FORCES IN MACHINING PREPARED BY SOUNDHAR.A

In the process of workpiece machining, as the depth of cut and the cutting speed increase, cutting forces rise and so does the temperature of the tool and the power consumed by the machining process. This demo outlines these aspects of orthogonal cutting. It also explores the influence of machining mechanics on tool selection and machine sizing. Voice Over: In the process of workpiece machining, as the depth of cut and the cutting speed increase, cutting forces rise and so does the temperature of the tool and the power consumed by the machining process. This demo outlines these aspects of orthogonal cutting. It also explores the influence of machining mechanics on tool selection and machine sizing. Click start. 2

Piispanen’s Card Model Voice Over: The machining mechanics process is best described by the Piispanen’s Card Model. This model includes four important items of the machining process: Workpiece Tool Chip Shear Plane Visual Guidelines: Fade in the labels in sync with the narration. Note to the designer: Please improve the visuals graphically. 3

Variables in Orthogonal Cutting Voice Over: The major variables in Orthogonal Cutting include: Undeformed chip thickness – which is the uncut chip indicated by t-zero Deformed chip thickness – which is the thickness of the chip formed represented by tc Rake angle – which is the angle made by the tool with the shear plane. This is represented by alpha in the image shown. Shear angle – which represented by phie in the image shown Cutting speed – which is the speed of the tool Visual Guidelines: Animate the tool cutting the workpiece. Stop at a point as shown above. Fade in the respective labels in sync with their narration descriptions. Note to the designer: Please improve the visuals graphically. 4

Kinematics of Orthogonal Cutting Voice over: Kinematics of orthogonal cutting are given by the equations for: Cutting ratio Shear strain in chip Shear strain rate and Relation between shear velocity, chip velocity and cutting speed Visual Guidelines: Fade in the respective equation in sync with their narration descriptions. Note to the designer: Please improve the visuals graphically. The velocity triangle should be shown imaginatively. 5

Forces in Orthogonal Cutting Voice Over: While machining forces acting on the workpiece and tool include: Thrust force, f-t and cutting force f-c that act along the workpiece axis and are perpendicular to the workpiece axis respectively. The normal force and the friction force represented by N and F respectively The resultant force R which drives the tool The resultant shear force opposing the movement of the tool determined by the normal force on shear plane given by N-s and shear force given by F-s. Going by the trigonometric rules, the shear plane forces are given by: And the tool chip interface resultant forces are given by: Visual Description: In sync with the first four narrations animate their respective lines on the diagram with labels along with the codes given on the right side of the slide above. In sync with the 5th narration fade in the equation on the bottom left of the screen. In sync with the 6th narration fade in the equation on the bottom right of the screen. Then move to the next slide. 6

Forces in Orthogonal Cutting Voice Over: These forces are related to material properties. For example, the shear plane stresses are given by: The cutting forces thus must cause the workpiece-material to fail along the shear plane for chip formation. Visual Description: Fade out the equations on the right & fade in the above equations. 7

Merchant’s Force Circle Voice Over: The forces in orthogonal cutting are best represented by the Merchant’s Force Circle. Visual Guidelines: Animate the force circle as a 3D wedge. 8

Energy Dissipation in Cutting Voice Over: Energy dissipation in cutting is along the tool and workpiece interface and along the shear plane. The specific cutting energy is given by: The specific friction energy is given by: The specific shear energy is given by: The heat due to shear deformation should approximately be equal to the sum of the friction heat and the heat due to secondary plastic deformation. This implies that the cutting power P-c should approximately be equal to the sum of shear zone power P-s and the friction zone power P-f. Visual Guidelines: Fade in the bold lines & their respective labels. Fade in the equation. Fade in the 1st equation on the left bottom of the screen. Fade in the 2nd equation on the left bottom of the screen. Before this also fade in the word ‘OR’. Then move to the next slide. 9

Energy Dissipation in Cutting Cutting Power: Shear Zone Power: Friction Zone Power: Voice Over: The cutting power is thus given by:…..Typically, if a perfectly sharp tool is used - 40 to 30 percentage of the energy is consumed at the tool – chip interface The shear plane is given by:….Considering the case of a perfectly sharp tool, 60 to 70 percentage of energy in metal cutting is consumed in the shear zone. And the friction zone power would be: Momentum and surface creation energies are negligible. Visual Guidelines: From the previous slide fade out the equations on the left & fade in the new equation one by one in sync with the narration as shown above. 10

Heat transfer to environment is negligible Cutting Temperatures Voice Over: The energy dissipated in cutting is converted into heat in shear zone, heat in tool chip interface and heat lost to the environment. However, heat transfer to environment is negligible. Visual Guidelines: Fade in the arrow and their respective labels in sync with the narration. Fade in the text below the image. Heat transfer to environment is negligible 11

Single-point Multi-point Identify the type of cutting process for each of the following: Shaping Single-point Multi-point Neither Planning Turning Boring Milling Drilling Grinding Honing Feedback when all options are selected correctly: That’s correct. Single point cutting processes include shaping, planning, turning and boring. Multi point cutting processes include milling & drilling. Feedback when any other of the option selected is wrong: Incorrect. Visual Guidelines: Please jumble the options in a zig-zag manner. 12

Machining grey cast iron produces continuous chips with BUE continuous chips without BUE discontinuous chips of irregular shape and size discontinuous chips of regular shape and size Feedback when option 3 is selected: That’s correct. In machining grey cast iron discontinuous chips of irregular shape and size are produced. Feedback when any other option is selected: Incorrect. 13

A low rake angle is desirable because it reduces the power consumed not desirable because it weakens the tool desirable because it reduces BUE not desirable at all Feedback when options 1, 2 & 3 are selected: That’s correct. A low rake angle is desirable because it reduces the power consumption and Built-Up-Edge at the cost of reducing the tool life. Feedback when options 1 or 2 or 3 or any two of them are selected are selected: Partially correct. Feedback when option 4 is selected: Incorrect. 14

The thickness of the chip is independent of cutting speed depth of cut tool material rake angle Feedback when option 2 is selected: That’s correct. The thickness of the chip is independent of depth of cut. Feedback when any other option is selected: Incorrect. 15

The cutting forces affect the power required the design of the machine tool the accuracy of the machined workpiece depends on the process parameters Feedback when options 1, 2 & 3 are selected: That’s correct. The cutting forces affect the power required, the design of the machine tool and the accuracy of the machined workpiece. Feedback when options 1 or 2 or 3 or any two of them are selected are selected: Partially correct. Feedback when option 4 is selected: Incorrect. 16