Don’t scrap that old mold! You could rebuild it with collapsible core tech

Collapsible core technology is a method for removing internal undercuts in parts, and is used primarily in caps and closures, plumbing components, and the medical industry. There are two types of collapsing cores: mechanical and flexing steel. The collapsing segments are either driven inward by dovetail-type flanges, or flexed inward with a spring force that allows it to collapse. 

But even though collapsing cores have been around for 30 years, the technology was never commercially successful, explained Hickok. What’s changed to cause the current resurgence?

Two things, said Hickok. “We’ve had tough economic times and people have challenged how things are made. ‘How can I get my profits back up?’ they’re asking. We’re starting to challenge traditional methods of mold manufacturing if a part has to be unscrewed. The bad news is you understand your costs and limitations with unscrewing molds. The good news is you understand your costs and limitations. What are you going to do different? This is pushing people to try technology they haven’t tried before."

The second factor has been the successful commercial development of Progressive's Dove Tail-style core. By having a cost-effective mechanical collapse option, some of the resistance and industry perception issues have been removed.

Typically, when mold designers look at the parts, they decide how to strip them out of the tool. Cycle time is considered. “They want to run the mold fast so is there an alternative to unscrewing molds,” said Hickok. “However, if you do a pie chart on how parts are made, a very small piece of that pie will use collapsing cores. If I can’t jump it or use an unscrewing mold, then I’ll use collapsible cores, so it’s a technology used reluctantly. It’s a perception in the industry that using collapsing cores is a technology of last resort.”

Benefits of collapsing core technology
1. Simplified system design. It eliminates a lot of parts, is simpler, and is flexible for cavitation layout. If, for instance, you’re molding a 28-mm cap in a 24-cavity mold that’s 14 by 9 inches wide and you want to use smaller press, it’s worth looking at it.
2. Simplified mold setup. This is often overlooked, but users say it’s one of the biggest benefits. Unscrewing molds are large; collapsing core molds are short and compact, and have a square design and an easier setup.
3. Multiple sequencing options. The Dove Tail core uses a simple two-stage ejection (watch an animation of the ejection). People have different preferences in hydraulic cylinders, servo motors, and so on, and there is significant flexibility in that area.
4. Less maintenance. It reduces the number of components, prevents oil leaks, and allows for in-press service time, thanks to a quick-lock feature that gives access to cores in the molding machine.
5. Different parts can be run in the same mold. For example, a tamper-evident-cap mold built by Tech Mold Inc. (Tempe, AZ) runs a standard cap and a thin-wall cap in the old mold base (see case study below).
6. Improved quality. Jump-thread-style molds can cause stress whitening and ovality, while unscrewing molds commonly have thread damage, in particular at the thread run-out. With collapsing cores, the mold gently moves away from the undercut and as a result, puts a lot less stress on the part.
7. Improved part design. Collapsible cores allow you to add features to the part and thin out the wall sections without needing an anti-rotation feature. “When you unscrew a cap, you have to run the thread all the way out to the top of the core, and this creates a very thin steel condition. With collapsible cores, you can stop the thread short and round it off, which saves a thin steel condition," explained Hickok. “With respect to jumped parts, as a general rule, if the ID of your part is less than 28 mm, it becomes difficult to strip. Also, a large radius on the threads is required for release from the tool. This limits the depth of the thread you can remove and therefore the amount of engagement with the bottle or other mating part.”
8. Reduced cycle time. With an unscrewing mold, the part wall thickness must handle the torque when releasing from the core. Collapsing cores move away from the undercut, putting less stress on the part. This means a warmer part can be ejected, which reduces cycle time.

The Dove Tail in action
One of the major uses of collapsible core technology is retrofitting older molds, says Progressive. This helps reduce costs by eliminating the major financial outlay for an entirely new mold. Rebuilding the B half of the mold with collapsible cores enables a molder to replace an old, tired mold with the new technology while keeping the A half in place.

Roehr worked with Tech Mold in modifying a four-cavity conventional strip mold for a tamper-evident closure. One of the cavity stacks was replaced with a Roehr Dove Tail Collapsible Core to demonstrate the technology at the recent K show. Phil Estrada, quoting manager and technical sales engineer for Tech Mold, says the company is in the early stages of working with Progressive and Roehr on collapsible core technology. “I don’t believe anyone has produced this particular type of closure with a Dove Tail core before,” notes Estrada, adding that there were several goals that Roehr wanted to achieve on this project.

First, it wanted to prove that a tamper-evident band closure could be molded with Dove Tail cores. Secondly, the demonstration showed that Dove Tail Collapsible Cores are interchangeable with the type of actions existing in the mold and can provide a simplified solution for producing tamper-evident closures. It also showed the ease of changing out the B half and installing collapsible cores. Dove Tail cores are replaceable from the parting line of the tool, which further simplifies changeovers on converted tools.

Dove Tail collapsing cores also eliminate unscrewing mechanisms and slides, and allow for undercuts in the part that couldn’t be molded conventionally. With the move toward thin-wall caps and closures to save money, the demonstration showed how the technology allowed the molder to make a thin-wall, tamper-evident closure since all undercuts are cleared before the closure is ejected off of the core.

“Normally you would need a thicker wall section to avoid damage to the closure’s features,” says Estrada. “Changing over an older unscrewing tool so that you no longer need the unscrewing mechanism can result in faster cycle times and simpler tool changes on the B half while retaining the existing A half. It also means that traditional areas in the mold that may have caused maintenance problems are eliminated.” —Clare Goldsberry