ME 366 Exam One
Advantages of Thread Rolling
(over machining) - Stronger threads and better fatigue resistance, higher production rates, better material usage
Types of Face Milling
Conventional face milling, partial face milling, end milling, profile milling, pocket milling and contour milling
Springback
When the bending pressure is removed, least energy remains in the bent part, causing it to recover partially toward its original shape
Reinforcing Ribs
Achieves increase stiffness without excessive wall thickness. These should be made thinner than the walls they reinforce to minimize sink marks on the outside
Sheet Metal Products
Airplanes, Furniture, Farm Equipment, Automotive, Appliance Housings, Containers/Cans
Examples of Abrasive Materials
Aluminum Oxide, Silicon Carbide, Cubic Boron Nitride, Diamon
Serrated Chip
Associated with difficult to machine metals at high cutting speeds. Cyclical chip forms with alternating high shear strain then low shear strain. Has a semi-continuos saw tooth appearance.
Ring Rolled Products
Ball and roller bearing races, steel tires for railcars, rings for pipes, pressure vessels, and rotating machinery.
Thermoformed Products
Bathtubs, contoured sky lights, internal door liners for refrigerators
Advantages of Cold Working
Better accuracy and part tolerance, better surface finish, strain hardening increases, no heating of work required
Sheet Metal Drawn Products
Beverage Cans, Ammunition shells, automotive body panels
Abrasive Cutting Advantages
Can be used on all types of materials, can produce fine surface finishes, can hold dimensions to extremely close tolerances
Extrusion
Compression process in which material is forced to flow through a die orifice to provide long continuous product whose cross section shape is determined by the shape of the orifice
Injection Unit
Consists of a barrel fed from one end by a hopper containing a supply of plastic pellets
Drilling
Creation of a round hole usually by means of a rotating too with two cutting edges
Three Dimensions of Machining Process
Cutting Speed (v - primary motion) Feed (f - secondary motion) Depth of Cut (d- penetration of tool below the original work surface)
Face Milling
Cutting tool moves across a piece perpendicular to the surface
Peripheral Milling
Cutting tool moves across piece parallel to the surface
Starting Form of Bulk Deformation
Cylindrical bars and billets. Rectangular billets and slabs
Impression Die Forging
Die contains cavity or impression that is imparted to work part. Metal flow is constrained so flash is created (good)
Advantages of Machining
Variety of work materials can be machine, most frequently metals. Variety of part shapes and special geometric features are possible. Good dimensional accuracy and surface finish.
Disadvantages of Machining
Wasteful of material, generating chips. Time consuming to shape a part
Open Die Forging
Work is compressed between two flat dies, allowing metal to flow laterally with minimum constraint
Shape Rolling
Work is deformed into contoured cross section rather than flat (rectangular)
Disadvantages of Warm Working
Work piece must be heated
Flashless Forging
Workpart is completely constrained in die with no excess
Edge- Bending
High Production, Pressure pad is required, dies are more complicated and costly.
Abrasive Materials
High hardness, wear resistance, high toughness, good friability (capacity to fracture when cutting edge dulls, to expose a new sharp edge)
Disadvantages of Cold Working
Higher forces required, surfaces starting must be free of scale and dirt, ductility and strain hardening limit the amount of forming that can be done
Advantages of Impression Die Forging
Higher production rates, less waste of metal, greater strength, favorable grain orientation in the metal (over machining)
Mill Turn Centers
Highly automated machine tool that can perform turning, milling and drilling operations in one setup
Clamping Unit
Hold the two halves of a mold in proper alignment with each other. Keeps mold closed during injection by applying a clamping force sufficient to resist injection force. Opens and closes mold at the appropriate times in the molding cycle
Abrasive Cutting
Material removal by the action of hard, abrasive particles usually in the form of a bonded wheel
Machining
Material removal process in which a sharp cutting tool is used to mechanically cut away material so that the desire part geometry remains.
Grinding
Material removal process in which abrasive particles are contained in a bonded grinding wheel that operates at very high surface speeds
Flashing
Melt is squeezed into parting surface between mold halves
Steps of Casting
Melt the metal, pour it into a mold, let it solidify
Corner Radii
Sharp corners, both internal and external, are undesirable. They interrupt the smooth flow of material which tends to create surface defects. Also cause stress concentrations
Punching
Sheet metal cutting to cut a piece of scrap(slug) out of a work.
Blanking
Sheet metal cutting to separate piece (called a blank) from surrounding stock
Sheet Metal Drawing
Sheet metal is formed to make cup shaped, box shaped, or other complex curved hollow shaped parts. The sheet metal blank is positioned over die cavity and then punch pushed metal into opening. length > diameter (deep drawing)
Stretch Forming
Sheet metal is stretched and simultaneously bent to achieve shape change
Draft Angle
A molded or casted part should be designed with a draft on its side to facilitate removal from the mold. This is especially important on the inside wall of a cup shaped part (plastic contracts)
Compression Molding
A molding process used for thermosetting plastics, rubber tires, and polymer matrix composite parts. (Amount of charge must be precisely controlled)
Sheet Metal Cutting
A punch pushed into the work causing plastic deformation. The punch penetrates into the work causing a smooth cut surface. Fracture is initiated at opposing cutting edges to separate the sheet
Investment Casting
- A pattern made of wax is coated with a refractory material to make the mold. The wax is then melted and poured away and replaced with molten metal. - It is a precision casting process capable of producing castings of high accuracy and intricate detail
Solidification of Pure Metals
- A pure metal solidifies at a constant temperature equal to its freezing points (same as melting point). - A think skin of solid metal is formed as the interface immediately after pouring, eventually forming a shell - Rate of freezing is dependent on the heat transfer of the mold and thermal properties of the metal
Directional Solidification
- Control which sections solidify first in order to minimize shrinkage defects. - Desirable for regions most distant from the liquid metal supply to freeze first and the solidification process to progress towards the riser. - Place sections with lower V/A rations away from the riser
Injection Molding Machine
- Injection Unit: melts and delivers polymer melt - Clamping Unit: Opens and closes mold each injection cycle
Solidification of Alloys
- Most alloys freeze over a range of temperatures
Permanent Mold Casting
- Reusable metal molds constructed of two sections designed for easy opening and closing - Molds are used for casting lower melting point allows are usually made of steel - Good dimensional control and surface finish - Rapid solidification caused by metal molds results in finer grain structure - stronger - High cost of mold
Thickness of Sheet Metal
0.4-6mm
Blow Molding Steps
1. Fabrication of the starting tube (parison) 2. Inflation of the tube to the desire final shape
Mask Manufacturing Flow
1. Plastic Pellets 2. Slit Die Extrusion (Sheet) 3. Thermoforming (Shape) 4. Trim (Cut off Excess) 5. Resulting Product
Draft Angle for Thermosets
1/2 - 1
Draft Angle for Thermoplastics
1/8 - 1/2
Draft Angle for Permanent Casting
2-3
Milling
Cutting of a plane or straight surface with a rotating multiple- cutting edge tool
Cope
Upper half of the mold in sand casting
Thread Rolling
Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies
High Cutting Temperature
Causes reduction of tool life, produces to chips that pose safety hazard to the machine operator, and can cause inaccuracies in part dimensions due to thermal expansion of work material
Gating System
Channels through which molten metals flows into the cavity (consists of downsprue and runner) in sand casting
Bulk Deformation
Characterized by significant deformations and massive shape changes
Hot Working
Deformation at temperatures above the recrystallization temperature (~0.5 melting temperature
Ring Rolling
Deformation process in which a thick walled ring of smaller diameter is rolled into a thing walled ring of larger diameter
Forging
Deformation process in which work is compressed between two dies (oldens of metal forming operations
Rolling
Deformation process in which work thickness is reduced by compressive forces exerted on two opposing rolls
Wire and Bar Drawing
Diameter of wire or bar is reduced by pulling it through a die opening
Down Milling
Direction of the cutter motion is the same as feed motion Chip thickness starts high and decreases
Up Milling
Direction of the motion of cutter teeth is opposite of the feed direction as the tool enters the work Chip thickness starts low and increases
Types of Machining Chips
Discontinuous Chips, Continuous Chip, Continuous Chip with BUE, Serrated Chip
Cutting Clearance
Distance between punch cutting edge and die cutting edge
Blind Hole
Drill does not exit the opposite side of the work
Through Hole
Drill exits the opposite side of the work
Witness Marks of IM
Ejection Pin Marks, Flash, Gate Locations
Forged Products
Engine crankshafts, connecting rods, gears, aircraft structural components, jet engine turbines
Turning Operations
Facing, Taper, Contour, Form, Chamfering, Cutoff, Threading, Boring, and Drilling
Mitigation to Shrinkage in IM
Fillers in plastic tend to reduce CTE Injection Pressure - high pressures force more material into the mold cavity Compaction time - longer time under pressure forces more material into cavity Molding temperature - higher temperature lower polymer melt viscosity, allowing more material to be packed into the mold
Thermoforming
Flat thermoplastic sheet or film is heated and deformed into a desired shape using a mold.
Upsetting and Heading
Forging process used to form heads on nails, bolts, and similar hardware products
Forming Shapes
Form turning, drilling and broaching
Modes of Tool Failure
Fracture Failure: cutting force becomes excessive and/or dynamic, leading to brittle fracture Temperature Failure: Cutting temperature is too high for the tool material Gradual Wear: Gradual wearing of the cutting tool (Preferred)
Barreling Effect
Friction between work and die surface constrains the lateral flow of work
Machining Factors
Generating - the part geometry determined by the feed trajectory of the cutting tool Forming - the part geometry is created by the shape of the cutting tool
Shape Rolled Products
I Beams, L Beams, U Channels, Railroad tracks, round and square bars
Injection Unit Barrel
Inside is a screw that rotates for mixing and heating a polymer. Acts as a ram to inject molten plastic into mold
Chills
Internal or external heat sinks that cause rapid freezing in certain regions of the casting
Weld Line/ Cold Shut
Lack of fusion where two portion of material flow together
Grit Size
Large grit size (~8): better for softer work pieces Small Grit (~250): better for harder work pieces
V- Bending
Low production, performed on a press brake, dies are simple and inexpensive
Disadvantages of Hot Working
Lower dimensional accuracy, higher energy required, surface reactions, shorter tool life
Advantages of Warm Working
Lower forces than cold working, more intricate geometries possible than cold working, need for post work annealing may be eliminated
Drag
Lower half of the mold in sand casting
Examples of Metal Casted Parts
Machine Frames, Dental Implants, Engine blocks, Pips, Bells, Statues, Jewelry, etc.
Pouring Cup
Minimizes splash and turbulence in sand casting
Centrifugal Casting
Mold is rotated at high speeds so the centrifugal forces distributes molten metal to outer regions of die cavity Ex: Pipes, Tubes, Bushings, Rings, etc - Internal shape should be perfectly round
Plastic Product Forms
Molded Parts, Extruded sections, films, sheets, insulation coating on electrical wires, fibers for textiles
Blow Molding
Molding process in which air pressure is sued to inflate soft plastic into a mold cavity. Important for making one piece hollow plastic parts such as bottles
Shrinkage During Solidification
Most metals increase density upon solidification and cooling and because of this a cavity may form near the center of the casting.
Disadvantages of Die Forging
Not capable of close tolerances and matching is often require to achieve accuracies and features needed
Primary Forms of Casting
Open Mold and Closed Mold
Flask
Outer container in sand casting
Warm Working
Performed above room temperature but below recrystallization temperature. ~0.3 of the melting temperature
Cold Working
Performed at room temperature or slightly above. Minimum or no machining is usually required.
Boring
Performed on the inside diameter of the existing whole (internal turning operation)
Injection Molding
Polymer is heated to a highly plastic state and is forced to flow under high pressure into a old cavity where it solidifies and the molding is then removed from the cavity.
Wire Coating
Polymer melt is applied to a bare wire as it is being pulled at a high speed through a die. A slight vacuum is drawn between the wire and the polymer to promote adhesion of coating
Advantages of Hot Working
Potential for substantial plastic deformation at low forces (n=0). Ductility is significantly increased (less chance of fracture). Isotropic material properties.
Casting of Metals
Process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity
Water Jet Cutting
Process that uses high pressure, high velocity stream of water directed at work surface for cutting; not suitable for brittle materials
Continuous Chip
Produced at high cutting speeds, small feeds and depths, and a sharp cutting edge. Low tool - chip friction. This is produces a good surface finish and normally happens with ductile materials
Discontinuous Chip
Produced from low cutting speeds, large feed and depth of cut, high tool - chip friction. Causes irregular surface and usually happens on brittle work materials
Continuous Chip with BUE
Produces at low to medium cutting speeds. The tool- chip friction causes portions of the chip to adhere to the rake face. This usually happens on ductile materials
High Shear Plane Angle
Produces lower shear forces, power, and temperature when machining
Slit Die Extrusion
Production of sheet and film by convention extrusion using a narrow slit as the die opening
Shearing
Separate large pieces of sheet metal
Drilling Operations
Reaming, taping, counterboring, countersinking, center drilling, spot facing
Bulk
Refers to work parts with relatively low surface area to volume rations
Roughing
Removal of large amounts of material from starting work part. Some material remains for finish cutting. This is done at high feeds and depths and low speeds
Finishing
Removal of material to complete a part's geometry. Final dimensions, tolerances and a finish can be done by this process. Low feeds and depths, and high cutting speeds
Riser
Reservoir in the mold to compensate for shrinkage during solidification (just be designed to freeze last) in sand casting
Parting Container
Separates the two halves in sand casting
Flat Rolling
Rotating rolls pull the workpiece into the gap and squeeze the workpiece to reduce its cross section
Turning
Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape
Type of Peripheral Milling
Slab milling, slotting, side milling, straddle milling, and form milling
Cold Shot
Solid particles due to incomplete melting or slag during contamination during pouring/injection
Extrusion Shapes
Solid, Hollow or patterned cross sections can be formed (Regular and Irregular)
Short Shot
Solidification occurs before the mold cavity fills completely
Generating Shapes
Straight Turning, Taper Turning, Contour Turning, Plain milling, profile milling
Sheet Metal Bending
Straining metal around a straight axis to take a permanent bend. Metal on the inside of the neutral plane is compressed, while metal on the outside of the neutral plane is stretched
Solidification Time
The total time required for a casting (or section of casting) to solidify after pouring. Dependent on size and shape of the casting and is based on Chvorinov's Rule.
Wall Thickness
Thick cross sections are wasteful of material, more likely to cause warping due to shrinkage and take longer to harder
Plate Stock
Thickness greater than 6mm
Forming and Generating Shapes
Thread cutting, slot milling
Multiple Cutting Edge Tools
Tool with more than one cutting edge, motion is relative to work achieved by rotating the tool. Drilling and milling use this type of tool.
Single Point Tools
Tool with one dominant cutting edge, point is usually rounded to form a nose radius, and is used primarily in turnings
Extrusion Products
Tubing, Pipes, Hoses, Structural Shapes, Sheet and Film, Continuous filaments , and coated electrical wire
Rolling Mill Configurations
Two High, Three High, Four High
Thermoplastics
Type of plastic in which the chemical structure remains unchanged during heating and shaping. Comprising more than 70% of total plastics
Thermosets
Type of plastic that undergoes a curing process during heating and shaping causing permanent changed in molecular structure
Core
Used to define internal feature if appropriate in sand casting
Grinding Wheel Shapes
straight, recessed two sides, metal wheel frame with abrasive bonded to the outside circumference abrasive cut off wheel
Draft Angle for Expendable Casting
~1