How to Create Perfect Plugs for Thermoformed Cups

We all know that the market for thermoformed food packaging is massive and that it continues to grow. With new developments in materials, tooling and downstream applications, we can expect to see many more containers for yogurt, water, pre-cut fruit and single-serve coffee (to name just a few).


Plugs are used in almost all tools designed for cup production. HYTAC materials are cast in sheet and rod form, with rods being used primarily in the design and development of plug assists for cups. Most toolmakers and processors will use turning machines or lathes to create conical plugs. During a recent trip, we spent some quality time with toolmakers and thermoformers to understand the challenges associated with creating the perfect cup plug.

As with CNC milling of syntactic foam, turning requires sharp, solid carbide inserts. In addition, operators need to be able and willing to adjust speeds in order to experiment with settings in order to get the optimal surface. When turning HYTAC XTL or B1X, you should see a solid, thin ribbon of scrap. Many processors choose to take advantage of the turning process in order to polish their plugs. This method can certainly impart an excellent surface finish. When using sandpaper, start with a low grit number such as 180 or 200 and then progress toward higher numbers until you are satisfied with the finish. We have seen some processors use 8 different grades of sandpaper while others use a Scotch Brite pad or Norton Scuff Pad.

After watching operators experiment with different speeds, feeds, cutters and polishing tools, we decided to review our previous guides and issue an updated version that you can download here. Our guides use Kennametal catalog numbers though others such as SGS (Germany) can also be used.

It is important that the tool holder has positive rake geometry (slanted upward at a 3.5 deg angle). Many metal cutting tools are designed with a negative rake and this does not offer an optimal finish for abrasive syntactic foam. The tooling designer and the machine operator should also confer to make sure speeds and feeds can be adjusted as needed.

Let us know what you think.