Chapter 13 Flashcards
Materials engineering
The study of the structure, properties, processing, and performance of engineering materials and the systems interactions.
Materials processing
The devienne and technology through which a material is converted into a useful shape with structure and properties that are optimized for the prosper service environment.
Casting
Liquid flows into and assumes the shape of a prepared container after solidifying
Material removal
Remove selected segments from oversized pieces.
Machining
The mechanical cutting of materials
Deformation processes
Exploit the ductility or plasticity of certain materials to produce a desired shape by mechanically moving or rearranging the solid.
Consolidation processes
Build a desired shape by putting smaller pieces together.
Powder metallurgy
Manufacture of a desired shape from particulate material, can involve casting.
Additive manufacturing or direct digital manufacturing
Includes a variety of processes developed to directly convert a computer drawing to a finished product by a layer by layer deposition of material.
Step one of casting
A container must be produced with a cavity having a desired shape and since (mold cavity) with due allowance for shrinkage. Mold material must withstand high temps.
Multiple use molds
Can be quite costly, but can be used multiple times
Single use molds
Preferred for the production of smaller quantities. Can not be used over and over.
Step 2
À melting process must be capable of providing molten material at the proper temperature, in the desired quantity, with acceptable quality, at a reasonable cost.
Step 3
A pouring technique must be devised to introduce molten metal into the mold.
Step 4
The solidification process should be properly designed and controlled. Shrinkage must not produce voids.
Step 5
It must be possible to remove the cast from the mold. With single use molds they are broken apart and destroyed after each cast, but multiple can be harder to remove
Step 6
Various cleaning finishing and inspection operations may be required after the casting is removed from the mold.
Pattern
An approximate duplicate of the final casting
Flask
The ridged metal or wood frame that holds the molding aggregate
Cope
In a horizontally parted two part mold, the top half of the flask is called this.
Drag
The bottom half of the flask is called this.
Core
A sand shape that is inserted into a mold to produce the internal features of a casting such as holes or passages.
Core boxes
Cores are produced in word metal or plastic tooling and are known as this.
A core print
A feature added to the pattern and is used to locate and support a core within the mold.
Mold cavity
A shaped hole into which the molten metal is poured into.
Rose
An additional void the the mold that also fills with molten metal. It provides a reservoir of additional liquid that can flow to compensate for any shrinkage.
Gating system
The channels that deliver the molten metal to the mold cavity.
Pouring cup
Portion of the gating system that recurved the molten metal and controls its delivery to the rest of the mold.
Sprue
From the pouring cup the metal travels down a sprue.
Runners
Horizontal channels that the metal travels down following the sprue.
Gates
Entrances into the mold cavity
Vents
May be included in a mold or core to provide an escape for the gases present.
Parting line or parting surface
Interface that separates the cope and stage halves of the flask.
Draft
Describes the taper ok the pattern that permits it to be withdrawn from the mold.
Casting
Process and the product when molten metal is poured and solidified in a mold.
Solicitation
Molten material is poured and allowed to freeze into shape
Gas porosity or solidification shrinkage
Casting defects
Nucleation
Occurs when stable particles of solid form from within the molten liquid. Solid state had a lower energy than the liquid.
Undercooking
The difference between the melting point and the actual temperature of nucleation is known as this.
Nucleation event
Produces a crystal or grain in the final casting. These grains can enhance mechanical properties.
Inoculation grain refinement
Introducing solid particle for enhanced mechanical properties
Second stage of solidification process
Growth, which occurs as the heat of fusion is extracted from the liquid material.
Directional solidification
Solidification interface sweeps continuously through the material, and can be used to ensure a sound casting.
Faster rates of cooling
Produce product with finer grain size and superior mechanical properties
Chill zone
The rapid nucleation that occurs when molten metal contacts the cold mold walls and a randomly oriented crystals are predicted in the surface of a casting. As additional heat is removed, the grains of the zone grow inward.
Columnar zone
Thin coin as grains produced by the crystals continuing to grow.
Equiaxed zone
New crystals occurs in the interior of the casting as this region is produced
Dross or slag
Can be trapped in the casting and impart surface finish machinability and mechanical properties. Lower pouring temperature cna reduce this or superheat.
Gating systems and dross
They can be designed to prevent it from flowing into the mold cavity. Filters can be inserted into the feeder channels of the mold.
Gas porosity
Bubbles formed by amounts of dissolved gas.
How to stop gas porosity
Prevent the gas from dissolving into the molten metal. Perform the melting under vacuum, or a flux. Superheat temps kept low.
Vacuum degassing
Sprays molten metal through a low pressure environment. The amount of dissolved gas in reduced.
Gas flushing
Passing small bubbles of inert or reactive gas through the metal resolved the bubbles.
Dissolved gas can react
With something to produce a low density compound that can be removed with the slag.
Museums and cold shuts
Defects produced as the metal begins to freeze before it had completely filled the mold.
Fluidity
The ability of a metal to flow and fill a mold
Fluidity is dependent on
Composition freezing temperature and the freezing range of the metal or alloy. Also surface tensions of oxide films. Most important is the pouring temp or amount of superheat.
High pouring temp
Higher fluidity.
Penetration
A casting surface that contains small particles of sand because the metal is too runny and flowed into voids.
To minimize heat loss
Use shirt channels with round or square cross sections.
Gates attached to thickest sections of a casting to control what
Shrinkage
Turbulent flow
Tends to promote absorption of gases, oxidation of the metal, and erosion of the mold. Gating systems are designed to minimize this.
Sprue well
Can be used to dissipate the kinetic energy of the falling metal and prevents splashing or turbulence.
Choke
Serves to control the rate of metal flow. If choke is located near base of sprue, the flow is slowed and rather smooth.
Runner extensions and runner wells
Because the first metal to enter the mold can likely contain contaminated, these will help trap it and keep it from tendering the cavity. Effective with aluminum casting as aluminum oxide have same density as molten aluminum.
Three stages of shrinkage
1 shrinkage of the liquid as it cools to the temp where solidification occurs. 2 solidification shrinkage as the liquid turns into solid. 3 solid metal contraction as the solidified material cools to room temp.
Metals that expand
Not all metals shrink during solidification, some actually expand.
How can casting. Prevent solidification
They can be designed to have solidification occur where freezing begins rather est away from the fed gate and then move towards it.
Alloys with large freezing ranges
Create shrinkage pores as they have a period of time when the material is in a slushy condition.
Pattern makers contraction
Casting will contact further as it cools to room temperature after solidification.
Hot tears
If the mold provides contraint during the time of contraction, cracking can occur.
Risers must
Solidify after casting
Riders should
Be designed to conserve metal
Yield
Casting weight divided by the goal weight of the metal poured, it is clear that there is a motivation to make the risers as small as possible, yet still able to perform their task.
Top riser
Sits on top of a casting. Have a shorter feeding distance, and occupy less space within the flask.
Side risers
Located adjacent to the mold cavity and displaced horizontally along the partying line.
Blind riser
If the riser is contained entirely within the mold. Blind riser is this
Open riser
Open to the atmosphere. Top riser is this.
Live risers
Receive the last hot metal that enters the mold and generally do so at the time when the metal I. The cavity has already begun to cook and solidify.
Dead risers
Fill with metal that had already flowed through the mold cavity.
Top risers are
Dead risers
Risers apart of gating system are
Live risers
Expendable mold processes
A new mold must be created for each casting
Reusable mold
A permanent mold, can be used again.
Pattern
A physical prepresentstion of the object to cast, modified dimensionally to reflect the casting process and the material being cast.
Allowances
Modifications incorporated into a pattern. Most important is the shrinkage allowance
To produce the desired final dimensions
The pattern must be slight larger than the room temperature casting.
Draft
Incorporated at all pattern surfaces that are parallel to the direction of withdraw to prevent damage to the mold.
Machining allowance or finish allowance
Added when smooth machines surfaces are required
Distortion
An additional allowance. Depends greatly on the configuration of the casting.
If a casting is to be made in a multitude metal mold
All pattern allowances should be incorporated into the machines cavity.
Core allowances
All allowances to the casting should be applied to the cores that create holes and interior passages.
