Milling machines have been around for well over 300 years. Due to their quality and speed, they are among the most applied industrial machining tools. Understanding the basics of ‘what is a milling machine?’ can give manufacturers a great alternative to stay ahead of the competition.
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This article will provide an in-depth guide to the working process of a milling machine. You will learn about the many different types of milling machines, tools, benefits, and a lot of other information that will improve the outcome of any operation. Without waiting any further, let us get into the heart of the matter right away.
A milling machine is an industrial machine tool that creates a part by removing material from a stationary workpiece with rotary cutting tools.
A milling machine is the main type of equipment used for milling, a subtractive manufacturing process, that can be controlled manually or with Computer Numerical Control (CNC). Milling machines can perform various functions by changing the shape and type of cutting tools. Due to this versatility, a milling machine is one of the most beneficial pieces of equipment in a workshop.
Eli Whitney invented the milling machine in in New Haven, Connecticut. Before the invention of the milling machine, workers used hand files to create parts manually. This process was highly time-consuming and completely dependent on the worker’s skill.
The development of a milling machine provided dedicated machinery that could create the part in less time and without requiring the manual skill of the workforce. Early milling machines were used for government contracts such as manufacturing rifle parts.
A milling machine can be used for many different purposes, such as machining flat surfaces, irregular surfaces, drilling, boring, threading, and slotting. Complex parts such as gears can be crafted easily with a milling machine. Milling machines are a multi-purpose machinery due to the wide variety of parts made using these.
There are many different types of milling machines, which leads to several variations in machine components. Some standard components that all milling machines share are:
Here is a detailed step-by-step working process for milling machines:
The process starts with designing the part to have a clear understanding of what is required. For CNC mills, the design process includes programming and making machine instruction files with CAM software. For manual milling machines, the part design can be a basic blueprint that includes the various dimensions.
The milling machine requires a proper setup before the machining starts. This includes adjusting the various settings. For CNC milling machines, the program is transferred to the control system. For manual milling machines, the various parameters of the machine are adjusted as per requirement.
The workpiece is mounted on the table securely. It is important to ensure that all the fixtures and clamps are tight. Any loose fixtures result in vibrations that can cause a poor-quality milling operation or even damage to the parts.
The milling process begins after the workpiece is fixed and the machine setup is complete. The rotary cutters remove material from the surface a little at a time. The path and shape of material removal depend on the type of milling tool and the required shape. The rate of cutting tool movement into the workpiece is called the feed rate.
Once the milling cycle completes, the part is removed and inspected for quality. If the quality is up to the required standard, the part is removed and sent for further processing. If it needs further work, the part undergoes another milling pass.
Having a good hold on how to use milling machines requires learning about the various parameters associated with these machines. These parameters are:
Vc = π x Dc x n ÷
Vf = Ff x n; where Ff is the feed per revolution.
There are many different ways to classify milling machines and many types of machines in each classification. These various milling machines are:
Spindle orientation refers to the direction of the spindle axis. There are three classifications in this regard:
A vertical milling machine has the spindle axis in the vertical plane. The cutting tool can penetrate deep into the workpiece for additional functions such as drilling and cutting. Vertical milling machines are present in two configurations: the bed mill and the turret mill. Generally, these machines have long and thin cutting tools.
A horizontal milling machine has a spindle axis in the horizontal plane. Therefore, the cutting tool approaches the workpiece from the side instead of the top. These machines generally come with a rotary table to provide an angled approach for the cutting tools. The cutting tool in horizontal milling machines is shorter and thicker.
A universal milling machine is capable of both horizontal and vertical milling machines. This is made possible by a worktable that can rotate to an almost perpendicular direction, providing access to complementary planes.
A vertical milling machine is considered better than a horizontal mill due to its higher versatility and more straightforward setup. This is why most milling machines are available in the vertical configuration. The maintenance requirement of vertical milling machines is lower than that horizontal counterparts.
The axes of a milling machine represent the degree of freedom of the cutting tool. Simply put, the cutting tool axis is the number of directions in which the cutting tool can move. Based on these criteria, the various milling machines are:
A 3-axis milling machine is the most basic type of equipment. The cutting tool is capable of moving in the three linear X, Y, and Z axes. 3-axis milling machines find a huge popularity due to their low cost and simple operations. The maintenance requirements of these machines is also lower compared to multi-axis options.
A 4-axis milling machine can move in the three linear axes as well as an additional rotary axis. The rotary axis can be any one of the A, B, and C axes. The A-axis rotates around the X-axis, B is rotary around the Y-axis, and C is rotary around the Z-axis. 4-axis milling machine can create highly complex parts due to the angular movement of the cutting tool.
A 5-axis milling machine uses all three linear axes and any two rotary axes. It is common to use rotary tables to simplify spindle axis complexity. 5-axis machines can create complex parts at a high speed suitable for mass production.
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A 6-axis milling machine can move in all three linear axes and three rotary axes. This provides the ability to machine the work surface from all sides simultaneously without repositioning. 6-axis milling machines can provide high precision suitable for any requirement. The production speed of this machinery is adequate for mass production.
There are many different types of milling machines based on how they are structured. These different types are:
A fixed bed milling machine has a stationary bed attached to the frame. Parts such as the knee and saddle assembly are not adjustable in the fixed bed mill. A fixed bed milling machine is a great option for performing cutting operations. Fewer movable parts also provide easier maintenance of the equipment.
A knee mill is a vertical milling machine configuration that mounts the worktable on a movable casting called the ‘knee’. The knee can travel vertically in the Z-axis. This provides the operator with the ability to adjust the vertical position of the worktable. Knee mills increase the milling machine’s versatility in operations such as drilling.
A planner mill is a simple setup that cuts flat surfaces on a workpiece perpendicular to the machine tool axis. These mills are most common in woodworking for creating finished timber. Planer mills are easy to operate and maintain due to their simple setup.
A C-frame mill has a fixed spindle and knee structure that is capable of only vertical movement (Z-axis). The X-axis and Y-axis are incorporated into the worktable. C-frame mills are used for mass production due to their high milling speed.
A traveling column milling machine has a column that can slide horizontally. The traveling column milling machine is used when machining very long parts is required. The column movement is made possible with guide rails on the machine bed.
A gantry mill has a long bed that supports a gantry frame. Multiple cutters can be mounted on this gantry frame. The mounted cutters are capable of horizontal movement along the gantry, similar to traveling column milling machines. It is used for the machining of large parts.
The various milling machines, based on the type of control mechanism, are:
A manual milling machine requires the operator to move the cutting tool around by hand. This is the cheapest option for milling machine control. However, it has the lowest precision due to the high human error involved.
A tracer-controlled milling machine uses a replica of the final part to guide the milling machine tool. A probe scans the replica counters and guides the cutting tool to create a similar pattern on the workpiece. It also involves a lot of manual effort to scan the replica with the probe. Additionally, it is a time-consuming and low-precision control system.
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A digital readout milling machine is a modified form of manual control that comes with a counter displaying the accurate tool position. This helps the operator in the precise positioning of the cutting tool without any human error. While it increases the precision over manual milling machines, it still requires a high time to machine. Complex shapes are hard to machine using this method.
A Computer Numerical Control milling machine uses programming instructions to control the cutting tool. Computer Numerical Control (CNC) programs are written in CAM software prior to the machining operations. CNC is the most precise and fastest way for cutting tool movement. Most industries extensively use CNC milling machines over any other control system.
There are many different operations for a milling machine. These operations are:
Slab milling is a type of operation that creates flat surfaces on a workpiece. It may be used for workpiece finishing or for reducing the thickness of the part. Slab milling generally uses a horizontally oriented cutting tool with multiple toothed edges. It is also known as plain milling.
Up milling operation describes the cutting tool rotation in the same direction as the feed. It is also called conventional machining. The down milling operation describes the cutting tool rotation in the opposite direction of the feed. Down milling is used for finishing the part.
Face milling uses a cutting tool positioned perpendicular to the workpiece to remove material from the surface. The cutting tool removes minimal material to create an accurate flat surface. It can utilize both a single-point and a multipoint cutting tool. It can also be used for smoothing parts.
An end mill uses a cylindrical cutter with toothed edges for the surface preparation of the workpieces. The direction of the cutter is similar to a drill bit. However, while a drill bit moves in the axial direction, an end mill moves sideways to remove chips from a work surface.
A gang mill is a type of milling machine in which a single arbor supports multiple cutting tools. The cutters may be synchronized to perform the same milling operation or individually adjusted to perform different operations.
Straddle milling uses two end mills mounted on two different sides of the same arbor. This provides the ability to work on two different workpiece surfaces simultaneously. A spacing collar is provided to adjust the space between the two cutters as per requirement.
A form milling machine inscribes a combination of curves and straight lines on a workpiece surface. It can also produce contours made entirely of curves. The curves produced by form milling cutters can be both concave and convex.
A peripheral mill setup has the milling cutter parallel to the workpiece instead of a perpendicular placement. The milling cutter can have a single-point or multipoint cutting edge on the sides. The sides remove material from the top of the work surface.
A plunge mill feeds the milling cutter in the z-axis to plunge deep into the workpiece. Once the milling cutter reaches the required depth, it is retracted back in the z-axis, positioned to another X, Y coordinate,e and plunged again into the workpiece.
Saw milling is a niche type of mill that is used for cutting logs for making lumber. Saw milling generally uses a circular or linear toothed cutter.
Groove milling is used to make slots and grooves of varying diameters in the workpiece. It applies a cylindrical cutting tool that plunges into a workpiece to a shallow depth and removes material from the tool side.
Thread milling is a niche mill that cuts internal or external threads in a workpiece. Threads are cut by the rotation of a single point, dual point, or triple point cutting tool.
Cam milling uses a universal dividing head in a vertical configuration to produce cams. The spindle axis and the cam mill axis are parallel to each other.
Gear milling is used to cut toothed gears into a round workpiece. A form-relieved cutter removes material to create the cavity between two gear teeth. The workpiece is then rotated by one gear space. The cutter then removes the next cavity. The operation follows till the gear is completely manufactured.
Angle milling is used to make angled surfaces on workpieces. It is also known as angular milling. The angle of the surface depends on the contour of the milling cutters.
Profile milling is used for finishing and semi-finishing of a workpiece surface. It removes a minimal amount of material from a workpiece to create exceptionally flat surfaces.
Side milling is used to cut a flat surface on the side of the workpieces. The cutting depth is adjustable through a vertical feed screw on the table.
Face milling is the most widely used milling technology. It is a highly versatile piece of equipment that can create a lot of different shapes on a workpiece surface. Most surface preparation stages incorporate a face mill or a slab mill.
A milling machine can cut a wide range of materials, such as:
Milling machines can use many different types of cutting tools, such as:
Milling machines find uses in almost every manufacturing sector. Some common industries that use these machines are:
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Milling machines have many benefits and a few limitations compared to other machining methods. Let us study each of these one by one:
New milling machines can cost around $10,000 and can go as high as $200,000. The cost of a new milling machine can vary depending on several factors, such as:
Milling machines working daily can easily last over 10 years with proper maintenance. Good quality milling machines can even push lifespan above 15 years. However, certain machine parts counted as consumables might require periodic replacement.
Yes, milling machines are easy to maintain. However, the maintenance requirement of the milling machine is specific to the particular machine you use. Follow the manufacturer’s guide to learn how to maintain your milling machine.
Selecting a milling machine should be done by evaluating the factors mentioned below:
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There are many options for buying a milling machine. Common choices are:
No, operating a milling machine is not hard. However, it requires a technical understanding of the equipment and the tooling. Therefore, only skilled operators should work on such equipment.
Milling machine parts have extreme strengths and speeds that can cut through the hardest materials. Therefore, they are a safety risk to the operator’s limbs and other body parts. These machines also have ultra-high voltages that can pose an electrocution hazard. Follow the safety guidance of the machine with adequate precautions such as guard rails and light curtains.
Milling machines have tremendously changed the possibilities of the part quality that can be achieved for the mass production of consumer components. The high precision of these machines even makes them the best choice for prototyping or research. If you are looking for the perfect solution for your manufacturing requirements, milling machines can be a great fit for you.
Here are the answers to some common queries regarding milling machines:
The difference between a milling machine and a lathe is that a milling machine uses a rotary cutting tool against a stationary workpiece. On the other hand, a lathe uses a rotating workpiece against a stationary cutting tool.
The difference between a milling machine and a router is that milling machines can cut through even the hardest materials. On the other hand, routers are used to carve intricate patterns into softer workpieces of limited thickness.
The difference between a milling machine and a drilling press is that a drill can only create small diameter holes linearly in a material. On the other hand, a mill is a versatile tool that can create any shape in a material at varying depths, linearly and transversely.
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