3-D laser scanning is a relatively new technology that yields a three dimensional virtual record of a real object. The concept is simple and similar to police radar, but requires the power of modern day computers to collect and process enormous amounts of discrete data instantaneously. The basic operation of laser scanning involves projecting a beam onto an object. An optical sensor similar to the kind in digital cameras records the reflection of the beam as X, Y and Z point coordinates in 3-D space. The end result is a 3-D record of the object of interest.
The competitive advantage that this technology provides is one of comprehensive virtual comparison that enables companies to source product from anywhere in the world quickly with 100 percent confidence in repeatability.
Consider the traditional process requirements of sourcing a geometrically complex casting typical of a centrifugal pump from a Low Cost Region (LCR). First, 2-D drawings are sent to a foundry for casting pattern creation. The drawings are interpreted and the pattern maker carves the pattern tool by hand using templates and traditional tools. Multiple castings are produced and machined for quality sample purposes.
Sample parts are shipped back to the factory and each particular drawing dimension is measured by hand and recorded. Because hydraulic performance is the primary market deliverable, complete pumps are then built and tested for proof of performance. This process is manual-labor intensive and has traditionally required many months to complete successfully. Non-conformances in part geometry can extend the timeline of the process even further.
In the 21st century, a 3-D model of the required part can be sent instantly over the Internet to any supplier anywhere in the world for production. The casting patterns for hydraulic parts (casings, impellers, etc.) are created by CNC machine from the 3-D model for maximum confidence in part geometry and accuracy. Once the pump manufacturer procures and receives these castings, the parts are scanned by 3-D laser, and then evaluated using powerful state-of-the-art computer software.
Provided the parts are within minimum tolerances, no further hydraulic testing is required, and they can be accepted for production without extensive performance tests. Conversely, the costs and project delays of hydraulic performance testing are avoided if there are significant part non-conformance issues due to production variation. A 3-D color map of the non-conformance is sent to the supplier for correction without further delay.
When the pump parts of interest are those that have been produced domestically, laser scanning assumes a larger, more important role in the process. In this case, it is necessary that any new tooling is identical to the legacy tooling to ensure that hydraulic performance is maintained across different suppliers. In this case, the first step of the process is to scan the casting tool of the legacy part. This scan data is then compared to the proposed 3-D model to eliminate any difference between multiple pattern tools. This process has been and continues to be successfully employed in various sourcing projects to eliminate risk of multiple qualification testing and tool modifications.
This color deviation map shows the 3-D variations between the 3-D model and the laser scan of the casting. This impeller was hydraulically accepted without performance testing.
This 3-D scan of an actual valve casting was used by a valve manufacturer to verify their 3-D model to ensure product consistency across multiple suppliers.
Many companies that have adopted scanning use it in conjunction with their CAD-based engineering systems. This use is a natural progression because of the similarity between the technologies since they both reside in virtual 3-D space. Typical applications can be divided into three general categories:
- Reverse Engineering: A CAD model is needed, but no drawings or records exist. For example, the U.S. Bobsled team used scanning to create a CAD model of a driver to run computer-based wind drag simulations.
- Reverse Modeling: A second cousin to Reverse Engineering, Reverse Modeling allows a CAD model to be checked against an actual part to ensure modeling accuracy.
- Computer Verification: Any part can be compared against its CAD model to ensure compliance with the specifications.
Laser scanning can be used in other, unique ways to improve processes and products that are divorced entirely from CAD-based engineering systems. Unlike the typical applications, these methods rely on the analysis of scan data files only. In the following example, we will see how and why one company also uses "CAD-less" analysis to improve processes and product.
Improving Foundry Processes
A corebox that creates a sand core used in the casting of a small pump impeller was procured from an external pattern shop to replace old tooling. As part of the production qualification process, it was discovered that the sand core could not be removed from the corebox, rendering the tool useless. Due to the small size of the corebox, traditional measurement techniques could not confirm reverse draft as the culprit. The part was sent to the quality assurance department for scanning and analysis, but there was no CAD model of the part.
In addition, laser scanning was so new to the organization, a method to analyze the data without a CAD model did not yet exist. A new measurement method literally had to be invented. Through a lot of trial (and mostly error), a simple technique was developed based on the basic concept that the core-making process could be simulated virtually.
3-D comparison of a pattern scan. Its mirrored scan quickly illustrated the root cause of production issues.
Simulating the foundry process with 3-D laser scans quickly highlights the areas of reverse draft (blue) in this corebox.
Analyzing impeller scans can show areas of casting asymmetry that contribute to impeller unbalance.
To simulate the process, two identical scans of the corebox were imported into powerful computer software; one scan represented the corebox, and the other represented the sand core itself. The scans were moved apart to represent the sand core leaving the corebox. The dimensional difference between the two scans is computed and illustrated as a 3-D color map. The reverse draft is illustrated as a negative difference (blue).This learning experience illustrates the ability to see into complex processes and measure complex attributes of real parts rather than relying on idealized CAD parts. The process of using only scanned data has developed and expanded during the past several years to explore more complex and varied process improvement opportunities.
Improved Impeller Balance Analysis
A recent project with the objective to improve impeller balance resulted in the development of a method that reveals the features that contribute to impeller unbalance. The basic concept behind the method relies on the simple idea that a balanced impeller should have the same shape and form from one side to the other. By making comparisons across the entire part, it is easily seen if the unbalance is due to variations in the casting or machining issues. This ability to differentiate between these two attributes was not possible before scanning technology. The general method was also extended to directly compare castings to their casting patterns which highlighted various opportunities to improve the casting process and further reduce impeller unbalance.
Comparing Symmetry of Parts
Scanning's ability to easily test for symmetry of complex parts that are typical of pump parts was also used in a recent project to improve the quality of double suction casings. A suspect casting pattern was scanned and tested for symmetry. The scan data was "mirrored" electronically, and then tested for symmetry by comparing the "left hand" side of the pattern to its "right hand" side. One revealing image showed that each side of the pattern was close in shape to the opposite side, but the location of the respective parts was not correct.
These few examples show how leveraging 3-D laser scanning technology on a regular basis can continuously improve quality by offering visual variation of complex products and processes.