Faculty of engineering Prod.eng&mech.des.department Mansoura university Faculty of engineering Prod.eng&mech.des.department Cutting forces Prepared By : Ahmed Sameh Adb-Elaziz Ahmed Sami Ahmed Ali Hassan

Introduction The manufacturing processes being developed for this reasons : New materials that are not suitable to traditional machining methods. New approaches to design and manufacture. More complicated designs. Tighter tolerances. Cutting is a balance between a number of factors: Cutting slowly will add costly time to manufacturing operations. Cutting faster will lead to decreased tool life, and extra time will be required to repair tools.

Standard Cutting Tools Hence cutting tools need: strength at elevated temperatures. high toughness . high wear resistance . high hardness. The cutting tools : Standard Cutting Tools

Graphical representation of the cutting process CUTTING THEORY THE MECHANISM OF CUTTING: Orthogonal Cutting Oblique Cutting Graphical representation of the cutting process

Cutting Tool Geometry Terminology Two categories: • Single point tools A cutting tool has one or more sharp cutting edges. The cutting edges serves to separate a chip from the parent work material. A cutting tool must posses a shape that is suited to the machining operation. Terminology Two categories: • Single point tools – Used for turning, boring, shaping, and planning. • Multiple cutting edge tools – Used for drilling, reaming, tapping, milling, broaching, and sawing.

Cutting Tool Forces Orthogonal force and oblique force There are three forces acting on the cutting tool: Tangential Force. Longitudinal Force. Radial Force. Forces in Metal Cutting ( orthogonal force ) : (1) Friction Force (F). (2) Normal Force to Friction (N) . (3) Shear Force (Fs). (4) Normal Force to Shear (Fn).

Forces in Metal Cutting Merchant Equation Thrust Force/Rake Angle

Shear and Normal Force Schematic illustration of the distribution of normal and shear stresses at the tool-chip interface (rake face). Note that, whereas the normal stress increases continuously toward the tip of the tool, the shear stress reaches a maximum and remains at that value (a phenomenon know as sticking; see Section 4.4.1).

Resharpening cutting tools Tool grinding is part science and part art, but can be an enjoyable side activity to working with the lathe. The essence of lathe tool grinding, as I think of it, is to undercut the tip of the tool to provide 'relief' so that the metal just below the cutting tip does not contact the work. This concentrates enough cutting force on the tip to cut into the metal of the work piece. The four sides of the blank are ground to a smooth, shiny finish. The ends are a coarse finish with a preformed angle of about 15 degrees.

Grind the left side relief. Grind the top rake. Round the tip. There are four-steps procedures to make our cutting tool: Grind the end relief . Grind the left side relief. Grind the top rake. Round the tip. Firstly: Grinding the End Relief : First we will grind the end of the tool blank. Use the coarse wheel of your bench grinder and hold the tool blank angled downwards from the tip to the rear and with the tip pointing to the left about 10-15 degrees.

Secondly: Grind the left side relief :- Grinding causes the tool blank to get quite hot so you will need to dip the end of the tool into a water bath every 15 seconds or so during the grinding operation. Here's a picture of the tool after grinding the end. Secondly: Grind the left side relief :- we hold the tool with the side at about a 10 degree angle to the grinding wheel.

Thirdly: Grind the top rake :- Now we grind the top surface to form the rake. Be careful during this operation not to grind down the cutting edge or you will end up with a tool whose tip is below the center line of the lathe. Fourth: Round the tip : We will round the tip to form a tool that is useful for facing and turning. Hold the tool so the tip touches the wheel and with the tool tilted downward. Rotate the tool against the wheel to round the tip to about a 1/32" radius

Here's the finished tool in action making a finishing cut on a facing operation: As a final step, you may wish to smooth the cutting tip on a fine diamond hone or oilstone. I've found that the tip tends to get smoothed pretty quickly after a few cuts, so I usually skip this step, but it does make a difference if you need a fine finish.

Summary: Factors Affecting Machining

Thank you