Injection Molding vs Thermoforming Plastic

Plastic products are so common nowadays that you can find products made via plastic in nearly every store you walk into.  Walk down the electronics aisle of any retail store and you are bound to find USB drives, memory cards, webcams, headphones, speakers, etc all made from plastic.  Usually these products are all made via injection molding but, they are generally packaged in a thermoformed blister pack or utilize some other type of thermoformed packaging on the inside to help hold the product in place inside a bigger container such a cardboard box.  Generally speaking, if a plastic product is small, has multiple moving parts and has intricate geometry, it is more likely than not made via injection molding.  Likewise, unless we are talking about packaging like what I mentioned above, products that don’t have lots of moving parts, are simple in shape, are larger with less intricate geometry, etc. many times are thermoformed.  Below are some examples made from each process:

Injection molding:

• Phones
• USB dongles
• small flashlights
• action figures
• toy cars
• toy kitchen sets
• toy airplanes
• Printers
• computer parts
• radios
• Legos
• RC cars

Thermoforming:

• Packaging
• Playground slides
• Sleds
• Protective Covers
• Dunnage containers
• Fenders
• Bumpers
• Food storage containers
• Skylights
• Silverware trays
• Seats
• Radomes
• ATV parts
• Lawnmower parts
• Halloween masks
• Car top luggage carriers

The above lists of plastic parts are an extremely small sampling of what is being made via thermoforming and injection molding.  You can view a small sampling of what Arrowhead has made via thermoforming by clicking here.  There are other processes as well for molding plastic, but these two are probably the most versatile.

Generally speaking, parts produced via injection molding are going to be the least expensive parts to purchase.  So why on earth would anyone ever look at having a plastic part thermoformed?

Unfortunately, injection molding does have some disadvantages:

• Tool Cost: The initial investment to buy an injection molded tool is often times 8 to 10 times more expensive than thermoform tooling.  Thus, it typically doesn’t make sense to injection mold a part until the part design has been perfected and the sales potential is very strong. Similarly, the cost to scale up and produce a tool that makes multiple parts a time is very expensive.
• Part limitations: Parts that are extremely thin and parts that are extremely thick cannot be produced with injection molding.
• Tool size/weight: Injection molds are large, heavy and usually require forktrucks to move
• Molded in stress: Injection molding also introduces some stress into the part thus making it more susceptible to warping at elevated temperatures as compared to a thermoformed parts.
• Surface cosmetics: Switching textures in injection molding is a very costly, time consuming process as the surface off the mold has to be changed.
• Laminates and graphics: It is not possible to apply laminates to injection molded parts.  Thus, any decorating or graphics have to be done post molding and require a secondary process such as painting

So do these disadvantages also affect the thermoforming process?

• Tool Cost: Relatively speaking, thermoforming is the most the affordable method of producing plastic parts to tool up for.   Very simple tools made from inexpensive materials can be produced to test out a part’s design.  Everything from wood and urethane to fiberglass and aluminum can be utilized…it just depends on how many parts are needed off the tooling and how critical the part geometry is.   Furthermore, modifying a thermoforming tool is almost always much cheaper to do than modifying an injection molding tool.  Thus, it is usually a good idea to look at utilizing thermoforming in the early stages of product development and product launch.  After the design has been perfected and sales potential is strong, it may be time to start looking at injection molding to increase margins…assuming the part can even be injection molded.  Or, before taking the fiscal plunge into injection molding, it make make sense to look at scaling up and making a tool where one tool makes multiple parts at a time.  This is another way to increase output and cut down part costs in thermoforming.
• Part Limitations: For the most part, thermoforming is not limited by the same limitations in regards to thickness that injection molding is.  Parts as thin .010” or less can be thermoformed and parts as thick as .600” can be thermoformed.  The real limiting factor on starting sheet thickness for a thermoformed part is the capability of the sheet supplier.  Arrowhead partners with a group of sheet suppliers who are constantly on the cutting edge of product development and are always pushing the envelope in regards to sheet thickness and types of material available.
• Tool size/weight: Relatively speaking, thermoforming tools are much lighter than injection molding tools….especially when Arrowhead’s proprietary Eco-tool© is utilized.  This type of tool allows can be run on high volume rotary machines (usually only aluminum tools can), yet are much lighter and much more affordable than aluminum.
• Molded in stress: Thermoforming doesn’t require the plastic polymer reach the same temperature as an injection molded part.  In injection molding, the pellets are heated until they are molten and then they are injected into a mold cavity where they take the shape of the cavity and they are quickly cooled down with cooling lines.  This can lock in stress.  With thermoforming, a hot sheet of material is heated until it is malleable.  It is not heated until it is molten.  The sheet is then placed over a mold and the sheet is pulled against the mold surface via vacuum. The part is then cooled down with fans on the top side and sometimes cooling lines on the opposite side.    This results in a longer cycle time, but also allows the material to cool slower alleviating any internal stresses.  The process more closely resembles annealing (heating something up and cooling slowly to relieve internal stress)  than injection molding does
• Surface cosmetics – With thermoforming, it is very easy to switch the textured look of the surface of a part. This comes at no extra tooling costs and at many times no extra cost in regards to the part pricing.  Read more about switching textures on thermoformed parts here.
• Laminates – Thermoforming has a unique advantage over many other plastic processes in regards to laminates. Decorative films and laminates of all colors and types are available.   Many of these laminates are formable.  Furthermore, sheets of plastic can have a pre distorted image on them.  This image looks normal once the 2D sheet of plastic is formed into a 3D shape.  For instance, a pre distorted image of a face could be printed on a sheet of plastic.  That sheet of material could then be formed over a tool that is in the shape of the face and the image would thus come out to look as if the image was painted on the part after it was formed.  A good example of this are the plastic Halloween masks you see depicting past Presidents, celebrities, etc.

As you can see, thermoforming is a very unique process allowing many advantages over other types of plastic molding.  Thermoforming used to be referred to as a “black art” and is one of those plastic molding processes that many people don’t realize is available until they have already learned about other, more well-known processes.  However, the days of thermoforming being a black art are over.  The molding process has evolved in a way that allows thermoformers to produce parts with geometry, textures and looks we never thought was possible 20 years ago.

Sometimes due to geometry or other factors, the only way to produce a part is with injection molding.  Likewise, at times, thermoforming may be the only feasible way to produce a part.  Other times, a company will want to move to injection molding after a market has been established, a design has been proven and sales potential warrants the large initial investment.  But, until those criteria are met, prototypes and production parts usually have to be made in order to get the project started.  Thermoforming allows for the prototyping, initial product launch and initial production runs to be produced in an affordable and expedient manner.  For a little bit more info about Arrowhead’s thermoforming plant, click here.  Likewise, for more information about our various methods of thermoforming we utilize, please visit our “thermoformed plastic processes” page by clicking here.

Unsure of whether thermoforming is a good fit for your part?  If so, give me a call and let’s talk about it.