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