New machine tools and tooling methods eclipse traditional machining (figure)

Eclipse Mold Mould sets a good example for efficient zero-tolerance machining in high-end machining centers.

For mold manufacturers, it is strongly hoped that the cutting of the mold will achieve a zero-tolerance level of cutting without margin, and Eclipse Mold mold company just proves this fact. The company has a mold shop that produces approximately 140 sets of molds per year, including a significant amount of mold repair services, but this business accounts for only about 40% of its total workload. The company's other 60% of its revenue comes from its three injection molding plants, which are located on the outskirts of Detroit. In fact, the company's plant has a total of 42 injection molding machines, and its working pressure ranges from 22 to 750 tons.

Figure 1 The core surface of this automotive mold is finished without any margin. In addition to polishing with very light media,
In fact, the mold does not require manual polishing. The side of the cavity can be seen in the figure, and its surface quality can be seen on its closed surface.

The molds used on these injection presses at Eclipse Mold are manufactured by the company's Clinton Township headquarters, located northwest of Detroit, about 20 miles from downtown. To a certain extent, the company uses almost zero-tolerance machining for all of these molds. Steve Craprotta, vice president and general manager of the company, said: “The molds with no tolerance machining are faster, longer lasting, and less expensive to repair. The molded parts are of good quality and cleanliness. We rely on these results every day. For the sake of life, we know the precious meaning of these processing methods."

For Mr. Cra-protta's statement, his customers also agreed. Only 15% of the molds produced by Eclipse Tooling each year are used in the company's own factory, and the rest of the molds are shipped to large Tier 1 automotive suppliers, including many familiar US and Japanese automakers. Mr. Craprotta said without exaggeration: “All our customers think that our company's mold shop is the best.” The reason why he emphasizes this point is to make people convinced: if you want to make a workshop Maintaining its competitive position in the market and achieving a level of zero tolerance machining is an integral part.

In 1976, Mr. Steve's father, Fred Craprotta, founded the Eclipse mold company, and his father has been actively leading and managing the company so far. The company has been expanded several times. In 1989, the company moved to its current headquarters. The combined number of employees in the three factories of the company is 150.

Eclipse Mold Company specializes in the production of molds for secondary injection molds. Such molds typically consist of a core or cavity, but must be matched with the other two half-drawing dies or side molds that are rotated 180° to accommodate the second injection molding of the mold. Mr. Craprotta explained: “If these molds are processed in a common process, then hand-polished and point-by-point grinding, it will cost us a lot of valuable time, that is, it is difficult to meet the delivery time requirements and can not meet our own production. Progress requirements. "If you can machine the closed face of the mold to a zero tolerance size (in many cases, even to the extent of negative margin), you can greatly save the point-by-point grinding time of the mold. He said that when the one side of the mold is matched with the other side, and when the mold is rotated or mated with the other half of the mold, the mating surface can be almost perfect.

Most of the molds produced by Eclipse Mold Company are high-precision, multi-cavity complex molds. The largest mold size is 40×50 in, and the small mold size is 8×8 in. The most common medium-sized mold is used. 300-700t injection molding press. Of these molds, approximately 70% to 80% of the molds work mechanically, such as skateboards, hoists, telescopic cores, and other similar tools.

Eclipse Mold believes that the rigidity of its machining center is a key factor in zero tolerance machining

Makino's V55 vertical machining center has a spindle speed of up to 20,000 r/min with HSK interface and a shank that is mounted with a hot fit.
The semi-finishing on this machine can be seen from the illustration.

The use of zero-tolerance machining process not only replaces a large number of mold-by-point grinding time, but also improves the level of flow production of mechanical parts. For example, the hoist can be placed directly into the crypt and requires only a small amount of adjustment, or simply does not require any adjustment.

The zero tolerance machining of the mold relies mainly on the three state-of-the-art machining centers installed in the shop. The V55 and V56 vertical machining centers are provided by Makino (in the Mason area of ​​Ohio) and the other DMC-1500. The machining center is supplied by Johnford. All of these machines were introduced through Single Source Technologies Technologies (SST), a distributor in the Auburn Hills area of ​​Michigan.

Mr. Craprotta said: “The rigidity and precision of Makino's machine tools are particularly suitable for our molds with zero tolerance machining.” Johnford's machine tools, equipped with a large 30×50 in table, can meet the growing processing scale of our workshops. The needs of the mold. According to Mr. Craprotta, the machine's zero-tolerance machining is as good as a small vertical machining center.

Milling of hard materials

Eclipse Tooling began working with SST Technologies in 1992, when the company introduced the first high-speed milling machine from Makino for the processing of graphite electrodes. Mr. Craprotta recalled: “We learned a new concept about high-speed machining from the machining experience of this machine.” When the dealer began to promote the concept of zero-tolerance machining with hard-milled mold parts, it caused Eclipse. The attention of the mold company. In 2001, the company purchased the first machining center through this dealer for the milling of hard materials.

Compared with the ordinary milling process, when we first encountered the milling of hard materials, it seemed to be difficult and risky. If a tool breaks or burns out and the expensive mold is scrapped, it will become an intractable bitter fruit. It is unimaginable for machine operators to face the pressure of such high-precision hard material milling every day. He said: "The pressure is really too big."

Mr. Craprotta said: "Our company is the first to get involved in this process area. We are in front of other processing workshops. We have some room for maneuver for the transition to this process." Initially, the shop was based on its machine tool. The degree of confidence in the tool and tool path begins to reduce the machining allowance of the mold, reducing it from 0.003 in to 0.002 in and 0.001 in.

After all the appropriate technical support for zero tolerance machining, we have proved that our approach is more sensible. For example, the shop began to use balanced tools and HSK interfaces for thermal expansion and contraction tool holders, and upgraded the CAM programming software. When the operator saw that this new operating principle and operating procedures were very comfortable, and felt how the process could work handily, they finally changed their original work attitude.

Mr. Craprotta said that later, they were not only more eager to participate in the zero tolerance machining of the mold, but also began to carry out negative tolerance cutting on the closed interview of the mold. This change in attitude has probably gone through a year. Finally, Mr. Craprotta came to the conclusion: “In this period, there have been some tensions, uneasiness and anxiety in the workshop, which is really not easy.”

He himself first played an exemplary role and trusted programmers. As programmers develop increasingly high tolerances on the mold closing surface, it ensures that the machine operator is confident that the tool's machining path is trustworthy. The shop uses PowerMill software, which is supplied by Delcam (in the Windsor area of ​​Ontario) to create tool paths for zero tolerance cutting.

John Zube, one of the most experienced programmers in the shop, said that good communication and communication between programmers and machine operators is critical. As a programmer in the workshop, Mr. Zube said: "In the transition period of technology, I spent a long time in the workshop, and I am still working on it." He added that from the workshop Some of the comments and suggestions I got told him what to do and what to do could make the work better. "We need to learn from each other."

It is also important to get feedback from the mold manufacturing business unit. Reports from these jobs have helped programmers and machine operators a lot, helping to further improve their performance.

Rigid, precise and efficient machining of machine tools

Mr. Craprotta's requirements for machine tool selection for hard material milling are summarized as follows: Try to purchase a machine with the best rigidity and high machining accuracy. The rigidity of the machine tool is critical because the machine with high rigidity can minimize the vibration of the tool tip on the machine. He added, of course, that the design of the rest of the tool must also be very reasonable, and it also requires a low radial runout and good stability. The vertical machining center provided by Makino includes, in addition to its good rigid structure, its box-type guide rails with linear ball bearings, the bed and columns with appropriate quality, and the lead screws with support at both ends. .

Makino's machine tools have a spindle speed of up to 20,000 r/min. When a small tool on a machine tool is operated under high-speed feed and low depth of cut, it is necessary to use such a high-speed rotating spindle in order to achieve proper chip load. Mr. Craprotta explained: “When machining on these machines, we can see that the heat on the spindle does not increase rapidly. Our machines work continuously for 10 hours every day, and there has never been a Z-axis depth problem.”

Mr. Craprotta added: “The machine must have a high degree of precision – not only the center of the machine, but also the full range of accuracy of the entire machine.” To ensure the small movement of the ultra-small tool, the machine must also Configure a glass scale with a resolution of one millionth of an inch. The cutting accuracy of the tool finishing can reach 0.010 in, generally up to 0.030 in. Eclipse Tooling's tolerances for daily machining of core and cavity surfaces are up to ±0.0004 in. Its surface roughness can range from 16 to 24 rms.

Figure 3 The secondary injection mold on this injection press can be rotated 180° on the platen and then a second injection molding of the soft plastic.
Since the closed surface of the mold must be sealed at the same time in both directions, the precision machining without manual work after the mold is completed can ensure that the point-by-point grinding time of the mold is reduced to a minimum.

There are still some difficulties in the quantitative analysis of effective cutting in the processing workshop. Compared with the machining of other machine tools, there is very little opportunity to see how fast the tool on the Makino machine can execute the tool path program. Mr. Craprotta follows SST Technologies' software for the software used in small machine control systems. The features of Super Geometric Intelligence enable these machines to process servo commands at high speeds with minimal, forward-looking conditions to avoid surface effects and without compromising processing speed.

Mr. Craprotta said that Johnford's machine tools have great advantages. He said: "The outstanding value lies in its high cost performance." This machine is equipped with a 90° bridge beam and an offset Y-axis guide, so that the deviation of the extension stroke is reduced to a minimum. A condition required to process large molds. The box-type guide rails on the Y-axis and the Z-axis help to increase the rigidity of the machine tool, but the linear guide rails are used on the X-axis, which facilitates the precise movement of heavy workpieces.

However, Mr. Craprotta said that the shop had the best results from this machine because SST Technologies commissioned the axes of the machine before shipment, making it more suitable for milling hard materials. . Mr. Craprotta stated: “We have taken full advantage of this machine because it is suitable for high-speed precision machining. That is to say, we have to make some minor improvements to this machine to make it It can meet the requirements of zero tolerance machining.” More importantly, the extended stroke of this machine allows the shop to produce multi-cavity molds to meet the production requirements of large automotive interior parts. Mr. Craprotta said: "For us, this has always been the fastest growing field."

The surface of the mold and the mechanical parts are machined using a zero tolerance process. Details about the mold are shown in the close up view above

Finally, in the milling of hard materials, he emphasized the importance of adopting an unmanned mode of operation, with at least one shift per day using an unmanned mode of operation. In general, Eclipse Mold's first and second shifts per day are handled by an operator and are responsible for the monitoring of seven CNC machine tools. In the third shift, the hard material milling operation on the vertical machining center adopts the unmanned operation mode, although the actual working load in the workshop does not always make such a request.

I hope to bring more benefits

Thanks to the zero-tolerance machining that has enabled Eclipse Molding to increase productivity, Mr. Craprotta is convinced that his shop can fully handle the machining of other parts based on its traditional customer base. The goal of the shop is to provide high cavity, high precision workpiece machining services to customers in the medical device or aerospace industry. Mr. Craprotta is convinced that they don't need to be eager to find molds from overseas moldmakers like their counterparts in the automotive industry, and they are particularly appreciative of the advanced mold shop and its production capacity in southeastern Michigan.

Mr. Craprotta, on behalf of Eclipse Mold Tooling and other mold makers in the region, said: “Many mold shops in this state have developed mold manufacturing processes that are globally competitive. We don’t want to be the best secret company, and some Large mold manufacturers often overlook this problem, and they believe that only low-cost countries can provide the most cost-effective solution."

Of course, he is convinced that Eclipse Mold can outperform any other processing plant in terms of processing quality and quality service. He said: "Zero tolerance machining has made a great contribution to our company's acquisition of this position." Now, in order to further improve efficiency, the shop began to shift its attention to the company's lean production technology.