Plastic electronic products with LED’s incorporated into the design can be effectively produced with two-shot molding. A translucent insert can be molded into the design to spread or colour the LED light.

The process starts similar to normal injection molding with the mold closing to form the first cavity. In this initial setting, the runner for the first cavity is aligned with the sprue of the base material, while the runner for the secondary step is sealed off. The first material is then injected and fills the first cavity.

Undercut features complicate and, in some cases, prevent part ejection. Get rid of them if you can, but maybe that’s not possible, if, for example, you need a side action, sliding shutoff or pick out. One alternative may be using sliding shutoffs and pass-through cores, or by changing the parting line and draft angles to provide an easier mold build. These reduce tooling costs as you avoid additional pieces to the mold that add to manufacturing costs. In addition to the rise in manufacturing costs of using hand-loaded inserts, this also may have an impact on your piece part price because of longer cycle times and manual mold operation.

Our helpful design aid demonstrates part features that are too thin or too thick, bad bosses, right and wrong ribs, and other considerations to be mindful of while designing parts for injection molding.

Two shot injection molding offers freedom to the designer, as it negates the use of multiple steps in manufacturing. It provides molding manufacturer with many advantages such as lower manufacturing cost, better aesthetics and ergonomics, superior mechanical bonds and lower production times. Many products, such as toys, automotive parts, medical equipment, containers and toiletries can be manufactured using this method.

Items such as toothbrushes can be perfectly molded with two-shot molding. A rigid base plastic can be used with a softer rubber second shot for better grip and coloration.

Finally, consider an overmolding option. Depending on the part, it might cost you more upfront, but could potentially save you money later. For example, overmolding a gasket on a part upfront might be an added cost, but it can save costs later from having someone install a gasket manually.

Maybe you’re designing a snap-together case for some medical components, or two interlocking halves of a portable radio. Why build two mating parts when you can make one? Redesign the snaps so that the halves can be fit together from either direction, thus building a so-called “universal” part. Only one mold is needed, saving production expenses up front. And you can now mold twice as many of one part, instead of half the quantities of two.

However, maybe your molding project calls for only a handful of parts. No worries. Protolabs builds cost-effective molds for production quantities as low as 25 pieces, often within a few days of ordering.

Pretty parts are nice, but they often require bead blasting, EDM, or high mold polish to achieve an elevated level of cosmetic appearance. This drives up tooling costs. Anything greater than a PM-F0 (as machined) finish requires some level of hand work, up to an SPI-A2 mirror finish using Grade #2 diamond buff. Avoid fine finishes such as these unless they’re required for the job. One thing to consider regarding cosmetics is to let Protolabs know if you need the entire half of the mold polished or maybe just one small area. You could save costs by only polishing the area needed versus the entire side of a mold. When requesting a custom finish, just send Protolabs a color-coded image of the critical areas and desired finish level for each area.

Everyone wants to save money on manufactured parts. It sounds simple, but one of the easiest ways to reduce price-per-piece cost in injection molding is by increasing part quantity. That is because the initial upfront cost to design and machine the mold amortizes over more parts. At Protolabs, for example, up to 25,000 parts or more can be molded from the same tool.

The molds used in two-shot molding consist of different tool sets. In a rotating platen setup, the tools share the same core, but not the same cavities. The runners must be designed as such to be shut off during the molding steps in which it is not active.

Products manufactured using two shot injection molding exhibit great mechanical properties. During the molding process, different levels of the product form a molecular bond given good material selection. This bond is often stronger than conventional molding and assembly, and even stronger than other advanced methods such as over- and insert molding.

Got a family of parts that all fit together? How about multiple molding projects at one time? There’s no reason to build a mold for each individual part, provided A) everything is made of the same plastic, B) each part is roughly the same size (e.g., have similar processing times), and C) can all be squeezed into the same cavity, while still allowing for proper mold functioning.

As the name suggests, this process makes use of two injection shots instead of just one as in conventional injection molding. A special mold is used in this process that accommodates the requirements of these two shots. The mold and its supporting systems are designed to perform two shots without having to remove the partially finished product in between steps.

Some injection-molded parts go through multiple iterations until a final, workable design emerges. Instead of purchasing a new mold for every revision, a little clever planning will allow the same mold to be used multiple times. Starting with the smallest, most basic part design, mold as many pieces as needed, then re-machine the mold to include additional part features, or a larger, taller version of the same part, and mold again. This is not an exact science, but given the right part, this re-use approach can save dollars on tooling development.

After the first step, the mold opens and the platen containing the product rotates 180 degrees on a horizontal axis to align with the sprue of the second step. In this step, the first cavity is sealed off from any injection. As the sprue of the second material is now aligned with the runner for the second cavity, the second shot now commences to mold the remainder of the product.

While injection molding may seem costly compared to processes like CNC machining and 3D printing, the ability to scale and manufacture thousands of parts makes it a cost-effective solution for mass production. Determining the cost of injection molding is a combination of several factors. The main determinant of molding cost is the amount of time it takes to produce the tooling. This means, the more complex the part's geometry, the higher your manufacturing costs will be. Simple parts, without undercuts or more advanced surface finishes, will be the most affordable.

This is where two shot injection molding really come to its own. Two-shot molding enables a production line to maufacture more complex products, with less production steps than ever before. Consider the conventional injection molding process: If a certain product was to consist of two different materials, they would have had to be molded seperately, in two different molds, followed by a manual assembly step. In two-shot injection molding, these two constituents are not only molded in one mold setup, but they are also fused together, eliminating the need for any assembly.

A deciding benefit of two shot injection molding is the saving on production time. As multiple levels of a product can be added in this process, there is often no need to do secondary assembly of the item. What would have been a complete secondary step in manufacturing with conventional injection molding, can now be done in one combined molding process.

The process of two-shot injection molding can manufacture ergonomically designed products to perfection. Structural plastic can easily be covered or added on using materials that are more suited for human interface. Soft, rubbery material is better equipped for the human hand as it provides better grip and a softer touch.

Get machined parts anodized and chromate plated with our quick-turn finishing option. Eligible materials include aluminum 6061/6082 and 7075.

When investigating manufacturing methods for a future product, injection molding professionals will quickly find that overmolding and two-shot molding are very similar processes. In both processes, molding is done in multiple steps, using multiple materials. Both processes have similar benefits as well, such as savings in time and costs on secondary assembly steps. They do, however, have enough differences to give each merit in its respective field.

Two shot molding enables the designer to utilize the best of multiple materials. Engineering plastics may have many good, but vastly different properties. The designer can combine good structural properties of a hard plastic with the soft and appealing nature of a different material to achieve the desired results accurately.

It is relatively easy to remove metal from an existing metal mold. Adding metal, on the other hand, can be difficult or, for all practical purposes, impossible with rapid injection molding. To look at this from the part perspective, you can add plastic, but you can’t take it away. Designing with this in mind is called “metal safe.”

1. Eliminate undercuts 2. Get rid of unnecessary features 3. Use a core cavity approach 4. Reduce cosmetic finishes and appearances 5. Design self-mating parts 6. Modify and reuse molds 7. Pay attention to DFM analysis 8. Use a multi-cavity or family mold9. Choose on-demand production option10. Consider part size11. Use overmolding

When considering materials to be used for two-shot molding, it is important to take the chemistry into account. Not all materials bond perfectly, but some may form a very strong molecular bond. An adhesion compatibility chart is given below.

Plastic storage containers can be manufactured with this process. Different colours can be added, along with rubbery edges to seal lids, or soft container surfaces to protect contents.

It is really situation-specific to decide which process suits a product better. Two-shot injection molding is usually a more expensive process but provides the designer with higher manufacturing precision and a better mechanical bond.

In general, two-shot injection molding requires a more complicated, and therefore expensive setup. Two-shot molds typically have a rotating platen that holds the semi-finished product. While this is a more complicated mold design, it does provide the process with higher manufacturing precision. As the product does not need to be removed and handled between steps, this eliminates human or machine error.

Overmolding utilizes a simpler mold setup, but can not provide the same repeatability, precision and process stability as two-shot molding does. The unit is the cost is however usually lower than that of a two-shot operation. Overmolding does provide the designer the ability to mold over a metal substrate (e.g. scissor blades), which makes it ideal for certain applications.

Proto Labs, Inc. 5540 Pioneer Creek Dr. Maple Plain, MN 55359 United States P: 877-479-3680 F: 763-479-2679 E: [email protected]

Every quote for an injection-molded part at Protolabs is accompanied by a free design for manufacturability (DFM) analysis. This identifies potential problem areas, or opportunities for design improvement. Insufficient draft angles, “un-machinable” features, impossible geometries—these are just a few examples in which part designs can and should be improved before clicking the “accept” button. Be sure to review these suggestions thoroughly, and contact an applications engineer at Protolabs with any design-related questions.

The plastic injection molding industry has come a long way since its beginning. It has grown a lot in terms of its efficiency and cost effectiveness, but also in new and innovative ways to manufacture products. One of these innovative ways is the process of two-shot molding. This process is sometimes known as multi-material injection molding, 2 colour injection molding, 2k injection molding or double-shot injection molding.

Always consider part extents. In molding-speak, that means how big is the part, and will it fit comfortably in the mold while allowing for sprues, runners, ejector pins, and all the other considerations needed to make a mold work. Protolabs’ maximum part size for injection molding is currently 18.9 in. (480mm) by 29.6 in. (751mm) with a maximum depth from the parting line of 4 in. (101mm) deep. However, larger parts like these, in turn, require a larger mold. This may have an impact on your mold and part costs.

Textured surfaces, molded part numbers, and company logos look cool, but be prepared to pay a bit extra for these and other non-mission critical features. That said, permanent part numbers are a requirement for many aerospace and military applications. Use a mill-friendly font such as Century Gothic Bold, Arial, or Verdana (san-serif fonts), keep it above 20 pt., and don’t go much deeper than 0.010 to 0.015 inch. Also, be prepared to increase draft if part ejection is a concern.

Two shot injection molding works well here due to the desirable properties of plastic in a water environment. Hard-wearing base areas can be combined with softer seal surfaces.

In addition, maybe you can join some of those parts with a living hinge? This method is a great way, for example, to mold two halves of a clamshell-style container. These parts would otherwise need a pin-type assembly to open and close. The only caveat here is that a flexible and tough material must be used, such as polypropylene (PP).

When compared to conventional molding and assembly, or even with modern processes such as insert molding, two-shot molding provides very accurate manufacturing. As the semi finished product does not need to be removed from the mold in between steps, there is no chance of material misalignment. If thermal effects are properly controlled through good product design, the final result can truly be as accurate as the mold itself.

Still another way to reduce molding costs, depending on your part volumes, is to consider on-demand manufacturing. At Protolabs, two injection molding service options are available (see table below). One is best suited for those who need smaller part quantities, usually associated with prototyping. The other option, Protolabs calls it on-demand manufacturing, is a good fit for those who require slightly larger part quantities, typically up to 10,000-plus parts from aluminum molds. On-demand production can be a great option to manage demand volatility of your parts, reduce total cost of ownership, and leverage cost-efficient bridge tooling.

Maybe you are after a higher volume of parts? You can still achieve high volumes using aluminum tooling with two-, four-, or eight-cavity molds depending on size and part geometry that can reduce your piece part price, although this would impact your tooling costs.

In no instance during this process is the product ever removed, shifted or moved in the mold. The final product is therefore manufactured as accurate as the mold itself, barring any post process imperfections due to elements such as irregular cooling.

Products that are manufactured in a two-shot process can look very good while also retaining the structural properties that are required from them. In this process, the load-bearing structural part can be molded in the first step while the finishing touches can be added using a more appealing material in the second step.

Our digital factories create prototypes and low-volume parts fast, while our manufacturing network, offers advanced capabilities and volume pricing.

In two shot injection molding, a product is formed by injecting two different materials into the same mold. These materials are not injected simultaneously, but rather in succession. It is, however, done in one manufacturing step in which the product is not ejected from the mold between the two shots.

Medical equipment such as bone saws can be manufactured using two-shot molding. Rubber grips are very important in the function of this equipment. Two-shot molded items also improve hygiene as there are fewer crevices where sub-parts interface, as compared to conventionally assembled items.

Tough Black (Loctite Henkel 3843) and Ceramic-Filled (BASF 3280) are two new advanced photopolymer materials now available for 3D printing.

If you need an electronics housing or similar box-shaped part, you can either sink the wall cavities deep into the mold base, requiring long thin tools to machine ribs into the mold, or machine the aluminum material down around the core and mold the part around it. The latter approach is known as a core cavity, and is a far more cost-effective method of molding tall walls and ribbed surfaces. Better yet, this makes it easier to provide smooth surface finishes, adequate venting, improved ejection, and can eliminate the need for super-steep draft angles.

In cases where adhesion combinations are unknown, an adhesion test needs to be done before two-shot molding can commence. In cases where the inherent bonding ability is not sufficient, undercuts, shoulders or grooves may be added into the design to lock the two components together.

In addition to per-unit costs, consider the material. Many plastics overlap in strength and functionality, but some are inherently easier to mold, driving down part costs. You can experiment with different materials in the interactive quote you receive when you upload your design to Protolabs.