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DMI HARD CHROMIUM PLATING FOR AUTOMOTIVE
The process of hard chromium plating of press dies for automotive press shops that was universally practiced in Japan, was not performed in Europe until the establishment of technology transfer agreement between DMT and Koka Chrome Industries in 1989.
The main European specialist in chrome, DMI, now offers all the improvements in quality control and cost savings that this process involves for the majority of European car manufacturers.
ADVANTAGES IN DIES MANUFATURING
Cost savings
DMI chromium plating allows for the use of cheaper grades of flake grey cast iron and eliminates the need for exotic alloys of nodular cast iron. Cost savings of up to 30% on material are possible. Typical materials used, where hard chromium plating is extensively employed, are FC25 quality equivalent to GG25 or PS11.
Easier machining
Flake grey cast iron is more easily machined, gives longer life to cutter heads and allows for more efficient use of the die cutting machinery.
FUNCTIONAL ADVANTAGES
Hardness and wear resistance
DMI chromium plating has a hardness of 900VPN. This is four to five times that of cast iron, has a low co-efficient of friction and a high resistance to wear and scoring.
The low friction and non-stick properties of DMI hard chromium enables the reduction or elimination of lubricant in the drawing process and thus reduces the cost and environmental problems of oil spray, handling and oil removal. Also decreases the down time of the presses, so far necessary to polish and repair press dies during production.
Non-stick surfaces
Chrome homogeneous layer is resistant to the adhesion of zinc or other particles on the surface of the die, preventing the formation of grains and reducing the need for polishing the dies during production.
Visual wear indicator
A chrome layer of 25 microns thickness is an excellent visual indicator of wear. When the chrome is worn in the most critical areas of the die, these areas are visible. The rapid removal of chrome and the surface re-chroming ensures that the die will maintain its original profile throughout its life. This in turn allows avoiding maintenance brazing, and the die can be reintroduced into the production process with minimum downtime.
Die homogeneous profile
The accurately maintained die profile and stabilised performance of the die surface results in consistent panel profile and improved panel fit. Therefore, no cleaning is required and die replacement is done quickly.
QUALITY ADVANTAGES
Better performance using coated steel
Almost all manufacturers now use double sided zinc coated steel as a standard specification. The open grain structure of cast iron encourages any loose particles of zinc or other debris to bond and built up on the surface of the punch.
The low friction and non-stick properties of DMI hard chromium and the ability of chromium to "seal" the open grain structure of the cast iron, provides a homogeneous "non-stick" condition, which discourages the build up of zinc on the tool surfaces so that any particles are removed by the panel. Any particles which do find their way onto the surface can be removed quickly and easily by wiping over with a cloth.
Draw related press downtime, panel re-work, scrap rates, die maintenance and press "try out" are significantly reduced.
COSTS SAVING
PRACTICAL ADVANTAGES
Fast processing
DMI chrome can be applied within two to three days (or even in a shorter term in case of emergency).
The process includes preliminary polishing, the fabrication of the anode, the chromium bath and final polishing.
Removal of the chromium can be performed in parallel without delay.
