Art of Simulation

Mastering mixed-model assembly with simulation

Brian Harrington  /   Apr 18, 2017

Automotive simulation expert Brian Harrington explains why tools like SIMUL8 are key to the successful implementation and ongoing performance of mixed-model manufacturing systems.

Watch the ‘Balancing Mixed-Model Assembly Lines with Simulation’ webinar for more details and learn about how SIMUL8 is used to design, launch, and improve automotive production programs.

Why is mixed-model assembly on the rise?

Today’s manufacturing lines are tasked with being more flexible to maximize profitability and efficiency. To help meet this challenge, many manufacturers now utilize mixed-model assembly. This is where a group of products are produced on the same assembly line, without long delays to change tooling.

Such assembly lines improve production flexibility, help meet the increasingly diverse needs of customers and reduce the duplication of costly resources.

It’s particularly prominent in the automotive industry, where the idea of a dedicated plant to manufacture one vehicle type is now a thing of the past. With advances in manufacturing tools and technology, today’s assembly plants are more capable of producing a family of vehicles.


“By 2017, Ford will increase its global flexible manufacturing to produce on average four different models at each plant around the world to allow for greater adaptability based on varying customer demand.”

Source: 100 Years of the Moving Assembly Line, Ford

What has led to the growth of automotive mixed-model manufacturing?

With vehicle programs costing billions of dollars to develop and launch, OEM manufacturers and suppliers are continually looking at ways to maximize efficiency to increase profitability.

The rise of mixed-model assembly can be attributed to a range of factors:

    • Shorterning vehicle development times: product and manufacturing engineers are facing increasingly shorter timescales to launch vehicle programs.


    • Increased, global competition: we are trying to beat an increasing range of competitors to market, with narrowing profit margins.


    • The need to exceed customer expectations: customers need to be satisfied by delivering high-quality products, within a reasonable time after placing their order.


  • Being flexible to changing customer demands: producing a family of products is key to satisfying the changing needs of customers, as well as meeting the increasing desire for mass vehicle customization options.


Implementing flexible manufacturing successfully using simulation

When we look at manufacturing multiple vehicles in one facility, there can be conflicting objectives:

  • We are trying to cut costs
  • We want to reduce the overall time to market
  • We are aiming to produce the highest quality product possible

As you can see, manufacturers are really tasked with doing much more for less. These competing objectives are often why simulation tools like SIMUL8 are utilized as they provide the evidence needed to reduce risk when implementing effective mixed-model manufacturing facilities.

Although mixed-model assembly has many advantages, it can increase the complexity of plant layout, logistics, and material flow. Simulation provides us with the means to prototype and test these elements to ensure that a plant has the capability to optimize inventory levels, lead times and resource utilization.


5 ways simulation can support mixed-model manufacturing planning

Discrete event simulation is a computer-based model that mimics the operation of any real or proposed system. Software like SIMUL8 enables you to easily visualize manufacturing processes. You can then quickly measure, test and experiment with any changes to your processes in a cost-effective, risk-free environment.

With the added ability to import our real-life assembly line data, simulation allows us to accurately model all the considerations, complexities, and variance involved in mixed model assembly, including:


1. Identifying and optimizing takt times / cycle times
Lean, mixed-model assembly lines are optimized to customer demand, especially the takt times needed to produce the right product mix within the right time.

Going far beyond what we could handle in precedence diagrams, simulation allows us to easily consider the effect of factors like shared resources across different processes or vehicle types, with each having unique cycle times.


2. Discovering the right product mix and scheduling scheme to maximize throughput
Similarly, we can set up and analyze different ‘what if’ scenarios and adjust our product mix accordingly. For example, producing these in a blend, a random fashion or in small batch sizes.

Simulation can test these approaches to identify which has the biggest impact on jobs per hour/overall throughput. Even an increase of half a job per hour could make a huge difference in profit!


3. Accounting for the impact of downtime, changeover times and tool set-ups
With simulation, we can use exponential and erlang distributions to calculate downtime and repair times for every task, or at station level across the assembly.

We can also do this for any changeovers and tool set-ups, so every time a different vehicle type travels through an asset that might require a tool setup or changeover; this will be accounted for in the simulation.


4. Proving the impact of new technology or flexible tools to build a business case for investment
As well as identifying where existing machinery is causing bottlenecks due to factors like changeovers and tool setups, simulation can be used to make a business case for investment in equipment that can improve mixed-model assembly.

For example, a simulation could prove the impact on cycle times of introducing a flexible tool with multiple faces; where instead of doing a full changeover, the table would rotate for each vehicle type. Rather than relying on AutoCAD layouts, spreadsheet calculations or even basic whiteboards to work through this process, a simulation can run comprehensive scenario testing in a very visual way. This allows your stakeholders and board members to see the impact of investing in new production tools and technology for themselves.


5. Comparing different routing options
Similar to above, we can test whether the manufacturing process might benefit from having a dedicated weld table for each unique product type, to completely eliminate changeovers and tool setups. Simulation can answer questions like ‘If we use parallel machines, will the sequence to get out of sync with late vehicles? Do we release one when one has a longer cycle time? Do we maintain the cycle time?’.

We can run mixed products through these routing decisions and from our simulation throughput results, we can easily identify whether or not we are going to meet the target value.


Learn more about how simulation software is used by automotive manufacturers

From these examples, we can see how simulation has become an invaluable tool for planning, testing and implementing mixed-model assembly processes.

With the ability to run an entire facility in a simulation environment, manufacturers can easily and quickly conduct ‘what if’ analysis to get the answers they need to maximize throughput in a cost-effective environment.

Take a look at our resources to learn more about automotive simulation, or contact a member of our team to arrange a demo of SIMUL8.

About the author

Brian Harrington

Brian Harrington

Brian Harrington is a Six Sigma Black Belt with 20 years operations research and simulation experience at Ford Motor Company. He designs and implements manufacturing process improvements which incorporate many conflicting objectives such as robust, flexible, and lean systems. As part of FMC’s “Advanced Manufacturing Team” he has expertise in several simulation packages, including over 20 years with SIMUL8.