Injection Molding Conformal Cooling, May Needs 1,500 Metal 3D Printer in the Future

Time:2019-06-03 08:50:40 / Popularity: / Source:

According to relevant data, conformal cooling technology of injection molding was first proposed by Professor Sachs of Massachusetts Institute of Technology in 1997. He believes that this technology will be one of the four main applications of 3d printing technology. After 20 years of continuous development of 3d printing technology, scale application of this technology in mold industry has also been confirmed. According to data, in some molding factory, current conformal cooling mold business has accounted for 40% of total business.

"In next 10 years, China's mold industry needs 1,500 metal 3D printer."

Conformal cooling method of injection molding differs from conventional cooling method. Shape of cooling water channel varies with shape of the injection molded product, and is no longer a conventional linear shape. 3D printing technology can avoid limitation of cross-drilling in manufacture of cooling water circuit. Conformal cooling water channel of 3d printing technology can also design different cooling circuits according to cooling requirements, so as to dissipate heat at a uniform speed to promote uniform heat dissipation.
For molding factory, because quality of mold directly determines efficiency of injection molding and quality of product, thus determining added value of product, so how to efficiently cool plastic product in minimum cycle time becomes a key consideration in the design and manufacturing process of conformal cooling injection molding, and cooling plays an important role during this period.
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Principle of conformal cooling is to rapidly reduce temperature of plastic part in a uniform continuous manner, injection molded parts cannot be taken out of injection moulding die during cooling process until cooling is sufficient, and then injection molded parts is taken out from injection moulding die. Any hot spot will delay injection molding cycle of injection molded parts, which may cause warpage and dent of injection molded parts after demolding, and may damage quality of surface of plastic part. Rapid cooling is removal of heat from injection molded parts by passage of coolant in mold. Speed and uniformity of this cooling effect is determined by speed of fluid passage and cooling fluid passing through it.
In traditional injection moulding die, cooling water circuit creates an internal network through cross-drilling and adjusts flow rate and direction through a built-in fluid plug. Application of metal 3D printing technology in manufacture of mold cooling waterways has broken through limitations of cross-drilling methods on cooling waterway design. Now molding factory can design conformal waterways that are closer to mold cooling surface with smooth corners, faster flow rates and higher cooling efficiency.
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Conventional in-mold cooling channels are achieved by secondary processing. By cross-drilling, internal network of straight tube is produced, flow rate and direction are adjusted by built-in fluid plug. This method has its limitations, shape of water network is limited, so cooling passage is far from surface of mold, cooling efficiency is low. Not only that, but also additional processing and assembly time, and risk that blind spot network may be blocked; and in complex cases, in order to reserve cooling channel, injection moulding die needs to be cut into several parts to be manufactured and then spliced into a single piece of injection moulding die, which leads to additional manufacturing steps and also shortens life of injection moulding die.
Difference between conformal cooling method and conventional cooling method is that shape of cooling water channel changes with shape of injection moulding products, and is no longer linear. This cooling water channel solves problem that distance between traditional cooling water channel and surface of mold cavity is inconsistent, so that injection moulding products can be uniformly cooled and cooling efficiency is higher.
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3D printing manufacturing frees people from limitations of cross drilling. Now you can design inner channel closer to cooling surface of injection moulding die with smooth corners, faster flow, increase efficiency of heat transfer to coolant; you can also design different cooling circuits based on cooling requirements, aiming to dissipate heat at a consistent speed to promote uniformity of heat dissipation. Coolant throughput is critical to cooling rate of injection moulding die, and smooth corners must be designed to reduce pressure loss along passage.
It is reported that metal powder selective laser melting (SLM) 3D printing technology can also be produced in cooling channels as small as 1.4 mm in diameter. One of benefits of powdered 3D printing manufacturing technology is that powder melts a slightly textured surface that increases surface area of cooling contact, resulting in better heat transfer, which increases cooling efficiency and forming a small turbulence in the channel, thereby achieving self-cleaning of the channel. Conformal cooling injection molding made by 3d printing technology can improve injection molding efficiency by 70% or more. For example, an ice scraper mold can be processed by additive manufacturing method, which can reduce injection molding cycle from 80 seconds to 40 seconds. This means that production speed of injection molded parts has doubled.
Other major advantages of conformal cooling molds manufactured by additive manufacturing include: ability to form more uniform plastic articles, zero defects in article, and avoiding dents due to uneven cooling rates. In addition, when developing new injection moulding products, it helps to complete development of new products with fewer iterations.
Of course, more advantages include: In manufacture of complex molds, additive manufacturing methods are faster than traditional methods due to reduced cooling channel processing and splicing.
It should be noted that molds produced by additive have a low surface precision, and final surface precision is obtained by post-finishing and polishing. At this stage, traditional machining and complementary manufacturing advantages complement each other.
In 2007, Shi Yusheng and Wu Zhigang proposed a design method of conformal cooling water channel based on discrete/aggregate model, and established a heat transfer model with circular, elliptical, semi-elliptical and U-shaped cooling channels. Moreover scented box mold was successfully fabricated using selective laser sintering (SLS) technology.
Cross-sectional shape of cooling water channel processed by 3d printing technology is diverse, and may be U-shaped, circular, elliptical and so on. Conformal cooling water channel adopts SLM forming process for 3d printing technology, and cross section adopts circular cross section, which not only reduces accumulation of thermal stress at the corners, but also avoids mold damage caused by stress concentration during injection molding. It can also accurately learn from design experience of traditional injection molding cooling water channels to better control wall temperature of mold. Cooling of an impeller can be divided into two parts: end surface and blade. Specific cooling scheme is as follows:
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  • Cooling scheme for cavity.
Option 1, cooling channel diameter is 3mm, pipeline has one water inlet and one water outlet, as shown in Figure 2a.
In scheme 2, cooling channel diameter is 4mm, and overall shape of cooling water channel is a ring shape, as shown in Fig. 2b.
Option 3, cooling channel diameter is 3mm, pipeline has 3 water inlets and 3 water outlets, as shown in Figure 2c.
In scheme 4, diameter of cooling channel is 4 mm, and overall shape of cooling channel is rectangular, as shown in Fig. 2d.
  • Cooling of core.
In Scheme A, cooling water channel has a diameter of 6 mm, and overall shape of cooling water channel is a ring shape, as shown in Fig. 2e.
In Scheme B, cooling channel has a diameter of 6 mm, and overall shape of cooling channel is rectangular, as shown in Fig. 2f.
In pre-free cooling design, a software Moldflow is used. Moldflow is a professional injection molding CAE software with powerful functions. It is widely used in mold flow analysis in the field of injection molding. Moldflow 2014 version is designed for use with contoured cooling channels, with powerful design and optimization features. In the future, with continuous development and application of 3D printing technology, conformal cooling technology will gradually become a hot spot in the research of injection molding cooling system. Use of 3D printing technology to manufacture conformal cooling mold not only simplifies processing process, but also facilitates design of conformal cooling water channel, and improves design efficiency to make cooling water channel more conformable.

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