Mechatronics

Module 1

Topics

• Fundamentals of machining• Method to increase accuracy and

productivity• Special Tool Holders

Fundamentals of machining

• Machining is the manufacturing process in which the size, shape or surface properties of a part are changed by removing excess materiel.

• High Accuracy and good surface finish are required.

Basic machine Tool

• Lathe or turning machine• Drilling or boring machine• Milling machine• Shaper or planer • Grinder

Material Removal

• Chemical – Electro Chemical machining(ECM)• Electrical – electrical discharge machining

(EDM)• Thermal – laser beam machining.

Metal removal rate

• Cutting speed• Size of cut– Feed– depth

Cutting Speed (v)

• Cutting speed defined as the relative velocity between cutting tool and work materiel.

• Unit- feet per minute , meters per minute• NC- Spindle speed (angular velocity of work

piece , rev/min)• Spindle speed N= 12v/∏D• D average diameter in inches

Depth of cut (d)

• Defined as the distance the cutting tool projects below the original surface of the work

• Expressed in thousandths in an inch or in millimeter

Feed (f)

• Defined as the relative lateral movement between tool and work piece during the machine operation.

• Inches per revolution , mm per revolution• Milling operation- length units per tooth –

inches per tooth, mm per tooth• NC machine- length per minute- feed rate.• Feed rate – feed X spindle speed

Metal removal rate

• The product of proper speed feed, and depth of cut determines the metal removal rate(MPR)

• Volume – units per minute.• Productivity of the machine during cutting is

proportional to MPR

Methods of Improving Machine Accuracy

• Tool Deflection & Chatter• Lead screws• Thermal Deformations

Tool Deflection & Chatter

• The force of the tool edge against the work piece in milling & turning deflects the tool and tool holder and causes dimensional error.

• This error can be removed by increasing stiffness of the construction of tool mounting

• Chatter -Vibratory response due to tool deflection

• If cutting tool deflects at one more than average, and as result a lump is left on the workpiece at the point .

• Chatter occurs as a function Of the machine structure, too, workpiece material, and cutting condition.

Lead screws

• In accuracies due to mechanical linkage between leadscrew and the tool.

• In order to improve the accuracy , this mechanism must be time in varient ( no heating effect) and linear ( no backlash and friction)

Thermal deformation

• Sources of heat– Marching process– Spindle and driving motors– Friction of slideways & lead screws

• A temp difference of 1˚C along 1000 mm can cause an error of 0.01 mm

• Machine tool manufacture must take the thermal effects into considerations in design stage of the machine.

• It can avoid by removing hi-power motor, providing large heat removing surface, use of low friction bearings,symmetrical distribution of heat sources.

• Heat effect can not completely removed• Precise machining are always located in an air-

conditioned environment or separate room