Fixtures

A manufacturing fixture holds parts during the manufacturing process. Fixtures come in a wide range of types.

In their simplest form, they may be a series of pins sticking up from a flat surface to keep a part from sliding. They can also be much more complicated, with a series of mechanical or hydraulic clamps to lock a part down into an automated rotating frame.

For Lean application, think simplicity first. Most often, a manufacturing fixture is simply a way of adding an extra set of hands. The need for precision in those cases is minimal. When precision requirements are low for a manufacturing fixture, teams should attempt to build them on their own. Tooling groups normally build the manufacturing fixture when more sophistication is needed.

Kaizen teams, though, should use their most valuable tool at their disposal-creativity. Use a block of wood that has been recessed with a router. Cut down a piece of pipe to hold a grease gun in place. Use a welder’s clamp bolted to a tabletop. Use anything that adds that third hand to you.

First of all, it is important to be able to identify when a manufacturing fixture might be useful. First, look for any process where an octopus would have better luck-essentially, anything where it would benefit you to have a third hand.

One very common situation is when a person is installing a fastener. He may be trying to align a screw, a screwdriver, and a part all at once. Or he may be trying to hold a wrench, socket, nut, bolt, and two parts.

Look for processes where parts are dropped frequently. Look for times when two people are working together on a process, with one holding something in place for the other-essentially acting as a human manufacturing fixture.

Look for times when people are cutting near their hands. These are all opportunities to save fatigue and time, as well as possibly prevent injury.

Another strong opportunity for fixturing is during an assembly process. A manufacturing fixture can be designed to let one assembly slide easily into another. This can dramatically reduce adjustment time, and possibly reduce damage during the assembly process. Fixtures such as these are very useful for installing subassemblies with one-touch installation.

Also look for quality problems related to alignment issues. The tooling group is best suited to make manufacturing fixtures with the precision required for part alignment. These fixtures are indexed to make sure the parts are oriented correctly, and then hold them firmly while the parts are fastened.

Don’t go for overkill. Make the manufacturing fixture “strong enough”. Many times, people think a manufacturing fixture has to be beautifully handcrafted. Not true.

I once designed a fixture for a pneumatic grease gun. I used a piece of PVC pipe with a slot cut to guide the handle of the grease gun. I screwed it to a 2×4 and clamped the board to a bench. The part getting lubricated was positioned with two small pieces of round-bar welded to a track. That makeshift device cost me 20 minutes and about $5 to make, and 2 years later it was still in use. You don’t always have to spend much money to make a fixture.

Some basic points on designing a manufacturing fixture:

1. Make your manufacturing fixture simple. Simple means less cost to maintain and less opportunity to break.
2. Make it easy to use. They should not slow people down.
3. Make it have a purpose. Don’t fixture something just to have a fixture. Make sure there is a problem you are solving.
4. Make your manufacturing fixture as cheaply as possible.
5. Make it strong enough, but no stronger. Heavy duty is more expensive, and often bulky and hard to use. Match the strength and durability to the need.
6. Make your manufacturing fixture as precise as required. In a manufacturing fixture, precision might be needed for alignment. In another, it may not be. Make sure the precision of your device matches the need. Precision costs money.
7. Be creative on where to use it. For example, you can build a manufacturing fixture into a transport cart.
8. Build in reference points in your fixture. Account for variance in the system-uneven floors, varying air pressure in wheels, and variation in carts, for example, might make a part on a cart and an installation fixture hard to match up. If the fixture grabs onto a fixed point on the part, if can make the installation process much easier than trying to match the height independently.