December 2011 calendar part
December's Part

The correct answer is:

b. Metallyte films reduce packaging tears and therefore keep food fresher.

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Cool Parts Calendar Tip PARTING LINES
 There are several ways to address parting line challenges Read more
KEEPING YOUR PART IN LINE When you are developing a 3D CAD model to be injection molded, you may not spend much time thinking about where its parting line will be, but it’s worth keeping in mind as the location can affect your part in several ways. On some parts the location for the parting line is obviously right down the middle, while for more complex parts it may not be so obvious. Take, for example, a simple cup. The outer face is formed by one mold half (A-side), while the cup’s inner surface and brim will be formed by the other mold half (B-side). The parting line occurs along the outside edge of the brim of the cup.

For other designs, the parting line location is not so obvious. These tend to be “free-form” shapes with soft edges. An example would be the familiar green molded-plastic toy soldiers. Most are designed to be injection molded in two-part, straight pull molds, and if you look carefully, you can see the seam around each figure where the two halves of the mold meet.

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January calendar part
January's Part

This parts application and the correct answer is:

An optical lens for a LED application

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Cool Parts Calendar Tip BEING TRANSPARENT Recommendations for coloring opaque resins Read more
Being Transparent
 After years of experience in mixing colorant into resin pellets, we have developed a new standard for the ratio of transparent colorant added to clear resins. This 1% ratio applies to all of the transparent colorants we stock, including:

Trans Red UN3012TR
Trans Amber UN2034TR
Trans Green UN6881TR
Trans Blue UN5016TR
Trans Grey UN7903TR
Customers can, of course, provide their own pre-compounded transparent resins at any color ratio they choose, and current customers who are already having parts made using a different colorant ratio can continue to do so.

The decision to standardize on a 1% ratio for transparent colors was based on experimentation at varying ratios of colorant to clear base resin. The ideal colorant ratio turned out to be significantly lower than the 3% ratio Protomold recommends for coloring opaque resins.

Our tests showed that, at ratios higher than 1%, the resulting color is too dark, particularly in thick areas, and transparency suffers. At less than 1%, the mixing of colorant into the base can be too uneven, producing a marbleized or swirling effect. This occurs because colorant pellets are added to base resin pellets to produce a “salt and pepper” mixture in the hopper of the molding press. As pellets are heated and compressed in the barrel of the press, color from the dye pellets mixes with the melted base resin pellets. When processing a “salt and pepper” colorant mix at the press, the resin only goes through one extrusion process from hopper to part through the barrel. Pre-compounded resins, where the pellets are mixed to a uniform color, go through multiple extrusion cycles to help make the color distribution more uniform. The fewer dye pellets per volume of base, the more dispersed they are and the greater the likelihood that some areas of base resin will receive little color before injection. At less than 1% color, this lack of wide dispersion starts to become clearly visible.

Note that even at our recommended 1% ratio, some color variation within and between parts can be expected. As suggested earlier, the best color consistency will always be achieved using customer-supplied pre-compounded resins.

To learn more about the “salt and pepper” process and colorant & color matching, read this past Protomold Design Tip. If you have any questions, feel free to contact our Customer Service Engineers at 877.479.3680.

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February calendar part
February's Part

The correct answer is:

Toyota Super Olefin Polymer

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What is the TSOP material used in some car bumpers?


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Cool Parts Calendar Tip THE WORD ON WORDS Text on a part deserves the designer’s careful attention. Read more
The Word on Words (and Numbers) There are plenty of reasons to add letters and numbers to a part. Text can serve to identify or brand the item, aid in assembly, or convey instructions to the end-user. In many processes, adding text to a part is a secondary operation; letters and numbers are written, printed, stamped, decaled, or otherwise appended to an existing item. In machining, alphanumeric text—either raised above or recessed into the surface—can be an integrated feature of the part. Properly designed, this can eliminate a step in production while producing clear copy that is as durable as the part itself.

In most cases, while it conveys information, text is a cosmetic rather than functional feature of the machined part. But while it serves a different purpose than other features, it is subject to the same milling standards. Because text tends to be smaller than most features, includes lots of narrow lines, points, and curves, all in tight spaces, and must be legible to serve its function, it must be designed with an understanding of the machining process.

In designing parts for First Cut’s automated machining process, you need to consider three factors. The first is the minimum size of our cutters, .020 inches. The second is the round shape of our cutters. And the third is the directions in which our 3-axis, six-sided cutting process can approach a workpiece.

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Learn more about text injection molded parts
March calendar part
March's Part

The application and correct answer is a:

Cooling fan and tunnel way for battery charger

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Cool Parts Calendar Tip LOOKING GOOD Determine just how important cosmetics will be to your design. Read more
The Protomold Guide to Looking Good First, the bad news: injection molded parts are subject to a host of cosmetic flaws including sink, gate vestiges, ejector pin blemishes, drag marks, texture flaws, knit lines, burns, flash, and inconsistent coloring. The good news is that adherence to basic design rules will eliminate many of these problems. Thoughtful planning will further reduce the risk. And judicious prototyping will allow you to eliminate virtually any avoidable problems that remain.
The first step is to determine just how important cosmetics will be to your design. In a faceplate, looks may be your first consideration. In an internal part, they may be your last, freeing you to focus on other matters like function and cost. In some cases, improving appearance will require tradeoffs, but this is not always the case. Good function and good manufacturability often go hand-in-hand with good appearance.
For example, proper attention to draft doesn’t just ensure ease of ejection; it prevents unsightly drag marks. Maintaining even wall thickness helps prevent functional weakness due to incomplete filling and poor fit due to warp, but it also helps prevent unsightly sink in thick areas and the flash and burn that can result from overly high injection pressures needed to force resin though thin sections. In short, following standard design guidelines will help prevent many cosmetic flaws.
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April calendar part
April's Part

The correct answer is:

8%

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According to the American Chemistry Council, today’s average car is what percentage of plastic (by weight)?


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Cool Parts Calendar Tip CHOOSING SIDES A-side and B-side are such fundamental concepts for injection molding. Read more
Choosing Sides When you start looking into injection molding, one of the first things you notice is that everyone talks about the “A-side” and the “B-side.” These terms refer to one side or the other of an injection mold. When a mold is manufactured to make your part, some of your part’s outer surface is created by the A-side and some by the B-side. A-side and B-side are such fundamental concepts for injection molding that nobody bothers to explain what these two terms really mean. There is a complex web of factors and consequences around which side of your part is assigned to the A-side, and which to the B-side. Understanding the implications can help you design better parts and to avoid unpleasant surprises down the road.

Most of the constraints and attributes around “sidedness” in injection molding track back two basic factors. First is physics: plastic shrinks as it cools. Second is the conventional design of injection molding machines. Almost all injection molding presses are built so they inject molten plastic into one side of a mold (conventionally called the A-side), and have the part ejection system in the other side of the mold (conventionally called the B-side). In Figure 1, the injection unit of the press is on the left side, and the clamping unit (which incorporates the ejection system) is on the right side.

Choosing Sides

When you start looking into injection molding, one of the first things you notice is that everyone talks about the “A-side” and the “B-side.” These terms refer to one side or the other of an injection mold. When a mold is manufactured to make your part, some of your part’s outer surface is created by the A-side and some by the B-side. A-side and B-side are such fundamental concepts for injection molding that nobody bothers to explain what these two terms really mean. There is a complex web of factors and consequences around which side of your part is assigned to the A-side, and which to the B-side. Understanding the implications can help you design better parts and to avoid unpleasant surprises down the road.

Most of the constraints and attributes around “sidedness” in injection molding track back two basic factors. First is physics: plastic shrinks as it cools. Second is the conventional design of injection molding machines. Almost all injection molding presses are built so they inject molten plastic into one side of a mold (conventionally called the A-side), and have the part ejection system in the other side of the mold (conventionally called the B-side). In Figure 1, the injection unit of the press is on the left side, and the clamping unit (which incorporates the ejection system) is on the right side.

One of the main drivers for choosing which side of your part is the A-side and which is the B-side is ejection. It seems plausible that when the mold opens after forming your part, it will just tumble out to make room for the next cycle. Such is not the case, however. Since the plastic shrinks as it cools, it shrinks around any convex parts of the mold, and it holds on tight. And, except for a few rare geometries, your part will hang on to both sides of the mold. Injection molding presses are designed with this in mind, though, and the press can use quite a bit of force to pull the mold open. Your part will generally stay in the half of the mold that has the most convex surface area. If that side is the B-side, no problem, the ejector system will push the part out of the B-side to get ready for the next cycle. If that side is the A-side, then everything stops until the molding process technician can figure out how to pry the part out of the A-side without damaging the mold.

Part surfaces can be extremely convoluted, with ribs, bosses, cores, through-holes and other features adding to each side’s tendency to grip the mold. In some cases, identifying the A- and B-sides requires both software tools and a fair amount of experience and intuition on the part of Protomold design staff. Even so, sometimes minor changes to the mold design or manufacturing process are required to ensure the part will stick to the B-side.

Whether you design your part to have a particular A/B orientation or simply approve the orientation chosen by Protomold, the orientation of your part to the mold halves will make a difference in cosmetics.

Depending on gate type, the A-side of a part may show vestiges of the gate, particularly if a hot tip gate is used. This is significant because the A-side is often the cosmetic side of a part, e.g., the outside of a case or shell. These vestiges can be anticipated and camouflaged or covered, for example, with decals.

The B-side will typically show ejector marks. These are usually less critical, as the B-side is often the hidden, non-cosmetic side of a part. There are exceptions—a concave plastic tray designed to be set into a surface, for example—in which case, the marks can be anticipated and treated in the same way as gate vestiges.

Your free ProtoQuote® interactive quote will provide a design analysis that will show how Protomold has decided to assign sides. In your quote, surfaces formed by the mold’s A-side are colored green, those formed by the B-side are blue, and, if present, surfaces formed by side-actions will be shades of pink. You will be asked to sign off on these aspects of the design, along with the gate and ejector placement, as part of the order confirmation process.

There is sometimes latitude in part orientation, and simple changes to your part design will often allow different orientations. As always, questions about side assignment or any other aspect of part design can be answered by our Customer Service Engineers at 877.479.3680.

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May Calendar Part
May's Part

The correct answer is:

281 lbs.

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How much did a Guinness World Record ball of cling film, measuring over 11 feet in circumference, weigh?


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Cool Parts Calendar Tip THROUGH THICK AND THIN Uniform wall thickness in injection molding. Read more
Through Thick and Thin To understand the importance of uniform wall thickness in rapid injection molding, imagine that the fluid injected into a mold is water rather than plastic resin. In a properly vented mold, the water, following the path of least resistance, will quickly and uniformly fill every nook and cranny regardless of the shape and size of the mold’s features. Resin, too, follows a path of least resistance through the mold, but in other respects resin is not at all like water. First, it is far more viscous than water and must be driven under pressure into the mold. Second, as it cools resin becomes viscous and eventually solidifies. And finally, after it solidifies—even after it feels cool to the touch—a molded plastic part can continue to shrink for hours. As a result, if a part is not properly designed a mold may be difficult or impossible to fill uniformly with resin.

In general, two types of features can cause thickness-related fill problems. The first is an “island” of aluminum, or core. This is a raised mold feature that forms a thin area in a plastic wall and through which the resin must flow. The second is an island of plastic, or cavity, a thick area of the wall that must be filled. Each represents a deviation from even wall thickness and presents its own challenges.

An example of an aluminum island is a decal recess in an otherwise uniform wall. If the recess reduces wall thickness significantly, resin will typically find a path of least resistance on either side of the recess. It will flow around the aluminum island and may fill the entire rest of the mold before backfilling the thin area. By then, the resin will have cooled, so the flow fronts that meet in that area may not fully meld, resulting in a cosmetically—possibly even functionally—compromised knit line. Also, if the thin area is not vented, it can form a “gas trap,” in which air is compressed by the advancing resin. As a gas is compressed it heats up in accordance with the ideal gas law (PV=nRT) and can “burn” the resin.

There is a simple way to create your decal recess without leaving a thin area in the wall; simply couple the recess on one side of the wall with a bulge on the other. In this way, the wall maintains its thickness and simply takes a slight detour. If the curve of the detour is smooth, the advancing resin will not slow, and the recess will fill right along with the surrounding wall area.

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June Calendar Part
June's Part

The correct answer is:

Wood pulp and are moisture permeable

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NatureFlex™ compostable films are made from these materials?


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Cool Parts Calendar Tip MACHINING: When, Why & How Read more
Firstcut Machining: When, Why & How Computer Numerical Control (CNC) machining uses programmed toolpaths to automate the motion of a machine tool. Once the required motions are programmed, the process produces (almost) identical parts quickly and efficiently. The key hurdle is in programming the toolpaths. Even with today’s Computer-Aided Manufacturing (CAM) software tools, programming the toolpaths has been time-consuming and costly, requiring a skilled human programmer to select the correct machining strategy for each area of the design. The cost of programming the toolpaths has meant that producing only a single part by CNC machining can be very expensive. Normally it takes a fair number of pieces to bring the per-part cost down to a reasonable level. It can also sometimes be difficult to find machine shops that will accept an order for very small numbers of machined parts because it ties up a scarce resource: the CNC programmer.

Our Firstcut CNC machining service replaces the costly human programmer with about a million lines of sophisticated code running on a massive parallel compute cluster (see Figure 1). Since the non-recurring “engineering” requires no human labor, a single machined part costs far less, and short runs become fast and affordable. It is so affordable that it can compare favorably with additive RP processes like stereolithography (SLA) or three-dimensional printing (3DP) while delivering a solid, rather than layered, product.

Faster lead times and low cost at low volumes are features which differentiate Firstcut’s automated machining and Protomold’s rapid injection molding. Many designers choose to machine prototype parts in the early phases of product development before molding prototypes for larger scale functional testing in later phases. But Firstcut’s automated machining is more than a low volume stand-in for rapid injection molding. The process has some capabilities significantly different than those of injection molding that make it an even more valuable addition to the developer’s tool kit.

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July Calendar Part
July's Part

The application and correct answer is:

Drive mechanism for a portable label printer

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Cool Parts Calendar Tip ROUND PARTS Keep your options open when designing round parts. Read more
Round Like a Wheel, Not Like an Egg When making round parts—gears, pistons, plugs, and anything else that needs to fit, seal, or spin—start by asking yourself just how round it needs to be. If the answer is “as round as possible,” you probably need a center gate. The reason is that, in injection molding, resin fans out into the mold from the gate. With a center gate, that means an expanding flow front that stops at the outside edge of the mold where it meets the parting line once the mold is full. In Figure 1, because filling and cooling occur at roughly the same time around the radius, the part stays as round as possible.

If you’re designing a Frisbee®, which has featureless material at its center point, gate location can be easy, but what if there is a hole or feature at the center of your part that keeps you from placing a gate there? If roundness is important, you may need to consider adding a dome that can be machined off, or a plug in the hole that can be drilled or machined out.

The alternative to adding material at a challenging center point is to place your gate off center, resulting in an off-center fill pattern and inviting potential problems. If your part has a center core and you use an off-center gate, a knit line will form where the material flows to meet around the core (see Figure 5). That knit line will almost certainly cool and shrink differently from the rest of the material. Even without a core, an off-center gate means unequal flow length as resin moves toward the edges of your part. Uneven cooling can result in a slight egg shape in the resulting part—definitely not what you want in a spinning or precisely fitted part.

A center gate on a round part is particularly important with glass-reinforced resins. The radial fill allows the fiber filler to align in the outward direction of flow like the spokes on a wagon wheel. As the resin cools, this will offset the effect of transverse/perpendicular shrink, which can adversely affect flatness.
It is important to consider your ultimate goals and keep your options open when designing round parts. While adding material (like the domes or plugs mentioned earlier) to the part may require additional processes, the benefit of uniform radial fill will help make your part as strong, round, and balanced as possible and reduce the likelihood of problems. If you have questions about this tip, or other items regarding part design for injection molding, contact our Customer Service Engineers at 877.479.3680. We will be glad to discuss the function of your part and help with design considerations.

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August Calendar Part
August's Part

The application and correct answer is:

A hand paddle for kayaking

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Cool Parts Calendar Tip RESIN FLOW Texture: When Things Get Rough Read more
Resin Flow Surface finish on a plastic part can serve many functions, from improving grip to hiding fingerprints to facilitating paint adhesion. Protomold offers seven finishes on molded parts: five polishes and two textures. The five levels of polish are created using manual mold polishing techniques; the two levels of texture are achieved by bead blasting the mold surface after applying a manual base polish.

Protomold’s available textures are light bead blast (T1) and medium bead blast (T2). Many factors can influence your choice of texture. The most obvious is the intended function of the finished part. Either texture can provide an attractive, non-reflective surface. If grip is an issue, that may influence your choice between light and medium texture. Other factors may include secondary processes to be applied to the part and the part’s esthetic fit with other components of your finished product.

The resin being used can also affect texture choice. For example, olefin resins such as polypropylene can have a waxy feel and, in conditions of high humidity, can become slippery. An appropriate texture can reduce these problems. In such cases, the ability to texture the part’s surface can expand your range of usable resins.

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Protomold surface finishes
September Calendar Part
September's Part

The application and correct answer is:

Printer head carriage for RP machine

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Cool Parts Calendar Tip RESIN COLORANT What Color is Your Prototype? Read more
What Color is Your Prototype? Injection molded parts, for all their many shapes and sizes, all start out pretty much the same—as small plastic pellets. The base colors of those pellets vary somewhat depending on the resin, but they all fall somewhere on a monochromatic scale from clear through various shades of natural to black. Turning those dull little pellets into the rainbow of colors that comes out of molding presses requires the addition of colorant, which can be a fairly simple or fairly involved process. The complexity depends on how picky you are about your color.

If all you want, for example, is “red,” Protomold can add a stocked colorant to your base resin at no charge. In fact, you can have your choice of Cherry Red, Flame Red, or Transparent Red, among others, though the exact color you end up with may depend somewhat on the shade of the base resin. If you want to see all the choices we offer, go to Protomold stocked colorants. Of course, how closely the final color resembles the color you see on your screen may depend on the screen itself, but it will certainly be red. If, on the other hand, you want a very specific color, say the blue of your corporate logo or the color-matched cap of a spray-paint can, the process becomes more complicated.

There are basically two ways to get colored injection molded parts. The simplest is to mix dye pellets into a batch of base resin pellets. As the pellets are heated and compressed for injection into the mold, the base resin and dye pellets melt and mix together before being injected into the mold.

In short, if you need approximate colors, for general appearance or any other reason, Protomold can provide a range of colorants at no charge. For specific colors, maximum consistency, and protection of specialized resin characteristics, outside vendors can provide the colored resins and Protomold can deliver the parts. If you have any questions, feel free to contact our Customer Service Engineers at 877.479.3680.


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Protomold stocked colorants
October Calendar Part
October's Part

The correct answer is:

Skylights

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The Liter of Light program in the Philippines recycles plastic soft drink bottles into which product?


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Cool Parts Calendar Tip Matched Mating Parts Two mating parts may be exactly the same. Read more
MATCHED MATING PARTS Normally, when we think of a pair of mating parts we think of left and right, front and back, or top and bottom, with the two parts being distinct from one another. There are, however, situations in which two mating parts may be exactly the same. In other words, you could reach into a bin of identical parts, pull out any two and join them. The advantages of such self-mating design include lower manufacturing cost—the parts can be made in a single mold instead of two or more—and lower cost of maintaining inventory.

Clearly, if mating parts can be made identical, it makes sense to do so. The problem is that parts with potential to be self-mating are not always easy to recognize. Their geometry can range from very simple to very complex, but one trait their assembly will always share is rotational symmetry (as opposed to bilateral or mirror image symmetry). Wikipedia describes an object with rotational symmetry as one “that looks the same after a certain amount of rotation.”

In its simplest form—a rectangular box—the part would be both bilaterally and rotationally symmetrical. With the addition of hinges at the back and latches at the front, however, the assembly remains rotationally symmetrical but is no longer bilaterally symmetrical. It is the distribution of hinge parts on the back edge and latch parts on the front edge that makes this part self-mating.

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November Calendar Part
November's Part

The application and correct answer is:

Part of a laparoscopic surgical device

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Can you guess this part’s application? Is it …


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Cool Parts Calendar Tip BOSSES – GOOD & BAD Bosses are typically used to assist in assembly. Read more
BOSSES – GOOD & BAD Princeton’s WordNet defines “emboss” as “raise in relief,” and that’s exactly what a boss is: a feature raised above a surface. In plastic parts, bosses are typically used to assist in assembly, as a receptacle for a screw or threaded insert or as the locator for a mating pin on another part.

Because of its function, a boss must have sufficient strength to do its job. This dictates a minimum size for the feature. At the same time, because a boss rises from a surface, it thickens the surface at that point raising the risk of sink or development of voids as the part cools. The challenge: bosses should be big enough to do their job but not big enough to cause avoidable sink in the surface from where they rise.

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December Calendar Part
December's Part

The correct answer is:

Military pilots

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The injection molded HANS® head and neck support device made from renewably-sourced Zytel RS polyamide is designed for use by …


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Cool Parts Calendar Tip Parting Lines There are several ways to address parting line challenges. Read more
Keeping Your Part in Line When you are developing a 3D CAD model to be injection molded, you may not spend much time thinking about where its parting line will be, but it’s worth keeping in mind as the location can affect your part in several ways. On some parts the location for the parting line is obviously right down the middle, while for more complex parts it may not be so obvious. Take, for example, a simple cup. The outer face is formed by one mold half (A-side), while the cup’s inner surface and brim will be formed by the other mold half (B-side). The parting line occurs along the outside edge of the brim of the cup.

For other designs, the parting line location is not so obvious. These tend to be “free-form” shapes with soft edges. An example would be the familiar green molded-plastic toy soldiers. Most are designed to be injection molded in two-part, straight pull molds, and if you look carefully, you can see the seam around each figure where the two halves of the mold meet.

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"Protomold was a very easy way to get injection molded parts quickly and inexpensively."

— Grant Newton, DTS, Inc.

Customer Testimonials

"Great service and quality! I'm glad to have found you guys."

— Terry Smiley, Powervision, Inc

Customer Testimonials

"Thank you for your great support and service."

— Robert Dupont, Convergent Design

Customer Testimonials

"Great company to work with! A fantastic place to start with a new product."

— Greg Amundson, CornerFlex Insta-Trim

Customer Testimonials

"AMAZING! The speed that you turned the parts around is a complete game changer. I anticipate using Proto Labs often."

— Tyler Williams, Moto Excellence

Customer Testimonials

"Protomold is the best prototype service I have ever used in 35 years."

— Bill Zuk, MAG USA

Have you ordered parts from one of our Proto Labs services, Protomold or Firstcut, and would like to nominate your part for the 2013 Cool Parts Calendar? Send us an email..