Practice Questions

Question 1

What is the difference between additive, subtractive, and formative manufacturing methods? Explain in which production situations you can consider each of them.

Answer 1

Additive Manufacturing: Builds parts layer by layer (e.g., 3D printing). Useful for prototyping and complex designs. Advantages: minimal waste, high customization. Disadvantages: slower production, weaker mechanical properties for some methods.
Subtractive Manufacturing: Removes material from a solid block (e.g., CNC milling). Useful for high precision and strong mechanical properties. Disadvantages: material waste, limited geometries.

Formative Manufacturing: Shapes materials into molds (e.g., injection molding). Ideal for mass production. Advantages: high speed, low cost per part. Disadvantages: expensive tooling.

Question 2

Can you give a few examples of additive manufacturing methods?

Answer 2

FDM (Fused Deposition Modeling), SLA (Stereolithography), SLS (Selective Laser Sintering).

Question 3

Can you describe FDM and their advantages and disadvantages?

Answer 3

FDM: Low cost, accessible; weaker parts due to layer adhesion.

Question 4

Can you describe SLA and their advantages and disadvantages?

Answer 4

SLA: High resolution; brittle materials.

Question 5

Can you describe SLS and their advantages and disadvantages?

Answer 5

SLS: No support structures needed; expensive machines.

Question 6

Can you describe the components of an FDM 3D printer?

Answer 6

Frame, build platform, extruder, nozzle, filament spool, motors, and control board.

Question 7

What are advantages and disadvantages of FDM?

Answer 7

Cost-Effective, Wide Material Selection, Ease of Use, Scalability; Layer Bonding Weakness, Surface Finish, Dimensional Accuracy, Support Structures, Material Limitations

Question 8

What is the general procedure for printing a prototype using FDM, going from CAD file to printed model?

Answer 8

CAD design → Export STL file → Slice in software → Adjust settings (e.g., infill, layer height) → Send to printer → Print

Question 9

How can you best design a product that will be produced by injection molding? What are the critical design features that you should try to implement?

Answer 9

Critical features: Uniform wall thickness, draft angles, ribs for strength, avoid undercuts, and proper gate locations.

Question 10

Can you describe the different components of a typical CNC milled injection mold?

Answer 10

Core, cavity, runner system, gate, ejector pins, cooling channels.

Question 11

Can you describe a logical CNC milling toolpath sequence (and the steps required for programming them in SolidWorks CAM) for an injection mold with multiple flat surfaces at different heights (like most drone frames in the project)?

Answer 11

Steps: Stock setup → Rough milling → Semi-finishing → Finishing. Use CAM software like SolidWorks to program.

Question 12

Explain where you generally place the ejection pins for injection molds.

Answer 12

Place pins at thick sections, away from visible surfaces to avoid marks. Avoid bending at the edges

Question 13

Describe the different milling tools you used in this project and for which operations you’ve used them.

Answer 13

Tools: End mills (flat or ball-nose), drills, chamfer tools. Operations: roughing, contouring, drilling.

Question 14

Which material properties of polymers are especially useful in a process such as injection molding?

Answer 14

Important properties: Melt flow index, thermal stability, shrinkage, and mechanical strength.

Question 15

What are the advantages of using either amorphous or semi-crystalline polymers in injection molding?

Answer 15

Amorphous: Better dimensional stability, transparent (e.g., ABS, PC).
Semi-crystalline: High strength, lower shrinkage (e.g., PP, PE).

Question 16

Describe the different components of an injection molding machine.

Answer 16

Hopper, barrel, screw, heaters, clamping unit, ejector system.

Question 17

Explain step by step how an injection molding machine produces the product from plastic pellets.

Answer 17

Plastic pellets → Melting → Injection into mold → Cooling → Ejection.

Question 18

Which different phases are there in the injection molding process and what happens to the polymer during those phases?

Answer 18

Phases: Fill (melt flows in), Pack (reduce shrinkage), Cool (solidify), Eject (remove part).

Question 19

At which locations do you place the gates in a mold to minimize production artefacts?

Answer 19

Place gates near thick sections.

Question 20

Can you name some of the defects and artefacts that can arise from a poorly designed injection mold?

Answer 20

Flash, warping, sink marks, short shots, weld lines.

Question 21

In Moldex3D simulations, what is the significance of the following results: (1) pressure distribution at end of packing and end of filling, (2) volumetric shrinkage, (3) shear stress, (4) distributions of temperature throughout the process, and (5) melt front time?

Answer 21

Pressure Distribution: Uniform across the part.
Volumetric Shrinkage: Low and consistent.
Shear Stress: Minimized to avoid degradation.
Temperature Distribution: Even to avoid hotspots.
Melt Front Time: Synchronized to avoid weld lines.

Question 22

What is the desired outcome for these spatial distributions for a well-designed mold? In other words, what should the results look like in an ideal case?

Answer 22

Uniform filling, minimal shrinkage, balanced cooling, and proper pressure maintenance.