Basic Interview Questions on Plastic Part Design Part-2

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You can find a lot of injection molding parts around you. With the advancement in plastic technologies and advantages of plastic over metal parts. Industries are converting their metal parts into Injection molded plastic parts. Therefore injection molding field has lot of scope. This article covers commonly asked interview questions on plastic part design.

We suggest you to also read article on plastic part design guidelinesmaterial selection, Injection molding process and Injection molding defects.

What is MFI in plastics?

MFI stands for ” Melt Flow Index. It is a measure of the ease of flow of the melt thermoplastic polymer in grams over the course of 10 min at a certain standard temperature (ie, 230°C).

Why fillers and additives are used in injection molding?

Fillers and additives are used with plastic material to modify its properties. Cost of fillers and additives are less than plastic granules. That results in low material cost.

Commonly used additives are glass fibers, UV stabilizers, Impact modifiers and lubricants e.t.c

What is parting plane in injection Mold?

The parting plane is the contact surface of the two halves (core and cavity) of the mold that separate when the mold opens and closes. Read this article fore more details on types of injection mold.

What are sliders and Lifters in injection molding tool?

Sliders and lifters are used in mold assembly to form the undercuts in the product.

What is maximum and minimum wall thickness in injection molded parts?

The minimum or maximum plastic part wall thickness is dependent on the part size, material and design. 

For example, Injection molding a 100 mm long part in 0.6 mm thickness looks difficult. But manufacturing the same part in 2 mm thickness with localized 5 mm in 0.6 mm looks feasible. 

What are cooling media used in injection molding?

Cooling inside injection mold, is accomplished through the use of a Mold Temperature Control (MTC) system.

MTC is used to remove heat from the mold and maintain the correct part temperature during injection molding.

What are various mold finishes?

Various options for mold finish are available for part finish and texture requirements. SPI and VDI are one of many standards used for part finishes. Read this article to know in detail about SPI mold finish in injection molding.

What is clamping force in injection molding?

Clamping force is the force applied to a mold by the clamping unit of an injection molding machine to keep the mold closed. This force is applied during the injection of molten plastic into the mold. Insufficient clamping force can results in flashes in molded part.

How Clamping Force is Calculated and what is its application?

Clamping Force can be calculated from the cavity pressure inside the mold and the shot projected area. The calculated clamping force in tonnage can be used to select an injection molding machine for a part.

What is the difference between two and three plate injection mold?

Two plate injection mold has one parting plane and the mold splits into two halves at parting plane. The runner system must be located on this parting plane.

Whereas three plate injection molds have two parting planes, Mold splits into three sections every time the part is ejected. Read this article to in detail about two and three plate injection mold.


To sum up, there are a lot of opportunities for mechanical engineers in injection molding. If you are fresher or switching to injection molding field. You can start learning plastic part design guidelinesmaterial selectionInjection molding defects and manufacturing process. 

Got Questions?  We will be happy to help.

If you think we missed Something?  You can add to this article by sending message in the comment box. We will do our best to add it in this post. 

If you want to add more interview questions. You can comment or write an article on this.

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