TPE Injection Molding

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TPE Injection Molding – Thermoplastic Elastomers

Flexible thermoplastic elastomers are molded with plastic injection molding with Rebling for a wide range of applications. The ability of these thermoplastic materials to be processed by conventional plastic injection molding machines and their inherently short cycle times compared to the cure time of thermosetting rubbers has provided engineers and designers with a cheaper alternative when defining flexible plastics. In addition, there are standard compounds that provide mechanical properties, hardness, chemical resistance and elasticity that are not available with thermosetting rubber.

Molds for thermoplastic elastomers or TPE injection molding parts such as cable strain reliefs, over-casting of handles or other components, airplane helmets and medical devices.

Properties Of Thermoplastic Elastomers – TPE injection molding

The TPE injection molding is available in durometers which are generally between 30 and 95 on the Shore A hardness scale, depending on the class of material selected.

These flexible resources, commonly referred to as TPRs or TPEs, typically fall into four classes of thermoplastic materials: polyester copolymers olefin; polyurethane; and styrene block copolymers. PVC is another option for flexible thermoplastic materials.

TPE injection molding
TPE injection molding

Two types of styrene elastomers are available for plastic injection molding. The styrene-ethylene / butylene-styrene (SEBS) block and the styrene-butadiene-styrene (SBS) block. Trade names for these materials include KRATON® D and KRATON® G. Elastomers of the SEBS block have higher temperature resistance and resistance to longer outdoor exposure, while the SBS block should be restricted to indoor applications. Both types are resistant to water, acids, and bases, but are both attacked by solvents. Both types can be formatted in different colors.

Polyurethanes are known for their excellent abrasion resistance and load-bearing capacity. Polyester, polyether, and polycaprolactone based urethane grades work well in the plastic injection molding process. Polyester types have better mechanical properties, while polyether types have improved low-temperature properties and hydrolysis resistance. The polycaprolactone group offers better hydrolysis resistance than polyester-based urethanes while providing similar mechanical properties.

All urethane can be molded in a wide range of colors and is available in a variety of grades for special applications including flame-retardant materials.

Olefins have the lowest density of all thermoplastic elastomers. DuPont Engage® is an example of this material that is available in pure and color quality. Olefinic offers excellent flexibility at temperatures as low as -60 ° F.

Polyester copolymers provide flexibility and fatigue over a wide temperature range. DuPont Hytrel® is an example of this type of elastomer. This group is generally priced higher than olefin and styrene-based elastomers.

Guide To Thermoplastic Elastomers

Authorized design engineers have extensive experience in optimizing the design of plastic parts in terms of functionality, cosmetics, cost, and processing. As with other thermoplastic materials, the preservation of the entire wall thickness is essential for the production of aesthetically pleasing castings. Ribs and inserts must be used to prick thick sections. The thickness of the ribs shall not exceed 50% of the wall thickness. Built-in bosses can also produce sinking signals if not properly designed. In order to minimize and eliminate these issues, construction engineers should be consulted before the final plan is issued. This design planning is provided free of charge.

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Plastic Injection Molding And Mold Polishing

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The business of plastic injection molding is mostly scientific and technical, yet there is this element of undefined experience that can only be termed “black art”.  Mold polishing seems to fall into this category for many engineers and mold techs.

If the part has blemishes of one sort or another, or is sticking in the cavities, or maybe not filling properly, very often the solution is related to the surface finish.

This is often overlooked, which is unfortunate because it is much less costly than a major engineering change, for example. When the process has been tweaked over and over again, maybe take a second or third look at the mold polish, it could hold the answer.

Learn more about plastic injection molding and mold polishing.

Plastic Injection Molding Machines

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Lately, I have noticed a trend in which companies gradually reduce their plastic injection molding machine supplier base to just one company. This makes a lot of sense, in many ways, yet it also is limiting in other ways.

Sure you can get great discounts by buying several machines from the same supplier, such as Engel,  but once you get more or less into a mono-culture, you miss out on the innovations of other companies.

This presents somewhat of a dilemma for companies however. Perhaps one way to deal with this issue is to have various brands on the floor, each specializing in the things they do best. Hydraulic vs. electric, rotary presses, vertical, or stack molding presses are some examples.

Learn more about the injection moulding of plastic parts.

Tip For Better Plastic Injection Molding

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A small, but very effective tip for easier plastic injection molding set up is to standardize the clamping slots on the top and bottom plates of all mold bases. This little trick might seem obvious, but it is surprising how many custom molders have every size imaginable in their mold base inventory.

With this method you need only one size clamp, which can be custom made or likely purchased. The set up techs won’t need to be fumbling about for the right size clamp, there will be no shims under clamps and you can be sure the molds are held in place securely.

This is also a good idea from the standpoint of training. There is enough to learn without adding another item to the list of how to set up a plastic injection mold. Once this is in place, it will quickly become a SOP, standard operating procedure.

All your future designs must have this incorporated, which, for some reason, is not as easy as it might seem. You likely will still have the occasional mold that comes in the wrong size, but in time they will all be standardized.

Learn more about plastic injection molding and injection mold making.

Plastic Injection Molding Bosses

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Have you ever had an awesome boss while working in anything related to plastic injection molding? Since I have been in this business, which goes back to 1978, I have had quite a few good and some less than good bosses.

One excellent boss I had in a plastic injection molding company was from Switzerland and his name was Karl. Every day he was immaculately dressed and on top of everything that went on in every aspect of the company. It took me a long time to get hired and I knew I was in for a real experience, but I wanted to learn my trade from the best.

The very first day I was standing with the foreman looking over some prints. There was no heat on because it was early spring, so the shop was pretty cool. I had my cold hands in my shop coat pockets when Karl spied me. He marched right over, yanked my hands out from my pockets, and proceeded to slap them, telling me to “never put your hands in your pockets!”

I should have known better, having lived in Northern Europe for a few years, but, hey, it was cold! In the end, we became good friends and I did learn a great deal of craftsmanship from this old schoolmaster.

One of the nicest I had was an elderly man who had the unfortunate bad habit of smoking and drinking coffe all the time. This was back before the days of no smoking in the shop, so his fingers were actually yellow from the smoke. What made him nice was that he was so patient with us apprentices, but what made him almost intolerable was his breath!

He used to come up to each of us every morning to greet us and give us an assignment or check on our work. That is when his kindness became his curse. Because he was only inches away from our face we just had to eventually breathe in his absolutely horrible stench of a breath! More than one guy actually gagged and nearly vomited!

Another boss I had was a Russian who grew up in the German part of Brazil.  He could speak so many languages and seemed to know a million people. He was great because he took the time to explain things without making any of us beginners feel like idiots.

What about you, do you have any stories of a good or bad boss in your plastic injection molding or mold making career?

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