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The company is a leading supplier of automobile components that focuses on
modules and systems such as chassis modules, cockpit modules, automatic
braking systems (ABS), air-bag systems, telematics and electronics. It has
increased the integration of its products in order to help its customers
reduce weight, part count, assembly time, and inventory. assemblies.
Previous
process of designing and building fixtures
Designing and
building fixtures is a critical task for any automotive manufacturer. The
primary task of the fixture is to control and manage dimensional accuracy
at the point of production. Fixtures are especially important in
inspecting components that could be deformed by their own weight. With
many parts from different sources coming together during assembly, if a
problem occurs it’s important to be able to quickly determine which of the
components are out of tolerance. In the past, the company used the
following process to design and build fixtures. The first step was
receiving the solid model that provides the geometric definition of the
part being manufactured. The fixture designers then converted the model
into the software they used to design fixtures and developed a concept
design for the fixture itself, including applying the gap needed to
account for manufacturing variation in the production components. After
the design was approved, the model was then converted to a computer
numerical control (CNC) program used to produce the fixture on a machining
center.
After the fixture
was produced, key dimensions were inspected with a coordinate measuring
machine (CMM). The CMM is only capable of measuring one point at a time
and must be moved manually into position prior to each measurement. The
amount of time required to digitize a part with a CMM depends on its
complexity. Even fairly simple fixtures could take several days. As the
complexity rises, the time required rises quickly to the point that it
becomes impractical to completely inspect more complex fixtures. Once the
part was digitized, the point cloud generated by the CMM then needed to be
converted, first into a surface model and then into a solid model. This
was another difficult task that could take a few days for fairly complex
fixtures and as much as two weeks for the most challenging.
Software
automates fixture design
The company's
engineers developed a new process that provides substantial improvements.
The process begins by using RapidFit software from Materialise, Leuven,
Belgium, to automate the fixture design process. Engineers first define
the support system with base plates and beams. They indicate the contact
points where fixture elements are needed and define the type of contact.
Then the RapidFit software designs the fixture, precisely fitting the
contacts to the part automatically. The fixtures have a well-defined
geometry so they will fit to the part only on the specific spots that have
been defined by the user.
New fixture
building process
The features that
provide the measuring function in the fixture are then built using an FDM
machine. The FDM process builds accurate, complex parts using a variety of
high-performance engineering materials like ABS, polycarbonate and
polyphenylsulfone. Software provided with the machine automatically slices
and orients STL CAD files for a selected part to fit within a given
system's build envelope. The software then generates precise extrusion
paths for the specified build materials along with any additional support
structures. The FDM head moves in two horizontal axes across a foundation
and deposits a layer of material for each slice. The material is heated by
the FDM head so it comes out in a semiliquid state. The successive layers
fuse together and solidify to build up an accurate, three-dimensional
model of the design.
Smaller fixtures
are produced to specifications on the FDM and attached to base plates.
Features used in larger fixtures are extended using Alufix beams that
provide a flexible fixturing system made out of high-tensile aerospace
aluminum. The Alufix system uses open bores that allow combinations in any
direction while maintaining the horizontal and vertical grid. The system
is made of pre-machined modular components that include precision bars,
base plates, angle plates, clamps, connectors and datum blocks that can be
assembled according to an inspector's needs. This modularity makes it
ideal for inspecting products as they evolve in size and shape. Once the
manufacturing process is complete, the fixture can be disassembled and
rebuilt into new configurations for diverse future uses. The company's
technicians can assemble typical fixtures in about 30 minutes.
New fixture
inspection process
The accuracy of
the fixtures must be maintained within +/-0.2% over 200 mm, which means
that 1.5 mm is the overall allowable tolerance after final assembly. The
process of inspecting the fixtures has been greatly improved through the
use of laser scanning. Laser scanning systems work by projecting a line of
laser light onto surfaces while cameras continuously triangulate the
changing distance and profile of the laser line as it sweeps along,
enabling the object to be accurately replicated. The laser probe computer
translates the video image of the line into 3D coordinates, providing
real-time data renderings that give the operator immediate feedback on
areas that might have been missed. Laser scanners are able to quickly
measure large parts while generating far greater numbers of data points
than probes without the need for templates or fixtures. Since there is no
contact tip on a laser scanner that must physically touch the object, the
problems of depressing soft objects, measuring small details, capturing
complex free form surfaces are eliminated.
The company
selected SURVEYOR® DS Series – 3D Laser Scanning System from Laser Design
Inc., Minneapolis, MN, for scanning the Rapid Fixtured parts. Laser
Design’s Rapid Profile Scanning (RPS) Model 150 laser scanning probe
captures up to 14,400 points per second and features digital (ASCII)
coordinate output, a visible beam, a Class II rating for safe and
easy-to-see operations, and a long standoff to prevent crashes during
dynamic part scanning. It offers a large measurement range, enhanced
specularity performance, and automatic adjustments for surface color and
finish. Dual CCD receptors are standard to assist with steep sidewall and
recessed geometry capture. Other features include PC-based electronics for
easy integration and a Non-Gaussian, beam spreader design to eliminate hot
spot syndrome. With no moving parts and a completely solid-state
construction, the RPS probe line requires minimum maintenance. The
accuracy of the Laser Design probes has been tested to Sigma 3 reliability
– the highest in the scanning metrology industry.
The inspection
process proceeds as follows. The fixtures are set up for laser scanning
using various jigs. The laser scanner is calibrated and set up. The
operator scans the fixture with the probe almost as if he was spraying the
fixture with paint. The resulting point cloud is then imported into Color
Error Mapping Inspection software which compares the scan data to the
original CAD model to view any discrepancy as a color variation to
highlight out of tolerance conditions of the part scanned. This allows
everyone interested in quality of the body-positioned part to see where
the shape of the part varies from its original design intent. This greatly
speeds up the analysis of any problems and allows all involved to
understand what needs to be changed in either the tooling or the
manufacturing process. The combination of the new fixture design methods,
rapid prototyping, modular assembly, and laser scanning inspection has
dramatically improved the process of building fixtures at the company. |
