Polylactic Acid (PLA) injection molding

Polylactic Acid, or PLA, is a biodegradable and eco-friendly thermoplastic derived from renewable resources like corn starch. PLA has a wide range of applications, but one of the most popular uses for this material is injection molding. Injection molding is a manufacturing process that involves injecting molten PLA into a mold cavity. This process can be used to create everything from medical devices to packaging. One of the benefits of using PLA for injection molding is that it does not produce harmful emissions during the manufacturing process.

Why those important for injection molding cost

injection molding cost
injection molding cost
  • Part size- bigger parts mean a bigger mold, which means that bigger steel will increase the steel cost for the injection mold.
  • Part design- the more complex a part is, the more detailed the mold has to be. Some complicated parts will require special features to be added, such as lifters or sliders. Therefore, you should be open to advice from your mold maker and see if there’s anywhere that you can alter the part design to save on injection mold costs.
  • Materials: Depending on the part material of choice, the injection mold will have to be made of a particular material. For instance, if corrosive plastic-like PVC is to be used, the mold will have to be stainless steel to avoid any damage, ultimately bump the price up.
  • Part finish requirements- where parts have high gloss surface requirements, then more expensive steel and precise technical polishing will be vital, adding to the price.
  • Production volume- higher volume molds need more cavities, and so the mold will be larger. They also require a higher steel grade to last for longer, which impacts the injection mold cost.
  • Country of manufacture- different countries have different wage rates. If your mold is made in a country where labor costs are low, then you’ll naturally save money. In China, the average cost of an injection mold is around 40% less than in western nations.

Introduction: What is Polylactic Acid?

Polylactic Acid (PLA) is a biodegradable and bioactive thermoplastic derived from renewable resources, such as corn starch. PLA has been used in a variety of applications, including food packaging, medical devices, and 3D printing filaments. Injection molding is a process that can be used to create parts and products from thermoplastic materials like PLA. Injection molding involves injecting molten material into a mold cavity, where it cools and hardens to the desired shape.Injection molding is an efficient and cost-effective way to produce large quantities of polylactic acid products.Polylactic Acid is an ideal material for injection molding due to its high melting point and low density.


The heated barrel and rotating screw is fed with material from the hopper.
By heat, friction, and shear force, the material melted by the rotation of the screw is forced through a check valve to the front.


The screw is forced forward from the back end by a hydraulic ram after having been moved forward by the shot of material at the front.


The tool remains closed until the plastic has completely cooled and hardened in the mould tool cavity. This is usually the longest portion of the injection moulding process.


The next moulding is performed by back-moving the screw. The tool opens and the plastic part is ejected. Next, the tool closes, and the injection molding process is repeated at 1.

The Benefits of Polylactic Acid

Polylactic acid (PLA) is a biodegradable and eco-friendly plastic that has many applications in the injection molding industry. PLA is made from renewable resources, making it a sustainable choice for businesses and consumers alike.

PLA is also strong and durable, making it ideal for a wide range of products, from food packaging to medical devices. In addition, PLA can be transparent or opaque, making it versatile for different applications.

Overall, choosing PLA for injection molding provides many benefits for businesses and consumers. It is a sustainable choice that helps reduce environmental impact, while also being durable and versatile. As the demand for sustainable and eco-friendly products continues to grow, PLA will likely become even more popular in the injection molding industry.

Polylactic Acid is a versatile plastic that can be used for injection molding, 3D printing, and as a biodegradable material. Polylactic Acid has many benefits over other plastics, including its environmental friendliness and its ability to be molded into complex shapes.

MaterialsPlastic manufacturers often select a standard grade of plastic for a similar application or based on supplier recommendations. However, these resins may not be optimal. In plastic selection, there are many factors to consider, including:
Heat: The stress created by normal and extreme conditions of use and during the assembly, finishing, and shipping processes.
Chemical resistance is a property affecting part performance when solids, liquids, or gases are in contact.
Agency approvals: Standards developed by the government or the private sector for properties like heat resistance, flammability, and mechanical and electrical performance.
Assemblage: During the assembly process at plastic factory, the plastic is bonded, mechanically fastened, and welded.
Finish: Ability of the material to come out of the mold with the desired appearance values, such as gloss and smoothness.
Price: The price of resin, costs of manufacturing, maintenance, assembly, disassembly, and other costs to reduce labor, finishing, and tools.
Access: The availability of resin from the point of view of the amount required for production of plastic manufacturer.
Draft AnglesA draft angle makes it easier to remove a cooled, finished part from a mold . Draft angles are an essential component of injection molding. Minimizing friction during the part release process can achieve a uniform surface finish and reduced wear and tear on the mold at plastic factory.
An angle of the draft is measured according to the direction of pull. Draft angles of at least 0.5° for the cavity and 1.0° for the core are suggested by most design engineers for parts with sufficient draft. The tool must also be designed with more draft if a textured surface is desired and steel shut-off surfaces.
Wall ThicknessThe wall thickness of injection molded parts is also an important consideration. An injection molded part from plastic products supplier with a proper and uniform wall thickness is less prone to structural and cosmetic problems.
Most resins have a typical wall thickness ranging from .04 – .150. Yet, it is recommended that you obtain thickness specifications for your material(s) of choice by consulting with an injection molder/design engineer and plastic manufacturer.
Wall thickness should be analyzed during the design process to ensure that parts don’t sink, warp, or become non-functional.
RibsAs ribs are used to reinforce the walls of your injection molded parts without increasing their thickness, they are a valuable component in injection molded parts. Rib design should reduce mold flow length when designing complex parts and ensure that the ribs are appropriately connected to increase the part’s strength.
Ribs should not exceed 2/3 of the wall thickness, depending on the material used. WIDE ribs may create sinking and design problems. It is typical for a design engineer and plastic manufacturer to core out some fabric to reduce shrinkage and keep the strength.
If the height of the ribs exceeds 3 times the wall thickness, this could result in the part being short/unable to be filled. Rib placement, thickness, and length are critical factors in determining the viability of a part in its early design phases.
GatesIn a mold part, a gate is a point at which liquid plastic flows into it. Injection molded parts have at least one gate, but they are often produced with multiple gates. Runner and gate locations influence polymer molecules’ orientation and how the part shrinks during cooling. As a result, gate location affects your part’s design and functionality.
The gate should be placed at the end of a long and narrow part if it must be straight. It is recommended to have a gate positioned in the centre of parts that must be perfectly round.
With the input of your plastic manufacturer team, you will be able to make optimal decisions regarding gate placement and injection points.
Ejector PinsMold ejector pins (located on the B-side/core of the mold) are used to release plastic parts from a mold after being molded. The design and positioning of ejector pins should be considered as early in the process as possible by plastic manufacturers. This is even though they are usually a relatively minor concern in the early design phases. Indentations and marks can result from improperly placed ejector pins, so proper placement should be considered in the early phases.
Ejector pins are typically located at the bottom of side walls, depending on the draft, texture, depth, and type of material. You might be able to confirm that your initial ejector pin placement was correct by reviewing the design. In addition, you may be able to make further changes to improve production outcomes.
Sink MarksSink marks can appear on the injection molded plastic part during injection moulding when the material shrinks more in thicker areas such as ribs and bosses. In this case, the sink mark is caused by thicker areas cooling slower than thin ones, and the different cooling rates lead to a depression on the adjoining wall.
Sink marks are formed due to several factors including the processing method, the geometry of the part, the material selection, and the tooling design. The geometry and material selection of the part may not be able to be adjusted based on its specifications, but there are several options to eliminate sink areas.
Sinking can be influenced by tooling design (e.g., cooling channel design, gate type and gate size), depending on the part and its application. The manipulation of process conditions (for example, packing pressure, time, phase of packing, and conditions) can also reduce sink. Further, minor tool modifications (e.g., foaming or gas assist) can reduce sink. It is best to consult your injection molder and plastic manufacturer regarding the most effective method to minimize sink in injection-molded parts.
Parting LinesFor more complex parts and/or complex shapes, it is important to note where the parting line is located.
Having your design shared with your injection molder can greatly influence your finished product’s production and functionality since designers and molders tend to evaluate parts differently. The challenge of parting lines can be addressed in several ways.
It’s important to be aware of the importance of the parting line when designing your initial concept, but you are not limited to that. You may be able to locate other possible locations using CAD software and mold flow analysis. When you work with an injection molder, they keep your part end use in mind and help you determine where the parting lines should be placed.
Special FeaturesIt is essential to design plastic parts so that mold tools can open them and eject them without difficulty. Injection molds release parts by separating the two sides in opposite directions. A side action may be necessary in some instances, where special features such as holes, undercuts, or shoulders prevent the release from occurring.
Coring is pulled in a direction opposite that of mold separation as a side action. In some cases, costs may increase due to this flexibility in part design.
When designing and developing a product, you (plastic manufacturers )were having the right injection molder, and engineer on your side is essential. You can avoid many issues by working with them. In integrating these elements into your product design process and working with a plastics engineer who has experience with these materials, your goal will be to get your product to market as quickly and cost-effectively as possible.

Injection Molding with Polylactic Acid

Injection molding is a process that injection molds melted plastic into a desired shape. In order to do this, polylactic acid, or PLA, is injected into a mold at high pressure. PLA is a type of thermoplastic, meaning it can be molded when heated and will retain its shape when cooled.

PLA is made from renewable resources like corn starch or sugar cane, making it a more environmentally friendly option than other types of plastic. It also has a lower melting point than other plastics, so less energy is required to heat it during the injection molding process. In general, the manufacturing process for PLA is similar to that of other plastics, such as ABS or polystyrene.

The Drawbacks of Polylactic Acid Injection Molding

Polylactic acid is a thermoplastic resin made from lactic acid. It can be injection molded, extruded, or cast. It is biodegradable and often used as an alternative to petroleum-based plastics. However, there are some drawbacks to using polylactic acid for injection molding.

One drawback is that polylactic acid has a lower melting point than other plastics. This can cause problems during the injection molding process, as the material may not flow evenly through the machine. Additionally, PLA isn’t as strong as other plastics and isn’t suitable for all applications. It also tends to be more expensive than traditional plastics. Polylactic acid is more brittle than other plastics, so it is more likely to crack or break during the molding process.

Another drawback of using polylactic acid for injection molding is that it produces a lot of harmful emissions when it is melted down and molded. These emissions can contribute to climate change and air pollution.

Overall, though, PLA is a good option for injection molding when environmental friendliness is a priority. 

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