Applying Lean Principles to Thermoforming

by Bruce Hayward

Are you still batch processing, building inventory and scrapping obsolete products? 

As a leader within your manufacturing organization I trust you have taken the "Lean Journey" and understand the principles of a lean enterprise. The days of large batch processing and building inventories should seem to be a thing of the past, but they continue to exist. Some of this could relate to the culture of the organization, however, it could be related to the equipment that you continue to buy. Within the foam thermoforming market there are two manufacturing operations choices: wide web and narrow web processing.

  Sheet Width Millimeter Sheet Width Inches
Narrow Web 400mm - 900mm 16 inch – 35 inch
Wide Web 1,100mm – 1,500mm 42 inch – 58 inch
Wide mold vs. Narrow mold
Wide mold vs. Narrow mold

Historically, wide web production process has been the predominate configuration due to the ability to form more units with a mold that is up to 80% wider. More units per cycle sounds very intriguing; after all, maximum production output is your goal. However, it is important to consider other costs including: capital, set up, scrap and meeting customer demand.

Before reading on, please keep in mind that Commodore sells both wide and narrow solutions. This includes extruders, thermoformer, molds and trim tools. We would be happy to sell you whatever you want. Also Commodore runs a foam production plant that runs 24/7 and has first-hand experience on the tradeoffs of wide and narrow sheet production. The intent of this article is to make sure you, the customer, are successful with the implementation of your project in the short and long term.

Capital Cost

The average cost of a wide thermoformer is $460k, or approximately 53% more than the narrow thermoformers average cost of $300k. Quickly you can come to the conclusion that for 53% more money you can get an 50%- 80% wider mold. This makes sense if you have one product that has enough demand to justify constantly running on the wide machine.

However, this mentality can be a trap, especially for companies with a diverse product mix that requires multiple molds and changeovers. Furthermore, it can be instant failure for a company just starting to serve a new market.

The cost of tooling needs to be considered when looking at total capital expenditures. Consider the cost from a recent proposal that included nine molds, which was comprised of two meat trays, three absorbent meat trays and four hinge lid tools.

  Wide Sheet Proposal Narrow Sheet Proposal
Mold and Trim Tool Cost $922k $395k
Thermoformer Cost $460k (1 Thermoformer) $600k (2 Thermoformers)
Total Capital Cost $1,382k $995k

The wide molds cost more than twice the cost of the narrow molds. Add in the cost of a thermoformer to the molds and it will become apparent to the capital cost tradeoffs. The narrow sheet scenario has a lower capital spend, but is able to run two thermoformers while the wide solution is limited to one. To further make the point, if capital spend was kept the same, a third narrow thermoformer could be purchased, adding even greater flexibility. This would allow for three different products to be produced at the same time, eliminating the need for large batches.

The argument can be made that the wide thermoformer can produce more when it is setup but this leads us to the next discussion of the time it takes to set up a wide versus a narrow sheet machine.

Set up

When considering the physical size of a wide mold it takes extra effort to safely handle the setup of the mold and the trim tool. Quite often fork trucks, hydraulic lifts and/or overhead cranes are required. In comparison, push carts and manual lifting can accomplish a changeover on a narrow thermoformer. One can argue that principles of SMED (single minute exchange of dies) can be incorporated and should be encouraged to embrace lean. However, once the tools are in place, the effort to make sure all cavities are forming correctly and the trim is accurate takes greater effort for wider sheet because the greater number of rows and columns. We find that the efforts to setup a narrow mold versus a wide mold with additional cavities are not a linear effort but more of an exponential effort. Dependent relationships of managing temperatures of sheet/mold while ensuring forming accuracy can be challenging when dialing in seven cavities in a row versus four. The same holds true for a seven up mold (seven rows) versus a four up mold. Constraints can continue to build if shear keys are required for hinge lid lunch boxes.

Scrap

During set up, efforts are taken to optimize the process on the thermoformer to make sure all cavities on the mold are formed and trimmed accurately. During this time scrap is being generated. Not to say that scrap is not being generated with narrow sheet but the time it requires to optimize all the cavities is exponentially greater based on the number of cavities. The simple analogy, it is easier to juggle 3 balls than it is to juggle 5 balls.

Machine Footprint

Due to the physical nature of a wide thermoformer the footprint is going to be much larger requiring greater factory space. The picture below reveals the difference in size of the trim press. In an effort to understand scale, the two layouts demonstrate the variations in size of an entire thermoformer.

Wide vs narrow trim press
Wide web application on the left and narrow web application on the right.
Diagram of wide and narrow machine footprints

Mold Storage Space and Material Handling

Storage requirements for wider molds are going to be greater due to the size difference. Fork trucks will be required for the larger molds while some of the narrow molds can be managed with carts.

Storage of Finished Products

Perhaps old school batch processors can argue that once the wide job is set up several weeks' worth of inventory can be produced and stored.  This mentality would require significant amount of warehouse space for storing the inventory. In addition, the risk of damage by the constant traffic generated from storing batched products also increases. Furthermore, a quality defect could be detected after the large batch has been produced requiring the batch to be scrapped. The above thought process goes against the lean principles of pulling product through production to ship to the demand of the customer.

Extruding wide versus narrow sheet

It's also important to look upstream from thermoforming to the extrusion process. The capital cost of producing wide versus narrow is not significant enough to make an argument. Making a wider sheet has challenges associated with managing surface finish uniformity and flatness. The exponential factor also applies to extruding a wider sheet when it comes to set up and scrap. Also the rolls are larger and heavier which would require equipment for material handling. Storage of the larger rolls would require greater space due to physical size but also to support the large batch runs required to feed the thermoformers.

Today's Business Challenges

Perhaps you may be fortunate that your business only runs 3 or 4 different products and your machines are constantly set up with the same job. I congratulate you for being able to secure this business for at least the short term. I don't see this scenario being sustainable based on the business our foam plant supports nor do I see this at the customers I visit around the world.

Having a nimble production process that allows for multiple machines to run different products in parallel while quickly changing over products to meet the demands of the customer is the key to developing a lean enterprise.

I trust this break down can help you in the future when evaluating the tradeoffs of wide versus narrow production. I welcome you to contact me if you would like to have further discussion on how Commodore can help improve your performance.