Machine Shop Inspection To Go
Today's portable device alternatives include 6-axis, arm-type universal gages, portable arms, laser trackers and scanning systems. They provide accurate measurements within a range of 15-100 microns depending on the system. While this does not make them suitable for the high precision work done by CMMs in the lab, this degree of accuracy is entirely adequate for many of the measurement tasks found on the shop floor.
Speed: The Big Issue
Speed is the dealmaker for shops considering the use of portable measurement devices next to their machines. On the shop floor, uptime is what matters and technologies that best contributes to maximizing metal cutting time rule the day. Using portable devices for making in-process checks or first piece inspections (if accuracy permits), takes the least amount of time because no time is wasted getting parts to a remote measurement location and then waiting for inspection results to come back.
The key to getting fast measurement results from a portable device at or near a machine tool is preparation. Before it is time to measure the part, the portable users should know exactly what results they will be looking for and what steps will be required to get them.
For the latest generation of arm-type gages this means simply knowing what features to measure, selecting them using an ultra-friendly graphic user interface and following the prompts. Users can perform even the most complex evaluations on the shop floor using portable arms equipped with the same software found on CMMs. This type of software uses a CAD model to generate efficient probe paths and allows for the generation of as much as 90% of a measurement program off-line before even taking the portable measurement device to the part.
What’s more, if a first piece CMM inspection program already exists for measuring a part, users can import all or part of the program into the portable software package with minimal changes. This eliminates most of the programming. Pretty much all that needs to be done is to take the portable coordinate measuring machine to the part, orient the part to the device and measure.
In a guided inspection routine, the user interface, using the CAD model as a reference, will show the operator where to probe the part and then immediately display the measurement results. Color-coding (green/red) on the CAD model view of the part will indicate where it is in or out of tolerance. This kind of instant feedback is a win-win for the manufacturing and quality departments. Portable users on the shop floor obtain measurement results immediately,without tying up the CMMs in the Quality Lab, which often have a heavy workload on other tasks.
Streamlined pass/fail inspections are only the beginning of the benefits that can be realized by using a portable measuring system with CAD-based software on the shop floor near CNC machines. Other advantages of portable inspection include:
Measure First, Question Later:
- On-Machine Troubleshooting: Rather than breaking down a manufacturing setup and bringing it to the CMM lab in pieces, bring a CMM (i.e. a portable device) to the machine. Problem solving using data gathered on the machine is much more effective than measuring the end product off the machine and then trying to work your way back through the process to figure what went wrong. If you suspect a problem with a particular process or machine, you can take measurements very quickly and make informed change decisions based on data, not on a ‘hunch’.
- Advanced planning, in spite of its many virtues, doesn’t solve all problems. Unforeseen issues sometimes arise. The CAD model may be out of date or special fixturing may make it impossible to measure all of a part’s features as planned. But that’s okay. Even in these situations, portable measurement machines prove how extraordinarily flexible they can be. Operators can measure all of the features that they can reach without having to stop the inspection to modify the program to accommodate the features that cannot be inspected at this particular time. If necessary, the program can be modified back at the operator’s desk later, without taking up valuable machine time. This “shoot first and ask questions later” approach has become the default mode of operation for many portable users who employ video and laser tracking probes to evaluate the form and fit of sheet metal.
- Fitting Conclusions: Even though a part on a machine has a problem, it is not always necessary to scrap it. Those familiar with CMMs already know how to use their software’s best-fit capabilities to answer a wide range of questions about a part. Things like: This casting is malformed, but is there enough material available to make a good part from it anyway? Is there enough material available on this bad part to re-machine it and make a good one? By reorienting this rejected part in three dimensions within the measurement program, can I match up the critical features more closely to the CAD model and avoid rejecting it? Answering these questions and others like them present opportunities for salvaging valuable parts with many, perhaps hundreds, of hours invested in them. Now these same analytical capabilities are available on the shop floor using the latest portable measurement devices and software.
- Process Problem Solving: Good manufacturing people are ingenious when it comes to devising on-the-spot solutions to dimensional problems that materialize unexpectedly. These impromptu adaptations may include the use of shims, special fixtures and ad hoc machine tool offsets. These allow the machinist to ship good parts out the door without having to double back and find the root cause of the problem and correct it. They can use portable systems as an aid for making these improvisations faster and with greater accuracy. Once the immediate problem is solved, the next step is to use the portable measurement system to follow the out of spec condition back through the various manufacturing operations to identify and fix the root cause of the problem. These changes will be based on knowing instead of guessing what to do. From then on, machinists won’t have to rely on their memory or handwritten notes for making little tweaks to jury-rig their processes to make good parts. They can use the CAD model and CAM program as delivered to the shop floor and others can replicate the good results consistently without having to know any special tricks.
- Different Types of Users: While portable measurement devices are very easy to understand and use, they support a broad range of user capabilities. Novice operators can use a simple, intuitive UI to check basic characteristics of their parts or pre-programmed measurement routines written by CMM experts to check more complicated geometry. So they can quickly learn to perform in process checks or do pass/fail inspections of their own parts.
- Those who already have a working knowledge of CAD and CAM will have little trouble using advanced portable devices and software to expedite setups or troubleshoot manufacturing process problems. Quality assurance staff can help deploy portable measurement approaches to get measurement results faster and closer to the process while eliminating bottlenecks at the CMM in the laboratory, so product development work is not continually interrupted to keep manufacturing on schedule.
Portable Final Thoughts
Portable devices with CAD-based measurement software are no longer specialty items but mainstream tools that can be used to detect the causes of dimensional problems where they occur. Some portable devices can be programmed off-line and the measurement programs can be used interchangeably with CMMs in the lab. By measuring at or near the machine you can strip out measurement related time wasters and reduce the measurement backlog at the CMM to improve new program delivery cycles.