Ch 17 Theory of metal machining

What are the disadvantages of machining and other material removal processes?

1. Wasteful of material 2. Time consuming

What are the traditional machine tools used to perform 1. Turning 2. Drilling 3. Milling

1. Turning - lathes 2. Drilling - drill presses 3. Milling - milling machines

A lathe is used to perform which one of the following manufacturing operations: 1.Broaching, 2.Drilling, 3.Lapping, 4.Milling, 5.Turning

5. Turning

What are the three basic categories of material removal processes?

1. Conventional machining 2. Abrasive processes 3. Nontraditional machining

Name the three most common machining processes

1. Milling 2. Drilling 3. Turning This belongs to the category of Conventional machining

What are the two most common types of milling?

1. Peripheral milling 2. Face milling

What are the two basic categories of cutting tools in machining?

1. Single-point-tool, used in Turning 2. Multiple-cutting-edge-tool, used in Drilling and Milling

Identify some of the reasons why machining is commercially and technologically important.

1. Variety of work materials 2. Variety of part shapes and geometric features 3. Dimensional accuracy 4. Good surface finish

Define this symbols in machining 1. α 2. 𝛷 3. 𝜸

1. α = rake angle of cutting tool 2. 𝛷 = shear plane angle 3. 𝜸 = shear strain

In using the Orthogonal cutting model to approximate a turning operation, the chip thickness before the cut (to) corresponds to which one ot the following cutting conditions in turning: 1. depth of cut, d 2. feed f 3. speed v

2. feed f

The chip thickness ratio is which one of the following: 1.tc/to, 2.to/tc, 3.f/d, 4.to/w where tc = chip thickness after the cut, to = chip thickness before cut, f = feed, d = depth, w = width of cut

2.to/tc

A roughing operation generally involves which one of the following combinations of cutting conditions: 1. high v, f and d 2. high v, low f and d 3. low v, high f and d 4. low v, f and d where v = cutting speed, f = feed and d = depth

3. low v, high f and d

Define this terms for a turning operation in a orthogonal operation: 1. Feed f 2. Depth d 3. Feed force Ff

In a orthogonal operation 1. Feed f = Chip thickness before cut to 2. Depth d = Width of cut w 3. Feed force Ff = Thrust force Ft

What distinguishes machining from other manufacturing processes?

Material is removed from the work part with a sharp cutting tool so that the remaining material is the desired part geometry. Machining is necessary where tight tolerances on dimensions and finishes are required, because machining is capable of producing precise dimensions. Applied to all material removal processes. Performed after other processes. Unwanted material is removed in the form of chips by hard tools.

Identify these symbols in machining: Pc Fc Pg E Pu/U ∆T K 𝜌C T K and m

Pc = cutting power, N-m/s Fc = cutting force, N Pg = gross power of the machine tool motor, W E = mechanical efficiency of machine tool, typical 90% Pu/U = unit power, P ∆T = temperature rise at tool-chip interface K = thermal diffusivity of the work material 𝜌C = volumetric specific heat of work material T = meauserd tool-chip interface temperature K and m = parameters depend on cutting conditions and work material

Are cutting speed lowest in roughing or finishing?

Roughing

Identify the two forces that can be measured in the Orthogonal metal cutting model.

1. Cutting force Fc 2. Thrust force Ft

What are the parameters of a machining operation that are included within the scope of cutting conditions?

1. Cutting speed v 2. Feed f 3. Depth d

Name and briefly describe the four types of chips that occur in metal cutting.

1. Discontinuous chip: When relatively brittle materials are machined at low cutting speeds, the chip tend to form into separate segments. Large feed and depth of cut. High tool-chip friction. Major disadvantage: Could result in poor surface finish. 2. Continuous chip: When ductile work materials are cut at high speeds and small feeds and depths, long continuous chips are formed. Sharp cutting edge. Low tool-chip friction. Usually considered the ideal condition for efficient cutting action. 3. Continuous chip with built-up edge (BUE): When machining ductile materials at low-to-medium cutting speeds, friction between tool and chip tends to cause portions of the work material to adhere to the rake face of the tool near the cutting edge. 4. Serrated chip: These chips are semi-continuous in the sense that they possess a saw-tooth appearance.

Identify the four forces that act upon the chip in the Orthogonal metal cutting model but cannot be measured directly in an operation.

1. Friction force F 2. Normal force to friction N 3. Shear force Fs 4. Normal force to shear Fn

Which of the following are the characteristics of the orthogonal cutting model (three best answers): 1. A circular cutting edge is used 2. A multiple-cutting.edge tool is used 3. A single-point tool is used 4. Only two dimensions play an active role in this analysis 5. The cutting edge is parallel to the direction of cutting speed 6. The cutting edge is perpendicular to the direction of cutting speed 7. The two elements of tool geometry are rake and relief angle

3. A single-point tool is used 4. Only two dimensions play an active role in this analysis 6. The cutting edge is perpendicular to the direction of cutting speed

Which one of the four types of chip would be expected in a turning operation conducted at low cutting speed on a brittle work material: 1. Continuous 2. Continuous with built-up-edge 3. Discontinuous 4. Serrated

3. Discontinuous

Which of the following manufacturing processes are classified as material removal processes (two correct answers): 1.Casting, 2.Drawing, 3.Extrusion, 4.Forging, 5.Grinding, 6.Machining, 7.Molding, 8.Pressworking, 9.Spinning

5. Grinding 6. Machining

Why are the cutting temperature important?

It is important because high temperatures 1. Reduce tool life 2. Produce hot chips - Not safe for workers 3. Can cause inaccuracies in part dimensions due to thermal expansion of the work material

What is the formula for the material removal rate RMR (mm^3/s).

RMR = v f d

Explain the difference between roughing and finishing operations in machining.

Roughing - Used to remove large amounts of material from the starting work part. Creates shape close to desired geometry, but leave some material for finish cutting. High feeds and depths, low speeds Finishing - Used after roughing to complete the part and achieve the final dimensions, tolerances and surface finish. Low feed and depths, high cutting speeds