98% Of Structural Engineer Interviews Can't Escape These Questions

1,Plastic Material Properties & Selection

2,How to prevent excessive gear noise? Use materials like POM, PA which have wear resistance, fatigue resistance, impact resistance, and self-lubrication.

3,What does "mold core/cavity directly from block" mean? It refers to machining the part directly from a single block of steel, as opposed to using inserts.

4,Rib thickness is typically 0.6~0.7 times the main wall thickness to avoid sink marks.

5,Undercut release methods: Internal lifter, external slider.

6,Plastic part gating methods: Direct gate, edge gate, fan gate, pin-point gate, cashew gate, submarine gate.

7,Keypad design considerations: Button clearance, wall thickness shouldn't be too thick, appropriate key travel distance.

8,PCB thickness: 0.8~1mm.

9,Difference between "Tiao" and "Si"? Both are 0.01mm; "Tiao" is Taiwanese term, "Si" is Hong Kong term.

10,Aesthetic gaps can solve step/mismatch issues.

11,Plastics suitable for ultrasonic welding: PA, PC, PE, PP, PS, ABS.

12,Minimum clearance for lifter movement: 3mm.

13,Distance between reverse lip and snap-fit: about 10mm (too close causes insufficient deformation).

14,Gate location selection: Thick sections, shortest flow path, areas not affecting appearance or function.

15,Workflow:

1. Attend product kick-off meeting, understand client needs and product functions.
2. ID performs industrial design, review ID, analyze moldability, assembly, part splitting, surface treatment.
3. Detail structural design, review structure, prototype sampling, prototype assembly, optimize structure based on prototype issues.
4. Conduct DFM (Design for Manufacturability) review, confirm mold opening.
5. Mold follow-up, trial shots, summarize issues, propose improvements.

Follow pilot production, propose improvements for pilot production issues.

16,Injection Molding Defects & Improvement Solutions:

1. Sink Marks: Wall too thick - core out.
2. Flow Marks: Increase venting - add inserts.
3. Flash: Reduce injection pressure, increase clamping force, lower melt temperature, re-fit mold.
4. Weld Lines: Increase front mold temperature, improve gate location, add ribs, reduce injection speed.
5. Short Shot: Improve gate location, increase injection pressure, increase thickness.
6. Flow Hesitation/Shadow Marks: Increase mold temperature, surface treatment, design gradual thickness transitions.
7. Scratches/Dragging: Increase draft angle, polish mold.
8. Ejector Pin Marks/Whitening: Increase draft angle, polish mold, add ejector pins.
9. Silver Streaks: Material not dried properly.
10. Black Specks: Material overheated/decomposed; foreign matter in material or unclean dryer; poor pigment dispersion.

17,Spring material? How to detail on 2D drawing?

Materials: Stainless steel 304, Phosphor bronze.

2D drawing dimensions: Inner/outer diameter, number of active coils, length, wire diameter.

18,Methods for fixing product parts?

Screws, snap-fits, ultrasonic welding, adhesive bonding, press-fit, heat staking, threading.

19,Waterproofing structures?

Overmolding, ultrasonic welding, adhesive, O-rings, potting.

20,How to improve products when problems are encountered?

Trial shot problems

Design problems

Production problems

21,Difference between three-plate mold and two-plate mold?

Three-plate mold has an additional movable stripper plate. Two-plate molds use large sprue gates (runners attached to part, manual removal). Three-plate molds use pinpoint gates (small connection, automatic separation).

22,Function of cold slug well?

Prevents cold material at the front from entering the cavity, causing stress concentration and reduced part strength.

23,Surface treatment processes for metal materials?

Plating, electrophoresis, anodizing, brushing, painting, laser engraving.

24,Rib (reinforcing rib) design considerations:

Thickness is 0.4~0.7 of wall thickness, not exceeding 0.7 to avoid sink marks.

Appropriate draft angle.

Minimize stress at the base to prevent sink marks.

25,What systems is a mold divided into?

Gating - Forming - Venting - Cooling - Ejection.

26.How to test electronic products?

Drop test, function test, button test, charge/discharge test, waterproof test.

Testing equipment listed: Alcohol abrasion tester, electric tensile tester, button life tester, rain test chamber, salt spray tester (for hardware), electric blast drying oven, vibration simulator, airtightness tester, leak point tester.

27,Butt shut-off vs. side shut-off?

Butt shut-off: Core and cavity meet face-to-face. Side shut-off: Core and cavity meet laterally, requiring safety clearance. Preference: Butt shut-off > side shut-off > lifter.

28,Principle & Function of surface treatment processes?

• Principle: Forming a surface layer with special properties via physical/chemical methods. Improves appearance, texture, functionality.
• Function: Alter appearance (color, gloss, lines), texture (feel, roughness), functionality (hardening, anti-fingerprint, scratch resistance).
• Three key elements: Smoothness, film thickness, adhesion.

29,Key Points of Structural Design (Bosses/Snap-fits/Lips)

Structural Review Content:

A. Reasonableness of product wall thickness, rib thickness.

B. Boss pilot hole and outer diameter sizes, snap-fit engagement (considering rigid snap ~0.7mm, flexible snap <0.5mm).

C. Ease of assembly, need for fool-proofing design.

D. Appropriateness of clearances, button-to-hole clearance, component interference.

30,Two-shot molding vs. Overmolding:

Two-shot mold: Can make different colors, high precision, more wear-resistant, better appearance. Requires two molds. Part isn't removed; mold rotates within machine.

Overmolding: Simpler structural design, higher scrap. First shot part is removed and placed into another mold for the second shot.