Arbor milling
Process Characteristics
Cuts surfaces parallel to rotational axis of the tool unlike Drilling(Perpendicular to Axis)
Multipoint cutter creates discontinuous chips
Capable of producing flat, shaped, or contoured surfaces on workpiece
Cutters supported on an arbor (mandrel)
High metal removal rate
Sweeps chipped material away as it works
Process Schematic
This process Progressively makes a surface to your specifications as the material is moved against the milling tool or the workpiece stays stationary while the arbor milling cutter moves across it to provide desired shape. There are two types of milling that involve the directional movement of the workpiece, Conventional and Climb. If the workpiece is moving the opposite direction of the Tool rotation this is called Conventional Milling. If the workpiece is moving the same direction as the tool rotation, this is called Climb Milling.
Setup and Equipment
Arbor milling is commonly performed on a horizontal milling machine. The tool is mounted on an arbor/Mandrel (like an axle) that is suspended between the spindle and arbor support. This type of machine allows the tool to be placed in numerous positions in relation to the workpiece.
Workpiece Materials
The workpiece involved in arbor milling can be a flat material or a shaped material, either one can be worked with desirable results. The hardness of the materials milled should be no harder than Rockwell C25(Rockwell scale), but workpieces harder than this can be successfully milled. Materials with good or excellent machinability include aluminum, brass, mild steel, cast iron, and thermoset plastics. Though initially ductile, stainless steel tends to work harden and thus has only a fair compatibility with this milling process (though it is in the feasible range).
Tooling Materials
Although high speed tool steel has been used in the past it is quickly being replaced by carbide, ceramic, or diamond tooling. Because carbide inserts are long lasting and easily replaced, they lend themselves to high production. Ceramic tools are brittle but can withstand high temperatures. This makes high speed machining possible. Diamond tools are used to achieve a superior surface finish (though they are used for non-ferrous and non-metallic materials.
Tolerances and Surface Finish
In most applications, tolerances can be held within +-0.005 in. For precision application, tolerances can be held within +-0.001 in. It is possible to have a surface finish range of 32 to 500 microinches, but typically the range is 63 to 200 microinches. Finish cuts will generate surfaces near 32 to 63 micro inches, roughing cuts near 200 microinches.
Tool Styles and Possibilities
Arbor Milling Possibilities
The most common tool styles used in arbor milling are: double angle, form relived, plane, and staggered tooth Among many other tool styles. The double angle milling cutter can make a wide variety of V shaped cuts with straight surfaces in the material. A form relieved milling cutter can produce U shaped cuts with curved surfaces, unlike the double angle cutter, into the material. A plane milling cutter can produce surfaces similar to a planer but can make make varying contours across the material. A staggered tooth milling cutter can produce a rectangular groove in the material at varying depths and widths. some of these can be combined together to make specific shapes. The typical width of cuts made by arbor milling range from .25 in. to 6 in, ant the typical depths range from .02 in. to .05 in.See Also Milling cutter
Effects on Work Material Properties
Mechanical properties of the workpiece may be affected with a built-up edge or dull tool. Arbor Milling can create an untempered martensitic layer on the surface of heat-treated alloy steels, about 0.001 in. thick. Other materials are effected very little by arbor milling.
Process Conditions
Shown are the suggested ranges for cutting speeds and feed rates using high speed tool steel under dry cutting conditions at a 0.015 in. depth of cut. Generally cutting speeds are lower for hard materials, higher for soft materials. Both cutting speeds and feed rates can be substantially increased when coolants are used and carbide tooling is substituted for steel tooling. Typical Speeds and Feeds
Workpiece Material
Hardness (Hardness Brinell scale)
Cutting Speed (sfpm)
Feed Rate (ipt)
Aluminum
70 to 125
300 to 500
0.006 to 0.010
Brass
60 to 100
110 to 275
0.007 to 0.009
Cast Iron
250 to 320
30 to 55
0.005 to 0.006
Mild Steel
275 to 325
60 to 80
0.006
Stainless Steel
275 to 325
40 to 55
0.006
Plastics
…
150 to 350
0.006
Lubrication and Cooling
Due to high cutting speeds a cutting fluid is required to lubricate and cool the tool and workpiece. The fluids can increase tool life, cutting speeds, and the quality of the finished surface. There are three common cutting fluids: mineral, synthetic, and water-soluble oils. These fluids can be applied by spraying, misting, or flooding the workpiece.
Fluids and Applications
Workpeice
Cutting Fluid
Application method
Aluminum
None, mineral oil, fatty oil
Spray, flood
Brass
Mineral oil, specialty fluid
Spray, flood
Cast Iron
Soluble oil, chemical and synthetic oil, none
Spray, flood
Mild Steel
Chemical and synthetic oil, soluble oil
Spray, flood
Stainless Steel
Sulferized mineral oil, fally soluble oil, chemical and synthetic oil
Spray, flood
Plastics
Mineral oil, soluble oil, cold air, none
Spray, flood, air jet
Production Cost Elements
Things that contribute to the cost of production are setup, load/unload, idle, and cutting time. Also tool, labor, overhead, and equipment costs contribute to production costs.
Time Calculations
The actual milling time can be calculated if these elements are known: diameter of cutting tool, overtravel, approach distance, length of workpiece, depth of cut, feed rate, rapid traverse rate and rapid traverse distance.
Formulas
Milling Time = L/F
Traverse Time = T/Tr
rpm = (4*V)/D
Feed Rate = f*N*rpm
Diameter of cutter (in.) = D
Depth of cut (in.) = d
Length of workpeice (in.) = W
Length of cut (in.) = L
Rapid traverse distance (in.) = T
Rapid traverse rate (in.) = Tr
Number of teeth in cutter = N
Cutter feed rate (ipm) = F
Cutting speed (sfpm) = V
Feed per tooth = f
Approach distance (in.) = A
Overtravel = O
rpm = revolutions per minute
Safety
Certain risks to operators personal health are produced during the process of arbor milling that should be taken into consideration when choosing and using this process. Safety hazards that exist are:
A sharp rotating tool
Hot and or very sharp material chips from milling process
Fluids used in cooling or other processes during cutting can cause skin irritation and if not removed may cause health risks for consumers.
Notes
^ Todd, Robert H., Dell K. Allen, and Leo Alting. Manufacturing Processes Reference Guide. New York: Industrial Press Inc.1994.Pg 7.
^ a b Todd, p.10
^ a b Todd, p.11
References
Todd, Robert H., Dell K. Allen, and Leo Alting. Manufacturing Processes Reference Guide. New York: Industrial Press Inc.1994.ISBN 0-8311-3049-0
Information borrowed liberally from “Manufacturing Processes Reference Guide”, Industrial Press Inc. 1994 with the permission of Dr. Dell K. Allen
http://class.et.byu.edu/mfg130/processes/descriptions/mechanicalreduction/arbormilling.htm
See also
Milling machine
Metalworking
Milling cutter
Machining
Categories: Machine tools
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