MECHENG352 - Process Planning Flashcards
Definition of process planning
“the systematic determination of the methods by
which a product is to be manufactured
economically and competitively”.
Two basic activities of process planning
- Two basic activities:
– Determination of a macro-plan based on machine tools
– Decomposition of the macro-plan into specific machining
operations related to a single tool use; this is called a
micro-plan
Input and output of manufacturing system
Input: Raw materials
Output: Products
Basic steps in developing a process plan
Part requirements
Raw workpiece
Macro: Manufacturing operations and sequences
Macro: Machine tools
Micro: Setup/Figure/Cutting tools
Micro: Machining conditions
Selection of raw material
Material: governed by the functional requirements of the part and cost
Shape: rod, slab, billet, or just a rough forging
Size: governed by the dimensional accuracy along with the form of the workpiece.
Considerations for manufacturing operations
- Part
– surface finish and tolerance requirements
– feature accessibility and workpiece setup
– workpiece structure, e.g. rigidity
– production volume - Machine tools and cutting tools
– availability
– capability
Factors in selecting machine tools
- Workpiece-related attributes
– Type of material and raw material form
– kind of machining features, dimensions, tolerance - Machine tool-related attributes
– mode of operation (e.g. manual, automatic or numerically
controlled)
– type of operation (e.g. turning, milling and grinding)
– tooling capabilities (e.g. size and type of the tool magazine)
– automatic tool-changing capabilities - Production volume-related information
– production quantity
– order frequency
What is machining setup and what does it normally involve:
- Machining set-up is a process of accurately locating and securing the workpiece on the machine tool using proper jigs & fixtures before machining processes commence.
- It normally involves,
– Positioning the workpiece on a machine bed (or chuck)
– Initial clamping-down
– Clocking the workpiece to make sure it is in the required orientation
– Final clamping-down
Setup planning decisions and selection criteria
Things to decide:
* Number of set-ups;
* Sequence of set-ups;
* Grouping of operations;
* Machining datum
Selection criteria:
* Part features and geometry
* Dimension/datum
* Tolerance requirements
Datum types
- Datum Types
– Functional/design/dimensional/tolerance datum
– Machining datum
– Inspection datum
– Assembly datum - All datum must be machined surfaces and/or
have a good surface finish
Purpose of drilling
Cut vertically to make a hole
Blind hole always have a conical bottom
Twist drills cannot be used for finishing or semi-finish operations following a roughing operation
Countersinking: when it is performed, how it enters workpiece
- Countersinking is often performed after
drilling to provide space for the head of a
fastener, such as a screw, to sit flush with
the workpiece surface. - A countersink tool enters the workpiece
axially and enlarges the top portion of an
existing hole to a cone-shaped opening.
Counterboring: when it is performed, what it does, what the pilot does
- Counterboring is often performed after
drilling to provide space for the head of
a fastener, such as a bolt, to sit below
the surface of a part. - A counterbore tool enlarges the top
portion of an existing hole to the
diameter of the tool. - The counterboring tool has a pilot on
the end to guide it straight into the
existing hole.
Face Milling: what it is, can it cut vertically, finishing cuts?
- A face mill machines a flat surface of the
workpiece in order to provide a smooth
finish - Multiple passes axially and sideways
- A face mill cutter is not to be used to cut
vertically - A face mill may be used for semi-finishing,
finishing as well as roughing operations
End / profile milling: how it cuts, features that can be machined, can it cut vertically?
- An end mill mainly uses its peripheral
teeth to cut sideways. - Common features that can be machined
are profile, open slot and open pocket. - Multiple passes axially and sideways
- An end mill cutter is not to be used to
cut vertically - An end mill may be used for semifinishing, finishing as well as roughing
operations
Slot Drilling: can it cut vertically, features that can be machined, finishing?
- A slot drill may cut both vertically and
sideways, though it is not
recommended to replace a twist drill
for hole-making operations - Features that can be machined:
(closed) slot, (closed) pocket - Multiple passes axially and sideways
- A slot drill may be used for semifinishing, finishing as well as roughing
operations
Chamfer millers: what it does, typical angle?
- A chamfer end mill makes a peripheral cut
along an edge of the workpiece or a
feature to create an angled surface, known
as a chamfer - This chamfer, typically with a 45 degree
angle, can be machined on either the
exterior or interior of a part and can follow
either a straight or curved path.
Boring: when it is commonly performed?
- A borer enters the workpiece axially and
cuts along an internal surface (by
profiling sometimes) to form different
features - The boring tool is a single-point cutting
tool, which can be set to cut the desired
diameter by using an adjustable boring
head - Boring is commonly performed after
drilling a hole in order to enlarge the
diameter or obtain more precise
dimensions
Reaming (finishing operation): when it is performed?
- A reamer always enters the workpiece
axially to enlarge an existing hole to the
diameter of the tool - Reaming removes a minimal amount of
material and is often performed after
drilling to obtain both a more accurate
diameter and a smoother internal finish - Material allowance
– < 0.2 mm for soft materials
– < 0.13 mm for hard materials
Tapping
- A tap enters the workpiece axially and
cuts internal threads into an existing
hole - The existing hole is typically drilled by
the required tap drill size that will
accommodate the desired tap - Roll form tapping
Vc, Vf, ap, ae
Milling: vc
vc (v) – cutting speed
vf (fm) – feed rate
ap – depth of cut (cut depth)
(step depth)
ae – width of cut (step over)
Calculation of material removal rate
Material Removal Rate = vf ×ap × ae
Tool wear evolution
- Three regions of tool wear
evolution
– Region I – Primary or initial
wear
– Region II – Steady-state
wear
– Region III – Tertiary or
accelerated wear - VB = 0.10-1.00 mm
KB and VB meanings
Crater wear (KB)
Flank wear (VB)
With fixed VB = how does cutting speed affect tool life
- The higher the cutting speed (v1 > v2
> v3) – the higher the wearing rate
– the shorter the tool life (T1<T2<T3)
vTn = C : name the terms
v – cutting speed (m/min)
T – tool life (min) (related to VB)
n – an exponent depending on other cutting parameters
C – constant
Order of importance of terms in extended taylors formula
v => vf => ap
2 types of tool wear
Flank wear (VB)
Crater wear (KB)
Selecting values in extended taylor formula
Select biggest Ap possible, then select biggest v_f possible, then calculate v based on chosen vf and ap. This is while T is fixed.
Machining models
Maximum Production Rate Model
Minimum Cost Model
MaximumProduction Rate Model:
Tu= nonproductive time per piece (t1)
+ machining time per piece (tc)
+ tool changing time per piece (tt)
Minimum Cost Model:
Cu=nonproductive cost per piece
+ machining time cost per piece
+ tool changing cost per piece
+ tooling cost per piece
Generative Process Planning
It is a knowledge-based CAPP system
Knowledge database + Inference engine (if-then)
How to represent knowldge and do inferencing
Basic constrol constructs:
- sequence structure
- selection structure
- iteration structure
Advanced control construct
- Flowcharts
- Decision tables
- Decision trees
- Decision criteria
