MANUFACTURING PROCESSES

Transcription

1 MANUFACTURING PROCESSES - AMEM 201 Lecture 8: 8 Machining Processes Milling DR. SOTIRIS L. OMIROU Milling Machining - Definition Milling is one of the basic machining processes that allows large amounts of material to be removed quickly. Milling is a very versatile process capable of producing simple two dimensional flat shapes to complex three dimensional interlaced surface configurations. 2 1

2 Milling Machining - Definition At all types of milling machines, the cutting tool performs a rotational motion, that is the cutting motion. The rotation axis of the tool could be horizontal or vertical, depending on machinetool version. The feeding motion is achieved either by part or tool, or both, usually on three perpendicular directions. 3 The Milling process Milling Machining - Definition 4 2

3 Milling Machining video 1 5 Milling Machining video 2 6 3

4 In In order order to to perform a flat flat surface by by milling operation, a relative motion has has to to be be between the the milling tool tool and and part. part. In In this this respect the the milling tool tool will will have have a rotation motion, that that is is the the main main cutting motion, and and either either the the tool tool or or part part has has to to perform a translation motion, that that is is the the feeding motion. Milling Machining video 3 Main cutting motion Click here for animation Milling Tool Machined Surface Feeding motion Part Swarfs 7 Horizontal Milling Machine Milling Machine Tools - Types X axis motion Y axis motion Z axis motion Horizontal spindle - Designed for peripheral milling operations 8 4

5 Vertical Milling Machine Milling Machine Tools - Types X axis motion Y axis motion Z axis motion Vertical spindle - Designed for face milling operations 9 Milling Machine Tools - Types Vertical Milling Machining center Tool Post 10 5

6 Milling Machine Tools - Types Automatic Tool Change on a Vertical Milling Machining center 11 Up Milling & Down Milling Up milling Down milling Also called conventional milling, - Wheel rotation opposite of the feed - The chip formed by each cutter tooth starts out very thin and increases its thickness - The length of the chip is relatively longer - Tool life is relatively shorter - Need more clamping force to hold the work part still. Also called climb milling, - Wheel rotation is parallel to the feed - The chip formed by each cutter tooth starts out thick and leaves out thin - The length of the chip is relatively short - Tool life is relatively longer - Need less clamping force to hold the work part still. 6

7 Milling Operations on a Horizontal Milling Machine Slab milling: Cutter width extends beyond the work piece on both sides 13 Milling Operations on a Horizontal Milling Machine Slotting (Slot milling): Cutter width is less than the work piece width, creating a slot. If the cutter is very thin, it can be used to cut a work part into two, called saw milling. 14 7

8 Milling Operations on a Horizontal Milling Machine Side milling: Cutter, machines the side of the work piece. 15 Milling Operations on a Horizontal Milling Machine Straddle milling: Similar to side milling, but cutting takes on both sides of the work part simultaneously. 16 8

9 Milling Operations on a Horizontal Milling Machine Form milling: The cutter has the desired form of the part Milling of a concave half circle Milling of a gear 17 Milling Operations on a Vertical Milling Machine Face milling: The cutter with a relatively large diameter removes a layer from the upper side of the part 18 9

10 Milling Operations on a Vertical Milling Machine End milling: Cutters diameter is less than the work part s width 19 Milling Operations on a Vertical Milling Machine Profile milling (also contouring or shaping): Outside periphery of flat part is cut 20 10

11 Milling Operations on a Vertical Milling Machine Pocket milling: The cutter removes material creating a cavity (rectangular, circular etc.) 21 Milling Operations on a Vertical Milling Machine 3-Dimensinal surface milling: The cutter (ball end mill) removes material, moving in 3 directions simultaneously.) 22 11

12 Milling Operations on a Vertical Milling Machine 3-Dimensinal surface milling: 23 Milling Operations on a Vertical Milling Machine 24 12

13 Milling Operations on a Vertical Milling Machine Slot milling T-Slot milling 25 Surface Machining on a Vertical Milling Machine Horizontal flat surface Vertical flat surface Profile surface 26 13

14 Milling Tools - End Mills The most common cutting tool used with a vertical mill is an end-mill, which looks like a stubby twist drill with a flattened end. An end mill can cut into a workpiece either vertically, like a drill, or horizontally using the side of the end mill to do the cutting. This horizontal cutting operation imposes heavy lateral forces on the tool and the mill, so both must be rigidly constructed 27 Milling Tools - End Mills Flat end-mills for:: pockets slots edge trim facing Ball-end mills make rounded pockets or spherical pockets; also fillets Corner-rounders form rounded corners! Conical end-mill for chamfers 28 14

15 Milling Tools - Drills and Reamers standard drill: will flex/walk, follow pilot stub drill for less walk/greater rigidity center drill establishes hole position with no walk reamers (straight or spiral) finish off hole (last several thousandths) precise hole diameter for insertion of dowel pins, bearings, etc. plunge while spinning, extract still countersink: for screw heads & deburring hole 29 Work-holding for milling operations Several types of fixtures are commonly used to hold parts while milling them. The most common is a vise

16 Work-holding for milling operations Another common alternative is to clamp the part directly to the machine table using clamps. Therefore all milling machine tables have T-slots along the length to allow placement of the clamps. 31 Work-holding for milling operations Another common work-holding method is an indexed vise, which allows the part to be rotated so as to expose a different surface to the milling tool quickly

17 Work-holding for milling operations Definition of part Setup If f the machine tool needs to access different facets of the part to cut some shapes, then the part may need to be released and re-fixtured fixtured. Each fixed position is called a setup.. In one setup,, multiple tools can be used to cut different shapes, or features on the part. When the setup or tool is changed, the machinist must locate the part that is, the coordinates of the part with respect to the tool must be determined. Each machine table gives feedback about the relative motion of the table along each axis (X, Y, and Z). A primary goal in every machining process is to limit to minimum the number of required part setups