Optical measuring systems: laser technology at Simrax

Simrax, member of the Freudenberg group, the Dutch subsidiary of Freudenberg, producing seals for shock absorbers and water pumps, has reduced the number of rejects and boosted quality by installing a laser distance measurement system.

About Simrax

Simrax in Kerkrade, the Netherlands is specialized in sealing techniques and it manufactures and sells seals for shock absorbers and water pumps. Simrax is a subsidiary of Freudenberg Dichtungs- und Schwingungstechniek GmbH & Co.KG, which operates from establishments all over the globe and is a manufacturer for the automobile, shoe, leather and textile industries as well as the household and construction industries. In the Netherlands, Simrax employs about 180 people.

Background

A shock absorber seal consists of three parts: a metal part (washer or shell), a spring and a rubber pre-form mould. The Shock Absorber Seals (SAS) department processes these parts into one unit. This department, working in three shifts, produces about 150,000 seals for shock absorbers every day, in several different series. This happens for suppliers in the automobile industry including Monroe, Volkswagen, Stabilus and Koni. Simrax processes various kinds of rubber, according to its own formulas, to obtain a mixture and cuts this to the correct size. The iron ring is provided with a layer of material that ensures proper bonding so that the rubber adheres to the ring properly at a later stage. The SAS department takes the ‘vulcanising’ for its account, and this is where the rubber is pressed onto the iron ring at a high temperature. After cooling down, the seal goes into a cutting machine where it is cut to the correct size and provided with a spring. This is followed by an automatic spring check and the seal is subsequently checked again manually. At the end of the production process, another inspection takes place and this is generally at random. In total, the production cycle is 4 minutes per product.

Supplying the wrong products

Simrax was looking for quality improvement for the cutting machine in the SAS department, where they make seals for shock absorbers. A short conveyor belt supplies the cutting machine where seals are cut to size. Via hopper-feed, the products are correctly positioned on the conveyor belt. However, sometimes this does not happen correctly and the seals are either upside down or sometimes the rubber sticks out over the edge, which results in the seals being folded double in the cutting machine. The problem was that it was difficult to notice when the product was the wrong way around in the cutting machine. A consequence of this was that the product was often cut incorrectly and, even worse, these products were delivered to the client. To guarantee a better quality, Simrax was searching for a fitting solution.

The Freudenberg establishment in the United Kingdom, which functions as the lead centre for the SAS department in Kerkrade, has a new cutting machine in operation that has been equipped with Omron technology. Roger Zoontjens, Electro Mechanic for the SAS department at Simrax, explains:  ‘At our British branch, the Omron system detects the seal as well as the spring that is placed on top. I did a test to see whether this system would also be suitable for our existing machine. It proved to be rather inefficient for this specific application. Together with Omron, we started looking for better solutions.’

The solution

Omron tested the possibilities in its establishment in Hoofddorp and the most suitable solution they found was a distance measurement via a laser system. The supply on the conveyor belt has not changed. However, the laser detects products that are not properly positioned and the machine automatically comes to a stop. This enables the staff to correctly position the product on the machine or to remove a faulty seal. The result is that all products that enter the cutting machine are in the correct position and the quality of the manufactured products has increased considerably.

Rectilinear programming

Simrax manufactures several product series of various dimensions per day. The distance measured by the laser differs per product. It is very easy for the technical department to set the correct dimensions in the switch box. ‘Programming the PLC with Omron is straightforward’, says Roger Zoontjens. ‘The software is open and accessible and therefore it does not matter which machine is involved. Even if I did not develop a machine myself, it is easy for me to program the PLC. It is not even necessary to know the machines specifications. If I need additional documentation, I can just download this via the website. In my experience, this is characteristic of Omron’.

No more complaints

The cutting machine is standing still more often than before due to upside down products. To the employers, this seems to cost more time. However, preventing the delivery of faulty products and the higher percentage of good products delivered amply make up for this. ‘Customer complaints is the worst thing that can happen to us’, says Mark Hof, Process Engineer at the SAS department of Simrax. ‘Instead, we show our clients the measures we are taking to improve and maintain the quality of the products that we supply them with. Satisfaction and quality are most important. In addition, this investment has yielded quite a sum as we now do not have faulty products being returned.’

Other applications

This positive experience with the cutting machine also prompted Simrax to apply laser technology in the press. Roger Zoontjens explains: ‘We were looking for a way to measure the quantity of manufactured products. Previously, we used to do this by means of a rough estimate, by counting the completed moulds. However, as we could not see whether the moulds were actually filled with product, the actual number of manufactured products could only be assessed at the end of the production process. Similar to the cutting machine situation, Omron brainstormed with us about a solution and put testing equipment at our disposal. The laser technology worked very well, even at high temperatures. ‘The laser detects with distance measurements whether the moulds are filled with rubber pre-forms. If the deviation is too large, the PLC gives a signal and an empty mould is registered in the OEE. Now, Simrax knows the actual number of products that are completing the cycle.

Safety

Even though the laser has a high safety level (category 2), for extra safety Simrax has installed an extra release signal. ‘In this way, the laser can never shine in the eyes of a staff member’, says Roger Zoontjens. ‘In addition, the laser is programmed as such that it is only active when it is in actual pressing mode. So, during other conditions such as during the warming up and the basic position, the laser is deactivated. This kind of thing is very easy to program in Omron’.

Now that the most urgent problem has been solved and Simrax is no longer delivering faulty products, the company is planning to look at other improvements that can be achieved. It is possible to use a measuring system on other presses. Perhaps new savings can be realized by means of specific measuring possibilities, for instance preventing moulds from breaking due to double loads in the mould. In this way, quality is further improved step by step.