What is Injection Molding

Injection molding is a manufacturing process for producing parts in large quantities. It is mostly used for mass production of items which need to be manufactured in thousands or even millions.

Injection molding can be done with a wide variety of plastic polymers. In the process, the product is first designed followed by designing of the mold. The mold is made from either steel or aluminum and it is precision-machined to incorporate the intricacies of the final product.

Once the mold is designed, it can be used for manufacturing the products in bulk. During the manufacturing process, the raw material which is generally plastic is fed into a heated barrel and mixed using a helical shaped screw.

The molten plastic is then forced injected into the mold cavity, where it cools and solidifies to the design of the mold cavity.

 

Most Used Materials for Injection

Injection molding makes use of many thermoplastics for manufacturing products. Some of the most commonly used materials for injection molding are as follows:

 

Acrylonitrile Butadiene Styrene (ABS)

ABS is an opaque thermoplastic and an amorphous polymer. It is a flexible and lightweight item which is used for manufacturing many items used in our daily lives.

The advantage of using ABS is that it can be modified to make improvements in impact resistance, toughness, and heat resistance.

When ABS is molded in high temperature, it improves the gloss and heat resistance of the product while molding in low-temperature results in high impact resistance and strength.

 

Polyethylene

Polyethylene is one of the most popular plastics used for injection molding. It was developed by the German and Italian scientists.

The two most common types of plastics used are high-density polyethylene (HDPE) and low-density polyethylene (LDPE). Using polyethylene for injection molding has the distinct advantages of high-level ductility, tensile strength, impact resistance, and recyclability.

The higher the density of polyethylene uses, the stronger, more rigid, and heat resistant the product is.

 

Polycarbonate

Polycarbonate plastics are naturally transparent plastics used to manufacture a variety of products through injection molding.

It is particularly suitable for manufacturing products with high impact resistance and transparency. The polycarbonates can go through large deformations but still not crack or break, unlike other plastics.

It is commonly used to manufacture medical products, eyewear lenses, automotive components, and cell phones.

 

Polyamide

Polyamides are used in different applications due to its excellent electrical properties, toughness, wear resistance, and chemical resistance. It has a high degree of stability which provides the added strength to the products.

It has very good resistance to abrasion, impact, and chemicals. It is widely used for manufacturing medical products, automotive products, sports equipment, industrial components etc.

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Polypropylene (PP)

PP is a very common plastic which is characterized by its flexibility. It also has a high melting point, high-stress resistance, and excellent impact strength.

It is also chemical resistant and does not break down due to reactions with water, acids, detergents etc.  It is mostly used for manufacturing utensils, apparels, automotive parts, etc.

 

Common Applications of Injection Molding

Injection molding has a very wide variety of applications. It can be used to manufacture simple daily use products and also highly complex products. Some of the most common applications of injection molding are discussed below:

 

Automotive and Transportation

Injection molding is used for manufacturing most of the automotive parts like dashboards, bumpers, grills, doors, front covers, etc. are all manufactured through the injection molding process.

The importance of the process can be understood from the fact that about 90% of the automotive parts are produced using injection molding.

Medical Products

The injection molding process is commonly used for manufacturing of medical devices in large quantities. It can be used to produce medical devices with high precision and consistency.

The injection molding industry is witnessing the highest growth rate of about 6% annually in the medical device manufacturing segment.

 

Daily Use Products

Many of the products used in our daily lives are manufactured using injection molding. Products like plastic bottles, plastic containers, plastic furniture, toys etc. are all manufactured using injection molding technology.

The products manufactured through this process are lightweight and durable which last for a long time.

 

Consumable and Electronics

The consumables and electronic items are also widely manufactured using the injection molding technology.

Electronic products and accessories like cell phones, cell phone accessories like casings, earphones, tablet covers, camera body, remote controls, electronic parts for TVs and computers etc. are manufactured using injection molding.

 

Packaging

One of the most common and popular applications of injection molding technology is packaging. In the year 2016, packaging was the leading injection molding application with a total demand of 43,385 kilotons.

This application is used for packaging of food items and other non-food items also. It helps to keep the products safe and prevents the damage during transit.

 

Building and Construction

Injection molding is also finding widespread application and popularity in the building and construction industry. Plastic is lighter and stronger than wood and some other metal products.

It also has the added advantage of being recyclable. Injection molding is used for manufacturing products like roofing vents, railing gaskets, deck fasteners, window and door frame components etc. which are quite commonly used in the building and construction industry.

 

Advantages of Injection Molding

There are many advantages to using injection molding. Some of the major advantages are as follows:

 

Efficient Process

Injection molding is a highly efficient process. It can be used to manufacture a large number of precise and consistent parts with minimal time.

The process can be used to manufacture products with negligible or nil error quicker.

Once the product design and the mold design are completed, the plastic injection molding can manufacture the products very fast. Manufacturing the products in bulk also brings down the cost of manufacturing significantly.

 

Cost-Effective

Manufacturing products using plastic injection molding technology is very cost-effective. The major cost is incurred upfront in product designing and mold designing.

Once this is done the products can be manufactured in large quantities which bring down the total manufacturing cost considerably.

Eco-Friendly

Manufacturing using the injection molding process is also eco-friendly. The modern injection molding machines produce minimal plastic scrap during manufacturing. They also use considerably lesser power-about 20-50% less- than the older machines.

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Fast Production

Injection molding allows manufacturing products in bulk in a very short time period. It is very fast compared to other forms of plastic molding.

Once the injection molds have been designed and the presses are pre-programmed, the time taken in the actual molding process is quite less.

The exact time depends on the complexity of the mold but on an average 15-20 seconds pass between each cycle time.

 

High-Quality Product

The products manufactured using the injection molding technology are of high-quality.

The process allows the flexibility to manufacture using more than one plastic resin. Hence, the manufacturers can use a combination of plastics to get the best product.

Fillers can also be added to the plastics while manufacturing which further increases the strength of the product.

The products manufactured using this process do not have joints, they are seamless and produced in a single mold. This means that there are no weak areas and the products are very durable and of high quality.

 

The Downside of Injection Molding

There are few drawbacks of using injection molding also which are as follows:

High Tooling Cost

Designing the appropriate tool is a very time consuming and resource intensive part of the injection molding process. It requires a lot of effort to get the mold design correct prior to the mass production of the final product.

 

Difficult to Make Changes to the Mold

The molds are made of mostly steel or aluminum which makes it difficult to make changes once the mold has been designed.

Mostly making any change in the mold design involves considerable time and effort and, in some situations, it may mean to scrap a part of the mold or even the entire mold also and start designing the mold from the scratch again.

 

Suitable only for Bulk Production

Injection molding process is only suitable for bulk manufacturing. The product designing and mold designing involves investment which can only be offset if the products are manufactured in large quantities.

Manufacturing in small batches or in small numbers will not provide the cost-efficiency which bulk manufacturing provides.

 

The process of Injection Molding

The injection molding manufacturing process involves three distinct phases- designing the product, designing the mold, and the production process.

The manufacturing process starts after the product design and mold design stages are completed. During the manufacturing process, the mold is clamped in the press and the ejection system of the mold is configured.

The plastic is then heated to a predetermined temperature and is driven by a screw through the gates to the mold. Once the mold is filled, the screw remains intact which applies the pressure to the duration of reaching a predetermined cooling temperature.

Once this point is reached, the screw is withdrawn followed by an opening of the mold and ejection of the final manufactured part.

 

Trends of Injection Molding

The injection molding industry has undergone considerable changes. The process has become highly automated and is moving toward even higher levels of automation.

The manufacturing process is controlled by robotics which further increases the efficiency of production. The use of greater automation leads to faster, accurate, and more adaptable manufacturing process.

The industry is also shifting towards being eco-friendlier and more sustainable. The latest injection molding machines produce lesser plastic scrap during the production process and also consume 20-50% lesser energy than the older machines.

The injection molding industry is also witnessing greater emphasis on outsourcing of work. More and more work is being outsourced to countries like China which offer quality products at much cost-effective rates.

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How to Do Injection Molding Quality Control

There are stringent quality control measures which should be followed for producing the best quality products through injection molding process.

The raw materials should be verified for conformance upon their receipt. The parts should be visually inspected directly out of the molding machine.

They should be checked for different defects like sink marks, short marks, burn marks, flash marks etc. To ensure the process accuracy of the product, it is very important to control the process by measuring the temperature of the mold and the product.

The temperature of the mold significantly affects the shrinkage, process cycle, and accuracy of the product, it is important to ensure the stabilities of these factors by measuring the temperature distribution.

The temperature distribution on the product should also be measured to verify the cooling effect to make corrective cooling for insufficiently cooled parts.

 

Cost of Injection Molding

The cost of making a mold depends on several factors. Making molds from steel is costlier than aluminum. However, the steel made molds will have a longer lifespan which will compensate for the initial cost.

Hardened steel molds last the longest and are costlier to make. The cost of the mold also depends on the number of cavities in the mold. The more the number of cavities the higher will be the cost.

The mold base which holds all of the cavities also influences the cost. The cost of the base is ascertained based on its size, the type of steel used to manufacture it, and the customization required.

 

The Best Injection Molding Machines

Injection molding machines consist primarily of two basic parts- injection unit and clamping unit. The machines differ in both injection unit sizes and clamping units used.

The clamping mechanism moves either horizontally or vertically. Most of the modern injection molding machines are horizontal machines.

There are many manufacturers of injection molding machines in the market with each offering unique features. However, the brands which are the most popular and the best to buy are Husky, Arburg, Engel, and Nissei.

 

How to Design for Injection Molding

The key to leveraging the injection molding is to ensure bulk manufacturing. When bulk production is done, it provides the maximum cost-efficiency to the manufacturers. While undertaking bulk production, it is important to optimize the design before the actual production starts.

The molding can be improved by selecting designs which only require minimal materials.

The steel molds are costlier to build than the aluminum ones but they offer longer lifespan which will offset the initial higher investment on them.

The tryout times can be reduced by eliminating superfluous features. It is also highly recommended to use core activities during production and to reduce cosmetic finishes and appearances.

 

How Chinese Factory are Playing an Important Role in Injection Molding

Chinese factories are playing a crucial role in the injection molding industry. China is one of the largest markets globally for manufacturing products using an injection molding process.

China is the largest injection molding machine market in the world. China’s production of injection molding machines is expected to rise steadily during the period 2018-22.

The Chinese manufacturing infrastructure combined with their state-of-the-art machinery and abundance of skilled workforce make them the leaders in injection molding manufacturing.

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