Face milling is generally the first machining process with a material billet in a milling machine. It serves to prepare the material for the follow-on processes by creating flat surfaces on the workpiece.
There are several approaches to face milling that offer particular benefits and advantages, so this article is presented to you as a primer in this important but little discussed operation, offering practical tips and methods that can help ensure a successful first stage machining operation.
Face milling is the first stage of machining a billet or workpiece. It is used for flattening and smoothing the upper and side surfaces of the work. The main characteristic of this process is that the machine axis or spindle is perpendicular to the workpiece.
The face milling process can be manual or automatic – and it can be the first part of an integrated CNC program or tool path that completes the entire machining.
The advantage of a CNC programmed face milling operation is consistency in tool movements and precise multi-axis feeds, resulting in faster processing, more uniform and potentially more aggressive cutting and significantly better surface finish
Face milling uses a variety of high speed steel and carbide insert cutting tools, including end mills, shell mills, and fly cutters. The tool rotates generally clockwise (viewed from above) and the machine feeds the workpiece across the tool face, peripheral cutting for most of the motion.
What is Face Milling?
Face milling is a machining process used for preparing large, flat surfaces on a workpiece. This can be preparatory, in perfecting the squaring of a material billet that is to be the subject of extensive machining, or it can be a finishing operation to render a mating or seal surface perfectly flat and perpendicular, ready for assembly/fitting.
The process generally uses a larger diameter cutting tool with multiple teeth, removing material from one or more faces of a workpiece to create a flat surface.
In most milling operations, the cutting tool rotates on a vertical axis perpendicular to the workpiece, and each tooth on the tool removes a small amount of material as it passes over the workpiece.
This can be via end-milling, using the end face cutting surfaces of an end mill, or it can involve tool side face cutting using a slot milling tool or side cutter.
In some cases, face milling will be performed on a horizontal axis milling machine. At times, this can use a long axis tool as a side cutter, making a whole face cut in a single pass.
Face milling is used to flatten faces on all mill-cut materials, including metals, plastics, composites and even wood.
What is the Process of Face Milling?
- Cutting speed and feed rate must be chosen based on the material being machined and the cutting tool being used – there is a recommended range of linear velocity/cut depth/feed rate for tip types cutting selected materials. Excessive cutter speed, cut depth and feed rates will accelerate tool wear and deliver poor surface finish. Insufficient feed rate can cause the cutter tips to chip or break.
- The cutters must be aligned with the workpiece to ensure even cutting across the whole surface. Misalignment can result in uneven cutting, poor surface finish, and premature tool wear.
- Removal of cuttings (chip evacuation) is particularly critical in face milling a horizontal surface. Chips left in the path of the cutter can cause tool damage and poor surface finish, by getting dragged into the next cut pass. Cuttings must be flushed away by sufficient coolant flow, to keep the tool path clear.
- Good machine setup is critical, in achieving accurate and consistent results. Ensure that the machine is level, the workpiece is securely clamped, and the cutting tool is properly mounted.
- Good observation of cutting conditions avoids problems. Look at the surface finish to understand tool wear or chip buildup. Inspection and adjustment will deliver better results.
Choosing the Ideal Cutting Tool for Face Milling
Choosing an appropriate cutter for face milling is based on several factors; the material to be machined; the surface quality required; and the capabilities of the machine being used.
- The material to be machined has a significant influence on cutter selection. Hard materials like stainless steel, titanium and high Carbon or hardened steels require carbide cutters. More free cutting materials such as aAluminum and brass can be cut with high speed steel cutters, though insert cutters will give good results on these materials.
- The surface finish desired from the face milling operation can also influence the type of cutter needed. For roughing operations, a cutter with more teeth and a roughing-appropriate geometry will allow faster processing. Conversely, for finishing operations and better surface finish, fewer teeth and a sharper cutting edge is more effective, despite the need for lower feed rates and shallower cuts.
- Machine power and maximum spindle speed will affect cutter selection. More powerful and faster spindle machines can often handle larger cutters and a higher tooth count.
- The diameter of the cutter can be selected based on the width of the surface being machined, for faster processing. A larger cutter will allow material to be removed faster, but a smaller diameter cutter often results in a smoother surface finish.
- The insert geometry, particularly the rake and clearance ang;es, must be selected to suit the material to be machined and the target surface finish. There is a compromise to be struck between a positive rake angle – which reduces cutting forces and improves surface finish – and a negative rake angle – which improves tool life in harder materials.
Tips for Choosing the Right Tool
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Four Types of Face Milling Operations
It is commonly used in manufacturing processes such as the production of engine blocks, gearboxes, and other machine components that require a flat surface for proper functionality.
Face milling can also be used to create a finished surface on a workpiece or to remove material in preparation for additional machining processes.
Four types of face milling operational method are commonly used, to suit the work:
- In plain milling, the cutting tool passes over the surface of the workpiece in a straight line across the face of the cutter, cutting at the circumference only. This results in a flat surface with visible parallel lines as telltales of the tool edge, generally referred to as witness marks.
- Side milling passes the cutting tool at an angle to the workpiece surface, using the side flutes of a slot drill/side cutter to perform the cut. This is used to create chamfers or bevels.
- End milling is in essence the same as plain milling, but the cutting tips are on the end of the tool and cuts can be a combination of plunge and side cutting. This produces a flat surface perpendicular to the workpiece surface and also results in linear witness marks from traverse cutting and circular witness marks from plunge cutting.
- In circular milling, the toolpath is either overlapping circular motion or a spiral. This method is best suited to cutting circular flats and leaves characteristic witness marks in concentric rings or spirals. Concentric cuts leave start/stop point tool diameter circular witness marks at the start/finish of each loop.
Face Milling vs. Peripheral Milling: What’s the Difference?
Face milling and peripheral milling are the two basic modes of cutter interaction with the workpiece. They differ in the orientation of the cutting tool, relative to the work.
- In face milling, the cuter tool is oriented perpendicular to the surface it is applied to and removes material from. The cutting tool applied in face milling has cutting faces/inserts at its periphery that wrap around onto the end face. This allows it to remove material in both axial (plunge cut) and radial (side cutter) modes.
- Peripheral milling (also known as conventional milling) the cutting tool axis is oriented parallel to the surface it is addressing. In a horizontal axis machine, this mode cuts across the upper surface. In a more common vertical axis machine, the cutter addresses the sides of the workpiece. In this mode, the cutting tool is used in a peripheral or circumferential milling mode and it removes material with the cutting flutes running spiral around the tool axis.
Face milling is generally used to create flat surfaces or to remove large amounts of material from the upper surface of a workpiece. Peripheral milling is primarily used for more precise operations such as contouring and slotting.
Face milling is better adapted to removing large amounts of material quickly, while peripheral milling is used for precise operations and can produce more uniform and regular surface finish.
Practical Tips to Optimize Face Milling Processes
Optimization of face milling operations is necessary for high quality outcomes at fast throughput:
- Select a cutter that is appropriate for the material to be processed, the surface finish requirement and the milling machine doing the work. Cutting tips with sharp edges, fewer teeth and positive rake angle is better suited to finishing operations.
- Cutting parameters such as spindle speed, feed rate and cut depth must be optimized. Higher spindle speeds and feed rates will increase throughput, at some cost to quality. Overly aggressive parameters can result in low quality, loss of precision, poor surface finish and excessive tool wear.
- Vibration will badly affect surface finish and reduced tool life, even causing tip breakage. Effective tool clamping and good machine/workpiece rigidity will help minimize vibrations, improving surface quality by reducing chatter.
- Appropriate coolant will reduce heat buildup during cutting and prevent chip build-up on the cutting tool. Effective cooling and cuttings removal greatly improves tool life and surface finish.
Kemal’s Custom Milling Services
The Kemal team has vast experience in providing complex, high quality and cost effective custom milling services. Our in-house 3 and 4 axis machining centers offer a service that fits 80 to 90% of jobs that our clients present – and our specialist 6+ axis partner companies complete our service provision.
You will see one supplier, one QA process and a seamless delivery of services – and we are able to access the specialist experience that these aspects of your project requires.
We will be pleased to hear from you and delighted to investigate how our services can give you the outcomes you need – fast, reliable and cost effective quality defines our services.
This article covers the basics of milling setup for face and peripheral milling. For deeper study you may wish to read more here and here, or you may prefer to contact us to discuss your needs.