing literature is full of examples of value stream maps. The problem is that they are all wrong.
Well, maybe not exactly wrong, but I have yet to see value stream maps that include the level of detail that defines material movement. In talking with operators, the focus is on their process, and justifiably so, but it’s as if the components needed by a process just magically show up when needed and the products produced by the process are magically removed and off to their next step. Occasionally you’ll see a kanban board symbol…but a picking list, never!
Visualizing a complete production system
A complete production system includes:
- How component parts are ordered
- How component parts are received
- How component parts are moved from their stocking location to the actual point of use on the shop floor
- How defective components are removed and returned or scrapped
- How defective products are reprocessed for correction
- How defective products are torn down if components can be reclaimed
- How good products are moved along to the next process
- How good products are put away in inventory
Some people would argue that the point of a value stream map is only to surface waste in order to focus on kaizen activities. That’s true and is definitely the top benefit of a value stream map. However, value stream maps are an excellent way to document your processes in very specific detail.
Importance of understanding material movements
Let’s look at just one example of the material movements that could come into play for a typical machining process. The process uses 2 components that are machined and then bolted together into a single unit. The first component is high value and is controlled in restricted inventory. Only when that part is used is the specific quantity released from the stockroom to the point of use location in the work cell. That’s done with a picking list.
The second component is lower value and is shipped shrink-wrapped on full pallets. It’s high volume so when a pallet is emptied, a new pallet is moved by forklift from the stockroom to an inventory location near the work cell and then individual units of the component are loaded into workcell flow racks at true point of use.
In this case, we have a two-step movement to get components from stores to point of use. Control of this movement could be via a picking list, a kanban, a fixed card, or managed by a warehouse management system (WMS).
The third component are the bolts which are not managed in stock at all but expensed to WIP on receipt and then held in buckets at the work cell locations. A material handler lets a planner know when the bucket is getting low – visually.
In this simple example, we have 3 different approaches to move materials and options from fully automated to entirely visual with no transactions.
Do your value stream maps distinguish how the parts move or is it magic?
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Author: Phil Coy