Solutions Current Issues > April/May/June 2008 > BENNY & BRUCE
Email LinkTHE MOLD MAKER’S ROLE IN DESIGNING FOR MANUFACTURABILITY
BRUCE: Hey, Benny, I asked Dave Johnson to join us today to talk a little more about designing for manufacturability.
BENNY: That’s cool. You and I talked before about using Pro/E’s visualization tools to create virtual prototypes, and how we use other tools — like MoldFlow Plastics Adviser — to analyze designs before manufacturing. We can talk with Dave about modules like Pro/Mold Design, Pro/NC-Mill and Expert Machinist that help with tooling and mold-making.
DESIGNING WITH THE MOLD IN MIND
KEY ISSUES
- Location of Parting Lines
- Depth & Number of Undercuts
- Radiused Corners
- Thread Design
- Stack Tolerance
- Locator Pins
- Material Shrinkage and Expansion
BRUCE: Right. A lot of our customers ask us to help them cut costs and shorten production cycles because they know we understand the entire process. And with all his experience in manufacturing — most of it in the tooling and machining trades — Dave definitely knows how to make design improvements that matter on the production line.
BENNY: Hey, Dave! Thanks for joining us. We were just talking about your background, and how valuable it is to have you managing our Rapid Tooling Center.
DAVE: Thanks, Benny. And thanks for having me. You know, it was exactly one year ago this month that I was your guest for this column.
BRUCE: That’s right! So Dave, let’s get right to it. As engineers, many times … well, okay, most of the time … once we finish designing a part, we’re pretty confident it’s right. And some of us can be a little sensitive about making any changes. Not me, of course. And not Benny. Actually, not any engineers I know. But it could happen.
DAVE: Oh, sure. In fact, I can’t say I’ve ever seen either one of you react to having to change one of your designs. Not that I haven’t seen you — just that I can’t say!
BENNY: Busted! But egos aside, part of what RL Hudson’s customers expect us to do is help lower costs and improve their speed to market, and the only way to do that is to make sure their parts and assemblies are designed for both effective operation and efficient manufacturing.
BRUCE: And the best way to do that is for the design engineers to work with the mold makers from the outset. After all, from a cost perspective, 70% of the cost of manufacturing is determined by the design, right Dave?
DAVE: Right.That team approach and the fact that we operate our own Rapid Tooling Center is a huge part of the value RL Hudson customers receive. While in engineering, your focus is on the operational effectiveness of a part or assembly, in rapid tooling we focus on ensuring efficient manufacturing without compromising the integrity of the design.
BRUCE: Can you give our readers some examples of the kinds of things you might typically see that can be improved from that perspective?
DAVE: Sure. With molded parts, it’s important to consider where the parting line should be. We also want to minimize the depth and number of undercuts — generally tooling costs go up with every undercut. And it’s usually better to incorporate radiused corners, rather than sharp corners, to aid in material flow.
BENNY: What about holes? You should consider the depth of a pocket or the diameter of the tool — generally avoid small, long holes and enlarge the diameter as much as possible, right?
DAVE: Right.We also look at thread design, stack tolerance, the positioning of locator pins, the shrinkage and expansion of the material being used, draft allowances, materials compatibility, precision requirements, the type of mold — it all matters. And we look at the design as it would be in a mold — in two halves. It changes your perspective, but it’s important. The simpler, the better.
BENNY: Let’s look at a specific example where changes in design improved manufacturability. What about the plastic connecter we worked on the other day?
DAVE: Great example. It was a well-designed part, but by carefully removing some material, and making changes to the fillet radii, we were able to make the crosssections more consistent. This eliminated sudden changes that could have caused mold filling issues like warping or shrinkage.
BRUCE: We also moved the small lifter hole away from the cross-section wall to prevent it from accidentally filling during production.
DAVE: And finally, we changed the bead shape where a tube attaches. Adding a flattened area on the upper section, which is where there was a parting line, reducing the risk of any flash cutting the hose when attached, and the overall design change also made attaching the hose easier.
BENNY: Does the fact that we use Pro/E and other Pro/E modules across the organization make design changes and improvements any easier from the mold maker’s perspective?
DAVE: Absolutely. Considering all the options and issues is complicated enough. With integrated software, it’s much easier. First, we immediately eliminate any file translation problems that could occur with IGES or STEP files, along with the time it would take to repair a file. We also significantly reduce the time and cost of handling design changes which, by themselves, could bring production to a standstill.
BRUCE: Pro/Mold Design also facilitates the application of rubber and plastic material properties to minimize shrink and warp, and simplify the creation of gating, runners, sprues, sliders and lifters, and vents and cooling channels.
DAVE: And we can generate the mold cores and cavities, including all of the functions you named, Bruce, directly from the Pro/E model. Because it’s all associated with the original Pro/E design model, as changes are made, almost everything automatically updates downstream.
BENNY: Plus, together with Moldflow, which we discussed in the last issue of Solutions, we can simulate the injection process so we can identify areas that might be prone to air pockets or poor fill.
DAVE: That’s right. Mold flow simulation is just one more check we use to visualize what will happen when the material meets the mold. Expert Machinist uses our expertise in machining and the specific type of machining being done, to streamline the whole programming process. Then,we use Pro/NC-Mill to define and optimize the machining of the mold, which also helps reduce time and potential errors.
BRUCE: So, with Pro/E we’re optimizing design and manufacturing from beginning to end. Taking a look at how we use Pro/E to design better, more cost effective parts makes it easy to see why so many of our customers consider RL Hudson part of their own competitive advantage.
BENNY: Sure does. Thanks for coming, Dave.
DAVE: Thanks for having me. Same time next year?
BRUCE: You bet.
If you have questions about Pro/E or any other design engineering topic, please email Benny and Bruce at benny&bruce@rlhudson.com.
Pro/E®,Pro/ENGINEER®,Pro/Mold Design®,Pro/NC-Mill® and Magnetic Marelli, Inc. are registered trademarks of Parametric Technology Corporation (PTC). Moldflow Plastics Advisers® is a registered trademark of Moldflow Corporation.
