General Recommendations for Milling Operations

                   General Recommendations for Milling Operations

 

         

          Troubleshooting Guide for Milling Operations

 

            

             Machined Surface Features in Face Milling

            Figure 24.13  Machined surface features in face milling.  See also Fig. 24.6.

 

 

                        Edge Defects in Face Milling

 

      Figure 24.14  Edge defects in face milling:  (a)  burr formation along workpiece edge, (b)   breakout along workpiece edge, and (c) how it can be avoided by increasing the lead angle (see also last row in Table 24.4).

Milling Cutter

Face-Milling Cutter with Index able Inserts

Figure 24.5  A face-milling cutter with index able inserts.  Source:  Courtesy of Ingersoll Cutting Tool Company. 

Effect of Insert Shape on Feed Marks on a Face-Milled Surface

Figure 24.6  Schematic illustration of the effect of insert shape on feed marks on a face-milled surface:

 (a)  small corner radius, 

 (b) corner flat on insert, and 

 (c) wiper, consisting of small radius followed by a large radius which leaves   smoother feed marks.   

 (d)  Feed marks due to various insert shapes. 

            Face-Milling Cutter

        

                    Figure 24.7  Terminology for a face-milling cutter.

      Effect of Lead Angle on Undeformed Chip Thickness in Face Milling

Figure 24.8  The effect of the lead angle on the undeformed chip thickness in face milling.  Note that as the lead angle increases, the chip thickness decreases, but the length of contact (i.e., chip width) increases.  The edges of the insert must be sufficiently large to accommodate the contact length increase.

 

   Position of Cutter and Insert in Face Milling

 

Figure 24.9  (a)  Relative position of the cutter and insert as it first engages the workpiece in face milling.

(b)  Insert positions towards the end of cut.

     (c)  Examples of exit angles of insert, showing desirable (positive or negative angle) and undesirable (zero angle) positions.  In all figures, the cutter spindle is perpendicular to the page and rotates clockwise.

                 

                   Ball Nose End Mills

Figure 24.10  Ball nose end mills.  These cutters are able to produce elaborate contours and are often used in the machining of dies and molds.  (See also Fig. 24.2d.)  Source:  Courtesy of Dijet, Inc. 

 

                                Cutters

 

    Figure 24.11  Cutters for (a) straddle milling, (b) form milling, (c) slotting, and (d) slitting with a milling cutter. 

            

               T-Slot Cutting and Shell Mill

 

               Figure 24.12  (a)  T-slot cutting with a milling cutter.  (b)  A shell mill.

Machining Processes

Machining Processes Used to Produce

Various Shapes:  Milling, Broaching, Sawing, and Filing; Gear Manufacturing .

 

Parts Made with Machining Processes 

 

Milling Cutters and Milling Operations

 

Figure 24.2  Some basic types of milling cutters and milling operations.  (a)  Peripheral milling. 

(b)  Face milling.  (c) 

End milling.  (d)

  Ball-end mill with index able coated-carbide inserts machining a cavity in a die block.

 (e)  Milling a sculptured surface with an end mill, using a five-axis numerical control machine.  Source:

 (d)  Courtesy of Iscar.  (e)  Courtesy of The Ingersoll Milling Machine Co.

Milling Operations

Figure 24.3  (a)  Schematic illustration of conventional milling and climb milling.  (b)  lab-milling operation showing depth-of-cut, d; feed per tooth, f; chip depth-of-cut, tc; and workpiece speed, v. 

(c)  Schematic illustration of cutter travel distance, lc, to reach full depth-of-cut.

Face-Milling Operation

Figure 24.4  Face-milling operation showing (a) action of an insert in face milling; (b) climb milling; (c) conventional milling; (d) dimensions in face milling.  The width of cut, w, is not necessarily the same as the cutter radius.

         Summary of Peripheral Milling Parameters and Formulas

 

Parts of UH Milling Machine

Universal Horizontal Milling Machine

Milling Machine Parts

•         Base

•         Gives support and rigidity to machine.

•         Acts as reservoir for cutting fluids.

•         Column face

•         Precision-machined and scraped section used to support and guide. knee when moved vertically.

•         Knee

•         Houses feed mechanism.

•         Attached to column face and moved vertically.

•         Saddle

•         On top of knee

•         Moved in or out by

   Means of cross feed hand wheel (manually or automatically)

•         Swivel table housing

•         Fastened to saddle on universal milling machine.

•         Enables table to be swiveled 45º either side of centerline

•         Table

•         Rests on guide ways in saddle and travels left and right

•         Supports vise and work

•         Cross feed hand wheel

•         Used to move table in and out

•         Table hand wheel

•         Used to move table left and right

•         Feed dial

•         Used to regulate table feeds

•         Spindle

•         Provides drive for attachments, arbors, cutters

•         Over arm

•         Provides for correct alignment and support of arbor and various attachments

•         Can be adjusted and locked in various positions.

•         Arbor support

•         Fitted to over arm and can be clamped

•         Aligns and supports various  attachments

•         Elevating screw

•         Gives upward or downward movement to knee and table (manually or automatically)

•         Spindle speed dial

•         Set by crank used to regulate spindle speed.

Backlash Eliminator

•         Eliminates backlash (play) between nut and table lead screw

•       Permits operation of climb (down) milling

•       Two independent nuts mounted on lead screw

•       Nuts engage common crown gear which meshes with rack

•       Axial movement of rack controlled by backlash eliminator engaging knob on front of saddle

•       Turning knob in, nuts forced to move along lead screw in opposite directions

•     Machine Backlash Eliminator

Milling Machines

Horizontal Milling Machines

Manufacturing-type

•Cutter height is controlled by vertical movement of headstock

2. Special-type

•   Designed for specific milling operations

3.  Knee-and-column-type

•   Relationship between cutter height and work controlled by vertical movement of         table.

Manufacturing-Type

Used primarily for quantity production of identical parts •Distinctive features

•Automatic cycle of cutter and work approach

•Rapid movement during non-cutting cycle

•Automatic spindle stop.

Manufacturing-Type

Two common types

•Plain manufacturing type

•Small plain automatic knee and column type.

Plain Manufacturing Type Milling Machine

  

Special-Type Machines 

•Designed for individual milling operations. •Used for only one particular type of job.

•Completely automatic

•Employed when hundreds or thousands of similar pieces are to be machined.

Machining Centers

•Capable of handling wide variety of work all in one setup.

•Straight and contour milling, drilling, reaming, tapping, and boring

Capable of high production rates while still maintaining high degree of accuracy.

•Rugged construction, reliable controls

•Anti-backlash ball screws.

Knee-and-Column-Type
Milling Machines

Machines in this class fall into three categories: •Plain horizontal milling machine.

•Universal horizontal milling machines.

•Vertical milling machines.

Universal Horizontal
Milling Machines

•         Difference from plain horizontal machine is addition of table swivel housing.

•         Located between table and saddle.

•         Permits table to be swiveled 45º in either direction in a horizontal plane.

•       Used for milling of helical grooves in twist drills, milling cutters, and gears.