What do mechanical engineer interviews ask most?

CAD habits, calculations and FEA, tolerances and GD&T, materials, design for manufacturing, 8D and FMEA, testing, suppliers and the norms of the industry.

Will I have to bring a design?

Often: a drawing, a model or photos of a part you designed. Be ready to explain each choice and what you would change.

Is there a technical test?

Sometimes: a short calculation, a drawing to read or a part to sketch. Practise basic strength, deflection and fits by hand.

Which CAD system should I name?

The one you know best, honestly; SolidWorks, CATIA and Siemens NX are the most common in ads.

How should I prepare in a week?

Pick two parts you designed and prepare their story, review tolerances and GD&T, and practise one 8D and one FMEA example aloud.

Mechanical engineer interview questions, with worked answers

Sixteen questions that mechanical engineer interviews ask again and again, from junior and mechanical engineer to senior mechanical engineer, lead or principal engineer, engineering manager, head of engineering and technical director. For each: what the interviewer is checking, a short answer, the full answer in plain words, a weak answer to avoid, and a likely follow-up.

The cvscored teamPublished 27 Oct 2026 · Updated 27 Oct 2026

Contents

How to use these questions
What a mechanical engineer is expected to know
CAD and design
FEA and calculations
Tolerances and GD&T
Materials
Design for manufacturing
Root cause and risk: 8D and FMEA
Testing and validation
Working with suppliers
Norms and rules
The product lifecycle
Senior mechanical engineer, lead or principal engineer, engineering manager and head of engineering
Your CV for these questions
Key takeaways
Frequently asked questions
More on the mechanical engineer role

How to use these questions

Practise each short answer aloud, then add a part you designed yourself: what it had to do, what you chose, how you proved it and what you would change now. Many interviews ask you to bring a drawing or a model, or to sketch a design on a whiteboard, so practise talking through a part with a pen in your hand.

What a mechanical engineer is expected to know

Design: a 3D CAD system, drawings with tolerances, and the design intent behind a model.
Proof: hand calculations, FEA and tests, and how each checks the others.
Making it: materials, manufacturing processes such as CNC machining, casting or moulding, and what drives cost.
Quality: 8D and FMEA, drawings and changes released inside an ISO 9001 system.
Norms: the norms of the country and industry, and the EU's rules where a product is sold in the EU.

CAD and design

How do you build a CAD model that someone else can change a year later?

What they check: clean modelling habits, which save a team hours on every change.

Short answer: "I model the design intent, not just the shape. Sketches are fully constrained and dimensioned to the features that matter, such as a bore to the mounting face. Key sizes sit in a few named parameters. Features are in a sensible order with clear names, and parts in an assembly are mated to each other's functional faces, so a change moves what should move and nothing else."

The full answer: Start simple and add detail late: fillets and chamfers last, because they break first. Avoid references to faces created by later features. In an assembly, use sub-assemblies that match how the product is built. Check the model with the drawing: if a dimension on the drawing does not exist in the model, the intent is wrong. Store everything in the PLM system, the product lifecycle management system, with its revision, so nobody works on a copy.

A weak answer: "I just model until it looks right." Follow-up: "The housing must grow by 10 millimetres." Show which parameter you change and what follows from it.

Which CAD systems have you used, and how fast could you work in ours?

What they check: honest depth in one system and the ability to learn another.

Short answer: "I have used SolidWorks for three years for machined and sheet metal parts, and CATIA on one project for larger surfaces. The concepts are the same in Siemens NX: sketches, features, assemblies, drawings. I would expect to be productive in a few weeks, faster with the company's templates and a colleague to ask."

The full answer: CATIA and Siemens NX are common in automotive and aerospace, with large assemblies and complex surfaces; SolidWorks, Inventor and Creo in machine building and smaller companies. What moves between them is modelling discipline, drawing standards and PLM habits. Name the modules you used, such as sheet metal, weldments, surfacing or simulation, and the size of the assemblies.

A weak answer: "I know all CAD systems." Follow-up: "Show us a model you built." Talk through its feature tree and why it is built that way.

FEA and calculations

When do you trust an FEA result, and when not?

What they check: that you treat simulation as a tool to check, not as an answer machine.

Short answer: "FEA, finite element analysis, splits a part into small elements and solves for stress and deflection. I trust a result when the loads and supports match reality, the mesh is fine enough that a finer one changes little, and a hand calculation of a simple case lands close. I do not trust a peak stress at a sharp corner or a point load: that is often a singularity of the model, not the real part."

The full answer: Most FEA errors are in the setup: a fixed support that is really a bolted flange, a missing preload, a material taken as linear beyond its yield. Do a convergence check on the region you care about. Compare with a beam or plate formula first. Read deflections as well as stress: a part can be strong and still too soft. Where it matters, plan a test with strain gauges at the points the model says are critical, and correct the model with the result. Tools differ, such as Ansys, Abaqus or the simulation inside the CAD system, but the checks are the same.

A weak answer: "The colours were green, so it was fine." Follow-up: "The test failed where the model showed a low stress." Check the load path, the supports and the contact settings in the model.

A shaft broke in a field test after a few weeks. How do you check the design?

What they check: fatigue, the most common way a machine part fails, and a method to find out why.

Short answer: "A break after weeks of normal use points to fatigue, so I look at the fracture surface: fatigue leaves beach marks from a start point, often at a notch such as a keyway, a shoulder or a groove. Then I check the real loads, with the bending and torsion that change each turn, and the fatigue strength at that notch, with its stress concentration and surface finish."

The full answer: Static strength is rarely the problem; changing loads are. Compare the stress amplitude at the notch with the endurance limit of the material, reduced for size, finish and the notch, and add a safety factor. Common fixes are a larger fillet radius, moving the notch out of the high-stress zone, a better surface, or a material with higher fatigue strength. Measure the loads in the field if the design assumed them. German practice often uses the FKM guideline in Germany for such checks; the method of the company should be named in the report.

A weak answer: "We make the shaft thicker." That may move the problem. Follow-up: "The customer needs a fix next week." Contain it first, such as a lower load limit or more frequent checks, then the design change.

Tolerances and GD&T

How do you choose a tolerance, and what is GD&T for?

What they check: that you set tolerances by function and cost, and can read the language of modern drawings.

Short answer: "A tolerance should be as wide as the function allows, because every tighter step costs money in production and inspection. GD&T, geometric dimensioning and tolerancing, describes form, orientation and position with datums, so the drawing says how a part is measured and what really matters: for example the position of a hole pattern relative to the face it bolts to."

The full answer: Two systems are in use: ASME Y14.5 in the US and ISO GPS, the international geometrical product specifications such as ISO 1101, in Europe and much of the rest of the world. They look alike but differ in details, so the drawing must say which applies. Datums should be functional faces that also work for fixturing. Fits for shafts and holes follow the international ISO 286 system, such as H7 for a bore; general tolerances often follow ISO 2768. Talk to the people who make and measure the part before you fix a tight value.

A weak answer: "I take the default of the drawing template." Follow-up: "The supplier says the position tolerance cannot be met." Check whether the function needs it; if it does, change the process, the datum scheme or the design.

Explain a tolerance stack-up and how you would run one.

What they check: that you can prove an assembly fits before parts are made.

Short answer: "A stack-up adds up the tolerances along a chain of parts to find the range of a gap or a fit that matters, such as the clearance between a rotor and its housing. Worst case adds every tolerance at its limit and always works, but is expensive. Statistical, root sum square, assumes parts vary around their middle and gives a smaller, more realistic range, with a small risk."

The full answer: Draw the chain as a loop from one face of the gap back to the other, with each dimension and its tolerance. Include form and position tolerances, not only sizes. Use worst case for safety-critical fits and small production runs; statistical methods for large runs with capable processes. If the gap fails, tighten only the few tolerances that contribute most.

A weak answer: "The CAD assembly showed no collision." CAD shows nominal sizes only. Follow-up: "Three parts come from different suppliers." Agree the measurements and the process capability with each.

Materials

How do you choose a material for a new part?

What they check: a method of choice, not a favourite material.

Short answer: "I start from the requirements: loads and stiffness, temperature, environment such as water or chemicals, weight, the number of parts per year and the target cost. That narrows the families: steel, aluminium, plastics, composites. Then the process and the material go together: an aluminium casting, a machined steel part or an injection moulded glass-filled plastic. I check the data sheet values, the fatigue strength and availability."

The full answer: Compare candidates on what matters per unit weight or cost, such as stiffness per kilogram. Watch for corrosion between different metals in contact, creep in plastics under constant load, and the effect of heat treatment or welding. Material names differ by country: European EN names, such as 42CrMo4 in the German DIN EN system, against US AISI and SAE grades, so a drawing for several countries names its norm. In the EU, the REACH and RoHS rules of the EU limit some substances, so check them for parts sold there.

A weak answer: "We always use stainless steel; it is safe." Follow-up: "The part must be 40 percent lighter." Compare aluminium, a fibre-filled plastic and a new geometry, with the cost of each.

Design for manufacturing

How do you design a part that is cheap and easy to manufacture?

What they check: design for manufacturing and assembly, which decides most of a product's cost before production starts.

Short answer: "I choose the process early and design for it: draft angles and even walls for moulding and casting, tool access and standard radii for machining, bend radii for sheet metal. I cut the number of parts, use standard parts, and make assembly obvious, with one direction and features that prevent wrong fitting. And I ask manufacturing to review the design before release, not after."

The full answer: Most of the cost is fixed by the design, so a tight tolerance or an extra set-up on a CNC machine is paid for in every part. Count the steps of assembly and ask for each part whether it must be separate. Compare processes by volume: machining for small runs, casting or moulding when the tool pays back. Lean thinking helps: every extra step, part or check is waste the customer does not pay for.

A weak answer: "Production will find a way." Follow-up: "Purchasing finds a cheaper process after release." Check the drawing against it and run a change through the normal release.

Root cause and risk: 8D and FMEA

A customer reports cracked housings. How do you run the 8D?

What they check: a structured method of problem solving, standard in automotive and much of industry.

Short answer: "8D, the eight disciplines, is a team method. I form a small team, describe the problem with facts: which parts, how many, since when. Then containment, so no more bad parts reach the customer, such as sorting the stock. Then the root cause, with tools like the five whys and a fishbone diagram, proved by test. Then the corrective action, its validation, and changes that stop it coming back, such as the FMEA and the control plan."

The full answer: Keep two causes apart: why it happened, and why we did not detect it. Prove the cause by switching it on and off, for example parts made the old and the new way. A good 8D report is short, has photos and data, and names an owner and a date for every action. Root cause work fails when the team jumps to a solution in the first meeting.

A weak answer: "We would replace the parts and move on." Follow-up: "The cause is at a supplier." The supplier runs its own 8D, and you review it and check its actions.

How do you run a design FMEA?

What they check: that you use FMEA to find risks early, not to fill in a form at the end.

Short answer: "An FMEA, failure mode and effects analysis, goes through each function of a design and asks how it could fail, what the effect would be and why it could happen. Each failure gets a rating for severity, occurrence and detection, and the high ones get actions, such as a design change or a test. I run it early with design, test, quality and production in the room."

The full answer: A design FMEA looks at the product; a process FMEA at how it is made. In automotive, the joint AIAG and VDA FMEA handbook, from the US and German industry bodies, replaced the old risk number with an action priority, so a high severity always gets attention. The FMEA feeds the test plan and the control plan, and it is updated with every field problem. It belongs inside the quality system.

A weak answer: "Quality fills in the FMEA before the audit." Follow-up: "The team rates everything as low risk." Ask for the evidence behind each rating.

Testing and validation

How do you plan the testing and validation of a new product?

What they check: that you prove a design against its requirements before the customer does.

Short answer: "I start from the requirements and the FMEA: each requirement and each high risk needs a test, a calculation or an inspection that proves it. That becomes a test plan, often called a DVP&R, a design verification plan and report, with the test, the sample size, the pass criteria and the date. Verification proves we built it right; validation proves it does the job for the user."

The full answer: Plan the long tests first, such as endurance, corrosion or temperature cycles, because they decide the date. Test parts from the real process where you can, not only hand-made prototypes. Use statistics to choose the sample size and read the spread, and analyse the data, for example in MATLAB or Python. A failed test is information: record it, find the cause, and test again after the change.

A weak answer: "We test the first prototype, and if it works we release." Follow-up: "There is no time for the full endurance test." Agree a reduced plan with its risk in writing, and finish the test in parallel.

Working with suppliers

How do you work with a supplier on a new part?

What they check: that you can get a part made to the drawing, on time, by someone outside the company.

Short answer: "I send a released drawing and model with the request for a quote, together with purchasing, and talk the critical features through with the supplier's engineers before the order. Their feedback on tolerances and process often saves cost. Then a sample approval: first parts measured against the drawing, with the report the industry uses."

The full answer: The approval differs by industry: the PPAP of the US automotive body AIAG, the German VDA approval in German automotive, and first article inspection in aerospace. Agree the critical characteristics and how they are measured, so both sides measure the same way. Track the dates of tools and samples in the project plan. When a problem comes up, solve it together with data rather than blame.

A weak answer: "Purchasing handles suppliers." Follow-up: "The first samples fail on three dimensions." Check whether the drawing, the measurement or the process is wrong, and agree a corrected sample date.

Norms and rules

Which norms and rules apply when you design a machine to sell in Europe and the US?

What they check: that you know where the rules come from and that they differ by market.

Short answer: "For the EU, the EU Machinery Directive, replaced by the EU Machinery Regulation from January 2027, sets the safety requirements, and CE marking under EU law shows the machine meets them. Harmonised norms such as ISO 12100 on risk assessment, an international norm, give a way to prove it. In the US there is no CE marking: OSHA rules in the US apply at the workplace, and US customers often ask for ANSI or ASME norms in the US."

The full answer: Start with a risk assessment and keep the technical file, which the EU rules require for CE marking in the EU. The UK has its own UKCA marking in the UK, alongside recognition of CE for now. Norms are of three kinds: international ISO norms, European EN norms, often published in Germany as DIN EN ISO by DIN, the German body, and national ones such as ASME in the US, BS in the UK, SN in Switzerland or the BIS norms in India. Name the norm and its year on the drawing or in the file.

A weak answer: "We put a CE sticker on it." Follow-up: "Who signs the declaration?" The manufacturer in the EU, after the risk assessment and the technical file are complete.

The product lifecycle

How do you handle a design change once the product is in production?

What they check: engineering change management across the product lifecycle.

Short answer: "Through the change process: a change request with the reason, a check of what it affects, such as parts in stock, tools, the FMEA, tests and the customer's approval, then a change order with the new revision and a date from which it applies. The PLM system holds the revisions, and the bill of materials in SAP follows it, so production builds the right version."

The full answer: Product lifecycle management covers a product from concept through production and service to the end of its life. Every change has a cost beyond the design, so group small changes where you can. Decide what happens to old parts: use up, rework or scrap. Some customers, such as in automotive, must approve changes first. Late in the life, plan for parts that are no longer made and for spare parts.

A weak answer: "I update the model and send the new drawing to production." Follow-up: "The change is urgent for safety." Use the fast track of the process, but still record it and check what it affects.

Senior mechanical engineer, lead or principal engineer, engineering manager and head of engineering

These questions come up for senior mechanical engineer, lead or principal engineer, engineering manager, head of engineering and technical director roles, where the work becomes decisions for a team and plans for many projects.

As lead or principal engineer, how do you settle a technical choice the team disagrees about?

What they check: technical leadership without rank: decisions based on facts.

Short answer: "I write down the options and the criteria we agree matter, such as cost, weight, risk and time, and ask each side for its evidence. Where facts are missing, a quick calculation or test settles it. Then I decide, explain why, and record it, so the team can move on even if not everyone agrees."

The full answer: A lead engineer is judged on design reviews that catch problems early and on choices that hold up. Separate reversible decisions, which should be fast, from expensive ones, such as a tool or a material, which deserve a test. Keep a short decision log, and revisit a choice only when new facts arrive.

A weak answer: "As the senior person, I decide." Follow-up: "Your choice turns out wrong." Say so early, change course and share what you learned.

As engineering manager or head of engineering, how do you plan the work of the department?

What they check: at the top of the ladder, that you can match people, projects and budget.

Short answer: "I list the projects with their value and dates, and the skills each needs, and compare with the people we have. That shows where we are short and what must wait. I agree the priorities with the managing director and sales, review progress monthly through project gates, and keep time for problems from the field, because they always come."

The full answer: A head of engineering or technical director answers for the products, the engineering methods and the people. Build standards that make the team faster, such as CAD templates, a design review checklist and a common calculation method. Grow specialists and leads, hire for the gaps, and present to the board the technical risks and what they cost.

A weak answer: "Engineers plan their own work." Follow-up: "Sales promised a date engineering cannot meet." Show the plan, offer options such as a smaller first version, and agree the date together.

Your CV for these questions

An interviewer picks a design from your CV and asks how you got there: the requirement, the choice, the proof and the result. Give every claim its own figure and put it under the job it came from:

Skill	Weak line	Strong line, with proof
CAD	3D CAD.	Built the parametric model of a conveyor family in SolidWorks; a new size now takes 2 days, not 2 weeks.
Tolerances	GD&T.	Reworked the drawings of a valve body to ISO GPS with functional datums; scrap at the supplier fell by half.
FMEA	FMEA experience.	Ran the design FMEA of a new actuator with 5 teams; 9 high risks closed before the first prototype.
Suppliers	Supplier contact.	Brought 40 new parts to series production with 6 suppliers; every first sample approved by the second round.
Lead	Team lead.	Led 4 engineers on a new machine platform; design reviews at each gate and launch on the planned month.

Check your CV against a real mechanical engineer job to see which of these results it asks for and which you cannot show yet.

Key takeaways

Start every answer from the requirement and the load, then the choice and how you proved it.
Check FEA with a hand calculation and a test; never trust colours alone.
Set tolerances by function, and say which GD&T system the drawing follows: ASME in the US or ISO GPS.
Use 8D and FMEA as methods to find causes and risks, not as forms.
Name each norm with its country, the EU or ISO, and design for the market you sell in.

Frequently asked questions

What do mechanical engineer interviews ask most?: CAD habits, calculations and FEA, tolerances and GD&T, materials, design for manufacturing, 8D and FMEA, testing, suppliers and the norms of the industry.
Will I have to bring a design?: Often: a drawing, a model or photos of a part you designed. Be ready to explain each choice and what you would change.
Is there a technical test?: Sometimes: a short calculation, a drawing to read or a part to sketch. Practise basic strength, deflection and fits by hand.
Which CAD system should I name?: The one you know best, honestly; SolidWorks, CATIA and Siemens NX are the most common in ads.
How should I prepare in a week?: Pick two parts you designed and prepare their story, review tolerances and GD&T, and practise one 8D and one FMEA example aloud.