CAD software streamlines design data handling

Until recently, it took an excruciatingly long time for the Navy to obtain certain parts for its equipment, especially where the parts were designed many years ago. An average lead time of 300 days created frequent delays in getting military equipment back in service. Then, the Navy streamlined the process with a new system, called Rapid Acquisition of Manufactured Parts (RAMP), which is described later.

Reasons for the former turtle-like pace can be summed up in three words: paper, complexity, and age. First, the information required to design and manufacture a part (or assembly) typically consists of drawings, specifications, and instructions to shop personnel, all on paper.

Where the assembly is a complex weapons system, the package of paper information grows to huge proportions. Typically, several subcontractors prepare this information, each interpreting differently the contractor’s drawing requirements. As a result, the package often contains inconsistencies, incomplete or inaccurate information, or extraneous information.

Old designs complicate the situation further. Where the parts were designed many years ago, the information degrades over time — drawings are lost, aperture cards (microfilm) deteriorate, and details become fuzzy as copies are copied. Moreover, the original materials and manufacturing processes may become obsolete.

Years later when replacement parts are needed, engineers must reassemble all of the data before the parts can be manufactured. This often requires reverse engineering, a process in which the engineer measures an original part to recreate some or all of the design information (see box). It may also be necessary to revise the design to accommodate new requirements. This takes time, which means higher cost and later delivery.

Further, as time passes, the original parts vendors may go out of business, while others either have no interest in manufacturing small quantities of parts or they charge a high price for doing so.

Obviously, a more efficient way of handling product data would avoid these problems and benefit both the Navy and its many suppliers, including, for example, manufacturers of drivetrain components and control electronics for mobile equipment.

RAMP to the rescue

To cut excessive lead time, the Naval Supply Systems Command initiated the RAMP program in 1986. Its primary objective: shorten the 300-day average lead time for delivery of small quantities of parts to a mere 30 days. Another objective was to obtain quality parts the first time they are made, and at reasonable cost. The Navy selected the South Carolina Research Authority (SCRA), North Charleston, S.C., as prime contractor for the program.

The SCRA formed a team to come up with a more efficient way to handle product data and support flexible computerintegrated manufacturing (FCIM). The SCRA FCIM Team — including Arthur D. Little, Battelle, Grumman Data Systems, and SEACOR (Systems Engineeering As sociates Co.) — developed a product data translation system (PDTrans), that rapidly converts paper data into a computerized digital format for use by designers and manufacturers.

Mechanical and electrical parts

PDTrans exists in two configurations: one for machined mechanical parts and one for printed wiring assemblies, as typified by Figures 1 and 2. Both of these versions create digital product data either for new designs — generated on a CAD system — or for existing designs — usually by scanning paper drawings and specifications or aperture cards. In a physical sense, the two configurations, Figure 3, are the same: a commercial CAD/CAM workstation with CAD/CAE and database management software, plus translation software developed by the SCRA FCIM Team. But the similarity ends there.

Mechanical. The first configuration, for mechanical parts, converts paper data into a digital format that is consistent with an evolving international standard for exchanging product data, called STEP (See box). Using an SCRA system that includes feature-based CAD software and an SCRA translator, a user can convert a moderately complex mechanical part from paper to STEP format in about an hour.

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This digital information is delivered, either electronically or by cartridge tape, to a manufacturing facility. There, engineers enter the data into an automated process planning software program, which processes the data for use in manufacturing the part.

Electrical. The printed-wiring assembly configuration converts product data from paper format into industry standard digital files, such as IGES, EDIF, and IPC- 350. This information is packaged in a data file that meets the requirements of MIL-STD-1840A, Automated Interchange of Technical Information, and is sent to a printed-wiring assembly manufacturer. Here, as before, the manufacturer enters the data into an automated process planning program. Eventually, these electrical product data files will also be available in a STEP-compatible version.

With the help of PDTrans, the RAMP program manufactures mechanical and electrical components at locations such as a machined parts operation at the Charleston Naval Shipyard and a printed wiring assembly plant at the Naval Air Warfare Center in Indianapolis. In less than one year, the Charleston facility has manufactured thousands of machined parts ranging from steel tread parts, skid plates, and debris shields for Army bulldozers to shipping adapters for warheads that are to be dismantled.

Using RAMP FCIM technology, the Naval Aviation Depot in Cherry Point, N.C., modernized a machine shop plus a turbine engine blade and vane repair facility.

Defense suppliers to become paperless

The Department of Defense (DoD) has begun to convert from the present paperintensive acquisition processes to an automated procurement system, starting with weapons systems. Under this concept, manufacturers will receive orders and submit design data for parts and assemblies in a digital format that conforms to STEP regardless of the CAD system they use. This information will be used to manufacture, operate, and support the weapons systems.

Eventually, the DoD will expand this requirement to include proposals for other (nonweapons) systems. And other government agencies will implement similar requirements.

Reverse engineering

One of the factors that determine manufacturing lead time is the need to reverse-engineer old parts and upgrade their design. For example, a maintenance facility responsible for rebuilding old equipment may be faced with insufficient design information on a 20-yr old drivetrain component or the need to upgrade that component to meet tougher requirements.

A focal point for this technology is the Cleveland Advanced Manufacturing Program (CAMP), which two years ago launched a Manufacturing Resource Facility (MRF) at the Unified Technologies Center of the Cuyahoga Community College in Cleveland. Designed to help manufacturing companies improve productivity, this facility replicates a modern factory floor environment and contains separate areas for CAD/CAM, quality improvement (metrology), equipment upgrade, and special projects.

Experts from the National Institute of Standards and Technology (NIST) Great Lakes Manufacturing Technology Center, a division of CAMP, provide assistance in manufacturing and CAD/CAM technology. They have helped numerous companies to evaluate, select, and apply CAD/CAM systems, or apply reverse engineering and rapid prototyping techniques.

Reverse-engineering projects generally come from companies that don’t have up-to-date drawings of products they intend to manufacture. Reasons for the lack of drawings vary. Some companies, which traditionally made products directly from templates or forms, have decided to upgrade to a CAD system so they can easily store drawings and revise designs. In other cases, the drawings are either old, incomplete, and outdated, or they no longer exist.

In one example, MTD Products Inc., a manufacturer of tractors and mowers, asked the staff to develop a 3D CAD drawing of a sheet metal tractor hood and revise it to eliminate unneeded vent holes in one side. Because the hood is symmetrical about its centerline except for the vent holes, engineers used a laser to scan the unvented side, then generated a mirror image (without vents) for the other half. The sides of the hood have an abrupt change in contour in one area, which require close dimensional control to ensure clearance between the inside of the hood and moving parts of the tractor. Based on programmed instructions, the laser system scanned this area in more detail to ensure its accurate definition on the CAD drawing.

In another case, Misco, a manufacturer of optical instruments, requested MRF to develop a 3D CAD drawing of a plastic refractometer lens and then modify the design to incorporate an additional light source on the top. After scanning the part and developing a basic drawing, MRF experts added a top enclosure for a battery and LED under the direction of Misco engineers.

Scanning methods. MRF engineers use either a coordinate measuring machine (CMM) or a laser scanner to establish the geometry of a part. A coordinate measuring machine, typically used for quality control measurements, is programmed to trace the outline of a part by moving a probe in a series of parallel sweeps across the part until the entire surface has been covered. The process is slow and the degree to which CMMs can be programmed for this purpose is limited. However, CMMs are better suited than lasers to handle parts with vertical sides, such as flat plates with stamped or cut shapes.

Laser scanning is accomplished with a laser that is installed in a CNC machine in much the same way as a machining tool. The part to be scanned is placed on the movable bed of the machine tool and moved past the laser beam in a series of parallel scans until the entire surface is covered. Engineers can program the laser to scan specified areas of the part in more detail than others. For example, the distance between scan lines can be adjusted to a value as low as 0.002 in. Laser scanning is generally more efficient and takes less time than a CMM, the laser process being at least four times faster, according to Raymond Benne, technical program manager for CAD/CAM/CAE Systems.

After a part has been scanned, software converts the dimensional data to a standard format, such as IGES, for use in preparing CAD drawings or for downloaded to computer-aided manufacturing (CAM) programs. If needed, the MRF manufacturers parts from the CAD data for the customer. MRF uses a variety of CAD software programs and computer hardware to be compatible with customer systems. The most commonly used CAD programs are Euclid, Pro/Engineer, and Intergraph EMS.

Engineers also perform 2D reverse engineering, using a commercial drawing scanner with a 3 CCD camera that has up to 800 dots per inch (dpi) resolution. In one project, they scanned a 1940 vintage drawing of the inside of a grand piano where the drawing had no dimensions. The scanned drawing was converted to vector format, using a raster-to-vector converter program, then the software calculated the dimensions and added them to the drawing.

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