Injection Molding 101

Kevin BrookerNovember 26, 2008

Before jumping into how Nordic ski gear is made, I thought it prudent to spend some time explaining several manufacturing techniques. These methods are used in almost every piece of gear we use. While eager to start explaining individual pieces of ski gear, having the back ground and basic understanding of manufacturing techniques will keep all of us speaking the same language and hopefully give the reader a better insight into the production and hidden costs of our beloved equipment.

Don’t believe I’m pulling the old “bait and switch” when you’re looking to read about honeycomb cores with carbon fiber nano-tube matrix layup but have to start with injection molding plastics. It’s cliché and unimaginative writing to use the line about plastics from “The Graduate” but Mr. Robinson was correct; plastics are everywhere. Injection molded plastic has none of the sex appeal of carbon fiber but it is a very important part of ski equipment. Components of bindings, boots, pole grips, baskets, and many other pieces of ski equipment are all made by injection molding plastic.

In the simplest of terms, Injection Molding (IM) is forcing liquefied plastic into the cavity of a mold, waiting for the plastic to harden (cool) and ejecting the finished part. Repeat until the number of finished pieces has been made. Putting water into an ice cube tray, allowing it to freeze before popping the ice out and refilling the tray is not much different.

Len Johnson, owner of Jenex V2 Rollerski agreed to help with the How it’s Made series. In addition to explaining rollerski manufacturing, Len was kind enough to set up tours and spend a day with me at three of his vendors explaining how Jenex products come to market. One of these shops, Poly-Ject, Inc. (, handles all of Jenex’s injection molded plastics supplying Jenex with over twenty molded parts used in their line of rollerskis and tuning tools. The photos are for illustration purposes and most are not of the Jenex products.

Steve Thibeault, President of Poly-Ject, starts the tour in the machine shop where the molds are made. The mold for the Jenex split rim is placed onto a table.

Figure 1 – Both halves of the mold. The pins are retracted and the cooling ports on top have hose connectors.

In addition to the shape of the cavity, the mold contains areas for the plastic to enter and fill the cavity. Ejection pins are used to push the cooled part out of the mold and are positioned to apply even pressure, and to minimize being seen. The ejection pin marks are the small, approximately ¼” diameter, circles found on IM parts.

Figure 3 – CNC milling machine. Operator’s station on right.

The inside of the molds have an almost mirror finish which helps the machinist inspect the cavity. If any texturing is needed it is added after the polished inspection.

Steve was not sure of the exact time needed to create the mold for the Jenex split rim wheel but figured “…at least 60 hours goes into a mold of this size and complexity. And honestly, this is a simple mold. It’ll last for approximately 100,000 cycles before needing to be replaced.”

Steve brings me into the molding room to the Nigata MD385Wi22 molding machine. At somewhere near twenty feet long, eight feet tall and six feet wide I am amazed at how clean and quiet it is while operating. The air handling system for the room creates more noise and there is only a slight hint of the odor of melting plastic.

Figure 5 – Metering and additive hopper.

Figure 7 – sprue and taper.

The part is now ready to be included as a component of the Jenex line.

Figure 9 – And you thought they only made aspirin.

Kevin Brooker

Kevin is 42 years old, married with two children and living in Post Mills, Vermont. He began racing bicycles at sixteen and continued pursuing individual sports. After a six-year layoff, Kevin has returned to athletics racing in biathlon events. He has written numerous articles for FasterSkier, including a series on his return to racing and his current "How It's Made" series.

Loading Facebook Comments ...

Leave a Reply