Moldmaking Technology
Production Quality Aluminum Moldmaking
September 2004
Speed is everything for Dynamic Plastics, Inc. Their market niche demands it and one manufacturer among many benefited from it in the development stage of their unique and innovative product: the Segway™ Human Transporter. Dynamic Plastics specializes in rapid manufacturing of prototype plastic injection molds for customers who need small but high-quality parts runs — which DP also provides from its 25,000 square foot facility at Chesterfield Township, Michigan.
“What sets us apart from a lot of our competition is our triple-duty moldmakers. For most jobs, they not only write toolpaths and do the machining; they do their own design work. Our choice of what we feel is the cad/cam/cnc program with the most user-friendly interface allows our crew the latitude to apply a wide variety of their skills to get the whole process done quickly and accurately.”
Dynamic Plastics’ skilled designer/programmer/machinists, materials selection experience, and shop floor scheduling flexibility are key to the shop’s reliability. With design and toolpathing driven by Mastercam® software – which co-owner Jim Connell calls pace-setting -- Dynamic Plastics is highly competitive in many time-critical prototyping scenarios. Accurate-the-first-time machining in high-quality aluminum set them up for production right from the prototype stage.
J. R. Hoell, for Segway, LLC, had outsourced to DP earlier in his career and asked Mr. Connell and his partner, Joe Doss, to bid on moldmaking and limited production of several parts during the development of the ingenious Segway HT. For Segway, this added up to production-quality parts in product-introduction quantities – minus the added start-up expense of steel tooling.
The beginning of a movement 
Market headlines today read, “Segway Opens 30 New Dealerships, Expanding Company's Presence Into 26 States.” No surprise. Dean Kamen, founder of Segway’s parent, DEKA Research and Development, holds more than 150 U.S. and foreign patents related to medical devices, climate control systems, and helicopter design. Watching a young man in a wheelchair struggling to get over a curb, Mr. Kamen realized that the problem wasn't ineffective wheelchairs; it was that world infrastructure was designed for people who could balance. So he and his team created Segway’s predecessor, the IBOT™ Mobility System, a self-balancing mobility device that enables users to climb stairs and negotiate sand, rocks, and curbs. By restoring balance, the IBOT also elevated users so they could see the world at eye level by maintaining equilibrium while raised on its two rear wheels!
For people with full mobility, using a balance machine had far-reaching possibilities. Sophisticated computer programming was added, the electronics and drive systems evolved, and Dean chose the right partners—not just investors with money but people willing to invest in his vision.
Forward motion for practical travel
The Segway Human Transporter took on a life of its own. A new company was established and key outside suppliers who would play an integral role throughout the development process were brought on board. Among them was Dynamic Plastics.
Co-owner Joe Doss was DP’s project manager for Segway projects and worked out production details and time-saving mold design alternatives with Segway technicians and designers. Mr. Doss felt that Segway’s team were particularly open to talk over ideas and listen to suggestions. He says, “We tried to use our experience with materials and Mastercam (by CN Software, Tolland, CT) to help make the projects more ‘toolable,’ for improved production speed and quality.”
Versatility is a must
The speed and direction of the Segway HT are controlled by the angle and direction in which the rider leans; function controls and indicators are in the handlebar. One handgrip steers the HT in a 0” turning radius and the control shaft telescopes to adjust to individual riders’ comfort. Dynamic Plastics made the prototype/production molds for the control shaft’s two-part height adjust collar, a two-piece ferrule with overmolding and, as the project progressed, battery cases, trim parts and a three-part, multi-material wedge for the braking mechanism.
Along the way, DP machined main housing and gearbox casing prototypes composite]from the same QC7 aluminum used for the molds. The extra-hard QC7 aluminum is the foundation of DP’s turnaround time and production quality. Using Mastercam-optimized feed/speed rates, Dynamic Plastics machines the QC7 so no material gums up the tooling or stock, and finished molds are capable of running upwards of 50,000 parts with steel-like precision.
Cutting Time
As Tooling Foreman, Tom Prebelich ran the program through the shop. “Our technicians can take virtually any kind of file into Mastercam,” Mr. Prebelich observes, “and move the job right along. In a real rush situation, we’ll separate the customer’s model, design the cavity mold, and hand that off to another operator so machining begins on the job even before the whole mold is designed.”: 13 designer/programmer/machinists, no waiting!
Four projections in the mold cavity telescope into the mating part to allow for a rib at both the top and bottom surface to capture washers inside the piece at two levels. When the threaded female ferrule is drawn over the resulting four-part cylindrical cone of the male, the washers are compressed, creating ample friction to set the handlebar height firmly. Initial designs called for solid rings of plastic at different levels. The DP team worked through a suggestion with Segway to interrupt the rings of plastic without having integral mold action or moveable pieces. Pete Anders, DP’s Molding Foreman, worked with Mr. Doss and Mr. Prebelich to establish the molding process parameters and parts sequences. This simplified tooling, further reducing cost by saving time in designing the action and machining it.
Getting down to the parts
Segway sent AutoCAD part files for this that DP technicians brought into Mastercam for any revisions, and for toolpathing. Loose, hand-inserted mold pieces form the threads of the male ferrule. Says Mr. Prebelich, “We take the two pieces together and drop them into the larger, ejector side of the tool. It’s closed, the plastic is injected and, when the tool opens, the mold pieces are ejected with part.” They must be hand separated during the limited-production startup period but the time (read: $$$) spent on handling as part of the production process was surprisingly less and the cutting time far faster than cutting steel for prototype tooling.
A softer, hand-grip part is overmolded on the female ferrule after it’s molded with threads by replacing the two threaded hand-loads with two for the second shot. DP has currently been performing 10,000-part runs for Segway using hand-inserted mold parts but, now that production is ramping up, the tooling will be augmented with slides, pushing the pieces together into the mold as it closes and changing them for the second shot.
“The production time constraints and our own quality control don’t leave room for dealing with flash, either,” reports Mr. Prebelich. “The mold parts must fit right the first time out. Using MoldPlus (an add-in for Mastercam) we copy the run-off and parting line surfaces for the cavity mold into the core mold layer for that perfect fit. In the seven years we have used MoldPlus, it has given us a time savings of up to 70% on the most complex jobs.”
Cutting in real time
“We like to do an intermediate “semi-rough” surface toolpath, stepping down to a ¼-inch bullnose mill with a.020-inch radius,” Mr. Prebelich says, “to get it closer to the finish dimensions but still perform a fairly aggressive cut. Since our software remembers what it has cut, I was able to use the leftover feature with a much smaller cutter — a .060-inch flat or ball mill, depending on the geometry — to clean up stock from corners and details missed by the larger cutters. Finally, surface finish contour and, in some places, surface finish parallel toolpathing gave us an extremely clean mold surface finish.”
Rather than adding machining time, Dynamic Plastics’ three-step progression of toolpaths results in faster results. Running appropriate feed-and-speed rates for each successive cutter in the progression keeps feed speeds high without pushing the tools to their respective limits. With this rough to semi-rough to finish combination, larger cutters give greater speed while leftover, with its quick cleanup, completes the details with time to spare.
Reports on the Segway HT hail the machine for its superb functionality, elegant design, and high quality. Mr. Doss says that “Mastercam gave us the accuracy needed to produce parts of a level of quality in keeping with Segway’s engineering idealism.”
Growing a Flexible Shop
Dynamic Plastics owners Joe Doss and Jim Connell tell a story typical of many niche moldmakers: he started in a garage, invested in quality cad/cam/cnc software, took increasingly complex rush-delivery jobs, hired, trained, and expanded his workforce. That was 11 years ago.
Now Dynamic Plastics employs 12 moldmakers and 13 support/management staff. “We’re always being pushed to get things ‘today’ at production quality,” says Tom Prebelich. “We’re now in the process of fine-tuning production even further using the Solids functions of Mastercam. Our moldmakers can’t believe it’s so easy to use. The time saved by Solids offsets the learning curve with no slowdown on the floor, so they’ve getting up to speed by using Solids on real projects.”
The configuration of Dynamic Plastics’ production process — from their choice of materials, software, and equipment to the decision to train their technicians as designers/programmers/machinists — contributes mightily to the company’s niche.
And the customers are happy. They get rapid prototyping at first-line production quality and production runs that suit their startup needs, all from a single, low-cost mold. Dynamic Plastics’ QC department consistently confirms that their products meet customers’ quality specifications. With escalating market pressure for higher quality, economy and faster turnaround, flexible, knowledgeable niche shops like Dynamic Plastics are in the catbird seat.
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