Does High-Precision Thermoforming Spell the End of Medical Injection Molding?
When a new medical device has been created and is ready for mass production, the decision about which manufacturing process to use can be a difficult one.
Medical devices are commonly manufactured using injection molding, where molten plastic is injected into molds of steel or aluminum to create a finely detailed finished product. However, medical injection molding may become a thing of the past as a new process gains attention.
In thermoforming, a thermoplastic sheet is clamped to a frame and heated until it is soft. The sheet is then brought over a three-dimensional mold or die and pressure applied to make it conform to the shape. Often the pressure comes from sandwiching the sheet between two molds, a male and a female, a process called pressure forming.
For high-volume production of small pieces, medical injection molding is still the more cost-effective technique. However when manufacturing larger pieces, such as the housing on a piece of medical equipment, thermoforming is proving to be a good alternative to traditional medical injection molding techniques.
In the past, thermoforming processes had difficulty matching the level of detail that medical injection molding offered. Newly developed processes have allowed thermoforming to be used over much more complicated molds, including details with radii as small as 0.005 in.
For some applications, thermoforming is better than injection molding
Although in many processes thermoforming is merely as good as medical injection molding, there is one area in which it excels. Designs that involve two plastic pieces that connect through a tongue-and-groove snap-fit during assembly are quite expensive to make with traditional injection molding techniques. The undercuts required for the piece necessitate the use of collapsible cores in the molds which add time and cost to the manufacturing process.
When using thermoforming, such designs are much simpler to manufacture. With tolerances as tight as 0.015 in, thermoforming can create the precision designs necessary for a tight fit, and with tooling costs as much as 75% less than medical injection molding.
One of the reasons thermoforming has become such an effective manufacturing technique is the memory of the thermoplastic sheets, which make them want to retain their form after molding. This makes the material both elastic enough to bend when snapping together, but rigid enough not to deform under use, which would risk causing the pieces to unhook and open.
Consider all techniques
Both industrial thermoforming and traditional medical injection molding have their strengths and weaknesses. When considering the manufacturer for a new piece of equipment, these techniques and others should all be explored.
The designer of a new medical device often doesn't understand the subtleties of each manufacturing technique and which would be best suited. This is why it is beneficial to investigate a number of manufacturers and see which one can offer the best combination of cost, reliability, and expertise. The experienced manufacturing engineers can discuss the relative merits of each manufacturing technique.