Laying it on the line

Quality Canada speaks with Peter Detmers of Mitutoyo Canada about the merits of in-line measurement.

What is in-line technology?

[Peter Detmers] A coordinate measuring machine (CMM) is a device for measuring the physical geometrical characteristics of an object. This machine may be manually controlled by an operator or it may be computer controlled. Measurements are defined by a probe attached to the third moving axis of this machine. Probes may be mechanical, optical, laser, or white light, among others. In-line measurements are done for many different reasons, including an increase in throughput based on the number of measurements required and better control by cell operators to ensure product being made meet specs before bad parts are made, improvements in productivity through less scrap, less down time sorting parts, and assurance that parts are within spec before they get shipped to customers. But frankly, this sometimes leads people to avoid in-line since the idea of automation brings up many obstacles. Cost is certainly one obstacle, as well as complexity of some manufacturing cells based on number of machines, and types of processes. Complexity of the part being produced can also be an obstacle.

What are the quality measuring tools (CMMs, lasers, etc.) you would use for in-line measurement in a manufacturing environment?

There is a wide range of goods on the market today used for in-line applications. The machines are available in a wide range of sizes and designs with a variety of different probe technologies. They can be operated manually or automatically through computer/software control. They are offered in various configurations such as benchtop, free-standing, handheld and portable. Some of the most typical for in-line measuring applications are surface finish equipment, roundness measuring, vision systems, form measuring, laser micrometers, not to mention various small tools that can be integrated into measuring systems to perform quality checks and offer flexibility for various applications that can be integrated into the manufacturing line.

What are the main advantages of in-line measurement versus off-line measurement?

In-line measurements assist in maintaining process capability by allowing measurements to be made at the time the part is made. Data is then available to machine operators to make necessary corrections to maintain the quality of parts. We have done projects where the in-line measurement data is monitored and the offsets are automatically fed to machine controllers to improve the process capability. Other aspects to in-line measurements is that part sorting, good, bad or warning can be determined immediately, ensuring that only good quality parts are released to customers.

Is it cost-effective to go with an in-line measurement system?

This would certainly depend on the reason for deciding to go in-line. What is the cost of scrap parts? What is the cost of shipping bad parts? What are the costs in time and labour of measuring offline versus inline. Many of our systems, from CMM, to form measuring to Vision, are not part dependent, meaning when you experience an engineering change, you simply modify the part program and production continues. If the part itself changes, for instance the production contract of part x is three years, when you bid on the next version of part x, if you have a flexible gauging solution, the cost of measurement for the next generation contract is less.

What are the key considerations a manufacturer should take into account for in-line versus off-line?

In many cases the decision is based on the number of parts to be measured. What throughput is required? Is it feasible to meet the quantity by transferring parts to an off-line area?

What are the specs involved? If the part tolerance is too tight then in-line may not be practical or even possible.What is the capability of the process to maintain good quality parts? If a process is very capable, the sampling rate will likely be low such as a couple of parts per hour. However if the process is very difficult to maintain, greater part inspection is required.

Can the measurements be fed back to machine controllers to make the necessary adjustments to improve part quality? What is the overall costs, relative to the off-line method in time, labour, etc.

Is it essential to have automation on a line for in-line measurement?

It is not essential and in some cases, due to costs or other factors, not even preferable. However, we have done many projects, some with automation and some without, and both have challenges that can be overcome with proper planning and expertise. Moving parts around is actually the easy part. The “decision making” after the parts are measured is really where most of the complexity comes from. QC

Peter Detmers is national sales manager for Mitutoyo Canada Inc., Mississauga, ON.

www.mitutoyo.com