Vacuum flow is critical to the process of vacuum forming. After heating the sheet to its forming temperature, vacuum must follow immediately as the tool is raised. The vacuum pump and hoses, the seals on the table and the clamp frame all play a pivotal role in creating effective vacuum to achieve well defined formed parts.
Select the Right Vacuum Pump for Your Application
For smaller desktop machines, we recommend robust pumps that require very little maintenance, like the Formech 450DT and 508DT. Those that cope with dirt well and have a slightly higher flow rate include the Formech 508FS, 686 and 1372.
On larger floor standing machines with vacuum tanks, you’ll want a pump that can support constant use and measure oil levels, like the Formech 1250, 1500, 2440, HD & TF Series.
Use Vacuum Tanks with Demanding Materials
Vacuum tanks allow you to create instant vacuum, stored from the vacuum pump, instead of waiting for the pump to generate the vacuum. Tanks are useful when working with more demanding materials like polycarbonate and APET.
Determine the Positioning of Your Vacuum Holes
Drilled with a hand drill, vacuum holes should be positioned at the lowest point in cavities or at changes in sections. Every corner requires a hole and they should generally be spaced 25mm (1”) apart.
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The thinner the material, the smaller diameter the vacuum hole – usually 1mm diameter holes for materials up to 2mm, and 1.5mm diameter for materials above 2mm in thickness. To minimize witness marks when working with materials below 1mm, create 0.75mm or less diameter holes. Polypropylene will tend to seek out any holes or gaps in tooling, so try to keep the vacuum holes as small as possible.
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Create an Even Vacuum Flow
When using multiple tools, try to create an even vacuum flow from the main central vacuum hole on the table, to the underside of each of the tools. Use spacers for vacuum flow to raise each tool off the baseboard. Since most of our education customers are not concentrated on long production runs, they can use wire mesh, washers, thin plywood strips or double sided foam tape spacers.
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Keep in mind that raising a tool/mold off the baseboard by 1mm – instead of drilling vacuum holes all around the perimeter of the tool – will produce a much stronger vacuum flow and greater air release pressure.
If you have uniform heating and an even spread of vacuum holes, then the pull of the vacuum will be most visible, where the sheet has the least resistance.
It is easier for the vacuum to pull the sheet over a void than over the tool surface, where it will have a cooling effect on the sheet.
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Eliminate Air Pockets
High sided tools will create large pockets of air that the vacuum pump or tank will need to remove.
Any voids that contain air on the underside of the tool will also have to be removed by the vacuum system. These voids can be reduced by using blocks of wood or any solid material to fill the space.
Consider Alternative to Vacuum Holes
Positioning and deployment of vacuum holes can be a very time-consuming task requiring a high level of skill and experience. Another consideration is Alwapor, an innovative new porous resin with similar strength and robustness to aluminum yet eliminates the need for vacuum holes.
Learn more about vacuum flow, holes, pumps and tanks on Formech’s website here.
