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Cutoff and grinding
Bob Johnson
Copyright © 2019 Investment Casting Institute. This presentation is protected by US and International copyright laws. Reproduction and distribution of the presentation without written permission of the Investment Casting Institute is prohibited.
Necessary evils of castings
• With some very limited exceptions all
castings require separation from the
gating and runner system.
– Counter gravity casting can evacuate the
runner after part solidification
– Not all parts lend themselves to this
process
Cutoff
• Most times we think of a saw first.
• Band saws
– Vertical
– Horizontal
– Conventional
• Dry or with coolant
– High speed
• Friction saw blade
Cutoff
• Abrasive cutoff (silicon carbide) is also
a consideration
• Material types will drive the selection
– Aluminum and mild steels
• Most often conventional band saw
– Tougher steels
• Friction saw
• Abrasives
– Nickel and cobalt based
• Abrasives
Large parts and tough alloys
• Parts that are too big to take to the
blade call for:
– Special saws (hand held devices or large
automated systems)
– Plasma cutting
• Tough alloys
– Plasma
– Waterjet
Workplace environmental
• Noise
• Dust / particles
• Heat
• Weights
• Location
– Usually close to casting operation
Management
• Management is 100% responsible to
assure the success of the cutoff
operation.
– Clear instructions
– Systematic approach
• Large gains achieved by cooperative efforts
• Gating system designed to facilitate
cutoff success
Operator issues
• Instructions understood?
– How/where to start cutting
• Where does the part stop/start
– Which equipment type
• Conventional/specialty
– Sub-cutting
• Multiple cuts to allow best access to part
Cut with care
• Cutting is faster than grinding
• Operators have a tendency to close-cut
to save grind time.
• Nicking and cutting into the parts can
result
• Time saved can result in rework or
parts being scrapped
Are we done yet???
• Part and process design may allow
skipping of post-cutoff grinding
– Gates can sometimes be placed where the
subsequent process steps will remove the
remnants
– Some materials are crack-sensitive and do
not tolerate cutoff and grinding stresses
• Cold working via CNC machining can
eliminate NDT rejects due to grind cracks
Gate grinding
• NDT grade castings generally require
higher gate material mass ratios
• Larger gates = longer grind times
• Long times immediately trigger
thoughts of time efficiency
– The search begins
Efficient grinding
• Let’s consider grinding to be a 2-step
process
– Rough and fine
• Rough grind eats away the bulk of the
material and does it quickly
• Fine grinding uses smoother belts or
wheels and leaves a better finish while
allowing the operator to work the
surface gradually reducing the chance
of over-grinding
Hand grind or automation?
• Everyone wants to incorporate
automation but roadblocks are:
– Capital costs for equipment
– Equipment capabilities/flexibility
– Part volumes
– Fixtures
– Mold designs
• Benefits are:
– Speed
– Accuracy and consistency
Hand grinding
• Rapidly becoming a lost art
– Mundane task
– Loud
– Hot
– Dirty
– Can be heavy
– Dangerous
Hand grinding benefits
• Very flexible
– Shifting from job to job quickly
– Little dedicated fixturing
– The right choice for lower volumes
• Spares applications
• Prototypes
• Low volume production
– Easily adjusted to accommodate changes
Automated grinding
• Capital intense approach
– Equipment
– Fixtures
• Programming required
• Specialized abrasives often required
• Footprint requirements
• Wax assemblies must be designed for
equipment capabilities (compromised?)
Automated advantages
• Ergonomics
– Reduced handling
– Controlled environment
• Dust/particles
• Process control
– Consistency and better capabilities
• The potential to make grinding a one-
step operation
• And this stuff looks really cool on the
website!
So where are we at?
• The employee market has been moving
away from manual labor for a long
time.
• OSHA regulations concerning
workplace environment become tighter
all the time making compliance more
difficult
• Component complexity for US made
products is increasing
More complex parts?
• Over the past 25 years we have seen a
better understanding of what the
investment casting process can do
• Complexity and size have been moved
to the right due to a cooperative effort
between product designers and the
investment casting community.
– The plan is working…..
More complex parts?
• Complexity and size coupled with
higher performance requirements
drives differential masses within parts
• Simply, mass variations = gating
complexity = more cutoff and grind
activities
Unconventional wisdom
• CNC machining has significantly
impacted part designs.
• Capabilities are such that machining
becomes an option on some parts for
gating removal
• CNC equipment is versatile and price
competitive
Work together for success
• Collaborative efforts between the
designers and the casting provider can
enhance processing efficiencies
• Reduce unnecessary processing where
parts will get machined later
• Eliminate non-value added processing
• Open a dialogue between the designer,
producer, and the user to gain
efficiency.
Are we done yet?
Thank you for your attention
We encourage any questions
that you may have