Plastic Casting Process:The Ultimate FAQ Guide

Plastic casting process is simple, but if you never learn it, it will be difficult to understand the details.

Check this complete FAQ guide to check all the plastic casting process and benefit your business.

What is Plastic Casting Process?

It refers to a plastic part manufacturing process which involves the introduction of a liquefied plastic material allowing its solidification in a mold.

It depends on atmospheric pressure in filling the mold.

What are the Benefits of Plastic Casting Process?

  • It is a comparatively simple process of plastic forming method since it does not involve a number of elements and procedures.
  • Products made as a result of plastic casting process has little or no internal stress hence guaranteeing a quality finish for the specific application.
  • It helps in reducing assembly which implies that you can use it to create items in a single complete component hence getting rid of the need to assemble different pieces.
  • The cost of equipment, mold and tooling which you use in the plastic casting process is relatively low.
  • This process also produces products that are comparatively lightweight hence ideal for a wide range of applications.
  • You can design the casting molds to produce a wide range of part surface textures including smooth, semi-smooth as well as rough.
  • It is a suitable method for making complex profiles hence ideal for a wide range of applications.

Are there Drawbacks of Plastic Casting Process?

Plastic casting

Plastic casting – Photo courtesy: Wikimedia

  • In some instances, the dimensional tolerances might not be ideal as you would expect or to match the particular requirements.
  • The rate of output in plastic casting tends to be somewhat slow and also has comparatively long cycle times.
  • In some cases, it can be difficult to manage air bubbles and moisture and could possibly lead to a wide range of challenges.

How does Plastic Casting Process Compare to Plastic Thermoforming?

In plastic casting, you can create a hollow mold from a master that you can hand-sculpt or even print it in 3D.

The casting plastic material hardens into the mold then the master is either burnt or removed to form the final part.

On the other hand, in plastic thermoforming, a plastic sheet is heated then pressed between two mold halves to enable it to form a part.

What is the difference between Plastic Casting and Plastic Molding?

Plastic casting is basically the act of pouring the plastic liquid into the mold cavity which cures after a particular duration through a chemical reaction and cooling under set parameters.

On the other hand, plastic molding refers to the act forming a cavity which carries a reverse or negative impression of an original model.

What Parts are made by Plastic Casting Process?

Cast plastic toys

Cast plastic toys – Photo courtesy: Internet toys

They are quite a number and some of the major ones include;

  • Toys
  • Automotive parts and components
  • Packaging bottles
  • Storage containers

What Plastic Materials can you cast?

  • Polystyrene
  • Acrylic
  • Nylon type 6
  • Polyester
  • Polyurethane

What are the Steps Involved in Plastic Casting Process?

They include the following;

i. Patternmaking

This is the first step in the process which involves designing of a physical model.

Patternmaking can use computer-assisted systems to design the dimensions and geometry of the mold.

It follows by packing of aggregated plastic material around the pattern.

ii. Core Making

It is the second step in the process which involves placing of solid materials inside the mold cavity as a way of creating interior surfaces of a casting.

Most of the plastic part designs need the inclusion of cores in the casting mold.

iii. Molding

This is the third step of this process which also allows you as the manufacturer to create the casting mold.

The plastic material fills the casting mold model which is subsequently allowed to harden to a point of removing it from the cavity and beginning of casting of the component.

iv. Melting and Pouring

You must ensure that you melt the plastic material properly before placing it in the mold.

Once you have melted it accordingly depending on various properties of the plastic, you then pour the molten plastic in the casting mold to allow it to cool and also harden.

v. Finishing

In some instances, plastic can fill in the cracks in sprues or casting mold thus making it a necessity for you to finish the plastic following casting.

You can use different ways of finishing techniques to accomplish this.

Once you achieve proper appearance and texture, you can as well proceed to further post-treatment process like a painting of electroplating depending on various elements.

What is Resin Casting?

It refers to the type of casting or embedding of a wide range of objects in epoxy resin where silicon or resin casting molds are used.

What Affects the Quality of Plastic Casting Process?

· Quality of Raw Material

It is necessary to ensure that the quality of the plastic material you are using reaches to the level of the required standard to prevent defects such as residuals, sticky sands, and air holes.

· The Design Process of Tool Castings

It is always vital to make sure that you depend on plastic material and work condition during designing as a way of determining shape as well as the size of machine tool casting.

· Operation of the Casting Process

The process operation needs to be reasonable and the technical level of workers also should increase to enhance production quality and rates of plastic tool casting.

· Plastic Casting Technique

It is also fundamental to ensure that you select reasonable casting methods depending on the size, structure, weight, and properties of the plastic sheet material and work conditions as a way of producing high-quality parts.

What is the difference between Cast Plastic and Extruded Plastic?

Cast plastic is manufactured by a process whereby MMA liquid is pressurized into a monomer which is submerged in warm water resulting in the polymerization process.

It has a greater variance as far as thickness tolerance is concerned.

Extruded plastic, on the other hand, refers to a type of plastic materials manufactured by a continuous production process.

It has a better tolerance on the thickness and you can still achieve tighter tolerances by prior arrangement with extrusion mill.

What are the Common Defects in Plastic Casting Process?

They are quite a several and some of the common ones include the following;

· Mismatch

It arises as a result of misalignment of the lower and upper parts of the casting and misplacement of the core at the parting line.

To prevent this defect from occurring you need to ensure that you properly align the pattern or the mold boxes.

· Shrinkage Cavity

It refers to the formation of a cavity in casting as a result of volumetric contraction.

It is usually caused either by extremely high pouring temperature or inconsistent or unregulated solidification of molten plastic material.

An ideal remedy for this defect is by applying the code of directional solidification in mold design.

· Slag Inclusion

It is a defect caused when molten plastic material that contains slag particles is poured inside mold cavity and gets solidified.

A suitable approach for this defect is by getting rid of slag particles from molten plastic material before pouring it in mold cavity.

· Swell

It occurs as a result of enlargement of mold cavity due to molten plastic pressure that leads to enlargement of the entire casting.

· Blowholes

It is a defect commonly as a result of entrapped gases on the surface of the casting due to plastic resin solidifying and causing a rounded cavity.

The ideal way of preventing this from happening is by making sure that you carry out sufficient ramming.

· Misrun

This defect occurs when molten plastic solidifies before entirely filling the mold cavity then leaves a space in the mold.

A common cause for this defect is low temperatures of molten plastic which reduces fluidity and improper gating system as well as a thin section.

An ideal remedy for this defect is avoiding thin section and also ensuring proper gating system.

· Pinholes

Are usually tiny holes of about 2 mm and appears on the casting’s surface.

It happens as a result of the dissolution of gases in the molten plastic.

The rapid rate of solidification is the best approach for preventing this defect from occurring.

· Sponginess

This is an external defect with several small cavities closely knit within the plastic casting.

It is usually as a result of scurf and dirt held mechanically in the suspension of molten plastic.

It can also be as a result of imperfect skimming in the ladle.

An ideal way of preventing this is by removing the slag particles from molten plastic proper skimming.

Is there Size Limitation is Plastic Casting Process?

No. As long as you have the right materials and equipment you can cast any size of plastic material.

How do you Choose Suitable Mould for Plastic Casting?

You need to consider a number of factors which include the following;

Mold

Mold

· Application of the Part

In this case, it would be vital to determine whether the application requires a part that is rigid or flexible.

You also need to know the kind of temperature and pressure it needs to withstand as well as any possibility of the chemical or any other element exposure.

· Special Appearance Consideration

You also have to determine whether there is a specific type of finish for the final plastic part.

· Quality Standards

When choosing the mold for plastic casting it is necessary to make sure that you go for those that match the recommended quality specifications.

It helps in preventing or reducing risks associated with numerous elements that surround the usage of the parts.

What is Dimension Tolerance in Plastic Casting?

Plastic casting tolerance is the undesirable thou acceptable variations in dimensions from the intended specifications.

Therefore, to cast plastic parts with accurate dimensions, you must maintain tight tolerance.

You can achieve this by carefully designing the mold, understanding properties of plastic, controlling both heating and pouring processes.

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