Plastic injection molding manufacturing defects and problems and How to minimize them?

 

Injection molding is a widely used manufacturing process for plastic products. Almost 30% of plastic products are manufactured by injection molding. There are various Injection molding defects which affect the quality of the product. Let's have a look at some of the injection molding defects, their causes, and remedies

FLOW LINES

These are lines or a wavy pattern of different coloration than the surrounding material. Ther might also appear as ring-shaped or wavefronts near gates, etc.

Causes

These are caused mainly due to premature cooling of the initial jet of the material before the mold cavity gets filled. Sudden change in wall thickness can also cause this, due to the variation of cooling speed.

Consequences 

These won’t impact the strength of the component, but may affect the aesthetics in some cases. Such as sunglasses, etc

Remedies  

• Increase the injection speed and pressure so that the material fills the cavity before it undergoes premature cooling. We can increase the diameter of the nozzle to increase the pressure.

• Increasing the material temperature will also avoid the premature cooling of the material. However, we should not increase the temperature too high as it may cause burn marks.

• Mold design 

1. Providing round corners in areas of varying thickness may prevent a sudden change in the velocity of the material.
2. The mold design should allow a smooth flow of material to prevent drastic variation.
3. Relocate mold gates at a distance from the mold coolant.

BURN MARKS

They appear as a black or dark-colored discoloration around the edge or the surface of a plastic part.

Causes 

Over heating of the mold cavity, excessive injection speed and temperatures of materials causes burn marks

Consequences 

Burn marks won’t affect the integrity of the part but are aesthetically unpleasing. Burn marks may affect the part of the burning is to an extent where it would degrade the material.

Remedies  

• Lower material temperature to avoid overheating

• Enlarge escape vents and gates to allow the trapped air to escape.

• Provide a smooth flow of material, to avoid trapped air.

• Shorten the cycle time so that if any air is trapped it won’t have time to overheat.

Sink marks

These are small depressions on the surface in the thicker area which would have been otherwise flat.

Causes 

When the the material in the interior cools rapidly its contracts, cause inward pulling of the outer material which is still in the molten state. This results in sink marks on the surface.

Consequences  

Although sink marks don’t affect the product strength or function, they drastically affect the quality and aesthetics of the product.

Remedies  

• Make part walls as uniform as we can.

• Make ribs instead of increasing wall thickness where strength is required.

• Place gates locations to allow thicker sections to fill first.

• Increase holding pressure and time to allow the material at the surface to cool properly.

Vacuum voids / Air pockets 

Trapped air bubbles or empty spaces that appear in the finished product are air pockets or voids 

Cause 

Inadequate pressure to force trapped air to escape from the mold cavity is the major cause of this. Also, if the material near the mold walls cools too quickly it causes shrinkage and pulls the material outwards which causes voids.

Consequences  

Manufacturers consider these as a minor defect, but if the extent is large it may hamper the strength and function of the product.

Remedies  

• Raise the injection pressure to force the air out.

• Ensure uniform cooling

Jetting

It is a visible flow pattern on the product mostly as lines over the surface. These appear similar to flow lines defects.

Causes 

Jetting is caused mainly due to excessive injection pressure and premature cooling of the initial jet. The jet squirts out of the nozzle and cools over the mold walls. This cooled material is then dragged by the further incoming molten material causing the pattern.

Consequences 

Drastically hamper aesthetics.

Remedies 

• Decrease the injection pressure to provide a smoother flow of the material into the cavity.

• Placing the mold gate in such a way that the material is filled across the mold rather than through the length.

• Increase mold temperature to prevent solidification of the initial jet.

SHORT SHOT

It is Improper or no filling of a part of the cavity which causes incomplete finished product. We can see that in missing prongs of plastic forks, incomplete pieces of any plastic product.

                       

Causes 

Narrow or blocked gates cause improper filling of the cavity, inadequate venting resulting in back pressure of air, Material too viscous or the mold too cool that it solidifies even before the complete filling of the cavity.

Consequences

Incomplete or a missing part of the finished product

Remedies 

• Provide wider channels for the mold to ensure proper flow.

• Balance the flow paths so that they fill with equal pressures

• Select a less viscous material

• Increase the temperature to increase the viscosity

Burrs or flash 

 

Small protrusions over the surface of the finished products are called burrs or flash defect.

Causes 

This is mainly related to mold health and mold design. Worn mold or improper clamping of the mold helps material escape the cavity, poor design of mold causing improper fitting, gaps, etc. Improper holding pressures also aids in this.

Consequences

This is generally considered as minor defect, but adds to reworking on the product for critical requirements, increasing manufacturing time.

Remedies

Proper design of the mold with suitable holding pressure can reduce this defect.

Other defects

• Strings – These are string link remains at the end of the product from the previous shot. Caused mainly due to high nozzle temperature, and uncooled material at the entry of the gate.

• Blisters – Raised layers on the surface are called blisters. This occurs when the material remains molten for a long time.

• Welding lines – These are partition like lines which occur due to cooling of the material after splitting off when the are converged. This is a result of low material bonding and hampers the strength of the product.

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What are Plastics?

 

Photo by Markus Spiske on Unsplash

The term "plastic" is derived from the Greek word "plastikos", meaning fit for molding. This refers to the material’s malleability, or plasticity during manufacture, which allows it to be cast, pressed, or extruded into a variety of shapes - such as films, fibers, plates, tubes, bottles, boxes, and much more.

Can you imagine a world without plastics??..... They have revolutionized almost every sector on the planet. Try looking around, you will find at least half a dozen plastic items around you.

 It's really difficult to imagine a life without plastics. In this article, we will try to know about these groundbreaking materials and their technology. Let us know how mankind found them. But before that, we will see what are plastics?

What are plastics? Why are they preferred?

Plasticity, as defined is a property of a material under which it can be easily shaped or molded. Every element on earth exhibits plasticity under a range of physical parameters. 

When elements (mostly metals) undergo plastic deformation, its irreversible, beyond their ultimate yield strength or elastic limit. There are mainly two types of plastic viz. Thermoplastics and Thermosetting plastics.

Thermoplastics – They can be heated to melt and can be cooled to harden again and again.

Thermosetting – These, when heated, undergo a chemical change to form a network, these cannot be reheated to reshape.

 Now, what separates plastics from metals? since both exhibit plasticity to a reasonable extent. Here are few factors which provide plastics with an upper edge over metals - 

 

1. Weight

  The weight of an object is an important factor to be considered when it comes to the efficiency of the products. Plastic parts often weigh significantly less than the same parts if were made from metal. Below is a table showing comparative figures.

Materials	Density*	Materials	Density*
Plastics		Metals
Polypropelene(PP)	980	Aluminium	2700
Polycarbonate	1400	Iron	7874
Cellulose Acetate	1290	Copper	8960

 

 This gives an upper hand to plastics where strength and wear resistance is not a concern. This is the reason that almost 11% of a car's weight these days is plastic. This has significantly increased its efficiency.

 

2. Strength to weight ratio

For decades the strength of plastics was a concern for many product designers as they are very weak when it comes to thermal and wear resistance, thanks to their low melting points. However, with advances in plastic composites, and the addition of carbon fibers, plastic’s S to W ratio has increased drastically. In some cases they even outperform metals.

  

3. Production time

When it comes to industries, production time is a very important factor for the the efficiency of the business. The plastic manufacturing processes, such as injection molding and thermoforming offer fast mass production over metal fabrication processes such as milling, cutting, etc.

 

4. Design compatibility & cost

While metal parts require various operations for complex designs such as tapping, threading, grinding, etc. Plastics can be manufactured in one go with thermoforming and injection molding. This drastically reduces labor and tooling costs and the overall cost of the product.

 

5. Also, plastics do not readily oxidize or rather react with the environment, which makes it best for use in oxygen and moisture-rich environments. They being a good insulator also separates them from metals.

You can find more about the comparison here

 

The major disadvantages that plastics offers are low wear resistance and structural strength. Thus they cant be used as building blocks for heavy operations.

The origin of plastics

 

It has been found that naturally occurring plastics have been used since the 1200s as horns and tortoise shells by, The Horners Company, London. Plastics were synthetically produced since the 19th century.

 The material which is related to the destruction of wildlife whenever we hear of it was invented to save wildlife. Wow….What an irony!!! Combs, Piano keys, billiards balls, etc were made of ivory. Panic had started spreading regarding the extinction of elephants. 

In 1867 a billiards manufacturing company offered 10,000$ for anyone who would come up with a substitute for this. A few years later, John Wesely Hyatt came up with a material which he called celluloid, which was made from a polymer found in plants. 

And then… the plastics revolution began. They started to be manufactured from petroleum and gasses but still were unavailable for the general public. 

But things changed after World War 2, where plastics were used in helmets, aircraft, guns, etc plastic companies were in search of a new market for their products. The plastics entered the market for the general public, with cling wraps, containers, toys, etc and people discovered the potential of plastics. 

Bakelite was the first synthetically manufactured plastic in the early 20th century, and the rest is history.

You can find the timeline here

 

Current scenario 

 

Plastics have been extensively used in a wide variety of sectors (almost all), from pharmaceuticals, construction to automobiles, electronics, etc. They have become an integral part of any industry. It is really difficult to imagine life without plastic. Let us have a look at the applications sector by sector.

1. Construction – Piping, seals, gaskets, electric linings, etc

2. Electronics – Mobile, T.V sets, Laptops, Lighting, etc

3. Packaging – Cling wraps, food containers, bubble wraps, bottles, etc

4. Cosmetic and grooming – Combs, brushes, clothing, etc

5. Transport - Automobiles, Aeroplanes, Ships, etc

6. Medical – Syringes, Tablet packaging, Infrastructure, masks, PPE kits, etc

So we can say, the plastic industry plays a major part in the economy and posses a promising future in a few decades.

Plastics are mainly manufactured on large scale using two techniques viz. Thermoforming and Injection molding. It is also manufactured using other techniques like 3D printing but to a small scale where high accuracy is required.

Plastic posses a great threat towards the environment, this is since it isn’t readily biodegradable and has always been a concern for many environmentalists.

 

 

 

What will be the fate of Plastics?

 

 

To evaluate this we must take into consideration some factors like reliability, environmental impact, ease and cost of production, ease of use, availability, etc. First, let us consider a hypothetical situation where we were to ban all the plastic products on earth one day and evaluate the consequences.

Now, let's start our day without plastics. You get up from bed, and rush to brush your teeth, without a brush!!...yes you can chew neem twigs, Then you rush to toilet…wait you cant wash...sanitary ware was plastic too. 

You think of boiling eggs for breakfast, the egg tray was also plastic…you start sweating in panic and try to switch on your fan…the electric fixture was also plastic…Duh!! There was more plastic than humans around me. 

This was just a trailer, to conclude…life without plastics is very very difficult if not impossible. So to completely eradicate plastic from our life is not an option at all, and I don’t think there is a need to take such a step. There are many sectors where the use of plastic is inevitable like transport, construction, electronics, etc. Thus plastics are an integral part of our day to day life.

With advanced manufacturing techniques like injection molding and thermoforming, it becomes easier and cheaper to manufacture even the most complex of products. So its also beneficial from a business point of view.

Let's take a look at the environmental impacts that plastics have. India consumes about 13 million tonnes of plastic and recycles only about 4 million tonnes. Hundreds of marine species have been reported of ingesting plastic. Studies suggest that even human waste contains plastics. 

This synthetic has penetrated deep in our environment and is causing a significant imbalance. The lack of infrastructure for plastic collection and recycling is the major cause of this problem.

 If this scenario continues, it is estimated by 2050 there will be more plastic than fishes in the ocean, also there are very few cheap alternatives for plastics. It is almost impossible to replace plastic in some sectors like automobiles, construction, electronics, etc.

The government all around the world are emphasizing on the plastic ban for bags, straws, containers, etc and giving an alternative paper-based packaging.

Hmmm…so it seems the major drawback of plastics are the threats to the environment. We can't stop using plastic, we cant continue using it, What exactly should we do then??

We have to accept the fact that it is impossible to stop using plastics at least in a few sectors, as long as there is no environment friendly and cheap substitute available. For sectors such as packaging, where bio-friendly substitutes are available, we should emphasize on using them. 

The government should focus on the recycling of plastics more and build a proper supply chain for reusing plastic with minimal dumping. By taking these measures we can use plastics more efficiently, at least till there is no better substitute available.

 

You can find more about plastic pollution here

 

Conclusion

 

 

It has taken great efforts to invent and innovate plastic as it is today. The use of plastic is very wide and has become an integral part of our daily routine. It is impossible to imagine a life without them.

While plastics possessing a major threat to the environment the use of them is inevitable. 

With advanced manufacturing techniques, the production of plastic had become very easy. As the population is growing, the use of plastics will also grow. We will see a great boom in this industry in the coming decades with advancements in manufacturing techniques and composite materials.

 

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How to survive in space? - Learn from the super animal

Pic credits - BBC Earth

Space, the most mysterious and unexplored part of our universe. Whatever occurs outside of earth’s atmosphere we call it space, and is home to millions and millions of celestial bodies. Temperatures ranging from sub zero to millions degree Celsius, absence of atmosphere, very high and low pressures, etc are few characteristics of this. 

But can we really survive these harsh conditions??.....Of course not, if we are exposed in space we will eventually die due to no oxygen, or may shrink into a ball due to high pressures, may get even torn apart. But there is one super creature, who can even survive in space.

It even survived the K-T event about 66 million years ago which caused extinction of dinosaurs. It is estimated that this animal has been roaming earth since 600 million years.

 

WHAT MAKES THEM UNIQUE?

Tardigrades a.k.a. water bears are such super species that have managed to survive even in the harshest conditions over the time of evolution. They are present from the deepest of oceans to the tallest of mountains As long as it has food available it can survive any condition, all thanks to cryptobiosis, a state where it dies to survive. 

What??... You need to die to survive?...not really. It is the state where the animals metabolic rate is so low(almost 0.01% of normal levels), like it’s almost dead. We say that it has turned into a tun state. In cold temperatures, this state prevents the growth of ice crystals. 

 

They also have another defence for when they are in water. When the water they live in is low on oxygen, they will stretch out and allow their metabolic rate to reduce. In this state, their muscles absorb oxygen and water well enough that they can survive. In drought like conditions they lose almost but 3% of their water..

 In fact they dry themselves up with lower metabolism. They can stay in this state for decades when they get contacted with water they again regain life, just as we use dehydrated onions. Their space surviving abilities are the main aspect which distinguishes them from other animals.

 Some believe that their origin is extra terrestrial.  Even temperatures up to 150 degrees Celsius and as low as -235 degrees C(just above absolute zero) won't spell the creature's doom.

 

SPACE RADIATIONS?

Space is not just fatal because of the temepratures and pressures, there are numerous harmful radiations which will penetrate in your cells and permanently damage the DNA. The biggest concern regarding this is the formation of reactive oxygen species due to radiations. 

These molecules roam throughout the body to cause all harm. Surprisingly Tardigrades in their tun state generate abnormal amount of anti-oxidants, which effectively neutralize those roaming, evil reactive oxygen species. 

You say any condition, boil them, freeze them, throw them into space, Tardigrades have evolved to survive. We can call it a beast when it comes to survival.

Due to above remarkable survival ability, this creature has always been a keen interest for researchers.

 

CONCLUSION 

Tardigrades are one of the few species that have survived even the harshest of conditions. Due to this, they have always been in the interest of space researchers. It may happen that using their techniques we might be able to store humans for decades, and revive them again.

 Does this mean time travel?? Because even after decades of storage , the age of the body will still remain the same. Will this make us immortal??....Well, this is an area yet to be researched more, but one can expect similar results.

REFERENCES

• https://www.livescience.com/57985-tardigrade-facts.html
• https://www.popularmechanics.com/space/a11137/tardigrades-water-bears/

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