Materials

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

As cutting speed increases, tool life decreases. The harder the workpiece is, the lower tool life is

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

As hot hardness increases, so does cost of cutting tool; mainly because of production costs of making material into reliable tool

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

Benefits to mechanical properties of the material, avoid contamination so electroplating can take place

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

Chromium, vanadium, tungsten, cobalt; higher strength and hardness at high temps

What are the consequences if a cutting tool chips?

poor surface finish, less dimensional control, cutting force increases, can be indicative of future failure

What precautions would you take in machining with brittle tool materials, especially ceramics? Explain.

prevent chipping by using negative rake angles prevent tool failure with steady supply of cutting fluids

Explain how different types of chips produced determine overall quality of the cutting operation

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

Briefly describe: what are the four types of chips produced in metal cutting

Continuous chips: formed with ductile materials, machined at high cutting speeds and/or high rake angles. Discontinuous chips: produced by brittle materials, and consist of segments attached firmly or loosely to each other Built-up edge chips (BUE): layers of material of from workpiece gradually deposit on the tool tip Serrated or segmented or non-homogenous chips: semi-continuous chips with large zone of low shear strains and small zones of high shear strain

List the prototyping processes that are best suited for the production of ceramic parts

For direct production of ceramic parts, three-dimensional printing is likely the best option. Fuel-desposition modeling with proper binding

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

Physical - hardness, toughness, thermal conductivity and thermal expansion coefficient Chemical - must be inert to workpiece at certain temp

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

because diamonds and CBN are brittle, interruppted cutting should be avoided tool geometry and setting is important; workpiece must be suitable for diamond or CBN

The cutting force increases with the depth of cut and decreasing rake angle. Explain why.

deeper cuts remove more material, higher force as rake angle decrease, shear angle decreases

What are the effects of performing a cutting operation with a dull tool?

increased top radius, increases cutting force induces residual stresses, tearing, cracking increases BUE formation

Why does temperature have such an important effect on tool life?

materials become weaker and less hard at high temps chemical reactivity increases with temp as does diffusion between workpiece and tool effectiveness of cutting fluids is comprimised at high temp, leading to more tool wear

Explain the consequences of allowing temperatures to rise to high levels in cutting

tool wear accelerated reduces dimensional accuracy induces thermal damage

List and explain the considerations involved in determining whether a cutting tool should be reconditioned, recycled, or discarded after use.

Economic considerations: Reconditioning - requires skilled laborers, grinders, etc Recycling - used to reclaim expensive parts

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

FDM- sand or finish surface to rid of extruded filament, then paint Stereolithography - post-curing, then roughening, then paint

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

Not always, low cutting speeds removes less material, which is economically undesirable Can also lead to BUE an discontinuous chips, poor surface finish

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

Power is a function of force and velocity, there is velocity in the cutting direction but no velocity in the thrust direction

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

Tools are brittle and weak in tension, negative rake angles have lower tendency to cause tensile stress and chipping

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

Yes, high speed machining conveys heat from cutting zone through the chip

Are the locations of maximum temperature and crater wear related? If so, explain why

Yes, higher temperature means higher wear b/c of diffusion(material removed from rake face)

Can rapid-prototyped parts be made of paper?

Yes, laminated-object manufacturing process produces parts from paper or plastic.

How can a mold for sand casting be produced using rapid prototyping techniques

a sand is the powder used and a binder produces the desired shape

Is material ductility important for machinability? Explain

ductility affects type of chip, which affects surface finish, which affects machinability

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

filament outline suggests that the material was produced in FDM, which requires fusing after extrusion, possible with thermoplastics, difficult with thermosets

Which tool-material properties are suitable for interrupted cutting operations? Why?

tools with high impact strength and toughness (high-speed steel and carbides) low thermal expansion and high thermal conductivity are desirable