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December 6, 2002

4 Min Read
Creative engineering and manufacturing win job back from low-labor-cost zone

Who says all the work has to go to the land of little pay? One molder explored several options for its customer and served up a winner.

Mfg_SLG_Fig1.jpgThe two-piece underbed storage container was being made in a low-labor-cost area of Eastern Europe until engineering creativity and technology brought it into Germany.In an age when manufacturing moves en masse to regions with low-cost labor, one molder proved that offering a high-quality, efficient solution defeated the draw of cheap wages. The product in question is a molded under-the-bed storage container made for a major Swedish-based furniture company. Until recently, it was produced in one of the low-labor-cost areas of Eastern Europe. Now, it is being made by SLG Kunststoff-Fabrik & Formenbau of Bernau, Germany.

How did SLG win this job? First, it took the initiative to show the customer how it could have a better product. Then, it demonstrated how it could provide consistently higher quality. Finally, to make the offer irresistible, it showed how to cut the finished piece cost.

New Design, New Production System
The container is 70 cm wide, 77 cm long, and 20 cm high (27.6 by 30.3 by 7.9 inches) and is molded of polypropylene. There is also a PP-molded top lid to protect the contents. For easy access, the lid can be opened from two sides thanks to a molded-in living hinge.

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The family stack mold designed by SLG allowed the company to reduce costs while increasing product functionality.

The design of the current unit, which was proposed to the client by SLG, integrates several different features in the two elements—box and lid—that combine to eliminate the small assembly components formerly glued or clipped on.

The glued-on container feet are now part of the container bottom. A modification of the immersion angle allowed SLG to offer the customer a notable reduction in stacking height. Optimizing the placement of strengthening ribs in the lid improved the operation and durability of the living hinge—even with its wall thickness reduced to 1.8 mm. The thinner wall contributed to both material and overall cost reduction. (Note: The author has two of the older units under his bed. According to him, SLG’s units are a big improvement.)

SLG’s production strategy for this product is based on a stack mold that it designed in its in-house moldmaking facilities. Weighing 14 metric tons (15.5 U.S. tons), the mold has 36 control circuits and 12 needle-valve nozzles. Before deciding on that strategy, the company first looked at molding the two components separately on different 15,000-kN (1500-metric-ton) injection machines, and determined it was not viable. It also investigated using a two-cavity family mold on a 3000-metric-ton machine, but that, too, did not prove feasible.

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SLG turned to Demag Ergotech for a systems-level solution that included full automation and handling. The robotic end-of-arm tooling flexes the still-warm living hinge of the lid (below) to help ensure smooth operation and durability.

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The economically advantageous solution SLG found was to use the stack mold on a single molding machine with a clamp force of 1500 metric tons, which was acquired specifically for this project from Demag Ergotech. A concern arose about the difference between the mass of the container, which weighs about 2500g (5.5 lb), and the 700g (1.5-lb) lid. The cascade control system of the Ergotech 1500/1500-16000 system selected solved that problem by ensuring reproducible, controlled cavity filling and a precise flow of the melt fronts at the living hinge.

Product handling features a robot traveling along the longitudinal axis of the machine. A twin gripper dips into the two mold parting lines to remove both container and lid. It also flexes the freshly molded living hinge to maximize service life. The system, which is running on three shifts, went into large-scale production of the improved product just six months after SLG’s first contact with the customer. Both container and lid can be stacked tighter on Euro pallets, thus saving valuable storage space during transport and in the retailer’s warehouses.

SLG, which is in its second generation as a family-run organization, has 130 employees. Its 25 injection machines range from 250 to 15,000 kN (25 to 1500 metric tons) and handle shot weights from 1g to 10 kg (22 lb). It produces about 1200 different parts and in 2001 had an annual turnover of E20 million. Services include product design and development, prototyping, construction, technical design, moldmaking, large-scale injection molding, post-production assembly, and surface finishing. Its quality management system was certified to EN ISO 9001:2000 in 2001.

Contact information
SLG Kunststoff-Fabrik &
  Formenbau GmbH
Bernau/Schwarzwald, Germany
Dieter Stockkamp; +49 (7675) 90 51 0
www.slg-kunststoff.de
[email protected]

Demag Ergotech USA, Strongsville, OH
(440) 876-6455
www.demagergotech-usa.com
[email protected]

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