A product family is a group of products that require similar processing steps, similar processing times, and share common equipment. Manufacturers organize their products into families, and these families define which products run on which production lines. A tight and logical product family definition is critical to your success in creating a robust flow line, which is a production line that responds to changes in mix and volume easily, with a minimum of readjustment. Failure to define your product family well leads to unexpected “surprises” when changes occur. Murphy’s Law tells us that if something can go wrong, it will, and a well-defined product family is a necessary requirement to reduce Murphy’s impact.
Product families often are not defined by manufacturing leadership teams. The sales, marketing, or financial departments have done this work, and have defined families with little or no regard to the flow of the product through the manufacturing processes. Traditional family definitions are usually based on the end-use or sales channels for the finished product, rather than the manufacturing processing paths and resource use of the products. In analyzing the manufacturing paths your products follow, you must not assume that existing family definitions have to be accepted as they are today.
1. Family members in mixed-model flow lines are selected first on the commonality of their processing paths, as defined on the product’s individual Process Flow Diagram. Mixed-model lines are designed to build a family of similar products that share common manufacturing processes. By grouping products in this manner, you can optimize resource utilization and improve production flexibility.
2. A second characteristic that needs to be examined is the process work content per product. Large differences in labor or machine times among products in the same process make it difficult to achieve a smooth work flow. Although some time differences are normal and expected in a line building a mix of products, large swings in work content cause imbalances and constraints that may be very difficult to overcome. As a rule of thumb, work content times should be within a 30% range, with no individual model being greater or less than 30% of the average time. If the work content within a family can be kept within this range, line balancing is much easier. In a later chapter, you will take a look at refining family definitions for your power tools factory based on standard work content times.
3. A third factor to be considered in the definition of product families, is the degree of common materials consumed. Each product probably has some material that is unique, but a lack of material commonality between products increases greatly the amount of physical space required for material presentation, and the complexity of that material delivery. Material handling challenges alone limit the number of different models that can be produced on the same line. Some family definitions are driven almost entirely by material considerations. High volume environments must give serious consideration to the issue of material presentation, the physical space required, and the frequency of delivery. Too much variety may force you to sequence or kit the material. Kitting materials is not a show stopper, but it does involve additional material handling and line management. Note that if ideal material presentation can improve operator productivity and reduce part selection errors, then kitting and sequencing material may be well-worth the additional effort.
Building multiple products on the same line has many benefits for the flow manufacturer. A multi-product flow line can build a wide variety of products in a small factory floor footprint. Floor space utilization is important to any manufacturer, for it alleviates the costs of brick and mortar expansion. Different products also have different sales cycles. If product lines are dedicated to a small number of products, the alternating peaks and valleys of the products’ sales cycles can lead to severe under-utilization of assets, or to the “hire and fire” cycle of operators, in an attempt to match production capacity to market conditions. The larger the number of products you build on a single line, the less vulnerable you are to swings in the sales cycles.
Producing in a mixed model mode also helps reduce daily demand variability that naturally occurs for individual products. Forecasters know this phenomenon well: the forecast for families of products is typically more accurate than forecasts for individual products. On any given day, it would be unlikely that demand for all products is up. Some may be up, others down, and when you add them together, volatility smooths out. The more products you combine on the same line, the smoother the overall demand expected on a day-to-day basis.
Objective: Group products and models by process commonality on your Process Flow Matrix. Each group will constitute a product family.
Key Result: Finalize the list of products to be included in your line design. Make adjustments to the Master Plan Workbook.