Living in the "real world", chipmakers are living in the labratory conditions where most ideal cutting parameters are achieved. Real world chipmakers are confronted with necessary changes to their cutting conditions that may involve a machine problem, a cutting tool material problem or can be as simple as a change in the cutting tool geometry.
Understanding the terminology and nomenclature of cutting tools is key to the ability to decide and use specific cutting tool geometry for specific applications. Using the proper geometry for specific applications will greatly aide in both tool life and machining sucess.
To understand cutting tool geometry, one must understand the basic cutting tools ... the single point tool used in turning. The effects the related angles have on a single point tool are also basic to understanding to milling cutters, end mills, drills, taps and most other cutting tools. This blog post outlines the important areas of cutting tool geometry as they relate to the single point turning tool and briefly as they relate to other cutting tools.
Cutting Tool Terminology
Shank
The shank is the main body of the tool. If the tool contains inserted cutters, the shank supports the cutter bit.
Face
The surface against which the chips bear as they are severed.
Nose Radius
This term generally means the rounded tip of the cutting end. This strengthens the cutting edge, improves finish and tool life. Too large a radius increases radial forces and induces chatter. Too small a radius may result in chipping or prevent proper distribution of the heat and thus break down the properties of the cutting tool material.
Chipbreaker
A groove formed in or on the shoulder of the face of the tool for the purpose of breaking up the chip. A chipbreaker of the shoulder type may be formed directly on the tool face or may consist of a separate piece that is held by brazing or clamping.
Rake
A tool is said to have rake when the tool face or surface against which the chips bear as they are severed is inclined for the purpose of either increasing or decreasing the bluntness of the edge. The amount of the rake is measured by two angles called the "back rake" and the "side rake". Rake may be "positive" ( more blunt ) or "negative" ( less blunt ) depending on the inclination angle.
Functions of the Various Angles in Cutting Tool Geometry :
Radial Rake Angle ( Milling ) -- Side Rake Angle ( Single Point Turning Tool )
This angle has a major effect on power efficiency and tool life.
Axial Rake Angle ( Milling ) -- Back Rake Angle ( Single Point Turning Tool )
This angle controls the chip flow and the strength of the cutting edges.
Corner ( Chamfer ) ( Milling ) -- Side Cutting Edge Angle ( Single Point Turning Tool )
This angle reduces the thickness of the chip.
True Rake Angle ( Milling ) ( Single Point Turning Tool )
True rake angle is considered the most significant angle on the cutting tool for metal removing.
The combination of radial rake, axial rake and corner angle determines the shear angle thus power requirements, tool force and temperature at the cut. The higher the positive true rake angle, the lower the cutting force, the power requirements and heat generated at the cut. The rake angle is most often determined by the cutting tool material and the rigidity of the machine tool.
Inclination Angle ( Milling and Turning )
The inclination angle most significantly effects the direction the cutting chip will flow. A posiitive inclination angle directs the chip outward and a negative angle directs the chip toward the center of the cutter. Also, any change in the axial rake angle, radial rake angle or chamfer angle will also change the direction of chip flow.
Dish Angle ( Milling ) -- End Cutting Edge Angle ( Single Point Turning Tool )
This angle provides clearance between the cutter and the finished surface. An angle close to zero does provide strength, but also causes rubbing, generates heat and can thus negatively effect surface finish. Too large an angle weakens the tool. Flats parallel to the finished surface can often be added to the end cutting edge or dish angle to assist in improving the surface finish.
Clearance Angles ( Milling and Single Point Turning Tool )
Primary clearance is directly below the cutting edge and prevents the cutter or tool from rubbing on the workpiece. The secondary clearance is on the tool form of the cutter or the shank of the single point turning tool. This clearance must be large enough to clear the workpiece and permit the chips to escape. Too large of a secondary angle may result in the weakening of the cutter or the tool.
NOTE :
One of the most important variables in machining is rigidity. Rigidity applies to many areas including the set-up and workholding, the machine tool itself, the cutting tool and the workpiece. Even though many other guidelines have been adhered to, where a lack of rigidity exists in any of these areas, a change in cutter geometry, cutting tool material, cutting conditions or a combination of these factors may be required.
Information in this article was taken from Kentech's KipwareEDU® - Mechanical Engineering Version. If you found this information helpful ... we invite you to explore all our versions of KipwareEDU® ... just click here.
No comments:
Post a Comment