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Medical Plastic Injection Moulding ? Procedure and Products

In 1868, John Wesley Hyatt developed the first plastic injection mold, and the plastic injection moulding process. He used the plunger method to successfully inject hot, liquid celluloid, often called the first thermoplastic, into a split-die mold. This process was little changed until James Hendry built the first screw plastic injection mold in 1946. Today, nearly all industrial and medical plastic injection moulding processes use the screw method.

Plastic moulding is a very methodological and technical process. Thus it needs experts in this type of manufacturing business for it to meet the safety terms and to be competitive in the market. A very scientific and systematic mechanical study is first made before going into this endeavor. Here I have discussed some known plastic injection moulding process that can help you to understand the various ways it is done for industry specific plastic products.

1. Injection Moulding.

Examples of applications: Medical plastic laryngeal mask components, laboratory products, extraction systems, toys, aircraft undercarriage components, kitchen utensils, bottle caps, and cell phone stands.

In Injection Moulding, melted plastic is forced into a mold cavity. Once cooled, the mold can be removed. This plastic injection moulding process is commonly used in mass-production or prototyping of a product. Typically this process is used to produce plastic mouldings where the relatively high tooling cost can be justified by low unit costs and tolerances which cannot be achieved by other moulding processes.

2. Blow Moulding.

Examples of applications: Automotive, Toys, Recreational, tubes and containers, Medical, Housework Appliances

The process is divided into three steps: injection, blowing and ejection. Blow moulding is like plastic injection moulding except that hot liquid plastic pours out of a barrel vertically in a molten tube. The mold closes on it and forces it outward to conform to the inside shape of the mold. When it is cooled, the hollow part is formed. Equipments needed in setting-up a blow moulding business are relatively higher than injection moulding.

3. Compression Moulding.

Examples of applications:  Automotive exterior panels especially for commercial vehicles, Radio & appliance knobs, ash trays & electrical parts.

In this type of plastic moulding, a slug of hard plastic is pressed between two heated mold halves. Compression moulding usually uses vertical presses instead of the horizontal presses used for injection and blow moulding. The parts formed are then air-cooled. Prices of equipments used for compression moulding are moderate.

4. Film Insert Moulding.

Examples of applications: FIM can be used to apply clear scratch-resistant hard coats, logos, text and graphics in any color or combination of colors to plastic parts prior to injection molding.

This plastic moulding technique imbeds an image beneath the surface of a molded part. A material like film or fabric is inserted into a mold. Plastic is then injected.

5. Gas Assist Moulding

Examples of applications:  Flat panels for office equipment, Computer enclosures, Furniture, i.e. tabletops, Automotive panels, Domestic appliances – e.g. fridges.

Also called gas injection moulding is used to create plastic parts with hollow interiors. Partial shot of plastic is then followed by high-pressure gas to fill the mold cavity with plastic.

6. Rotational Moulding.

Examples of applications:  All kinds of plastics mostly hollow Plastic Parts.

Hollow molds packed with powdered plastic are secured to pipe-like spokes that extend from a central hub. The molds rotate on separate axes at once. The hub swings the whole mold to a closed furnace room causing the powder to melt and stick to the insides of the tools. As the molds turn slowly, the tools move into a cooling room. Here, sprayed water causes the plastic to harden into a hollow part. In this type of plastic moulding, tooling costs are low and piece prices are high. Cycle time takes about 40-45 minutes.

7. Structural Foam Moulding.

Examples of applications: Typical products are large trash containers, freeway sand safety containers and in-ground housing for water systems.

Structural foam moulding is a process of plastic injection moulding usually used for parts that require thicker walls than standard injection moulding. Inserting a small amount of nitrogen or chemical blow agent into the plastic material makes the walls thicker. Foaming happens as the melted plastic material enters the mold cavity. A thin plastic skin forms and solidifies in the mold wall. This type of plastic moulding can be used with any thermoplastic that can be injection molded.

8. Thermoforming.

Examples of applications: Clamshells, Trays, Blisters, Displays, Guards, Covers, Totes, Shields, medical plastics

In this plastic moulding process, sheets of pre-extruded rigid plastics are horizontally heated and sucked down into hollow one-piece tools. When the hot plastic solidifies, its shape conforms to that of the mold. Tooling costs are usually low and piece prices vary on the machinery.

Plastics Injection Molding

We are agents for a variety of Hong Kong and China owned factories.

Our primary business is plastic injection tools and moulded parts.  This part of the business has grown very rapidly during the last 2 years and we have now formed a joint venture with our China based toolmaker to provide a more complete service in-house; toolmaking, moulding and assembly.  

For plastic components, our significant benefits include:

low tooling cost,

very quick turn-around time with an average job taking 35-40 days for the first samples,

both toolmaking and moulding done in-house,

our own assembly factory provides the facilities to do light assembly of plastic and metal components, specialised packaging and other value added services.

Because of these benefits, we have been able to assist many customers by helping them get their new products to market quickly and economically.

For some other customers, we have made single cavity trial tools to allow them to test a concept of a new/complex product before they proceed further with multi-cavity tooling.

While our name is Short Run Plastics, we do much much more than this and many of our plastic moulding jobs are of significant volume.

In addition to the plastics, we also offer a broad range of metalwork and other components and services as listed in the menus above.

 We are based in Hong Kong and currently supply customers in Australia, UK, Austria and the USA.

Our suppliers are all located in southern China, typically within 3 hours travelling from Hong Kong. 

If you are looking for something that is not listed on our web site, please do not hesitate to contact us and we will give you a prompt reply as to whether we can assist you or not.  We concentrate on southern China where most products are available but not all.

“Micromold, Inc. specializes in small, intricate precision plastic and metal injection molding for a variety of applications spanning numerous industries. www.micromoldinc.com Please take a moment to browse our web site. If you have any questions, special requirements or would like to request a quote, please call us at (951) 684-7130

Related Plastic Injection Articles

Conformal Cooling Channel Design for Plastic Injection Molding

The constant temperature mold of molding plastic parts with high precision contours is of significance in determining not only the productivity of the injection molding process but also the product quality. A solution to this challenge is the rapid thermal response molding process in which uniform temperature overall the mold part ensures the product quality by preventing differential shrinkage, internal stress and mold release problems (Li, 2001). Many Computer-Aided-Engineering (CAE) and optimization methods have been carried out to observe and fine-tune the influences of the thermal system (Park et al., 1998). The results of these research works are obtained by using thermal analysis modules of commercial CAE packages such as C-Mold or Moldflow which are based on the initial designs generated by the human. By given an initial thermal configuration design, efficiency and quality of the molded part can be predicted before an actual plastic mold is manufactured. One more necessary step for the complete automation in the molding thermal system is to generate the initial design for the conformal cooling channels.For example <a rel=”nofollow” onclick=”javascript:pageTracker._trackPageview(‘/outgoing/article_exit_link’);” href=”http://www.cikmold.com”> casting mould,mold making,plastic injection mold </a> etc. In this paper, a featured-based approach to this problem is proposed. Super-quadrics is presented as a tool for recognizing the plastic part shapes and an algorithm is applied for generating the center line of the thermal sub-system of each individual surface. Finally, these sub sets of center lines are combined to create a unique center line which is the guide line for generating the cooling channel of the thermal system.

Conformal cooling channel, as the name implies, refers to the channels that conform to the surface of the mould cavity. Conformal cooling channels have demonstrated simultaneous improvement in production rate and part quality as compared with conventional production tools. In the previous researches, cooling line design and fabrication have been confined to relatively simple configuration, primarily due to the limits of the fabrication method used to make tools, but also due to the lack of appropriate design methodology. Emergence of Solid Freeform Fabrication processes with the ability to fabricate 3-D feature with almost arbitrary complexity is exceedingly useful to mould design process (Xu et al., 2001). The remaining problem to be solved is how to optimize the design process of the thermal system. In this paper, a systematic method for designing cooling channel is proposed. Firstly, the feature recognition algorithm is applied to identify and decompose the moulded part into manageable sections so-called cooling zones. In the next step, a sub-system of cooling channel is generated for each cooling zone. These sub-systems of cooling channels are further decomposed into smaller elements called cooling cells which are easy to be analysed. Lastly, the combination process of these sub-systems is done to create a complete conformal cooling system for the whole plastic part based on the constraints of the combination algorithm and design rules.

Nowadays, feature-based modeling has been a standard for 3D designs. Most of the complex shapes are obtained by synthesizing from sets of simple features. This design strategy is not sensitive to the part geometry; therefore, it keeps the simplicity of the design routine no matter how complicated the geometry of the part is. For the same purposes of simplicity and efficiency, the molded part is segmented into sub-features that must be recognized for the partial thermal system designs. Feature recognition has drawn much attention from researchers and been proposed in literatures (Lentz et al., 1993). The majority of these has based on machining feature recognition techniques which can be classified in three categories: graph-based methods, volumetric methods and hint-based methods. Although recent machining feature recognition technique can be a good solver for parts with complicated intersecting feature, this technique is not appropriate for detecting shape feature for thermal system design of plastic products. In plastic products, free-form surfaces are mostly used and hence, free-form features have to be processed. Furthermore, a shape feature in a plastic part may blend smoothly to another feature and the boundaries between features can not be explicitly defined. With these two reasons, neither graph-based methods, volumetric methods nor hint-based methods can be applied.

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