Versatile Gauging
Autoparts giant Linamar Corp. uses a new, flexible comparator in its prototyping process
October 25, 2011
Shop floor measurement with reprogrammable comparator.
The Frank Hasenfratz Centre of Excellence in Manufacturing, a.k.a. The Centre, sits in the heart of Guelph, Ont., which is no surprise since it is owned and operated by Linamar Corp., the well-known automotive parts supplier. And in the heart of this unique, experimental prototyping and short-run production facility sits the company’s quality assurance laboratory.
While QA departments are important in many different types of shops, when you are prototyping and developing processes for next-generation car parts for some of the biggest names in the industry, it becomes an indispensable department. It also cannot become the source of a major bottleneck.
The Centre, opened two years ago, was created to introduce higher levels of innovation to the process of engineering Linamar’s products. The Centre focuses on advanced tooling, fixture and gauging analysis, product testing, and R&D.
“The purpose of The Centre is to be the front line for every new product and changed product that will be produced by Linamar’s plants around the world,” said The Centre’s Quality Assurance Manager Dan Gheorghiu. “Lessons learned by the many worldwide plants also are centralized here, and solutions are formed here that, in turn, help those facilities run better.”
This means developing, testing, and proving out processes are done at The Centre first as a prototype, then as a small-batch test production run, before moving into large-scale production.
“These are parts that have never been created before anywhere else in the world, and it is up to us to experiment and figure out the best way to produce them,” said Gheorghiu.
The Centre’s machinists first make sample parts followed by the prototype. Then the part moves through the automotive supply chain’s production part approval process (PPAP), which helps to ensure that production has both the ability to produce parts with consistent quality and the actual production will run at the desired rate.
It is only then that a small production test run is performed.
A typical project takes four to five months, but this time frame can vary highly depending on a number of factors, including how fast the customer wants to move a part into production.
“We may be doing things here that our production facilities have never seen before because they are busy with ongoing production work,” said Gheorghiu. “We produce very flexible processes today. We no longer get five years out of one part. Production needs can change very quickly, and we need to be at the forefront of technology.”
The Centre also focuses on creating systems that keep production costs low while developing custom fixturing and testing gauging, machine tools, CNCs, tooling, and coordinate measuring machines (CMMs).
“We investigate any unique technology and process that can be beneficial when implemented into Linamar’s production lines,” said Gheorghiu.
Production Measurement
When you create new processes for a company the size of Linamar, innovation is important. However, as OEM platforms change, and part runs shrink, flexibility also becomes important. So, too, is the cost of the process.
The cost of gauging is one area that The Centre is focusing on reducing. There are several ways to test that a process is producing a quality part and it conforms to the necessary specifications.
Hard gauges typically are fast, easy to use, and highly repeatable. The downside, according to Gheorghiu, is that these comparative fixtures are expensive, as well as being both difficult and costly to change out. They also have long lead-times due to their bespoke nature.
One-off, custom gauges are also expensive, and these costs often are written off over just one installation.
“For measuring some part features, hard gauging can be very expensive, even reaching $15,000 for a single-feature gauge,” said Gheorghiu. “Then, once the program is over, there is no other task this dedicated style of gauging can perform. In today’s economy we have to be flexible. No one wants to waste money.”
CMMs offer high accuracy, traceability, and absolute measurement. They have flexible and comprehensive software packages that allow them to measure even the most complex parts. However, these machines must be used in temperature-controlled rooms, and both calibration and measuring cycle times can be high.
“The volume of measuring work can become a major problem in many production environments, and the CMM can become a bottleneck,” said Gheorghiu.
To tackle a new part being developed at The Centre, another option was chosen.
The company partnered with industrial metrology manufacturer Renishaw to test the company’s new Equator™ gauging system. The Equator is a comparator, meaning that it measures parts against the dimensions of known part. The operator is presented with clearly defined deviations from the nominals and is able to make offsets to the machining process.
The system was designed to allow production engineers to better compensate for thermal changes in the operating environment. It can be preprogrammed for multiple parts and reprogrammed for design changes. This reprogrammable gauging style is an alternative to dedicated hard gauging and custom, one-off gauging.
The machine itself uses a parallel kinematic structure to allow for high-speed scanning and fast moves between features, while retaining the stiffness that is necessary for the point-to-point repeatability critical to accurate measurement.
For normal production purposes, measurement on a CMM can be the best route, but is not the only technique available. Some situations, such as those found in a shop floor environment, are not ideal for a CMM.
“One of the primary factors in our decision-making was the fact that we needed to inspect 100 percent of the parts from our initial 200-part test run,” explained The Centre’s Quality Engineer Jane Martin. “It is very common that 100 percent measuring is performed during the prototyping stage, but it can be expensive and therefore difficult to reproduce at the production level.”
The cycle time of the part is 17 minutes, which created the two parts for testing. However, the cycle time of the measuring process on the company’s CMM for the two parts ended up being 40 minutes.
“This made it unfeasible for the operator to create the part and measure it before the next parts were ready,” said Martin. “The measuring time using the Equator system is under 2.5 minutes per part. The CMM was simply too slow for this particular application. Hard gauging was not economically feasible either.”
This type of gauging will also have a use at the end of this particular part run because it can be reprogrammed to test another part.
The Process
The measuring process starts in this setup when the master part is calibrated on a CMM. This master is then measured on the comparator. Subsequent parts are compared to the master part relative to CAD nominals. The gauge typically is remastered as temperature changes.
“We have found that mastering needs to be done frequently due to temperature shifts, but calibration done very infrequently,” said Martin.
A comparison uncertainty of ± 0.002 mm or better can be achieved immediately after remastering.
“Due to the scalability of the Equator system, this type of gauge is perfect for high-volume production and prototyping work. We think that the ideal situation lets the gauge be the workhorse and the CMM be the mastering machine,” said Renishaw Canada General Manager Dafydd Williams.
The software compatibility is an important part of the process as well.
“We developed this system to be able to run virtually any company’s I++ CMM program out of the box, giving us compatibility with a very high percentage of the CMM software on the market today,” said Williams.
The software is also significant for the output it generates. A comma-separated value (CSV) file produced by the Equator’s software suite can be imported into any statistical process control (SPC) software.
“With a traditional CMM there is some work that must be done during a changeover of parts,” said Martin. “With this gauge that time is reduced.”
The presentation of gathered information from the measuring process is done in a manner that saves time and reduces errors. Like many processes in a machine shop, errors most often occur during measurement, when the human element is added to the equation.
“This particular system has a unique way of showing how far out of spec your part is,” said Martin. “The amount of material on a critical feature is shown by how much it deviates from the norm. You can instantly see that there is either too much material left on that feature, or too little. This helps reduce scrap caused by offsets being entered in the wrong direction.”
After a few days of work, this new type of gauging system has begun measuring the small-batch production run.
“We have seen what it can do in a small scale. The 200 first-run parts now are being followed by a small batch of 1,400 parts,” said Gheorghiu. “We are not the supplier, but we are able to do this work. Our mandate now is to see how we can use this technology in other plants. I learned from this gauge that there are options out there. When you are in the front lines of production, you don’t necessarily have the time and money to experiment. We can.”
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