Producing Shapes Flashcards
What are the 3 types of basic milling?
Slab milling
Face milling
End milling
For up milling, what does the smoothness of a generated surface depend on?
The sharpness of the cutting edges
What’s broaching used for?
To machine internal and external surfaces i.e. holes (circular or irregular) or keyways
Describe the process of face/end milling
The cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface
For up milling, what factors contribute to a poor surface finish?
Slide-Cut mechanism results in poor surface finish
Chips can also be carried onto the newly machined surface contributing to a poorer (rougher) surface finish
Describe backlash
Backlash refers to the “play” or excessive amount of clearance between the machine hand wheel screw and the nut attached to the machine table or slide
Name the processes used to produce shaped parts
Milling Planing Shaping Broaching Sawing
For slab milling, what is the equation for the allowances for approach?
La = ((D^2)/4 - (D/2 - dc)^2)^(1/2)
La = allowances for approach, D = Diameter of cutting tool, dc = depth of cut
For up milling, what are the drawbacks of the sliding mechanism?
Sliding action causes work hardening on the material and can dull the cutting edges
For an end mill cutting steel, what should the depth of cut be?
No more than 1 half of the diameter of the tool
Describe the broach tool
Has multiple teeth, with each tooth standing slightly higher than the previous tooth
Uses a single pass to machine the workpiece
The feed per tooth is the change in height of two successive teeth called rise per tooth (RPT)
Has cutting teeth (made up of roughening teeth and semi-finishing teeth) and finishing teeth
Describe shaping
Cutting tool moves across fixed workpiece in one direction
Used to produce parts much like planing but the parts are much smaller
What is the feed of the table (fm) related to and what are its units?
Related to the amount of metal each tool removes per minute
inches per min
What is the main downside to down milling?
Backlash
What are the methods of producing surfaces for milling (i.e. not categories of milling)?
Up milling (conventional milling) Down milling
What can a metalworking planer produce?
Accurate, flat surfaces
Various cross-sections with grooves and notches along the length of the workpiece
What are the 2 construction options for planing machines?
Double-housing planer
Open side planer
Describe sawing
Cutting operation with a blade consisting of many small teeth
Each tooth removes a small amount of material
Unlike broaching uses many passes to finish machining
For all milling processes, what is the equation for cutting speed?
Ns = Vc / (pi*D)
Ns = Cutting speed, Vc = Cutting Velocity, D = Diameter of cutting tool
Describe the process of down milling
The cutter rotation is in the same direction as the feed rate
Chips decrease in thickness as the tooth rotates through the workpiece
Teeth engage at a specific point where the depth of cut is at maximum
No slide-cut mechanism so tool life is longer BUT increased load on tooling and machine
Chips are carried away from the cutting surface so cannot impair surface finish
The cutter pulls a workpiece towards itself and pushes the workpiece down onto the table
Cutting force tends to hold workpiece against machining table so lower clamping force is sufficient
What is the most common type of construction for a milling machine?
Column-knee construction
For face/end milling, what’s the overrun equal to?
When W < D/2:
Lo = La = (W(D-w))^(1/2)
WhenW >= D/2
Lo = La = D/2
For slab milling, what is the equation for cutting time (t)?
t = (L + La) / fm
t = cutting time, L = length of cut, La = allowance for approach, fm = feed of the table
What’s the general equation for material removal rate (MRR)?
MRR = Removed volume / Cutting time
Describe the process of up milling
The cutter rotates against the feed direction of the workpiece
Chips increase in thickness as the tooth rotates through the workpiece
Depth of cut starts at zero and increases
Tooth initially slides along the surface until the pressure on the material is enough to start cutting
The cutter pushes the workpiece away and lifts it from the table (tends to loosen the workpiece from a holding device, a higher clamping force is required)
For all milling processes, what’s the equation for material removal rate (MRR)?
Removed volume = L x W x dc
Therefore
MRR = W x fm x dc
L = length of cut, W = width of cut, dc = depth of cut, fm = feed of table
What’s an advantage of planing and shaping?
Cheap, compared to milling and grinding
For face/end milling, what’s the equation for cutting time (t)?
t = (L +La +Lo) / fm
L= Length of cut, La = Allowance for approach, Lo = Overrun, fm = feed of the table
How are the depth of teeth, land behind cutting edge and the radius of the gullet related to pitch?
Depth of teeth: D = 0.4P
Land behind cutting edge: L = 0.25P
Radius of gullet: R = 0.25P
What is the depth of cut equal to for broaching?
The sum of RPT
Describe the process of peripheral/slab milling
The axis of cutter rotation is parallel to the machining surface of the workpiece
For all milling processes, what is the equation for the feed of the table (fm)?
fm = ft x n x Ns
fm = feed of the table, ft = feed per tooth, n = number of teeth, Ns = Cutting speed
What are planing and shaping often used for?
To produce large dies and other tooling
For broaching, define the pitch
The distance between 2 successive teeth
