by Tim Wilson
Is shop floor measuring a good option for you?
CMMs are critical components to many metalworking operations, and there is a strong trend to have these capabilities right on the shop floor, rather than having to move a part to a metrology lab. But to hold accuracy in a production environment, a CMM has to be specialized to handle the challenges associated with what can be a noisy, dirty environment, sometimes with limited space.
“Unlike traditional CMMs which require compressed air, shop floor CMMs are usually hard bearing machines,” says Ian Murray, CMM business unit manager at Canadian Measurement Metrology. “In these machines, the bearing ways are usually covered by bellows to prevent dust and contaminants from affecting the drive system.”
Temperature variation is a critical concern for a shop floor CMM, as it will affect size and position parameters for probes. The important thing is to implement the minimum solution to achieve a required target specification. For example, it is possible to fit temperature compensation onto a CMM to allow a certain amount of temperature variation for a certain level of metrology, and to do so at a low cost. Alternately, a shop floor manager can build a temperature controlled environment around the machine for better temperature control and metrology–though that obviously comes at a significantly greater expense.
“We have a line of CMMs specifically engineered to survive and thrive in harsh shop floor environments,” says Eric Bennett, product manager at Hexagon Metrology. “The 4.5.4 SF and 7.10.7 SF, unlike most quality lab CMMs, include advanced thermal compensation algorithms that can correct for large changes in ambient temperature common on the shop floor. A network of thermal sensors within the CMM structure automatically monitors these changes.”
“Another concern on the shop floor is air-borne contamination. If there is particulate in the air, the CMM is protected by special bellow covers, so that there is nothing for the operator to worry about,” says Bennett.
Access can also be an issue. Production environments in the aerospace and automotive industries, for example, require easy CMM access to speed efficiency. They also have intricate parts that can be difficult to access.
“A small footprint CMM for typical work is usually advantageous,” says Paul Gane, a sales manager at Renishaw. “It’s cheaper to buy, and uses up less factory space.”
Gane notes that Renishaw’s probing technology can be used on a CMM structure with a Renishaw controller and software, or a CMM structure with the controller and software from another manufacturer. Some of the capabilities and performance will be necessarily defined by the other technologies, but Renishaw’s precision technology has a broad application base.
“A small sensor and head will free up workpiece volume in any particular working envelope,” he says. “The modularity of our SP25 probe enables the end user to extend the system in a cost effective manner, as circumstances dictate.”
Renishaw’s modular SP25 has the added advantage of helping out in case of a crash–an uncommon but potentially devastating event. The parts break away to minimize damage, and if damage does occur, a replacement part can be exchanged: simply plug it in, recalibrate, and start running again.
This kind of versatility and flexibility makes sense given the growing demand: Murray estimates that 55 per cent of new inquiries at his company are for shop floor CMMs.
“The Romer Absolute Portable Arm is a CMM with dual carbon fibre tube construction which doesn’t lock up when the temperature changes,” says Murray. “It provides sensory feedback to the operator, which enables the operator to take measurements in even the harshest of environments.”
The Romer arm is also wireless, so electrical issues would not be a concern here. However, for more accurate measurements on the shop floor, Murray recommends the Hexagon Metrology shop floor 454SF or 7107SF CMM.
“The SF series of CMMs is resilient to environmental conditions on the shop-floor, such as temperature, vibration and dirt,” he says.
These machines will still not deliver to the higher accuracy found in a metrology lab environment, but often this is not required. As it stands, process checks are becoming standard in numerous industries, and if a job shop wants to keep up with supply-chain requirements, having a flexible CMM on the floor can make a world of difference.
“Our machines are on castors, so they can be easily maneuvered on the shop floor to support manufacturing processes,” says Bennett.
“It was not that long ago that metrology was exclusive to the lab, but now shop-hardened CMMs can help address bottlenecks there.” SMT
Tim Wilson is a contributing editor. [email protected]