Thermoforming - Plastics

Here are some vocabulary regardinhg the snap fit feature:

• Perimeter Snap Fit: With perimeter snap fit, the perimeter of the formed area of the front and back halves are given a draft angle and are sized so they lock together. This re-closeable mechanism resembles a dovetail joint and is most commonly used for clamshells. Similarly, partial perimeter snap fit occurs when the undercut areas on the mold are only in a few places along the perimeter of the mold. This is often a little more complicated to design and machine versus a full perimeter snap fit.
• Pushpins: Pushpins use the principal of a round peg in a square hole—they lock together using an interference fit. This type of re-closable closure can often be molded in several places on a thermoformed package where additional closure force is needed. Pushpins are the typical closure for VeriLock® and are used to supplement closure for clamshells and to re-close VeriShel®.
• RF Bar and Tear Sealing: RF bar sealing welds two pieces of plastic together using heat, pressure and radio frequency. This permanent seal, or weld, is usually made in strips, or bars, along the outer flange of a package and is regularly used on clamshells. RF tear sealing welds the entire perimeter of two pieces of plastic together while at the same time trimming. This permanent closure uses heat, pressure, radio frequency and RF tooling that has a special profile to allow simultaneous sealing and cutting. RF tear sealing provides a clean look and is often used to seal blisters and two-piece clamshells as well as our VeriMag® products.
• Label/Sticker Application: Manually wrapping a label or sticker around the edge of a closed clamshell is a permanent closure method, depending on the type of label stock and adhesive used.
• Stitching/Stapling: Stitching or stapling a thermoformed package is a simple, permanent closure method.

The so called Pushpins (locking buttons) have been around since the 70's (maybe before the 70's) much before the VeriLock patent. The locking buttons have 3 types of securing packages, mainly clamshells. The soft, hard, and permanent lock, they all have different applications and the design changes slightly, the permanent lock has a secondary operation.

For the lololamoto clamshell I would recommend the soft lock (for reuse purposes) if a frame is not going to be used. If a male/female frame is going to be used then I recommend the ClickLock, it has a single or double male/female bump(s) opposite the hinge end. Please note, for an hinge to function the clamshell has to have a male/female frame for the purpose of thinning the hinge so it is flexible enough and not to distort the package.

Thanks, but people without clamshell packaging background, therminoloy like ClickLock & Softlock doesn't means anything.

What's make them different, the friction, the geometry, the quantity, the depth....? I wonder why there is no literature on this field. There is plenty documentation on snap fit for injection molding but none on thermoforming.

Keep in mind, thermoforming is a combination of science and art, no two parts are ever thermoformed the same using the same mold, unlike injection molding where science can be applied so the outcome is always the same. Over the years I have made many improvements on existing thermoformed packages, the Box Clamshell and the ClickLock being one of them and that is why you do not see them because they do not get published. Now you know why I created this Group on GrabCad. See an example of one of my designs using a frame box clamshell with a light closing and opening. The reason of this design is so the consumer can open the package without force and be able to retain the contents (product) inside the clamshell. When a clamshell is too tight and the product is very light, in most cases the product flies and drops on the floor thus damaging it.

That is why people have to ask questions to a specific project because there are so many factors involved from light gauge thermoforming to heavy gauge vacuum forming from retail to industrial applications. In your case I could just design the clamshell for you but then you and the people from this group would have learned nothing. Asking the "necessary" questions is the key to understand thermoforming. You are almost here with your package design.

Take a look how far thermoforming can go. See one of my designs during the COVID.

www.gomaskgo.com

https://www.youtube.com/watch?v=HubZInAs0-A

All he needs is a pair of scissors to open the package. And by the way, the package could have been designed differently. One thing is right, the product is protected.

Some working principle are common knowledge and can be observe with many material i.e. Framed is more heavy duty than flat pack for sure due to stifness reinforcement done by vertical wall or even stiffer with step design as the model you just posted.

A vertical lock will take advantage from the double U hinge, because it give more flexibility (so the lock friction and tolerances is less sensitive). But such design create an important undercut that can't be mold without a moving part in the mold (like lifter, expandable cavity...).

Are the round cut on the hinge cap a plus as per the one design for injection living hinge or it doesn't mater?

Nice design. For sure we can achieve extremly intringing part with thermoforming, but thinner is the material and more accurate will be the stacking. On this project with 4mm PVC, the tolerances accumulation was a nightmare (done in Porto area by the way).

As far as the undercuts, the plastic can easily be blown off or pull from the mold with the "right" design, just round the corners to a maximum before it becomes an issue holding the package together.

The reason for the "U" shape hinge so it forms into a sharp corner and thins the plastic thus folding with ease. The "round hinge" will not do the job. And as I mention before, the height of the frame helps the thinning of the hinge. A flat package can be folded with a Die-Cut perforated hinge and female elongated cavities (soft lock) to accept the round male button.

You mean Port as in Porto, Portugal?

Forgot to mention, your package part parting line has to be offset so it does not slide out from a flat clamshell upon impact. meaning, must have a wall on the side of your part.

I have worked with thermoforming thickness accumulation, do not recommend if the fit has to be very accurate.

yes, in Europe

Northern of Portugal (Porto) exports injection molds all over the World. The professionals start at very young age, it has a very good apprenticeship program, just like me.

lololamoto, can you share your final design for further opinions?

Job on going, will post it as soon as it's done.

This is what I finally end up doing. But I really doubt to be able to removed the sheet from the mold with such an undercut. Also I am not sure the top and bottom will fit due to the hinge, I probably have to add some gap to allow the rotation of the cover to the base.

@Carlos: I change the hinge by making it opposite way to get the same bed level for both the base & Lid. Hope it will work on this way too.

lololamoto, for the hinge to work to its maximum function it has to be next to the walls so it thins out thus making it more flexible and it reduces the warping around that area and it will also allows the two halves make better closure contact.

In the next couple of days I will find some time to design what I think is the design for your part.

As far as severe undercuts in most cases it requires a removeable insert piece (cam), see your posting on page 29 of 45.

Vaccum forming guide by Formech

I think your package can work well with locking buttons. next couple of days I will design a package and get feed back from the group.

If I understand well, here is the hinge as close as possible to the wall. I'm on the good track?

Yes, double or single hinge it is best always to get it close to the wall.

Thanks, ready to print the mold and make some test to find out where are the problem.

• Retrieve the part from the mold due to undercut
• Living hinge and base/lid cover fitting

But new question raise:

How extra cm should be the sheet compar to the part on such low depth (13mm)? The thermoforming frame will be build just for this project.

Where should the air hole be done? I believed where the material can't get easily (corner, and undercut)?

Vacuum holes about 30mm apart into the corners and the vacuum drill about .75mm diameter.

It is up to you if you want to wait for my design in which will give you some tips and also simplified with a purpose.

Of course, so we can understand better the design specification of clamshell with lock and hinge, tolerances, friction... and at the end write down some rules from it.

As per your explanation, here are the pattern for vaccum holes, that make quite a lot.

Unfortunatly, the thermoforming failed. Sounds like home made vaccum works fine with very tiny PET (like 0.2mm), but mine is 0.7mm and it didn't want to be form even after melting the protection film in my oven.

you doing awesome Work.