The appearance requirements of medical mould are relatively high. In addition to the absence of epitome, air trap, and pull, the degree of smoothness must be very high. How to make a mirror effect for mould? Polishing is needed to achieve this effect. Mold polishing has two purposes: one, increase the smoothness of mold, so that surface of product produced by the mold is smooth and beautiful; another, easy to demould, so plastic is not stuck on the mold and can not be removed. Mold polishing is generally a process in which the surface of the cavity of the mold is polished by using oil stone, sandpaper, polishing paste, etc., so that the working surface of mold can be bright as a mirror, which is called mold grinding.
Medical mould polishing should not use the finest oil stone, sandpaper, and (grinding) polishing paste from the beginning, so that rough texture cannot be polished. The effect in that way is that the surface looks very bright, but The rough lines show up once the side is illuminated. Therefore, it should be polished from coarse oil stone, sandpaper or (grinding) polishing paste, then polished with finer oil stone, sandpaper or (grinding) polishing paste, and finally polished with the finest (grinding) polishing paste. It looks more troublesome and has many processes. Actually not slow, step by step, grind the rough grain, then proceed to the following process, and will not be reworked, then meet the requirements. Mold polishing is usually roughing the surface of machined mold cavity firstly by coarse oil stone to grind out the tool marks of machine; Then grind traces of rough stone by fine oil stone; Finally grind mold cavity surface by (grinding) polishing paste to achieve a mirror effect. This is the whole process of medical mould polishing. Of course, if possible, you can use an ultrasonic polishing machine to polish the mold, which is more efficient and more labor-saving.
A few days ago, Luo Baihui, general secretary of International Model Association, said in an interview that, with changes in economic climate and globalization of competition, the mold manufacturing industry has undergone dramatic changes in the past 10 years. Standardized single precision parts have replaced hand-mounted Parts, standardized basic parts and components are generally promoted and applied, and more and more customers have production networks around the world. Mold makers are able to reasonably produce molds, assemble as quickly as possible, and ensure every part has its replacement suppliers worldwide.
Years of experience make Hafo Mould an export in the field of medical mould.
- High standard engineering technology
The continuous introduction of 3D-CAD design, CAD/CAM, and machining centers can realize the industrial production of molds. Moreover, high-speed milling (HSC) and combined workpiece machining have become the latest technology in the field of mold making. These new developments have replaced traditional processes such as profile milling and EDM, as well as a small amount of wire-conducting spark machining. The high surface quality achieved by HSC milling has made time-consuming surface finishes no longer needed after EDM. High-quality metal removal production processes have replaced individual assembly and counter-molding of mold inserts, and instead are centralized assembly.
Unified and high precision Mold inserts for industrial production promote the balance of the sprue system. The latest technology for injection molding of thermoplastics is hot runner system, while the latest technology for injection molding of elastomers is cold runner system.
- New injection molding process
The imagination and ability of mold manufacturing designers and production experts have also stood the test. They have to turn many of innovations that have been made in process of engineering over the past decade into successful practices. However, hot runner injection systems or gas injection methods have also been continuously applied.
The development of these mold manufacturing technologies also requires close cooperation from customers (such as injection molding plants), end users, materials and equipment manufacturers. Increasing mold complexity (the number of cavities, the combination of different processes) also forces mold manufacturing to become more standardized. Compared to the situation 10-15 years ago, it is difficult for ordinary mold makers to be competitive in today’s market. However, changing the product concept to mold design will always be the main task of mold manufacturing industry.
- Micro injection molding process
Micro-injection molds are generally lighter than 1 gram, but the total weight of parts contained in the product is only 0.01 gram. The geometry of these micro-injected parts is as varied as large injection molded parts.
For molded micro-components, there are two systems that can be chosen from. The first type is a combination of non-standard injection molding devices consisting of a clamping device, a material preparation, an injection device, a mold and so on. In this case, the mold is equipped with a rotating plate so that the whole object can be taken out of the mold easily.
The second type is called variable temperature injection molding. The basic principle is to heat the mold to melting temperature of plastic being processed in each cycle to promote filling of the mold cavity. Once the cavity is filled, it cools down. To reduce the cooling time, as few mold inserts are subject to temperature cycling. The remaining mold structure is maintained at the demolding temperature and mold insert relies on electrical heating, so its cross-sectional area determines the strength of heating.
Cooling mold insert is quite challenging. Because of small size, it is difficult to have space to concentrate the cooling channels. They have a small cross-sectional area and high flow resistance to any cooling liquid. Therefore, air is an ideal cooling medium.
With the variable temperature method, a cycle time of 15 seconds is currently available for injection molding, although the insert has to withstand a temperature of 200 ° C to 50 ° C in each cycle.
In addition to cooling, another particular problem is caused by venting of mold during the micro-injection process. Exhaust is accomplished by a dividing line between inserts. At the current stage of development, note is still large. In a four-cavity mold, contents of cavity account for 30%-50% of injected weight. There is no hot runner system suitable for micro injection molding.
Micro molds can be made by microetching or micromachining. With spark erosion processing method, the radius can reach 20μm, the roughness depth can reach 0.2μm; And the wire conductive spark machining method has a radius of 30μm and a roughness depth of 0.1μm.
Micro mould including sensor case moulding of portable hearing aid, or component mould of microswitch. In experimental applications, it has been possible to make plate-shaped components from polyoxymethylene (POM) with a thickness of only 0.01-0.03 mm. The exhaust passage of the conventional injection mold is 0.03 mm.
- New steel
Steel produced by powder metallurgy or HIP (high temperature equalization) method has been widely used, and has made an important contribution to the improvement of the quality of injection molds. In this way, high precision of finished product can be maintained in the long-term operation, and size of mold can be deviated within a range of at most 5 μm. To prevent flashing, vent width must be less than 5μm.
A similar process can be used for processing of rubber. In this field, compression molding techniques for manually unloading molded parts are also widely used. With the innovative concept of silicone injection molding, automated production of rubber objects will become possible in the future.
The transition from compression molding to injection molding is an important prerequisite for improved working conditions. A large amount of water vapor and gas are usually discharged during the rubber vulcanization process. Because the pressure is vertical, it is only possible to evacuate gas from operator’s station. With injection molding, gas rises directly into the extraction system while the operator stands next to the mold. With automated injection molding, the entire mold station, including manual handling of unloading plastic parts, is most effective as an extraction gas.
With advent of elastic molded parts, the application of liquid silicones will likely become more extensive than processing of natural rubber. The combination of silicone with other materials has been considered feasible. And injection molds required for these processes have emerged.
- Injection molding assembly using multi-component molds
Multi-component mold replaces individual components of assembly and is a prominent feature of molding manufacturing part of injection molding equipment manufacturer. Injection molds are the core of production department, and acceptance of new product concepts promotes the integration of internal technologies, leading to cooperation between applied research, automation technology and mechanical engineering departments.
Multi-component injection molds for hard/soft composites occupy a particularly important position. These include functional components with complete seals, as well as “soft-touch” containment (such as toothbrush moulding, screwdriver mould, razor case mould, and moulding of shock absorbers for appliances). For this purpose, a solid thermoplastic part is made on the first workbench. On the second table, the molded part receives a seal, in most cases consisting of a thermoplastic elastomer (TPE). When the mold alternates between two stations, it usually rotates. This turntable may be part of the injection molding machine.
In general, design of multi-color or multi-component injection molding depends on the specified operation (complexity of the finished product, number of parts produced, etc.). For each project, customer-defined requirements determine the overall design and cycle time. The aim is to concentrate any assembly process into injection molding process.
As the need for deeper integration of individual components during injection process continues, more complex molds are created, as well as a combination of thermoplastic and rubber elastomeric components. This requires a cooled mold for thermoplastic material and a heated mold for vulcanization of rubber. The combination of different temperature, thermal diffusivity ratios and different processing techniques places great demands on resolution of interdisciplinary issues.
Some tips about 3D printing (especially in medical mould)
Today, 3D printing and a variety of printing materials (plastics, rubber, composites, metals, waxes and sands) have brought great convenience to many industries, such as automotive, aerospace, healthcare and medical. We are integrating 3D printing including mold making.
So what benefits can mold manufacturing get from 3D printing technology?
In fact, the following aspects of mold manufacturing are able to use 3D printing technology:
o Forming (blow molding, LSR, RTV, EPS, injection molding, pulp molds, soluble cores, FRP molds, etc.)
o Mold (melting mold, sand mold, spinning, etc.)
o Forming (thermoforming, metal hydroforming, etc.)
o Machining, assembly and inspection (fixed fixtures, mobile fixtures, modular fixtures, etc…)
o Robot end effector (gripper)
There are many advantages to making a mold with 3D printing:
1) Shorter mold production cycle
3D printing molds shorten the entire product development cycle and become source of drive innovation. In the past, companies sometimes chose to postpone or abandon product design updates because they also needed to invest heavily in new molds. By reducing mold preparation time and enabling existing design tools to be quickly updated, 3D printing enables companies to withstand more frequent replacement and improvement of molds. It enables the mold design cycle to keep pace with product design cycle.
2) Reduced manufacturing costs
If cost of current 3D printing of metal is higher than the cost of traditional metal manufacturing processes, cost reduction is easier to achieve in the field of plastic products.
Metal 3D printed mould have economic advantages in the production of small, discontinuous series of end products (because the fixed costs of these products are difficult to amortize), or for specific geometries (optimized for 3D printing). Especially when materials used are very expensive, and traditional mold manufacturing leads to a high material scrap rate, 3D printing has a cost advantage.
In addition, the ability of 3D printing to produce precision mould in a matter of hours can have a positive impact on manufacturing processes and profits. Especially when production downtime and / or mold inventory is very expensive.
Finally, it is sometimes case that mold is modified after the start of production. The flexibility of 3D printing allows engineers to experiment with countless iterations at the same time and reduce upfront costs due to mold design modifications.
3) Improvements in mold design to add more functionality to the end product
In general, special metallurgical methods of metallic 3D printing can improve the metal microstructure and produce fully dense printed parts that are as good or better than those of forged or cast materials (depending on heat treatment and test direction). Additive manufacturing offers engineers unlimited options to improve mold design. When target parts consist of several sub-parts, 3D printing has the ability to integrate design and reduce the number of parts. This simplifies product assembly process and reduces tolerances.
In addition, it is able to integrate complex product features, enable high-performance end products to be manufactured faster and with fewer product defects. For example, the overall quality of an injection molded part is affected by heat transfer between injected material and cooling fluid flowing through the fixture. If manufactured using conventional techniques, passages that direct the cooling material are generally straight, resulting in a slower and uneven cooling effect in the molded part.
And 3D printing can achieve any shape of cooling channels to ensure that the shape of the cooling, more optimized and uniform, ultimately leading to higher quality parts and lower scrap rate. In addition, faster heat removal significantly reduces cycle time of injection molding because in general cooling time can account for up to 70% of entire injection cycle.
4) Optimization tools are more ergonomic and improve minimum performance
3D printing reduces threshold for validating new tools that address unmet needs in the manufacturing process, enabling more mobile fixtures and fixtures to be built into the manufacturing process. Traditionally, because of considerable cost and effort required to redesign and manufacture them, design of tool and orresponding device are always used as long as possible. With the application of 3D printing technology, companies can refurbish any tool at any time, not just those that have been scrapped and do not meet the requirements.
Due to the small time and initial cost required, 3D printing makes it more economical to optimize tools for better marginal performance. Technicians can then design ergonomics more to improve their operational comfort, reduce processing time, and make them easier to use and easier to store. Although doing so may only reduce the assembly operation for a few seconds.