When designing a new factory, production line or manufacturing process, a critical measure of success is demonstrating that the shiny new design fits the brief.
Several key questions need to be proved out…
- Will it produce the required target volume within the specified time?
- Can it achieve the right product quality?
- How will the design perform with different products and product mixes?
- Is the design resilient and robust?
- Does the design meet the needs of the customer?
Coupled together, this asks – can the design meet the target capacity?
Getting plant capacity right can be like walking a tightrope! If production is under utilised and capacity not maximised the business will experience low profit margins and a poor ROI. Conversely, running the production over capacity will lead to poor reliability with frequent equipment breakdowns, failures resulting in lengthy downtimes and lost throughput.
Over the years, I have witnessed the demonstration of plant capacity calculated by simply attempting to add the capacity of individual processes or unit operations. This over simplistic approach is prone failure since the reality is that the real rate determining step is always the weakest link in the process chain, the bottleneck, the piece of equipment with the lowest production capacity. However, there are other factors which should be considered and factored into any calcs.
What is the process equipment’s availability to do work?
How often is the process, plant or equipment actually available to do valuable work? This should factor all scheduled downtime for maintenance and repair and make allowances for any unplanned downtime due to equipment failure and breakdown. Some processes require start-up periods, staged shutdowns and product changeovers all of which must be factored in to the plants capacity to do work. The actual availability for productive work is therefore what was planned in production minus any unplanned stoppages or shutdowns.
It is worth mentioning that many manufactures use OEE (overall equipment effectiveness) as the benchmark and baseline metric for performance. This is the percentage of planned production which is actually productive. The OEE calculation take three main losses into account, losses due to availability, performance and quality. Calculating the availability loss takes into account both the scheduled stops plus anything which stops the planned production such as equipment failure or waiting on raw materials, labour or transportation.
How do different products perform in the plant equipment?
Most production lines will manufacture a range of products all with differing specifications and tolerances. All will require different amounts of processing, utilise all or some of the operations and may require processing in different orders. The planned schedule for production of the order of products and customer demand plays a significant role on the overall capacity of the plant. For example, some processes operate on a seasonal basis with some product types in high demand at certain times of the year.
What is the range of operating conditions for the plant equipment?
Many process operations have specific settings depending on the product type, this could be furnace temperatures or dwell times. It could be cutting speeds or mixing residence times. The specific operating conditions that are product dependant should to be included in any capacity calculations.
More often than not, when conducting those all important capacity calcs, spreadsheets come to the rescue. These are great for basic modelling for capacity calculations and have long been the mainstay for engineers and project managers. The main drawback of spreadsheets is that they are static in their nature. Processes however, are dynamic beasts with complex interactions all of which affect the overall process performance. Spreadsheets become complex and can be prone to human error. Furthermore, convincing the stakeholders that the design meets the scope and is value for money is a difficult exercise, especially if with data inserted into PowerPoint!
Simulation for Design
Rather than crawling over spreadsheets, the PS56 team work alongside engineers to create a computer model of their design. The model provides a dynamic working visualisation of the design, simulating the flow of materials through the process. Virtually any scenario can be tested to assess how production plans, product mixes, resource constraints or equipment reliability impact performance and capacity. The model effectively stress tests the design. It provides a platform for the engineer to test and validate changes within the simulation. This is a powerful way to validate the design, generate consensus and acts as a great way communicate the design to the stakeholders.