Abstract Digital control is an automatic control technology developed in modern times. It is a method of using digital signals to control the movement of machine tools and their processing processes. This article discusses the characteristics and technical points of CNC machining of molds, and explores the application of CNC machining in mold manufacturing.

Keywords mold manufacturing; CNC machining; CNC turning technology; CNC milling technology

1. CNC machining of molds

1) Characteristics of CNC machining of molds< /p>

(1) The manufacturing of molds is single-piece production. Each mold is a new project with different structural characteristics. The development of each mold is a creative work.

(2) The development of molds is not the final product, but serves the development of new products. Generally, the development of new products by enterprises is not fixed in quantity and time, resulting in strong randomness in mold production. , poor planning, including large customer changes and product changes, so there are higher requirements for the personnel of mold manufacturing companies, requiring employees of mold companies to respond quickly, that is, they must have sufficient basic knowledge and practical experience.

(3) Mold manufacturing must be fast. The development cycle of new products is getting shorter and shorter, and molds are one of the most time-consuming projects in new product development. The mold development cycle is shortened accordingly, so molds must have a very fast response from quotation to design and manufacturing. In particular, the mold manufacturing process must be fast to meet customer requirements. Therefore, it is required that the processing procedures of the mold should be highly integrated and the process should be optimized to complete as much processing of the mold as possible in the shortest processing process.

(4) The mold structure is uncertain. The mold needs to be designed according to the shape and structural elements of the part. At the same time, because the products formed by the mold are often new products, changes need to be made during the mold development process, or the shape or structure of the product needs to be adjusted after the mold trial. And these changes require reworking.

(5) Mold processing requires high manufacturing precision. In order to ensure the accuracy of formed products, mold processing errors must be effectively controlled at all times, otherwise the errors on the mold will be amplified on the product. The surface roughness of the mold is required to be high. In order to achieve a smooth surface of the part and to make the melt flow smoothly in the mold, the injection mold or die-casting mold must have a lower surface roughness value.

2) Technical points of mold CNC processing

(1) The mold is produced in a single piece, and there are few opportunities to repeat the mold opening. Therefore, the programming workload of CNC machining is large, and there are higher requirements for programmers and operators of CNC machining.

(2) The mold has many structural components and the CNC machining workload is large. Molds usually have mold bases, cavities, cores, inserts or sliders, electrodes and other components, which need to be formed by CNC machining.

(3) The cavity surface of the mold is complex and has a great impact on the appearance quality of the formed product. Therefore, sufficient accuracy must be achieved when processing the cavity surface, and mold fitter trimming must be minimized and preferably avoided. and hand polish work.

(4) Mold parts generally require multiple processes to complete the processing. They should be completed in one installation as much as possible. This can avoid positioning errors caused by multiple installations and reduce installation time. Usually, mold forming parts are processed by rough milling, fine milling, drilling, etc., and tools of different sizes are used for processing. Reasonable arrangement of the processing sequence and selection of tools have become one of the key factors to improve efficiency.

(5) The mold requires high precision. Usually the mold tolerance range is 1/5 to 1/10 of the formed product, and the precision requirements at the fitting are higher. Only by achieving sufficient accuracy can we ensure that no material overflows, so the machining error must be strictly controlled during CNC machining.

(6) Molds are usually "semi-finished products" and need to be repaired by a mold fitter or other processing, such as EDM, etc. Therefore, when processing, the convenience of subsequent processes must be taken into consideration, such as for subsequent Processes provide easy-to-use benchmarks, etc.

(7) Mold materials usually use very hard steel, such as H13 steel used in die-casting molds. Usually, after heat treatment, the hardness will reach 52~58HRC, while the hardness of forging molds is higher. Therefore, high-hardness carbide tools must be used during CNC machining, and reasonable cutting amounts must be selected for processing. If conditions permit, it is best to use high-speed milling for processing.

(8) Processing of mold electrodes. In mold processing, sharp corners, ribs and other parts cannot be machined in place. In addition, some products with special requirements require EDM, and EDM requires electrodes. A discharge gap needs to be set during electrode processing. Mold electrodes usually use pure copper or graphite. Graphite has the characteristics of easy processing, fast electrical processing speed, and low price. However, during CNC processing, graphite dust causes great damage to the machine tool. A special dust collection device or immersion in liquid is required. For processing, a special CNC graphite machining center is required.

(9) Standardization is an effective way to improve efficiency and shorten processing time. For molds, try to use standard parts to reduce the processing workload.

At the same time, in the mold design and manufacturing process, using standard design methods, such as standardizing and serializing the diameter of the holes, can reduce the number of tool changes and improve processing efficiency.

2. Application of CNC machining in mold manufacturing

1) CNC machining technology of molds can be divided into different energy conversion forms:

(1 ) CNC machining technology. CNC turning technology and CNC milling technology are often used in mold manufacturing. These technologies are developing in the direction of high-speed cutting.

(2) CNC electrical machining technology, such as CNC EDM technology and CNC wire cutting technology.

(3) CNC special processing technology. Including various emerging CNC processing technologies that are not yet widely used, usually using light energy, sound energy, ultrasonic waves, etc. to complete processing, such as rapid prototyping technology, etc.

These processing methods provide new process methods and processing methods for modern mold manufacturing, and enrich the production methods of molds. But the most widely used are CNC milling machines and machining centers; CNC wire cutting and CNC EDM are also very commonly used in CNC mold processing; and CNC lathes are mainly used to process standard parts such as mold rods and mold cavities of rotary bodies. Or core; the application of CNC drilling machines can also play a role in improving processing accuracy and shortening the processing cycle.

In the CNC manufacturing of molds, the application of CNC machining can improve machining accuracy, shorten the manufacturing cycle, and reduce manufacturing costs. At the same time, due to the wide application of CNC machining, it can reduce over-reliance on the experience of mold fitters. . Therefore, the application of CNC machining in molds has brought revolutionary changes to mold manufacturing. Currently, advanced mold manufacturing companies mainly use CNC machining to manufacture molds, and arrange the mold manufacturing process with CNC machining as the core.

2) CNC turning processing

CNC turning is mainly used for the processing of standard parts in mold processing, such as various rod parts such as tops, guide posts, reset rods, etc. In addition, CNC turning is also used in rotary body molds, such as injection molds for bottles and basins, forging dies for shafts and disk parts, and punches for stamping molds.

3) CNC milling

CNC milling is the most widely used and typical in mold processing. It can process various complex curved surfaces, as well as planes, holes, etc. For molds with complex contours or curved surfaces, such as electrodes for EDM, injection molds, die-casting molds, etc., CNC milling can be used.

4) CNC wire-cut EDM processing

For fine and complex shapes, special material molds, plastic inlaid cavities and inserts, and molds with special-shaped grooves, data can be used Wire EDM processing. Wire cutting is mainly used in various straight-wall mold processing, such as concave and convex molds in stamping molds, inserts and sliders in injection molds, electrodes for EDM, etc.

5) CNC EDM processing

Mold cavities and holes, including various plastic molds, rubber molds, forging dies, die-casting dies, rolling and drawing dies, etc. CNC EDM can be used.

In short, molds have the characteristics of complex structure, complex surface, high precision requirements, high hardness of materials used, and short manufacturing cycle. The application of CNC processing molds can greatly improve the processing accuracy, reduce manual operations, improve processing efficiency, and shorten the mold manufacturing cycle. At the same time, the CNC machining of molds is somewhat typical and has higher requirements than the CNC machining of ordinary products.

References

[1] Qiu Yanlong. Practical Technical Manual of Mold Fitter [M]. Beijing: China Electric Power Press, 2010.01

[2] Liu Hongpu. Practical skills of mold fitters [M]. Beijing: Machinery Industry Press, 2006.01

[3] Zhang Nengwu. Common technical manual for mold fitters [M]. Shanghai: Shanghai Science and Technology Press, 2008.10

[4] Zhang Nengwu. Mold fitter skills training tutorial [M]. Beijing: National Defense Industry Press, 2006.04

[5] Zhang Nengwu. Mold worker operating techniques and examples [M]. Shanghai: Shanghai Science and Technology Press, 2009.06