Medical Molding

The appearance requirements of medical mold 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 mold? Polishing is needed to achieve this effect. Mold polishing has two purposes: one, to increase the smoothness of decay, so that surface of the product produced by the mold is smooth and beautiful; another, to make it accessible to demould, so plastic is not stuck on the mold and can not be removed. Mold polishing is generally a process in which the mold’s cavity’s surface is polished using oil stone, sandpaper, polishing paste, etc. The working surface of the mold can be bright as a mirror, which is called mold grinding.

Medical mold polishing should not use the most delicate oil stone, sandpaper, and (grinding) polishing paste from the beginning, so that rough texture cannot be polished. The effect is that the surface looks very bright, but The irregular 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 more delicate oil stone, sandpaper, or (grinding) polishing paste, and finally polished with the finest (grinding) polishing paste. It looks more troublesome and has many processes. Not slow, step by step, grind the rough grain, then proceed to the following procedure, and will not be reworked, then meet the requirements. Mold polishing usually roughs the surface of machined mold cavity firstly by coarse oil stone to grind out the tool marks of the 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 mold 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 the International Model Association, said that the mold manufacturing industry had undergone dramatic changes in the economic climate and globalization of competition. Standardized single precision parts have replaced hand-mounted Parts, standardized essential parts and components are generally promoted and applied, and more and more customers have production networks around the world. Mold makers can reasonably produce molds, assemble them 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 mold.

1. 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 mold-making technology. These new developments have replaced traditional processes such as profile milling and EDM and 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 the hot runner system, while the latest technology for injection molding of elastomers is the cold runner system.

2. 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 innovations made in the process of engineering over the past decade into successful practices. However, hot runner injection systems or gas injection methods have also been continuously applied.

Developing 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 makes mold manufacturing 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 the mold manufacturing industry.

3. Microinjection 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, two systems can be chosen. 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, etc. In this case, the mold is equipped with a rotating plate to take the whole object out of the mold easily.

The second type is called variable temperature injection molding. The basic principle is to heat the mold to the melting temperature of plastic being processed in each cycle to promote the filling of the mold cavity. Once the hole is filled, it cools down. Few mold inserts are subject to temperature cycling to reduce the cooling time. The remaining mold structure is maintained at the demolding temperature, and the mold insert relies on electrical heating, so its cross-sectional area determines the strength of heating.

Cooling mold insert is quite challenging. Because of its small size, it isn’t easy to have space to concentrate the cooling channels. They have a small cross-sectional area and high flow resistance to any cooling liquid. Therefore, the air is an ideal cooling medium.

With the variable temperature method, a cycle time of 15 seconds is currently available for injection molding. However, the insert must withstand a temperature of 200 ° C to 50 ° C in each cycle.

In addition to cooling, another problem is caused by mold venting during the microinjection process. A dividing line between inserts accomplishes exhaust. At the current stage of development, the note is still significant. In a four-cavity mold, cavity contents account for 30%-50% of the injected weight. There is no hot runner system suitable for micro injection molding.

Micro molds can be made by micro etching or micromachining. With the 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 mold, including sensor case molding of portable hearing aid or component mold of the microswitch. In practical 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.

4. New steel

Steel produced by powder metallurgy or HIP (high-temperature equalization) method has been widely used and improved injection mold quality. In this way, the high precision of the finished product can be maintained in the long-term operation, and the mold size can deviate within a range of at most five μm. To prevent flashing, the vent width must be less than 5μm.

A similar process can be used for the processing of rubber. In this field, compression molding techniques for manually unloading molded parts are 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 to injection molding is essential for improved working conditions. Many 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 the operator’s station. With injection molding, gas rises directly into the extraction system while the operator stands next to the mold. The entire mold station, including manual handling of unloading plastic parts, is most effective as an extraction gas with automated injection molding.

With the advent of elastic molded parts, the application of liquid silicones will likely become more extensive than natural rubber processing. The combination of silicone with other materials has been considered feasible. And injection molds required for these processes have emerged.

5. Injection molding assembly using multi-component molds

Multi-component mold replaces individual assembly components and is a prominent feature of molding manufacturing part of injection molding equipment manufacturer. Injection molds are the core of the production department. Accepting 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 critical position. These include functional components with complete seals and “soft-touch” containment (such as toothbrush molding, screwdriver mold, razor case mold, and molding 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, multi-color or multi-component injection molding design 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 the injection molding process.

As the need for deeper integration of individual components during the injection process continues, more complex molds are created and a combination of thermoplastic and rubber elastomeric components. This requires cooled mildew for thermoplastic material and a heated mold for vulcanization of rubber. Different temperatures, thermal diffusivity ratios, and different processing techniques place excellent demands on resolving interdisciplinary issues.

Some tips about 3D printing (especially in medical mold)

Today, 3D printing and various 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?

The following aspects of mold manufacturing can use 3D printing technology:

o Forming (blow molding, LSR, RTV, EPS, injection molding, pulp molds, soluble cores, FRP molds, etc.)

o Mold (melting mildew, 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 a source of driving 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 allows companies to withstand more frequent replacement and improvement of molds. It will allow the mold design cycle to keep pace with the product cycle.

2) Reduced manufacturing costs

If the cost of current 3D printing of metal is higher than traditional metal manufacturing processes, cost reduction is easier to achieve in plastic products.

Metal 3D printed molds have economic advantages in producing small, discontinuous series of end products (because the fixed costs of these products are challenging to amortize) or specific geometries (optimized for 3D printing). Especially when materials are costly 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 mold in a matter of hours can positively impact manufacturing processes and profits. Especially when production downtime and mold inventory are costly.

Finally, it is sometimes the case that the mold is modified after production. 3D printing allows engineers to experiment with countless iterations simultaneously and reduce upfront costs due to mold design modifications.

3) Improvements in mold design to add more functionality to the end product

In general, unique metallurgical methods of metallic 3D printing can improve the metal microstructure and produce fully dense printed parts that are as good or better than 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 can integrate design and reduce the number of factors. This simplifies the product assembly process and reduces tolerances.

In addition, it can integrate complex product features and 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 form of the cooling is more optimized and uniform, ultimately leading to higher quality parts and lower scrap rate. In addition, faster heat removal significantly reduces the cycle time of injection molding because, in general, cooling time can account for up to 70% of the entire injection cycle.

4) Optimization tools are more ergonomic and improve minimum performance

3D printing reduces the 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 the considerable cost and effort required to redesign and manufacture them, the design of tools and corresponding devices is always used for as long as possible. With the application of 3D printing technology, companies can refurbish any instrument at any time, not just those that have been scrapped and do not meet the requirements.

Due to the short 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.