Machining: Family of Material Removal Processes

Material is removed from a starting work part to create a desired geometry

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Principle of the process

Structure/Configuration

Process modeling

Defects

Design For Manufacturing (DFM)

Process variation

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Machining Process - Concept

Material In Removal of chips Material Out

- Not any type of materials could be cut: ceramic not

- There is a family of machining processes: abrasive, etc

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Various types of machining processes

Turning Drilling

Peripheral milling

Face milling

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What function and quality level can machining processes achieve?

- Dimension accuracy: 0.025 mm

- Surface quality: 0.4 µm

- Any shape

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What are generic features with any machining operations to make cutting processes work?

- Two motions: tool motion and work motion

- Primary speed and secondary speed (or feed (rate)

- Relative motion between the two motions generates mechanics to form chips and remove them

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Cutting Tools Cutting Mechanisms

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Cutting Tools Major cutting parameters

Material Removal Rate

MRR = (v)(f)(d)

Module 6 9

Principle of the process

Structure/Configuration

Process modeling

Defects

Design For Manufacturing (DFM)

Process variation

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Engineering Analysis

- Machine equipment to do material removal process: Chip formation, energy, and power

- Tool life: tool failure causes quality problem

- Productivity

- Quality assurance

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Theory of chip formation

Ls

tc

to

- Chip thickness ratio, r = to/tc (tc > to)

- MRR = (v)(to)()(w)

Orthogonal Cutting Model –converts 3d to 2d

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Theory of chip formation

MRRPPergySpecificEnorUnitPower

EPPngPowerGrossCuttiVFPerCuttingPow

CU

Cg

CC

/:)(

/::

E- Efficiency that accounts for loss of the machine tool

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Tool life

-Fracture failure: force becomes excessive, causing sudden brittle fracture

- Temperature failure: temperature is too high, causing the material at the tool point to soften

- Gradual wear: (1) crater wear (2) flank wear

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- The objective of selecting tools should ensure that only the gradual wear mode will occur

- Tool design: materials and geometry

- Except for tool design parameters (system parameters), tool life is a function of operating parameters

(d) (f) (v)Cooling methods ( fluids)

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Productivity is also called removal rate which is computed by the following equation:

(d) (f) (v)

Example:- Rough cutting (f: 0.4-1.25mm/rev; d=2.5-20mm)- Finish cutting (f: 0.125-0.4mm/rev; d=0.75-2.0mm)

Productivity

Quality System parameters

Operating parameters

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Summary

System parameters Operating parameters

Tool

Material

(d) (f) (v) -> Power

Cooling methods

Goal: Select operating parameters to ensure no failure with the whole system and satisfactory quality

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Principle of the process

Structure/Configuration

Process modeling

Defects

Design For Manufacturing (DFM)

Process variation

Design Considerations in Machining Design parts that require little, and if possible, no machining

• Use net shape or near net shape processes Specify tolerances

• Use tighter tolerances only where required Specify surface finish

• Use better surface finishes where required Avoid machining sharp features (i.e. internal corners) where

possible• Require sharp cutting tools that can break more easily

Avoid deep holes that must be bored• Difficult to maintain tool stiffness

Provide seats for drilling Design part so standard cutting tools can access easily

Design Considerations in Machining Design with materials that have good machinability Design part features that used standard cutting tools

• Avoid unusual hole sizes, threads, angles, and shapes requiring special form tools or special contouring

Design part with simpler geometries• Minimize or avoid angles and contours where possible

Design parts to have as few setups, one if possible• I.E. changing position of part and changing cutting tool

Design Considerations in Machining Design machined part sizes that are close to standard available stock

sizes• Less material to cut

Design machined parts to be rigid enough to withstand cutting forces and clamping• Avoid thin and narrow parts

Avoid undercuts as they require additional setups and special tooling

Summary:

1.Machining is a material removal process by cutting tools on work material (stock).

2.For machining, one need to select tools and operation parameters (v, f, d).

3.The selection criteria: tool life, quality.

4.The productivity is the multiplication of v, f, d.

5.Operating principle: chip formation with two important angles (rake angle, and frank angle).

6.DFM rules