sean dalton [email protected]
TRANSCRIPT
IntroductionIntroduction
Computer 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.
Machining stragegiesMachining stragegies
Graphical simulation is available to allow the user to verify the toolpath before cutting material.
Powermill has a number of machining strategies which include:- Area clearance- Finish maching- Detail maching
Efficient use of these tools will enable the user to achieve the best possible finish in the shortest possible.
ToolsTools
A 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 mill- Slot drill- End mill- Ball nose
Powermill interfacePowermill interface
Powermill interfacePowermill interface
The left hand icons represent the viewing options available and are subdivided into:
- Orthogonal views- Isometric views- Interactive zoom commands.
Dynamics zoom feature include- Ctrl + mouse = Dynamic zoom- Shift + mouse = Dynamic pan- Ctrl + shift + mouse = Dynamic rotate
The right hand menu is where all the created be the user is stored.
Powermill interfacePowermill interface
The 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 links- Define tool axis- Area Clearance- Finishing- Drilling- Collision checking - Simulation
Define block size:Define 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.
Set feed rates:Set feed rates:
Feed rates determine - Rapid speed: the feedrate during non cutting moves
- Plunge speed: the feedrate while cutting vertically
- Cutting speed: the feedrate while moving horizontally throught the material
- Spindle speed: the speed at which the cutter rotates.
Set start point, and heights:Set start point, and heights:
Start from: defines the location the cutter goes to before and after each machining activity
Rapid move heigths define the heights above the workpiece at which it is safe to move rapidly- Safz is the heigth above the
workpiece where all move can be ‘Rapid’
- Startz is the height to which it is safe to plunge downwards.
Define leads and links:Define 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.
Define tool axis:Define tool axis:
This is used to set the direction of the tool axis which using either:- 5 axis positioning- Continuous 5 axis machining- (see video)
We will concentrate on 3 axis machining only.
Tool definition:Tool 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.
Area Clearance:Area 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
Area Clearance Z levels:Area Clearance Z levels:
This section define levels at which raster machining is performed in doing area clearance.
These can be defined by - Number: Subdivides the total depth in to a prefined number of Z levels
- Stepdown: Steps down by a specified amount each time and complete
Area Clearance toolpath:Area Clearance toolpath:
General machining options include:
- Raster or profile: default is raster
- Stepover: Distance between parallel cuts
- Tolerance: - 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.
Finishing:Finishing:
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.
Finishing stragegiesFinishing stragegies
A wide variety of strategies are available, most important are:
- Raster- Constant Z- Pencil etc.
Raster ParametersRaster Parameters
The main parameter for raster machining are:
- Tool: Selecting from list already created.
- Tolerance: determines how closely machining moves adhere to the part geometry
- Thickness: 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 axis
Image shows vertical move at end of each pass.
Leads and links:Leads 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.
Leads and links optionsLeads and links options
Controls how each successive tool path is joined the next.
- SafeZ: tool retracts to the SafeZ after each cut
- Skim: 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.
Rest machiningRest machining
A 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.
Collision checking:Collision checking:
Collision checking is a facility which enable powermill to check for potential collision between cutter holder between work piece or clamps.
Simulation:Simulation:
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 clearance
- Block following finishing.
Machining/Cusp tolerance:Machining/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.