Face milling cutters have cutting edges on both the end face perpendicular to the arbor and the outer circumference, and are mainly used for milling flat surfaces. The cutting edges on the outer circumference are the main cutting edges, while the cutting edges on the end face function like scrapers. Compared to shell end mills, face milling cutters have shorter cutting edges.

High-speed steel face milling cutters are generally used for machining medium-width flat surfaces. The standard cutter diameter range is 80–250 mm. Carbide face milling cutters offer higher cutting efficiency and machining quality than high-speed steel milling cutters, hence carbide face milling cutters are widely used for machining flat surfaces.

Face milling cutters are primarily used for machining flat surfaces and are characterized by: high production efficiency; good rigidity, allowing for larger feed rates; multiple teeth engaging in cutting simultaneously, resulting in good working stability; and the use of a insert structure, which facilitates blade sharpening and replacement, and extends tool life.

Face milling cutters are divided into two main categories: one type involves brazing carbide inserts onto the blades, which are then mounted onto the cutter body, known as inserted blade face milling cutters; the second type involves directly mounting carbide inserts onto the cutter body and securing them with screws, etc., known as indexable clamp-on milling cutters. Face milling cutters have two rake angles: axial rake angle and radial rake angle. The direction of these two rake angles, i.e., positive (+), negative (-), or zero, is selected based on the material of the workpiece and the cutting conditions.

The structure of carbide face milling cutters can be divided into three types: integral brazed type, clamp-on brazed type, and indexable type.

Clamp-on brazed face milling cutters involve brazing carbide inserts onto small tool heads, which are then mechanically clamped into the tool body slots. When the tool head is worn out, it can be replaced with a new one, thus extending the service life of the tool body.

A commonly used indexable face milling cutter consists of the tool body, shim, clamping screw, insert, wedge, and eccentric pin, among other components. The shim is clamped onto the tool body by the wedge and clamping screw. Before tightening the clamping screw, the eccentric pin is rotated to adjust the axial runout of the axial support point of the shim within a certain range. The insert is placed on the shim and then clamped by the wedge and clamping screw. The eccentric pin also prevents excessive axial force on the shim during cutting, which could cause axial movement. After the cutting edge is worn, the insert can be indexed or replaced to continue use.

Main Structural Parameters

(1) Diameter and Number of Teeth

Diameter and number of teeth are the two main structural parameters of face milling cutters. To adapt to different cutting requirements, national standards specify that face milling cutters of the same diameter are divided into three types based on tooth count: coarse, medium, and fine. Taking a diameter of 100 mm as an example, the coarse, medium, and fine tooth counts are 5, 6, and 8 teeth respectively.

(2) Geometric Angles

The main geometric angles of indexable face milling cutters are the lead angle (κr), back rake angle (γp), and side rake angle (γf). The lead angle includes 45°, 60°, 75°, and 90°, with 75° being the most commonly used. A 90° lead angle should be selected for machining surfaces with shoulders or thin-walled workpieces.

The back rake angle (γp) and side rake angle (γf) can be combined into three types: positive rake angle type, negative rake angle type, and positive-negative rake angle type. The positive rake angle type is used for machining general materials; for example, when milling ordinary steel and cast iron, γp=7°, γf=0° are commonly used, and when milling aluminum alloy, γp=18°, γf=11° are commonly used. The negative rake angle type is used for machining cast steel and hard materials, commonly using γp=-7°, γf=-6°. The positive-negative rake angle type has good impact resistance and chip evacuation performance, is suitable for milling general steel and cast iron, and is often used on machining centers, with common values of γp=12°, γf=-8°.

Selection of Face Milling Cutters

The primary tool for machining flat workpieces is the face milling cutter, whose cutting edges are distributed around the circumference and end face. Among them, the cutting edges on the end face are the minor cutting edges. The diameter of face milling cutters is relatively large, so when selecting a tool, the blade and tool body are usually separated to achieve long-term use.

Selection of Diameter

The selection of face milling cutter diameter is mainly divided into three situations:

(1) When the surface area is not large, pay attention to selecting a tool or milling cutter with a diameter larger than the width of the surface when choosing the tool, so that single-pass face milling can be achieved. When the width of the face milling cutter reaches 1.3–1.6 times the width of the machined surface, it can effectively ensure good chip formation and evacuation.

(2) When machining large surface areas, it is necessary to select a milling cutter with an appropriate diameter and perform multiple passes to mill the surface. Among these, the diameter of the milling cutter is limited by machine tool constraints, depth and width of cut, and the size of the inserts and tool.

(3) When machining small surfaces or scattered workpieces, it is necessary to select end mills with smaller diameters for milling. To maximize machining efficiency, the milling cutter should have 2/3 of its diameter in contact with the workpiece, i.e., the milling cutter diameter should be 1.5 times the width of the cut. During climb milling, rational use of this ratio of tool diameter to cutting width will ensure that the milling cutter enters the workpiece at a very suitable angle. If it is uncertain whether the machine tool has sufficient power to maintain the milling cutter cutting at this ratio, the axial depth of cut can be completed in two or more passes to maintain the ratio of milling cutter diameter to cutting width as much as possible. [1]

Selection of Number of Milling Cutter Teeth

When selecting a milling cutter for machining, the number of teeth of the milling cutter needs to be considered. For example, a 100mm diameter coarse-tooth milling cutter has only 6 teeth, while a 100mm diameter fine-tooth milling cutter can have 8 teeth. The density of the teeth affects production efficiency and product quality. If the teeth are dense, production efficiency will be higher, and the quality of the machined workpiece will be better, but dense teeth can also lead to inconvenient chip evacuation. Based on the diameter size and tooth density, they can be divided into coarse-tooth, fine-tooth, and close-tooth.

Coarse teeth are used for rough machining of workpieces, with 1–1.5 inserts per 25.4mm diameter, and have a large chip pocket. This type of tool is used for cutting soft materials that produce continuous chips, using long inserts and large width of cut. Close teeth are beneficial for stable condition machining, generally used for rough machining of cast iron, and also suitable for shallow cuts, narrow cuts of high-temperature alloys, and when no chip pocket is needed. Fine teeth are used for finish milling, with an axial depth of cut of 0.25–0.64mm, small cutting load per tooth, and low power requirement, such as for machining thin-walled materials. The tooth pitch determines the number of teeth simultaneously engaged in cutting during milling. During cutting, at least one insert should be cutting to avoid milling impact, which can lead to tool damage and machine overload.

Furthermore, the selection of the number of inserts must allow chips to curl properly and easily leave the cutting area. Improper chip pocket space will cause chip jamming, damage the cutting edge, and possibly damage the workpiece. At the same time, the inserts should have sufficient density to ensure that at least one insert is cutting at any time during the cutting process. If this cannot be guaranteed, severe impact will occur, leading to cutting edge chipping, tool damage, and machine overload.

Selection of Tool Angles

The cutting angles of the tool can be positioned relative to the radial plane and axial plane as positive rake angle, negative rake angle, and zero rake angle. Since zero rake angle causes the entire cutting edge to impact the workpiece simultaneously, it is generally not used. The selection of face milling cutter angles affects the contact mode in face milling. To minimize tool impact, reduce tool breakage, and avoid face contact mode (like STUV), while considering the tool entry angle, the geometric angles of the face milling cutter should also be taken into account. The combination of radial and axial rake angles determines the cutting angle. Common basic combinations include: negative radial rake angle and negative axial rake angle; positive radial rake angle and positive axial rake angle; negative radial rake angle and positive axial rake angle; positive radial rake angle and negative axial rake angle.

Tools with both axial and radial rake angles negative (hereinafter referred to as "double negative") are mostly used for rough machining of cast iron and cast steel, but require high machine power and sufficient rigidity. The cutting edges of "double negative" inserts have high strength and can withstand heavy cutting loads. Tools with both angles negative also require high rigidity of the machine tool, workpiece, and fixture.

Tools with both axial and radial rake angles positive (hereinafter referred to as "double positive") have an increased cutting angle, resulting in light cutting and smooth chip evacuation, but the cutting edge strength is relatively poor. This combination is suitable for machining soft materials, stainless steel, heat-resistant steel, ordinary steel, and cast iron, etc. This combination should be preferred when using low-power machine tools, when the rigidity of the technological system is insufficient, and when built-up edge may occur.

The combination of negative radial rake angle and positive axial rake angle: the negative radial rake angle improves the strength of the cutting edge, while the positive axial rake angle generates a shearing force. This combination provides strong impact resistance during machining and a sharper cutting edge, making it suitable for heavy-duty milling of steel, cast steel, and cast iron.

The combination of positive radial rake angle and negative axial rake angle causes the chip to break below the center, causing the chip to scratch the machined surface, resulting in poor chip evacuation.

Selection of Milling Inserts

The choice of milling inserts for face milling is also a consideration. In some machining situations, selecting pressed inserts is more appropriate, while in other cases, ground inserts are necessary.

For rough machining, pressed inserts are preferably selected, as this can reduce machining costs. The dimensional accuracy and sharpness of pressed inserts are inferior to ground inserts, but the edge strength of pressed inserts is better, suitable for rough milling, impact resistance, and capable of with larger back engagement and feed rates. Pressed inserts have chip breaker grooves on the rake face, which can reduce cutting forces, as well as friction with the workpiece and chips, lowering power requirements. However, the surface of pressed inserts is not as tight as ground inserts, dimensional accuracy is poorer, and the height difference between cutting edges on the milling cutter body can be significant. Because pressed inserts are inexpensive, they are widely used in production.

For finish milling, it is best to choose ground inserts. This type of insert has better dimensional accuracy, so the positioning accuracy of the cutting edge during milling is higher, resulting in higher machining accuracy and lower surface roughness. Additionally, the development trend of ground milling inserts for finish machining is to grind chip breaker grooves, forming a large positive rake cutting edge, allowing the insert to cut with small feed rates and small depths of cut. Carbide inserts without a sharp rake angle, when used with small feed rates and small depths of cut, will cause the tool tip to rub against the workpiece, reducing tool life.