This article illustrates that teamwork by four companies cuts the time from mold design to finished part down to hours instead of weeks. The companies formed Rapid Use of Shop Hours (RUSH) team—pooling their expertise in mold making, computer-aided design (CAD)/computer-aided manufacturing (CAM) software, machine tools, and controls. The team members were Pleasant Precision Inc., a supplier of interchangeable insert mold systems; PTC, which supplied the tool design and NC toolpath software; Makino, a manufacturer of computer numerical control (CNC) machining centers; and Dynisco, which supplied the hot runner control. The RUSH team generated an injection mold design and numerical control toolpath data, machined and assembled a production injection mold, and installed hot runner controls to regulate plastic flow internally in the tool.
IN PLASTIC INJECTION MOLDING, even moderately complex mold design and toolmaking can take from eight to 12 weeks to finish. A team of four companies decided that they could do better—much better—by taking a product from art to part in just one day. What’s more, the companies went out on a limb by doing it at the National Plastics Exposition—the U.S. plastics industry’s largest trade show attended by, arguably, the industry’s toughest critics.
The companies formed what they call a ILUSH team—an acronym for “Rapid Use of Shop Hours”—pooling their expertise in moldmaking, CAD/CAM software, machine tools, and controls. The team members were Pleasant Precision Inc., a supplier of interchangeable insert mold systems; PTC, which supplied the tool design and NC toolpath software; Makino, a manufacturer of CNC machining centers; and Dynisco, which supplied the hot runner control.
Daily Design ... And More
Starting each morning of the show, the RUSH team generated an injection mold design and numerical control toolpath data, machined and assembled a production injection mold, and installed hot runner controls to regulate plastic flow internally in the tool. At the end of each day, a newly finished mold was installed on a 190-ton injection press, producing good-quality plastic parts. By Friday, when the show concluded, the RUSH team had attained its goal. Five molds were built in five days, producing a different part each afternoon.
The parts—a magnet holder, cell phone front and back, paper clip, and bookmark—had reasonably complex geometry. The mold inserts and components were produced from hardened tool steel on a high-speed CNC machining center. The molds had acceptable quality surface finishes and parting lines, and molds were assembled without the need for additional benchwork after machining. The high-speed machining center produced tools successfully, despite being located on an exhibit hall floor—a less-than-ideal environment. The molds were built with state-of-the-art technology.
Each team member played a distinct role in time compression of toolmaking. A modular mold system from Pleasant Precision, also known as Team PPI, of Kenton, Ohio, saved time by using interchangeable mold inserts in a standardized moldbase, or master frame. The inserts encompass the mold core and cavity, from which parts are molded. In this case, four insert sets—one for each part—were housed in the standard master frame, which is the main body of the mold. The company compares its system to the concept of a safety razor, in which the master frame is like the razor handle and inserts are the replaceable razor cartridges.
Pleasant Precision’s president, Ron Pleasant, who came up with the idea of producing a mold a day, claimed that the company’s mold system, which is marketed under the name Round Mate, can save up to 30 percent of design and build time. The master frame contains standardized components, such as the ejector system, gating, nozzles, and built-in water jackets for cooling. Standardizing these components in the master frame eliminated much of the chase work associated with manufacturing new components with every new mold, he explained.
Standardization of mold parts can cut design time, Pleasant said. For instance, the Round Mate system includes water-cooled inserts ready to be combined with the master frame. The work needed to add cooling channels is eliminated, because they are in the mold before it is machined.
Pleasant argued that standardization can also save time in CAD/CAM design. Take ejector pins, for example, which knock out the molded plastic part from the mold. Multiple operations are normally required to put one ejector pin in a mold, including spotting, drilling, and finishing operations. Plus, there are holes that have to be drilled into the core plate and the ejector plate. “There are 18 different operations that are all nested into the fact that you chose a 1/16-inch ejector pin,” Pleasant said.
With the Round Mate system, once an ejector pin was designed for Monday’s mold, the same design information could be brought to bear on ejector pins used in Tuesday’s mold, and so on, he explained. “That is important. You can do that with any size pin, and with the Round Mate system, it’s likely that many of those things are going to be very much the same.”
The same design concept can be applied to other components in the tool—such as vents, runners, and gates— that allowed the design process to be highly automated. The molds were designed with Pro/Moldesign and tool- paths were generated with Pro/NC. Both are modules from the Pro/Engineer 2000i family of solid modeling software. Pro/Engineer software is written so that changes to a design are automatically reflected in all of the tooling and NC data, according to PTC Inc. of Waltham, Mass.
Joseph Lichtenberg, vice president of technical marketing for production applications at PTC, said that feature simplifies design changes. “It’s easy to take the model from one version to another, or to take one model and easily extend it into a family of models,” he said.
A software module splits the mold design into appropriate components, cores, cavities, and inserts, to generate and adjust parting line geometry, which is usually a time-consuming endeavor, he added. In addition, it allows components to be selected and placed from libraries. For example, the appropriate ejector pins were selected from a library, and immediately incorporated into the mold design. When the ejector pins are placed in the mold design, all of the holes are automatically made in the plates with the proper offsets, he said.
Lichtenberg said that PTC has been working with machine tool vendors to optimize the software for highspeed machining, which played a key role in the RUSH project, because it helped to cut machining time, and eliminate handwork and polishing. He noted that highspeed machining is much more than taking out sharp corners and rounding them off. “It’s a strategy that forces completely new toolpaths from the ground up.”
According to Lichtenberg, Pro/NC, for example, ensures that the cutting tool encounters a constant load for the entire toolpath, which allows more efficient roughing. It also uses a technique called climb cutting, which is a more aggressive way for the tool to engage and remove the steel, and also results in a better surface finish, Lichtenberg said. Other efficient machining techniques include eliminating plunges, being smart about approaches and exits, and eliminating sharp corners, he added.
According to Charles Farah, PTC’s product manager for NC operations, high-speed machining minimizes the need for time-consuming processes like burning, which requires burning sharp corners out of the steel on an electrical discharge machine. He noted that the parts picked for molding did not require burning. He also observed that the high-speed machining center used to machine the inserts used very small tools very efficiently. The parts that were chosen did not require machining of any corners smaller than 0.25 mm, which was the diameter of the smallest tool, he said.
In addition, the high-speed machining center was able to produce small steps and step-overs at high speed, resulting in a smooth surface finish. Steps were in the range of 0.001 to 0.002 inch, he said. Finished tools did not require any benchwork, or hand finishing, after machining. In conventional toolmaking, benchwork is often required during mold assembly, for a better fit between parting lines or improved surface finish. If the parting line, where the two halves of the mold come together, makes a poor fit, the parts will flash during molding, leaving excess plastic at the shutoff surfaces.
Bill Bayak, vice president of marketing of Makino Inc. in Mason, Ohio, said the extreme rigidity and accuracy of the V33 CNC machining center, as well as the tight tolerances of the Round Mate mold system, helped to eliminate benchwork. Bayak noted that the V33 was designed specifically for die and mold applications. He added that the V33 has extremely high volumetric accuracy, which is important in die and mold applications where movement is in three dimensions.
Another timesaving feature, said Bayak, was to have the CAD system tightly linked to CAM data, eliminating the need for a file to pass through IGES or another translation system. “If you send something through an IGES file, there is a good chance that your programmer is going to spend some time cleaning up the model. If he spends two or three hours cleaning up the model, that’s two or three hours lost,” Bayak said. He added that it’s important for the CAD/CAM programmer and the operator of the machining center to work together closely. In other words, the machine tool operator should have input on what would be the best approach for getting the most accuracy in finishing the tool.
The RUSH team did not cut corners. It machined production tools from reasonably hard tool steel, not soft metal such as aluminum. All the molds were machined from DH2F H-13 tool steel, hardened to 40 Rockwell, supplied by International Mold Steel. (The only exception was the slides, necessary for undercuts, on the first mold, which were of S-7 steel, hardened to 54 Rockwell.)
Given the time constraints of the project, the choice was made to go with medium-hardness steel. Although H-13 can be fully hardened to as high as 52 Rockwell, Pleasant said that the 40 Rockwell hardness of the H-13 steel used in the molds produced tools capable of hundreds of thousands of shots. “It’s a very nice, very clean, very specialized mold steel,” Pleasant said of the DH2F steel. “The material handled the high-speed machining techniques very well.”
Pleasant said that working with high-speed machining led to some new machining techniques. “We learned how to drill ejector pinholes in a different manner,” he said. In conventional moldmaking, ejector pins are drilled from the face; then the piece is flipped over and finished from the back, he explained. In this case, using some techniques from the V33 machining center, NC programming software, and specialized drill bits, the holes were drilled and finished from the face only. This eliminates a setup, because holes didn’t have to be finished from the back.
Pleasant noted that the V33 machine tool had a high degree of flexibility, and was capable of performing all the work that was described in the CAD/CAM model— gates, runners, part details, ejector pins, and venting. “Everything that was necessary was in the tooling magazine,” he said. Starting the job in the morning, the machine went right down the job list, eliminating the need for more setups that would be required in working with more than one machine tool. Keeping the entire machining process in one machine tool was key to completing tools in one day, he said.
Although the V33 machining center was extremely rigid, the floor on which it was sitting was not—which surprised Bayak. Floor vibrations from the exhibit hall floor caused some very tiny tools on the V33 to break, forcing Makino to slow down its feed rates a bit. The V33’s proprietary Super Geometric Intelligence servo control operates in two modes: the high-performance mode and high-precision mode.
The high-performance mode, in which the floor vibrations caused a problem, is used for roughing and semi-finishing. It allows for a little less accuracy, but reaches the machine’s highest feed rate. Bayak got around the vibration problem by switching the machine to high-accuracy mode, with a slightly slower feed rate, which solved the problem. He suggested that if the machine were on a normal shop-floor foundation, it could have been run faster.
The fourth major component in the RUSH process was the computerized hot runner control, which regulates the flow of plastic in the mold. The Round Mate multiposition system is a family mold; in other words, it can mold different parts simultaneously in the same master frame. The project turned out a total of five molds during the week and could set any four into the frame at one time. The inserts for the magnet holder and the paper clip were two-cavity molds, in which two parts were molded in each insert. The halves of the cell phone housing and the bookmark were single-cavity molds.
To mold good parts every time, it is critical to dehver the right amount of plastic to each mold. Each day, a new insert was installed in the master frame, with its own unique processing requirements.
In order to meet those processing requirements, a Dynamic Feed hot runner manifold, supplied by Dynisco HotRunners of Gloucester, Mass., was used to deliver the right amount of plastic for each part. The Round Mate system is quick-change tooling that allows the mold inserts to be changed to a new insert in 10 minutes or less. The Dynamic Feed further compressed the time by automatically adjusting the injection profile—cavity pressure over time—for each new mold, compensating for differing cavity size and complexity.
Injection molding machines traditionally have one point of control on the press, explained Bill Hume, vice president of marketing for Dynisco HotRunners. Making a process change to one cavity affects all the others. The Dynamic Feed control overrides the control on the press, bringing the process control to the mold itself, providing independent real-time control to each cavity, he said. When a new insert was ready, the press was stopped just long enough to quick change to the next insert, automatically adjust to the new part, and begin molding a new part instantly.
Developing the skills and learning new techniques took practice, said Pleasant. He came up with the idea of producing a tool a day in January, and recruited PTC, Makino, and Dynisco for the job. For several months, the companies met with each other and formed what was essentially a new company, discussing how to approach the job, and how to design and build the molds. One challenge for the design team was to fully understand how to drive a tool around the surface of the steel at high speed, he noted.
In fact, the RUSH team spent almost eight weeks making the mold inserts prior to the show. “We were practicing and learning, developing our skills and techniques for doing this in one day, and it took a lot of work,” said Pleasant. The team had to develop a good environment for communication, and decide what would and would not work in programming and machining. “We went through the process and developed it and fine-tuned it, until it fell into place,” he said.
Although the RUSH team had the benefit of a dry run, Pleasant said the techniques that were learned would be a benefit in the real world environment. He believes that building production injection molds in a three-day time frame is realistic, depending on the queue of jobs in a tool shop.
Getting An Early Start
Tool design started early, at 7:30 every morning. Once the programs were ready, sometime after 9 a.m., they were fed into the machine tool, which ran throughout the day. Programming often lasted until about 11 a.m., so it ran concurrently with the machining at least part of the day. When the machining was completed, the insert was assembled, and brought to the injection press, where it replaced one of the four mold inserts in the master frame. The team had a goal of finishing assembling the tools each day by 4 p.m. The first four days, Round Mate was finishing tool assembly by around 4:30. On the last day, Friday, mold assembly was finished an hour earlier than planned.
By Friday, the RUSH team was at the top of its game. Starting with the CAD model of the bookmark in Pro/En- gineer, the team designed the injection mold assembly between 7:15 and 9:50 a.m. Between 8:10 and 11:35 a.m., the NC toolpath was generated. Machining the bookmark cavity on the Makino V33 began at 9:15 and continued until 3 p.m. Final mold assembly with the Round Mate inserts started at 3 p.m. and was completed by 3:15.
The mold insert was brought directly to the injection molding machine, where it was installed in the master frame. Mold changeover took about 10 minutes. All of the parts were molded of acrylonitrile-butadiene- styrene, or ABS. In every instance, good parts were produced on the first shot.