3 Fundamentals of press design

500 Solid forming (Forging)
Table 6.7.6: Mechanical properties of carbides
Carbide types E-modulus Ultimate strength
Co content Density Hardness Compressive strength Bending strength
% by weight g/cm 3 HV N/mm 2 N/mm 2 N/mm 2
15 14.0 1,150 530,000 4,000 2,400
20 13.5 1,050 480,000 3,800 2,600
25 13.1 900 450,000 3,300 2,600
30 12.7 800 420,000 3,100 2,700
was far below that of hot forming tool steels. In view of the successful
implementation of environmentally friendly water-soluble lubricants,
the factor thermal shock resistance is expected to continue to be a subject
of particular interest.
Thus, investigations are concentrated on tool steels which are
derived from hot forming tool steels, i.e. those which have a relatively
low carbon content. These tool steels demonstrate superior wear and
heat resistance properties as well as very good thermal shock resistance.
A number of different die materials are being developed concurrently,
for example using nickel-based alloys (Inconell 718), which have
already produced good results in bar extrusion (temperatures 1,150 °C,
pressures of 900 to 1,100 N/mm 2 ) and isotherm forging applications.
Die coatings (VDI 3198)
The cost-effectiveness of cold forging processes depends largely on the
tool costs and accordingly on the achievable service life of dies. Die
wear influences the dimensional stability and surface quality of the produced
workpieces. There are two main types of wear resistant coatings
considered for use in forging technology. Coatings, for example using
adding-on processes such as CVD or PVD processes, and coatings
obtained through reaction layers such as nitriding and ion implantation.
Processes which have proven successful for cold forming dies
include the CVD and PVD techniques, which permit service life to be
more than doubled (cf. Sect. 4.1.3).
An essential prerequisite for a successful coating is good adhesion
between the coating material and the substrate, whose hardness and
compressive strength must provide adequate support. High-speed steels,
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998