Combined application of mold 3D printing and processing machine tools

Mold is an indispensable process equipment in industrial production, widely used in machinery, home appliances, electronic products, as well as agriculture, national defense, aerospace and other fields. High-quality molds are the guarantee of product quality. As people's requirements for product styling and functions continue to increase, the industry demands higher precision, surface quality and service life of molds. In order to adapt to the rapid update of products, iterative mold production cycle is positive. Constantly compressed. The development of science and technology is driving the innovation of modern industrial technology. The advanced technologies such as additive manufacturing technology, intelligent manufacturing system, high-performance cutting tools and high-speed processing machines represented by 3D printing are making the ancient industry of molds flourish.

1. The difference between mold making and part processing

Although mold making and part processing belong to the same category of processing, the difference between the two is large. One of the characteristics of mold processing is unity, each set of molds is different, even the molds of the series products only have similarities, unless the product batch is large, the same mold will be added, but the number is not much . Molds rarely use a tool changer for CNC machining because the machining of each mold can be regarded as a trial process. Although many CNC programming softwares have modular programming functions, that is, similar molds can apply the same parameters, but in details such as deep grooves and steep slopes, the cutting parameters should be re-adjusted according to the clamping length of the tool, and even the tool specifications can be changed. To prevent overcutting caused by tool vibration. Part processing is usually mass-produced, so the parameters after single-piece trial processing can be used in batch copy production. At this time, the use of the tool magazine can greatly improve the speed and correctness of tool change. In other words, after the programming is completed, the batch processing of the parts can be completed by replacing the worn tools as needed during the machining process. If mold processing is as simple as mass production of parts, then an intelligent machining machine with a high-precision on-machine measurement feedback system is required.

2. Parting surface matching

The parting surface mold is an important fitting process in the plastic mold processing. With the display agent mixed with the ratio of red powder and oil, the upper and lower molds are closely combined with the craftsmanship of the fitter to achieve the classification of the injection molded product. There is no cloak on the surface, and the parting line on the product is extremely slender. When the parting surface of the mold is flat, the fitting is relatively simple, and the finishing allowance reserved on the upper and lower mold parting surfaces can be removed by the grinding machine, so that the upper and lower molds are closely matched. When the parting surface of the mold is non-planar, the difficulty of the mold is greatly increased, which is mainly caused by the processing precision of the parting surface. Usually, a ball cutter is used to machine a non-planar parting surface. Compared with a flat-bottomed knife, the contact area of ​​the ball cutter is small and easy to wear, which makes the processed surface and the computer model have a large difference. For large molds, this loss deviation is even more serious. Although the experienced CNC programmer divides the non-half-shaped surface into several areas to offset the deviation to offset the deviation, the wear surface and the wear surface will be added with the appropriate mold allowance, but the mold is still the work of the mold fitter. It is a wrestling between the work of the fitter and the precision of CNC machining. If the mold is machined by the intelligent machining machine mentioned above, the non-planar machining accuracy and tool loss can be fed back to the intelligent control system of the machine tool through precision measurement, thus compensating the non-planar finishing, greatly reducing the non-plane. The difficulty of the plane matching. At present, the processing cost of this type of precision mold is high, but with the continuous innovation and replacement of technology, the popularization of precision mold processing is a trend in the development of the mold industry.

3. 3D printing technology is applied to the design and manufacture of molds

3D printing is a hot topic in recent years. Whether it is the industry or the Internet, its presence can be seen everywhere. It originated from the laboratory. It was active in the top of the manufacturing industry, but suddenly entered the homes of ordinary people in the form of desktop models. Nowadays, it is made in the manufacturing industry by various additive manufacturing methods such as plastics, resins, metals and ceramics. Popularized. The introduction of 3D printing technology in the product design and development process can significantly shorten development time and reduce development costs. In the development of the mold, the trial production of the mold, the processing of special parts and the repair of the mold can be applied to the 3D printing technology.

Investment casting is a common high-precision product casting technology. Its production process can be roughly divided into six steps: wax injection mold design, wax sample production, sand shell production, casting, post-treatment and inspection. We will introduce 3D printing technology in the design of wax injection molds and the production of wax parts. In the development of stainless steel precision casting products, it is often encountered in small batch customization or trial production of tableware and faucets. For example, some famous foreign restaurants or chefs' custom pots often add their trademarks to the pot handle or the cover ear. There are various schemes such as handwritten signature and registered trademark for selection during the development process. In order to save the test cost and shorten the development cycle, the parts of the product trademark in the mold are usually made interchangeable. Suppose a handle needs to test three different trademarks. The position of the product trademark in the mold is to be made into three identically sized inserts, and then three electrodes are made according to the trademark style and formed on the EDM machine. Although wax injection molds are mostly made of easy-to-cut aluminum alloys, CNC machining inserts, copper electrode engraving and EDM machining require at least 9 hours to complete. Considering the molding temperature of the wax sample and the low injection pressure, the 3D printer is equipped with the appropriate consumables, and the required three inserts can be printed in just 3 hours. This not only greatly shortens the processing time, but also does not occupy the CNC and the EDM machine. The advantages are obvious. For personalized one-piece custom products, you can use the appropriate consumables to replace the traditional wax samples directly with the printed parts, while the parts with higher precision requirements or jewelry can also be used for 3D printing wax molds. Production.

4. Fork mold making example

Disposable tableware such as forks are often used when dining out (see photo). The demand for disposable forks is very large. With the continuous improvement of the mold manufacturing process, the average single-layer mold has been increased from less than 20 pieces to 40 pieces. The production efficiency of single sets of molds has doubled. . The huge demand also has strict requirements on the quality of the single fork. Under the premise of ensuring the strength of the fork, it should be made as light as possible. Therefore, the product design of the fork is very important, especially the rib at the bottom of the fork. .

Taking a set of 40-piece disposable fork plastic molds using CI-5050 mold base as an example, the flexible processing of cavity and parting surface is analyzed. The processing of this set of molds has two characteristics: one is the large-area non-planar CNC machining; the other is the deep and narrow groove processing where the reinforcing ribs are located. For the cavity of the plastic mold, the conventional method is to use ordinary hard-rail CNC machining, and the machining of the right-angle or small rounded residual position and the deep and narrow grooves are performed by electric discharge machining. The hard-rail CNC is suitable for processing large-sized plastic molds, especially for rough machining, but the finishing speed is relatively slow. The advantage of EDM is high precision, and the surface hardness of the cavity will increase. However, there is obviously no advantage in using this mold: 1 This mold has many mold cavities, and the ribs are narrow and deep, so the loss of the electrode is very serious. Multiple roughing and finishing electrodes are required, and the same cavity requires multiple EDM to compensate for electrode losses. The 240 cavities are uniformly distributed in a ring shape. For an ordinary three-axis electric spark machine, the alignment and the number of the electrodes are complicated, and the cavity is misplaced or even mistyped. 3 The surface of the whole fork requires polishing, so the hardened electric fire pattern increases the difficulty of polishing.

In view of the above situation, the ordinary hard rail CNC and the line rail engraving and milling machine are combined to process the fork mold. Firstly, roughing and semi-finishing are performed by ordinary hard-track CNC according to the conventional processing method, and then the parting surface and the cavity are subjected to sub-region finishing by a line-track engraving and milling machine, and all the reinforcing ribs are engraved. The wire rail engraving and milling machine has high speed and fast feed rate. It is suitable for processing soft metal and engraving. If it is used for roughing, the efficiency will be much lower, and the loss of machine tools and tools will be serious. The wire rib engraving and milling machine is combined with the specially-grinding forming tool to sculpt the ribs of the fork, which not only has a fast speed, but also saves a lot of electrode material costs and processing costs. The surface roughness of the processed cavity is high, which is convenient for the later polishing process, and is convenient for later debugging to balance the strength and weight of the fork.

5 Conclusion

Fast, efficient and high precision is the development trend of mold making today. It is necessary to rationally use existing processing equipment to continuously transform new technologies and new processes into mold productivity and improve the level of mold production.