PDR Vehicle Panel Metallurgy & Body Structure 2 — Questions and Answers
Question 1: Which type of vehicle panel construction most commonly uses a sandwich of two steel skins bonded to a core material?
- Monocoque construction
- Composite or laminated panel construction (Correct answer)
- Unibody roll-formed panels
- Hydroformed structural rails
Correct answer: Composite or laminated panel construction
Laminated or composite panels use two thin metal skins bonded to a structural core (often adhesive or foam), which can delaminate during aggressive PDR attempts.
Question 2: A technician notices that a hood panel has a distinctly different 'push feel' than expected — spongy rather than firm. This most likely indicates:
- The panel is aluminum instead of steel
- The panel is a bonded composite or has delaminated inner layers (Correct answer)
- The metal has been over-hardened by the sun
- The dent is too shallow to feel resistance
Correct answer: The panel is a bonded composite or has delaminated inner layers
A spongy feel under the rod typically signals a composite or laminated panel where the inner bonding has failed or separated, requiring a different repair approach.
Question 3: Why is heat application (e.g., heat gun or heat lamp) sometimes used before PDR on aluminum panels?
- To make the paint softer for polishing
- To temporarily restore ductility and reduce work-hardening effects, making the metal more workable (Correct answer)
- To cause the aluminum to expand and self-repair
- To magnetize the aluminum surface for tool adhesion
Correct answer: To temporarily restore ductility and reduce work-hardening effects, making the metal more workable
Carefully applied heat can relieve work-hardening in aluminum, temporarily restoring ductility and allowing the technician more working cycles before the metal fatigues.
Question 4: The 'grain direction' of a metal panel is most relevant to PDR because:
- It determines the panel's color uniformity
- Working against the grain can cause micro-tears, while working with the grain allows smoother metal movement (Correct answer)
- Grain direction only matters for fiberglass panels
- Panels rolled in one direction are lighter than bi-directional rolled panels
Correct answer: Working against the grain can cause micro-tears, while working with the grain allows smoother metal movement
Steel is rolled in a specific direction during manufacturing, creating a grain; pushing metal with the grain yields smoother deformation, while working against it increases cracking risk.
Question 5: Which term describes the permanent deformation zone of a metal panel where it has been stretched beyond its elastic limit?
- Elastic deformation zone
- Plastic deformation zone (Correct answer)
- Tensile recovery zone
- Compression rebound area
Correct answer: Plastic deformation zone
The plastic deformation zone is where metal has been permanently stretched beyond its yield point; PDR works to reshape this zone without adding further stretch.
Question 6: Dual-phase steel (DP steel) used in modern body panels differs from mild steel primarily in that it:
- Contains two coats of factory paint
- Has a microstructure combining ferrite and martensite phases, giving it high strength with better formability than UHSS (Correct answer)
- Is made from two layers of mild steel welded together
- Is always thicker than single-phase steel panels
Correct answer: Has a microstructure combining ferrite and martensite phases, giving it high strength with better formability than UHSS
DP steel's dual-phase microstructure (ferrite + martensite) gives it higher strength than mild steel while retaining more formability than full UHSS, making it a moderate PDR challenge.
Question 7: When a PDR technician observes 'stress whitening' in a dark-painted panel after working a dent, this typically indicates:
- Successful repair with paint still intact
- Micro-cracking or excessive stretching of the paint layer due to over-manipulation of the metal (Correct answer)
- Normal oxidation of the clear coat during repair
- Glue residue from a pull tab left on the surface
Correct answer: Micro-cracking or excessive stretching of the paint layer due to over-manipulation of the metal
Stress whitening occurs when the paint and clear coat are micro-cracked from excessive metal movement, signaling the technician has pushed the metal too aggressively.
PDR Vehicle Panel Metallurgy & Body Structure 2
Which type of vehicle panel construction most commonly uses a sandwich of two steel skins bonded to a core material?