IN PROCESS GAUGING
“In grinding, small details can have a huge impact on the overall performance of the machining process, whether we are talking about the cycle time, dimensional tolerance, or roughness of parts. Everything depends on microns, which in turn rely on both the machine and the operators.” Francesco states: “There are processes where technology can help and others that rely solely on manual operations. Here, mistakes can be made and there is a compelling argument to install an in-process gauging system.”
In-process gauging is an ancillary system that can measure the part while it is being ground and, in real-time, automatically control the in-feed of the grinding wheel so that every part produced by the machine is in tolerance according to the manufacturing specifications (see the picture below). It provides a 100% production validation check that can even automatically compensate for wear on the grinding wheel. Due to the harsh machining environment found in the grinding process, the gauging operation is performed with the gauge’s fingers in physical contact with the workpiece; it is the only way to get a reliable diameter measurement in such conditions. Over the decades this solution has increased in reliability and robustness, and today a few vendors, such as Balance Systems, are recognised as offering great solutions.
The cycle time for a mid-size part on regular OD manual grinders can be around three to six minutes. With this type of machine tool, the dimensional accuracy of the part is subject to human error as the operator must measure the diameter of the workpiece, calculate the residual overstock, and then proceed with the next machining step. In order to reduce the risk of scrapping any parts, operators tend to be conservative and remove less material than necessary. So, a vicious loop that increases the cycle time is established which, in turn, increases the labour costs. By using an in-process gauging system, this process is done automatically by the machine with a ramp-up of production volume achieved.
“The investment for these systems starts from 6,000 USD up to tens of thousands, depending on the complexity of the part and the level of automation. My teams in North America and the UK and I are getting more interest for these solutions every year, especially for older machine tools. Just to give you an idea, we recently turned an almost 30-year-old machine into a semi-automatic piece of equipment capable of achieving a 60 second cycle time [picture below]. We used a VM25 amplifier with a diametral-axial flagging system TG200, all designed and manufactured by Balance Systems. The ballpark investment was around 20k USD, with a final benefit in terms of productivity that was straightforward, especially from a financial point of view. With this electronic system, users can also carry out shape analysis of every part without removing it from the machine.”
Of course, behind every improvement there is always a price to pay, the old adage being ‘you get nothing for nothing’. As well as the initial investment to source and install the equipment, there are other hidden costs to consider. The training of the personnel on using this kind of equipment is the first one, which includes: how to handle the change-over between different production batches, the periodic cleaning of the gauges, and also the handling of unpredictable (hopefully rare) system crashes that typically happen during the loading/unloading of the parts or due to incorrect interpolation of the axes.
“The implementation of a gauging system like this, in my experience poses a challenge for both sides. The end-user must adapt the internal SOP [Standard Operating Procedure] matching the requirements of the new gauges. All machinists and maintenance staff have to be informed and trained about the new equipment, how to operate and care for it.
“For the supplier the challenge is the installation of a robust in-process gauging system, including the integration of the signals into the machine tool. There can be a broad range of technological ‘hurdles’ to overcome in the field. So, I strongly recommend only approaching experts with a proven track record in these applications
It is important to note that in-process gauging systems cannot be installed in every type of grinding machine. For example, centreless and double-disc machines have obvious limitations due to their machining concept, making it very difficult (in some cases impossible) to locate an external element, such as the gauges, in contact with the part while it is machined. However, Francesco told us that there are solutions called ‘pre-process’ and ‘post-process’ gauging systems that allow automating the grinding cycle even on these machines, making the challenging KPIs of today’s manufacturing world achievable.
Looking at the numbers shared above, it’s clear to see how it would be worth investing in such a solution: A 6-minute versus 1-minute cycle time, without and with an in-process gauging system respectively, is a very powerful argument. Whether you need to produce medium volume batches or extended volume runs, the ROI of an in-process gauging system is extremely attractive. What could your company do with six times the production capacity?