Ch.9 Sheet Lamination

Question 1

Benefits of bond-then-form

Answer 1

• less shrinkage, distortion, residual stress
• paper feedstock are pattern making material –> suitable for finishing operations
• fabricate large parts rapidly
• variety of build materials
• feedstock non-toxic, stable, easy to handle
• unused material cut from cross section slice profile used as support

Question 2

Drawbacks of bond-then-form

Answer 2

• most paper require coating to prevent water absorption/excessive wear
• z-direction accuracy difficult to control
• mechanical/thermal properties inhomogeneous
• small part feature likely damaged during decubing

Question 3

Advantage of form-then-bond

Answer 3

• facilitates control of parts with internal features
• no danger of cutting previous layer
• laser power/knife pressure less demanding
• decubing process eliminated

Question 4

Disadvantages of form-then-bond

Answer 4

process requires external supports for overhangs

alignment system required to align layers

Question 5

what is Ultrasonic additive manufacturing (UAM)

Answer 5

process combining ultrasonic metal seam and CNC milling.
parts are built from bottom up where the foils are layered and then trimmed using CNC milling.

Question 6

benefits of UAM

Answer 6

low temperature diffusion: suitable with embedded parts
thermal residual stress/thermally induced deformation not a concern

dimensional accuracy depended on CNC milling –> eliminates stair stepping/layer thickness dependent accuracy

Question 7

limitations of UAM

Answer 7

lack of support material to build complex overhangs

mechanical properties highly anisotropic

labor-intensive post-processing

Question 8

what are the four layer joining methods using sheet lamination?

Answer 8

adhesive bonding
thermal bonding
sheet metal clamping
UAM

Question 9

what is adhesive or glue bonding?

Answer 9

layer bonding by placing a thin coat of glue or thermoplastic polymer (depending on the build material) on one side to adhere to previous layer. Used for functional prototypes or proof-of-concept.

Question 10

what is thermal bonding?

Answer 10

layer bonding where one side of the sheet is coated with a bonding agent that melts under a heat source and adheres the two layers together as the agent cools and solidifies

Question 11

what is sheet metal clamping?

Answer 11

clamp layers together using a clamping mechanism or bolting, helps with alignment of layers and makes it easier to disassemble to modify a particular cross-section.

Question 12

what is the physical bonding process in ultrasonic additive manufacturing and the conditions
required for a high quality bond.

Answer 12

rotating sonotrode applies normal force to thin metal foil. sonotrode oscillates transversely at 20KHz frequency

condition for high quality bond: Linear weld density (LWD) and part strength

Question 13

what is LWD?

Answer 13

LWD = % of interface bonded/total length of interface

Question 14

what are the 4 significant process parameters in UAM?

Answer 14

oscillation amplitude: controls amount of ultrasonic energy available for bonding

normal force: how much force needed to achieve metallurgical bonds

travel speed: welding exposure time

temperature: elevated temps help to facilitate bond formation

Question 15

How does oscillation amplitude affect the build quality

Answer 15

oscillation amplitude:
large amplitude –> greater plastic/elastic deformation–> better welding

too high –> excessive stress/fatigue –> damage bonds and previous bonds

Question 16

How does normal force affect build quality?

Answer 16

optimal –> best
lower –> lower LWD or no bond
higher –> lower LWD, damage bonds

Question 17

how does travel speed affect build quality?

Answer 17

high speed –> shorter exposure

excessive exposure –> damage bonds/metal fatigue

Question 18

How does temperature affect build quality in UAM?

Answer 18

optimal heating conditions –> reduces flow stress –> better bonds

excess heating –>
foil sticks to sonotrode
damage embedded electronics
metallurgical aging (brittleness)
enhance oxide formation

Question 19

what are the 3 types of defects that occur in UAM and how to reduce the occurrence of each?

Answer 19

Type 1: layer/layer
- voids due to foil roughness/insufficient input energy

minimize by light surface machining after each layer or post heat treatment

Type 2: layer/layer damage
- damaged layer/layer interface due to excess input energy

minimize by post-process heat treatment

Type 3: between adjacent foil strips within layers
- gaps/overlaps due to inaccurate foil placement

minimize by 50% or randomized overlaps across successive layers

Question 20

Why do parts built with ultrasonic additive manufacturing have highly anisotropic mechanical
properties?

Answer 20

due to presence of defects, alignment of grain boundaries, interfacial plastic deformation

in-plane stronger due to rolling of metal foil –> elongates grain structure