A CNC milling centre and a metal 3D printer (DMLS) are both available to produce a titanium bracket. The bracket has an internal cooling channel that spirals through its core. Which process should be selected and why?

CNC milling, because it achieves tighter tolerances than DMLS DMLS, because internal channels are geometrically inaccessible to subtractive cutting tools CNC milling, because titanium cannot be sintered by laser DMLS, because additive manufacturing always produces better surface finish

An engineer compares FDM and SLA printed test coupons. The FDM part breaks along a layer boundary under tensile load perpendicular to the build direction, while the SLA part resists more uniformly. What property best explains the FDM failure mode?

FDM uses lower-strength materials than SLA resins Layer adhesion anisotropy: FDM parts are weaker perpendicular to the layer direction FDM nozzles are too large to produce accurate geometry SLA parts are post-cured under UV, making them inherently stronger than FDM

A production engineer needs 500 identical functional nylon housings with complex internal geometry. SLS and FDM are both capable of printing the part. Which process is the better production choice and what is the key advantage?

FDM, because it is faster per part than SLS SLS, because unfused powder acts as its own support, enabling dense packing of multiple parts per build without support removal labour FDM, because nylon cannot be sintered by laser SLS, because SLS parts have superior surface finish to all other AM processes

The GE LEAP engine fuel nozzle is frequently cited as an additive manufacturing landmark. What combination of outcomes made it so significant?

Reducing material cost by 50% and doubling production rate compared to casting Consolidating 20 brazed parts into 1 printed part, achieving 25% weight reduction and 5× greater durability with a geometry impossible to manufacture otherwise Eliminating the need for heat treatment of superalloy parts after printing Achieving surface finishes tighter than ±0.01 mm directly from the DMLS machine

Topology optimisation software analyses a bracket and recommends removing 60% of its original volume, leaving an organic web of load-bearing struts. Why must this optimised design almost always be manufactured additively rather than by CNC machining?

CNC machines cannot process the file formats produced by topology optimisation software The organic, lattice-like internal geometry has enclosed voids and undercuts that cutting tools cannot reach CNC milling cannot work with metals strong enough to replace the removed volume Topology-optimised parts are always made from polymer, which cannot be machined

A medical device company is printing patient-specific titanium (Ti6Al4V) implants using SLM. After printing, quality engineers specify hot isostatic pressing (HIP). What does HIP address?

HIP dissolves residual support structures inside the titanium part HIP uses high pressure and temperature to close internal porosity in the printed metal, improving fatigue life and mechanical properties HIP coats the implant surface with a biocompatible ceramic layer HIP heat-treats the alloy to relieve residual stresses from the laser scan pattern

An engineer compares tolerance capability across processes for a critical bore diameter. Ranked from tightest to loosest typical tolerance, which ordering is correct?

FDM → SLS → DMLS → SLA → CNC machining CNC machining (±0.01 mm) → SLA (±0.1 mm) → DMLS (±0.1–0.2 mm) → SLS (±0.3 mm) → FDM (±0.5 mm) SLA → CNC machining → DMLS → SLS → FDM DMLS → SLA → CNC machining → FDM → SLS

90% of modern hearing aid shells are 3D printed, each unique to a patient's ear canal scan. This production model is best described as which manufacturing paradigm?

Batch production: grouping similar geometries into production runs to reduce setup cost Mass customisation: producing large volumes of individually unique products economically Craft production: hand-forming each shell from an impression taken by an audiologist Flexible manufacturing: using reconfigurable fixtures to adapt one mould to multiple ear profiles

A design engineer is creating a part for FDM printing. The self-supporting angle rule states overhangs steeper than 45° from the build plate require support structures. An angled wall has a 40° overhang from vertical (i.e., 50° from horizontal). Does it require supports?

Yes — any overhang from vertical requires support structures in FDM No — the wall is 50° from the build plate, which exceeds the 45° self-supporting threshold Yes — only walls perfectly vertical (90° from build plate) are self-supporting No — FDM never requires support structures because the previous layer always supports the next

A hybrid manufacturing centre (DMG Mori LASERTEC type) deposits metal powder using a laser cladding head, then immediately machines the deposited region with a milling spindle on the same machine. What is the primary engineering advantage of this combined approach over a separate print-then-machine workflow?

The laser cladding process produces faster material deposition than DMLS powder bed systems Critical internal surfaces can be machined between deposited layers before they become inaccessible, achieving tight tolerances inside enclosed features The milling spindle removes support structures more cleanly than hand-finishing Combining processes in one machine eliminates the need for heat treatment of metal parts

Inconel 718 and AlSi10Mg are both used in DMLS aerospace applications. An engineer must choose one for a combustion chamber liner exposed to 900°C exhaust gases and high cyclic stress. Which alloy is appropriate and why?

AlSi10Mg, because aluminium alloys have higher thermal conductivity, drawing heat away from the liner Inconel 718, because it retains strength and oxidation resistance at temperatures that cause AlSi10Mg to lose structural integrity AlSi10Mg, because its lower density reduces the thermal mass the engine must heat Inconel 718 and AlSi10Mg perform equivalently at 900°C; the choice depends only on cost

An additive manufacturing bureau receives an SLA order for 200 dental surgical guides (small, palm-sized parts). The bureau's FDM farm could print them faster per machine-hour but the dentist specifies SLA. Synthesising accuracy, material, and clinical requirements, which factor most strongly justifies the SLA specification?

SLA resins are inherently biocompatible while FDM filaments are always toxic SLA's ±0.1 mm accuracy and smooth surface finish are critical for guides that must precisely locate surgical drill positions on patient anatomy SLA prints faster than FDM for small parts, reducing patient waiting time FDM cannot print dental-grade resins, making SLA the only technically possible choice