• Milling Machine Definition
• Milling Machine Operation

• Please be aware of the hours of operation of the lab and the limitations of each machine as explained in this manual. Here is a list of available equipment: Horizontal Bandsaws (2) Disc Sander (1) Vertical Bandsaw (1) CNC Milling Machines (2) Drill Presses (3) CNC Lathe (1).
• Answers in manufacturing engineering a cnc vertical milling machine has to cut a straight slot of 10 mm width and 2 mm depth by a cutter of 10 mm diameter between points 0 0 and 100 100 on the xy plane dimensions in mm'.

CNC machining is a highly utilised subtractive manufacturing technology. Computer numerical control systems offer less need for manpower and higher levels of automation.

Carbide-Tipped T-Slot End Mills Made of carbide-tipped steel, these end mills maintain a sharper, harder edge at high temperatures than high-speed steel. Use them to create slots in machine tool tables, indexing tables, and other workholding surfaces. Illustrates gear cutting milling operation. Spur, helical gears are cut on a milling machine with the help of an indexing mechanism. The operation of gear cutting is cutting of equally spaced, identical gear teeth on a gear blank by handling it on a universal dividing head and then indexing it.

One of these automated fabrication methods is CNC milling. It is a process where rotary cutters remove material, which makes it the opposite of CNC turning.

The milling centres do not just perform the cutting automatically, but also the changing of tools. During the average process of creating a finished product from a block of metal, for example, various tools are used.

So let’s see what milling tools are used on the machines and what are the purposes of each.

What Are the Types of Milling Cutters?

The most common types of milling cutters are:

• End mill
• Face mill
• Ball cutter
• Slab mill
• Side-and-face cutter
• Involute gear cutter
• Fly cutter
• Hollow mill
• Shell mill
• Roughing end mill
• Dovetail cutter
• Wood ruff cutter

First, we should start with one of the primary questions.

What is the difference between end milling and face milling?

These are two of the most prevalent milling operations, each using different types of cutters – the and mill and the face mill. The difference between end milling and face milling is that an end mill uses both the end and the sides of the cutter, whereas face milling is used for horizontal cutting.

End mill

These tools usually have a flat bottom but not always. Round and radiused cutters are also available. End mills are similar to drills in the sense that they can cut axially. But the advantage for milling lies with the possibility of lateral cutting.

Face mill

Face mills cannot cut axially. Instead, the cutting edges are always located on the sides of the cutting head. The cutting teeth are replaceable carbide inserts.

This makes the lifetime of a tool longer while maintaining a good cutting quality.

Ball cutter

Ball cutters, also known as ball mills, have a hemispherical cutting tip. The objective is to maintain a corner radius for perpendicular faces.

Slab mill

Slab mills are not that common with modern machining centres. Rather, they are still used with manual milling machines to quickly machine large surfaces. That is also why slab milling is often called surface milling.

The slab itself spins in a horizontal position between the spindle and the support.

Side-and-face cutter

A predecessor for the end mill. Side-and-face cutters have teeth around the circumference as well as on one side. This makes the functionality very similar to end mills but their popularity has waned over the years with the advancement of other technologies.

Involute gear cutter

There is a special cutting tool for milling involute gears. There are different cutters available to produce gears within a certain number of teeth.

Fly cutter

These tools have the same function as face mills. They consist of a central body that holds either one or two tool bits (double-end fly cutters).

Face mills are better for high quality cutting. Fly cutters are just cheaper and the cutting bits are often made at the shop by a machinist rather than bought from stores.

Hollow mill

Hollow mills are basically the opposite of face mills. Here, the workpiece is fed into the inner part of the mill to produce a cylindrical outcome.

Roughing end mill

As the name says, these are pretty much end mills with a slight difference. The roughing end mill has jagged teeth. These make the cutting process faster than with a regular end mill.

The cut bits of metal are smaller than usual and therefore easier to clear. Multiple teeth come into contact with the workpiece at the same time. This reduces chatter and vibration, which could otherwise be larger because of the jagged teeth.

Woodruff cutter

Woodruff, or keyseat/keyway cutters are used to cut keyslots into parts, for example shafts. The cutting tools have teeth perpendicular to the outside diameter to produce suitable slots for woodruff keys.

Thread mill

The name of this tool says everything you need to know about its purpose. Thread mills are used for producing tapped holes.

Threading operations are usually carried out on drilling equipment. Using a thread mill, though, is more stable and has less limitations regarding the environment.

What Materials Are Used for Cutting Tools?

As you could see, there are a lot of different machine tools available for wide range of purposes. The same applies to the materials used to make these tools.

Let’s dig deeper to look at the most common materials for milling bits.

Carbon steel

The cheapest of the bunch. And this is exactly why it still finds use. As carbon steel is not very durable, it is only suitable for low-speed operations.

Carbon steel loses its hardness at 200° C. This is the reason for lower speeds – to keep the heating effect low.

High-speed steel

High-speed steel, a grade of tool steels, has a few alloying elements added to it to provide better response to heat and wear than a regular carbon steel. While the life cycle of such a tool goes up, so does the cost.

Loses its hardness at 600° C. Therefore, higher milling speeds are suitable for these tool steels.

Cemented carbides

This material is harder than high-speed steel but the toughness qualities are not that impressive. The higher hardness provides better protection against wear but lower toughness levels make it a little more susceptible to cracking and chipping.

The upper temperature of use is at 900° C.

Cutting ceramic

Cutting ceramics are even harder than cemented carbides but lose in the toughness aspect. Both aluminium oxide and silicon nitride are used to produce these tools with varying properties.

Cutting ceramic tools are prone to cracking when used on hard materials and with high temperatures. Therefore, they are not really suitable for machining steels, for example. Otherwise a short tool life is to be expected.

Selecting the Right Machine Tool

As is the norm in manufacturing, the choice of method or tool comes down to a balance between speed, cost and quality. The cost depends on both the price of the tool, the wear machining results in, and the time it takes (speed) to produce the parts.

Choosing the material of the tool

Regular carbon steels are usually out of the option pool because of their limited capabilities. HSS (high-speed steel) is therefore the most inexpensive one to get the job done. At the same time, its rate of wear means that in the long run, there are better options.

Cobalt-bearing HSS, for example, are suitable for even quicker milling. This makes them sufficiently adequate for most jobs.

Cemented carbide is another step towards high performance milling because of the aforementioned properties of such milling machine tools. In the long run, they are a more cost-efficient choice while the up-front costs are higher.

Diameter

This is quite simple. A tool with a large diameter is able to mill the part quicker. Limitations apply based on the geometry of the final part.

For example, if certain inside radii are necessary, the tool cannot deviate from them. At the same time, you can use a large tool for milling away the bulk of it and apply a smaller one to finish the inside corners.

Tool coating

There are some different coatings available to protect the tools from wear. For example, a titanium nitride coating increases the tool’s lifespan but also the cost of it.

Such a coating reduces stickiness of the cutting material which can be a problem with aluminium. Therefore, less lubricant is necessary during the cutting process.

Number of flutes

Flutes are the channels on a milling bit. More flutes allow a higher feed rate because less material is removed.

At the same time, this increases the overall diameter of the milling cutter. This leaves less room for swarf.

Angle of helix

The helix angle, along with the rotation speed of the spindle, determines the cutting speed or feed rate. A steeper angle is suitable for softer materials and metals.

Choosing the right milling cutters for your job needs an understanding of the materials, parameters and definitely some experience. The final outcome depends on these choices and a machinist must understand what material cutters are suitable for cutting different mediums.

A good choice leads to high feed rates and therefore shorter cutting times as well as lower costs.

When choosing a CNC machining service, make sure that they have all the necessary tools to make your parts.

Milling Machine Operations :

• Fig.illustrates the plain and slab milling operation. It is a method of producing a plain, flat, horizontal surface parallel to the axis of rotation of the cutter.
• This is also called slab milling. This operation produces flat surfaces on the workpiece. Feed and depth of cut are selected, the rotating milling cutter is moved from one end of the workpiece to another end to complete the one pairs of plain milling operation.

• Fig. illustrates the face milling operation. It is a method of producing a flat surface at right angles to the axis of the cutter.
• This operation produces a flat surface at the face on the workpiece. This surface is perpendicular to the surface prepared in plain milling operation. This operation is performed by face milling cutter mounted on stub arbor of milling machine. Depth of cut is set according to the need and crossfeed is given to the work table.

3) Side milling

• Fig. illustrates the side milling operation. It is the operation of the production of a flat vertical surface on the side of a work-piece by using a side milling cutter.
• This operation produces flat and vertical surfaces at the sides of the workpiece. In this operation depth of cut is adjusted by adjusting the vertical feed screw of the workpiece.

• Fig. illustrates angular milling operation. It is a method of producing a flat surface making an angle to the axis of the cutter.
• Angular milling operation is used to produce an angular surface on the workpiece. The produced surface makes an angle with the axis of the spindle which is not a right angle. Production of the ‘V‟ shaped groove is the example of angular milling operation.

5) Gang-milling

• Fig. illustrates the gang milling operation. It is a method of milling utilizing two or more cutters simultaneously having the same or different diameters mounted on the arbor of the milling machine.
• As the name indicates, this operation produces several surfaces of a workpiece simultaneously using a gang of milling cutters. During this operation, the workpiece mounted on the table is fed against the revolving milling cutters.

6) Form milling

• Fig. illustrates the form milling operation. It is, a method of producing a surface having an irregular outline.
• This operation produces irregular contours on the work surface. These irregular contours may be convex, concave, or of any other shape. This operation is done comparatively at a very low cutter speed than plain milling operation.

7) End milling

• Fig. illustrates end milling operation. It is a method of milling slots, flat surfaces, and profiles by end mills.
• End milling operation produces flat vertical surfaces, flat horizontal surfaces, and other flat surfaces making an angle from table surface using milling cutter named as an end mill. This operation is preferably carried out on a vertical milling machine.

8) Profile milling

• Fig. illustrates profile milling operation. It is the operation of reproduction of an outline of a template or complex shape of a master die on a workpiece.
• In this operation a template of complex shape or master die is used. A tracer and milling cutter are synchronized together concerning their movements. Tracer reads the template or master die and milling cutter generates the same shape on the workpiece. Profile milling is an operation used to generate the shape of a template or die.

9) Saw milling

• Fig. illustrates sawmilling operation. It is a method of producing deep slots and cutting materials into the required length by slitting saws.
• Saw milling operation produces narrow slots or grooves into the workpiece using the saw milling cutter. This operation is also used to cut the workpiece into two equal or unequal pieces which cut is also known as “parting off”.

• Fig. illustrates keyway milling operation. keyways for shaft or hub are produced by these operations.
• The operation of producing keyways, grooves, slots of varying shapes and sizes is called slot milling operation. Slot milling operation can use any type of milling cutter like plain milling cutter, metal slitting saw, or side milling cutter. Selection of a cutter depends upon type and size of slot or groove to be produced.

• Fig. illustrates gear cutting milling operation. Spur, helical gears are cut on a milling machine with the help of an indexing mechanism.
• The operation of gear cutting is cutting of equally spaced, identical gear teeth on a gear blank by handling it on a universal dividing head and then indexing it. The cutter used for this operation is cylindrical type or end mill type. The cutter selection also depends upon tooth profile and their spacing.

13) Flute milling

• It is a method of grooving or cutting of flutes on drills, reamers, taps, etc,

14. Straddle Milling Operation

• This is similar to the side milling operation. Two side milling cutters are mounted on the same arbor. Distance between them is so adjusted that both sides of the workpiece can be milled simultaneously. Hexagonal bolt can be produced by this operation by rotating the workpiece only two times as this operation produces two parallel faces of bolt simultaneously.

15. Helical Milling Operation

Milling Machine Definition

• Helical milling produces helical flutes or grooves on the periphery of a cylindrical or conical workpiece. This is performed by swiveling the table to the required helix angle, then rotating and feeding the workpiece against revolving cutting edges of the milling cutter. Helical gears and drills and reamers are made by this operation.

16. Cam Milling Operation

• The operation cam milling is used to produce the cam on the milling machine. In this operation cam blank is mounted at the end of the dividing head spindle and the end mill is held in the vertical milling attachment.

17. Thread Milling Operation

• The operation thread milling produces threads using thread milling centers. This operation needs three simultaneous movements revolving movement of cutter, simultaneous longitudinal movement of cutter, feed movement to the workpiece through a table.
• For each thread, the revolving cutter is fed longitudinally by a distance equal to the pitch of the thread. The depth of the cut is normally adjusted equal to the full depth of threads.

18. Fly Cutting :

• Fly cutting, which is also called single-point milling, is one of the most versatile milling operations. It is done with a single-point cutting tool shaped like a lathe tool bit. It is held and rotated by a fly cutter arbor. You can grind this cutter to almost any form that you need, as shown in Figure.
• Formed cutters are expensive. There are times when you need a special form cutter for a very limited number of parts. It is more economical to grind the desired form on a lathe-type tool bit than to buy a preground form cutter, which is very expensive and usually suitable only for one particular job.

19. Drilling :

The milling machine may be used effectively for drilling, since the accurate location of the hole may be secured utilizing the feed screw graduations. Spacing holes in a circular path, such as the holes in an index plate, may be accomplished by indexing with the index head positioned vertically.

Twist drills may be supported in drill chucks fastened in the milling machine spindle or mounted directly in milling machine collets or adapters. The workpiece to be drilled is fastened to the milling machine table by clamps, vises, or angle plates.

20. Boring :

• Various types of boring tool holders may be used for boring on the milling machine. the boring tools being provided with either straight shanks to be held in chucks and holders or taper shanks to fit collets and adapters. The two attachments most commonly used for boring are the fly cutter arbor and the offset boring head.
• The single-edge cutting tool used for boring on the milling machine is the same as a lathe cutter bit. Cutting speeds feeds, and depth of cut should be the same as that prescribed for lathe operations.

Milling Machine Operation