Milling


Introduction 
Milling Equipment 
Milling Process Performance(Software available here) 
Milling Research 
Milling Technology Update


INTRODUCTION

WHAT IS MILLING?

Milling is the process of cutting away material by feeding a workpiece past a rotating multiple tooth cutter. The cutting action of the many teeth around the milling cutter provides a fast method of machining. The machined surface may be flat,angular, or curved. The surface may also be milled to any combination of shapes. The machine for holding the workpiece, rotating the cutter, and feeding it is known as the Milling machine.
View a typical milling operation. This movie is from the MIT-NMIS Machine Shop Tutorial

CLASSIFICATION OF MILLING



Peripheral Milling

In peripheral (or slab) milling, the milled surface is generated by teeth located on the periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel to the workpiece surface to be machined.

(Kalpakjian S., Introduction to Manufacturing Processes)

Face Milling


In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface. The milled surface results from the action of cutting edges located on the periphery and face of the cutter.
 

End Milling

The cutter in end milling generally rotates on an axis vertical to the workpiece. It can be tilted to machine tapered surfaces. Cutting teeth are located on both the end face of the cutter and the periphery of the cutter body.

METHODS OF MILLING

Up Milling

Up milling is also referred to as conventional milling. The direction of the cutter rotation opposes the feed motion. For example, if the cutter rotates clockwise , the workpiece is fed to the right in up milling.

(Boothroyd G. & Knight W., Fundamentals of Machining and Machine Tools)

Down Milling

Down milling is also referred to as climb milling. The direction of cutter rotation is same as the feed motion. For example, if the cutter rotates counterclockwise , the workpiece is fed to the right in down milling.

(Boothroyd G. & Knight W., Fundamentals of Machining and Machine Tools)

The chip formation in down milling is opposite to the chip formation in up milling. The figure for down milling shows that the cutter tooth is almost parallel to the top surface of the workpiece. The cutter tooth begins to mill the full chip thickness. Then the chip thickness gradually decreases.


Other milling operations are shown in the figure.

(Kalpakjian S., Introduction to Manufacturing Processes)


MILLING EQUIPMENT

The milling machine is one of the most versatile machine tools in existence. In addition to straight milling of flat and irregularly shaped surfaces, it can perform gear and thread cutting, drilling, boring and slotting operations which are normally handled on machine tools designed specifically for these specific operations.

The above is a Bridgeport CNC Milling Machine

Types of Milling Machines

Milling machines can be broadly classified into the following types:

  • Column and knee type of milling machines
  • Bed type
  • Rotary table
  • Tracer controlled

  • Milling Cutters

    A milling cutter is a cutting tool that is used on a milling machine. Milling cutters are available in many standard and special types, forms, diameters, and widths.The teeth maybe straight (parallel to the axis of rotation) or at a helix angle. The helix angle helps a slow engagement of the tool distributing the forces .The cutter may be right-hand (to turn clockwise) or left-hand (to turn counterclockwise).The figure shows a typical end milling cutter.

     

    Features of Milling Cutters

    Some of the terms used to identify the major features of a milling cutter are given in the figure.



    (Olivo C.T., Machine Tool Technology and Manufacturing Processes, C Thomas Olivo and Associates)

    Types of Milling Cutters




    MILLING PROCESS PERFORMANCE

    Calculation of Machining parameters in End Milling and Face Milling

    Some important machining parameters like machining time, material removal rate, power etc. are calculated for face milling and end milling processes. These parameters are defined below:
     
     
  • Face Milling Process Performance
  • End Milling Process Parameters
  • End Milling Chip Advisor

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    MILLING RESEARCH

    Milling Research areas can be divided into four broad areas

  • Force Modeling
  • Surface texture modeling
  • Control Strategies
  • Tool wear / tool failure
  • Force Modeling

  • End Milling Simulation Model developed at University of Illinois, Urbana-Champaign
  • Face Milling Simulation Model developed at Purdue University, Indiana

  •  

    Surface Texture Modeling

    Control Stategies

    Tool wear / tool failure

    Stewart platform as a Machine tool

  • A 3 DOF parallel link mechanism is being developed in the SMARTCUTS project at the University of illinois, Urbana-Champaign.
  • NC Milling

  • NC Milling and Error Assessment - Movie at Iowa State University

  •  

    Stewart platform as a Machine tool

  • A 3 DOF parallel link mechanism is being developed in the SMARTCUTS project at the University of illinois, Urbana-Champaign.

  • TECHNOLOGY UPDATE

    STEWART PLATFORM as a Machine tool

    VARIAX


    Researchers have been looking at a device called a parallel kinematic link mechanism to replace the conventional base and tower milling machine tool. The analysis showed that the type of motion and forces needed could be provided in large part by a mechanism called Stewart platform- a type of parallel kinematic link mechanism. A number of research labs and a few companies are working at aspects of this design. Giddings and Lewis have designed the VARIAX (shown above) and Ingersoll Milling Co. have designed the octahedral hexapod. These machine tools consist of a lower platform, an upper platform and six legs that connect the two. The top platform (head) contains the machine spindle and the bottom platform (bed) holds the workpiece. The six legs perform the task of positioning the head woth respect to the bed. Since the machine has no prescribed axis, no linear bearings and no ways in which to travel it offers extraordinary machine stiffness. For more on this machine tool look up the following links:
     

  • A 3 DOF parallel link mechanism is being developed in the SMARTCUTS project at the University of illinois, Urbana-Champaign. Machine Tool Structures page.
  • Miscellaneous Links

  • MIT - NMIS Machine Shop Tutorial
  • Society of Mechanical Engineers
  • Manufacturer's Information Network
  • Thomas Registry
  • TradeWave Galaxy
  • METAL Machining and Fabrication
  • CNC Manufacturing Systems
  • WWW Virtual Library: Mechanical Engineering
  • Precision Machined Products Association Home Page
  • Bibliography

    1. Kalpakjian S., Introduction to Manufacuring Processes,
    2. Olivo C.T., Machine Tool Technology and Manufacturing Processes, C Thomas Olivo and Associates
    3. DeVries W.R., Analysis of Material Removal Processes,
    4. Lambert B.K., Milling: Methods and Machines, Society of manufacturing Engineers,
    5. A Treatise on Milling and Milling Machines, The Cincinnati Milling Machine Co.,
    6. Boothroyd G. & Knight W., Fundamentals of Machining and Machine Tools,