DMI Automotive, Inc.
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Phone: (517) 548-1414 - Fax: (517) 548-1711
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DMI Automotive, Inc.
Manufacturing and Operational Advantages

DIE MANUFACTURING ADVANTAGES

Cheaper material costs
DMI chromium plating allows 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 in Japan are FC25 and FC30 which are equivalent ot GG25 and PS11.

Easier machining
Flake grey cast iron is more easily machined, gives longer life to cutter heads and allows more efficient use of die cutting machinery.


OPERATIONAL ADVANTAGES

Hardness and wear resistance
DMI chromium plated dies have a surface hardness greater than 1000HV (71 HRC), four to five times that of cast iron, and have a high resistance to wear and scoring (see graph below).

Heardness and wear resistance

Low friction - High Lubricity
Low friction properties enable the reduction or elimination of lubricant and removes the environmental problems of oil spray. The graph below shows a simulated test of male and female draw bead conditions which was created under laboratory conditions. Draw bead sections were produced in different base materials and surface treatments as indicated. Zinc coated material was drawn through the test pieces. The blank holder pressure required to stop material movement was measured. Dry tool steel was the worst performer and was used as the base pressure. It can be seen that chromium, unlike other materials, performs equally as well without as with lubricant. This property enables a chromium plated die to lose the oil film locally without scoring the panel and damage to the die surface.

B/H SHIFT, kN

CHROMIUM AND ZINC COATED STEEL

Almost all manufacturers now use coated steels for corrosion resistance and double sided zinc coated steel is becoming the standard specification.

The "non-stick" properties of chromium and the ability of chromium to "seal" the open grain structure provide dramatic solutions to zinc build up on die surfaces.

Resistance to pimples
The open grain structure of cast iron encourages any loose particles of zinc to bond to the surface of the punch. During the course of a press run the zinc particles build up on the surface of the punch.

Pimples are formed on the panel when the particles of zinc are compressed between the surface of the punch and the surface of the blank resulting in unacceptable panel quality.

The polished layer of chromium on the surface of the punch provides a "non- stick" condition which discourages the build up of zinc on the punch and transfers the zinc particle to the surface of the blank which then leaves the press. The result is an improvement in panel quality, less rework and significant reduction in press downtime since the surface of the punch no longer requires stoning to remove bonded zinc particles from the surface of the cast iron.

Any zinc particles which do find their way onto the surface of the punch can quickly be removed by wiping over with a cloth.

SAVINGS

Reduced press down time
Draw related press down time reduction of up to 90% has been reported.

Press down time
Press down time

Reduced rework and scrap
Zinc build up on the blank holder faces is eliminated resulting in reduction in scoring and thus reduction in rework or scrapping of the panels.

Rework rates
Rework Rates

Scrap rates
Scrap Rates

Reduced die maintenance
Damage to the die surface through scoring and seizure is also eliminated.

Choice of materials
Chromium tool surfaces allow a wide range of choice of coated material, often resulting in significant savings in material cost.

CHROMIUM - A WEAR INDICATOR

A 25 micron chromium layer will act as a wear indicator. As a tool wears, the chromium thickness can be easily monitored using an electronic thickness meter. When the chromium has worn it can quickly be replaced by de-chroming and re-chroming the die. Because the die retains its original profile to within 25 µm throughout its working life the panel also maintains a constant profile.

Die Preparation
DMI technicians carry out basic preparation of the die surface including local welding of small defects, stoning of repaired areas and polishing of draw beads and radii prior to chrome plating if required.


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