Creating Flow in a Mixed Model Manufacturing

1. Flow Manufacturing

Flow manufacturing is the best way to manufacture with the least amount of waste. Flow manufacturing is building the product in a continuous manner w/o any stoppages or bracktracking.

We should always try to create continuous one-piece flow first and when we can't flow, we should pull through a signaling method (e.g. kanban.) 
     Kanban should be seem as a temporary countermeasure to our inability to create flow  

Flow manufacturing is not a new concept. E.g. Henry Ford's 1913 factory in Highland Park with one product: Model T and no product variation at all (...any color you as long as it was black!) 
Variation killed Ford's flow concept. Customers wanted more options.
2. Flow in a complex product mix
Creating flow is not new; however, many companies struggle with implementing flow. Many lean initiatives stall after mapping. They look at the complexity of their environment. They are overwhelmed and they do not know where to begin, and too many questions are left unanswered:

- Product variety and mix

- Demand changes

I hear often, Toyota can achieve flow in a complex environment because it can level the demand for months to create stable mix for their factories. They say they can't apply lean tools of flow and pull in their dynamic environments

3. Challenges of the real factory

Very few plants can afford to purchase and dedicate equipment to each product.

Share equipment for build multiple products is common. With more new products and demand variation, complexity sets in. Better scheduling systems are added which in turn adds more to the complexity. Where is complexity?

- High product mix: products with many options, variation in lead time and cycle time.

- Shared resources: equipment. Capital intensive monuments with focus on max utilization

- Information flows: scheduling is difficult and change by the minute. constant review of inventory and priorities to adjust schedule. MRP.

4. Using Value Stream Mapping

Value stream mapping is great tool perform as follow:

Step1 - Select a product family

Step2 - Create a current-state map

Step3 - Create a future-state map using lean principles

Step4 - Implement the future state through structured continuous improvement activities

5. It looks very straight forward so why many lean initiatives stall after creating?

The difficulty lies in applying these steps in factories that have a high mix of products that must travel through the same value stream.

6. Mixed model production plant

Mixed model production means producing a large variety of mix of products or products variation through the same value stream at the pull of the customer.
Mix model is really a countermeasure to variability. We applied mixed model techniques where variability is high. Therefore, lean principles apply in a non consistent and level schedule. 
7. Product family
A product family is a determined group of products that are treated as one:

- We use the total demand of the product family rather than the individual volume for each product.
     A product family is different to a product type: wrenches and clamps can be one product family. Processes define a product family not functionality of the product.  

- Flexibility is built-in to produce the right product at the right time by increasing the number of products types in the mix and increasing the total volume: when demand is down on one product, we can build another product whose demand has increased. This eliminates overproduction & inventory while increasing delivery

     Once again, a product family is defined by the processes - common operations and their respective work content
- Any mix of products for a product family can be produced, as long as the total volume does not exceed total family volume.
The key for creating a mixed model factory is selecting the right product family, understanding the total demand for the product and treating it as one product for scheduling.

8. Creating product families
Product family is a grid that contains a list of processes (columns) and a list of products (rows.) Tips:

- When products flow from one process to the next and then back to the first process: List the process as many times as this action takes in order to show product flow

- when product must require a specific equipment. break process by equipment

- When alternative machines (could run but are not the primary choice) use "A". If there are multiple alternate processes, use A1, A2, A3, and so on.

- If product variation does not affect manufacturing processes (e.g. packaging, graphics,different languages, etc,) it may be easier to place only the base model number.

Creating family products:

- sort by similar downstream processes. Downstream, starting with the customer, the point when continuous flow must end and pull begins.

- Products in a product family share about 80% of the same downstream processes.

- the total work content of downstream process steps for each part in the product family should be within 30% of each other. Use the range of work content:

(Highest value - lowest value) / Highest value x 100