List of 37 Mechanical Engineer Interview Questions & Answers
-
1.
Why did you become a mechanical engineer?
How to Answer
You will likely be asked a variation of this question in addition to 'tell me about yourself.' A successful answer will highlight your personal story in addition to your technical aptitude, as both are important to communicate to a potential employer. Be honest, and keep the story simple. You do not have to tell your entire life story, but do be prepared to explain in more detail in case the interviewer has a follow-up question.
Jason's Answer
"I have always been motivated by curiosity and learning more about the world. When I was younger, I liked to take apart toys to see how they worked. In high school, I found that I really enjoyed my woodworking classes as well as drafting and mathematics. I also wanted to help address larger problems facing humanity, such as global warming and poverty. As I studied mechanical engineering in college, I found that I really liked the design and prototyping process, as it allowed me to combine my curiosity and creativity with the technical skills I learned from my coursework. As a professional mechanical engineer, I am looking for a position where I can apply these skills to solving real-world problems, and I believe that this role is an excellent fit for doing so."
-
2.
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.
Jason's Answer
"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."
-
3.
How would you describe your communication style?
How to Answer
Good communication is highly sought-after across career paths. In this case, successful engineers must be able to communicate their ideas clearly and effectively in addition to working well with others. Focus on highlighting your strengths, drawing from examples in your professional career thus far. It can also be helpful to more specifically speak to your written and verbal communication so your interviewer has a more detailed picture.
Jason's Answer
"I consider myself adept at both written and verbal communication. I am especially proud of my ability to communicate to non-technical audiences. I enjoy participating in design reviews, especially when I am able to use CAD software to break down a concept. When working with vendors, I tend to prefer written communication, and Ihave confidence in my ability to communicate via email and technical writing as well."
-
4.
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.
Jason's Answer
"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."
-
5.
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.
Jason's Answer
"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."
-
6.
What types of manufacturing technologies have you worked with?
How to Answer
If you are interviewing for a Design role, then you'll likely be asked about your experience with manufacturing. In Mechanical Engineering, this is often a combination of software experience (such as CAD) as well as direct or tangential experience working with a given manufacturing method. They may ask you specifically about the type of skill for which they are looking. If you have direct experience, then it is useful to start with that.
Jason's Answer
"I have direct experience with manual and CNC machining, which I learned in my internships as well as in my university's machine shop. I am comfortable working with SolidWorks 3D Modeling software, and I have designed parts for machining as well as laser cutting and sheet metal. I am interested in learning more about other manufacturing methods as well. If hired, I would do my best to leverage these experiences in addition to learning new skills."
-
7.
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.
Jason's Answer
"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."
-
8.
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.
Jason's Answer
"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."
-
9.
Where do you see yourself going in your career, and how will this role help you get there?
How to Answer
Engineers are often asked these questions to gauge whether or not the position is a long term fit. It's okay if you don't have a detailed plan, just be honest and keep it simple. This is a great opportunity to highlight aspects of the role that interest you. When preparing a response to this question, be sure to paint a picture that allows the interviewer to see how you both mutually benefit from having you in this position.
Jason's Answer
"I'm glad you asked! I'm looking to learn more about the manufacturing process, specifically injection molding. I'm interested in a management position later in my career, s right now I'm looking for a hands-on role to gain more experience first. Because this position involves working alongside the manufacturing team, I think it would be an excellent way to gain experience towards my career goals."
-
10.
What is the difference between static friction and kinetic friction?
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, static friction describes friction between two solid objects that are not moving relative to each other. If you park your car on a hill, static friction can prevent it from rolling down the hill, even though there aren't any moving components. This is different from kinetic friction, which typically describes the friction between two objects that are moving relative to each other. Static friction is typically higher than kinetic friction, but this is not always the case.
Jason's Answer
"Static friction and kinetic friction both refer to force that resists relative motion between two objects. The difference is that static friction refers to friction between objects at rest, whereas kinetic friction describes friction between moving objects. If my car broke down on the way to this interview and I were to push it, then static friction would pertain to the initial force it would take to get it moving. Kinetic friction would describe the force required to keep it moving once it is in motion. In both cases, the friction would be between the rubber tires and the asphalt surface of the road and proportional to the normal force being exerted on the vehicle."
-
11.
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.
Jason's Answer
"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."
-
12.
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.
Jason's Answer
"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."
-
13.
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.
Jason's Answer
"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."
-
14.
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.
Jason's Answer
"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."
-
15.
What interests you about working for our company?
How to Answer
This question is very common in Mechanical Engineering interviews. Engineers often work in roles where they have a high impact on the company's success, so the company wants to know that you're invested in their success as well. An effective answer will touch upon your interest in the company while also highlighting how you can contribute as a potential hire.
Jason's Answer
"One thing that really interests me about your company is the focus on sustainable materials and eco-friendly manufacturing. As an engineer growing up in the 21st century, I want to make an impact on reducing the carbon footprint of manufactured goods. I think that we will have many more recycled and sustainable materials in the future, and I would like to learn more about these emerging fields. In addition, I read about the weekly team dinner events that your company hosts across all departments. Team culture is very important to me as well, and I think this could be a great fit if I'm hired."
-
16.
What do you know about our company?
How to Answer
This is often a question asked early in an interview to gauge familiarity with the company, and also as a way to see if the interviewee has done any background research into the company or their work product. Engineers are expected to have a high-level understanding of the business they work for, but you don't need to have encyclopedic knowledge at the interview stage. When preparing for this sort of question, take a look over their website and additional online presence, including any recent headlines or relevant information.
Jason's Answer
"I initially discovered your company while searching for full-time roles in the Denver area. After doing some research, I found myself impressed by the breadth of products you offer. I also enjoyed the educational resources available on your website, as I learned a lot about the manufacture of engine seals from reading them. I know that your company offers manufacturing and design services for small- to mid-size businesses, which interests me because I am looking to grow expertise in both areas in the next phase of my career."
-
17.
What is your ideal work environment?
How to Answer
As a Mechanical Engineer, there are a variety of possible work environments. You may find yourself working in an office, a manufacturing plant, a machine shop, or a research lab. Work environment also involves other attributes, such as the team, work culture, or the resources available at the company. It's useful to consider what you've read or learned about the position thus far to include in your answer.
Jason's Answer
"I find myself working best when I am able to collaborate with others to achieve a mutual goal. I think this position in Test Engineering is an excellent fit for me, because I will be a part of the Research & Design group of your company. I enjoy working in laboratory environments, because I like to work first-hand with the data being collected. Being able to design test fixtures and collaborate on data analysis projects is something that I look forward to if hired."
-
18.
Can you tell me about a project you've worked on?
How to Answer
Often interviewers will ask Mechanical Engineers to walk them through a project or problem that they've worked on before. They might frame the question in a way to focus on a specific type of problem. Choose a project you are confident about and remember well in case the interviewer decides to ask follow up questions. It's often useful to outline the task, then discuss your process, and finally present the result. It's okay if the project did not succeed - the most important thing is what you contributed and how you learned from the experience.
Jason's Answer
"In college, I was part of a Capstone team working on a solar desalination machine. The machine reflected sunlight onto a copper pipe, which heated up seawater to produce water vapor. Unfortunately, the mechanism for rotating the mirror was broken and needed to be rotated by hand. It was my job to repair it while my team focused on other improvements. I decided to research mechanical clocks in our school's library. Through this research, I realized that there was a critical design flaw. The escapement anchor's axis of rotation had to be aligned with the suspension spring. After realizing this, we were able to restore the solar tracking functionality. This project taught me the importance of understanding the theories behind a particular design. I hope to remember this lesson as I proceed throughout my career."
-
19.
What is your 'shop' experience?
How to Answer
These types of questions are more common for roles where operating equipment is a central part of the job. It's important to recognize that your answer will be interpreted in the context of what the hiring manager is looking for, so be sure to research the team and position ahead of the interview. You can also use this opportunity to help shape a story about your professional journey. If you don't have considerable experience yet, then take some time to prepare any relevant, transferrable experience you do have.
Jason's Answer
"My shop experience started with woodworking class in high school. I took two years of classes, where I learned to operate power tools in addition to learning basic shop safety. In college, I took manual machining classes, where I learned the basics of mill and lathe operation. I believe that learning these hands-on skills has helped me become a better engineer. If hired, I would be excited to build on these experiences by contributing to prototyping work as needed by the team."
-
20.
What is a free-body diagram? When would you use one?
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, free-body diagrams are taught in most introductory physics classes, and this question is sometimes asked as a starting point for further technical questions. You may be asked to draw one or simply describe what they are. Make sure to label gravitational force, normal force, frictional force, and any external forces applied to the body in question. You may also be asked to use a free-body diagram in the context of a real-world problem.
Jason's Answer
"Free-body diagrams describe the forces acting on an object, showing them as vectors with both magnitude and direction. For example, a falling bowling ball would have a gravitational force vector pulling straight down. A rolling bowling ball would also have a normal force vector that is perpendicular to the surface it is rolling on. I would use a free-body diagram if I was trying to visualize the net forces acting on an object. Depending on the situation, I might follow up with a Finite Element Analysis model to analyze the expected behavior of the design, or I might come up with a set of equations to determine the amount of force required to achieve the design goal."
-
21.
What are the phases of the Carnot cycle?
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, the Carnot cycle generally describes the conversion of heat into work via four ideal thermodynamic phases. It is most often used in relation to an engine, specifically an internal combustion engine. However, it can also be applied to refrigeration systems. The cycle consists of two phases of compression and two phases of expansion, one of which is isothermal (same temperature) while the other is adiabatic (no heat transfer) and reversible (no friction). This question may be asked to gauge your familiarity with thermodynamics, which may or may not be directly relevant for the role.
Jason's Answer
"The Carnot cycle consists of compression and expansion. Starting with isothermal compression, it is followed by adiabatic compression, then reversible isothermal expansion, and finally reversible adiabatic expansion. In internal combustion engines, this is happening inside of the piston as fuel is injected and then ignited. I learned about these concepts in my Thermodynamics class, and Iknow that they can also apply to refrigeration cycles as well."
-
22.
What is a Factor of Safety (FoS), and when would you use 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, a Factor of Safety (FoS) expresses the degree to which a system is reinforced to avoid failure at a given load. In order to have a Factor of Safety, a system must be able to have a determinable failure point as well as nominal load. For example, a steel walkway with a FoS of 4 means that it is designed to withstand quadruple the nominal load without breaking. Using a FoS may be a legal requirement in some industries, typically when the failure of a machine would cause loss of life or injury.
Jason's Answer
"A Factor of Safety refers to how much stronger a system is compared to what it needs to be for a given load. I would utilize this when designing a system with a known nominal load, such as a bike pedal arm, to ensure that it would not break during operation and cause injury to the user. I also know that regulations may call for a certain minimum Factor of Safety depending on the type of equipment being designed."
-
23.
How would you calculate the maximum deflection of a cantilevered beam?
How to Answer
This question is asked to gauge whether or not the interviewee is familiar with Euler-Bernoulli beam theory, which is typically covered in the first years of engineering school. A cantilevered beam refers to a structure that is fixed on one end and allowed to flex or bend on the other end, like a diving board at a swimming pool. You can calculate the deflection using the force applied (F), the length of the beam (L), the elastic modulus of the material (E), and the cross sectional area moment of inertia (I). The specific equation is (FL^3)/(3EI).
Jason's Answer
"Assuming a single load at the end, the deflection can be calculated by utilizing the Euler-Bernoulli equation for the deflection of a cantilevered beam. Given the length of the beam, the cross-section, the force applied, and the material's elastic modulus, I would be able to calculate the amount of distance the free end will travel using the equation (FL^3)/(3EI). If the load was not placed at the end of the beam, then I would need to utilize a different equation."
-
24.
You have a lever that must lift 50 pounds. The lever is 1 foot long with a fulcrum point 4 inches from the right side, which must supply the lifting force. How much force needs to be applied to the left-hand side? What mechanical advantage is this?
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 describes a lever, which is a type of simple machine that creates mechanical advantage. The amount of mechanical advantage depends on the location of the fulcrum or rotation point. In this case, the fulcrum is 4 inches from the right side of a 12 inch lever, so it is 8 inches away from the left-hand side. The equation for a lever system is F1D1 = F2D2, which states that the forces applied on the left-hand and right-hand side are equal when multiplied by their respective distance from the fulcrum. Mechanical advantage can be determined by dividing the applied load on the right-hand side by the force applied to the left-hand side to find the amplification of the force.
Jason's Answer
"The force required is 25 pounds. This can be found by multiplying 50 pounds by four inches, then dividing by eight inches using the equation F1D1 = F2D2. This results in a mechanical advantage of two, meaning that this lever will apply a load on the right-hand side that is double the force supplied to the left-hand side."
-
25.
A gear rotates at 5 rpm and interfaces with a smaller gear in a 10:1 ratio. How fast does the second gear spin? If the first gear applies 10N*m of torque, then what does the second gear experience?
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, gears are elements of power transmission systems that involve rotating elements with teeth that mesh together. If the gears are different diameters, then the two gears will experience different amounts of torque and will spin at different speeds. The key to solving this is to remember that rotational speed is inversely proportional to gear ratio, whereas torque has the opposite relationship (proportional). A smaller gear coupled with a larger gear will spin faster but carry a smaller rotational force.
Jason's Answer
"The second gear would spin at ten times the speed of the first gear, or 50 rotations per second. This can be calculated by multiplying the larger gear's rotational speed by the gear ratio of 10-to-1. Conversely, the torque is calculated by dividing the larger gear's applied torque by the gear ratio, which yields 1 Newton-meter of torque."
-
26.
A force of 5 N compresses two identical springs in series by 10 cm. What will be the total distance that the same springs in parallel are compressed?
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, springs can be generally described by Hooke's law (F = kx), which states that the amount of distance extended or compressed in a spring is proportional to the force applied by a spring constant (k). This question can be solved by using the effective spring constant, which is the sum of the individual spring constants in series, and the sum of their reciprocals in parallel. The springs are identical and thus have the same spring constant, which simplifies to k_eq = 2*k in series and k_eq = 2/k in parallel. We observe that the springs in parallel would have an effective spring constant that is half of the effective spring constant in series. Using Hooke's law, we can conclude that they would be compressed by half the distance.
Jason's Answer
"The springs in parallel would be compressed by half of the distance, or 5 cm. This can be determined by using Hooke's law as well as the relationship between the effective spring constant in series and in parallel. The effective spring constant in series would be the force (5 Newtons) divided by the compression distance (0.05 meters), resulting in 100 Newtons per meter. Because the springs are identical, their effective spring constant in parallel is exactly half of that in series. Therefore, the spring constant in parallel would be 50 Newtons per meter, which would compress the springs by 5 centimeters in response to a 5 Newton force."
-
27.
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.
Jason's Answer
"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."
-
28.
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.
Jason's Answer
"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."
-
29.
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.
Jason's Answer
"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."
-
30.
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.
Jason's Answer
"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."
-
31.
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.
Jason's Answer
"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."
-
32.
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.
Jason's Answer
"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."
-
33.
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.
Jason's Answer
"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."
-
34.
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.
Jason's Answer
"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."
-
35.
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.
Jason's Answer
"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."
-
36.
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.
Jason's Answer
"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."
-
37.
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).
Jason's Answer
"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."