RAPID MANUFACTURING COURSE HOW TO ELIMINATE STAIR STEP ERROR ON MANUFACTURED SURFACE

1. MEE2016-RAPID MANUFACTURING
TECHNOLOGY
J COMPONENT REVIEW 1
BY-
ABHISHEK SHARMA
15BPI0012
RINKY SINGH
15BPI0050

2. TOPIC-ELEMINATING THE STAIR
STEP ERROR IN ADDITIVE
MANUFACTURED SURFACE

3. Aim- The aim of this study is to show the
general feasibility of new methods to
reduce the stair step effect of layer
manufactured surfaces.

4. INTRODUCTION
 Rapid Prototyping (RP) is the process of building prototypes in slices using a layered
approach.
 RP processes such as Selective Laser Sintering (SLS), Stereolithography (SLA) and 3D
Printing have been developed
 RP allows prototypes with complex and intricate shapes to be built very easily. The cost
and time advantages associated has made RP extremely popular with product designers
during the early design stages.
 The popularity of RP has naturally led to the extension of using additive layering
manufacturing techniques to manufacture tools, dies and industrial parts in a rapid
manner.

5.  Parts created by AM have to consistently satisfy critical geometric tolerances or the parts
should be accurate.
 There is a need to study RP parameters that influence tolerances on critical features of the
manufactured part. Due to the nascent stage of RM technology, the effect of the RM process
parameters on form errors has not been researched in detail.
 Accuracy in additive manufacturing (AM) is evaluated by dimensional errors, form errors and
surface roughness of manufactured parts.
 Types of form errors are : cylindricity errors, staircase errors & flatness errors

6. PROCESS PARAMETERS
 The main process parameters in RP are :
 Orientation: Orientation refers to the direction with respect to the part in which
the slices are built in the machine.
 Slicing: Slicing can be performed uniformly by using slices of equal height or by
adaptive slicing using slices of unequal heights. Slicing refers to the
segmentation of the part into layers.
 Supports: Supports are additional materials which are added during
manufacturing to support holes, overhangs and unsupported features.
 Tool path planning: It refers to the determination of the geometric path for
building each individual layer.

7. Rapid Manufacturing (RM) processes have evolved from the Rapid Prototyping (RP) paradigm and
are increasingly being used to manufacture parts, tools and dies in addition to prototypes. The
advantages of RP methods to produce complex shapes without the use of specialized tooling can
naturally be extended to RM processes. For RM to be accepted as a mainstream manufacturing
process, parts created by RM have to consistently satisfy critical geometric tolerances
specifications for various features of the part. The process parameters, namely slice thickness,
orientation, support structures and 2D tool path planning, directly impact the final part accuracy
both individually and in combination with each other. The generation of form errors in parts
manufactured by RM depends upon the process parameters chosen by the designer during the
part build.
Form errors in layered manufacturing are:
1. Flatness & straightness errors
2. Cylindricity errors
3. Stairstep errors

8. STAIR STEP ERROR
The staircase effect has been the major concern for
industry to widely adopt rapid prototyping technologies.
It will not only worsen the surface quality but also create
errors on the parts built.AM process approximates the
object by layers with vertical edges, the stacking of the
layers does not match the original CAD model very well,
thus causing the formation of staircase-like surfaces.
The reduction of staircase effects can be categorized into
different classes contour shaping, and optimization of
the build orientation. Processes approximate objects
using layers, therefore the part being produced may
exhibit staircase effect. The extent of this staircase effect
depends on the layer thickness and the relative
orientation of the build direction and the face normal.
The minimum layer thickness for a given process is
known. Therefore for a given process, the primary factor
that determines the extent of staircase effect is the angle
between the build orientation and the face normal

9. METHODS TO REDUCE STAIR
CASE ERROR
Adaptive slicing:
the staircase effect is closely related to the layer thickness. The staircase error
increases with the layer thickness and can therefore be reduced by using thinner
layers. However, simply using thin layers will increase the number of layers and
thus the build time. A number of adaptive slicing methods have been developed
by considering the geometric features of the model, so that the error can be
reduced without a corresponding increase in the build time. An adaptive slicing
algorithm that can vary the layer thickness in relation to local geometry was
proposed.

10. Four criteria (cusp height, maximum deviation, chord length, and volumetric error
per unit length) are identified, and the layer thickness is adjusted such that one of
the four is met. Some approaches adaptively slice the STL file of a part model to
deposit a variable- layer thickness according to the geometric information extracted
from the STL file. Another class of adaptive slicing methods use the original CAD
model for the adaptive slicing and then employ piecewise-linear approximation for
the slices in that case, the surface curvature contained in the CAD model is used to
determine the slicing error .

11. Ball Burnishing
 Burnishing is the plastic deformation of a surface due to sliding contact with another
object. Visually, burnishing smears the texture of a rough surface and makes it shinier.
Burnishing may occur on any sliding surface if the contact stress locally exceeds the yield
strength of the material.
 It’s major function is to make parts look bright or “burnished”.
 Ball burnishing is a method for post processing of surfaces. Unlike cutting processes, in
ball burnishing no material is removed. Due to a rolling contact between the roller and the
surface, plastic deformation of the surface irregularities occur which results in a
smoothing of the surface.
 Therefore, ball burnishing will be used as a bulk forming operation to smooth the edges of
slicing layers. Furthermore, the influence of various ball burnishing parameters on the
surface quality will be investigated by studying of various literatures on ball burnishing

13. INFLUENCE OF BURNISHING PARAMETERS
Influence of burnishing parameters
1. BALL DIAMETER: The surface flattening increases with the increase of the
ball diameter. This effect can be explained by the shape of the rolling ball. If the
diameter is small, the ball forms a groove on the surface instead of flattening.
In this case even an increase in pressure does not improve the surface
flattening. Therefore, the ball diameter must be large relative to the slicing layer
thickness to get a better surface better finishing.
2. ROLLING PRESSURE: if a ball burnishing process is applied, an increase in
the hydraulic pressure results in a better leveling of the surface. The best
average leveling is in the range of 40 mpa with a remaining unevenness of 40
%.

14. SLICING THICKNESS: The deformation required to smooth the edge of a
thinner slicing layer is less than the deformation which has to be applied
to smooth the stair steps of thicker slicing layer. Consequently, by using
the same rolling force better leveling can be achieved for thinner slicing
layer

15. Thank You!