me122

machining fact, cutting temperature

98% of the energy consumed in machining is converted into heat, up to 1100 degrees F

what is shearing in sheet metal forming?

A process that involves cutting sheet metal plates, bars, tubes through the use of a punch and a die.

What material is particularly good for manufacturing complex parts through extrusion?

Aluminum. (can be manufactured to make complex parts with multiple features) can help reduce costs through easier assembly and lower number of parts.

What is blanking? What is fine blanking?

Blanking is shearing sheet metal with a punch or die. Fine blanking is the same process but done in a compressive environment.

What are sheet metal forming processes? examples?

Bulk deformation: heavy machinery applies stresses in 3 dimensions to change workpiece. (ex. bending of a rod) sheet-metal forming: 2 dimensional stresses applied, lower force than bulk forming needed. (ex. bending of sheet) tube bending could be either, depending on wall thickness and tube diameter

What are the different kinds of die in sheet metal forming?

Compound die: Piercing and blanking occur sequentially in a single stroke of the ram. Higher productivity but more expensive. Progressive die: Two different dies are mounted on a ram. Sheet is fed into first die, where a hole is pierced. It is then fed into the second die where blanking occurs.

What are the three major categories of material removing processes?

Conventional Machining Abrasive Processes Nontraditional Machining

What are cutting conditions/parameters to consider in machining?

Cutting speed feed rate (lateral movement of tool) depth of cut

What are the two main types of extrusion, and explain? Explain other extrusion types as well.

Direct: process in which the die head is held stationary, and the material is forced through it by a moving ram Indirect: process in which the material is held stationary, and the die assembly moves against the material, creating pressure needed for material to flow through die hydrostatic extrusion: process in which the chamber is filled with fluid, and the pressure is transmitted to the billet by a ram. good because there is no friction to overcome along container walls. lateral: process in which extruded part exits perpendicular to the punch impact: punch impacts workpiece rather than apply pressure to it. operation done at higher speed and shorter stroke than conventional extrusion. process usually done cold, permits thin sections and high production rates. hot extrusion: process used for metals and alloys that do not have sufficient ductility at room temperature. also used in order to reduce force needed. good lubrication needed. usually done at 50-75% of material's melting T.

What are general design recommendations for extrusion?

limit irregular shapes, sharp corners, thin webs in the middle avoid thin wall sections

What is LDR or limited drawing ratio?

maximum ratio of blank diameter to punch diameter that can be drawn without failure.

Difference between metal sheet and plate?

metal sheet thicker than .25 in. or 6 mm is generally referred to as plate

What are the design considerations for extrusion?

minimum wall thickness is dependent on the type of alloy for metals, particular shape, and smallest circumscribed-circle diameter (CCD) tolerances: flatness (±.004 per in. of width), straightness (.0125 in. per foot of length), twist (.5 degrees per foot)

machining fact, power and energy

most machines have a 90% efficiency

In bending for sheet metal forming, how to compensate for spring back?

overbending: rotary bending technique that uses a free cylindrical rocker to clamp and bend sheet. There is a small relief angle in lower die to allow for overbending. bottoming coining

What are the different types of milling operations?

peripheral (plain) milling: the axis of the tool is parallel to the surface of the work piece slap milling: cutter extends out on both sides slotting: cutter's width is smaller than workpiece. (if cutter is very thin, it is called saw milling) SIDE AND STRADDLE MILLING side milling: cutter machines the side of the workpiece straddle milling: side milling but on both sides of workpiece FACE MILLING face milling: the axis of the cutter is perpendicular to the workpiece conventional face milling: cutter overhangs the workpiece on both sides partial face milling: cutter overhangs the workpiece only on one side end milling: cutter diameter is less than the workpiece width (slots can be machined) profile milling: cutter machines periphery of the part pocket milling: type of end milling in which cutter machines a shallow pocket into flat parts surface contouring: a ball nose cutter is used to machine 3d surfaces

What are the two basic types of knee-column milling machines?

peripheral milling - horizontal milling machine face milling - vertical milling machine

What is drawing in sheet metal forming?

process used to make cup and box shaped parts and complex hollow parts. sheet metal is placed over a cavity and pushed down by a punch.

What are the different angles in right hand cutting tool? what is the nose radius?

rake angle: controls direction of chip flow relief angle: controls the rubbing at the tool-workpiece interface Nose radius controls the surface finish and tool strength, small radius leads to rougher surface, too large will reduce strength of tool

What are some operations related to drilling on a turning operation in machining?

reaming: used to enlarge a hole or improve surface finish. tapping: threading centering: used to drill a starting hole to obtain accurate hole location counterboring: used to provide a step so the bolt head is flushed with surface countersinking: same as counterboring, except step is cone shaped for flat head screws

Roll force can be reduced by

reducing friction taking smaller reductions increasing the workpiece temperature using rollers of smaller diameters applying tension to the workpiece to reduce compressive yield stress of material

What are some bending operations in sheet metal forming?

roll bending press-brake forming beading roll forming

list of rolling operations

shape rolling ring rolling thread rolling gear rolling roll piercing rolling mills *look up details on ppt.

sheet metal forming fact

shear angle for cutting metals with punch and die: by tilting punch face on angle, the cutting force can be greatly reduced

What are the 3 major categories of sheet-metal forming processes?

shearing, bending, drawing

what is explosive forming in sheet metal forming?

sheet metal is clamped and sealed over a die, vacuum is created in cavity over the die, shockwave produced by explosion above work piece shapes it

What influences drawing in sheet metal forming?

sheet metal mechanical properties sheet metal thickness punch force and speed clearance between die and punch friction between moving parts

What are the various shearing operations?

slotting perforating notching nibbling lancing slitting parting cutoff dinking *read ppt. for more detail

In rolling, sticking occurs at...coefficient of friction in what materials?

sticking occurs at high coefficient of friction, typically occurs with steel, stainless steel, steel alloys

What kind of turning operations are there?

straight turning taper turning profiling turning & external grooving facing face grooving boring drilling threading

force in hot extrusion fact

strain is sensitive to elevated temperature so it is difficult to measure the force accurately. extrusion pressure is also affected by ram speed

defects caused by rolling processes

surface defects: mainly caused by impurities in the metal, rust, dirt, or roll marks. surfaces should be cleaned. structural defects: wavy edges (when edges are thinner than center), zipper cracks (low ductility), edge cracks (low ductility), alligatoring

machining fact, cutting temp.

the effect of feed o temperature is not as strong as cutting speed. cutting speed has the most significant effect on the tool life, but temp., feed rate, cutting depth also influence

Sheet metal fact for shearing

the quality of the sheared edges greatly depends on the clearance. As clearance increases, material tends to be rounded as it is pulled into the die. There is also an increase in burrs along the edges. Typical range of clearance is 2-8% of sheet thickness

What is slitting in sheet metal forming?

(like a can-opener)the lengthwise shearing process that is used to cut coils of sheet metal into several rolls narrower width. Accurate constant width strips can be cut quickly and economically.

What are the different chip formations in machining? Explain.

Discontinuous chip: separate segments are formed when brittle material (cast iron) is machined at low speed. Large feed cutting depth creates high friction between tool and chip causing this type of chip formation. Continuous chip: formed when ductile material is machined at high speed. low friction between tool and chip causes long continuous chips Continuous chip with built up edge: formed when ductile material is machined at low to medium speed. Because of friction, portion of the material adheres to the surface of the cutting tool near the cutting edge. Rough surface is created. Serrated chip: formed when difficult to machine materials such as titanium alloys, stainless steel, nickel-based super alloys are machined at high cutting speed. This is due to alternating high and low shear strains.

machining fact, inserts

High speed and carbon steel cutting tools are made in one piece and either sharpened or discarded when they become dull. To reduce costs, inserts are used. Inserts have many cutting edges and shapes.

relationship between cross sectional area and die angle?

Higher optimum die angle correlates with greater reduction in cross sectional area

In rolling, spreading occurs at small .... to .... ratios.

In rolling, spreading occurs at small width to thickness ratios.

What is the value of the merchant equation in machining? Why is it not valid for actual machining?

It relates the shear angle to rake and friction angle. Not valid for actual machining because it assume shear strength of material remains constant during cutting and isn't affected by temp. or strain rate. larger shear angle results in thinner chips. increasing shear angle lowers cutting force

Difference between low and large die angle? The optimum angle depends on what?

Low die angle: higher friction at the die-billet interface, and requires larger ram force large die angle: leads to more turbulence in the metal flow, and requires larger ram force optimum die angle depends on material, lubricant, and temp.

What is the theory of chip formation?

Orthogonal cutting method: The method uses a wedge-shaped tool with a cutting edge perpendicular to direction of cutting speed. Chip is formed by shear deformation. Shear deformation occurs within a thin shear zone. (There also exists another shear zone between the chip and tool face, called secondary shear zone.) chip ratio is always less than 1. chip compression ratio measures how thick the chip is compared to depth of cut.

What is simple shearing in sheet metal forming?

Process in which a moving blade cuts along a straight line as the moving blade comes down across a fixed blade and shears the metal.

What is conventional machining? And what are it's four major categories?

Process in which a sharp cutting tool is used to mechanically cut the material to obtain desired shape. categories of operations: turning drilling milling other machining

What is abrasive machining process? And what are it's major categories?

Process in which abrasive material is used to mechanically remove material categories of operations: grinding other abrasive processes (lapping, honing, superfinishing)

What is hydroforming in sheet metal forming?

Process in which top die is replaced with rubber diaphragm filled with hydraulic fluid. high pressure needed to form parts. also tube hydroforming (used in cars and unusually shaped tubes)

What are nontraditional processes of material removing?

Process in which, instead of a sharp cutting tool or abrasive particles, various forms of energy are used to remove material. could be mechanical, thermal, electromechanical, or chemical categories of processes: mechanical energy electromechanical chemical thermal

What effect does high temperature have during machining?

Reduces tool life causes dimensional inaccuracy in work piece due to thermal expansion causes thermal damage to machined surface poses safety hazards, hot chips

Materials that can be extruded. Which are most suitable?

Steel, copper, aluminum, magnesium, plastics. Aluminum, copper, plastics are most suitable.

In machining, a knowledge of cutting forces is important because....

a machine tool with a suitable power has to be selected a machine tool has to be properly designed to avoid excess distortion, and eliminate vibrations the work piece must be able to withstand cutting forces without excess distortion.

In sheet metal forming, what is trimming and shaving?

Trimming: cutting away excess material from the perimeter of the part shaving: finishing operation to obtain smooth edges and greater dimensional accuracy

what is "extrusion"

a process in which a material, hot or cold, is pushed or pulled through a die. the material is plastically deformed under the compression in the die cavity

What are the 3 general types of machining? And explain them.

Turning: The material removal is achieved by a sharp cutting tool with single cutting edge. The speed motion is provided by the rotating workpiece and the feed motion is provided by cutting tool moving in a direction parallel to the axis of rotation of workpiece. Only cylindrical shapes can be generated. Drilling: The drilling operatio is used to create round holes. The cutting tool has two edges, it rotates and moves in a direction into the workpiece. Milling: The milling operation uses a rotating tool with multiple cutting edges. The speed motion is provided by the rotating tool and the feed motion is perpendicular to the axis of the rotation. The two types are peripheral and face milling.

What are the two types of peripheral milling?

Up milling (conventional milling): the direction of the linear velocity of the cutter is opposite of the direction of the feed. surface hardness does not affect tool life down milling (climb milling): the direction of the linear velocity of the cutter is the same as direction of the feed. chip length is shorter, tool life is increased, used in CNC machines

What are the disadvantages of machining?

Waste material slower production rate requires more labor adverse effects (surface finish, mechanical properties)

In machining, tool wear affects the quality of the surface finish and the economics of machining. What factors affect tool wear?

Workpiece and tool material machining parameters: cutting speed, feed, depth of cut cutting fluids tool geometry

How to avoid stretcher marks in sheet metal forming?

Yield point elongation is a characteristic of low-carbon steel. it produces stretcher marks or worms. To avoid these, reduce the thickness of the sheet metal by .5-1.5% by coldworking

machining fact, cutting fluids

acts as a coolant and lubricant, can also carry away chips cutting speeds can be tripled when fluid is used water is effective as coolant but causes rust oil prevents rust and provides lubrication but it is less effective as a coolant in practice, a combo of oil/wax and water is used

what are the advantages of cold extrusion over hot extrusion? what are the disadvantages?

advantages: work-hardening improves mechanical properties better surface finish due to lack of oxidization better dimensional accuracy the need for heating and cooling material is not needed similar production costs/rates with other manufacturing processes to create same part disadvantages: due to a high force being needed to extrude, tooling in cold extrusion is more expensive

sheet metal forming involves stretching and bending. certain parameters have a significant influence on the process. what are they?

anisotropy, grain size, residual stress, springback, elongation, wrinkle

machining fact, unit power - cutting speed

at low speed, most of the energy is absorbed by the tool. at high speed, most energy is absorbed by the chip

machining fact, chip breaker

breaks chips 3 kinds: radius positive rake 0 degree rake

What defects can occur in extrusion?

centerburst: internal cracks at the center of the part due to tensile stresses from large deformation in outer region of extruded part. (caused by high die angle, low extrusion ratio, impurities in the metal) piping: occurs in direct extrusion, formation of a sink hole at the end of the billet. (can be reduced by controlling friction and temp. gradient or adding a dummy block at the end of the billet) surface cracking: caused by high temperature, high friction, and/or high extrusion speed. (occurs especially in Aluminium)

without friction, the rolls cannot pull the workpiece into the roll gap. but more friction means more power requirement.

coefficient of friction in cold-working = .05 to .3 coefficient of friction in hot-rolling = .2 to .7

Design considerations when designing for bending?

cold-worked materials have directional properties. bend axis should be perpendicular to direction of cold-work to avoid surface cracks extremely ductile material to bend metal with radius less than thickness bends of 90 degrees or more shouldn't be done without determining if it's possible or not design with large bend radii use same bend radius for parts requiring multiple parts, saves time and expenses

What are the different kinds of spinning in sheet metal forming?

conventional spinning: rotating disk of sheet metal is progressively shaped over a mandrel to produce a rotationally symmetrical shape shear spinning: part is formed over a mandrel through shear deformation. diameter remains the same but thickness decreases. tube spinning: used to reduce wall thickness and increase length of tube

machining fact

cutting tool removes material by shear deformation of the material and forms chips.

Sheet metal shearing fact

deformation occurs as highly localized shear, fracture occurs when shear strength is exceeded

What are design considerations for piercing and blanking in sheet metal forming?

diameter of piercing hole should be thicker than thickness of sheet metal distance between holes should be greater than sheet metal thickness avoid small tolerances arrange pattern of parts to minimize scrap

What are the advantages of machining?

dimensional accuracy geometric features (variety of part shapes and intricate details with sharp corners are possible) variety of surface finishes (smooth, rough) variety of work materials (metals, plastics, composites)

Name some work holding methods in turning machining.

dog plate Jaws collet faceplate

What factors must be considered for the extrusion process?

extrusion ratio: ratio of the cross-sectional area of billet to that of the extruded product circumscribing-circle diameter: the diameter of the smallest circle that the extruded cross section will fit into shape factor: complexity of the extrusion, which is the ratio of the extruded part's perimeter to cross-sectional area speed of the ram lubricant temperature of the billet

what are the types of tool wear in machining?

flank wear: caused by the sliding of the tool along the surface crater wear: caused by the sliding of the tool along the surface, but most important is the tool-chip interface temperature. max crater depth corresponds to location of highest temp. nose wear chipping

machining fact, cutting forces

friction force normal force perpendicular to friction force shear force normal force perpendicular to shear force none of these forces can be directly measured but shear stress and coefficient of friction can be estimated

In rolling, to avoid spreading...

increase width to thickness ratio decrease friction use a pair of vertical rollers to constrain the edges

force in cold extrusion fact

the reality is that the extrusion process is not a frictionless process so the ideal equation grossly underestimates strain and pressure. friction exists between die and workpiece, and between billet and container wall

machining fact, operations on turning

threading boring drilling

What are some problems that can occur in turning operations? What are the probable causes?

tool breakage: lacks toughness and stiffness, wrong tool angles tool wear: improper tool material, wrong tool angle, ineffective cutting fluid rough surface finish: tool too sharp, chipped, or worn. feed too high. vibration/chatter dimensional variability: lack of stiffness in machine tool and work holding device, tool wear tool chatter: lack of stiffness in machine tool and work holding device, excessive tool overhang

talk about cost of extruding material

tooling cost and setup is expensive, but when actual parts are manufactured in significant quantities, cost is inexpensive

machining fact, different mill machines

universal milling machine: workpiece table can rotate in a horizontal plane. makes it easier to cut angular shapes and helixes ram mill: the ram can move in and out and rotate about its own axis. can machine a variety of shapes bed-type milling machine: instead of knee-column design, the work table is mounted directly to the bed of machine tool. provides more rigidity, and permits heavier feed rate and cutting depth. designed for high production

Advantage of extrusion?

wide variety of cross section of the extrusion can be tailor-made for a relatively low cost cost effective because it doesn't require the need for secondary machining

What are defects in drawing in sheet metal forming?

wrinkling in flange/wall earing tearing surface scratches