Basic Interview Questions on Plastic Part Design Part-2

You can find lot of injection molding parts around you. With the advancement in plastic technologies and advantages of plastic parts. Lot of industries are converting their metal parts into Injection molded plastic parts. Therefore injection molding field has lot of scope. This article covers commonly asked injection molded Plastic Part Design interview question with answers.

We suggest you to study plastic part design guidelinesmaterial selection, Injection molding process and molding defects topics.

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 gram 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 of the mold (for example core and cavity) that separate when the mold opens and closes.

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 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?

This cooling is accomplished through the use of a mold temperature control system that is used to remove heat from the mold and maintain the correct mold temperature for the specific plastic material and product design being employed

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.

Check out in detail about SPI mold finish here

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 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 ?

It 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 a injection molding machine for a part.

What is difference between single and two 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.

Check out in detail about injection molds here.


To sum up, there are 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 Question?  We will be happy to help.

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