Dimensional evaluation of prototype parts is essential prior to serial production. However, depending on material consistency, traditional tactile measurement sometimes cannot provide the required holistic view of measured components. For this reason, Kiekert, a global leader in vehicle locking systems, primarily relies on digital cross scanners for prototype inspection.

BMW, Daimler Benz, VW, Ford, General Motors, Fiat, Renault, Nissan - more than 50 international automobile brands use Kiekert's technology for side door latches, rear compartment latches, mini actuators and lock modules. Based in Heiligenhaus, near Dusseldorf, the company employs 5,000 staff and operates in nine countries. Six of these locations are production centres, six are involved in R&D and there are three sales and distribution centres.

The Inventor of the Central Locking System

Over the course of its 150-year history, the company has invented central locking and electromotive power servo locking, registered more than 1,200 patents, and developed and manufactured more than 1.5 billion vehicle locks. Its engineers are hard at work developing solutions to make driving even safer and more comfortable. In pursuit of this goal, modern measurement techniques and test procedures are used in quality assurance.

Kiekert's prototypes are subjected to extreme life-cycle testing in specially constructed test rigs. During the course of their development, all products have to pass countless load tests reflecting vehicle use under widely differing conditions around the world. The company headquarters in Heiligenhaus is also home to one of the automobile industry's leading acoustic laboratories. Amongst others, it features psychoacoustic measuring devices, a drivable acoustic chamber, high speed cameras and exclusive technology that is able to simulate specific driving movements.

Right at the start of the development process, at the prototype stage, Kiekert relies on the abilities of Nikon Metrology's digital cross scanners for its metrology requirements.

The Critical Pre-production Phase

Specialising entirely in assembling latch and lock modules, Kiekert is totally dependent on its supply chain. Particularly in the prototype and pre-production phases, this demands meticulous testing and precise coordination with suppliers producing the parts. Bearing in mind that a door lock consists of up to 130 individual parts, one can imagine the amount of time, work and energy involved in this process. The individual parts need to fit perfectly and operate like clockwork.

Complex functionality within this restricted space is dependent on absolute adherence to several hundred dimensions defining bearing locations, for example, or the accurate relative positions of two moving parts. Rarely are tolerances greater than 0.05 mm permitted. This is a level of precision that can be measured without problems by tactile coordinate measuring machines. Generally speaking, that is, but not in certain cases and not for Kiekert's component qualification.

Overall View Is Vital

As plastic components are unavoidably subject to a certain degree of deformation, it is important to measure the complete form of the part. Tactile inspection of individual measuring points and feature dimensions provides information that is too limited. The number of discrete measuring points, being finite, can never provide a full picture of a part being tested. This is particularly problematic when it needs to be mated with another part.

Hence it is vital to have a complete 3D overview of the component, which includes all surfaces and features. Only in this way can engineers draw conclusions regarding programming for subsequent production on machine tools. It also provides information to allow zero datum points in the part to be determined, taking natural warpage into account, allowing additional tactile tests can be conducted.

Scanning Instead of Tactile Probing

As soon as laser scanner technology became available at the beginning of the millennium, the first systems were used for quality assurance in Heiligenhaus. It was not long before Nikon Metrology's digital line scanners were used in Kiekert's largest production site in the Czech Republic as well as at production sites in Mexico and China.

It resulted in significant advantages. They included creation of high density point clouds for quickly identifying form and features; simplification of initial and detailed analysis of surfaces and sections; rapid measurement of free-form surfaces; CAD model comparisons; reduced measuring times and hence increased throughput; simplified processing of metrology data to be passed to processing and evaluation software; determination of ideal alignment points for geometric measurements; and digital copying of parts in a couple of minutes for reverse engineering.

Cross Scanning with Three Laser Lines

The Nikon Metrology XC65Dx digital cross scanner features three laser lines projected at different angles to measure complex shapes with a minimal number of motorised probe head rotations. With this setup, evaluation of prototype parts took a further leap forward in efficiency at Kiekert.

The scanner is able not only to acquire information on surfaces, but also to focus on features of components, such as slots, bearing points and holes. In most cases, it is able to do so in a single scan. The field of view covered by the three laser lines is 65 x 65 mm, whilst the precision level of the sensor is 12 μm.

With its 75,000 laser points per second data acquisition rate, the Nikon Metrology cross scanner, which is mounted on a bridge-type CMM, generates a high density 3D point cloud. Thanks to the part-to-CAD comparison colour display of Nikon Metrology's Focus Inspection software, the inspection results are immediately meaningful.

Six-fold Increase in Productivity

Unlike with first-generation analogue scanners, most parts no longer have to undergo a matt spray finishing process to eliminate unwanted reflections. It is due to the Enhanced Sensor Performance algorithm of Nikon Metrology's digital XC65Dx that automatically adjusts the laser source intensity per measured point, depending on surface reflectivity. It guarantees a homogenous, complete point cloud without flare.

Adaptations to the testing process to accommodate different prototypes are not a problem either, as the scanner movements are easy to program and can be generated automatically offline, based on CAD data using Nikon's Focus Scan software, saving a considerable amount of time.

Kiekert calculates that Nikon Metrology's laser cross scanners are five or six times more productive than analogue, single line scanners. Products can therefore be brought to market faster. Moreover, due to early involvement of suppliers to determine the ideal alignment points, the number of iterations when measuring prototype parts is drastically reduced.