Often the terms of vacuum forming and thermoforming are used interchangeably but the processes may actually be different for different professionals. In general terms, thermoforming refers to any process where the plastic is in a sheet form,is heated to soften and then placed into a mold. Thermoforming is a generic term nowadays and usually includes vacuum forming, pressure forming and twin sheet forming to form a coverall type of generic molding.
Within each process there is an incredible amount of tribal knowledge and tips and tricks; too much to cover in a blog posting. As an example, the “art” in developing a good thermoforming process may involve knowledge of snap back boxes, pre heats, female versus male molds as well a large scale sheets, draw down ratios, custom heats and more. Because of the complexity, we will stick to the basics in this blog posting today – vacuum forming and pressure forming 101. We will leave twin sheet thermoforming for a different time.
Vacuum forming is taking a sheet of thermoplastic and heating it up to soften it in preparation for molding. The softened sheet is positioned over the mold in preparation to be sucked down onto the surface of a mold. Afterwords, the formed sheet is removed from the mold, allowed to cool and then readied for further finishing. The product is trimmed and any secondary operations are completed prior to shipment.
In pressure forming, the sheet is heated and positioned the same as in vacuum forming, but a second piece of tooling (or box as some call it) with positive pressure is used in addition to the vacuum to push the sheet into the shape. Secondary trimming and additional operations are the same as in vacuum forming. The softened sheet prior to shaping may be stretched prior to the operation in order to get a better wall thickness distribution particularly in areas where the sheet will be stretched over the mold.
Each process has advantages. In vacuum forming, the pressures are lower and the overall costs of molds and set ups are usually lower. The process is ideal for larger parts and runs of less than 10,000 pieces.
Pressure forming on the other hand allows for more detail and surface texture to be added to the resulting part. Some claim that the walls are more uniform with less thinning in corners. Differences in cost are highly dependent on the processor and equipment.As far as which process is better for each part that is mostly a factor of design.
One option to consider in either process is using 3D printing to quickly produce a mold. FDM 3D printers allow you to choose your part density and by selecting a sparse style you can 3D print a prototype mold/short run mold quickly & cost effectively. This “quick to completion mold” opens up opportunities for low volume production, quick turn runs, verification of design and custom vacuum patterns for hard to draw areas in the tool.
Another aspect of using 3D printing is building a pattern for a traditional aluminum sand cast thermoforming tool. The pattern can be scaled up easily in the printer software to compensate for the shrinkage ratios as well as eliminate much of the hand work and polishing needs. With fewer skilled pattern makers working today molders need to find alternatives to patterns made from wood or resin board.
3D printing is the next stage of mold building evolution. Design moves from concept to CAD to mold directly using a 3D printer. This month we will be exploring thermoforming using 3D printing as well as blow molding tooling, but if you need to hear more NOW, we have a couple of options for you. Tune in for our webinar on June 9th at 9:00 where we will do an overview of vacuum forming and blow molding tooling done with 3D printing. You can register here: https://attendee.gotowebinar.com/register/8238370521790898948
You can also contact our offices for links to white papers, technical papers and case studies. Call 866-499-7500 or email firstname.lastname@example.org and we will be happy to share information about this technology with you.