Presentation on theme: "Fundamentals of Cutting and Cutting-Tool Materials & Cutting Fluids Presented by: Rita Silvernail Tony Cordisco John Congdon Richard Gasbarra."— Presentation transcript:
Fundamentals of Cutting and Cutting-Tool Materials & Cutting Fluids Presented by: Rita Silvernail Tony Cordisco John Congdon Richard Gasbarra
In chapter 20 the Fundamentals of Cutting the processes of cutting are among the most important of the manufacturing operations. They are necessary in order to get a finished part with the proper surface finish and dimensional accuracy. A large number of variables have significant influence on the mechanics of chip formation in cutting operations. Among the important process variables are tool shape and material, cutting conditions such as speed feed, and depth of cut, use of cutting fluids, and the characteristics of the workpiece material. Parameters influenced by these variables forces and power consumption, tool wear, surface finish and integrity, temperature and dimensional accuracy or the part. Machinability of materials depends not only on their intrinsic properties, but also on proper selection and control or the process variables. As we learned in chapter 21, cutting-tool material has been developed over the last 100 years for certain applications in the process of machining parts. The materials have a variety of mechanical and physical characteristics such as hot hardness, toughness,chemical stability,and resistance to wear. They also have developed many coatings to preserve the life of the tool so the selection of the right tool material depends not only on the material to be machined put the process to manufacture the part. Cutting fluids are also used to help preserve the part and the cutting tool,a good lubricant for slower speeds and high speeds a fluid with a cooling capacity. Choice of lubricant should be considered because they may have adverse effects on the part, machinery, personnel, and the environment.
Metal cutting Physics Idealized Chip Formation The figure below depicts an idealized, two dimensional view of the metal cutting process. The assumptions in this model are that the tool is perfectly sharp, that the cut depth t and the cutting speed V are constant, and that the cut depth is small compared to the cut width. In this idealized model, the material layer at the top is formed into a chip by a shearing process in the primary shear zone at AB. The chip slides up the rake face undergoing some secondary plastic flow due to the forces of friction. This idealized model correctly predicts that cutting force increases with cut depth, material hardness, and friction coefficient. Cutting forces are inversely proportional to rake angle. Power required increases with the feed rate. Built Up Edge One important effect that is not considered in the model above is built up edge. Under most cutting conditions, some of the cut material will attach to the cutting point. This tends to cause the cut to be deeper than the tip of the cutting tool and degrades surface finish. Also, periodically the built up edge will break off and remove some of the cutting tool. Thus, tool life is reduced. In general, built up edge can be reduced by Increasing cutting speed Decreasing feed rate Increasing ambient workpiece temperature Increasing rake angle Reducing friction (by applying cutting fluid) Calculating Speeds and Feeds Cutting speed refers to the speed at which the tool point of the cutter moves with respect to the work measured in feet per minute. Feed is the rate at which the work moves into the cutter measured in feed per tooth revolution. Feeds and speeds affect the time to finish a cut, tool life, finish of the machined surface, and power required of the machine The cutting speed is mostly determined by the material to be cut and the material of the tool. To find the right speed for any task, refer to the Machinery's Handbook or other reference. To calculate the proper spindle speed, divide the desired cutting speed by the circumference of the tool (or of the part if it is rotating) expressed in feet. The feed rate depends on the width and depth of cut, finish desired and many other variables. To calculate the desired feed setting from the feed rate, multiply feed per tooth per revolution by number of teeth and rpm of the spindle
Carbide Insert Cutting Tools Many different cutting tools are produced with carbide inserts for added strength and durability. The pictures on the left show various applications. The first slide shows a helical edge face mill. The next is a helical edged extended flute cutter used in a basic milling machine operation This a carbide tipped slot cutting blade used for making slots or grooves.
Diamond coated cutting tools There are many applications used for diamond coating. The coating will give extended life to your tooling. Some examples are diamond coatings for endmills in a variety of sizes.There are diamond tipped inserts available for various cutting applications. Also available are several types of diamond coated drill bits. Diamond coated endmills Diamond coated inserts Diamond coated drill bits
When does an end mill need resharpening When wear land reaches a certain level as a function of diameter and type of end mill (for values see table below). When the chips change to a blue color. When the quality of surface finish on the workpiece decreases When the accuracy is not achieved When large burrs appear on the edge of the workpiece When unusual noise and smoke appear When motor ampermeter level increases Trouble shooting endmill problems Breakage feed to fast slow down speed too high stock removal decrease feed /tooth too long flute length hold shank deeper too much wear resharpen tool Wear speed to fast slow down or use a coolant hard work material use higher grade tool biting chips change feed & speed improper feed&speed increase feed & speed improper cutting angle change to correct cutting angle small relief angle change to large relief angle
Short tool life too much cutting resharpen tool friction tough work material use premium tool Improper cutting angle change to proper cutting angle Rough surface feed to fast slow down to correct speed finish feed to slow speed tool up too much wear resharpen tool chip biting decrease stock removal Chip packing too high stock adjust speed or feed removal rate not enough chip space use less endmill flutes not enough coolant use air pressure Burrs too much wear on resharpen tool primary relief incorrect conditions correct milling conditions improper cutting angle correct cutting angle No dimensional excessive cutting decrease depth & width accuracy of cut lack of accuracy repair machine or holder not enough rigidity change machine, holder or cutting conditions