Automotive Engineering - August 2022 - 23

ADDITIVE MANUFACTURING FEATURE
Designers must consider the complexities they design
into parts, especially the holes and channels running
through them.
Wall thickness is a critical consideration for parts being designed
for AM both in terms of the part itself and any post-processing
that may be required.
finish. With this considered, if specific surface details
are designed into a product or part, certain design
rules are pertinent here.
Surface details can vary depending on the surface to
which they have been applied. The top side may include
a raised burr of the laser around the outer edge, whilst
the underside can appear more muted. Thus, for most
parts the best outcome is achieved by applying the text
on the side skins for the best and most consistent visibility.
Other recommendations are as follows:
* Minimum 0.5 mm (0.019 in.) wide and deep. The
same depth and width measurement results in superior
clarity.
* Embossed text is safer than extruded text, as small
details and edges can be vulnerable to break.
* Avoid embossing or extruding the surface details
too far. Try to keep them to around 0.5 mm; further
out can result in damage in post-processing and too
deep can result in trapped powder.
Solid vs. hollow parts
Hollowing can prevent the part from deforming and
achieve higher levels of accuracy and reliability.
However, based on 3DPrintUK's experience working
with PBF processes, the combination of powdered
material and hollow parts can result in trapped powder
within the sintered shell. When designing a hollowed
part, there are a few design options that avoid
trapped powder. These include designing in powder
escape holes, removing unwanted surfaces altogether
(i.e., bases), or including a locating lid.
AUTOMOTIVE ENGINEERING
Advantages of 3D printing
include the ability to design and
produce complex geometries
without the need for expensive
tooling. But important
considerations are required.
For customers, we will automatically hollow larger parts before printing
when above 15-20 mm (0.590-0.787 in.) on a case-by-case basis. For
customers who do want it printed solid we advise accordingly.
Interlocking / mechanical parts
When designing interlocking or mechanical parts, including a clearance
between parts is essential. This is because a gap between the
sintered surfaces prevents them from fusing together and becoming
a merged part. The tighter the tolerance, the more likely it is to fuse
together. Some general design rules for this are:
* In nearly all cases, a clearance between moving parts must be at
least 0.5 mm to guarantee a result.
* Contacting surfaces must be kept to 5 mm or below to guarantee
them not fusing. Longer shafts are likely to be too difficult or impossible
to free up.
* Think about how the trapped powder between the surfaces can be
removed. Sometimes a little force is enough to remove the powder.
Designing powder removal holes may also be needed.
* Dense volumes can refract more heat and harden the powder between
the surfaces. This means that the clearance may have to be
increased if this is flagged as a concern or if the part does not
function as intended.
Holes and channels
One of the key advantages of 3D printing is the ability to design and
produce complex geometries without the need for expensive or " impossible "
tooling. However, designers still must consider the complexities
August 2022 23
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Automotive Engineering - August 2022

Table of Contents for the Digital Edition of Automotive Engineering - August 2022
