After working for a while, it is inevitable to conduct interviews for new hires. Today, I'd like to share some questions I often ask when interviewing mechanical engineers. Everyone can reflect on these questions and consider whether they represent their skills and level.
What type of questions would be asked in a mechanical engineering interview?
First, I would ask what aspects they excel in, and then move on to asking questions from the following categories: transmission, frame, sheet metal, axle components, plate components, and knowledge about material selection (various types of steel, aluminum , alloys and other metals, as well as non-metallic materials such as plastics), heat treatment of parts, electroplating, painting and other surface treatments.
For transmissions, questions would focus on several aspects: gear drive, chain drive, belt wheel, synchronous belt drive.
1. Can you give an example of applying dimensional chains?
Dimensional chains: In the process of machining parts or assembling machines, the interconnected dimensions form a closed group, organized in a certain order. The individual dimensions that make up a dimensional chain are called links in the chain.
The dimension that indirectly guarantees precision in the assembly or machining process is called closed link, while the other dimensions are known as constituent links.
Dimension chains can be used to analyze and determine the dimensional accuracy of machine parts, ensuring machining and assembly accuracy.
2. What are the common types of ferrous metal materials? What is high quality carbon steel?
Ferrous metals typically refer to steel and cast iron; Steel is divided into carbon steel (commonly known as carbon steel) and alloy steel.
Carbon steel is divided into ordinary carbon steel, high-quality carbon steel and advanced carbon steel according to the quality of the steel (that is, the amount of harmful elements S, P in the steel). High quality carbon steel contains ≤0.040% S, P.
3. How to eliminate welding stresses in a welded part?
Methods for eliminating welding stress include heat treatment, mechanical methods, vibration and natural aging.
Post-weld heat treatment (annealing) is an effective method for eliminating residual stresses and is widely adopted. It can be categorized into general heat treatment and local heat treatment. The simplest method is aging treatment.
4. What are the commonly used heat treatment methods? (Name at least three) What is temperament?
Annealing, normalizing, quenching, tempering and hardening, among others.
Tempering treatment: It involves high temperature tempering after quenching, where tempering is carried out between 500-650℃.
5. What are the main failure modes of closed gear transmission (soft and hard tooth surface)? What is the principle of design verification?
The main failure mode of gear transmission with closed soft tooth surface is corrosion fatigue on the tooth surface. When designing, calculations should be based on the tooth surface contact resistance formula, and verification should be carried out using the tooth root bending fatigue resistance formula.
The main failure mode of closed hard tooth surface gear transmission is fatigue fracture of the tooth root. When designing, calculations should be based on the tooth root bending fatigue strength formula, and verification should be carried out using the tooth surface contact strength formula.
6. What is the function of a gearbox?
It modifies the speed and torque transmitted from the main engine to the machine. Mechanical coupling, fluid; fixed speed ratio, variable speed ratio.
7. Which industrial process are you most familiar with? For example, ironworks, ironworks or rolling mills.
For example, the production process flow of a medium thickness plate rolling shop: continuous casting billet → heating furnace → descaler → rolling mill → controlled cooling → straightening → cooling bed → cut to length → side shear → shear length → surface inspection and cleaning → stacking → storage → delivery
8. In the most extreme scenario, what could happen to a hydraulic cylinder subjected to a strong external shock?
Cylinder detachment; oil pipe rupture; deformation.
9. When checking a part under combined bending and torsional loads, which theory of strength should be chosen?
The third resistance theory must be used, calculating the bending stress.
10. What is the development trend of modern mechanical machining?
The development of manufacturing automation technology is profound: precision, integration, flexibility, networking, virtualization, intelligence and cleanliness.
11. What is the approximate carbon content of 45# steel?
The carbon content in 45# steel is about 0.42 to 0.50%. This type of steel, also known as “petroleum steel”, is commonly referred to as 45 steel in the GB standard. The market is mainly made up of hot-rolled stocks; cold rolled specifications range from 1.0 to 4.0mm.
12. What are some common casting defects?
The main defects observed in casting are: 1) sand holes, 2) sand adhesion, 3) bubbles, 4) contraction and porosity holes, 5) inclusion of sand and crusts, and 6) cracks.
13. What is the role of cutting fluid in metal cutting processes?
Cutting fluid serves four purposes in metal cutting processes: cooling, lubricating, cleaning, and rust prevention.
14. Give an example of what digital design involves.
Digital design incorporates support for the entire product development process, product innovation design, product-related data management, and control and optimization of the product development process within a company.
In short, it involves basic product modeling, optimization as the main objective, numerical control technologies as tools and data management as the central element.
15. What does computerization in production include?
Informatization in production involves the full utilization of advanced digital, intelligent and networked information technologies to revolutionize traditional design methods, production technologies, business strategies and management models.
Through cutting-edge computerization, high-quality, high-technology, value-added products are produced, paving the way from “Made in China” to “Made in China”.
16. What are the differences between rolling bearings and sliding bearings? Where are each of them used?
The bearings offer high-precision operation and some can support radial and axial loads simultaneously. They consume less lubricant, are easy to install and have a lower coefficient of friction compared to sliding bearings.
With their standardized, serialized and universal features, the bearings are convenient to use and maintain and can save manufacturing costs for sliding bearings that usually require expensive non-ferrous metals.
However, bearings are highly sensitive to foreign bodies such as metal shavings, have a shorter service life than plain bearings, and have lower load-bearing capacity for their size, so their radial size is large.
Therefore, plain bearings are often used where there is a high load and where compact size and structure are required (such as in internal combustion engine crankshaft bearings or rolling mill bearings).
Bearings generate more vibration and noise, making them unsuitable for applications that require high precision and low vibration; plain bearings are usually the best choice in these cases.
17. What is the meaning of CNC?
The meaning of CNC is Computer Numerical Control.
18. What are the differences between DC motors and AC motors?
A DC motor is characterized by a stationary magnetic field with the conductor moving within it, while an AC motor features a rotating magnetic field with the conductor stationary.
DC motors can adjust their speed by changing the input current, making them better at controlling speed. AC motors can adjust their output speed by changing the frequency of magnetic field changes. DC motors, with equal power, provide more torque at low speeds compared to AC motors.
Generally, DC motors require more maintenance than AC motors.
19. What is the difference between elastic and plastic deformation in metallic materials?
In metallic materials, elastic deformation is a temporary change in shape that is reversed when the applied force is removed.
Plastic deformation, on the other hand, is a permanent change in shape that occurs when the applied force exceeds a certain threshold and remains even after the force is removed.
Plastic deformation in mechanical components is often viewed as a type of structural failure. One of the tasks of structural design is to avoid plastic deformation in working components.
20. What is the function of a reducer?
To change the speed and torque transmitted from the main engine to the working machine. Available in mechanical and hydrodynamic coupling types; with fixed and adjustable speed ratios.
