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27 Cards in this Set

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Briefly describe: what are the four types ofchips produced in metal cutting?

Continuous chips: These are usuallyformed with ductile materials that are machined at high cutting speeds and/orhigh rake angles. Discontinuous chips: They are producedby brittle materials, and consist of segments that may be attached firmly orloosely to each other. (BUE): It iscalled BUE because layers of material of from workpiece gradually deposit onthe tool tip, thereby changing the tool geometry. Serrated chips: They are semi-continuous chips with largezone of low shear strains and small zones of high shear strain. Metals with lowthermal conductivity and strength that decrease sharply with temperatureproduce BUE

. Explain how different types of chips produced determineoverall quality of the cutting operation.

Continuous chips are associated with good surface finish andsteady cutting forces. Discontinuous chips result in poor surface finish andfluctuation of cutting forces. Built-up edge chips (BUE) result in poor surface finish. Serrated chips result in poor surface finish.

What is the relationship between cutting andtool life? What is the relationship between workpiece hardness and tool life?

T is tool life and V is cutting speed. C n VT the harder the workpiece is, the lower tool lifeis

4. How can a mold for sand casting be produced using rapidprototyping techniques?

a sand is the powder used and a binder produces the desiredshape. However, a pattern can be produced using any rapid prototypingtechnique.

List the prototyping processes that are bestsuited for the production of ceramic parts. Explain.

For direct production of ceramic parts, 3D printing is likelythe best option. With the proper binder, this can also be accomplished byfused-deposition modeling, and is also possible by selective laser sintering.However, the ceramic particles will abrade the tooling in FDM and require muchheat to fuse in SLS. The 3D printing approach, where a binder is sprayed ontothe ceramic particles, is the best approach for making green parts, which arethen fired in a furnace to fuse the powder.

6. Can rapid-prototyped parts be made of paper? Explain.

Yes, The laminated-object manufacturing process produced partsfrom paper or plastic.

Careful analysis of a rapid-prototyped partindicates that it is made up of layers with a distinct filament outline visibleon each layer. Is the material a thermoset or a thermoplastic?

The filament outline suggests that the material was producedin fused-deposition modeling. This process requires adjacent layers to fuseafter being extruded. Extrusion and bonding is with thermoplastics

Why are the metal parts in three-dimensionalprinting often infiltrated by another metal?

There are obvious benefits to the mechanical properties.Also, such materials cannot be contaminated, so that finishing operations cantake place if the material is infiltrated.

In making a prototype of a toy automobile, list thepost-rapid-prototyping finishing operations that you think would be necessary.Explain

Depends on the particular rapid-prototyping process used.Consider, fused-deposition modeling: It may be desirable to sand or finish thesurface because of the surface texture that exists from the extruded filament.A base coat and paint then can be applied

10. Are the locations of maximum temperature crater wearrelated?

The most significant factors in crater wear are diffusion andthe degree of chemical affinity between the tool and the chip. Thus, the higherthe temperature, the higher the wear.

11. Is material ductility important for machinability?Explain.

Ductility directly affects the type of chip produced which,affects surface finish, the nature of forces involved (less ductile materialsmay lead to tool chatter), and more ductile materials produce continues chipswhich may not be easy to control.

Tool life can be almost infinite at low cuttingspeeds. Would you then recommend that all machining be done at low speeds?

low cutting speeds remove less material in a given time.Lower cutting speeds also often also lead to the formation of a built-up edgeand discontinuous chips

Explain the consequences of allowingtemperatures to rise to high levels in cutting.

(a) Toolwear will be accelerated (b) dimensional changes in the workpiece reducingdimensional accuracy. (c) Excessively high temperatures in the cutting zone caninduce thermal damage and metallurgical changes to the machined surface

The cutting force increases with the depth of cut anddecreasing rake angle. Explain

Deeper cuts remove more material, thus requiring a highercutting force. As the rake angle, α, decreases, the shear angle, φdecreases and hence shear energy dissipation and cutting forces increase.

What are the consequences if a cutting tool chips?

Tool chipping has various effects, such as poor surfacefinish and dimensional control of the part being machined; possible temperaturerise; and cutting force fluctuations and increases. Chipping is indicative of aharmful condition for the cutting tool material, and often is followed by moreextreme failure.

What are the effects of performing a cuttingoperation with a dull tool? A very sharp tool?

Note that a dull tool has an increased tip radius as the tipradius increases (the tool dulls), the cutting force increases due to the factthat the effective rake angle is decreased. In addition, we can see thatshallow depths of cut may not be possible because the tool may simply ride overthe surface without producing chips. Another effect is inducing surfaceresidual stresses, tearing, and cracking of the machined surface due to theheat generated by the dull tool tip rubbing against this surface. Dull toolsalso increase the tendency for BUE formation

Can high-speed machining be performed without the use of acutting fluid?

Yes. In high speed machining, most of the heat is conveyedfrom the cutting zone through the chip, so the need for a cutting fluid is less

Given your understanding of the basic metal-cutting process,what are the important physical and chemical properties of a cutting tool?

Physically, hardness, toughness, thermalconductivity and thermal expansion coefficient. Chemically, it must be inert tothe work piece material at the cutting temperatures

Explain why the power requirements in cutting depend on thecutting force but not the thrust force.

Power is the time rate of doing work. Work=FD,so power=FV. There is a velocity in the cutting direction, so the product offorce and velocity in the cutting direction leads to a power requirement. Inthe thrust direction, there is no velocity.

Which tool-material properties are suitable for interruptedcutting operations?

it is desirable to have tools with a high impact strength andtoughness. one would prefer to use high-speed steels and carbides ininterrupted cutting operations. also desirable to utilize materials with lowcoefficients of thermal expansion and high thermal conductivity to minimizethermal stresses in the tool which could lead to tool failure.

Make a list of the alloying elements used in high-speedsteels. Explain what their functions are and why they are so effective incutting tools.

chromium, vanadium, tungsten, and cobalt. These elements imparthigher strength and higher hardness at elevated temperatures.

Why does temperature have such an important effect on toollife?

First, higher temperatures will weaken and soften anotherwise ideal material. Second, chemical reactivity typically increases withincreasing temperature, as does diffusion between the work piece and thecutting tool. Third, the effectiveness of cutting fluids is compromised atexcessive temperatures as there is higher friction to overcome. Finally, ininterrupted cutting, there can be excessive thermal shock if the temperaturesare high.

What precautions would you take in machiningwith brittle tool materials, especially ceramics?

we first want to prevent chipping, such as by using negativerake angles and reduce vibration and chatter. Also, brittleness of ceramictools applies to thermal gradients, as well as to strains. To prevent toolfailures due to thermal gradients, a steady supply of cutting fluidshould be applied, and selecting tougher tool materials.

Describe the necessary conditions for optimal utilization ofthe capabilities of diamond and cubic-boron-nitride cutting tools.

Because diamond and cBN are brittle, impact due to factorssuch as cutting-force fluctuations and poor quality of the machine tools usedmust be minimized. Machine tools should have sufficient stiffness to avoidchatter and vibrations. Tool geometry and setting is also important to minimizestresses and possible chipping. The workpiece material must be suitable fordiamond or cBN

Negative rake angles generally are preferred forceramic, diamond, and cubic- boron-nitride tools. Why?

these materials are brittle and relatively weak in tension.negative rake angles are preferred because of the lower tendency to cause tensilestresses and chipping of the tools.

Do you think that there is a relationshipbetween the cost of a cutting tool and its hot hardness? Explain.

as hot hardness increases, the cost of the tool materialincreases.

List and explain the considerations involved in determiningwhether a cutting tool should be reconditioned, recycled, or discarded afteruse.

Reconditioning requires skilled labor, grinders, and possiblyrecoating equipment. Other considerations are the cost of new tools andpossible recycling of tool materials, since many contain expensive materials ofstrategic importance such as tungsten and cobalt.