New machine tools and machining methods overshadow traditional machining

Eclipse Mold has set a good example for effective zero-tolerance machining in high-end machining centers.

For mold makers, it is strongly hoped that the machining of the mold can reach zero tolerance level of zero tolerance, and Eclipse Mold mold company just proved this fact. The company has a mold processing workshop, which can produce about 140 sets of molds per year, including a considerable number of mold repair services, but this business only accounts for about 40% of its total workload. The other 60% of the company's revenue comes from its three injection mold factories located in the suburbs of Detroit. In fact, there are 42 injection molding machines in the company's plant, and its working pressure ranges from 22 to 750 tons.

Fig. 1 After finishing the core surface of the car mold, no allowance is left. In addition to polishing with a very light medium, the mold actually does not require hand polishing. The side of the cavity can be seen in the figure, on the closed face it can be seen that it resembles the processed surface quality

The molds used on these injection molding presses at Eclipse Mold are manufactured by the company's headquarters at Clinton Township headquarters, which is located in the northwest of Detroit, about 20 miles from the city. To some extent, the company uses almost zero-tolerance cutting processes for the machining of all these molds. The company’s vice president and general manager, Steve Craprotta, said: “Machines with no-tolerance cutting work faster, have longer service life, and have lower maintenance costs, and the quality and cleanliness of molded parts are good. We rely on these results every day. For a living, we are fully aware of the precious significance of these processing methods."

For Mr. Cra-protta's statement, his customers also strongly agree. Only 15% of Eclipse Mold's annual molds are used in the company's own factory, and the remaining molds are shipped to large Tier 1 automotive suppliers, including many familiar American and Japanese automakers. Mr. Craprotta said without exaggeration: “All our customers think that our company's mold shop is the best.” The main reason why he emphasized this point is to make people believe: If you want to make a workshop Maintaining its competitive position in the market and achieving zero-tolerance processing levels is an indispensable part of it.

In 1976, Mr. Steve's father, Fred Craprotta, founded the Eclipse Mold Company. His father has been actively leading and managing this company so far. The company had expanded several times before, in 1989, the company moved to the current headquarters location. The company’s three factories have a total of 150 employees.

Eclipse Mold Company specializes in the production of molds for secondary injection molding. Such molds generally consist of a core or cavity, but must be mated with two other half-drawing molds or side molds that are rotated 180° to accommodate the mold's second injection. Mr. Craprotta explained: "If these molds are processed by ordinary processes and then hand-polished and point-by-point sanding operations, it will inevitably take us a lot of precious time, that is difficult to meet the delivery time requirements can not meet our own production Progress requirements.” If the closed surface of the mold can be machined to zero tolerance dimensions (in many cases, even to the extent of negative balance), the point-by-point grinding time of the mold can be greatly saved. He said that when one side of the mold is mated 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 are high-precision, multi-cavity complex molds. The largest mold size is 40×50 in, and the smaller mold size is 8×8 in. The most common medium mold is used 300 ~ 700t injection press. In these molds, about 70% to 80% of the molds work by mechanical action, such as using slides, hoists, telescoping cores, and other similar tools.

Figure 2 Eclipse Mold Company 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 20000 r/min, an HSK interface and a shank mounted with a hot-fit. From the illustration you can see the semi-finishing on this machine

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

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

Mr. Craprotta said: "The firmness and precision of Makino's machine tools are particularly suitable for our die zero-tolerance machining." And Johnford's machine tools are equipped with a large work bench of 30 x 50 in, which can meet the increasing processing of our workshop. Mold needs. According to Mr. Craprotota, the zero-tolerance cutting level of this machine is no less than a small vertical machining center.

Milling of hard materials

Eclipse Mold Co. began cooperation with SST Technologies in 1992. At the time, the company introduced the first high-speed milling machine from Makino Company for the production of graphite electrodes. Mr. Craprotta recalled: “We learned from the processing experience of this machine tool about the new concept of high-speed machining.” When the dealer began to sell this zero-tolerance machining concept with hard-milled mold parts, it caused Eclipse. Mold company's attention. In 2001, the company purchased the first machining center through this distributor for milling of hard materials.

Compared with the ordinary milling process, when we first encountered the milling of hard materials, it seemed to have certain difficulties and was adventurous. If a cutter breaks or burns and causes expensive molds to be scrapped, it will be a bitter pill. Every day it is faced with such high-precision hard material milling pressure, which is unimaginable for machine tool operators. He said: "The pressure is really too great."

Mr. Craprotta said: “Our company was the first to get involved in this process area. We walked in front of other processing plants. We have some room for the transition to this process.” Initially, the processing plant based on its The degree of confidence in the tool and tool path has begun to reduce the tooling allowance, reducing it from the original 0.003 in to 0.002 in and 0.001 in.

After all the appropriate technical support forces for zero-tolerance processing have been thoroughly investigated, it is also wise to prove our approach. For example, the machining shop began to use the thermal expansion and shrinkage tool and the balance tool and HSK interface, and upgrade the CAM programming software. When operators saw the new operating principles and operating procedures are very comfortable, and felt how the process can work with confidence, they finally changed their original working attitude.

Mr. Craprotta said that afterwards, they were not only more eager to participate in the zero-tolerance cutting of the die, but also began to perform negative tolerance cuts on the closed surface of the die. This change of attitude probably took a year. Finally, Mr. Craprotta came to the conclusion: "In this period, there have been some tensions, anxiety and anxiety in the processing plant. This is indeed a very difficult thing."

He first played an exemplary role and trusted programmers. When programmers create higher and higher accuracy tolerances on the mold closing surface, it ensures that the machine operator is convinced that the tool path is trustworthy. The shop uses PowerMill software, which is provided by Delcam (in Windsor, Ontario) to generate toolpaths for zero-tolerance cutting.

Mr. John Zube, a programmer who is the most experienced programmer in the processing workshop, said that the good communication and communication between programmers and machine operators is critical. As a programmer in the workshop, Mr. Zube said: “In the transition period, I spent a very long time in the workshop and I still work on this.” He added that from the workshop Some of the evaluations and suggestions received tell him what to do and what he can do to make the job better. "We need to learn from each other."

It's also important to get feedback from the mold manufacturing business. The reports from these jobs have brought great help to programmers and machine operators, which is conducive to further improving their performance.

Rigid, accurate and efficient machining of machine tools

Mr. Craprotta's requirements for the selection of machine tools for milling of hard materials are summed up as follows: Try to purchase machines with the best rigidity and machining accuracy. The rigidity of the machine tool is critical, because the rigid machine tool can minimize the vibration of the tool tip. He added that, of course, the design of other parts of the tool must also be very reasonable, but also requires low radial runout and good stability. The vertical machining center provided by Makino Company, in addition to its good rigid structure, includes its box rail with linear ball bearings, its bed and columns with proper quality, and screw rods with both ends supported. .

Makino's machine tools have a maximum spindle speed of up to 20000 r/min. When a small tool on a machine tool is operated at a high feed rate and a low depth of cut, it is necessary to use such a spindle that rotates at a high speed in order to achieve an appropriate 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 a day, and there has never been a Z-axis depth problem."

Mr. Craprotta added: "Machine must have high precision - not only the center range of the machine, but also the entire machine must maintain the same enough accuracy." In order to ensure the tiny movement of ultra-small tools, the machine must also Configure a glass scale with a resolution of one millionth of an inch. The cutting accuracy for tool finishing can be up to 0.010 in, typically up to 0.030 in. Eclipse Mold Co., Ltd. routinely cuts tolerances on cores and cavity surfaces to ±0.0004 in. Its surface roughness can reach 16-24 rms.

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

There is still some difficulty in quantitative analysis of effective cutting in the processing workshop. Compared with the machining conditions of other machine tools, there is little opportunity to see how quickly the tool on the Makino Machine Tool can execute the tool path program. Mr. Craprotta's use of software in small machine tool control systems follows SST's claim. The features of Super Geometric Intelligence enable these machines to process servo commands at high speeds with minimal forward-looking conditions, avoiding surface damage 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 offset Y-axis rails, so that the deviation of the extension stroke is minimized. This is A condition needed to process a large mold. The box rails on the Y-axis and Z-axis help to increase the rigidity of the machine, but the linear guides are used on the X-axis, which is conducive to the accurate movement of heavy workpieces.

However, Mr. Craprorotta said that the shop had obtained the best results from this machine, because before shipment, SST technology company commissioned each axis of the machine tool, making it more suitable for the milling of hard materials. . Mr. Craprotta stated: "We have fully exploited most of the advantages of this machine because it is suitable for high-speed precision machining. That is to say, we must also make some minor improvements to this machine to make it It is able to meet the requirements of zero-tolerance cutting processing.” And more importantly, the extended stroke of this machine can make the workshop to produce multi-cavity molds to meet the production requirements of large-scale automotive interior parts. Mr. Craprotta said: "For us, this has always been one of the fastest growing areas."

Figure 4 Mr. Steve Craprotta (pictured right) and Mr. John Montalbano, mold production manager, are checking together an already molded part that was produced from this 4-cavity mold. The surface and mechanical parts of the mold are machined using zero-tolerance machining. 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 unattended operation mode, where at least one shift per day uses an unattended operation mode. In general, the Eclipse Mold mold company works on the first and second shift every day, and is staffed by an operator who is responsible for the monitoring of seven CNC machine tools. In the third shift, all the milling operations of hard materials on the vertical machining center adopt the unattended operation mode, although the actual work load in the workshop does not always impose such requirements.

Hope to bring more benefits

Because of the zero-tolerance processing that enabled Eclipse Mold to increase its production efficiency, Mr. Craprotta was convinced that, on the basis of his original traditional customers, his machining shop could also fully undertake the processing of other types of parts. The goal of this workshop is to provide high-cavity, high-precision workpiece processing services for customers in the medical device or aerospace industries. Mr. Craprotta is convinced that they do not need to be as eager to seek overseas mold manufacturers to provide molds as their counterparts in the automotive industry, but also expressed special appreciation for the advanced mold processing workshops and their production capacity in the southeastern Michigan region.

Mr. Craprotta, on behalf of Eclipse Mold and other mold makers in the area, said: “Many die shops in this state have developed a globally competitive mold manufacturing process. We do not want to be the best company for confidentiality, and some Large mold manufacturers often overlook this issue. They believe that only low-cost countries can provide the most cost-effective solutions."

Of course, he is convinced that Eclipse Mold will outperform any other processing plant in terms of quality and service. He said: "Zero-tolerance processing has made great contributions to our company's struggle to achieve this status." Now, in order to further improve efficiency, the processing plant has begun to shift its attention to the company's lean production technology.