MockQuestions

Mechanical Engineer Mock Interview

37 Questions Created By

To help you prepare for your Mechanical Engineer interview, here are 37 interview questions and answer examples.

First Question

37 Mechanical Engineer Interview Questions

20 Interview Questions With Sample Answers

1.   You're asked to take the design for a load-bearing steel plate and create an aluminum design that can withstand the same load. What design considerations would you keep in mind?

How to Answer

This question is being asked to gauge knowledge in material selection as it pertains to machine design. In material science, strength refers to the resistance to deformation when a load is applied. Steels are generally stronger than aluminum alloys, so one important change is that an aluminum plate would need to be thicker in order to handle the same load. This is a fairly open-ended question, so you can be creative in your response and draw upon many different material properties. These may include machinability, hardness, corrosion resistance, weldability, density, cost, or malleability.

Written by Jason Toby on October 12th, 2020

Answer Example

"I know that aluminum has a Young's Modulus that is roughly one third that of steel, and is also roughly three times less dense. Due to the difference in strength between the two materials, the aluminum plate would need to be thicker in order to bear the same load. This may result in a more expensive part, especially to optimize thickness with higher strength alloys that are more energy-intensive to produce. I also know that aluminum is difficult to weld when compared to steel, so I would use fasteners or rivets in the design unless welding was absolutely necessary."

Written by Jason Toby on October 12th, 2020

2.   What types of standard views do you include in a drawing for manufacture?

How to Answer

This question is typically asked for roles in manufacturing or design, where you may be asked to create or interpret technical drawings as part of your role. Manufacturing drawings are a type of technical drawing utilized to communicate how a part is manufactured. There are three standard views included in manufacturing drawings: top, front, and side. Be sure to include some additional detail in your answer to communicate your experience in this subject to the interviewer.

Written by Jason Toby on October 12th, 2020

Answer Example

"If I were preparing a drawing for manufacture, then I would make sure to include a top, front, and side view. This is because these views communicate the dimensions of a part to a manufacturer. Additionally, I would include an isometric view to give additional perspective on what the part will look like once it is made. I know that sometimes only critical dimensions are listed if a CAD file is included, which may depend on the vendor's requirements or the type of part being manufactured."

Written by Jason Toby on October 12th, 2020

3.   What is the difference between an interference fit and a clearance fit, and when might you use them?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, press fits and clearance fits are types of engineering fits that generally refer to the sizing of a hole and a shaft in General Dimensioning and Tolerancing (GD&T). This is a system for defining and communicating tolerances with two main regulating bodies: International Organization for Standardization (ISO) and American National Standards Institute (ANSI). Interference fits are in both systems, but clearance fits in the ANSI system are referred to as running or sliding fits (RC). An interference fit generally describes a shaft that is oversized relative to the hole, and therefore requires some considerable force to assemble. An RC or clearance fit is one where the shaft is smaller than the hole, enabling the two to slide or rotate when assembled.

Written by Jason Toby on October 12th, 2020

Answer Example

"Both interference fits and clearance fits are types of sizing tolerances applied to a hole and a shaft. An interference fit describes a shaft that is oversized relative to the hole, whereas a clearance fit describes a shaft that is undersized relative to the hole. I would use an interference fit to permanently attach two parts that I do not want to separate, such as a ball bearing with an interference fit between a shaft and inner race. I know that sometimes these parts are heated and cooled in order to assemble without excessive force applied. I would use a clearance fit when I want two parts to be able to move or spin freely, such as the inside of a door hinge."

Written by Jason Toby on October 12th, 2020

4.   Why are screws generally not ideal for location in fixture design? What is a better way to do it?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, fixtures are generally responsible for locating parts in three dimensional space in addition to providing clamping force to secure the part. Parts can generally move or rotate in one of twelve degrees of freedom. These come from rotation or translation on the X, Y, and Z axes. Screws are not ideal for location because they have relatively loose tolerances, allowing the part to vary in location slightly every time it is installed. A better way is to use dowel pins, which are tightly-machined cylinders that are usually pressed into one end with an interference fit and slid into the other end with a clearance fit or location fit.

Written by Jason Toby on October 12th, 2020

Answer Example

"In fixture design, screws are not ideal for location because they have relatively loose tolerances compared to the precision required in a work fixture. If I design a fixture that relies on screws, then the part can still move slightly in the X and Y axes, where Z is the axis of the screw. A better way to do this would be to use two dowel pins, which have much tighter tolerances. I believe that kinematic mounts are also used in some cases to further restrict the degrees of freedom."

Written by Jason Toby on October 12th, 2020

5.   In CAD Design, what is 'surface modeling,' and what makes it different from 'solid modeling?'

How to Answer

If you are a candidate for a design role, or a position where Computer Aided Design (CAD) software will be used, you may be asked about your experience working with different modeling methods. Surface modeling and solid modeling are two different techniques used in CAD work, with the difference being whether or not you are creating surfaces or solids. Surfaces have no thickness, and were developed for the automotive and aerospace industries for contoured parts such as turbine blades and car bodies. Solid models have a thickness to them, and they are used for general manufacturing of parts like engine blocks, machine shafts and gears. When these methods are used together, they are known as hybrid modeling; they can be used to create intricate parts with the added capabilities of surface modeling.

Written by Jason Toby on October 12th, 2020

Answer Example

"From my experience in product design, I know that the main difference is whether or not you are creating surfaces or solids within the design. Surfaces have no thickness, and they can be used to create complex geometries that would be difficult to design using solid modeling techniques. This could be used for a wind turbine blade, for example. Solid modeling is a more general purpose technique that generally uses extrusions, revolves, and sweeps to add and subtract material to create a solid. These can be used together in hybrid modeling to allow for additional contours and the ability to alter each part face individually."

Written by Jason Toby on October 12th, 2020

6.   What does 'parametric' refer with regards to 3D modeling software?

How to Answer

If you are a candidate for a design role, then this question may be asked to gauge your familiarity with different types of Computer Aided Design (CAD) software. Parametric modeling is a popular type of modeling within the engineering world, and it describes software that defines geometry with a series of relationships (or parameters). It is similar to drawing shapes in Microsoft Powerpoint in that they can be changed at any point in the process, whereas direct modeling is more like drawing in Microsoft Paint. Once you lay down a layer, it is fixed and can only be erased or drawn over. Direct modeling is often more simple and intuitive in the earlier phases of design, but it can be more time consuming to modify as the design progresses.

Written by Jason Toby on October 12th, 2020

Answer Example

"Parametric refers to a type of approach within 3D modeling or Computer Aided Design (CAD) software. The parameters refer to the relationships that define the geometry in the software, which can be changed as the design progresses through different iterations. An example of this type of software would be SolidWorks. Another approach would be direct modeling, which involves drawing or dimensioning a shape directly without the use of constraints. An example of this would be Google Sketchup. These methods can be used in parallel as well, such as software like PTC's Creo which is capable of both."

Written by Jason Toby on October 12th, 2020

7.   What is the difference between 'top-down' and 'bottom-up' design?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, top-down and bottom-up are different ways to approach information processing and are typically used as design methodologies. You may be asked this question if you are working in product development. Top-down design starts with a higher level system view that is slowly broken down into subsystems. Bottom-up design starts at the subsystem or component level and builds up from there. It's often useful to relate this to a real-world design problem.

Written by Jason Toby on October 12th, 2020

Answer Example

"Top-down design and bottom-up design are two different ways to approach a particular problem. Top-down design begins with a higher-level view of a system and then breaks down into specific subsystems as development continues. Bottom-up design starts with the subsystem or component and builds upward until a complete system is reached. As an example, if I were designing a wheelbarrow, then top-down design would initially ask how heavy it needed to be or the load it needs to carry. Bottom-up design might instead focus on a particular wheel diameter needed or the shear strength of the axle in the wheel."

Written by Jason Toby on October 12th, 2020

8.   You're inspecting the surface of a machined steel plate to make sure it is within 0.005 inches of flatness across its surface. What does flatness refer to, and how do you measure it?

How to Answer

Your interviewer will likely ask you situation- and knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, flatness refers to a type of Geometric Dimensioning and Tolerancing (GD&T) callout. This is a specific parameter that refers to the distance between two parallel planes that define a surface profile. It's a measurement of how flat a surface is relative to its own shape, and it doesn't require a reference plane or datum (unlike the GD&T parallelism callout). Therefore, the part must be secured such that the measuring tool is parallel to the nominal surface measurement. Measuring profiles that are not nominally flat can usually be done with a computer-controlled probe on a machine called a CMM, which compares the probe measurements to a 3D Model to measure the variation of the surface profile.

Written by Jason Toby on October 12th, 2020

Answer Example

"Flatness is a measurement of the surface deviation relative to its own profile. In order to measure it, I would secure it to a work surface and use a height gauge to measure the total variation. However, the measured surface would need to be secured such that it is parallel to the measuring tool's reference plane, otherwise the data points will need to be adjusted. A CMM is a great way to do this because it uses a computer-controlled probe and a 3D Model as reference, but a height gauge could be used as well if clamped correctly."

Written by Jason Toby on October 12th, 2020

9.   What does 'circularity' refer to?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, circularity refers to a type of geometric dimensioning and tolerancing (GD&T) callout. It describes how close an object's surface is to a true circle. It's also sometimes called roundness. Its value corresponds to the distance between two concentric circles that contain the deviation of a 2D profile or cross section. The three-dimensional version is referred to as cylindricity. GD&T callouts like this are very useful when communicating designs to manufacturers, and knowing them well can help you stand out in a mechanical engineering interview.

Written by Jason Toby on October 12th, 2020

Answer Example

"Circularity is a type of GD&T callout. It measures how much a circular profile deviates from a true circle, and is measured on a 2D profile and not a 3D surface. It can be measured via a dial gauge that is set up on a lathe, measuring the total variation that the gauge travels in one rotation. In design, I would use circularity if I was concerned with the overall variation of a specific circular profile, rather than the cylindricity across the entire surface."

Written by Jason Toby on October 12th, 2020

10.   What is the difference between stainless steel and tool steel?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. This question is asking about what makes stainless steel unique among steels, specifically in contrast with tool steel. Stainless steel is known for its resistance to rust or corrosion, and it is generally classified by having at least 11% of the element chromium (Cr) in its chemical composition. In contrast, tool steels are known for their hardness, or their ability to resist deformation. Like their name, tool steels are typically used to make tools, and are characterized by their carbon content, typically between 0.5% and 1.5% by weight.

Written by Jason Toby on October 12th, 2020

Answer Example

"Stainless steel and tool steel are both types of steel, which is a metal composed of iron and carbon with other elements added to create specific properties. Stainless steel generally contains over 11% of chromium by weight and is known for its resistance to corrosion. Tool steel generally contains between 0.5% and 1.5% of carbon by weight and is known for its hardness. Tool steel is useful for drill bits and injection molds as they both require a high resistance to abrasion."

Written by Jason Toby on October 12th, 2020

11.   How would you define a simple machine? What is an example?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, a machine is any device that changes the direction or magnitude of a force applied, and a simple machine is the simplest possible design required to create that change. There are six classical examples of simple machines: lever, wheel and axle, pulley, inclined plane, wedge, and screw.

Written by Jason Toby on October 12th, 2020

Answer Example

"I would define a simple machine as the most basic mechanism required to create a change in direction or magnitude of a force applied. An example of this would be a pulley. A pulley changes the direction of a force applied by directing it along the circumference of a wheel and axle."

Written by Jason Toby on October 12th, 2020

12.   What is the 'Young's Modulus' of a material?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. This is a fairly straightforward question regarding material properties. Young's Modulus, also referred to as the Modulus of Elasticity, is a measurement of the stiffness of a material. It defines the relationship between the deformation a material experiences (strain) to the force applied per unit area (stress). Young's Modulus can also be described as the slope of the linear portion of a stress-strain curve, and is very useful for predicting the amount that a designed part or assembly will deform when subjected to a given load.

Written by Jason Toby on October 12th, 2020

Answer Example

"The Young's Modulus is a measure of how stiff a material is, or how much it will deform when a load is applied. Specifically, it is the ratio between the stress and strain of a material in the elastic portion of a stress-strain curve. Given the same geometry and applied load, a material with a lower Young's Modulus will experience more deformation than a material with a higher Young's Modulus. This can be important when using tools like Finite Element Analysis (FEA) to predict when a particular design will fail when subjected to a certain load."

Written by Jason Toby on October 12th, 2020

13.   What does 'cold working' refer to? What effect does this have on a material's properties?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, cold working refers to processing a metal below its recrystallization temperature, which is usually one-third to one-half of the melting point. To do so, a high amount of pressure is applied in one of four general categories: squeezing, bending, shearing, and drawing. Doing so generally improves a material's tensile strength while reducing its ability to deform without breaking, also known as ductility. It can also be a way to shape metals into plates, sheets, and rods that are then used in manufacturing processes like machining.

Written by Jason Toby on October 12th, 2020

Answer Example

"Cold working refers to processing a material at a temperature below its recrystallization point. Processes like rolling, shearing, drawing, and bending are all examples of cold forming. Metals that have been processed this way will be stronger than they were originally, but they will also become more brittle. I believe that for some materials, these effects can be reduced with heat treatment after being cold worked, which allows the material to release the stored energy caused by cold working and become ductile again."

Written by Jason Toby on October 12th, 2020

14.   What is the difference between an end-mill and a drill-bit?

How to Answer

This is a common question to gauge a candidate's familiarity with machine shop equipment. Specifically, the milling machine, which is one of the most ubiquitous examples of machining equipment. An end-mill is a general term for a milling tool, and it differs from a drill-bit in its ability to cut in the radial direction and not just axially. The term 'end-mill' comes from the way the tool often ends in a flat, unlike drill bits which taper to points that allow them to bore into material more easily. Some end-mills are center cutting, which allows them to plunge into material like a drill-bit in addition to radial cutting.

Written by Jason Toby on October 12th, 2020

Answer Example

"The main difference is that end-mills are able to cut in the radial direction, whereas drill-bits are only able to plunge in the axial direction. I know that some end-mills can also plunge into material like a drill-bit, which would be called center cutting. However, I think drill-bits are a better fit for starting a hole, as they have a tapered tip that allows them to penetrate material. I also know that the vibration of endmills is important to consider, as they can break if too much stress is applied during a machining operation."

Written by Jason Toby on October 12th, 2020

15.   Why are sharp corners on internal geometry very difficult to machine?

How to Answer

This is a question that is often asked to gauge whether or not the candidate understands how to design parts for machining operations. Consider a case where you have designed a perfectly rectangular slot inside a block of steel. Because most basic cutting tools are round, it will not be able to leave a corner that is sharper than the radius of the tool itself. Special tools and processes are needed to create sharp corners, and internal features are much simpler to produce if they do not have sharp corners. Another option is an undercut, which extends the cut by one-half of the tool's diameter to create a pocket for a square part to fit in.

Written by Jason Toby on October 12th, 2020

Answer Example

"The reason sharp corners on internal geometry are difficult to machine is that most cutting tools are round, so they remove material with a fillet equal to the tool's radius. You can avoid this by including a radius in the design, or adding an undercut feature for manual or CNC machining. I know that there are ways to machine sharp corners internally, but they are very timeconsuming and expensive, and therefore not necessary for most designs."

Written by Jason Toby on October 12th, 2020

16.   You're designing a machined cylindrical part that is 0.525 inches in diameter with a 1/4 -20 threaded hole in its center. What shop equipment would you most likely use to manufacture this?

How to Answer

This question would be asked to gauge a candidate's experience with machining operations, which are largely handled on either a milling machine or a lathe. Lathe operations involve securing and rotating the part being worked on and positioning a cutting tool to remove material from the part. Lathes are ideal for cylindrical parts, but they can also be produced on computer-controlled (CNC) milling machines. Another aspect of this question involves the threaded hole, which is created using a tap. A tap is used to create female threads on the inside of parts, and 1/4 -20 (pronounced quarter-twenty) refers to the diameter and pitch of the screw threads.

Written by Jason Toby on October 12th, 2020

Answer Example

"I would design this part to be manufactured using a lathe because it is ideal for making cylindrical parts. Because 0.525 inches is not a common stock material size, I would likely start with a larger stock diameter, such as 0.625 inches or five-eighths. From there, a lathe can remove material by rotating the part and positioning the cutting tool to result in the 0.525 inch diameter. The 1/4 -20 thread can be created by drilling the appropriately sized pilot hole, which can be found on a standard drill and tap chart. The female thread can be cut with a tap, which can be done on the lathe or by using a hand tap."

Written by Jason Toby on October 12th, 2020

17.   How are LEGO bricks made?

How to Answer

During an engineering interview, you may be asked to explain how a particular product is made. This type of question tests a candidate's manufacturing knowledge, as well as your ability to communicate the steps required in the process. In the case of LEGOs, they are a well-known example of the manufacturing process known as injection molding. This involves starting with stock of plastic material in pellet form, then using high pressure and temperature to melt and inject it into a mold. Once the plastic part is formed inside the mold cavity, cylindrical rods known as ejector pins are used to knock it out, where it cools until it is ready for use.

Written by Jason Toby on October 12th, 2020

Answer Example

"LEGO bricks are manufactured by injection molding. Starting with tiny granules of plastic, they are heated and pressurized before being injected into a mold. This mold has cavities with negative space that is filled by the molten plastic, forming the shape of the LEGO bricks. In order to remove the part, the two sides of the mold are separated and ejector pins are used to remove the molded parts. Finally, the parts are cooled and sorted into kits to be packaged and sold as LEGO products."

Written by Jason Toby on October 12th, 2020

18.   What does 'draft' refer to in Injection Molding?

How to Answer

Your interviewer will likely ask you knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. In this case, injection molding is a process that involves heating and pressurizing a plastic material until it is molten, and injecting it into a steel mold with a cavity in the shape of the desired part. There are two sides to the mold, and a common issue is that parts get stuck when the mold is separating. Draft describes the practice of adding an angle or taper to the walls of the mold so that the part is less likely to get stuck. For example, the body of a plastic BIC lighter is more narrow at the top of the lighter and wider at the bottom, which allows it to be made at high volumes via the injection molding process.

Written by Jason Toby on October 12th, 2020

Answer Example

"Draft refers to the taper used in injection mold cavities that makes it easier for the parts to be ejected from the mold. This is used along with ejector pins to ensure the parts do not deform by getting stuck to the tool. I know that, in general, injection mold design involves considering the flow of plastic as it fills the cavity to minimize defects."

Written by Jason Toby on October 12th, 2020

19.   If you were looking for defects in an injection molded part, what would you look for?

How to Answer

Your interviewer will likely ask you situation- and knowledge-based questions to understand how well you are able to explain concepts to others. Be prepared for questions like this one by practicing a few possibilities ahead of time. This question is asking about your familiarity with injection molding, specifically what types of issues you might see in the parts produced by this process. Injection molding involves molten plastic that is pressurized and injected into a metal tool with a cavity in the shape of the desired part geometry. As the plastic flows through the mold, it will flow faster in some areas and slower in others. These can lead to defects such as drag, flash, and knit lines. This can be avoided by adjusting the wall thickness of the tool or by utilizing post-processing methods such as trimming the excess plastic that occurs at the separation lines (flash).

Written by Jason Toby on October 12th, 2020

Answer Example

"I would look out for issues such as drag, flash, and knit lines. I believe some of these can be avoided with post-processing as well as with changing the way the mold is designed. They result from the way the mold and material interact as the plastic flows into the tool. For example, flash refers to the excess material that fills the gap between the two sides of the mold, which can be removed in an additional process after the part is made."

Written by Jason Toby on October 12th, 2020

20.   How would you calculate the number of manholes in New York City?

How to Answer

In mechanical engineering interviews, you'll occasionally be asked a more abstract question that is difficult to prepare for on the spot. In general, the interviewer is more interested in understanding your thought process than getting a perfect answer. It is often impossible to solve these questions directly. In this case, start by establishing a strategy and naming your assumptions along the way. After the approach is defined, make an educated guess on what the answer is.

Written by Jason Toby on October 12th, 2020

Answer Example

"New York City is composed of five boroughs: the Bronx, Manhattan, Queens, Staten Island, and Brooklyn. Each neighborhood is broken into city blocks. Manholes are used to access the sewage, plumbing, and electrical connections below the street. Assuming each block is a rectangle, I would guess that each side of the block has a single manhole, giving 4 manholes per block. I would guess that there are 100,000 blocks across all of New York City, and therefore approximately 400,000 manholes in New York City."

Written by Jason Toby on October 12th, 2020

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