2IntroductionComputer Aided Manufacture is the name given to the process of generating cutter paths to Computer Numerical Control (CNC) machine tools to facilitate the manufacture of component directly from CAD models.The predominant machine is the CNC Milling machine as it the most versatile shape generating tool available.Specialist facilities are also available such, multiaxis machining, high speed and Nurbs machining are also available.
3Machining stragegiesGraphical simulation is available to allow the user to verify the toolpath before cutting material.Powermill has a number of machining strategies which include:Area clearanceFinish machingDetail machingEfficient use of these tools will enable the user to achieve the best possible finish in the shortest possible.
4ToolsA tool library is enables the user to define the tools he/she require to complete a job.A variety of tools are available, these include:Slab millSlot drillEnd millBall nose
6Powermill interfaceThe left hand icons represent the viewing options available and are subdivided into:Orthogonal viewsIsometric viewsInteractive zoom commands.Dynamics zoom feature includeCtrl + mouse = Dynamic zoomShift + mouse = Dynamic panCtrl + shift + mouse = Dynamic rotateThe right hand menu is where all the created be the user is stored.
7Powermill interfaceThe row of icons across the top respresents the approximate working sequence followed by the user. In summary, this is as follows:Define block size:Set feed rates:Set rapid heights and start points:Define leads and linksDefine tool axisArea ClearanceFinishingDrillingCollision checkingSimulation
8Define block size:The block size function allows the user the enter the physical size from which the part will be machined.This may be calculate automatically from the physical size of the CAD model.
9Set feed rates: Feed rates determine Rapid speed: the feedrate during non cutting movesPlunge speed: the feedrate while cutting verticallyCutting speed: the feedrate while moving horizontally throught the materialSpindle speed: the speed at which the cutter rotates.
10Set start point, and heights: Start from: defines the location the cutter goes to before and after each machining activityRapid move heigths define the heights above the workpiece at which it is safe to move rapidlySafz is the heigth above the workpiece where all move can be ‘Rapid’Startz is the height to which it is safe to plunge downwards.
11Define leads and links: Lead and links define how each cutter path movement is connected to the next.If defined correctly these can help to minimise wear on a machine by making direction changes as smooth as possible.
12Define tool axis:This is used to set the direction of the tool axis which using either:5 axis positioningContinuous 5 axis machining(see video)We will concentrate on 3 axis machining only.
13Tool definition:Before machining can take place tools must be defined.To define tools Select: Tools, Create, tool type etc.Follow tool create they can be activated and modified on to left hand feature manager.
14Area Clearance:Enable bulk material remove within a predefined allowance of the part geometry.Usually done by raster machining a predefined Z levels.Z levels defined using
15Area Clearance Z levels: This section define levels at which raster machining is performed in doing area clearance.These can be defined byNumber: Subdivides the total depth in to a prefined number of Z levelsStepdown: Steps down by a specified amount each time and complete
16Area Clearance toolpath: General machining options include:Raster or profile: default is rasterStepover: Distance between parallel cutsTolerance:Thickness: the amount of excess material left on.Select [apply] to generate the cutter paths.Finally choose [accept]This will result in a toolpath item being added to the toolpaths list.
17Finishing:After bulk material removal has taken place, finish machining is then carried out, first using a large cutter then a smaller cutter and so on.Finish machining is generally carried out using a ball nose cutter.
18Finishing stragegiesA wide variety of strategies are available, most important are:RasterConstant ZPencil etc.
19Raster Parameters The main parameter for raster machining are: Tool: Selecting from list already created.Tolerance: determines how closely machining moves adhere to the part geometryThickness: How much material is left on if any.Stepover: distance between parallel cuts (this can be calculated automatically base on the tolerance)Angle: Angle of the cut direction to the X axisImage shows vertical move at end of each pass.
20Leads and links:The previous slide shows inefficient vertical moves at the end of each pass.This can be fixeb by modifying the links.Select the icon on the finishing form and set all to skim.Shown opposite is an more efficient tool paths.
21Leads and links options Controls how each successive tool path is joined the next.SafeZ: tool retracts to the SafeZ after each cutSkim: tools retracts slightly before decending to commence next cut.Stepdown: Tool moves horizontally then decends.On surface: tool maintains contact with surface.Arc: Tool moves in an arc to minimise wear on machine during high speed machining.Toolpath properties can be modified after creation by selecting the cutter pather and the appropriate icon.
22Rest machiningA number of machining strategies are available while enable selective machining of regions which were inaccessible to a previous larger cutter.By defining the current tool and the previous (refernce tool) the software determines all locations were additional material can be removed.
23Collision checking:Collision checking is a facility which enable powermill to check for potential collision between cutter holder between work piece or clamps.
24Simulation:Powermill is equipped with a graphical simulation called viewmill.Simulation allows the user to perform a visual inspection of the machining process to check for errors before cutting metal.Images show.Block following area clearanceBlock following finishing.
25Machining/Cusp tolerance: Tolerances control the accuracy of machining.Machining tolerance: all machining is performed using straight line moves. This tolerance controls the number of stright line move necessary to keep with a specified distanc of the true surface.Cusp tolerance: A ball nose cutter leaves ‘ploughed field effect’. Cusp height controls the peak to vally height. Stepover can be set manually or can be calculated to achieve a specific cusp height.