6 Sigma Series: Using process mapping and value streams to identify problems

Identifying problems in Six Sigma starts with a very AS-IS detailed process map (as discussed here). For each step in our process maps, we should be adding:

  • Operation time + variation time (standard deviation).
  • Resources used in the process element: human, financial and natural.
  • Process step value: VA (Value Add) or NVA (Non Value Add).
  • Cost of resources consumed: personnel, facilities & material.

To further aid our identification of issues, we can use SIPOC (Suppliers, Inputs, Processes, Outputs, Customer). We can define each as:

  • Suppliers: the people that provide the materials consumed by the process.
  • Inputs: the ‘stuff’ that the suppliers provided.
  • Process: the actions taken to transform the inputs.
  • Outputs: the product or service resulting from the process.
  • Customer: the recipient of the process output.

From the SIPOC, we can start thinking about generating a VSM (Value Stream Map), which is an end-to-end chain of activities, events and processes required to deliver the output product. A VSM helps us to visualize the customer requirement, all the way through to the output.

4

KEY:

Task stats include:

  • Cycle time
  • Number of operators
  • Inventory
  • Reliability
  • Yield

Box score includes:

  • Scrap pieces per hour
  • Total value time
  • Total non-value time
  • Total lead time

You’ll see in the above diagram that we have a timeline with steps in it. The steps represent waste or waiting time.

 

Areas for improvement:

The below are potential areas for improvement in many processes:

  • Reduce / eliminate waste or waiting time.
  • Balance cycle times with Takt time:
    N.B. the cycle time is the time taken for the process to complete. The Takt time is the time required to deliver to customers’ expectations. To minimise waste, we should ensure that the cycle time = the Takt time. This should be adjusted for process efficiency. If we see an 80% process efficiency, then we should build a 20% buffer into the Takt.
  • Remove bottlenecks.
  • Increase / decrease inventory.
  • Speed up changeover time (the change from producing one component to another).
  • Optimize the physical layout of the flow.
  • Standardize processes and work methods.

 

Content based on study of the Six Sigma Black Belt course and Six Sigma for Dummies

Kieran Keene

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