Exam 2 Material Flashcards
Process where you heat a sheet of plastic, then form to a mold using a vacuum
Thermoforming
Advantages of Thermoforming (7 things)
very low tooling cost
low mold cost
low pressure req.
large parts easily formed
fast mold cycles
extremely adaptive to customer design needs
paint-able and colored plastic available
Disadvantages of Thermoforming (6 things)
high cost of raw mats
high scrap
unable to mold parts with negative draft (concave)
limited part shapes
inherent wall thickness variation
internal stresses common
what materials can be used for thermoforming molds?
Cast or machined aluminum
wood
epoxy
steel
Areal Draw Ratio formula
Surface Area of part being formed
/
area of sheet needed to make part
Area Ratio formula
area of sheet used to make part before forming
/
area of sheet used to make part after forming
estimated initial sheet thickness (gauge) formula
(areal draw ratio) * (final thickness)
Pre-stretching tool used to improve dimensional consistency when the draw ratio is sufficiently large. It’s like a plunger that presses the material into the mold prior to vacuuming.
Plug Assists
in thermoforming, how do you determine the width or length of a part?
the larger dimension is considered the length, the smaller is considered the width
What are the major differences between skin packs and blister packs?
Skin pack has plastic vacuum formed to the product, custom
Blister pack plastic is pre-formed prior to use with product, generic
this process is used to shape thermoplastic sheets and films into discrete parts
Thermoforming
this process is different from extrusion and injection molding because the material is not melted and higher pressures are not required.
Thermoforming
What are the principal steps to Rotational Molding?
- loading/charging
- heating (under rotation)
- cooling
- unloading/demolding
What’s the typical rotation ratio between axes in Rotational Molding?
3.75:1
What constraints exist to get even coating in Rotational Molding?
Rotate about 2 axes simultaneously
different rotation speeds (major axis > minor axis)
Ratio of rotations not a whole number
Slow rotation (< 60 RPM)
Which process is capable of molding much larger parts than the other common thermoplastics processes?
Rotational Molding
For which Thermoplastic process does the cost-effectiveness of the part increase with the size of the part?
Rotational Molding
What are some common thermoset processes?
Reaction injection molding
extrusion
spin casting
foam molding
compression molding
transfer molding
What’s the primary/most-common process for thermosetting plastics?
Compression Molding
What process preheats a preformed “pill”, then uses a plunger to force the preform into sprue, runners, and mold cavity?
Transfer Molding
Which process mixes two liquids, as they are injected into a mold at high speed?
Reaction Injection Molding (RIM)
What’s a downside of Reaction Injection Molding?
Controlling metering, mixing, temperature, and pressure are generally complex and expensive
Which process rotates a disk-shaped mold about it’s centroidal axis, then pours in material, in order to force the material throughout the mold?
Spin Casting (Also called Centrifugal Rubber Mold Casting)
What are the variables to consider with compression molding?
Material/Resin amount
Energy needed to heat material
Mold/material heating time
Compression force for that material
Cooling time/technique
What are the three most-common types of composites?
Particulate
Laminar
Fiber-Reinforced
Process requiring no special equipment
Particulate
Which process pulls a fiber through a resin and forms the composite through a mold?
Pultrusion
Process by which fibers are drawn through a resin bath, then immediately wrapped around a form to create the external shape of the mold.
Filament winding
Which composite process impregnates fiber or fiber-sheet with resin, layers them on top of one another, heats it, then removes the surrounding air to compress the layers, bonding them together?
Vacuum bag method (VARTM)
What are the main three variables in any thermoset- or thermoplastic-based composite processes?
Heat
Pressure
Time
What are the objectives of Manufacturing Operations? (3)
Produce parts that adequately perform their intended task
Manufacture from a selected material with the desired shape, precision, and properties
Optimize parts for their service environment
What are the three primary stages of Part Definition? (Design process)
Conceptual Stage - what does it need to do?
Functional Stage - What will the product look like and how will it behave?
Production Stage - How can the product be made profitably?
What are the procedures for product realization?
Design
Materials Selection
Process Selection
Production
Evaluation
Redesign or modification
What are the three main material properties, in the context of manufacturing? (General)
Mechanical
Physical
Environmental
What are the types of joining?
Mechanical
Chemical
Metallurgical
What plastic is most well-suited to welding?
Thermoplastic
What are the types of plastic welding?
Ultrasonic
Laser
Linear Friction
Hotplate, Hot gas, Extrusion, Implant, Microwave
Definition: Non-metallic material that fills the space between two surfaces to create a single joint.
Adhesive
OSHA is a part of which government agency?
US Department of Labor
What is an MSDS?
A Material Safety Data Sheet contains properties and safety information regarding a particular material.
What is the CAS and what do they do?
Chemical Abstracts Service. This service registers chemicals/materials and assigns them numeric values for indexing and identification in a database of all chemicals.
What are the types of hazards identified by the Hazard Communication Standard?
Chemical
Environmental
[War?]
Health hazards
Physical hazards
“Green Manufacturing” is aimed at this
Reducing the energy and material intensiveness of manufacturing processes
This refers to the amount of re-used material vs virgin material in a newly-formed plastic
Regrind Ratio
Regrind ratio (formula)
mass of reground-material/mass of virgin material
