ABOUT AUTOMATION

A. NEED FOR AUTOMATION FOR CLAMPING

B. TYPE OF AUTOMATION IN CLAMPING

C. SELECTION OF CLAMPING CLYINDER

D. SELECTION CRITERIA FOR THE TYPE OF AUTOMATION

A. Need of Automation for Clamping:

a-1        Saves Time - Manual clamping and declamping requires 15 to 20 seconds per clamp. For a fixture with multiple clamping points, the total time for clamping will be more than one minute. For uniform clamping, this time will be still more. This time can be saved by automatic clamping. The pay back period for the cost of automation can be estimated considering the net saving per job (Time saved x Machine hour rate).
Advantage of time saving is increase in production capacity of bottle neck machines.
a-2      Reduces operator fatigue - In manual clamping, the efficiency of the operator decreases due to fatigue. This may result in less clamping torque at the end of the shift, specifically for the elderly operators, causing reduction in safety. A humane approach is more important than the clamping efficiency. By introducing automatic clamping system, one operator can handle two or more machines simultaneously.
a-3        Improves quality of clamping - Only one point can be clamped at a time during manual clamping. To achieve uniform clamping, initially all the bolts are clamped with a light clamping force and then with a heavy clamping force. Clamping force at each bolt may vary. However with automation -  

• All clamps can be operated at the same time. There is no need of a light and heavy
  clamping force.
• Clamping force can be controlled as per the requirement, to control dimensional accuracy.
• Clamping force is consistent

^TOP

B. Types of automation in clamping:

Pneumatic Automation is used only for small aluminium components, due to force and space constraints. In majority of the applications, hydraulic or hydropneumatic clamping is preferred.
Hydraulic Automation is used in SPMs, where it need long stroke, speed, sequencing or high volumes.
Hydropneumatic Automation has two types:

i.   Hydropneumatic Intensifier is widely used on conventional machines and SPMs, where a      hydraulic power unit is not available on the machine. Low cost, simpler circuit and no oil      heating as compared to hydraulic power unit, are some of its advantages.
ii.  Hydropneumatic Pump combines advantages of hydraulic & hydropneumatic automation.      Longer stroke & sequencing is possible without oil heating problem.

Another consideration is the production volume.
Manual clamping is used in prototype production or batch production where production volumes are low. As the production increases, even conventional machines are dedicated for specific operation.
Hydropneumatic clamping is generally used at this production level (50 to 200 jobs per shift). SPM with hydraulic clamping is preferred when the production level goes near 1 job per minute.

^TOP

C. Selection of clamping cylinders:

c-1 Type of cylinder
Single acting, spring return cylinders are used with hydropneumatic intensifier. They are not recomended with hydraulic power unit.
Double acting cylinders are normally used with hydraulic power unit. These can be used with hydropneumatic intensifier by using air-oil pressure converter for return stroke.

c-2 Clamping force of cylinder
Stud-bolt size used in the existing fixture with manual clamping is the best clue for selecting the clamping force.

STUD SIZE	M 6	M 8	M 12	M 16	M 20	M 24
CLAMPING FORCE	2.5 kN	5 kN	10 kN	20 kN	30 kN	40 kN

^TOP

D. Selection criteria for the type of automation:

Criteria	Pneumatic	Hydraulic	Hydropneumatic
Cost	lowest	high	low
Clamping force	Light - 2 to 3 kN max. Higher forces if no space constraints	Medium and heavy - above 5 kN	Medium and heavy -From 5 kN to 100 kN
Clamping clyinder size	Bulky for even medium clamping force (Op.Pr. 5 bar)	compact (For SPM Op.Pr. 30 to 70 bar)	Most Compact for heavy forces (Op.Pr. 150 to 200 bar)
Clamping stroke	wide range- from short to very long	wide range-from short to very long	Short stroke - 50 mm max
Clamping speed	very fast	fast	fast
Impacte while clamping	present	not present	not present
Reliability	Low - as can be overpowered due to the compressibility of air	Most safe - due to the check valve and incompressibilty of oil	Safe - as factor of safety for force selection can be more
Sequenceing	possible	possible	difficult
Piping & circuit	compicated	compicated	simple
Oil heating promble	not present	present	not present
Return stroke speed and power	Fast due to double acting cylinder, but with low power	Fast, with power and positive due to double acting cylinder	Slugish due to spring return clyinder
No. of clamping points	no limite	no limite	limited, 3 to 5 perintensifier
Other Applications	Material handling, Valve actuation, Door movement	Feed cylinders, Earth moving Equip., Cutting, Hole punching, Deep drawing	Pressing assembly, Rivetting,Crimping, Cutting.

* Hydropneumatic automation referred above is with hydropneumatic intensifier. Hydropneumatic pump is not considered.

^TOP