April Tip: Get a feel for texture
As illustrated in the September 2003 Design Tip, Protomold offers the following two texture options:
PM-T1: SPI-C1 (600 grit stone, 10-12 Ra) followed by light bead blast
PM-T2: SPI-C1 followed by medium bead blast
If you plan to specify either of these textures via the drop-down menus of your ProtoQuote® you need to be aware of the fact that Rapid Injection Molding requires a different draft angle on vertical faces for each of these texture options: 3 degrees for PM-T1 and 5 degrees for PM-T2.

And also keep in mind that due to the line of sight nature of the mold texturing process, it may not be possible to texture rib-shaped areas of the part design such as those illustrated in Figure 1.

Figure 1 : Example "rib" geometries that cannot be textured.

Figure 2 : Examples of texture problems
caused by variations in part wall
thicknesses.
Another thing to remember is the effect part geometry may have on the quality of the desired texture, even if the mold itself is textured perfectly. For example, a wall with greater than nominal thickness will pull away from the textured mold surface during solidification, resulting in an untextured area on the surface of the part. And a wall with less than nominal thickness will tend to adhere more intimately to the textured surface, which can often result in a flat, chalky appearance on the part. Figure 2 illustrates examples.

So there are even more reasons to pay attention to the guidance in the October 2003 Design Tip about using consistent wall thicknesses.

You can visit the Protomold Design Guide for other helpful Rapid Injection Molding design information.
April Designer Survey: What is your toughest challenge when designing a part for Rapid Injection Molding?
Design Tips were initiated to help you understand and (hopefully) live within the limitations of Rapid Injection Molding so you could take advantage of the time and money savings that can result.

We've tried to cover most of the major topics like avoiding undercuts, using sufficient draft so the parts can be easily ejected and maintaining consistent wall thicknesses to help reduce warp or sinkage. We've also touched on the wide variety of materials that are available.

As you probably know, we're constantly working to address these limitations. But just to be sure we have our priorities straight, please tell us which of these issues gets in your way the most often.
Which of the following challenges you most when designing parts for Rapid Injection Molding?
Undercuts: Avoiding them so it can be a straight-pull mold.
Draft: Insuring there is sufficient draft to eject the part.
Walls: Maintaining nominal thicknesses to maintain part quality.
Materials: Selecting the optimal resin to meet the functional requirements.
Size: Living within the maximum part size envelope.
Let us know what you think, and we'll include the results in next month's Rapid Injection Molding Design Tips.

Suggestions for future survey questions related to the field of Rapid Injection Molding are welcome - just e-mail them to us at marketing@protomold.com.
March Designer Survey Results:
We asked "How often do you buy physical prototypes of your new part designs?"

Of the approximately 200 people that responded, it looks like about 75% routinely verify their designs via physical prototypes at least once.

It's likely that a large number of these parts are rapid prototypes (RP) made using stereolithography, fused deposition modeling, selective laser sintering or 3D printing. And once the form and fit of the design has been confirmed using RP, many people then use Rapid Injection Molding to check the functionality of their part and even get them into initial production volumes (they are "real parts" after all).

Rapid Injection Molding
From your 3D CAD model...

... to injection molded parts

Real Parts. Real Fast. Real Savings!
www.protomold.com
(763) 479-3680

© 2004 Protomold

To unsubscribe, please reply to this message with "remove" in the subject line.