Delicate Precision Requires Delicate Inspection
Quality razor blades from Feintechnik GmbH Eisfeld provide a shave as gentle as it is thorough. Feintechnik GmbH Eisfield collaborated with SmartVision GmbH to develop an inspection system to do the same—ensure quality while being thorough. A new production facility for triple-bladed razor heads has been equipped with ten In-Sight® vision systems to detect every potential defect—no mean feat at 1.3 to 1.5 million individual parts a day.
Under the inspecting eye of the In-Sight cameras, 13 individual parts are combined to form one blade unit. Two plastic housing halves surround three blades, between which eight “spacers” provide stability and ensure accuracy of the blade position. The correct distance between the blades ensures maximum flushing of the unit to guarantee clean, thorough shaving.
But as in most mechanical production facilities, defects can occur when producing individual parts before assembly. In the cutting and stamping process of the razor blades, tools are subjected to wear, plastic parts may be deformed during cold-riveting and, in extreme cases, fluctuating ambient temperatures may take production facilities to their tolerance limits. This made it all the more important for Feintechnik GmbH Eisfeld to identify potentially defective product parts during the production process itself. In the private label business, the company has a dual obligation: responsibility for the satisfaction of both its direct customer and the customer's customers.
The best by some margin
Four inspection stations scrutinize the delicate parts that make the razor blade units. Three stations are equipped with two In-Sight cameras each and one station has four In-Sight cameras. SmartVision GmbH (from Amberg), specialists in turnkey vision systems in electronics manufacturing as well as in the automotive and plastics industries, is responsible for the image processing. SmartVision GmbH chose independent and intelligent In-Sight cameras from Cognex, renowned for their sturdiness and reliability, for the image processing.
The blade unit is manufactured in reverse sequence from top to bottom on a work piece carrier, which carries four units in pairs. Production starts with the ”top cap” (the top plastic cover), which is introduced into the production process upside down. The top cap is designed so that all the subsequent components are anchored in four plastic rivet bolts, plus additional registration devices.
In the first step, a pick-and-place solution inserts the 0.1 mm-thick top blade into the top cap. Four spacers, punched out of coil, are then placed on top of the blade. After the first production step is complete, each of the four spacers is inspected by a separate In-Sight camera to ensure that all of them have been applied correctly and in position.
A particular challenge for the vision specialists at SmartVision GmbH was the surface reflections and low contrast of the silver blades and spacers. Red LED illumination ensures good contrast, making the aluminium of the spacers appear much brighter than the steel of the blade. The intelligent and flexible In-Sight cameras are able to ensure clear results and high quality images, despite possible reflections. Additionally, PatMax® technology detects patterns, even if the reflective behaviour of the inspection items changes. The In-Sight vision system software stores the inspection program as a tabular calculation, making it simple to compile and easy to adapt when production conditions are modified.
At the second production station, the next pick-and-place solution puts the central blade on the first line of spacers. Another set of four spacers are placed on top of the central blade. As at the first inspection station, two In-Sight cameras check for the presence and position of components.
In the last production step, the bottom blade is added and completed by the placement of the “guard bar” (the bottom plastic cover). The unit is joined together by a cold-riveting process. This phase completes production of the blade unit; however at two further inspection stations another six In-Sight cameras are used to identify potential defects. Two cameras initially check the cold-riveting, which guarantees the stability of the whole blade unit. In exceptional cases, there may be uncontrolled cracking. To detect cracking, the system inspects the shape and roundness of the rivet. Standard LED ring lamps with white light are used to achieve a good contrast for this inspection.
Gothic arch shapes accurately reflected
At the fourth inspection station, four In-Sight cameras perform the final quality inspection. The cameras detect the three blades as bright lines and can identify defects as dark interruptions. Each blade is just 0.3 mm wide and ground to the “Gothic arch shape” for optimum cutting results. This means that the incident light is only reflected within a very small angle. Moving the camera just a few centimetres is enough to render the blade completely invisible, no matter how sensitive the vision system. This is why each camera inspects just one blade. The four cameras are aligned so that the blades reflect brightly. The key factor here is less illumination and more focus on the position of the camera in relation to the blade. Lastly, the entire unit is examined for the presence and completeness of the foam edge and the lubricating strip.
In order to guard against undesired reflections, and to achieve optimum contrast, the experts at SmartVision GmbH used particularly high-quality illumination involving semi-transparent mirrors. This causes white light from a homogeneous light source behind a milky plastic disc to fall onto a semi-transparent mirror attached at an angle of 45degrees. This reflects the light onto the underside of the blade unit and back to the relevant In-Sight camera through the semi-transparent mirror. Although only a quarter of the initial quantity of light then falls on the camera downstream of the mirror arrangement, which is enough for the highly sensitive In-Sight system to accurately and reliably inspect the blades.
The member of staff responsible for the line can access the images of the inspected parts on a flat screen at any time. Images of defects are stored and can be used to evaluate the current production process.
The parts are only released for further processing once all the parts of the blade unit have passed inspection. The line rejects defective products, because safety comes first for gentle shaving with sharp blades.