Furthermore, in common practice, it is difficult to maintain
all the previous factors under a precise control necessary to
obtain reproducible results.
The materials of the parts to manufacture are another
key element to consider. The actual tendency is to use
materials, which allow us to obtain an optimum efficiencyfor the moulds, and dies. However, such materials present
the inconvenience of being difficult to machine [3]. Starting
from the dimensions and the geometry of the mould or die,
the tendency is also to perform all the machining operations
on a harden material with the bulk part or, alternatively,
perform the last semi-finishing or finishing operations with
the harden surface [4].
From what has been said previously, one can see that it
is necessary to have a deeper knowledge about the optimum
operation conditions, which will permit us to assure a cor-
rect dimensional precision and a good surface roughness.
In order to achieve this, the technique of factorial design is
to be employed as it will allow us to determine theoretical
models making it possible to select the optimum operation
conditions in a particular range of values only doing a small
number of experiments.
2. Manufacturing conditions
The optimum selection of cutting conditions is very im-
portant in manufacturing processes as these ones determine
surface quality and dimensional precision of the so obtained
parts. Thus, it is necessary to know, in advance, proper-
ties relating to surface quality and dimensional precision by
means of theoretical models which allow to do some predic-
tions taking into account cutting conditions such as: axial
depth of cut, radial depth of cut, feed per tooth (mm/z), and
cutting speed, etc.
This study is mainly focused on aspects related to surface
quality and dimensional precision, which are the most im-
portant parameters form the point of view of selecting the
optimum conditions of processes, as well as economical as-
pects. Functions making it possible to optimise parameters
related to surface quality in HSM will be obtained by means
of using design of experiments.
The considered parameters are: axial depth of cut (Ad),
radial depth of cut (Rd), feed per tooth (mm/z) (fz), and
cutting speed (Vc). The material used for manufacturing the
parts was a W-Nr. 1.2344, hardened steel (50–54 HRC).
The parts have been manufactured, without coolant,
in a HSM centre with vertical-spindle using only three
axis (Deckel Maho DMU 50 evolution with Heidenhain
control TNC 430 and maximum number of revolutions
= 18,000 rpm). Fig. 1 shows the HSM centre (left) and the
part and the tool holder (right) used in the experiments. Af-
ter manufacturing eight parts, the manufacture was started
with a new tool in order to assure that tool’s wear does
not affect surface roughness. A tool holder prebalanced, of
MST ref. DN40AD-CTH20-75 and a cutting tool of KO-
BELCO series MIRACLE: (Al, Ti) N-coated micro grain
carbide, two flute ball end mill VC2SBR0300, diameter
6mm, have been used as Fig. 2 shows.
The proposed prototype is shown in Fig. 3. As can be
observed, this prototype has different slope variations that
will allow us to analyse the influence of the angle in the
roughness values. Nevertheless, although these values have
been obtained by measuring the profile shown in Fig. 4,
an average roughness value is given in the present work.
Moreover, in order to analyse the influence of the type of
milling, that is, climb milling (A) and conventional milling
(B), each part has beenmanufactured following two different
strategies, as shown in Fig. 3, where all dimensions are in
millimetres. 高速切削模具用淬火钢英文文献和中文翻译(2):http://www.751com.cn/fanyi/lunwen_8043.html