Quality Magazine

Measurement: Fixture Success

May 30, 2012
Learn how sandwich plates can reduce space needed and increase efficiencies in your measuring room.

This shows the bottom of a horizontal plate with a hovercraft and drive system. Source: Witte

I have been receiving the same question from quality managers a lot lately: Are there solutions to reduce the space needed for all of my fixtures that would help us become more efficient at the same time? Over the years quality departments accumulate a variety of fixtures from current and previous programs that consume valuable space. Alongside these will be new programs that require new fixtures, also needing this valuable space. This lack of space can create inefficiencies and throughput challenges by having to navigate through a sea of fixtures. Wasted time can reduce actual productive work, and with the focus of speed to market every opportunity to reduce time is a strategic advantage.

So what are the options? Of course the easiest is to do nothing and hope to minimize lost time and inefficiencies through better controlled processes. One option is to re-optimize the current storage solution with a better mouse trap enabling ease of access and control. Another option is to start using a fixture recycling program through the use of modular fixtures, which can eliminate numerous redundant fixtures. Lastly, consider investing into a sandwich plate system to free up space and time.

Plates come in many different sizes and also can be created in nonstandard sizes. This is an example of a horizontal plate. Source: Witte

Sandwich Plates

Sandwich plates, also called surface plates, come in two main types: vertical and horizontal, and can be constructed of aluminum or steel. A vertical plate can be single or two sided with a user defined grid pattern enabling the user to quickly locate product on one or both sides, while the horizontal plate has a single sided grid based surface that can locate a variety of product. Both plates can reduce space requirements by eliminating the need for multiple fixtures and provide for a more efficient throughput process by minimizing the users’ time.

What plate sizes are available? Plates come in many different sizes and can be created in nonstandard sizes too. Larger items, like a vehicle, would require a plate slightly bigger than the largest vehicle that could be mounted on it. Plates can be placed on the coordinate measuring machine (CMM) table or mobile workstation, providing maximum flexibility for any size parts. Small plates are a good choice when working with castings or other small to mid-sized parts as the user gains the same benefits.

How are parts held on the plates? Holding points are located on the plates by using a grid pattern, positioned on to the plates by alignment pins and locked to the surface of the plate by a variety of connecting systems. The plate surfaces are very accurate and durable, making this process repeatable for many years.

How does the use of a plate save space? Consider an automotive side panel fixture. It would require two large side panel fixtures to be stored when not in use and maneuvered around when needed. With a vertical plate it would require one plate with the holding points for each side panel and with a few adjustments additional models such as a coupe, sedan, wagon and convertible can also be measured: By using the common holding points the change time is limited to removing and adding the vehicle specific holding points.

Additionally, fenders, doors, deck and trunk lids can also be placed on these plates. The space reduction can be noticed instantly and the amount of time spent searching and moving around fixtures is drastically reduced. Having two plates can increase efficiency by enabling one to be measured while the other is being staged for future use. So, instead of having fixtures for every component, this system reduces the entire fixture to simple towers. These towers are easily positioned on the plates and are stored on carts or trolleys, which can be vertical or horizontal depending on the length of the tower. The carts can hold towers for both side panels and potentially other variations of the vehicle. One cart with towers is about the same size as one side panel fixture.

In some cases space is not a major concern; when this is the case a two plate system provides for an increase in throughput and efficiency. The goal in most labs is to keep the CMM running as much as possible to maintain a high level of quality for all parts being measured. Downtime, in most cases, is nonproductive, so maximizing the users’ and machines’ time will maintain and potentially increase the flow of the process.

How are plates moved? There are many different ways of moving plates around inside a measuring room. In some cases these are fixed and do not require being moved; in most cases cranes can lift and place a plate into position. A hovercraft system can move the product around via air cushions located on the bottom of the plates. This system only requires two people to maneuver the plate effortlessly into position; other systems like a multidirectional drive can be used to provide additional flexibility in tight spaces. A parking system can be integrated along with a moving system to ensure ease of use and alignment repeatability.

Reducing Space

VW Mexico provides an example of reducing space in a measuring room: the metrology laboratory responsible for controlling the quality of the BIW components for the Jetta, Golf and new Beetle in Mexico has been using sandwich plate technology since September 2008. Before that, dedicated fixtures filled up all the floor space in the room and overhead space was utilized by a crane used to move fixtures in and out of the three CMMs. Changing from one part to the other was a task that took three hours on average by freeing up space for the maneuver, locating the fixture in the machine and doing the alignment. Approximately three fixture changes are made per machine per day. Besides the savings provided by the plate and holding towers concept in which 90% of the material used for the fixtures is reused, the space and time savings are significant. Twice as many fixtures can be stored in the same space, leaving free areas for transit that were not there before. Changing from one part to the other can take a maximum of thirty minutes and the alignment is easy because the plates never change position.

VW Mexico was able to work within their existing space to reduce and become more efficient through the use of both horizontal and vertical plates. Setup times have been reduced, throughput has increased and space has been freed up. This offers an example of planning and adjusting from an old legacy system that consumed space and exuded inefficiency to a proven model of efficiency.

Larger items, like a vehicle, would require a plate slightly bigger than the largest vehicle that could be mounted on it. Source: Witte

Planned Efficiency

An example of planned efficiency in a measuring room would be VW Chattanooga. The metrology laboratory responsible for controlling the quality at VW in Chattanooga uses two sandwich plates per CMM. Their primary focus is to reduce downtime per CMM, by using plates with a hovercraft system. Users can set up, stage and change out the fixtures in minimal time, thus keeping the CMM as active as possible. The amount of time to set up a plate and switchover time is insignificant compared to the old process of moving fixtures around via crane. The most commonly used fixtures remain set up or readily available to ensure fast processing. The lab is extremely organized and clean, making it easy to find what is needed when it is needed. Everything is set up for repeatability to ensure minimal setup time.

Another advantage is that fixtures are always available when mounted on plates with an integrated drive system. The user is free to move the plate to different locations throughout the lab for management presentations and optical or alternative inspection methods away from the CMM.

With Chattanooga being a fairly new facility it did not have to work with an existing legacy like VW Mexico, enabling them the ability to build the most efficient system from the beginning. Having the two plate system provides for less downtime through the entire process.

What should you consider when looking for a solution to reduce the space needed and increase efficiencies? Consider the primary objective: faster throughput, reduced space and increased efficiencies. Review the current processes in place to determine what can be improved and explore options like sandwich plates. As in the two examples from VW, the use of plates can provide a solution to accomplish most challenges faced by the quality leaders in the marketplace. Q

Tech Tips

Sandwich plates can be constructed of aluminum or steel and come in two main types: vertical and horizontal.

A vertical plate can be single or double sided with a user defined grid pattern, while the horizontal plate has a single sided grid-based surface.

Both types of plates can reduce space requirements by eliminating the need for multiple fixtures.