Face Milling: Definition, Process, Tools, and Operations
Milling machines can be used to carry out a range of operations, all designed for different purposes. Face milling is a specific milling machine operation used to create flat surfaces with a fine surface finish on a workpiece.
This article will discuss what face milling is, its definition, process, tools, and operations.
What Is Face Milling?
Face milling is a process used to cut material from the top face of a workpiece. Face milling is done using a milling machine or a machine center, and uses an end mill, fly cutters, or shell mill tools. All of these tools achieve a similar result, which is to remove material from the top surface of a workpiece. Shell mills are one of the most common tools used to parallel workpiece surfaces or create fine surface finishes.
What Is Face Milling Used For?
Face milling is primarily used to create a flat face on a workpiece. While creating a flat face can be achieved with other processes, face milling is the quickest way to create one. Milling is also used to create a fine surface finish when compared to other machining methods.
What Is Face Milling Also Called?
Face milling is also referred to as face machining and shell milling, machining being a generic term for milling and shell referring to the use of a shell milling tool. Face milling and shell milling are interchangeable if the milling tool being used is a shell tool, whereas face machining is used when describing the wider machining process.
What Are the Features of a Face Milling Cutter?
A face milling cutter consists of an arbor, cutting head, two keys, a retaining bolt, and the cutting tips. The arbor is used by the machine to hold the tool. The retaining bolt screws through the center of the cutting head and the arbor. The two keys prevent the cutting head and arbor from rotating separately, and the tips are used as the cutting surface. The tips are the most unique parts of any face milling cutter and can be changed on every tool for different tip materials and shapes depending on the application.
How Does Face Milling Differ From the Other Types of Milling?
There are many functions of milling, and each serves a different purpose. For example, one type of milling is peripheral milling. Peripheral milling is similar to face milling as it is used to create a flat surface and remove material quickly. However, in peripheral milling, the side of the milling tools is used as the cutting edge. Peripheral milling is able to remove a larger amount of material per unit of time due to having a larger cutting surface in contact with the workpiece. Other forms of milling include: chamfer, profile, and shoulder, which are all used to create different forms of geometry. Whereas face milling is used to create a flat surface.
How Does the Face Milling Process Work?
There are four main steps to the face milling process which are listed and described below:
1. Arrange the Workpiece
Fasten the workpiece to the table, usually using a vice. The workpiece should always be in the center of the vice to: ensure a uniform clamping force, prevent the workpiece from moving, and ensure that the cutter can cut the top surface of the work in its entirety. The workpiece may also require the use of parallels to ensure the work is not too far in or out of the vice clamp. Parallels must be used for this adjustment to make sure the work is level with the machine bed.
2. Place the Milling Machine
The level of the bed in relation to the cutting head must also be adjusted in the Z-direction to make sure the cutting head removes the right level of material. If adjustable, the spindle must be set perpendicular to the workpiece.
3. Set the Feed Rate and Spindle Speed
Set the feed rate and spindle speed for the desired application before machining. The feed rate and spindle speed will depend on the material being cut, the depth of the cut, the width of the cut, and the size and material of the milling cutter. As a rule of thumb, the more material is removed, the harder the material, or the larger the cutter, the slower the feed rate and spindle speed.
4. Perform Machining
The final step is to carry out the machining. For a Computer Numerically Controlled (CNC) machine, once the G-code instructions have been uploaded to the milling machine, the machine can operate independently of the operator. For manual milling machines, the operator will position the tool in line with the work and set the feed speed and spindle speed. The machine can then cut the top face of the workpiece at the desired speed.
How Long Does the Process of Face Milling Take?
The time taken to face mill a workpiece will depend on the size of the workpiece and the feed rate of the machine. The feed rate will vary on the depth of cut, width of cut, cutting speed, cutting diameter, and spindle speed. Most face milling operations are finished within a matter of minutes, however, times vary greatly. The time taken to face mill a part can be worked out using the formula below:
Tc=L/vf
Where:
Tc = Machining time
L =Length of the cut
vf = Feed rate
If the total length of the cut is 700 mm and the feed rate is 900 mm/min then:
Tc=700/900
Tc= 0.77 min = 46 seconds
What Is the Cutting Speed of Face Milling?
The cutting speed of face milling will vary with the material type and cutting tool used. A list of different cutting materials and their cutting speeds in m/min are listed in Table 1 below:
| Cutting Tool Material | Cutting Speed (m/min) |
|---|---|
Cutting Tool Material High-speed steel | Cutting Speed (m/min) 30–50 |
Cutting Tool Material Cemented carbide | Cutting Speed (m/min) 60–100 |
Cutting Tool Material Ceramics | Cutting Speed (m/min) 300–600 |
Cutting Tool Material Carbon boron nitride | Cutting Speed (m/min) 300–600 |
Cutting Tool Material Diamond | Cutting Speed (m/min) >800 |
When To Use Face Milling?
Face milling is used to remove a small amount of material from a workpiece's surface and to create a high-quality surface finish (without post-processing). The face milling process can create a finer surface finish because it removes a smaller amount of material at a time. Face milling can also be used to create a flat surface on a workpiece.
What Are the Materials That Can Be Used for Face Milling?
Cutting tools with different materials are used for different purposes. Materials including: diamond, carbide, and cobalt are used for high-speed cutting applications. In contrast, high-speed steel can be used for general face milling applications. Both ceramic and carbide can be used for specific applications in which finer surface finishes are required. All of these materials are significantly harder than the metals they are cutting which ensures that the tool is able to cut the workpiece and not the other way around.
How Does the Choice of Materials Affect Face Milling Effectiveness?
The type of material used for the cutting surface of the tool will affect the life span of the tool and its cutting speeds. Tools that use carbon steel can retain their cutting edge for a long time at a low-cost point. However, carbon steel is limited to a temperature of 250 °C, as above this the carbon steel will be abraded rapidly. This means carbon steels are not as fast or efficient as other materials. High-speed steel is alloyed carbon steel which improves the cutting speed and therefore efficiency of the tool. Stellite is a non-ferrous alloy that includes chromium and cobalt. It is extremely hard and able to achieve high cutting speeds at high temperatures, making it very efficient for mass-production parts.
How To Choose the Right Face Milling Tools?
There are two main categories of face milling tools—rough mills and finishing mills. Rough mills create a rougher surface finish but are able to remove material faster, and finishing mills are used to create a finer surface finish and a closer tolerance. Listed below are some tips on choosing the right face milling tools:
- Material: On the lower end are steels. Regular carbon steels are usually not hard enough for most milling operations, and high-speed steel, although low cost, wears fairly quickly and so is more expensive in the long run. In the mid-range are lots of high-speed steels with cutting tip coatings such as cobalt which increase the tool’s wear resistance. High-end materials used for face milling include cemented carbide which has a high wear resistance and high cutting speeds.
- Diameter: The tool diameter is a simple parameter. The larger the tool the faster the material can be removed. Generally face milling tool diameters are larger than the workpiece, so that the cut can be made in one pass.
- Coating: Coating can affect the cutting speed and life span of the tool. One example of a coating is titanium nitride; however, as well as increasing the life span this also increases the price point. Coatings can also reduce the friction of the cutting tool which reduces the need for lubrication.
- Flutes: Flutes are cutting channels in the tool. An increase in the number of flutes increases the maximum feed rate of the tool. However, it also reduces the space for the swarf to escape during cutting.
- Angle: The angle of the helix of the cutting edge affects the cutting speed. Steeper helix angles are suitable for soft metals and more shallow angles are suitable for harder materials including steel.
What Are the Right Tools for Face Milling?
There are three main tools for face milling as listed and discussed below:
1. End Mills
End mills are ideally suited for creating intricate finishes on a workpiece due to their cutting edge. This cutter has multiple teeth on the shank, which enables it to create various designs. End mills are somewhat similar in appearance to a drill. However, a drill can only cut axially, whereas an end mill can cut in all directions. This tool can be used for creating aesthetically pleasing designs.
2. Shell Mills
Shell mills are a popular choice for face milling. They are perfect for providing a consistent surface finish as they have multiple teeth with inserts on their edges. This design controls how the material is able to be removed and is, therefore, the right tool to use for hard materials as the multiple cutting edges enable the shell mill to remove larger pieces of material per pass.
3. Fly Cutters
Fly cutters are a type of tool used for face milling. They are a tool that has only one cutting edge and one insert. This tool is ideally suited for producing fine finishes without a high consumption of power. It is most commonly used for softer materials.
How Does the Choice of Tool Affect Face Milling Quality?
The quality of the finished product is directly affected by the choice of tool used in face milling. The choice of tool dictates the axial depth of the cut of the material and the cutting force while machining.
What Are the Different Types of Face Milling Operations?
Below are four types of face milling operations, each with its specific purposes:
1. General Face Milling
General face machining is the standard process used for milling and doesn't require any special considerations. General face milling is used for most face milling operations. The best tool to use for general face milling is a tool with a 45° entering angle.
2. Heavy-Duty Face Milling
Heavy-duty face milling involves large workpieces and large machining centers. Heavy-duty machining is used to remove a large amount of material and therefore requires more powerful milling machines. When heavy-duty milling, a tool with a 60° entering angle provides the best feed rates to improve milling efficiency.
3. High Feed Milling
High feed machining is carried out at high feed rates and cutting speeds of over 1000 m/min. When high feed milling, a shallow enter angle is required to allow for a high feed speed. An entry angle of 10° makes for the best feed rates.
4. Finishing With Wiper Inserts
Finishing with wiper inserts improves the surface finish of the part. A finer surface finish using a wiper insert can increase the aesthetic of the part. The need for wiper inserts increases with an increased feed rate per revolution, in order to maintain or improve the surface finish of the part.
What Are the Applications of Face Milling?
Face milling can be used in the following applications:
- Formatting a workpiece.
- Edge processing.
- Leveling surfaces.
- Incorporation of recesses, pockets, and hole patterns.
What Are the Advantages of Face Milling?
The advantages of face milling include:
- Smooth surface finish.
- Versatility of materials face milling can be used on (e.g., plastics, composites, metals).
- Higher feed rates.
- Reduced chatter.
- Well-balanced radial and axial cutting forces.
- Less breakout on the workpiece’s corner.
- Minimal entry shock.
- Lower radial forces directed into spindle bearings.
What Are the Disadvantages of Face Milling?
Face milling has some disadvantages including:
- Cannot cut corners.
- Burring or chipping may occur on the exit side of the cutter rotation.
- The larger body diameter has the potential to cause fixture clearance complications.
- Due to the lead angle, there is a reduced maximum depth of cut.
Is Face Milling Considered Expensive?
Face milling can be considered to be more expensive than other forms of milling processing. This is due to the fact that it requires a specialized cutting tool. However, this tool is extremely versatile and can be used across a wide range of materials such as: composites, plastics, and metals. While the initial up-front capital expenditure costs tend to be higher, a face mill can be used in a variety of different scenarios thus making it a cost-effective investment.
Can You Bore With a Face Mill?
Yes. Face mills can be used for boring and drilling. With a face mill, you can mill a surface and then cut out a large, cored bore with the same tool. Interpolating a face milling cutter may be the ideal choice for rough boring operations. Improved cutter designs and software improvements have allowed the face mill to be able to complete different types of holes.
What Is the Difference Between Face Milling and Peripheral Milling?
Face milling and peripheral milling are two of the most common types of milling operations and are extremely similar in how they operate. The difference between them is their suitability for fabricating features and their setup. For example, peripheral milling has a cutting tool that is parallel to the part, which enables the side of the cutter to grind away the workpiece top. Face milling on the other hand only removes a small portion of the workpiece using the cutter’s tip. Face milling is better suited for pieces that need a fine surface finish.
What Is the Difference Between Face Milling and Shell Milling?
A shell mill has multiple inserts on the outer edge and cutting teeth. This enables it to balance the cutting forces to have precise control over the amount of material that is removed by the cutter at high speeds. This allows for high-quality and consistent surface finishes on the workpiece. In contrast, face milling is better suited for workpieces requiring fine surface finishes and can only remove small portions of material with the cutting tip.
What Is the Difference Between Face Milling and End Milling?
Face milling and end milling are among some of the most common types of milling procedures. Each uses a different type of cutter—one uses an end mill and the other uses a face mill. The main difference between these two cutters is that an end mill uses both the sides and the end of the cutter, whereas a face mill only uses horizontal cutting. End mills are comparable to drills as they can cut axially, unlike face mills. Face mills only have cutting edges located on the sides of the head.
Summary
This article presented face milling, explained it, and discussed its process. To learn more about face milling, contact a Xometry representative.
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