Cutoff and grinding

Bob Johnson

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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