We can see a lot of injection molding parts around us. Industries are converting their metal parts into Injection molded plastic parts because of the low cost and other advantages of plastic parts. Therefore injection molding has a lot of scopes. This article covers commonly asked Plastic Part Design interview questions with answers.
We suggest you study plastic part design guidelines, material selection, Injection molding process, and molding defects topics.
What are different types of plastic?
We can classify plastic materials into two categories according to their chemical behavior.
1. Thermoset plastics cannot return to their original shape after heating. They are hard and durable. e.g. Polyurethanes, polyesters, and epoxy resin e,t,c
2. Thermoplastics can retain their original shape after heating. They are softer and less rigid in nature. Examples of thermoplastics are ABS, polycarbonate (PC), polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC), etc.
Read this article to know more about plastic material selection.
What is injection Moulding?
Injection molding is a plastic manufacturing process to achieve a high production rate.
Firstly, molten thermoplastic with high pressure injects into an injection mold during injection molding. As a result, molten plastic takes the injection mold core and cavity shape. After the solidification of molten plastic, the finished part is ejected out of the mold.
What are common injection molding defects?
Commonly found injection molding defects are short-shot, flow marks, flow-lines, sink marks, warpage, voids, flash, knit lines, and burn marks. Read this article for details on injection molding defects and how to control them here.
What is insert or over-molding?
Over-molding is a type of injection molding process where the first material is molded over another material.
Material selection is critical to achieving strong bonding between over-molded parts. We can also use primers and adhesives to increase the bonding strength.
What are the advantages of plastics compared to metals?
- Higher strength-to-weight ratio
- Lighter weight and improved ease of use.
- Low manufacturing costs for high production rate.
- Increased corrosion resistance
- Consolidation of multiple metal parts into a single plastic part
- Higher toughness compared to metal parts
- High structural strength
What are the disadvantages of plastics compared to metals?
- High initial tooling cost.
- Part design restrictions.
- A low production rate will be very costly.
- High lead time for tooling.
- The prototyping cost is very high.
What materials are used for making injection molding tools?
The selection of injection molding tool material depends on the following factors:
- Part Material
- Production Volume
- Tool cost constrains
- Part finish
We suggest you read this article for more details on injection molding tool materials.
Here is a list of injection molding tool materials you can select from.
- Heat Treating Tool Steels: H13 steel, Stavax tool steel, Ramax tool steel, S7 tool steel, stainless steel, etc
- Pre-Hardened Tool Steels: P20, NAK 50, NAK 55
What are the types of injection molds?
According to the Feeding System
According to the Number of Cavities
According to the Type of Mold Opening
Why Runner is required in injection molds?
A runner is a channel in the injection mold that moves the plastic from the injection molding machine barrel to the part.
What are the advantages of injection molding compared to other plastic manufacturing processes?
Advantages of injection molding
- High efficiency
- Complex part design
- Design flexibility
- Ability to use multiple plastic materials
- Ability to use multiple colors
- Reduced waste
- Dimensional accuracy
What are the types of gates used in injection molds?
- Sprue gate: Mold manufacturers prefer sprue gates for large components. Sprue gate mark is visible on the component ejection point, and the runner is not required.
- Edge gate: Suitable for square and rectangular components
- Ring gate: Suitable for cylindrical components to eliminate weld line defects.
- Diaphragm gate: Suitable for hollow and cylindrical components.
- Tab Gate: Suitable for solid, thick components
- Submarine Gate: Used for auto de-gating to reduce cycle time
- Reverse taper sprue Gate (Pin Gate): Used in three plate molds.
What are ejector Pins?
Ejector Pins application is to eject the part from the injection mold. They are located on the B-class surfaces because they leave marks on the molded part.
What are design guidelines for injection molding plastic part design?
Click this link to know more about plastic part design guidelines here !!
To sum up, a lot of opportunities are available for mechanical engineers in the plastic industry. If you are a fresher or switching to an injection molding field. You can start learning plastic part design guidelines, material selection, Injection molding defects, and manufacturing process.
We will keep adding more questions to Basic Interview questions and answers on plastic part design. Please add your comments or questions to Basic Interview questions and answers on plastic part design.
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Injection moulded questions and answers