Insight on Fixturing


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This Month's Insight on Fixturing Feature:

Hydraulic, Pneumatic, or Manual?

There are many different factors to consider when deciding which clamping method should be used on a fixture.  Each of them: hydraulic, pneumatic, and manual, all have their own unique qualities that may make them right for the job.  To find the best suitable clamping method for the job, we consider six main factors: cost, cycle time of the job, employee utilization, customer preference, clamping force, and component size. 

As can be expected, hydraulic and pneumatic fixtures tend to be more costly than their manual counterparts, due to the number of support features.  For example, hoses and fittings, valves, switches, intensifiers, and power supplies.  Not to mention the clamps themselves can be quite costly.  Also, if a pneumatic or hydraulic clamp were to malfunction, it may not be a quick fix and can lead to some lengthy downtime.

Which brings up another factor, the cycle time of the job.  The cycle time of the job is very important to take into consideration.  Let’s face it; the old adage “Chips Make Money” is true. If a machine is sitting idol while the operator is loading the part, the company is losing money.  Or maybe the machine is not being run at its’ fullest potential. Is there a clamping method to speed up the loading and unloading process? Is there one that could allow more parts to be run at time?

Those questions may be answered after looking at the employee utilization of the job.  Employee utilization is what task(s) the machine operator has to accomplish while the part is being machined.  If the machine operator has to complete secondary work on the part (i.e. sanding, de-burring), do they have enough time to manually tighten down 32 clamps?  Also, the machine operator maybe required to operate a couple of different machines at time.  This can strain their concentration, as well as limiting loading and unloading duties.

Customer preferences should also be considered.  After all the customer is always right.  Some customers may insist on using a clamping method, because they are familiar with it, view it to be more convenient for them (i.e. using existing shop air as the pneumatic clamping source), or they may just want to keep the job as simple as possible.  What ever the reason, listening to what the customer has to say, can be vital to the overall success of the project.

Sometimes the customer would like to use a particular clamping method, but because of the clamping force required it is not possible.  The clamping force of a given project depends on how the part is being machined.  The part maybe machined in such a way that if manual clamps were used the part could come out of the fixture.  It is important to find out the greatest amount of force exerted on the part at any one time during the machining process. Knowing the greatest force can help with determination of the clamping method to be used. 

The last factor that will be discussed is the component size.  Component size refers to the size of the clamp support features and the clamps themselves.  Take hydraulic or pneumatic clamps, they require much more room on the fixture than manual clamps.  This can limit the number of parts to be put on a fixture.  What are the pros and cons of using a smaller manual clamp that allows for more parts, but may sacrifice loading and unloading speed? As opposed to the pros and cons of use bulky hydraulic or pneumatic clamps that will speed up loading and unloading, but sacrifice the number of parts that can be machine at one time?

The six factors that were discussed above were not in any order of importance.  I would like to caution that cost is not the first thing to be considered, and conversely, component size is not the last factor to be considered.  All of the six factors should receive an equal amount of attention.  For example, a customer may have a project that they have budgeted a considerable amount of money towards.  Thus, one would think, making it possible to use hydraulic or pneumatic clamping.  However, what if the part they wanted to fixture is a small clevis pin with limited contact points? Is hydraulic or pneumatic clamping still the right choice?  Each job is different, and must be looked at from all directions.  Whether the fixturing project is large or small, considering the six factors just discussed will cover all the angles and allow the right clamping method to emerge.

Bill Tulloch
V.P. Engineering


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Copyright © 2006 InteliTool Manufacturing Services, Inc.
Last modified: September 12, 2006