Editing Computer-aided manufacturing (section)

== Machining process ==
Most machining progresses through many stages,<ref>[http://www.cnccookbook.com/CCCAMToolpaths.htm CAM Toolpath Strategies]. CNC Cookbook. Retrieved on 2012-01-17.</ref> each of which is implemented by a variety of basic and sophisticated strategies, depending on the part design, material, and software available.
;Roughing
: This process usually begins with raw stock, known as [[Billet (manufacturing)|billet]], or a rough casting which a CNC machine cuts roughly to shape of the final model, ignoring the fine details.  In milling, the result often gives the appearance of [[Terrace (agriculture)|terraces]] or steps, because the strategy has taken multiple "steps" down the part as it removes material. This takes the best advantage of the machine's ability by cutting material horizontally.  Common strategies are zig-zag clearing, offset clearing, plunge roughing, rest-roughing, and trochoidal milling (adaptive clearing). The goal at this stage is to remove the most material in the least time, without much concern for overall dimensional accuracy. When roughing a part, a small amount of extra material is purposely left behind to be removed in subsequent finishing operation(s).

;Semi-finishing

: This process begins with a roughed part that unevenly approximates the model and cuts to within a fixed offset distance from the model.  The semi-finishing pass must leave a small amount of material (called the scallop) so the tool can cut accurately, but not so little that the tool and material deflect away from the cutting surfaces.<ref>{{cite journal |last1=Agrawal |first1=Rajneesh Kumar |last2=Pratihar |first2=D.K. |last3=Roy Choudhury |first3=A. |title=Optimization of CNC isoscallop free form surface machining using a genetic algorithm |journal=International Journal of Machine Tools and Manufacture |date=June 2006 |volume=46 |issue=7–8 |pages=811–819 |doi=10.1016/j.ijmachtools.2005.07.028 }}</ref>  Common strategies are [[raster passes]], waterline passes, constant step-over passes, [[pencil milling]].

;Finishing
: Finishing involves many light passes across the material in fine steps to produce the finished part. When finishing a part, the steps between passes is minimal to prevent tool deflection and material spring back. In order to reduce the lateral tool load, tool engagement is reduced, while feed rates and spindle speeds are generally increased in order to maintain a target surface speed (SFM). A light chip load at high feed and RPM is often referred to as High Speed Machining (HSM), and can provide quick machining times with high quality results.<ref>{{Cite journal|last=Pasko|first=Rafal|date=1999<!--or later-->|title=HIGH SPEED MACHINING (HSM) – THE EFFECTIVE WAY OF MODERN CUTTING|url=http://fstroj.utc.sk/journal/engl/papers/034_2002.pdf|journal=International Workshop CA Systems and Technologies|access-date=2018-06-02|archive-date=2018-11-23|archive-url=https://web.archive.org/web/20181123175123/http://fstroj.utc.sk/journal/engl/papers/034_2002.pdf|url-status=dead}}</ref> The result of these lighter passes is a highly accurate part, with a  uniformly high [[surface finish]]. In addition to modifying speeds and feeds, machinists will often have finishing specific endmills, which never used as roughing endmills. This is done to protect the endmill from developing chips and flaws in the cutting surface, which would leave streaks and blemishes on the final part.

;Contour milling
: In milling applications on hardware with rotary table and/or rotary head axes, a separate finishing process called contouring can be performed.  Instead of stepping down in fine-grained increments to approximate a surface, the work piece or tool is rotated to make the cutting surfaces of the tool tangent to the ideal part features.  This produces an excellent surface finish with high dimensional accuracy. This process is commonly used to machine complex organic shapes such as turbine and impeller blades, which due to their complex curves and overlapping geometry, are impossible to machine with only three axis machines.<ref>{{cite journal |last1=Gomes |first1=Jefferson de Oliveira |last2=Almeida Jr |first2=Adelson Ribeiro de |last3=Silva |first3=Alex Sandro de Araújo |last4=Souza |first4=Guilherme Oliveira de |last5=Nunes |first5=Acson Machado |title=Evaluation of 5-axis HSC dynamic behavior when milling TiAl6V4 blades |journal=Journal of the Brazilian Society of Mechanical Sciences and Engineering |date=September 2010 |volume=32 |issue=3 |pages=208–217 |doi=10.1590/S1678-58782010000300003 |doi-access=free }}</ref>